C-GLYCOSIDE SYNTHESIS VIA GLYCAL ALKYLATION BY OLEFINIC DERIVATIVES

Treatment of peracetylated glycals with olefins in the presence of Lewis acids gave 2,3-unsaturated C-glycosides in good to excellent yields. The reaction was completely regioselective and showed a high degree of stereoselectivity leading mostly to the α-isomer. Generally the addition gave the C-glycoside with an unsaturated aglycone. However, with methylenecyclobutane and 1,1 disubstituted linear olefins halogeno derivatives were recovered. The reaction was also performed with acetylated 2-hydroxy glycals. In these conditions keto unsaturated α-C-glycosides were isolated.