The intermolecular migration of polyol stannylenes as a reaction contributing to the regioselectivity of substitution

Pairs of the partially protected glyco sides benzyl 4,6-O-benzylidene-beta- D-galactopyranoside, benzyl 2,3-di-O-benzyl-beta-D-galactopyranoside, benzy l 2,6-di-O-benzyl-alpha-D-galactopyranoside, and benzyl 2,3-di-O-benzyl-alp ha-D-glucopyranoside were treated with equimolar proportions of Bu2SnO in b enzene in the conditions of stannylene formation, and the resulting mixture was benzoylated in situ with benzoyl chloride. Estimation of the product o f benzoylation led to the following order of reactivity in the stannylenati on reaction: 2,3-diol > 4,6-diol, and 2,3-diol > 3,4-diol. An intermolecula r migration of dibutyltin between sugars was demonstrated. It is. considere d that these migrations contribute efficiently to the regiospecificity of t he stannylene reaction. (C) 2000 Elsevier Science Ltd. All rights reserved.