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

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 H2 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. [ABSTRACT FROM AUTHOR]