PHOTOCHEMICAL-REARRANGEMENT OF ALPHA-CHLORO-PROPIOPHENONES TO ALPHA-ARYLPROPANOIC ACIDS - STUDIES ON CHIRALITY TRANSFER AND SYNTHESIS OF (S)-(+)-IBUPROFEN AND (S)-(+)-KETOPROFEN

A new single-step efficient photochemical approach for alpha-arylpropanoic acids (4) from alpha-chloro-propiophenones (5) is described. It involves carbonyl triplet exicted state directed 1,2-aryl migration of the aryl substituent. The mode of this rearrangement is probed by the study of the photobehaviour of a set of optically active alpha-chloro-propiophenones. The results suggest that the nature of the carbonyl triplets (pi,pi(*)/pi,pi(*)) plays an important role in the chirality transfer. This method finds application in the synthesis of optically active ibuprogen (4e) and ketoprofen (26), through in moderate optical yields.