Reinvestigation of the synthesis of per-benzylated glycosylethenes: a new result.

Addition of vinylmagnesium bromide on the per-benzylated glucono-1,5-lactone gave, after reduction with Et3SiH/BF3.Et2O, a mixture of the desired beta-C-vinyl glucoside 1 and the unexpected beta-C-but-3-enyl glucoside 3 resulting from double addition of vinylmagnesium bromide on the lactone. Similar results have been obtained with the per-benzylated galactono-1,5-lactone. This side reaction was then been explored to prepare beta-C-but-3-enyl glycosides and other beta-C-glycosyl derivatives by employing different Grignard reagents. An alternative approach to the per-benzylated glycosylethenes has been studied and compared.