SYNTHESIS OF α-AMINO ACIDS USING TRANSITION METAL CATALYSIS - ALKYLATION OF SCHIFF BASES DERIVED FROM α-AMINO ACID ESTERS (REGIO, STEREO-SELECTIVITY)

Article abstract of DOI:10.1016/S0040-4020(01)86035-X

A general approach to the synthesis of γ,δ-unsaturated α-amino acid esters is described.Schiff bases derived from glycine and alanine esters were alkylated in the presence of palladium or molybdenium catalysts under neutral or basic conditions using allylic carbonates, esters or halides, (20-95 percent yield).These less stabilized nucleophiles reacted with the η³ allyl species on the side opposite to the palladium and they can be classified as soft nucleophiles.The regioselectivity was studied with various unsymmetrical electrophiles.After hydrolysis, several functionalized α-amino acids of biological interest (enzymes inhibitors) were obtained.Asymmetric palladium allylic alkylation of the benzophenone imine glycine methyl ester using Pd(OAc)2 + (+)DIOP was achieved with up to 68 percent ee; the enantioselective Pd-promoted alkylation of this new and useful prochiral nucleophile for the synthesis of α-amino acids is one of the highest ee known.