Reagent-Controlled α-Selective Dehydrative Glycosylation of 2,6-Dideoxy- and 2,3,6-Trideoxy Sugars.

We have found that activating either 2,3-bis(2,3,4-trimethoxyphenyl)cyclopropenone or 2,3-bis(2,3,4-trimethoxyphenyl)cyclopropene-1-thione with oxalyl bromide results in the formation of a species that promotes the glycosylation between 2,6-dideoxy-sugar hemiacetals and glycosyl acceptors in good yield and high α-selectivity. Both reactions are mild and tolerate a number of sensitive functional groups including highly acid-labile 2,3,6-trideoxy-sugar linkages.