GB2025964A - Cyclopropane Derivative - Google Patents

Abstract

Novel intermediate in the manufacture of pyrethroid insecticides has the following formula <IMAGE> The compound preferably has the same stereoisomeric form as the cyclopropane ring in (+)-3-carene. The novel intermediate can be prepared by a process which comprises oxidising 2-(2-hydroxymethyl-3,3- dimethylcyclopropyl)ethanal dimethyl acetal, for example by means of a chromium trioxide-pyridine complex or a pyridinium chlorochromate. The starting material is preferably derived from (+)-3-carene.

Description

SPECIFICATION Novel Intermediate in the Preparation of Cyclopropanecarboxylate Esters and Process for its Manufacture The invention relates to a compound which is a useful intermediate in the preparation of cyclopropanecarboxylate esters. The invention also relates to a process for the preparation of this intermediate.

The cyclopropanecarboxylate esters are insecticidally-active compounds known as "pyrethroids" and as they combine exceptionally good insecticidal properties with a very low mammalian toxicity, they are of considerable interest to the agrochemical industry and much effort has been expended in finding economic routes to them and to their principal intermediates.

The general formula of one class of these pyrethroid compounds may be represented as follows:

where each asterisk denotes an asymmetric carbon atom; each X is a halogen atom; and R is a member of a group of radicals known to impart insecticidal activity to the molecule, e.g. 3phenoxybenzyl or alpha-cyano-3-phenoxybenzyl.

It is known that the stereoisomeric form of the acid portion of the ester of formula I should be in the (1R,cis) form for maximum insecticidal activity, i.e. the absolute configuration at carbon atom 1 is R and the two hydrogen atoms on carbon atoms 1 and 2 are in a cis relationship.

This nomenclature is known as the Elliott nomenclature and is defined in M. Elliott, A. W.

Farnham, N.F. James, P.H. Needham and D.A.

Pullman, Nature, 1974, 248, 710.

It follows, therefore, that if these stereoisomeric esters of formula I are to be prepared, either a stereospecific chemical route is required or the desired stereoisomer must be obtained from a racemic form by physical separation techniques. The latter are expensive and laborious and not readily employed on an industrial scale. The Applicant has found a stereospecific route which uses as starting material the naturally-occurring substance (+)-3carene whose formula is as follows

This compound is an inexpensive readily-available natural terpene and the present application relates to an intermediate which can be used in a route to the (1 R,cis)-acid portion of the pyrethroid ester of formula I starting from (+)-3-carene.

The present invention provides a cyclopropane compound of the general formula

This compound may be named 1-(2,2 dimethoxyethyi)-3,3-dimethyl-cyclopropane-2- carbaldehyde. Preferably the compound of formula Ill is in the same stereoisomeric form as that of the cyclopropane ring present in naturallyoccurring (+)-3-carene.

The present invention also provides a process for the preparation of 1 -(2,2-dimethoxyetheyl)3,3-dimethylcyclopropane-2-carbaldehyde of formula Ill which comprises oxidising 2-(2hydroxymethyl-3,3-dimethylcyclopropyl)ethanal dimethyl acetal of formula

with a reagent capable of oxidising the hydroxymethyl group into a formyl group. The oxidation may conveniently be carried out by employing a chromium trioxide-pyridine complex or a pyridinium chlorochromate, for example as described in J. Org. Chem. 35(1970) No.

11,4000-4002 and Tetrahedron Letters 31 (1975) 2647-2650. Another method of oxidising the hydroxymethyl group involves catalytic dehydrogenation, for example in the presence of a copper chromite-catalyst, Other methods for conversion of a hydroxymethyl group into a formyl group can be found in "Methoden der organischen Chemie" (Houben-Weyl), Volume VII, Part 1(1945)159-192.

The starting material, compound IV, is a novel compound and is claimed in our copending application UK 30371/78 (K 361). A method of preparation of compound IV is also disclosed therein involving hydrolysis of 1-(2,2 dimethoxyethyl)-3,3-dimethyl-cyclopropylrnethyl acetate, for example, by employing an alkalinereacting medium.

The starting material is preferably derived from naturally-occurring (+)-3-carene as this enables the process according to the invention to yield a novel intermediate of formula Ill in a stereoisomeric form which, after conversion to a pyrethroid insecticide produces the highest level of pyrethroid insecticide activity.

The compound and process according to the invention are of interest as part of a multi-step process to pyrethroid insecticides, e.g. esters based on (1 R,cis)-2-(2,2-dichlorovinyl)-3,3- dimethyl-cyclopropane carboxylic acid and the dibromo analogues.

The following Example further illustrates the invention.

Example Preparation of 1 -(2,2-dimethoxyethyl)-3,3 dimethylcyclopropane-2-carbaldehyde (Compound Ill) A solution of (1 R,cis)-2-(2-hydroxymethyl-3,3- dimethylcyclopropyl)ethanal dimethyl acetal (84.8 mmol) in dichloromethane (80 ml) was added at once to a stirred solution of pyridinium chlorochromate (132 mmol) in dichloromethane (160 ml) in a 500 ml flask. After stirring for three hours at 200C the black precipitate present in the reaction mixture was filtered off and the precipitate was washed with three 50 ml portions of diethyl ether. The solvent was evaporated from the combined filtrates to give 100 ml of a residual liquid.This liquid was filtered and the diethyl ether was evaporated from the filtrate (400C/2 kPa) togive a residue (14.2 g) containing compound Ill in 100% 1 R,cis configuration purity 87%, yield 80.5%, determined by gas-liquid chromatography and nuclear magnetic resonance (NMR) spectroscopy. The NMR spectrum of compound III showed the following absorptions (at 90 Mhz, using a solution of compound Ill in deuterochioroform and relative to a tetramethylsilane standard): S=1.22 ppm singlet H3C-C-CH3 S=2.03 ppm double doublet HC-CH3-CH S=4.32 ppm triplet (H3C-0)2CH- b=1.33 ppm singlet K3C-C-CH3 S=3.34 ppm singIetHC-0-C-0-CH3 multiplets for the two H atoms bound to the ring.

Claims (7)

Claims

1. A cyclopropane compound of the formula

2. A compound according to Claim 1 in the same stereoisomeric form as that of the cyclopropane ring present in naturally-occurring (+)-3-carene.

3. A process for the preparation of 1-(2,2dimethoxyethyl )-3,3-dimethylcyclopropane-2carbaldehyde of formula Ill which comprises oxidising 2-(2-hydroxymethyl-3,3- dimethylcyclopropyl)ethanal dimethyl acetal of formula

with a reagent capable of oxidising the hydroxymethyl group into a formyl group.

4. A process according to Claim 3 wherein the oxidation is effected by employing a chromium trioxide-pyridine complex or a pyridinium chlorochromate.

5. A process according to Claim 3 or 4 wherein the starting material of formula IV is derived from naturally-occurring (+)-3-carene.

6. A process according to Claim 3 substantially as hereinbefore described with reference to the Example.

7. 1 -(2,2-dimethoxyethyl)-3,3- dimethyicyclopropane-2-carbaldehyde prepared by a process claimed in any one of Claims 3 to 6.