1,1,1-Trihalogeno-4-methylpentenes, method of preparing the same and use of the same in the preparation of 1,1-dihalogeno-4-methyl-1,3-pentadienes

1,1,1-Trihalogeno-4-methyl pentenes and 1,1-dihalogeno-4-methyl-1,3-pentadienes are produced. These compounds are of value as intermediates for the production of pyrethrin analogs which are of use as insecticides or agricultural chemicals.

The present invention relates to 1,1,1-trihalogeno-4-methylpentenes, a 
method for producing the same, and a method for producing 
1,1-dihalogeno-4-methyl-1,3-pentadienes from 
1,1,1-trihalogeno-4-methylpentenes. 
1,1,1-Trihalogeno-4-methylpentenes according to the present invention are 
novel compounds having the general formula: 
##STR1## 
(wherein X.sup.1, X.sup.2 and X.sup.3 are the same or different and each 
represents a halogen atom; Z stands for a group of the formula: 
##STR2## 
or a group of the formula: 
Referring to general formula [I], X.sup.1, X.sup.2 and X.sup.3, 
respectively, stand for a chlorine, bromine, fluorine or iodine atom, the 
preferred species being chlorine and bromine. The 
1,1,1-trihalogeno-4-methylpentenes represented by general formula [I] are 
of value as starting materials for the production of various important 
compounds. 
Among the compounds of general formula [I], 
1,1,1-trihalogeno-4-methyl-3-pentenes in particular are important 
intermediates for the synthesis of dihalogeno-vinyl chrysanthemumates 
which, as will be explained hereinafter, have recently come to claim 
attention as insecticides or agricultural chemicals and are of value also 
as intermediates for the synthesis of terpenoids. Furthermore, 
1,1,1-trihalogeno-4-methyl-4-pentenes, after isomeric conversion to 
1,1,1-trihalogeno-4-methyl-3-pentenes, are similarly of use as 
intermediates for the synthesis of dihalogeno-vinyl chrysanthemumates and 
other compounds. Dihalogeno-vinyl chrysanthemumates have high and 
sustained insecticidal activity against various species of insects in 
contrast to natural pyrethroid insecticides which are susceptible to 
photolysis [M. Elliot et al, Nature 244, 456 (1973)]. 
As a process for the synthesis of dihalogeno-vinyl chrysanthemumates, 
Japanese Pat. Application Laid Open No. 47531/1974 (corresponding to Ger. 
Pat. Appl. Laid Open No. 2326077) recently teaches a process which 
comprises oxidizing chrysanthemummonocarboxylic acid with ozone and 
subjecting the resultant correspnding aldehyde to the Wittig reaction. 
This process, however, is generally thought to be hardly adaptable to 
commercial production because it requires not only a costly starting 
material, i.e. chrysanthemummonocarboxylic acid but such time-consuming 
reactions as oxidation with ozone and Wittig reaction. 
Also recently disclosed is a process which comprises permitting an 
orthocarboxylic acid ester to act upon 3-methyl-2-buten-1-ol, then adding 
a tetrahalogenomethane to the reaction product and cyclizing the resultant 
adduct with alkali to obtain a cyclopropanecarboxylate. Since this process 
requires only a few reaction steps, each providing a good yield, it might 
appear to be commercially profitable. However, this process also has much 
to be desired partly because, up to this time, no effective synthetic 
route to the starting material 3-methyl-2-buten-1-1-ol is known and partly 
because of the high prices of orthocarboxylic acid esters. 
J. Farkas et al report a diazoacetic acid process in Collect. Czech. Chem. 
Commun. 24, 2230 (1959) (hereinafter referred to as Farkas process). This 
process comprises acetylating 1,1,1-trichloro-4-methyl-3-penten-2-ol, 
reducing the acetylation product with zinc-acetic acid to obtain 
1,1-dichloro-4-methyl-1,3-pentadiene and, then in a conventional manner, 
reacting the last-mentioned compound with diazoacetic acid or an ester 
thereof to obtain a cyclopropanecarboxylic acid or an ester thereof. This 
process is not commercially profitable, either, for it involves a 
time-consuming series of reactions for the synthesis of 
1,1-dichloro-4-methyl-1,3-pentadiene and, also, a complicated procedure, 
i.e. reduction with zinc-acetic acid. 
The research undertaken by us to develop a method for economical production 
of dihalogeno-vinyl chrysanthemumates led to the discovery of a synthetic 
intermediate which is instrumental in realizing a marked improvement in 
the Farkas process. 
Thus, 1,1,1-trihalogeno-4-methyl-3-pentenes are considerably superior to 
conventional 1,1,1-trihalogeno-2-acetoxy-4-methyl-3-pentenes as 
intermediate materials for the production of 
1,1-dihalogeno-4-methyl-1,3-pentadienes according to the Farkas process. 
When a 1,1,1-trihalogeno-4-methyl-3-pentene is employed, this material can 
be easily converted to the 1,1-dihalogeno-4-methyl-1,3-pentadiene of 
general formula [II] by a simple procedure, i.e. treatment with a basic 
reagent, as compared to the conventional costly and complicated procedure, 
i.e. using a stoichiometric amount of zinc for the reduction of a 
1,1,1-trihalogeno-2-acetoxy-4-methyl-3-pentene with zinc-acetic acid. 
##STR3## 
(wherein X and Y, respectively, represent one of X.sup.1, X.sup.2 and 
X.sup.3 of general formula [I]) 
As examples of said basic reagent, there may be mentioned alkali metal or 
alkaline earth metal hydroxides such as sodium hydroxide, potassium 
hydroxide, calcium hydroxide, barium hydroxide, etc.; alkali metal 
alcoholates such as sodium methoxide, sodium ethoxide, potassium 
methoxide, sodium tert-butoxide, potassium tert-butoxide, sodium 
tert-amyloxide, etc.; alkali metal hydrides such as sodium hydride, 
potassium hydride, etc.; alkali metal amindes such as sodium amide, etc.; 
organic amines such as 1,5-diazabicyclo[3,4,0]nonene-5 (briefly DBN), 
1,5-diazabicyclo[5,4,0]undecene-5(briefly OBU), 
2-dimethylamino-1-pyrroline, etc.; and organolithium compounds such as 
n-butyllithium, s-butyllithium, diisopropylaminolithium, and so forth. 
From the standpoints of economy and reaction efficiency, it is preferable 
to employ alkali metal alcoholates, alkali metal hydrides or alkali metal 
hydroxides. The proportion of said basic reagent is at least one molecular 
equivalent and, preferably, within the range of 1 to 2 equivalents. 
The reaction is preferably carried out in a solvent. As examples of said 
solvent, there may be mentioned aqueous solvents; alcohol solvents such as 
methanol, ethanol, etc.; aprotonic polar solvents such as 
N,N-dimethylformamide (hereinafter DMF), dimethylsulfoxide (briefly DMSO), 
etc.; and hydrocarbons such as benzene, toluene and so forth. When the 
basic reagent is an organic amine, it may be used in excess so that it 
will act also as a solvent. The reaction temperature is between room 
temperature and 150.degree. C., preferably within the range of 50.degree. 
to 130.degree. C. 
As illustrated hereinafter, a 1,1,1-trihalogeno-4-methyl-3-pentene may be 
reacted with diazoacetic acid or an ester thereof in a manner conventional 
per se and, then, the reaction product be de-hydrohalogenated to obtain 
the corresponding dihalogeno-vinyl chrysanthemumic acid or an ester 
thereof. 
##STR4## 
(wherein X and Y, respectively, represent one of X.sup.1, X.sup.2 and 
X.sup.3 ; and R is a hydrogen atom or an alcohol residue) 
The 1,1,1-trihalogeno-4-methylpentenes [I] of the present invention may be 
produced by removing R'OH from compounds of general formula [III]: 
##STR5## 
(wherein R.sup.1 is a hydrogen atom or an alkyl, cycloalkyl, aryl, aralkyl 
or acyl group; X.sup.1, X.sup.2 and X.sup.3 have the same meanings as 
defined in general formula [I]). 
More particularly, compounds of general formula [III] are such that R.sup.1 
is a hydrogen atom, an alkyl group of 1 to 20 carbon atoms, a cycloalkyl 
group of 6 to 20 carbon atoms, an aryl group of 6 to 15 carbon atoms, an 
aralkyl group of 7 to 20 carbon atoms or an acyl group of 1 to 10 carbon 
atoms, preferably representing hydrogen, methyl, ethyl, propyl, butyl, 
acetyl, propionyl, or butyryl, and X.sup.1, X.sup.2 and X.sup.3, 
respectively, are preferably chlorine or bromine. 
The reaction by which R.sup.1 OH is removed from a compound of general 
formula [III] is (i) dehydration where R.sup.1 is a hydrogen atom, (ii) 
dealcoholation where R.sup.1 is an alkyl, cycloalkyl, aryl or aralkyl 
group, and (iii) decarboxylation where R.sup.1 is an acyl group. 
The above dehydration, dealcoholation or decarboxylation reaction may be 
easily accomplished by heating a compound of general formula [III] in the 
presence of a strongly acid to weakly acid catalyst such as sulfuric acid, 
phosphoric acid, p-toluenesulfonic acid, phosphorus pentoxide, vanadium 
pentoxide, wolfram trioxide, etc. at a temperature ranging from room 
temperature to 120.degree. C. or, alternatively, heating the same either 
in gaseous phase or in liquid phase in the presence of silica gel, 
aluminum silicate, kieselguhr, pumice, Fuller's earth, activated alumina, 
activated carbon or the like at a temperature from 80.degree. to 
250.degree. C. In the latter case, Kieselguhr, for instance, may be used 
in combination with vanadium pentoxide, for instance, in the form of a 
supported catalyst to hasten the reaction. 
The aforementioned catalysts is used in a proportion of 0.01 to 30 weight 
percent, preferably 0.1 to 10 weight percent, based on compound of general 
formula [III]. 
While the composition of the reaction product varies somewhat according to 
the conditions of reaction, the dehydration, dealcoholation or 
decarboxylation of compounds of general formula [III] yields, as principal 
product compounds, 1,1,1-trihalogeno-4-methyl-3-pentene of general formula 
[I']: 
##STR6## 
and 1,1,1-trihalogeno-4-methyl-4-pentene of general formula [I"]: 
##STR7## 
In addition, byproducts such as 1,1-dihalogeno-4-methyl-1,3-pentadiene, 
etc. are also produced in minor amounts. 
Normally, the total selectivity for compound [I'] and compound [I"] is not 
less than 98 percent at a conversion of not less than 95 percent based on 
compound of general formula [III]. The ratio of 
1,1,1-trihalogeno-4-methyl-3-pentene to 
1,1,1-trihalogeno-4-methyl-4-pentene in the reaction product is normally 
within the range of 3 : 2 to 9 : 1, and by fractional distillation, 
1,1,1-trihalogeno-4-methyl-3-pentene can be isolated in high purity. In 
connection with this procedure, it is of utmost significance, for the 
purpose of producing a starting material for 
1,1-dihalogeno-4-methyl-1,3-pentadiene, to isomerize the 
1,1,1-trihalogeno-4-methyl-4-pentene, which is obtainable as a first 
distillate in the above procedure, to the correspnding 
1,1,1-trihalogeno-4-methyl-3-pentene. 
If this first distillate rich in 1,1,1-trihalogeno-4-methyl-4-pentene is 
returned to the reaction system of compound [III] in the presence of the 
aforementioned acid catalyst, it will isomerize to 
1,1,1-trihalogeno-4-methyl-3-pentene. In this manner, 
1,1,1-trihalogeno-4-methyl-3-pentene can be produced in good yield. 
The isomerization of 1,1,1-trihalogeno-4-methyl-4-pentene to 
1,1,1-trihalogeno-4-methyl-3-pentene may also be accomplished in an 
independent reaction step. In such a process, the reaction may be 
conducted between about 80.degree.C. and about 200.degree.C. particularly 
preferred is a temperature range of about 110.degree.to 170.degree.C. This 
isomerization reaction proceeds with heating time until finally it yields 
an equilibrium composition corresponding to the temperature employed. 
While said isomerization reaction proceeds under heating even in the 
absence of a catalyst, the following procedure may be followed to obtain a 
significantly increased rate of isomerization and to drastically reduce 
the reaction time required before an equilibrium composition or a 
conversion rate approaching it is obtained. Thus, the reaction system may 
be heated in the presence of, as a catalyst, at least a member selected 
from the class consisting of transition metals of Group 6B, Group 7B and 
Group 8 of Periodic Table of the Elements (such as Cr, Mn, Co, Ni, Ru, Ph, 
Pd, W, Ir, etc.) and compounds (e.g. oxides, inorganic acid salts, organic 
acid salts, complex compounds, etc.) of such transition metals. As an 
alternative, the reaction system may be heated in the presence of an acid 
catalyst such as sulfuric acid, phosphoric acid, boric acid, 
p-toluenesulfonic acid, acetonedisulfonic acid or the like. 
Referring to the catalysts thus employable, the compounds of transition 
metals of Group 6B, Group 7B and Group 8 are exemplified by chromium (III) 
acetylacetonate, molybdenum disulfide, wolfram trioxide, manganese (III) 
acetylacetonate, ruthenium trichloride, cobalt (II) acetylacetonate, 
cobalt hexamine chloride, rhodium (III) acetylacetonate, rhodium 
trichloride, iridium trichloride, Raney nickel, nickel (II) 
acetylacetonnate, palladium chloride, palladium black, palladium oxide, 
palladium acetate, 5% palladium-on-carbon and so forth. The catalyst may 
be employed in an amount ranging from 0.001 to 30 weight percent based on 
compound [I"] and, preferably, 0.1 to 10 weight percent on the same basis. 
The isomerization reaction may be carried out either batchwise or 
continuously. 
A compound [III] may be produced by adding a haloform to dimethyl vinyl 
carbinol or a derivative thereof, of general formula [IV], under 
conditions of radical reaction. 
##STR8## 
(wherein R.sup.1 is as defined in general formula [III]) 
The said conditions of radical reaction may be established by allowing a 
radical initiator to be present in the reaction system or by irradiation. 
As said radical initiator, there may be mentioned benzoyl peroxide (BPO), 
azobisisobutyronitrile (AIBN), acetyl peroxide, di-tert-butyl peroxide, 
tert-butyl hydroperoxide, cumene hydroperoxide and so forth. The radical 
initiator serves the purpose when used in a catalytic amount. The reaction 
may be conducted in the atmosphere or, alternatively, in an inert gas such 
as carbon dioxide, nitrogen, helium or the like. 
The haloforms that are preferred for the purposes of this reaction are 
chloroform and bromoform. It is sufficient to employ a molecular 
equivalent of haloform based on compound of general formula [IV], although 
2 to 20 equivalents of haloform may be employed, in which case the 
haloform will act also as a reaction solvent. Although a reaction solvent 
is not indispensable, there may be employed a solvent that will not 
directly interfere with the contemplated reaction, such solvent being 
exemplified by carbon disulfide, n-hexane, n-heptane and so forth. The 
reaction temperature is preferably somewhere between room temperature and 
100.degree. C. when the reaction is initiated by irradiation, or from 
70.degree. to 180.degree. C. when a radical reaction initiator is 
employed. 
Radical-addition reactions of halides, esters, alcohols, active methylene, 
etc. to olefins are well known and, broadly, the following two general 
procedures are available. 
a. Heating in the presence of both of an organic amine and a transition 
metal compound; 
b. Heating in the presence of a radical reaction initiator 
The first procedure a) is not applicable from a selectivity point of view. 
Thus, under the conditions of a), the addition of the haloform as X. and 
.CHX.sub.2 radicals predominates. The hithereto attempted radical-addition 
reaction of a haloform to an allylic alcohol, ether or ester yields a 
large proportion of telomer, for example as reported by Kharasch et al in 
J. Am. Chem. Soc. 69, 1105 (1947) and described by Lewis et al in J. Am. 
Chem. Soc. 76, 457 (1954), and the yield of 1 : 1 adduct is as low as 20 
to 30 percent as stated by Tarrant et al in J. Org. Chem. 26, 4646 (1961). 
Furthermore, it is known that a tertiary allylic alcohol such as dimethyl 
vinyl carbinol is ready to induce a dehydration reaction under heating. 
Notwithstanding this, subjecting a compound of general formula [IV] and a 
haloform together to the above-mentioned radical-reaction conditions 
enables one to selectively obtain a compound of general formula [III] 
without causing a dehydration reaction or being accompanied by 
telomerization. By way of illustration, we added a small amount of benzoyl 
peroxide (BPO) to 8.6 g of dimethyl vinyl carbinol in 50 ml of chloroform 
and reacted the mixture at 140.degree.C. and in a nitrogen atmosphere for 
16 hours. Gas-chromatographic analysis of the reaction product mixture 
revealed that the conversion of dimethyl vinyl carbinol was 78.2 percent 
and the selectivity for 1,1,1-trichloro-4-methyl-4-hexanol was 94.5 
percent. 
1,1,1-Trihalogeno-4-methyl-3-pentenes may be produced by the following 
procedure as well, although this procedure is less advantageous than the 
above procedure starting with compounds of general formula [III] in that 
the former procedure gives rise to larger amounts of byproducts. Thus, a 
1,1,1-trihalogeno-4-methyl-3-pentene may be produced by heating a tertiary 
allyl halide of general formula [V] together with a tetrahalogenomethane 
under radical reaction conditions. 
##STR9## 
(wherein X.sup.4 is a halogen atom) 
The above procedure entails production of a large proportion of a byproduct 
compound of general formula [VI]: 
##STR10## 
(wherein X.sup.1, X.sup.2 and X.sup.3 have the same meanings as defined in 
general formula [I]; X.sup.4 has the same meaning as defined in general 
formula [V]; and X.sup.5 is a halogen atom) 
The present invention will be further illustrated by way of the following 
examples, in which, unless otherwise specified, all NMR spectra were 
determined at 60 MHZ in carbon tetrachloride at room temperature, with 
tetramethylsilane as the internal reference.