Thermodynamically Controlled Regioselective Glycosylation of Fully Unprotected Sugars through Bis(boronate) Intermediates

Fully unprotected D-glucose, D-mannose, and D-fructose were regioselectively glycosylated with several phenylthioglycosides to afford glycosyl-β(16)-α/β-D-glucopyranose, glycosyl-β(11)-α-D-mannofuranoside, and glycosyl-β(11)-β-D-fructopyranose in good yields. The regioselectivity might have arisen from a thermodynamically controlled bis(phenylboronate) intermediate, which leaves only one free hydroxy group to be glycosylated in complete regioselectivity.