CS268965B1 - Process for preparing optically active cyano-3-phenoxybenzyl esters of substituted cyclopropanecarboxylic acids - Google Patents

Abstract

A method for preparing optically active oc-cyano-3-phenoxybenzyl esters of cyclopropanecarboxylic acids of the general formula 1, where X and Y represent a hydrogen atom or a halogen atom and Z represents an alkenyl group with 2 to 4 carbon atoms, each substituted by 2 to 4 halogen atoms, with the absolute configuration cis. -S, 1Rcis, consists in treating the corresponding diastereoisomer of the general formula X 3 with the configuration oc. -R, ■ IRCis, or its mixture with the diastereoisomer of the configuration oc. -S, 1Rcis, with ammonium carbonate in the presence of an inert organic solvent and optionally in the presence of seed crystals. The epimer obtained in this way is a highly effective insecticidal substance.

Description

The present invention relates to a process for the preparation of optically active <>C—cyano-3-phenoxy-benzyl esters of substituted cyclopropanecarboxylic acids of the general formula I, where X and V represent a hydrogen atom and Z represents an alkenyl group with 2 to 4 carbon atoms, each substituted by 2 to 4 halogen atoms, in the cX. -S, IRcis configuration, by epimerization of the corresponding stereoisomers of the general formula I in the -R, IRcis configuration. Epimerization is understood to mean a change in configuration at the benzyl carbon denoted in the formula I by the letter crC . The configuration notation used is based on the proposal of M. Elliot, N. F. Dones and 0. A. Pulman, described in more detail in the patent document Brit, Pat. 1 604 682 (Int. Cl? , C07C 121/75, application 30.5.19,78). The practical significance of this epimerization lies in the different insecticidal activity of the mentioned stereoisomers of the compound of formula I. It is known that stereoisomers of general formula I with the absolute configuration IRcis generally have much higher insecticidal activity than the corresponding diastereoisomers with the opposite configuration on the benzylic carbon ( e/- “R. IRcis). .

The above-mentioned epimerization takes place only in the presence of a catalyst. Various basic reagents from the group of ammonia, anions, quaternary ammonium compounds, ion exchangers, carbonates, hydroxides, alkoxides, amides, fluorides and hydrides of alkali metals have been used as catalysts (see for example British Pat. 1,582,594, British Pat. 1,582,595, British Pat. 1,599,876). However, the action of these catalysts is not always entirely satisfactory. Some catalysts from the group mentioned show low activity, allowing work only at impractically elevated temperatures, while others sometimes cause undesirable side reactions and separation problems.

The above disadvantages are eliminated by the method for preparing o/.-cyano-3-phenoxybenzyl esters of the general formula I in the configuration cA -S, IRcis, The essence of which consists in treating the corresponding diastereoisomer of the general formula I with the configuration o/ -R, IRcis, or any diastereoisomeric mixture of the general formula I with the configurations c>4-r, IRcis and <7/ -S, IRcis with ammonium carbonate in the presence of an inert organic solvent, for example alcohols and ethers. The crystallization of optically active isomers with the desired configuration can be initiated by the addition of seed crystals.

According to the invention, the epimerization can be carried out under conditions where both the formed and annihilated diastereoisomers of formula I remain dissolved in the reaction medium. In such a case, a mixture is formed containing both diastereoisomers in a thermodynamic ratio. This mixture can then be separated by known separation methods (e.g. liquid chromatography) and the undesired diastereoisomer can be returned to the next epimerization cycle.

More preferably, the epimerization according to the invention can be carried out under conditions where the desired diastereoisomer in the «4-s, IRcis configuration precipitates out of solution in the form of crystals during the reaction. In this procedure, with appropriate selection of reaction parameters (for example, temperature, amount and nature of the solvent), a more or less quantitative yield of the desired product can sometimes be achieved in a single epimerization cycle.

In the preparation process according to the invention, it is not necessary to start from a pure diastereoisomer of formula I with the configuration -R, IRcis, but it is possible to use technical mixtures of diastereoisomers with the configuration -R, IRcis and -S, IRcis. The amount of catalysts can be selected within a wide range, but an amount in the range of 2 to 10 weight percent is particularly preferred.

The preparation method according to the invention is explained in more detail in the following examples, which, however, do not limit the scope of the invention in any way, example 1 c^C-S, IRcis - -cyano-3-phenoxybenzyl-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (IJ X » Y =» H, Z « dibromovinyl) g of a technical mixture of ester I with the configuration -S, IRcis and -R, IRcis, is dissolved in 5 ml of isopropyl alcohol and stirred for 48 hours at room temperature in the presence of 0.2 g

CS 268965 Bl ammonium carbonate, then the crystalline product is filtered off with suction after cooling, washed with cold isopropyl alcohol and dried, obtaining the ester of configuration <4-s, ircis of formula I with the meaning given above, m.p. 100 °C, oC. ♦ 25° (1%, chloroform) in a yield of 1.8 g (90% of theory).

Example 2 eZ- -S, IRcis - ¢4-cyano-3-phenoxybenzyl-2,2-dimethyl-3-/2,2-dichlorovinyl/-cyclopropanecarboxylate (K X Y H, Z 2,2-dichlorovinyl) g of a technical mixture of isomers of configuration «Ζ-R, IRcis and eZ-s, IRcis of formula i with the meaning given above is dissolved in 4 ml of isopropyl alcohol and 0.2 ammonium carbonate and seed crystals are added. The mixture is stirred at room temperature for 48 hours, then slowly cooled to -5 °C, seed crystals of isomers in configuration cZ -s, IRcis are added. The separated crystalline substance is filtered off with suction and washed with cooled solvent. A practically pure isomer of configuration ¢-4 -S, IRcis is obtained, m.t. 60 °C, pC. » +34° (1%, chloroform).

Example 3 ¢4. -S, IRcis - 4Z.-cyano-3-phenoxy-4-fluorobenzyl-2,2-dimethyl-3-/2,2-dichloro-vinyl/-cyclopropanecarboxylate (Ij X 4-F, Y » H, Z « 2,2-dlchlorovinyl1) g of the technical mixture of isomers ¢4 -R, IRcis and ¢4 -S, IRcis of formula I with the meaning given above is dissolved in 25 ml of isopropyl alcohol, 1 g of ammonium carbonate is added and the mixture is stirred for 50 hours at 20 °C, then gradually cooled to 0 °C, the product is filtered off with suction, washed and dried. The ester obtained of configuration <Z -S, IRcis weighs 9 g, m.p. 50 °C, c4 θθ = 24.5° (c » Ι,Οζ chloroform).

Example 4

Establishment of thermodynamic equilibrium between cZ-R, IRcis- and cZ-S, IRcis diastereoisomers of the ester of general formula Ij X « Y H, Z >· 2,2-dichlorovinyl g of the above diastereoisomer I in the <sZ-R, IRcis configuration in 10 ml of a hexane-isopropyl alcohol mixture (10 : 1) was heated with 0.2 g of ammonium carbonate to boiling and the composition of the reaction mixture was continuously monitored by gas chromatography until equilibrium was reached (4r, IRcis : <Z S, IRcis Z' 1:1). A similar result was obtained by epimerization of the o/í- S, IRcis isomers under identical reaction conditions.

Example 5

Establishment of thermodynamic equilibrium between the cZ S, IRcis and cZ R, IRcis isomers of the ester of general formula I* X « Y » H, Z ³ 3,3,3-trifluoro-2-chloroprop~l-en-1-yl g of a mixture of cZ s, IRcis and «Ζ R, IRcis ester isomers (8:2) of the ester of general formula I with the meaning given above was heated with 10 ml of tetrahydrofuran and 0.2 g of ammonium carbonate at a temperature of 50 °C until equilibrium was established. After evaporation of the solvent in vacuo, the diastereoisomer c4 S IRcis crystallized from isopropanol after addition of seed crystals.

Claims (2)

SUBJECT OF THE INVENTION 1. A method for preparing optically active cZ-cyano-3-phenoxybenzyl esters of cyclopropanecarboxylic acids of the general formula I, where X and Y represent a hydrogen atom or a halogen atom and z represents an alkenyl group of 3 2 to 4 carbon atoms, each substituted by 2 to 4 halogen atoms, with an absolute configuration <4-3, IRcis, characterized in that the diastereoisomer of the general formula 1 with the configuration cZ-R, IRcis, or the diastereoisomers CS 268965 B1 isomeric mixture of general formula I with configurations of -R, iRcis and -s, IRcis is treated with ammonium carbonate in the presence of an inert organic solvent, for example alcohols and ethers and optionally in the presence of seed crystals of optically active isomers with the desired configuration. 2. The preparation method according to item 1, characterized in that the reaction is carried out in an inert organic solvent from the group of alcohols with 2 to 4 carbon atoms, at a temperature of -10 to +20 °C.