CH641136A5 - 2-(2-Hydroxymethyl-3,3-dimethylcyclopropyl)ethanal dimethyl acetal and process for its preparation - Google Patents

Description

The invention relates to compounds which are suitable as intermediates for the preparation of cyclopropane carboxylate esters and to a process for their preparation.

The cyclopropane carboxylate esters are insecticidally active compounds known as "pyrethroids" and in which extraordinarily good insecticidal properties are associated with low mammalian toxicity. They are of considerable interest for agrochemicals and great efforts have been made to develop economical processes for the production of their intermediates.

One group of these pyrethroid compounds has the following general formula

Hv ^ CHsCX.

(I)

CH-

COOR

are in a cis position to each other. This nomenclature 25 is known as the Elliott nomenclature (M. Elliott, A.W. Fara-ham, N.F. James, P.H. Needham and D.A. Pullman, Nature, 1974, 248,710).

It follows that if these stereoisomeric esters of the formula I are to be prepared, either a stereospecific chemical process must be used or the desired stereoisomer must be obtained from a racemic mixture by physical separation processes. The last-mentioned processes are complex and laborious and cannot easily be applied on an industrial scale.

A stereospecific procedure was developed, in which the naturally occurring (+) - 3-carene, the formula, is used as the starting substance

40

in which the asterisks each indicate an asymmetric carbon atom, X is a halogen atom and R is selected from the group of residues which are known to confer insecticidal activity on the molecule, e.g. a 3-phenoxybenzyl or a-cyano-3-phenoxybenzyl group. It is known that the acid portion of the ester of formula I should be in (1R, cis) form in order to give the compound maximum insecticidal activity, i.e. the absolute configuration on carbon atom I is R and the two hydrogen atoms on carbon atoms I and 2

. ch2-oh

(II)

50

This compound is an inexpensive, readily available naturally occurring terpene, and the invention relates to intermediates in a process for the preparation of the (IR, cis) acid portion of the pyrethroid ester of Formula 55 I from (+) - 3-carene.

The invention relates to a cyclopropane compound of the formula

-CH,

(III)

0-CH,

3rd

641 136

The compound can be referred to as 2- (2-hydroxymethyl-3,3-dimethylcyclopropyl) etheral dimethylacetal. The compound of formula III is preferably in the same stereoisomeric form as the cyclopropane ring of the naturally occurring (+) - 3-carene.

hydrolyzed.

The hydrolysis must be carried out so that the two methoxy groups are not attacked; generally this can be achieved by using an alkaline medium. Other hydrolysis conditions are given in "Methods of Organic Chemistry" (Houben-Wexl), Vol. VIII (1952) 418-423 and 638-639.

The compound IV used as starting substance can be prepared by (a) ozonolysis of (+) - 3-Ca ~ and subsequent reduction of the ozonolysis product in the presence of methanol and an acetalizing agent and (b) oxidation of the resulting product with a Peracid e.g. B. perbenzoic acid. Such an implementation is given in EP application 78 200 351.

The starting substance is preferably derived from naturally occurring (+) - 3-carene and this makes it possible to obtain the new intermediate of formula III according to the process of the invention in a stereoisomeric form which, after conversion into a pyrethroid insecticide, has the highest insecticidal activity results.

The compound and method of the invention are of particular interest as part of a multi-step process for the preparation of pyrethroid insecticides, e.g. Esters based on (1R, cis) -2- (2,2-dichloro-vinyl) -3,3-dimethyl-cyclopropanecarboxylic acid and their di-bromo analogs.

The invention is illustrated by the following example:

The invention also relates to a process for the preparation of 2- (2-hydroxymethyl-3,3-dimethylcyclopropyl) äthanal-dimethylacetal of the formula III, which is characterized in that s 1 - (2,2-dimethoxyethyl ) -3,3-dimethylcyclopropyl methyl acetate of the formula:

(IV)

20 example

2- (2-hydroxymethyl-3,3-dimethylcyclopropyl) etheral dimethylacetal (compound III)

75 ml of water, 30 ml of methanol, 152.2 mmol of sodium hydroxide and 145 mmol of 25 1R, cis-l- (2,2-dimethoxyethyl) -3,3-dimethylcyclopropyl methyl acetate were placed in a 250 ml flask. After stirring for 3 h at 20 ° C the methanol was evaporated at 40 ° C and 2 kPa. The remaining aqueous phase was saturated with sodium chloride and then extracted with 3 x 70 ml of diethyl ether. The 30 combined extracts were washed with 2 x 10 ml of water, dried over anhydrous magnesium sulfate and the solvent was evaporated. This gave 120.7 mmol of compound III (100% 1R, ice configuration, purity 98%, yield 83%, determined by gas-liquid chromatography-3s graph and nuclear magnetic resonance (NMR). The NMR spectrum of compound III showed the following absorptions ( at 90 MHz, solution of compound III in deuterochloroform, based on tetramethylsilane as standard):

40

S = 0.97 ppm singlet H3C-C-CH3 S = 3.00 ppm singlet H3C-0-C-0-CH3 8 = 4.40 ppm double doublet (H3CO) 2-CH-5 = 1.06 ppm Singlet H3C-C-CH3 5 = 3.06 ppm Singlet H3C-0-C-0-CH3

Multiplets for the two H atoms on the ring and for CH2OH and (H3CO) 2CHCH2.

Claims (5)

641136 PATENT CLAIMS 1. Cyclopropane compound of the formula 2. Compound according to claim 1, characterized in that it is in the same stereoisomeric form as the cyclopropane ring in naturally occurring (+) - 3-carene. 3. A process for the preparation of a cyclopropane compound of the formula III, characterized in that un2 ter alkaline conditions hydrolysed l- (2,2-dimethoxyethyl) -3,3-dimethylcyclopropylmethyl acetate of the formula i5. 4. The method according to claim 3, characterized in that one starts from a compound of formula IV, which is derived from naturally occurring (+) - 3-carene. 5. A compound of formula III which has been prepared by a method according to claim 3 or 4.