PROCESS FOR THE PREPARATION OF BICYCLOHEPTANE DERIVATIVES, AND NOVEL BICYCLOHEPTANE DERIVATIVES

Abstract: A process for the preparation of a 2-exo-hydroxy-7-oxa-bicyclo[2.2.1]heptane, wherein the corresponding cis 3,4-expoxycyclohexanol is cyclised by treatment with an acid. Specific 2-exo-hydroxy-7-oxabicyclo[2.2.1]heptanes and intermediates thereof.

Description: PROCESS FOR THE PREPARATION OF BICYCLOHEPTANE DERIVATIVES, AND NOVEL BICYCLOHEPTANE DERIVATIVES This invention relates to a process for the preparation of bicycloheptane derivatives, and to certain novel bicycloheptane derivatives. Our co-pending application claiming priority from US Application Serial No. 331,094 (our internal reference number K 3335) describes and claims certain novel compounds useful as herbicides. Certain ethers derived from the exo isomers of 2-hydroxy-7-oxabicyclo[2,2,1]heptane derivatives are especially useful; such ethers may be prepared from said hydroxy compounds. J. Chem. Soc. (c), 1969, pages 716-721, describes a process for the preparation of 2-endo-hydroxy-1-methyl-4-isopropyl-7- oxabicyclo[2,2,l]heptane, However, no method is known for the preparation of the corresponding exo compound and related compounds. The present invention therefore provides a process for the preparation of a 2-exo-hydroxy-7-oxabicyclo[2,2,1]heptane, which comprises cyclising the corresponding cis 3,4-epoxycyclohexanol by treatment with an acid. Preferably, the exo isomer of a compound of the general formula I is prepared by cyclisation of the cis isomer of a compound of the general formula II: EMI2.1 wherein R1 is a hydrogen atom; a C1- 10 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms or by a hydroxy group, a cyano group, a C14 alkoxy group, a C16 alkylsulphonyl group, a C 10 arylsulphonyl group, a C7 11 aralkylsulphonyl group, an azido group, a C 1-6 alkoxycarbonyl group, a hydroxycarbonyl group, a phosphoryl group, a phosphoryloxy group, or an amine oxide, carbamoyl or thiocarbamoyl group in which the nitrogen atom is substituted by hydrogen or by l or 2 C 1-4 alkyl groups; an aryl or aralkyl group, each containing from 6 to 11 carbon atoms, and 1 to 4 carbons in the alkyl portion, each optionally ring-substituted by one or more fluorine, chlorine and/or bromine atoms or by a C12 alkyl or alkoxy group optionally substituted by one or more fluorine and/or chlorine atoms; or a group CO2R6 or CON(R6)2 in which R6 is a hydrogen atom or a C16 alkyl group; R2 is a hydrogen atom or a straight-chain C16 alkyl group; each R3 is independently a hydrogen atom; a chlorine atom; a bromine atom; or a C 1-4 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms; or two R3's when located on adjacent carbon atoms together form an epoxide ring or a carbon-carbon bond; R4 is a hydrogen atom or a C1 4 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms; each R5 is independently a hydrogen atom; a C14 alkyl group optionally substituted by up to 3 fluorine chlorine and/or bromine atoms; a hydroxy group; or a C1 4 alkoxy group. Preferably RÚ is a hydrogen atom; a C1-4 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms or by OH, CN, a C 1-4 alkoxy group, a C16 alkylsulphonyl group, a phenylsulphonyl group, or a benzylsulphonyl group; or an aryl or aralkyl group each containing from 6 to 10 carbon atoms and 1 or 2 carbon atoms in any alkyl portion, optionally substituted by one or more fluorine, chlorine and/or bromine atoms or by a C 1-2 alkyl or alkoxy group each optionally substituted by one or more fluorine and/or chlorine atoms. More preferably, R1 is a hydrogen atom or a C 1-3 alkyl group optionally substituted by chlorine, for example a methyl, ethyl, n-propyl, isopropyl or l-chloro-l-methylethyl group. Preferably R2 is a straight-chain C 1-4 alkyl group, especially a methyl or ethyl group. Especially preferred for use in the process of the invention are compounds in which R1 is an isopropyl group and R2 Ú Ú is a methyl group; R and R2 are both ethyl groups; or R is a l-chloro-l-methylethyl group and RZ is a methyl group. Each R3 is preferably independently a hydrogen atom; a chlorine atom; a bromine atom; or a methyl or ethyl group. Most preferably each RB is a hydrogen atom. Preferably R4 is a hydrogen atom. Preferably each R5 is a methyl or ethyl group or, especially, a hydrogen atom. Most of the compounds of the general formulae I and II are novel. The invention therefore also provides a compound of the 1 4 and 5 general formula I or II per se, wherein R , R , R, R and R have the meanings given above, with the proviso that when R2 represents a methyl group and all of R3, R4 and R5 represent hydrogen atoms, then RI is other than an isopropyl group. The cyclization reaction is surprising in its relatively high yield of the exo-hydroxy configuration of the resulting 2-hydroxy-7-oxabicyclo [2,2,1] heptane. Many acids will catalyze this reaction, but a relatively strong acid, such as hydrochloric, sulphuric or sulphonic acids, or an acidic ion exchange resin, such as Amberlist (Trade Mark) sulphonic acid, is especially suitable. Preferably, the acid has a pKA of I or less. Most preferably, the acid is an organic sulphonic acid, for example an alkyl, alkaryl or aryl sulphonic acid, such as methanesulphonic, ethanesulphonic, p-toluenesulphonic, m-nitrobenzenesulphonic, 2, 4-dimethylbenzenesulphonic, or benzenesulphonic acid. Of these, p-toluenesulphonic acid is preferred. The amount of acid used is not critical; preferably it is used in amounts from 0,001 to 0.5 mole per mole of cisepoxycyclohexanol, suitably from 0.01 to about 0.1, and especially from 0.02 to 0.04 mole of acid per mole of cis-epoxycyclohexanol. The reaction is preferably carried out in the presence of an inert solvent. Suitable solvents include for example chlorinated hydrocarbons, ethers, hydrocarbons, and ketones. Typical chlorinated hydrocarbons contain from 1 to 4 chlorine atoms in combination with an alkane chain containing from 1 to carbon atoms or a benzene ring, for example carbon tetrachloride, chloroform, dichloromethane, chlorobenzene and 1,2- or 1,3-dichlorobenzene. Preferred ethers are generally those containing from 4 to 6 carbon atoms, for example diethyl ether, methyl tert-butyl ether and diisopropyl ether. Tetrahydrofuran and dioxane are also useful. Suitable alkanes contain for example from 5 to 10 carbon atoms; petroleum fractions rich in alkanes are suitable. Petroleum ether is also suitable. Cyclohexane and methylcyclohexane are examples of useful cycloalkane solvents containing from 6 to 8 carbon atoms. Suitable aromatic hydrocarbon solvents preferably contain from 6 to 10 carbon atoms, for example benzene, toluene, o-, m-, and p-xylene, the trimethylbenzenes and p-ethyltoluene. Suitable ketones include acetone and methyl ethyl ketone. If an excess of epoxycyclohexanol is present, this may, if desired, serve as solvent so that no additional solvent is necessary. Preferably the reaction is carried out in the substantial absence of water. The reaction temperature is conveniently in the range of from 0-750C, in particular from OOC to 500C. Suitably, the temperature is from 5"C to 400C, preferably from IOOC to 300C. The resulting 2-exo-hydroxy-7-oxabicyclo [2,2 lJheptane derivative may be purified by conventional techniques or converted without isolation into useful ether derivatives. The cis 3,4-epoxycyclohexanol used as starting material in the process according to the invention may be prepared by epoxidation of the corresponding cyclohexenol, using a suitable oxidising agent. Preferred cyclohexenols are those of the general formula. EMI5.1 in which R1, R2, R3, R4 and R5 have the meanings given above. Any oxidizing agent that will form the epoxyalcohol may be used. Preferred oxidising agents include peroxy acids, hydrogen peroxide and organic peroxides, such as m-chloroperbenzoic acid, peracetic acid, perphthalic acid, cumene hydroperoxide, persuccinic acid, pernonanoic acid, an alkyl hydroperoxide such as tert-butyl hydroperoxide, persulphuric acid and hydrogen peroxide. Preferably, the oxidation is carried out using an alkyl hydroperoxide or hydrogen peroxide and is conducted in the presence of an appropriate transition metal catalyst. Such a catalyst is preferably present in an amount of from about 0.0005 to 0.10 mole of catalyst per mole of peroxide, preferably from about 0.01 to 0.03 mole catalyst per mole of peroxide. Suitable transition metal catalysts are complexes of metals of atomic numbers 22-31, 40-49 and 72-81. Preferably the complex is an organic complex, for example with beta-diketones, o-hydroxybenzaldehydes or o-hydroxybenzophenones and particularly with acetylacetone. Catalysts containing molybdenum or, especially, vanadium, are preferred; for example, vanadium (IV) bis(2,4-pentanedionate) oxide is especially useful. The oxidizing agent may suitably be used in an amount from 0.5 to 3, preferably in an amount from 1.0 to 1.2 moles per mole of cyclohexenol, most preferably from 1.0-1.1 moles per mole of cyclohexenol. The treatment with an oxidizing agent is preferably conducted in a solvent, ideally of the type also useful in the subsequent cyclization as described above. The reaction temperature is conveniently in the range of about - IOOC to 750C, in particular from -10 to 500C. Generally, the preferred temperature is from -50C to 400 C, preferably from 10 C to 300C. The resulting epoxy-alcohol may be purified by conventional techniques or converted without isolation into the 2-exohydroxy-7-oxabicyclo [2,2,1]heptane by cyclization. Especially useful for obtaining a 2-exo-hydroxy-7 oxabicyclo[2,2,1]heptane is treatment of the appropriate cyclohexenol with either tert-butyl hydroperoxide and vanadium (IV) bis (2,4-pentanedioate) oxide as catalyst in a solvent, for example methylene chloride, or hydrogen peroxide and the vanadium catalyst in a solvent, for example acetone, followed by treatment of the intermediate epoxide, preferably in situ, with a sulphonic acid, particularly p-toluenesulphonic acid. In some cases, acid generated during the epoxidation step from a peroxy acid, e.g. m-chloroperbenzoic acid, produces the desired cyclised product directly. The epoxidation and ring closure steps may be carried out successively; alternatively, the 3-cyclohexen-1-ol may be treated conveniently with an oxidizing agent and an acid, to produce cyclisation of the epoxide in situ. Most of the compounds of the general formula III are novel, and the invention therefore also provides a compound of the general formula III per se, wherein RÚ , Rê, R , R4 and R have the meanings given above, with the proviso that R1 and R2 are not both hydrogen atoms, and with the proviso that when Rê represents a methyl group and all of R3, R4 and R5 represent hydrogen atoms, then R1 is other than an isopropyl group. The 2-exo-hydroxy-7-oxabicyclo[2,2,1]heptanes exhibit geometrical and optical isomerism. From the various optical and geometrical forms of the materials of the invention and various combinations thereof ethers may be prepared which usually have different herbicidal activities. The materials of formula I that have the OH group exo (formula Ia below) with respect to the oxygen-containing bridge result in exo ethers usually more herbicidally active than the ethers of the endo hydroxy form (formula Ib below) or the exo-endo mixture. EMI8.1 lS-exo-form lS-endo-form Formula Ia Formula Ib When R2 is hydrogen, then the compounds of formula Ia and Ib have the 1S absolute configuration shown above. Such compounds of the invention of Ia that correspond in configuration are preferred. In situations where the endo form is desired it can be obtained by oxidation of the 2-exo-hydroxy compound to the corresponding ketone followed by reduction of the ketone with sodium borohydride. The compounds of the general formula I are useful intermediates in the preparation of the corresponding novel ethers having herbicidal properties in which the hydrogen of the 2-hydroxy group is replaced by a group WCQ2- in which W is an optionally-substituted unsaturated group of up to 4 carbon atoms; an optionally substituted, aromatic or heterocyclic group containing up to 14 carbon atoms; a C3 10 cycloaliphatic group optionally substituted by C1 3 alkyl; or a C3 10 secondary alkyl group; and both of Q are hydrogen atoms or fluorine atoms. These ethers and their use to control the growth of unwanted plants are disclosed in our copending Application claiming priority from U.S. patent application Serial No. 331, 094, filed December 16, 1981, (our internal reference number K3335). Such ethers may be prepared by treating the 2-exo-hydroxy-7 oxabicyclo[2,2,ljheptane of formula I with a compound of the formula WCQ2L, in which L is a suitable leaving group, for example a halogen atom, such as bromine, chlorine or iodines or an organic sulphonyloxy group, for example a mesyloxy or tosyloxy group. The reaction is preferably carried out in the presence of a strong base and an inert diluent, and preferably in the presence of a catalyst. The strong base is suitably an alkali metal hydride, amide, hydroxide or carbonate, including, for example, sodium hydride, sodium amide, sodium hydroxide and potassium carbonate. Inert diluents are suitably organic solvents, such as ethers, sulphoxides, aromatic hydrocarbons and chlorinated hydrocarbons including, for example, diethyl ether, tetrahydrofuran, toluene, methylene chloride and the like. Suitable catalysts are organic bases, such as tertiary amines and ammonium compounds, for example triethylamine or benzyltriethylammonium chloride. The reaction is most conveniently carried out under normal pressures and ambient temperatures. Suitable temperatures for the reaction are from about 0 to about 1200C, preferably from 20 to 100"C. The 3-cyclohexen-1-ols can be synthesized as described below or obtained from natural sources. (a) Where R2 is methyl and R1 is isopropyl, and the remaining R's are hydrogen, the compound is terpinen-4-ol, which occurs naturally in optically active and racemic forms, or can be prepared by epoxidation of terpinolene, followed by reduction of the epoxide. (b) Substituted-l-oxaspiro(2,5)oct-5-enes are useful for preparing 3-cyclohexen-1-ols where R1 is substituted by OH, OR, SR, Nor2, N3, P(O)(OR)2. Treatment of a l-oxaspiro(2,5)oct-5-ene with water or an alcohol in the presence of a strong acid affords the corresponding 3-cyclohexen-1-ol substituted in the l-position by a hydroxymethyl or alkoxymethyl group. Treatment of l-oxaspiro(2,5)oct-5-ene with thiophenol, or an alkyl, C6 11 aryl, or C7 11 aralkyl mercaptan, in the presence of a catalyst, such as sodium hydride, and a suitable solvent, produces a thio-substituted 3-cyclohexen-1-ol that can be converted to the corresponding sulphonyl derivative in the course of the oxidation process described above. Where R is halo-substituted, the haloalkyl-substituted-3-cyclohexen-l-ol may be prepared by treating a spiro compound as defined above with an ethereal hydrohalogenic acid, e.g. hydrochloric acid. From the (haloalkyl) substituted compounds thus obtained (haloalkyl)-substituted ethers may be made which can then be dehydrochlorinated to yield the corresponding 4-alkenyl-substituted ethers (where R1 is alkenyl) with the use of a base. Compounds where R is alkenyl may also be made by rearrangement of the spiro compounds upon treatment with protic or Lewis acids-. Where R1 is substituted by an amine oxide group, a spiro compound as defined above may be treated with the appropirate dialkylamine in the presence of a catalyst such as triethylaluminum; the subsequent epoxidation step produces the amine oxide. Where R1 is dialkoxyphosphoryl, the compounds may be prepared by treatment of a 1-oxaspirol-[2,5]oc-5-ene with the appropriate phosphite ester. (c) Preparation of 3-cyclohexen-1-ols can be effected from suitably substituted phenols by Birch-type reduction: see for example Rodd's Chemistry of Carbon Compounds, Second Edition, Vol. II, Part B, pages 1-4 (1968). . (d) Where R is CO2R , CON(R) )2' , CN, or alkyl, the 3-cyclohexen-1-ols can be prepared starting from suitable Diels-Alder adducts, followed where appropriate by modification of R1. Examples 1 to 10 These Examples describe the preparation of compounds of the general formula III. Example 1: l,4-Diethyl-3-cyclohexen-1-ol To a stirred refluxing mixture of 600 ml of dry diethyl ether and 1600 ml of liquid ammonia was added 136 g of p-ethylanisole. After 15 minutes, there was added portionwise, at -35 to 32"C, a 26.4 g quantity of lithium ribbon over 1 hour. After an additional 15 minutes, 193 g of dry ethanol was added dropwise at -35 to -32"C. Stirring was continued until the blue colour disappeared, and the ammonia was allowed to evaporate on standing overnight. The residue was poured into 1 liter of ice water and extracted twice with diethyl ether. The combined ether extracts concentrated to a volume of about 300 ml were stirred with 250 ml of water containing 46 g of oxalic acid overnight at ambient temperature. This mixture was diluted with 1 liter of water and extracted twice with diethyl ether. The combined ether extracts were washed with 5% sodium bicarbonate and then with water. After drying, the ether solution was vacuum-concentrated to a residue of 104.4 g of 4-ethyl-3-cyclohexen-1-one; it was 94% pure by GLC analysis. 10.0g of this product was dissolved in 25 ml of diethyl ether, and added dropwise to a stirred solution of 35 ml of 3.2 M ethereal ethyl magnesium bromide in 75 ml of dry diethyl ether at gentle reflux. After one hour longer at reflux, the mixture was cooled and treated dropwise with 80 ml of water. The aqueous layer was extracted with diethyl ether and the combined ether layers were dried, concentrated, and Claisen distilled to give 7.3 g of the desired product, b.p. 82-86"C (5mm.). Example 2: 4-Methyl-1-(1-methyl-1-(phenylthio)ethyl)-3-cyclo- hexen-l-ol To a stirred solution of 76 g of 2,2,6-trimethyl-1oxaspiro (2,5)oct-5-ene in 300 ml of n-pentanol were added 2.0 g of 60% sodium hydride and 60 g of thiophenol. After 18 hours reflux, the mixture was vacuum concentrated at 90-950C. The residue was dissolved in methylene chloride and washed twice with 2N sodium hydroxide. The dried solution was Claisen distilled to give 106 g of crude product, b.p. 120-1250C. Recrystallization from 250 ml of hexane gave 69.1 g of the desired product, m.p. 73-740C. Example 3: (+)-4-Methyl-(l-(l-chloro-l-methylethyl))-3- cyclohexen-l-ol To a stirred solution of 15.2 g of 2,2,6-trimethyl-1oxaspiro(2,5)oct-5-ene in 200 ml of diethyl ether held at -100C was added dropwise 32 ml of 3.8 N ethereal hydrochloric acid. After one hour at 0-5"C, the mixture was washed with three 50 ml portions of water, dried and distilled to give 14.5 g of the desired product, b.p. 70-75"C (0.4 mm). Example 4: (+) -1-Hydroxy-alpha,alpha, 4-trimethyl-3-cyclo- hexen-l-acetonitrile To a stirred mixture of 7.0 g of zinc dust, 0.45 g of mercuric chloride and 4 ml of tetrahydrofuran, was added dropwise over 45 minutes at 20-250C a mixture of 9.7 g of 4-methyl-3-cyclohexen-1-one, 13.7 g of alpha-bromoisobutyronitrile and 25 ml of tetrahydrofuran. After an additional hour at 250C, the reaction mixture was cooled to 5-100C and treated dropwise with 50 ml of cold 10% sulphuric acid. To this was added 100 ml of methylene chloride, and the mixture was filtered. The filtrate was diluted with 100 ml of water and extracted twice with 100 ml portions of methylene chloride. The combined methylene chloride extracts were washed with aqueous sodium bicarbonate, dried and Claisen distilled to give 11.3 g of the desired product, b.p. 92-1020C (0.25 mm). Example 5: (+)-1- (1-hydroxy-1-methylethyl)-4-methyl-3-cyclo hexen-l-ol A mixture of 26.0 g of 2,2,6-trimethyl-1-oxaspiro(2,5)oct- 5-ene and 250 ml of 1% sulphuric acid was stirred magnetically for 20 hours, then extracted with four 100 ml portions of methylene chloride. The combined methylene chloride extracts were washed, dried, concentrated and Claisen distilled to give 22.4 g of the desired product, b.p. 78-81"C (0.15 mm). Example 6: (+)-4-Methyl-l-(l-methoxy-l-methylethyl)-3-cyclo- hexen-l-ol To a stirred solution of 0.8 g of p-toluenesulphonic acid in 125 ml of methanol held at 3-50C was added dropwise over 0.5 hour a solution of 15.2 g of 2,2,6-trimethyl-l-oxaspiro(2,5)oct- 5-ene in 25 ml of methanol. After an additional 2 hours at 5"C and 2 hours at 5-20"C, the mixture was treated with 2 ml of 15% sodium hydroxide and concentrated at a water pump at below 600 C. The residue was dissolved in methylene chloride, washed, dried and Claisen distilled to give 15.6 g of the desired product, b.p. 700C (0.2 mm). Example 7: 2,2,4-trimethyl-3-cyclohexen-1-ol A mixture of 352 g of p-methyldihydroanisole (85% purity), 1350 ml of diethyl ether, 38 g of oxalic acid and 900 ml of water was stirred mechanically for 21 hours at 25"C. The aqueous layer was separated and extracted twice with diethyl ether. The combined ether solutions were washed with sodium bicarbonate, dried, concentrated and Claisen distilled to give 250 g of 4-methyl-3-cyclohexen-I-one, b.p. 63-650C (13 mm). To a 500 ml 3-neck, round-bottom flask were charged 37.5 g of this product, 100 ml of diethyl ether, 89.5 g of methyl iodide and 0.3 g of methyltrioctylammonium chloride. This mixture was stirred mechanically at ambient temperature and treated with 30 g of granular sodium hydroxide. After 20 minutes at gentle reflux, heat was applied to maintain the reflux for 2 hours longer. The cooled mixture was diluted with diethyl ether and treated with water to dissolve the suspended salts. The ether was separated and the aqueous layer was extracted wtih diethyl ether. The combined ether extracts were washed, dried, concentrated and Claisen distilled to give 36.5 g of 2,2,4-trimethyl-3-cyclohexen-1-one, b.p. 60"C (10 mm). To a stirred solution of 27.6 g of this product in 250 ml of ethanol was added portionwise 7.6 g of sodium borohydride. A cooling bath was used to hold the temperature at 25-300C. After 2 hours the mixture was poured into water and extracted three times with methylene chloride. The combined methylene chloride extracts were washed, dried, concentrated and distilled to give 27.7 g of the desired product. Example 8: 1,2,2,4-Tetramethyl-3-cyclohexen-1-ol To a stirred solution of 80 ml of 2.9 M methyl magnesium chloride (in tetrahydrofuran) in 200 ml of dry tetrahydrofuran was added dropwise at 25-300C a solution of 27.6 g of 2,2,4-trimethyl-3-cyclohexen-1-one in 30 ml of tetrahydrofuran. After 1 hour longer at 250C and 1 hour at 45-50"C, the mixture was cooled and treated carefully with 50 ml of saturated ammonium sulphate. The mixture was extracted twice with diethyl ether and the combined ether extracts were dried, concentrated and distilled to give 12.5 g (A), b.p. 115-125"C (100 mm), which was mainly unchanged ketone starring material, 11.1 g (B), b.p. 125-115"C (100-50 mm), which was the desired product of 81% purity. The final cut of 2.0 g (C), b.p. 115-120"C (50-20 mm) was the desired product of 87% purity. Example 9: 1-Ethoxyearbonylmethyl-4-methyl-3-cyclohexen-1-ol To a stirred mixture of 26.0 g of zinc dust, 2.0 g of iodine and 40 ml of benzene was added rapidly at 65-75"C a solution of 22.0 g of 4-methyl-3-cyclohexen-1-one and 62.6 g of ethyl bromoacetate in 400 ml of benzene. After 5 hours at reflux the mixture was cooled to below 10 C and treated dropwise with 300 ml of 10% acetic acid. After 15 minutes, the layers were separated and the aqueous layer was extracted twice with 150 ml of benzene. The combined organic layers were washed successively with water, sodium bicarbonate solution and water. After drying and concentration, Claisen distillation gave 33.0 g of the desired product, b.p. 82-84"C (0.5 mm). Example 10: 1,2,2,4,6, 6Hexamethyl-3-cyclohexen-1-ol. To a stirred solution of 27.6 g of 2,2,4-trimethyl-3-cyclohexen-l-one and 62.5 g of methyl iodide in 350 ml of tetrahydrofuran was added portionwise with cooling at 25-350C 20.2 g of 50% sodium hydride. Tne reaction was completed by refluxing for an hour longer. The cooled mixture was filtered and the filter cake was washed with tetrahydrofuran. The filtrate was concentrated to low volume and poured into water. Three extractions with methylene chloride, followed by washing, drying, concentration and Claisen-distillation, gave 25.6 g of 2,2,4,6,6-pentamethyl3-cyclohexen-1-one. This was reacted with methyl magnesium bromide and reduced, as described in Example 7, to produce the desired product. Examples 11 to 13 These examples describe the preparation of compounds of the general formula II. Example 11: 3,4-cis-Epoxy-l-isopropyl-4-methylcyclohexanol To a solution of 30.8 g of (+)-terpinen-4-ol in 250 ml of toluene containing 1.0 g of vanadium (IV) bis(2,4-pentanedioate) oxide held at 450C was added 22.0 g of 90% tert-butyl hydroperoxide. Cooling was used to maintain the reaction temperature at 45-500C for several minutes. After two hours longer at the same temperature, the mixture was cooled, washed with 1 N sodium hydroxide, dried and Claisen distilled to give 30.6 g of the desired product, b.p. 750C (2 mm). Example 12: cis-3,4-Epoxy-2,2,4-trimethylcyclohexanol A solution of 27.7 g of the alcohol of Example 7 above in 250 ml of methylene chloride was treated with 1.0 g of vanadium (IV) bis(2,4-pentanedioate) oxide and 22.0 g of 90% tert-butylhydroperoxide. After stirring overnight at 250C, the mixture was washed with 1 N sodium hydroxide, dried and Claisen distilled to give 23.7 g of the desired products b.p. 58-610C (1 mm). Example 13: 3, 4-cis-Epoxy-1-isopropyl-4-methylcyclohexanol To a stirred, refluxing mixture of 15.4 g of terpinen-4-ol, 150 ml of propylene oxide and 0.3 g of vanadium (IV) bis(2,4pentanedioate) oxide was added dropwise over 15 minutes 5.4 g of 70% hydrogen peroxide. After 45 minutes longer, the mixture was vacuum-concentrated at 60at. The residue was shaken with a mixture of pentane and water and the dried pentane layer was vacuum concentrated to a residue water of 11.2 g. This product was identified as 3, 4-cis-epoxy-1-isopropyl-4-methylcyclohexanol by CLC and infrared. Examples 14 to 17 These Examples describe the preparation of compounds of the general formula I. Example 14: - (+)-2-exo-Hydroxy-1-methyl-4-isopropyl-7-oxabicy clo [2,2,1]heptane To a solution of 30.8 g of (+)-terpinen-4-ol and 0.8 g of vanadium (IV) bis(2,4-pentanedioate) oxide in 300 ml of methylene chloride was added 22.0 g of 90% tert-butyl hydroperoxide. The resulting reaction was held at reflux for 2 hours, after which 0.8 g of p-toluenesulphonic acid in 10 ml of glyme was added. The resulting reaction mixture was refluxed for an additional 1.5 hours, cooled and 0.8 g of anhydrous sodium acetate was added with stirring. After filtration, the filtrate was concentrated and Claisen distilled to give 28.4 g of the desired product, b.p. 80-95 (2 mm). Example 15: (-) -2-exo-Hydroxy-1-methyl-4-isopropyl-7-oxa bicyclo [2,2,1] heptane The procedure of Example 14 was repeated using (-)-ter pinen-4-ol ([a ; -28" (CHC13)). The distilled product was recrystallized from hexane to give the desired product having m.p. 83-850C and [ol]D +0.40 (CHCI3). Example 16: (+) -2-exo-Hydroxy-1-methyl-4- (1-methyl-I-(phenyl- sulphonyl)-ethyl)-7-oxabicyclo [2,2,1 ]heptane To a stirred, refluxing solution of 13.1 g of (+)-4-methyl l-(l-methyl-l-(phenylthio)ethyl)-3-cyclohexen-1-ol and 0.27 g of vanadium(IV) bis(2,4-pentanedioate) oxide in 130 ml of methylene chloride was added dropwise 10.0 g of 90% tert-butyl hydroperoxide over 10 minutes. The mixture was refluxed for one hour longer, and after cooling, washed, dried and vacuum concentrated at 50-550C. To the resulting residue of about 18 g 5 ml of glyme containing 0.4 g of p-toluenesulphonic acid was added. The mixture was stirred overnight at 5-25 C. Since an insoluble oil had formed, 100 ml of chloroform was added and the ether and pentane were removed by vacuum concentration. The residual chloroform solution was washed with potassium carbonate, dried and concentrated to a residue of 14.9 g. This residue was purified by dry column chromatography using a 30:220:500 mixture of tetrahydrofuran: ethyl acetate:hexane as eluent. This column was divided into 12 equal parts; fraction 10 gave 5 g of product. Recrystallization of fraction 10 from diethyl ether gave 3.0 g of the desired product, m.p. 108-1100C. Example 17: 2-Exo-hydroxy-1,3, 3-trimethyl-7-oxabicyclo [2,2,l]heptane To a stirred solution of 20.0 g of the epoxy-alcohol of Example 12 above in 200 ml of methylene chloride held at 250C was added dropwise over 20 min of glyme. After 1 hour longer the solution was washed with dilute potassium carbonate, dried, concentrated, and Claisen distilled to give 11.1 g, b.p. 55-77"C (1.0-0.1 mm). This was redistilled to give 2.8 g of the desired product, b.p. 77-80"C (3.0 mm). Examples 18 to 26 By methods analogous to those described in Examples 14 to 17, further compounds of the general formula I were prepared. Details are given in Table I. All compound prepared were racemic mixtures. Table I Example In the general formula, I Boiling Point No RÚ Rê R R4 ( C(mmHg)) 18 CH3 C2H5 H H H 72-74(1.5) 19 C H CH3 H H H 84-105(2) 20 CH3 CH3 H H H 80-87(5) 21 n-C4H9 CH3 H H H 95-100(1.5) 22 CH3 3 7 H H H 74-76(1) 23 phenyl CH3 H H H 112-118(0.15) 24 C2H5 C2H5 H H H 65-78(1) 25 CH3 CH3 H H both 60-80(0.1) CH3 26 C2H5O.CO.CH2 CH3 H H H Not measured Examples 27 to 34 By methods analogous to those described in Examples 14 to 17, further compounds of the general formula I were prepared. However, rather than being isolated and characterized, they were converted into ethers in situ by reaction with benzyl chloride, and the resulting benzyl ethers were characterized. The general method was as described below: To a solution of 1.7 g of (+)-2-exo-hydroxy-1-methyl-4isopropyl-7-oxabicyclo[2,2,1]heptane in 15 ml of dimethylformamide was added at room temperature 0.5 g of 50% sodium hydride. The resulting mixture was stirred overnight at room temperature, heated for an hour at 500C, cooled to room temperature, and after 1.5 g of benzyl chloride was added in one portion, stirred at room temperature for three hours, heated to 500C for one hour, cooled, poured into 50 ml of water, and extracted with'one 50 ml and two 25 ml portions of methylene chloride. The combined methylene chloride extracts were washed with 100 ml of water, dried and evaporated to give an orange oil. Claisen distillation yielded 1.5 g of(+)-2-exo-benzyloxy 1-methyl-4-isopropyl-7-oxabicyclo [2,2,1 ]heptane, b.p. 103"C at 0.08 mm. Details of the compounds of the general formula I, and their ethers, are given in Table II. In all cases, the compounds prepared were racemic mixtures, and in all cases except Example 34, all of R3, R4 and R5 in the general formula I ê were hydrogen atoms, and R was a methyl group. Table II Example In the1general formula I After etherifi No R cation; boiling point of benzyl ether ("C(mm Hg)) 27 1-methyl-1-methylsulphonylethyl not measured 28 1-chloro-1-methylethyl 120-122(0.15) 29 1-cyano-1-methylethyl 139-140(0.1) 30 l-hydroxy-l-methylethyl 114-115(0.1) 31 l-methoxy-l-methylethyl 110-115(0.1) 32 l-ethoxy-l-methylethyl 120-125(0.2) 33 l-isopropoxy-l-methylethyl 120-130(0.2) 34 The compound: 2-exo-hydroxy-1,3,3 4,5,5-hexamethyl-7-oxabicyclo [2,2,1]heptane 110-115(0.1)

Claims: CLAIMS 1. A process for the preparation of a 2-exo-hydroxy 7-oxabicyclo [ 2.2.1]heptane, characterized in that the corresponding cis 3,4-expoxycyclohexanol is cyclised by treatment with an acid. 2. A process according to claim 1 for preparing a compound of the general formula I, characterized in that as cis 3,4-epoxy cyclohexanol a compound is used of the general formula II EMI23.1 in which formulae R1 is a hydrogen atom; a C1 10 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms or by a hydroxy group, a cyano group, a C1 4 alkoxy group, a C16 alkylsulphonyl group, a C6 10 arylsulphonyl group, a C7 11 aralkylsulphonyl group, an azido group, a C 1-6 alkoxycarbonyl group, a hydroxycarbonyl group, a phosphoryl group, a phosphoryloxy group, or an amine oxide, carbamoyl or thiocarbamoyl group in which the nitrogen atom is substituted by hydrogen or by 1 or 2 C14 alkyl groups; an aryl or aralkyl group, each containing from6 to 11 carbon atoms, and 1 to 4 carbonatoms in the alkyl portion, each optionally ring-substituted by one or more fluorine, chlorine and/or bromine atoms or by a C12 alkyl or alkoxy group optionally substituted by one or more fluorine and/or chlorine atoms; or a group CO2R or CON(R 2 in which R6 is a hydrogen atom or a C16 alkyl group; R2 is a hydrogen atom or a straight-chain C 1-6 alkyl group; each RJ is independently a hydrogen atom; a chlorine atom; a bromine atom; or a C14 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms; or two R3's when located on adjacent carbon atoms together form an epoxide ring or a carban-carbon bond; R4 is a hydrogen atom or a C 1-4 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms; Each R5 is independently a hydrogen atom; a C 1-4 alkyl group optionally substituted by up to 3 fluorine chlorine and/or bromine atoms; a hydroxy group; or a C14 alkoxy group. 3. A process according to claim 2, characterized in that a compound of formula II is used wherein R1 is a hydrogen atom; a C 1-4 alkyl group optionally substituted by up to 3 fluorine, chlorine and/or bromine atoms or by OH, CN, a C 1-4 alkoxy group, a C16 alkylsulphonyl group, a phenylsulphonyl group, or a benzylsulphonyl group; or an aryl or aralkyl group each containing from 6 to 10 carbon atoms and 1 or 2 carbon atoms in any alkyl portion, optionally substituted by one or more fluorine, chlorine and/or bromine atoms or by a C12 alkyl or alkoxy group each optionally substituted by one or more fluorine and/or chlorine atoms. 4. A process according to claim 2 or 3, characterized in that a compound of formula II is used wherein R1 is a hydrogen atom or a C 1-3 alkyl group optionally substituted by chlorine. 5. A process according to any of claims 2-4, characterized in ê that a compound of formula II is used, wherein R is a straight-chain C14 alkyl group, each R3 is a hydrogen, chlorine or bromine atom or a methyl or ethyl group, R4is a hydrogen atom, and R5 is a hydrogen atom or a methyl or ethyl group. 6. A process according to any of claims 2-5, characterized in that a compound of formula II is used wherein R is an isopropyl group, Rê is a methyl group, RÚ and Rê are both ethyl groups or R1 is a l-chloro-l-methylethylgroup and R2 is a methyl group. 7. A process according to any of claims 1-6, characterized in that the cis 3,4-epoxy cyclohexanol is treated with an acid having a p KA of 1 or less. 8. A process according to any of claims 1-7, characterized in that the acid is an organic sulphonic acid. 9. A process according to claim 8, characterized in that the acid is p-toluene sulphonic acid. 10. A process according to any of claims 1-4, characterized in that the amount of acid used is in the range of 0.02 to 0.04 mole of acid per mole of cis - expoxy cyclohexanol. 11. A process according to any of claims 1-10 characterized in that the reaction is performed in the presence of an inert solvent. 12. A process according to any of claims 1-11, characterized in that the reaction is carried out at a temperature from 5-40"C. 13. A process according to any of claims 1-12, characterized in that the resulting compound of formula I is processed further without being previously recovered from the reaction mixture. 14. A process according to any of claims 1-13, characterized in that a compound of formula I is prepared which is subsequently converted into an ether derivative by reaction with a compound WQ2 L in which W is an optionally substituted unsaturated group of up to 4 carbon atoms; an optionally substituted aromatic or heterocyclic group containing up to 14 carbons; a C3 10 cycloaliphatic group optionally substituted by C13 alkyl, or a C3 10 secondary alkyl group; both of Q are hydrogen atoms or fluorine atoms, and L is a leaving group. 15. A process according to claim 14, characterized in that the leaving group L is selected from halogen atoms and organic sulphonyloxy groups. 16. A process according to any of claims 1-15, characterized in that as starting material a cis 3, 4-epoxy cyclohexanol is used prepared by epoxidation of the corresponding cyclohexenol with the aid of an oxidising agent. 17. A process according to claim 16, characterized in that the cis 3,4-epoxy cyclohexanol is prepared with the aid of an alkylhydroperoxide in the presence of a transition metal catalyst. 18. A process according to claim 16 or 17, characterized in that the cis 3,4-epoxycyclohexanol is converted to the 2-exo-hydroxy-7-oxabicyclo [2,2,1 ]heptane without previous isolation. 19. A process according to claim 1, carried out substantially as described in any of the Examples 14-34. 20. A compound of the general formula I EMI27.1 wherein R1, R2, R3, R4 and R5 have the meanings as defined 2 in claim 2, with the proviso that when R represents a methyl group and all of R3, R4 and R5 represent hydrogen atoms, R1 is other than an isopropyl group. 21. A compound of the general formula II EMI28.1 wherein R1, R2, R3, R4 and R5 have the meanings as defined ê in claim 2, with the proviso that when R represents a methyl group and all of R3, R4 and R5 represent hydrogen atoms, R1 is other than an isopropyl group. 22. A compound as claimed in claim 20 whenever prepared according to a process as claimed in any of claims 1-9. 23. A compound as claimed in claim 21 whenever prepared according to a process as claimed in claim 16 or 17 with reference to Examples 11-13. 24. A compound of the general formula III. EMI28.2 wherein R1 R2, R3, R4 and R5 have the meanings as defined in claim 2, with the proviso that R1 and R2 are not both hydrogen atoms and that when Rê represents a methyl group and all of R , R4 and R5 represent hydrogen atoms, R1 is other than an isopropyl group.

Inventors: PAYNE, GEORGE BERNSON
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1982
Main classification: C07D493
IPC codes: C07C45, C07D493, C07F9, A01N57, C07C43, C07D303, C07C35, A01N43, C07C29, C07D301, C07D307