Regioselective Methylation of the C-1 and C-3 Positions of 1,5-Anhydro-4,6-O-benzylidene-2-deoxy-3-O-mesyl-D-ribo-hex-1-enitol by the Reaction with Methylmagnesium Bromide or Methyl Cuprates

Abstract

1,5-Anhydro-4,6-O-benzylidene-2-deoxy-3-O-mesyl-D-ribo-hex-1-enitol reacted with alkylmagnesium bromides (RMgBr: R = C2H5–, (CH3)2CH–, or C2H5(CH3)CH–) to give the corresponding 1-β-C-glycopyranosides and 3-C-alkyl-D-arabino-hex-1-enitols, while the reaction with methylmagnesium bromide afforded 1-α-C- and 1-β-C-methyl-glycosides in a ratio of 1 : 1.5–2. On the other hand, when the reaction was carried out in the presence of Cul or CuBr–S(CH3)2, substitution took place at the C-3 position to afford the corresponding 3-C-methyl-D-arabino-hex-1-enitol.