Synthesis of glycosylthiols and reactivity studies

The acid-catalyzed reaction of 1,2-anhydro-3,4,6-tri-Obenzyl- R-D-glucopyranose (7) as glycosyl donor with bis-trimethylsilyl sulfide as acceptor affords the R-thiol. Hence, this sterically hindered S-nucleophile as acceptor should provide with O-glycosyl trichloroacetimidates as glycosyl donors that have nonparticipating groups at C-2, glycosylthiols with the thiol group in axial position. This was confirmed for various donors (4, 16-19) with the exception of the corresponding mannosyl donor (20). However, powerful participating groups at C-2 of the donor (23-28) governed the anomeric selectivity