Asymmetric Hydroformylation and Hydrocarboxylation of Enamides. Synthesis of Alanine and Proline

Carbonyltris(triphenylphosphine)hydridorhodium (1) catalyzed the hydroformylation of N-vinylimides in the presence of optically active 2, 3-0-isopropylidene-2, 3-dihydroxy-1, 4-bis(diphenylphosphino)butane (DIOP) or 2, 3-O-isopropylidene-2, 3-dihydroxy-1, 4-bis(5H-dibenzophospholyl)butane (DIPHOL) to afford optically active α-amido aldehydes. Linear disubstituted N-vinylimides or -amides reacted very sluggishly, while the cyclic N-acyl-2-pyrroline (19) was very reactive. In the unsubstituted N-vinylimides moderate (20-40% ee) asymmetric induction was observed. The optically active α-amido aldehydes were readily converted to the corresponding α-amino acids. Asymmetric hydrocarboxylation of the same substrates in the presence of bis(triphenylphosphine) palladium chloride (2) produced α-amido esters in low optical purity.