Stereoselective synthesis of C-glycosyl compounds via Michael addition of trimethylsilyl enol ethers and enamines to hex-1-enopyran-3-uloses

Abstract The titanium(IV)-catalyzed addition of trimethylsilyl enol ethers to 2,4,6-tri- O -acylhex - 1 - enopyran - 3 - uloses ( 3 and 4 ) gave stereoselectively 3,6 - di - O - acyl - 4 - deoxy - β - d - glycero -hex-3-enopyranosyl-2-ulose derivatives. The formation of the C -glycosyl bond was accompanied by a 2→3 acyl shift, followed by the elimination of the 4-acyloxy substituent. Similarly, the reaction of 1-pyrrolidinocyclohexene with 3 and 4 also led stereoselectively to 2-(2,4,6-tri- O -acyl-β- d - ribo -hexopyranosyl)cyclohexanones. In this Michael addition, among the eight possible diastereomers, only one was formed. The high stereocontrol of both C -glycosyl compound syntheses is …