The preparation of amino sugars and branched-chain sugars by palladium-catalyzed, allylic substitution of alkyl hex-2-enopyranosides

Abstract

Ethyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranoside (1) in the presence of triphenylphosphine and a catalytic amount of tetrakis(triphenylphosphine)palladium(0) reacted with a variety of amines or with reactive methylene compounds to give high yields of products aminated or C-alkylated, respectively, in an allylic position. Some analogous experiments were performed using the β-D-erythro anomer (2) and the α-D-threo epimer (3) of 1. The constitutions and configurations of the new products were established by means of mass spectra, 13C- and 1H-nmr spectra, and optical rotation data. The reactions of 1 were found to be highly regio- and stereoselective, giving almost exclusively 4-substituted 2-enopyranosides with retention of configuration, except in the case of dibenzylamine which produced a mixture of the corresponding enoside and its 2-substituted, 3,4-unsaturated isomer having the α-D-threo configuration. The reactions of 2 appeared slightly less selective although they, too, furnished mainly 4-substituted 2-enopyranosides with retention of configuration. Regioselectivity was low or lacking in two C-alkylations performed with 3, which gave mixtures of 4-substituted 2-enosides and 2-substituted 3-enosides. Some aspects of conformation and optical rotation in enopyranosides are discussed.