Vinyl glycosides in oligosaccharide synthesis: A strategy for the preparation of trisaccharide libraries based on latent-active glycosylation

Abstract

We postulate that the polymerization proceeds by electrophilic aromatic substitution; the dihydroxy(methy1)sulfonium cation (3) formed by protonation of the oxygen atom of the sulfinyl group serves as the active species (Scheme 2). 3 4 CH3 Scheme 2. Possible polymerization mechanisin for the formation of 1. The formation of 3 requires a strong protic acid such as trifluoromethanesulfonic acid (pK, = - 14.5).[13] The sulfonium cation 3 reacts with a benzene unit to form a hydroxy(methy1)- phenylsulfonium cation (4>, and successive electrophilic substitution results in the formation of poly(methylsu1fonio-1,4- phenylene salt). It has not been clarified why electrophilic substitution of 4 occurs at the para position.r141 The electron-donating property of the lone pair of the sulfonium group through 3d- 2p resonance might predominate over the electron-withdrawing effect in a strongly acidic media in analogy to electrophilic substitutions with aromatic sulfoxide.['