Stereoselective synthesis of C-glycosyl analogues of phenylalanine

Condensation of 1-[4,6-di-O-(tert-butyldimethylsilyl)-2,3-dideoxy-α-d-erythro-hex-2-enopyranosyl]-4-bromobenzene () with methyl 2-acetamidoacrylate in the presence of Pd(OAc)2, P(C6H4-O-CH3)3, and AgNO3, afforded the unsaturated C-glycosyl enamido ester in 80% yield. Reduction of compound in the presence of [Rh(COD)(R,R)-(Et-DuPHOS)]OTf gave the corresponding unsaturated C-glycosyl (R)-phenylalanine derivative, when the [Rh(COD)(S,S)-(Et-DuPHOS)]OTf catalyst gave the C-glycosyl (S)-phenylalanine derivative, in 67 and 79% yield, respectively. Bis-hydroxylation of compound , followed by acetylation afforded the C-mannopyranosyl phenylalanine derivative in overall 30% yield.