HERBICIDAL N-ALKENYL HETEROARYLYLOXYACETAMIDES

Abstract: The novel compounds of formula (I) wherein Het represents an optionally substituted, optionally benzofused nitrogen containing 5- or 6-membered heteroaromatic group; R<1> represents an alkyl, alkoxyalkyl or cycloalkyl group; R<2> represents a hydrogen atom, and R<3> represents an alkyl group, or R<2> and R<3> taken together form a single bond or a methylene group; and R<4>, R<5>, R<6>, R<7> and R<8> independently represent a hydrogen atom or a C1-C4 alkyl group, with the provisos that at least two of R<4>, R<5>, R<6>, R<7> and R<8> must represent an alkyl group; and 2-(5-trifluoromethyl-1,3,4-thiadiazol-2-yloxy)-N-methyl-N-(3,5,5-trimethylcyclohex-1-enyl)-acetamide is excluded; and herbicidal compositions containing such compounds as active ingredients can be utilized in various agricultural methods.

Description: HERBIC1DAL N-ALKENYL HETEROARYLYLOXYACETAMIDES 5 BACKGROUND OF THE INVENTION This invention relates to certain novel heteroarylyloxyacetic acid N- alkenylamides, the preparation of such compounds, herbicidal compositions 0 containing such compounds, and a method of combating undesired plant growth using such compounds. U.S. Patent No. 4,585,471 discloses, for example, a compound of formula European patent application EP 0 005 501 discloses benzofused oxazol- 5 2-yl- and thiazol-2-yl-oxyacetamides, in which the amido nitrogen atom is substituted by hydrogen atoms and/or by optionally substituted alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl or aryl groups. However, there is no disclosure of alkenyl-substituted compounds in which the double bond is located in the 1- position with respect to the nitrogen atom, nor to cycloalkenyl compounds. o European patent application EP 0 165 537 discloses a process for the preparation of benzofused oxazol-2-yl- and thiazol-2-yl-oxyacetamides, in which the amido nitrogen atom is substituted by one or two allyl groups, one cyclohex- SUBSTUUTE SHEET (RULE 26) 1-enyl, one cyclohex-3-enyl or one vinyl group. However, there is no disclosure of branched alkenyl compounds or of alkyl substituted cycloalkenyl compounds. International patent application WO 97/08160 discloses N-(1-isopropyl-2- methyl-1-propenyl)-heteroaryloxyacetamides. However, there is no disclosure of heteroaromatic oxyacetamides, in which the amido nitrogen atom forms an enamine derived from a ketone having different alkyl chains and/or has more than 7 carbon atoms. Although many of the known heteroaryloxyacetamides show considerable activity against various weeds, they are not completely satisfying with regard to their selectivity or persistence. The compounds of the present invention combine high herbicidal activity with the necessary selectivity and enhanced soil degradation. SUMMARY OF THE INVENTION We have now found, surprisingly, that new compounds of the formula I, wherein Het represents an optionally substituted, optionally benzofused nitrogen containing 5- or 6-membered heteroaromatic group; R 1 represents an alkyl, alkoxyalkyl or cycloalkyl group; R 2 represents a hydrogen atom, and R 3 represents an alkyl group, or R 2 and R 3 taken together form a single bond or a methylene group; and R 4 , R 5 , R 6 , R 7 and R 8 independently represent a hydrogen atom or a C.,-C 4 alkyl group with the provisos that a) at least two of R 4 , R 5 , R 6 , R 7 and R 8 must represent an alkyl group; and b) 2-(5-thfluoromethyl-1 ,3,4Jhiadiazol-2-yloxy)-N-methyl-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide is excluded; show excellent herbicidal activity at low dosages and possess higher selectivity in crops than those disclosed in the aforementioned patents. Accordingly, the present invention provides novel compounds of formula I, methods for controlling undesired plant growth by contacting said plants with a herbicidally effective amount of the compounds of formula I, selective herbicidal compositions containing the compounds of formula I as active ingredients, and new processes for the preparation of the compounds of formula I. The compounds of formula I possess an excellent selective herbicidal activity in certain crops, such as rice, maize, cereals, soybeans, sugarbeets, canola, sunflowers or potatoes, as well as enhanced soil degradation. Those and other objects and features of the invention will become more apparent from the detailed description set forth hereinbelow. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS It has surprisingly been found that the novel compounds of formula I show an excellent herbicidal activity against a broad range of weeds and exhibit a high degree of selectivity. The term "optionally benzofused nitrogen containing 5- or 6-membered heteroaromatic group" as used herein includes azoles, such as pyrrole, pyrazole, and imidazole, oxazoles, thiazoles, thiadiazoles, azines such as pyridine, pyrimidine, pyrazine, pyridazine and triazines. Optionally benzofused azoles are preferred. The term "Het" preferably represents a thiadiazolyl, benzoxazolyl or benzthiazolyl group which may be substituted by one or more halogen atoms or alkyl, haloalkyl or phenyl groups. When any groups are designated as being optionally substituted, the substituent groups which are optionally present may be any of those customarily employed in the modification and/or development of pesticidal compounds and are especially substituents that maintain or enhance the herbicidal activity associated with the compounds of the present invention, or influence persistence of action, soil or plant penetration, or any other desirable property of such herbicidal compounds. There may be one or more of the same or different substituents present in each part of the molecules. In relation to moieties defined above as comprising an optionally substituted heteroaryl group, optional substituents include halogen, especially fluorine, chlorine and bromine atoms, and nitro, cyano, amino, hydroxyl, C^- alkyl, C^-alkoxy, C^-haloalkyl, C^-haloalkenyl, C^-haloalkoxy, C - haloalkylthio and aryl groups such as phenyl. One to five substituents may be employed, with one to two substituents being preferred, and one substituent being most preferred. That term "Het" in particular represents a group selected from the formulae (1) and (2) (1) (2) in which R 9 represents a hydrogen or halogen atom or a haloalkyl group; X represents O or S; Y represents independently of each other, a halogen atom or an optionally substituted alkyl group; and n is an integer from 0 to 4. Y preferably is a fluoro or chloro atom or a C alkyl, C, .4 fluoroalkyl, C^ alkoxy or C,^ fluoroalkoxy group, and particularly, a chloro atom. SUBSTITUTE SHEET RUL£ 26 The variable n is preferably 0, 1 or 2, and is most preferably 0 or 1. The thiadiazole derivatives (1 ) and the benzoxazole (2) derivatives of formula I wherein X is an oxygen atom are particularly preferred. Generally, if any of the above mentioned moieties comprises an alkyl group, such groups, unless otherwise specified, may be linear or branched and may contain 1 to 6, preferably 1 to 4, carbon atoms. Examples of such groups are methyl, ethyl, propyl, butyl, isobutyl and tertiary-butyl groups. The alkyl portion of a haloalkyl, haloalkoxy, haloalkylthio, alkylthio or alkoxy group preferably has from 1 to 4 carbon atoms, and more preferably, 1 or 2 carbon atoms. Generally, if any of the above mentioned moieties comprises a alkoxyalkyl group, such groups, unless otherwise specified, may be linear or branched and may contain 2 to 6, and preferably 3 to 5, carbon atoms. Examples of such groups are methoxymethyl, 2-methoxyethyl, 3-methoxypropyl, 2-methoxy-1 - methylethyl and methoxybutyl. "Halogen" means a fluorine, chlorine, bromine or iodine atom, and preferably is fluorine, chlorine or bromine. Generally, if any of the above mentioned moieties comprises a haloalkyl group, such groups, unless otherwise specified, may be linear or branched and may contain 1 to 6, preferably 1 to 4, carbon atoms. Examples of such groups are halomethyl, haloethyl, halopropyl, haloisopropyl, halobutyl, haloisobutyl and halotertiary-butyl groups. Haloalkyl moieties of any groups within the definitions used herein can contain one or more halogen atoms, preferably fluorine, chlorine or bromine. Haloalkyl preferably is a mono-, di-, tri- or perfluoroalkyl group, especially trifluoromethyl, pentafluoroethyl, 2,2,2-thfluoroethyl or 1 , 1 , 1 - trifluoroprop-2-yl groups, with trifluoromethyl being most preferred. R 1 preferably is a C-^ alkyl, a C 2 . 6 alkoxyalkyl or C 3 . 7 cycloalkyl group, with ethyl, propyl, isopropyl, cyclopropyl and 2-methoxyethyl groups being most preferred. When R 2 and R 3 together form a single bond, the resulting ring system is a substituted cyclopent-1-enyl group. When R 2 and R 3 together form a methylene group, the resulting ring system is a substituted cyclohex-1-enyl group, e.g., a 3,3,5-trimethylcyclohex-1-enyl or a 3,5,5-trimethylcyclohex-1-enyl group. When R 2 represents a hydrogen atom and R 3 represents an alkyl group, in particular, a methyl group, the resulting branched alkenyl group is of the formula which preferably contains 8 to 12 carbon atoms, and more preferably, 9 or 10 carbon atoms. Most preferred is the 2,6-dimethylhept-3-en-1-yl group. R 4 through R 8 independently represent preferably a hydrogen or a C,^ alkyl group, in particular, a hydrogen atom or a methyl group, provided that at least at least two of these substituents are C M alkyl groups. Most preferred are those compounds of formula I, in which R 4 represents a hydrogen atom; R 5 and R 7 are methyl groups, and one of R 6 and R 8 is a methyl group and the other a hydrogen atom. Particularly preferred are the compounds of formula IA, wherein R 1 represents an alkyl or alkoxyalkyl group, in particular, a C 2 . 3 alkyl or 2- methoxyethyl group, Het represents a group selected from the formulae (1) and (2) (1) (2) in which X represents O or S; and Y represents a halogen atom, in particular, a chlorine atom, or a methyl group, n is 0 or 1 , and R 9 represents a C1-4 fluoroalkyl group, in particular, a trifluoromethyl group. Furthermore preferred are the compounds of formula IB, wherein R 1 represents a C|. 5 alkyl or C 3 . 5 alkoxyalkyl group, in particular an ethyl, isopropyl or 2-methoxyethyl group Het represents a group selected from the formulae (1) and (2) (1) (2) in which X represents O or S; and Y represents a halogen atom, in particular, a chlorine atom, or a methyl group, n is 0 or 1 ; R 9 represents a C^ fluoroalkyl group, in particular, a trifluoromethyl group; and the dashed line indicates the presence of a double bond in one or the other position, provided that R 1 represents a C 2.5 alkyl or C 3 . 5 alkoxyalkyl group, in the event that Het represents a group of formula (1 ). Particularly preferred are the compounds of formulae IB1 to IB4 wherein R 1 represents an ethyl or isopropyl group. wherein X represents O, R 1 represents a C,. 5 alkyl group, or a methoxy-C,^ alkyl group, in particular, a methyl, ethyl, isopropyl, methoxymethyl, 2-methoxyethyl or 2- methoxy-1-methylethyl group, and n is 0 or 1. Preferably, the compounds of formula I are obtained and used as an isomeric mixture of compounds of formula I which differ only in the location of the double bond. Thus, the present invention preferably relates to a mixture of isomeric compounds of formula I which differ only in the location of the double bond, in particular a mixture of the compounds of formula IB. The invention is exemplified by the following representative compounds: 2-(5-trifluoromethyl-[1 ,3,4Hhiadiazol-2-yloxy)-N-ethyl-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, SUBSTITUTE SHEET RUI-E 26 2-(5Jrifiuoromethyl-[1 ,3,4]Jhiadiazol-2-yloxy)-N-ethyl-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]Jhiadiazol-2-yloxy)-N-isopropyl-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-thfluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-isopropyl-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5Jrifluoromethyl-[1 ,3,4]Jhiadiazol-2-yloxy)-N-ethyl-N-(3,3,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5Jrifluoromethyl-[1 ,3,4]Jhiadiazol-2-yloxy)-N-ethyl-N-(3,4,4- trimethylcyclopent-1 -enyl)-acetamide, 2-(5Jrifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-isopropyl-N-(3,3,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-isopropyl-N-(3,4,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-ethyl-N-(3,3,5- trimethylcyclopent-1-enyl)-acetamide, 2-(5Jrifluoromethyl-[1,3,4]Jhiadiazol-2-yloxy)-N-ethyl-N-(2,4,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4Hhiadiazol-2-yloxy)-N-isopropyl-N-(3,3,5- trimethylcyclopent-1 -enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-isopropyl-N-(2,4,4- t methylcyclopent-1-enyl)-acetamide, 2-(5-thfluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en- 4-yl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept- 3-en-4-yl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]Jhiadiazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5- trimethylcyclohex-1 -enyl)-acetamide, 2-(5Jrifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-(2-methoxyethyl)-N-(2,6- dimethylhept-3-en-4-yl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-cyclopropyl-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-cyclopropyl-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-cyclopropyl-N-(2,6- dimethylhept-3-en-4-yl)-acetamide, 2-(benzoxazol-2-yloxy)-N-methyl-N-(3,3,5-trimethylcyclohex-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-methyl-N-(3,5,5-trimethylcyclohex-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclohex-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3,5,5-trimethylcyclohex-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3,3,4-trimethylcyclopent-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3,4,4-trimethylcyclopent-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,4,4-trimethyicyclopent-1-enyl)- acetamide, 2-(benzxazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclopent-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(2,4,4-trimethylcyclopent-1-enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(2,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)-acetamide, 2- (benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4-yl)-acetamide, 2-(benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-methyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-methyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-t methylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-methyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-methyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5-trimethylcyclohex- 1-enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5-trimethylcyclohex- 1-enyl)-acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5-trimethylcyclohex- 1-enyl)-acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5-trimethylcyclohex- 1-enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-methyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-methyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-ethyl-N-(3,3,5-thmethylcyclohex-1-enyl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-ethyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5-trimethylcyclohex- 1-enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3 , 5 , 5-trimethylcyclohex- 1-enyl)-acetamide, SUBSTITUTE SHEET (RUL£ 26) 2-(5-methyl-benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclohex-1-enyl)-acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,5,5-trimethylcyclohex-1-enyl)-acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,3,4-trimethylcyclopent-1-enyl)-acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,4,4-trimethylcyclopent-1-enyl)-acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,3,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclopent-1-enyl)-acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(2,4,4-trimethylcyclopent-1-enyl)-acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(2,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)-acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4-yl)-acetamide, 2-(benzothiazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(5-chloro-benzothiazol-2-yloxy)-N-ethyl-N-(3,3,4-trimethylcyclopent-1-enyl)- acetamide, SUBSTITUTE SHEET (RU.LE 26) 2-(5-chloro-benzothiazol-2-yloxy)-N-ethyl-N-(3,4,4-trimethylcyclopent-1-enyl)- acetamide. The compounds of formula I are oils, gums, or, predominantly, crystalline solid materials. They are superior by virtue of their valuable herbicidal properties. For example, they can be used in agriculture or related fields for the control of undesired plants. The compounds of general formula I possess a high herbicidal activity within a wide concentration range and at low dosages, and may be used in agriculture without any difficulties, in particular, for the selective control of undesired plants such as Alopecurus myosuroides, Echinochloa crus-galli, Setaria viridis, Galium aparine, Stellaria media, Veronica persica, Digitaria sanguinalis, Lolium perenne, Lamium purpureum, Viola arvensis, Abutilon theophrasti, Ipomoea purpurea and Amaranthus retroflexus by pre- and post-emergence application, and particularly in certain crops, such as maize and rice. The compounds of formula I can be prepared by conventional methods. A particularly suitable process for the preparation of the compounds of general formula I comprises the reaction of a compound of formula II: in which R\ R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 are as hereinbefore defined, with a compound of general formula III, Het— L 2 (Ml) in which Het is as hereinbefore defined, and one of L 1 and L 2 represents a hydroxy group and the other represents a leaving group. The reactions may be carried out in the absence or presence of a solvent which promotes the reaction or at least does not interfere with it. Preferred are polar, aprotic or protic solvents, suitable solvents being N,N- dimethylformamide, dimethylsulfoxide, sulfolane, acetone, acetonitrile, methyl ethyl ketone, or an ether, such as tetrahydrofuran or dioxane, or alcohols, or water, or mixtures thereof. The reaction is carried out at a temperature between ambient temperature and the reflux temperature of the reaction mixture, preferably at elevated temperature, especially at reflux temperature. Substantially equimolar amounts of reactants are typically used. The reaction may be carried out in the presence of a basic compound such as an alkali hydroxide, bicarbonate or carbonate, e.g. sodium or potassium hydroxide, bicarbonate or carbonate, an alkali alkoxide, e.g. sodium ethoxide, or an organic base such as triethylamine. In a particularly preferred embodiment, the process of the invention is carried out in the presence of a phase transfer catalyst, preferably a tetraalkyl-ammonium halide, and most preferably, tetraethyl-ammonium bromide. Suitable leaving groups L 1 or L 2 , respectively, are, for instance, alkyl- and arylsulfonyl, in particular, methylsulfonyl, alkyl- and arylsulfonyloxy or perfluoroalkylsulfonyloxy groups, and halogen atoms, particularly fluorine, chlorine and bromine. Certain of the compounds used as starting materials are known, while others are novel. The present invention also relates to the novel intermediates of formula II, wherein R\ R , R 5 , R 6 , R 7 and R 8 are as hereinbefore defined, R 2 represents a hydrogen atom, R 3 represents an alkyl group and L 1 represents a hydroxy group or a leaving group selected from alkyl- and arylsulfonyl, alkyl- and arylsulfonyloxy or perfluoroalkylsulfonyloxy groups and halogen atoms. Most preferred are the compounds of formula IIA wherein R 1 represents an alkyl or alkoxyalkyl group, and L 1 represents a hydroxy group or a halogen atom. The compounds of formula II are obtained from the corresponding imines of formula IV wherein R\ R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 are as defined for the compounds of formula I, by reaction with 2-chloroacetyl chloride and subsequent reaction with alkali acetate and deacylation with aqueous -alcoholic alkali hydroxide solution. The imines of formula IV can be prepared by condensation of a primary amine and the corresponding ketone. When unsymmetrical ketones are used, the resulting double bond in the corresponding compounds of formulae I and II can be formed in two different positions. The reaction product then contains a mixture of isomeric compounds of formulae I and II which differ only in the location of the double bond. Ketones which are readily commercially available, such as 3,5,5- trimethylcyclohexanone, 2,2,4-trimethylcyclopentanone, 2,4,4- trimethylcyclopentanone and di-(2-methylpropyl)-ketone or the like, are preferred. The condensation reaction between the ketone and the amine can be carried out by known procedures, as by removing the product water by azeotropic distillation. The elimination of the water may be accelerated by addition of acid or acid catalysts, such as hydrochloric acid, p-toluenesulfonic acid or ammonium sulfate, or basic compounds such as sodium or potassium hydroxide, and alkali carbonates, or by dehydrating agents such as TiCI 4 or molsieves. The present invention also concerns the methods of using the compounds of formula I as herbicides. Thus, this invention provides a method of combating undesired plant growth at a locus by treating the locus with herbicidally effective amount of a compound of formula I, typically incorporated into a herbicidal composition. As a useful action is by foliar spray application, the locus is most suitably the plants in a crop area, with typical crops being cereals, maize, soybeans, sunflower or cotton. However, application may also be to the soil for those compounds having pre-emergence herbicidal action, or to the water, e.g., for crops such as paddy rice. The invention also provides a method of combating undesired plant growth at a locus, comprising application of such a compound or composition. Particularly interesting activity has been found against grasses and broad leaf weeds, both pre- and post-emergence. Selectivity in important crop species such as wheat, barley, maize, rice and soybeans has also been found. In the methods of the present invention, the effective amount of the active ingredient, a compound of the invention, may be, for example, from 0.05 to 10 kg/ha, preferably 0.01 to 4 kg/ha, in particular, 0.05 -3 kg/ha, and most preferably, 0J to 1 kg/ha. The locus may be an agricultural or horticultural locus, comprising, for example, a plant or soil. In a preferred method the locus contains undesired plant growth and treatment is by foliar spray application. The compounds of general formula I exhibit herbicidal activity. Accordingly, the invention further provides a herbicidal composition which comprises an active ingredient, which is at least one compound of formula I as defined above, and one or more carriers. A method of making such a composition is also provided which comprises bringing a compound of formula I as defined above into association with the carrier(s). Such a composition may contain a single active ingredient or a mixture of several active ingredients of the present invention. It is also envisaged that different isomers or mixtures of isomers may have different levels or spectra of activity and thus compositions may comprise individual isomers or mixtures of isomers in order to broaden the scope of herbicidal activity of the composition. A composition according to the invention preferably contains from 0.5% to 95% by weight (w/w) of one or more active ingredients. An agronomically acceptable carrier in a composition according to the invention is any material with which the active ingredient can be formulated to facilitate application to the locus to be treated, which may, for example, be a plant, seed or soil, or to facilitate storage, transport or handling. The carrier may be solid or liquid, and includes material which is normally a gas but which has been compressed to form a liquid. The compositions may be manufactured into, e.g. emulsions, emulsifiable concentrates, solutions, oil-in-water emulsions, wettable powders, soluble powders, suspension concentrates, dusts, granules, water dispersible granules, microcapsules, gels, aerosols and other formulation types by well-established procedures. These procedures include intensive mixing and/or milling of the active ingredients with other substances, such as fillers, solvents, solid carriers, surface active compounds (surfactants), and optionally, solid and/or liquid auxiliaries and/or adjuvants. The form of the application, such as spraying, atomizing, dispersing or pouring, can be chosen in accordance with the desired objectives and the given circumstances of application. The solvents utilized may be aromatic hydrocarbons, e.g. Solvesso® 200, substituted naphthalenes, phthalic acid esters, e.g., dibutyl or dioctyl phthalate, aliphatic hydrocarbons, e.g., cyclohexane or paraffins, alcohols and glycols, as well as their ethers and esters, e.g. ethanol, ethyleneglycol mono- and dimethyl ether, ketones such as cyclohexanone, strongly polar solvents such as N- methyl-2-pyrrolidone, γ-butyrolactone, higher alkyl pyrrolidones, e.g. n- octylpyrrolidone or cyclohexylpyrrolidone, epoxidized plant oil esters, e.g. methylated coconut or soybean oil ester and water. Mixtures of different solvents are often suitable as carriers. Solid carriers, which may be used for dusts, wettable powders, water dispersible granules, or granules, can be mineral fillers, such as calcite, talc, kaolin, montmorillonite or attapulgite. The physical properties may be improved by addition of highly dispersed silica gel or polymers. Carriers for granules can be porous material, e.g., pumice, kaolin, sepiolite, bentonite or non-sorptive carriers such as calcite or sand. Additionally, a multitude of pre-granulated inorganic or organic materials can be used, such as dolomite or crushed plant residues. Herbicidal compositions are often formulated and transported in a concentrated form which is subsequently diluted by the user before application. The presence of small amounts of a carrier which is a surfactant facilitates this process of dilution. Thus, preferably at least one carrier in a composition according to the invention is a surfactant. For example, the composition may contain two or more carriers, at least one of which is a surfactant. The surfactants utilized can be nonionic, anionic, cationic or zwitterionic substances with good dispersing, emulsifying and wetting properties depending on the nature of the particular compound of formula I to be formulated. The term "surfactant" is also intended to encompass mixtures of two or more surfactants. Wettable powders usually contain 5 to 90% w/w of active ingredient and usually contain, in addition to a solid inert carrier, 3 to10% w/w of dispersing and wetting agents and, where necessary, 0 to 10% w/w of stabilizer(s) and/or other additives such as penetrants or retention enhancers (stickers). Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant, and may be diluted in the field with a further solid carrier to give a composition usually containing 0.5 to 10% w/w of active ingredient. Water dispersible granules and granules are usually prepared so as to have a size between 0J5 mm and 2.0 mm and may be manufactured by a variety of techniques. Generally, these types of granules will contain 0.5 to 90% w/w active ingredient and 0 to 20% w/w of additives such as stabilizer, surfactants, slow release modifiers and binding agents. The so-called "dry flowables" consist of relatively small granules having a relatively high concentration of active ingredient. Emulsifiable concentrates usually contain, in addition to a solvent or a mixture of solvents, 1 to 80% w/v active ingredient, 2 to 20% w/v emulsifiers and 0 to 20% w/v of other additives, such as stabilizers, penetrants and corrosion inhibitors. Suspension concentrates are usually milled so as to obtain a stable, non-sedimenting flowable product and usually contain 5 to 75% w/v active ingredient, 0.5 to 15% w/v of dispersing agents, 0J to 10% w/v of suspending agents such as protective colloids and thixotropic agents, 0 to 10% w/v of other additives such as defoamers, corrosion inhibitors, stabilizers, penetrants and retention enhancers (stickers), and water or an organic liquid in which the active ingredient is substantially insoluble. Certain organic solids or inorganic salts may be present dissolved in the formulation to assist in preventing sedimentation and crystallization, or as antifreeze agents, in the case of water. Aqueous dispersions and emulsions, for example, compositions obtained by diluting the formulated product according to the invention with water, also lie within the scope of the invention. Of particular interest in enhancing the duration of the protective activity of the compounds of this invention is the use of a carrier which will provide slow release of the pesticidal compounds into the environment of a plant which is to be protected. The biological activity of the active ingredient can also be increased by including an adjuvant in the spray dilution. An adjuvant is defined here as a substance which can increase the biological activity of an active ingredient but is not itself significantly biologically active. The adjuvant can either be included in the formulation as a coformulant or carrier, or can be added to the spray tank together with the formulation containing the active ingredient. As a commodity, the compositions are preferably in a concentrated form whereas the end user generally utilizes diluted compositions. The compositions may be diluted to a concentration down to 0.001% of active ingredient. The application rates usually are in the range from 0.01 to 10 kg a.i./ha. Examples of formulations according to the invention are: Emulsion Concentrate (EC) Active Ingredient Compound of Example 2 30 % (w/v) Emulsifier(s) Atlox ® 4856 B / Atlox ® 4858 B ) 5 % (w/v) (mixture containing calcium alkyl aryl sulfonate, fatty alcohol ethoxylates and light aromatics / mixture containing calcium alkyl aryl sulfonate, fatty alcohol ethoxylates and light aromatics) Solvent Shellsol ® A 2) to 1000 ml (mixture of C 9 - C 10 aromatic hydrocarbons) Suspension Concentrate (SO Active Ingredient Compound of Example 3 50 % (w/v) Dispersing agent Soprophor ® FL 3) 3 % (w/v) (polyoxyethylene polyaryl phenyl ether phosphate amine salt) Antifoaming agent Rhodorsil ® 422 3) 0.2 % (w/v) (nonionic aqueous emulsion of polydimethylsiloxanes) Structure agent Kelzan ® S 4) 0.2 % (w/v) (Xanthan gum) Antifreezing agent Propylene glycol 5 % (w/v) Biocidal agent Proxel ® 5) 0.1 % (w/v) (aqueous dipropylene glycol solution containing 20% 1 ,2-benisothiazolin-3-one) Water to 1000 ml Wettable Powder (WP) Active Ingredient Compound of Example 17 60 % (w/w) Wetting agent Atlox ® 4995 1) 2 % (w/w) (polyoxyethylene alkyl ether) SUBSTITUTE SHEET (RULΕ 26) Dispersing agent Witcosperse ® D-60 6) 3 % (w/w) (mixture of sodium salts of condensed naphthalene sulfonic acid and alkylarylpolyoxy acetates Carrier / Filler Kaolin 35 % (w/w) Water Dispersible Granules (WG) Active Ingredient Compound of Example 19 50 % (w/w) Dispersing / Witcosperse ® D-450 6) 8 % (w/w) Binding agent (mixture of sodium salts of condensed naphthalene sulfonic acid and alkyl sulfonates) Wetting agent Morwet® EFW 6) 2 % (w/w) (formaldehyde condensation product) Antifoaming agent Rhodorsil ® EP 6703 3) 1 % (w/w) (encapsulated silicone) Disintegrant Ag rimer ® ATF 7) 2 % (w/w) (cross-linked homopolymer of N-vinyl-2- pyrrolidone) Carrier / Filler Kaolin 35 % (w/w) 1) commercially available from ICI Surfactants 2) commercially available from Deutsche Shell AG 3) commercially available from Rhόne-Poulenc 4) commercially available from Kelco Co. 5) commercially available from Zeneca 6) commercially available from Witco 7) commercially available from International Speciality Products The compositions of this invention can also comprise other compounds having biological activity, e.g., compounds having similar or complementary pesticidal activity or compounds having plant growth regulating, fungicidal or insecticidal activity. These mixtures typically have a broader spectrum of activity than the compound of general formula I alone. Furthermore, the other components can be selected so as to exert a synergistic effect on the pesticidal activity of the compound of general formula I. Combinations of at least two herbicides can be included in a single formulation or later added in a suitable form during the preparation of the tank mix. Exemplary herbicides which can be used in such mixtures include the following: amethydione, bilanafos, metabenzthiazuron, metamitron, metribuzin, 2,4-D, 2,4-DB, 2,4-DP, alachlor, alloxydim, asulam, atrazine, bensulfuron, bentazon, bifenox, bromoxynil, butachlor, carfentratone, chloridazon, chlorimuron, chlorpropham, chlorsulfuron, chlortoluron, cinmethylin, clopyralid, cyanazine, cycloate, cyclosulfamuron, cycloxydim, dichlobenil, diclofop, dimethenamid, EPTC, ethiozin, fenoxaprop, flamprop, fluazifop, fluometuron, fluridone, fluroxypyr, fomesafen, glufosinate, glyphosate, haloxyfop, hexazinone, imazamethabenz, imazamethapyr, imazamox, imazapyr, imazaquin, imazethapyr, ioxynil, isoproturon, isoxaflutole, lactofen, MCPA, MCPP, mefenacet, metazachlor, metolachlor. metsulfuron, molinate, norflurazon, oryzalin, oxyfluorfen, pendimethalin, picloram, pretilachlor, propachlor, pyridate, quizalofop, sethoxydim, simetryn, terbutryn, thiobencarb, triallate, trifluralin, diflufenican, propanil, triclopyr, dicamba, desmedipham, acetochlor, fluoroglycofen, halosafen, tralkoxydim, amidosulfuron, cinosulfuron, nicosulfuron, pyrazosulfuron, sulfentrazone, thiameturon, thifensulfuron, triasulfuron, tribenuron, esprocarb, prosulfocarb, terbutylazin, benfuresate, clomazone, dimethazone, dithiopyr, isoxaben, quinchlorac, quinmerac, sulfosate. Mixtures with other active ingredients like fungicides, insecticides, acaricides and nematicides are also possible. A typical formulation containing a compound according to the invention may consist of 100-500 g of active ingredient (compound of formula I), 30 g of dispersing agent, 2 g of antifoaming agent, 2 g of structure agent, 50 g of anti- freezing agent, 0.5 g of a biocidal agent and water ad 1000 ml. Prior to use it is diluted with water to give the desired concentration of active ingredient. For a clearer understanding of the invention, specific examples are set forth below. These examples are merely illustrations and are not to be understood as limiting the scope and underlying principles of the invention in any way. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the following examples and foregoing description. Such modifications are also intended to fall within the scope of the appended claims. The structures of the compounds prepared in the following examples were additionally confirmed by NMR and mass spectrometry. Example 1 : Preparation of N-(3,3,5-trimethylcyclohex-1-enyl)-N-ethyl-2- hydroxyacetamide and N-(3,5,5-trimethylcyclohex-1-enyl)-N-ethyl-2- hydroxy acetamide 1A N-Ethyl-N-(3 1 3,5-trimethylcyclohexyliden)amine A total quantity of 140 g (ca. 3J mol) of gaseous ethylamine is bubbled into a stirred mixture of 3,3,5-trimethylcyclohexanone (42 g, 0.3 mol), p-toluene sulfonic acid (0.5 g) and toluene (150 ml) at room temperature over a period of ca. 2 days. The progress of the reaction is monitored periodically by the removal of small samples of the reaction mixture for mass spectrometric analysis. After the addition of about half of the ethylamine, when it appears that no more water is being generated and the p-toluenesuifonic acid has completely dissolved, anhydrous sodium sulfate (ca. 30 g) is added to the mixture. After stirring for a few minutes, the solid matter is filtered off, and a further portion of p-toluenesulfonic acid (0.5 g) is added. The addition of the ethylamine is then continued. When the ratio of product to starting material has risen to ca. 70:30, concentrated hydrochloric acid (0.5 ml) is added to the reaction mixture and the remaining quantity of ethylamine is then bubbled in. The reaction mixture is then diluted with an approximately equal volume of petroleum ether, and sodium hydroxide pellets (50 g) are added to the turbid solution. The mixture is shaken several times and the supernatant liquid is then decanted off and evaporated in vacuo to give crude product TA (40 g) as a yellow oil. Analysis of this by NMR and mass spectrometry indicates that the content of the product is ca. 75%. It is used without further purification in the following step. 1 B N-(3,3,5-Trimethylcvclohex-1-enyl)-N-ethyl-α-chloroacetamide and N- (3,5,5-Trimethylcyclohex-1-enyl)-N-ethyl-α-chloroacetamide A solution of 2-chloroacetyl chloride (22.3 g, 0J9 mol) in toluene (100 ml) is added dropwise over 30 minutes to a stirred mixture of 1A (40.0 g, ca. 0.18 mol) in toluene (400 ml) at 0 °C. During the addition, a light-coloured precipitate is formed. The mixture is allowed to warm gradually to room temperature and stirred for a further 16 hours. The mixture is then cooled again to ca. 0 °C and a solution of triethylamine (21.0 g, 0.205 mol) in toluene (100 ml) is added dropwise. After the addition is complete, the mixture is allowed to warm to room temperature and stirred for a further 5 hours, by which time analysis of a sample by thin layer chromatogaphy indicates that the reaction is complete. The precipitate which has formed is removed by filtration and the filtrate is washed five times with water (200 ml), dried over sodium sulfate and evaporated in vacuo. The resulting brown oil (46 g) is distilled through a Vigreux column under reduced pressure to give the product 1 B (33 g, 75%) as a colourless oil, b.p. 118-123 °C / 0.01 mmHg. NMR analysis shows that this consisted of a ca. 42:58 mixture of the 3,3,5- and the 3,5,5-trimethylcyclohex-1- enyl isomers. 1C N-(3,3,5-trimethylcvclohex-1-enyl)-N-ethyl-2-acetoxyacetamide and N- (3,5,5-trimethylcvclohex-1-enyl)-N-ethyl-2-acetoxyacetamide A mixture of sodium acetate (11.1 g, 0.135 mol), 1jB_ (33.0 g, 0J35 mol) and glacial acetic acid (40 ml) is refluxed for 16 hours and then allowed to cool to room temperature. The precipitate is filtered off and the filtrate is evaporated in vacuo. The residue is azeotroped twice with toluene (100 ml), to remove remaining traces of acetic acid. The resulting oil (ca. 42 g) is dissolved in dichloromethane (250 ml) and the solution is washed three times with water (100 ml), dried over sodium sulfate, filtered through a plug of silica gel and evaporated in vacuo to give 1C (29.0 g, 81%) as a pale-brown oil. This is used without further purification in the next step. 1 D N-(3,3,5-trimethylcvclohex-1 -enyl)-N-ethyl-2-hvdroxyacetamide and N- (3,5.5-trimethylcvclohex-1-enyl)-N-ethyl-2-hvdroxyacetamide A mixture of 1C (29.0 g, 0J09 mol) with a solution of potassium hydroxide (6J7 g, 0J 1 mol) in water (11 ml) and ethanol (44 ml) is refluxed for 24 hours and then cooled and evaporated in vacuo to give the crude product (21 g) as a brown oil. This is purified by flash chromatography, eluting with petroleum ether/ethyl acetate (4:1) to give ID (16.8 g, 69%) as a yellow oil. Example 2 Preparation of 2-(5-trifluoromethyl-1 ,3,4-thiadiazol-2-yloxy)-N-(3,5,5- trimethylcyclohexen-1 -yl)-N-ethylacetamide and 2-(5-trifluoromethyl-1 ,3,4- thiadiazol-2-yloxy)-N-(3,3,5-trimethylcyclohexen-1-yl)-N-ethylacetamide To a stirred solution of ID (16.8 g, 75 mmol) in acetone (450 ml) is added potassium carbonate (13.8 g, 100 mmol), followed by 2-methyl-sulfonyl-5- trifluoromethyl-1 ,3,4-thiadiazole (16.9 g, 73 mmol) and then tetraethyl ammonium bromide (2g). The mixture is stirred at room temperature for 30 hours. The precipitate is filtered off and the filtrate is evaporated in vacuo. The residue is dissolved in dichloromethane (250 ml) and the solution is washed twice with water (50 ml), dried over sodium sulfate and evaporated in vacuo to give the crude product (21 g) as a brown oil. Purification by flash chromatography, eluting with toluene/ ethyl acetate (9:1), gave 2 (11.9 g, 43%) as a pale brown oil. The identity and purity of the product are confirmed by 1 H NMR spectroscopy, which also showed that the isomer ratio is approximately 1 : 1 . 9 F NMR (CDCI 3 TFA) δ -17.8 ppm. Examples 3-16: Further compounds of the invention are prepared according to the general method of Examples 1 and 2 and are listed in Table 1. Table 1 The dashed line in the 3,3,5-trimethylcyclohexenyl groups indicates that the corresponding example is a mixture of isomeric compounds which differ only with respect to the position of the double bond. Example 17: Preparation of 2-(benzoxazol-2-y loxy)-N-ethyl-N-(3,3,5-trimethy lcyclohex-1 - enyl)- acetamide and 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide A solution of UQ (3.6 g, 16 mmol) in dry tetrahydrofuran (THF) (25 ml) is added dropwise to a stirred suspension of sodium hydride (0.66 g, 16.5 mmol) in dry THF (50 ml). After approximately 30 minutes, when no further hydrogen evolution is observed, a solution of 2-chlorobenzoxazole (2.3 g, 15 mmol) in dry THF (40 ml) is added dropwise to the stirred mixture, and the reaction is stirred at room temperature overnight. Water (ca. 2.0 ml) is added to the mixture, which is then evaporated in vacuo. Dichloromethane (150 ml) is added to the residue, and the organic phase is washed with water (4 x 100 ml), dried over sodium sulfate, and evaporated in vacuo. The residue is triturated with petroleum ether (5 ml) to give 2 (3.9 g, 77%) as a beige waxy solid. The identity and purity of the product are confirmed by 1 H NMR spectroscopy, which also shows that the isomer ratio is approximately 1 :1. Examples 18-59: Further compounds of the invention are prepared according to the general method of Examples 1 and 17 and are listed in Table 2. Table 2 SUBSTITUTE SHEET (RU.LE 26) the dashed line in for the 3,3,5-trimethylcyclohexenyl groups indicates that the correspnding example is a mixture of isomeric compounds which differ only with respect to the position of the double bond. Examples 60-75: Further compounds of the invention are prepared according to the general method of Examples 1 , 2 and 17 and are listed in Table 3. Table 3 Herbicidal Activity The compounds of the invention are tested pre- and post-emergence using the species in the table below. Plant Species Used TR.ZAW Triticum aestivum winter wheat ZEAMX Zea mays maize GLXMX Glycine max soybeans HORVW Hordeum vulgare winter barley ORYSA Oryza sativum rice ALOMY Alopecurus myosuroides blackgrass AMARU Amaranthus rudis waterhemp APESV Apera spica venti bentgrass DIGSA Digitaria sanguinalis crabgrass ECHCG Echinochloa crus-galli barnyardgrass LOLPE Lolium perenne eavers SETVI Setaria viridis green foxtail SETFA Setaria faberi giant foxtail Each pot is examined three weeks after treatment and phytotoxicity is expressed using a 0 to 100 % scale with 0 = no effect and 100 = total kill. PRE-emer ence Herbicidal Evaluation of Test Compounds: The pre-emergence herbicidal activity of the compounds of the present invention is exemplified by the following test in which the seeds of a variety of monocotyledonous and dicotyledonous plants are separately mixed with potting soil and planted on top of approximately one inch of soil in separate pots. After planting, the pots are sprayed with the selected aqueous acetone solution containing test compound in sufficient quantity to provide the equivalent of about 0.8 to 0J kg per hectare of test compound per pot. The treated pots are then placed on greenhouse benches, watered and cared for in accordance with conventional greenhouse procedures. The results are set out in Tables 4, 6 and 8 below. Post-emergence Herbicidal Evaluation of Test Compounds: The post-emergence herbicidal activity of the compounds of the present invention is demonstrated by the following test, wherein a variety of monocotyledonous and dicotyledonous plants are treated with formulations prepared from solutions of the test compounds in acetone containing 0.4 % by weight of an alkylphenol/ethylene oxide condensate available under the trade mark TRITON X-155. These acetone solutions are diluted with water and the resulting formulations applied at dosage levels equivalent to about 0.4 to 0.2 kg per hectare of test compound per pot. After spraying, the plants are placed on greenhouse benches and are cared for in the usual manner, commensurate with conventional greenhouse practices. The results of the test are set out in Tables 5, 7 and 9 below. Example A The compounds of the invention, i.e., the compounds of E.XAMPLE 3 and EXAMPLE 2 when compared to a mixture of 2-(5-thfiuoromethyl-1 ,3,4- thiadiazol-2-yloxy)-N-(3,5,5-trimethylcyclohexen-1-yl)-N-methylacetamide and 2-(5-trifluoromethyl-1 ,3,4-thiadiazol-2-yloxy)-N-(3,3,5-trimethylcyclohexen-1-yl)- N-methylacetamide (COMPOUND B), the state of the art (US Patent No. 4,585,471) display clearly better crop tolerance in wheat, maize, soybeans and rice than COMPOUND B, as shown in Table 4 below. This is particularly demonstrated by the compound of EXAMPLE 3 which shows good crop selectivity in wheat and soybeans up to the highest dose of 800 g/ha and in rice up to 400 g/ha exhibiting high levels of activity on grasses such as Alopecurus, Digitaria, Echinochloa and Setaria at these doses. COMPOUND B, shows marked stunting of wheat even at the lowest dose of 100 g/ha, however, activity on Alopecurus, an important grass weed for European cereals, is insufficient, indicating, that contrary to EXAMPLE 3, wheat selective control of Alopecurus is not achieved by COMPOUND B. In maize, the compound of EXAMPLE 3 shows good selectivity in maize and complete control of Setaria faberi at 200 g/ha, while the standard is only selective in maize at a dose of 100g/ha with insufficient activity on Setaria at this dose. The compound of EXAMPLE 2 also shows considerably better selectivity in maize than COMPOUND B, since it is entirely selective in maize up to 400 g/ha and provides high levels of grass activity, including Setaria, at maize selective doses. Table 4: PRE-EMERGENCE APPLICATION: compound Dose T Z G O A D E S g/ha R E L R L I C E Z A X Y O G H T A M M S M S C F W X A A Y A G A Example 2 800 30 50 20 95 100 100 100 100 Example 2 400 30 0 5 50 100 100 100 100 Example 2 200 20 0 0 15 90 100 100 100 Example 3 800 10 55 0 40 99 100 100 100 Example 3 400 5 20 0 0 95 100 100 100 Example 3 200 0 0 0 0 75 100 97 100 B 800 65 75 30 95 100 100 100 100 B 400 45 45 20 92 95 100 100 100 B 200 25 45 0 45 92 100 99 100 B 100 25 0 0 10 75 100 98 80 Example B When compared to a mixture of 2-(5-trifluoromethyl-1 ,3,4-thiadiazol-2-yloxy)-N- (3,5,5-trimethylcyclohexen-1-yl)-N-methylacetamide and 2-(5-trifluoromethyl- 1,3,4-thiadiazol-2-yloxy)-N-(3,3,5-trimethylcyclohexen-1-yl)-N-methylacetamide (COMPOUND B), the state of the art (US Patent No. 4,585,471), the compound of EaXAMPLE 3 clearly demonstrates better selectivity in wheat and rice than COMPOUND B since it is sufficiently selective in these crops up to the highest dose of 400 g/ha. COMPOUND B, however, is not sufficiently selective in wheat at 400 g/ha and shows only borderline selectivity in wheat at 200 g/ha. Table 5: POST-EMERGENCE APPLICATION Compound Dose g/ha T O A D S R R L I E Z Y O G T A z M S V W A Y A I Example 3 400 0 0 95 90 90 Example 3 200 0 0 70 80 60 B 400 35 20 95 90 90 B 200 20 0 85 90 70 Example C In addition, the compounds of the invention of Example 8 are tested pre- and post-emergence and compared with 2-(5-trifluoromethyl-1 ,3,4-thiadiazol-2- yloxy)-N-(2,4-dimethylhept-2-en-3-yl)-N-(2-methoxyethyl)acetamide COMPOUND C, the state of the art (International Patent Application WO 97/08160). Each pot is examined three weeks after treatment and phytotoxicity is assessed according to the rating system set forth below. Rating System % Difference in Growth Versus Untreated Control 0 - No effect 0 1 - Trace effect 1-5 2 - Slight effect 6-15 3 - Moderate effect 16-29 4 - Injury 30-44 5 - Definite injury 45-64 6 - Herbicidal effect 65-79 7 - Good herbicidal effect 80-90 8 - Approaching complete kill 91-99 9 - Complete kill 100 The compound of Example 8 displays clearly better crop tolerance in wheat, maize, soybeans and rice than COMPOUND C as shown in the following Tables 6 and 7: Table 6: PRE-EMERGENCE APPLICATION Compound g/ha T O A S E A G R R L E C M A Z Y O T H A L A S M V C R A W A Y I G U P C 800 7 7 9 9 9 8 2 400 5 5 8 8 9 7 0 200 1 2 8 8 8 0 0 100 0 0 5 4 5 0 0 50 0 0 2 0 2 0 0 EXAMPLE 800 4 2 9 9 9 8 7 8 400 2 0 9 9 9 8 3 200 2 0 8 8 8 6 0 100 0 0 7 8 7 0 0 50 0 0 5 6 4 0 0 The compound of EXAMPLE 8 showed clearly better selectivity in both wheat and rice than COMPOUND C, of PCT WO 97/08160. The compound of the invention was sufficiently selective in wheat at 400 g/ha and showed good selectivity in rice even at the highest dose of 800 g/ha, while Compound C was tolerated in both crops at the reduced dose of 200 g/ha only. Furthermore, the compound of the invention was considerably more active on monocotyledonous weeds (Alopecurus, Setaria, Echinochloa) and dicotyledonous weeds (Amaranthus, Galium). Table 7: POST-EMERGENCE APPLICATION Compound g/ha T H Z A A R O E L P z R A O E A V M M S W W X Y V COMPOUND C 400 4 4 5 8 6 200 2 0 3 4 4 EXAMPLE 8 400 2 0 3 8 8 200 0 0 0 7 5 The Compound of EXAMPLE 8 was sufficiently selective in wheat and barley at the highest dose of 400 g/ha and in maize at 200 g/ha. COMPOUND C was clearly less selective in these crops than the compound of the invention. Furthermore, the compound of the invention was markedly more active on Alopecurus myosuroides and Apera spica-venti, both of which are important grass weeds in European cereals. Both grasses were well controlled by the compound of the invention at the wheat and barley selective dose of 400 g/ha. COMPOUND C did not display sufficient levels of activity on Apera at any rate and Alopecurus control was not achieved at barley or wheat selective doses. Example D In the following testing, the compounds of the invention of Examples 17 and 19 were shown to exhibit excellent selectivity in wheat, barley, soybeans and rice as indicated by the results shown in Tables 8 and 9. At crop selective doses, both the Compounds of Examples 17 and 19 display high activity on Alopecurus, Brachiaria, Digitaria, Echinochloa, Setaria faben and S. viridis, when applied either in pre- or post-emergence. Table 8: PRE-EMERGENCE APPLICATION The compounds of the present invention of Examples 17 and 19 demonstrate good selectivity in wheat, barley, soybeans and rice. Furthermore high levels of activity on Alopecurus, Digitaria, Echinochloa, Setaria faben and S. viridis are recorded at crop selective doses. Table 9: POST-EMERGENCE APPLICATION Example E In the following test, the compound of the invention of Example 21 is tested in post-emergence application and compared with 2-(6- chlorobenzoxazol-2-yloxy)-N-(cylohex-1-enyl)-N-methyl-acetamide COMPOUND D, the state of the art (European Patent Application EP 0 165 537). The Compound of EXAMPLE 21 clearly showed better selectivity in barley than COMPOUND D, the compound of the state of the art as indicated by the results of Table 10. Table 10: POST-EMERGENCE APPLICATION Compound g/ha H A L A O L O P R O L E V M P S W Y E V COMPOUND D 400 35 95 70 95 200 5 90 60 90 100 0 85 55 70 EXAMPLE 21 400 15 98 90 95 200 5 96 85 90 100 0 85 60 85 The compound of the invention was clearly more tolerant in barley and more active on Alopecurus, Loiium and Apera, which are key grasses in grain cereals, than the compound of the state of the art. Thus the compound of the invention was sufficiently tolerant in barley up to 400 g/ha, while the highest rate tolerated by the compound of the state of the art was 200 g/ha. At the crop selective dose of 400 g/ha the compound of the invention showed good control of Alopecurus and Apera (98 and 95 %, respectively), while the compound of the state of the art displayed clearly less control of these grasses at the doses tolerated by barley.

Claims: 33379-00 What is claimed is: 1. A compound of the general formula (I) wherein Het represents an optionally substituted, optionally benzofused nitrogen containing 5- or 6-membered heteroaromatic group; R 1 represents an alkyl, alkoxyalkyl or cycloalkyl group; R 2 represents a hydrogen atom, and R 3 represents an alkyl group, or R 2 and R 3 taken together form a single bond or a methylene group; and R 4 , R 5 , R 6 , R 7 and R 8 independently represent a hydrogen atom or a C C 4 alkyl group, with the provisos that a) at least two of R 4 , R 5 , R 6 , R 7 and R 8 must represent an alkyl group; and b) 2-(5Jrifluoromethyl-1,3,4Jhiadiazol-2-yloxy)-N-methyl-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide is excluded. 2. A compound according to claim 1 wherein R 4 , R 5 , R 6 , R 7 and R 8 independently represent hydrogen or methyl. 3. A compound according to claim 1 or 2 wherein Het represents a thiadiazolyl, benzoxazolyl or benzothiazolyl group which may be substituted by one or more halogen atoms or alkyl, haloalkyl or phenyl groups. 4. A compound according to claim 3 wherein Het represents a group selected from the formulae (1) and (2) (1) (2) in which R 9 represents a hydrogen or halogen atom or a haloalkyl group; X represents O or S; Y represents independently of each other a halogen atom or an optionally substituted alkyl group; and n is an integer from 0 to 4. 5. A compound according to any of claims 1-4 wherein R 2 and R 3 taken together form a single bond or a methylene group. 6. A compound according to any of claims 1-5, wherein R 1 represents a C 2 . 5 alkyl, a cyclopropyl or a 2-methoxyethyl group. 7. A compound according to claim 1 of the formula IA, wherein R 1 represents an alkyl or alkoxyalkyl group, Het represents a group selected from the formulae (1) and (2) 25702 (1) (2) in which X represents O or S; and Y represents a halogen atom or a methyl group, n is 0 or 1 , and R 9 represents a C M fluoroalkyl group. 8. A compound according to claim 1 of the formula IB, wherein R 1 represents a C 2 . 5 alkyl or alkoxyalkyl group, Het represents a group selected from the formulae (1) and (2) (1) (2) in which X represents O or S; and Y represents a halogen atom or a methyl group, n is 0 or 1 ; R 9 represents a C fluoroalkyl group; and the dashed line indicates the presence of a double bond in one or the other position. 9. An isomeric mixture of the two compounds of formula IB of claim 8 which differ only in the location of the double bond. 10. A compound according to claims 7 to 9 selected from the group consisting of 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy -N-ethyl-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy -N-ethyl-N-(3,5,5- trirnethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy -N-isopropyl-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy -N-isopropyl-N-(3,5,5- trimethylcyciohex-1-enyl)-acetamide, 2-(5-trifl uoromethyl-[ 1 , 3 ,4]-th iad iazol-2-yloxy N-ethyl-N-(3,3,4- trimethylcyciopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy N-ethyl-N-(3,4,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy -N-isopropyl-N-(3,3,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy -N-isopropyl-N-(3,4,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy -N-ethyl-N-(3,3,5- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy -N-ethyl-N-(2,4,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy -N-isopropyl-N-(3,3,5- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy -N-isopropyl-N-(2,4,4- trimethylcyclopent-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yioxy -N-ethyl-N-(2,6-dimethylhept- 3-en-4-yi)-acetamide, SUBSTΓΠΠΈ SHEET RULE 26 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy)-N-isopropyl-N-(2,6- dimethylhept-3-en-4-yl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-(2-methoxyethyl)-N- (3,3,5-trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy)-N-(2-methoxyethyl)-N- (3,5,5-trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy)-N-(2-methoxyethyl)-N-(2,6- dimethylhept-3-en-4-yl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-cyclopropyl-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1 ,3,4]-thiadiazol-2-yloxy)-N-cyclopropyl-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-trifluoromethyl-[1,3,4]-thiadiazol-2-yloxy)-N-cyclopropyl-N-(2,6- dimethylhept-3-en-4-yl)-acetamide. 2-(benzoxazol-2-yloxy)-N-methyl-N-(3 , 3 , 5-trimethylcyclohex- 1 -enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-methyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3 , 3 , 5-trimethylcyclohex- 1 -enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3 , 5 , 5-trimethy lcyclohex- 1 -enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3,3,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(3,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,4-trimethylcyciopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzxazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(2,4,4-trimethyicyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(2,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)-acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-methyi-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-chloro-benzoxazoi-2-yloxy)-N-methyl-N-(3,5,5-trimethylcyciohex-1- enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(3,5,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1- enyl)-acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-methyl-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(6-chloro-benzoxazol-2-yioxy)-N-methy l-N-(3 , 5 , 5-trimethy lcyclohex- 1 - enyl)-acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(6-ch loro-benzoxazol-2-yloxy)-N-ethy l-N-(3 , 5 , 5-trimethy lcyclohex- 1 - enyl)-acetamide, 2-(benzoxazol-2-yloxy)-N-isopropyl-N-(3 , 3 , 5-trimethy lcyclohex- 1 -enyl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4- yl)-acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4- yl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(6-chloro-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-methyl-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-methyl-N-(3, 5, 5-trimethylcyclohex-1 - enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-ethyl-N-(3 , 3 , 5-trimethylcyclohex- 1 - enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-ethyl-N-(3,5,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-isopropyl-N-(3 , 3 , 5-trimethylcyclohex- 1 - enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5- trimethylcyclohex-1-enyl)-acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(5-methyl-benzoxazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4- yl)-acetamide. 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3 , 3 , 5-trimethylcyclohex- 1 -enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3 , 5 , 5-trimethylcyclohex- 1 -enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,3,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,5,5-trimethylcyclohex-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,3,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,3,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(3,4,4-trimethylcyciopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(3,3,5-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(2,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yioxy)-N-isopropyl-N-(3,3,5-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-isopropyi-N-(2,4,4-trimethylcyclopent-1-enyl)- acetamide, 2-(benzothiazol-2-yloxy)-N-ethyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, and 2-(benzothiazol-2-yloxy)-N-isopropyl-N-(2,6-dimethylhept-3-en-4-yl)- acetamide, 2-(benzothiazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,3,5-trimethylcyclohex-1- enyl)-acetamide, 2-(benzothiazol-2-yloxy)-N-(2-methoxyethyl)-N-(3,5,5-trimethylcyclohex-1- enyl)-acetamide, 2-(5-ch loro-benzothiazol-2-yloxy)-N-ethyl-N-(3 , 3 ,4-trimethylcyclopent- 1 - enyl)-acetamide, 2-(5-chloro-benzothiazol-2-yloxy)-N-ethyl-N-(3,4,4-trimethylcyclopent-1- enyl)-acetamide. 11. A process for the preparation of a compound according to any of the preceding claims, which comprises reacting a compound of the general formula II, in which R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 are as defined in claim 1 with a compound of general formula III, Het— L 2 (III) in which Het has the meaning given, and one of L 1 and L 2 represents a hydroxy group and the other represents a leaving group. 12. A compound of the general formula II, in which R 1 , R 4 , R 5 , R 6 , R 7 and R 8 are as defined in claim 1 , and R 2 represents a hydrogen atom, R 3 represents an alkyl group, and L 1 represents a hydroxy group or a leaving group selected from alkyl- and arylsulfonyl, alkyl- and arylsulfonyloxy, perfluoroalkylsulfonyloxy groups and halogen atoms. 13. A herbicidal composition comprising at least one compound according to any of claims 1 to 10 and at least one agronomically acceptable carrier. 14. A composition according to claim 13 comprising at least two carriers, at least one of which is a surface-active agent. 15. A method of combating undesired plant growth at a locus which comprises applying to the locus a herbicidally effective amount of a compound described in any of claims 1 to 10. 16. A method of combating undesired plant growth at a locus which comprises applying to the locus a herbicidally effective amount of a composition according to claim 13 or 14.

Inventors: BALTRUSCHAT HELMUT SIEGFRIED, KLEEMANN AXEL, MENGEL WERNER, NEWTON TREVOR WILLIAM, BALTRUSCHAT, HELMUT, SIEGFRIED, KLEEMANN, AXEL, MENGEL, WERNER, NEWTON, TREVOR, WILLIAM
Applicants: AMERICAN CYANAMID CO, BALTRUSCHAT HELMUT SIEGFRIED, KLEEMANN AXEL, MENGEL WERNER, NEWTON TREVOR WILLIAM, AMERICAN CYANAMID COMPANY, BALTRUSCHAT, HELMUT, SIEGFRIED, KLEEMANN, AXEL, MENGEL, WERNER, NEWTON, TREVOR, WILLIAM
Application year: 1998
Main classification: C07D285
IPC codes: A01N43, C07D213, C07D231, C07D239, C07D241, C07D251, C07D257, C07D263, C07D277, C07D285, C07D471