Photochemical rearrangement of α-chloro-propiophenones to α-arylpropanoic acids: studies on chirality transfer and synthesis of (S)-(+)-ibuprofen and (S)-(+)-ketoprofen

A new single-step efficient photocchemical approach for α-arylpropanoic acids (4) from α chloro-propiophenones (5) is described. It involves carbonyl triplet excited state directed 1,2-aryl migration of the aryl group which has been found to be highly dependent upon the nature of the aryl substituent. The mode of this rearrangement is probed by the study of the photobehaviour of a set of optically active α-chloro-propiophenones. The results suggest that the nature of the carbonyl triplets (n,π*/π,π*) plays an important role in the chirality transfer. This method finds application in the synthesis of optically active ibuprofen (4e) and ketoprofen (26), though in moderate optical yields.