Substituent position-driven reaction pathways in the heterogeneous one-pot reduction/asymmetric hydrogenation of nitro-substituted (E)-2,3-diphenylpropenoic acids over Pd catalyst

Abstract

The reaction pathway in the heterogeneous enantioselective hydrogenation of nitro-substituted (E)-2,3-diphenylpropenoic acids over Pd catalyst modified by cinchonidine is determined by the position of the substituent. The reaction route was indicated by the H 2 consumption curve and enantioselectivity of the final amino acid or 3-phenyl-1,2,3,4-tetrahydro-2-quinolone formed by intramolecular amidation. The obtained enantioselectivities were low with the exception of acids bearing nitro substituent in para position on the 3-phenyl moiety, the latter resulting in good, up to 80 % optical purity. The present study is the first to report the enantioselective heterogeneous catalytic preparation of 1,2,3,4-tetrahydro-2-quinolones and presents an attractive method for obtaining optically enriched 3-(4-aminophenyl)-2-phenylpropionic acids.