Silyl Group Migration in 1-O-Silyl Protected Sugars. Convenient Synthesis of 2-O-Unprotected Sugars.

Abstract Reaction of 2-O-unprotected 1-O-silyl-protected D-glucose and D-galactose derivatives 5a-d with benzyl bromide in the presence of sodium hydride as the base afforded 1-O-benzyl 2-O-silyl derivatives 6aα/β - 6dα/β. Thus, prior to anomeric O-benzylation, trans-1,2-silyl group migration takes place. Ensuing removal of the 2-O-silyl group furnishes 2-O-unprotected compounds 8aα/β - 8dα/β, which are useful building blocks. More prone to 1-O-silyl group migration is mannose as shown for derivatives of 4,6-O-benzylidene-D-mannose 9. Cis-1,2- and cis-2,3-silyl group migrations affording compounds 15 and 13 were already observed on deacetylation of the thexyldimethylsilyl 2,3-di-O-acetyl derivative 12β under Zemplen conditions.