Iodine and its interhalogen compounds: Versatile reagents in carbohydrate chemistry XII. Tuning promoter reactivity for thioglycoside activation

The reactivity of O-benzylated 1-thio-beta -D-galactopyranosides in iodine- promoted methanolysis reactions was shown to correlate with aglycone struct ure, as expected (R = p.NO2Ph < Ph < Bn < p.MeOPh < Me). The rate of methan olysis could be altered substantially through appropriate choice of promote r (ICl > IBr similar to I-2+DDQ > I-2), with even the unreactive nitropheny l thioglycoside undergoing complete reaction in less than 2 minutes in acet onitrile in the presence of ICl.