Method for the resolution of racemic 2-CP-difluoromethoxy phenyl)-3-methylbutyric acid

摘要

A method for the preparation of certain difluoromethoxyaromatic compounds useful as intermediates in the preparation of pyrethroid pesticides. The method comprises alkylating a p-substituted phenol with excess chlorodifluoromethane at atmospheric or superatmospheric pressure in the presence of a base, water, and an inert water miscible organic solvent or solvent mixture, alone or in the presence of benzyltriethylammonium chloride, to yield a difluoromethoxyaromatic compound; and, when said difluoroaromatic compound contains a side chain acetic acid ester having a chiral center, optionally, (a) hydrolyzing said ester to the corresponding racemic acid and thereafter resolving said racemic acid into its dextrorotatory (+) acid and levorotatory (-) acid isomers and recovering said (+) acid isomer, or (b) hydrolyzing said ester to the corresponding racemic acid, resolving said racemic acid into its d(+) acid and 1(-) acid isomers, recovering said d(+) acid for use in the preparation of pyrethroid product, esterifying the above-said 1(-) acid from the resolution, racemizing the thus-prepared 1(-) ester from said esterification, and hydrolyzing the same to obtain racemic acid which is recycled for admixture with the fresh racemic acid and subsequent resolution.