that participation of an (S)-ethoxycarbonylbenzyl auxiliary led to the formation of 1,2-cis glycosides, probably through a trans-fused dioxolenium ion intermediate. On the other hand, the use of an auxiliary with (R) configuration gave 1,2-trans glycosides, and this glycosylation proceeds through a cis-fused dioxolenium ion intermediate. The auxiliary could conveniently be removed by Birch reduction