Synthetic approach to exo-glycals from 1-C-vinyl-D-glycopyranose derivatives via an SN1′-substitution mechanism

This paper describes a novel synthetic approach to exo-glycals from 1-C-vinyl-D-glycopyranose derivatives via the S(N)1'-type substitution mechanism. The reaction of the 2,3,4,6-tetra-O-benzyl-1-C-vinyl-alpha-D-glycopyranose derivatives with several trimethylsilylated nucleophiles was investigated. The reactions in dichloromethane-acetonitrile (1: 1) at -78 degrees C in the presence of 20 mol% trimethylsilyl trifluoromethanesulfonate using allyltrimethylsilane and silyl enol ethers as the nucleophiles stereoselectively afforded the Z-exo-glycal derivatives in good yields.