STUDIES ON THE SYNTHESIS OF CHIRAL 2-(P.CHLOROPHENYL)-3-METHYLBUTANOIC ACID, A KEY-PRECURSOR OF FENVALERATE, BY HYDROCARBONYLATION REACTIONS

The preparation of racemic 2-(p.chlorophenyl)-3-methylbutanoic acid (2 ), a building block for (S,S)-Fenvalerate (an important broad spectrum insecticide), was effected by rhodium catalyzed hydroformylation of 2 -methyl-l-(p.chlorophenyl) propene (4) in the presence of excess of tr iphenylphosphine to inhibit substrate isomerization followed by mild o xidation of the resulting aldehyde 6: an overall yield of 88% was reac hed. Olefin 4 exhibits a very low tendency to undergo both hydrocarboe thoxylation and hydrocarboxylation in the presence of palladium comple xes as catalysts. Enantioselective hydrocarbonylation reactions carrie d out on olefin 4 afford unsatisfactory chemical and optical yields of the optically active ester 5 or acid 2.