CS257094B1 - Process for the preparation of α-S-cyano-3-phenoxybenzyl esters of 2,2-dimethyl-3- (2,2-dihydro-1-yl) cyclopropanecarboxylic acids - Google Patents

Abstract

The method for preparing alpha-cyano-3-phenoxybenzyl esters of 2,2-dimethyl-3-(2,2-dihalovinyl)-cyclopropanecarboxylic acids of the general formula I, where X and Y represent a hydrogen atom or a halogen atom and Z represents a 2,2-dichlorovinyl or 2,2-dibromovinyl group, with the absolute configuration [alpha-S, IR, 3Rj], by epimerization consists in treating the corresponding diastereoisomer of the general formula I with the configuration [alpha-R, IR, 3Rj], or its mixture with the configuration [alpha-S IR, 3Rj], with alkali or ammonium fluoride, optionally in the presence of an inert organic solvent and optionally in the presence of an inorganic fluoride carrier. The epimer obtained in this way is a highly effective insecticidal substance.

Description

The present invention relates to a process for the preparation of stereoisomers of alpha-cyano-3-phenoxybenzyl esters of 2,2-dimethyl-3- (2,2-dihalovinyl (cyclopropanecarboxylic acids of formula I) wherein X and Y are hydrogen or halogen and Z is 2 , 2-dichlorvinyl or 2,2-dibromvinyl group in the configuration (alpha-S, IR, 3r) by epimerization of the corresponding stereoisomers of formula I in the configuration (alpha-R, IR, 3rJ). The practical importance of epimerization lies in the different insecticidal activity of these diastereoisomers, since it is known (see, for example, P. Ackermann, P. Bourgouis, J. Drabek: Pestic. Sci. 11, 169, 1980), that stereoisomers of the general formula Even with the absolute configuration (alpha-S, IR, 3rJ) they have extremely high insecticidal activity, while the corresponding diastereoisomers with opposite configuration on benzyl carbon (alpha-R, IR, have insecticidal significantly lower efficiency.

The above epimerization takes place only in the presence of a catalyst. Hitherto, various bases from the group of ammonia, amines, quaternary ammonium compounds, ion exchangers, alkali carbonates, hydroxides, alkoxides, amides and hydrides have been used as catalysts (see, e.g., Brit. Pat. 1,582,594, Brit. Pat. 1,582,595, British Pat. 1,599,876). However, the action of these catalysts in said epimerization is not always entirely satisfactory. Some catalysts in this group exhibit low activity, allowing operation only at impractically elevated temperatures. Other catalysts of this group sometimes cause undesirable side reactions (e.g., hydrolysis, aminolysis, re-esterification, etc.), difficult to isolate and reduce product yields.

These disadvantages are overcome by a process for the preparation of the alpha-cyano-3-phenoxybenzyl esters of the general formula I in the configuration (alpha-S, IR, 3rJ) according to the invention which consists in reacting the corresponding diastereoisomer of the formula IR, 3rJ, alone or in admixture with other stereoisomers of formula I, is treated with an alkali or ammonium fluoride, optionally in the presence of an inert organic solvent and optionally in the presence of an inorganic fluoride carrier.

According to the invention, epimerization can be carried out under conditions where the products remain dissolved in the reaction medium. In this case, a mixture containing diastereoisomers of Jalpha-S, IR, 3rJ and (alpha-R, IR, 3rJ in equilibrium (thermodynamic) ratio) is formed, which is then to be separated by known separation techniques (e.g. crystallization) and undesired diastereoisomer ge must be submitted to the next epimerization cycle.

More preferably, the ipimerization is carried out under conditions where the diastereoisomer in the configuration (alpha-S, IR, 3Rj is gradually eliminated from the solution or from the melt in the form of crystals), with suitable choice of reaction parameters (e.g. temperature, amount and nature of solvent) and, in a preferred embodiment ^1, result in a practically quantitative yield of the desired diastereoisomer in a single epimerization cycle.

In principle, it is possible to carry out the epimerization in an inert organic solvent selected from the group of alcohols, hydrocarbons, ethers, nitriles, amides, sulfoxides or sulfones, or it is also possible to work without a solvent. Sometimes it is advantageous to use an inorganic carrier with a large surface area (e.g. alumina) to increase the efficiency of the catalyst. The temperature can be selected from -15 to 80 ° C. The amount of catalyst can also be varied within a wide range, but preferably in the range of 0.5 to 10 weight percent.

In the process according to the invention, it is not necessary to start from pure stereoisomers of formula (I) having the configuration (alpha-R, IR, 3r), preferably from an equimolar mixture of diastereoisomers (alpha-R, IR, 3rJ and [alpha-S, IR.

The preparation process of the present invention is illustrated by the following examples, which are not intended to limit the scope of the invention in any way.

Example 1

Jalpha-S, IR, 3R] alpha-Cyano-3-phenoxybenzyl-2,2-dimethyl-3- (dichlorvinyl) -cyclopropanecarboxylate g ester [alpha- (R, S), IR, 3r] o [Χΐρθ = 16.5 ° (10%, benzene) is dissolved in 40 ml of isopropanol and 2 g of freshly overburdened potassium fluoride is added. The mixture was stirred at room temperature for 20 hours, then cooled to -5 ° C and the precipitated crystalline solid was filtered off with suction. It is washed with ice-cold isopropyl alcohol and air-dried. There was thus obtained an ester of formula I wherein XaY = HaZ = 2,2-dichlorvinyl, [alpha-S, IR, 3r] configuration, m.p. 60 ° C

[.Alpha.] D @ 20 = + 34 DEG (1%, chloroform).

Example 2 [alpha-S, IR, 3r], alpha-Cyano-3-phenoxybenzyl-3- (2,2-dibromvinyl) -2,2-dimethylcyclopropanecarboxylate g of a mixture of esters of the [alpha-S, IR, 3r] configuration and [ alpha-S, IR, 3rJ, where = + 14 °, (1%, benzene), is dissolved in 5 ml of isopropyl alcohol in the presence of 0.4 g of calcined potassium fluoride. After stirring at room temperature for 12 hours, the crystalline product is sucked off, washed with cold isopropanol and air dried. An ester of formula I is obtained in a quantitative manner, wherein XaY = HaZ = 2,2-dibromvinyl, [alpha-S, IR, 3rJ, m.p. 100 ° C, [α] D = + 25 ° (1%, chloroform).

Example 3 [alpha-S, IR, 3R] alpha-Cyano-3-phenoxy-4-fluorobenzyl-2,2-dimethyl-3- (2,2-dichlorvinyl) -cyclopropanecarboxylate ester ester configuration [alpha- (R, S) IR, 3rJ, exhibiting [endo ^{= + 7} ° ^'5 ° ^{<= c 2'} ° 'rofom ^CHL P) were dissolved in 25 ml of isopropanol, treated with 0.8 g of potassium fluoride and annealed mixture was stirred for 40 hours at 20 After cooling to 0 ° C, the product is filtered off with suction, washed and dried. The obtained [alpha-S, IR, 3rJ] ether weighs 9.86 g (98.6%), mp 50-52 ° C and [.alpha.] D @ 20 +24.5 DEG (c = 1.0, chloroform).

Claims (4)

A process for the preparation of 2,2-dimethyl-3- (2,2-dihalovinyl) -cyclopropanecarboxylic acids alpha-S-cyano-3-phenoxybenzyl esters of the general formula I, wherein X and Y are hydrogen or halogen and z is 2.2 -dichlorvinyl or 2,2-dlbromvinyl group, with an absolute configuration of [alpha-S, IR, 3rJ, epimerization], characterized in that the corresponding etereoisomer of the formula I with the configuration of [alpha-R, IR, 3rJ or a stereoisomeric mixture of X is treated with an alkali or ammonium fluoride, optionally in the presence of an inert organic solvent and optionally in the presence of an inorganic fluoride carrier. 2. A process according to claim 2, wherein the mixture is in which the stereoisomers [alpha-R, IR, 3R] and [alpha-S, IR, 3r] are present in a molar ratio of 4: 6 to 6: 4. 3. A process according to claim 2, wherein seed crystals are used during epimerization. 4. Process according to claim 1, characterized in that the epimerization is carried out in an inert organic solvent from the group of alcohols having 2 to 6 carbon atoms.