Direct selective and controlled protection of multiple hydroxyl groups in polyols via iterative regeneration of stannylene acetals

A direct selective protection (O-benzylation) of two or more hydroxyl groups in polyols displaying diverse structural patterns was made possible by the establishment of conditions that enable an efficient turnover for the Bu2Sn group, initially at the corresponding stannylene acetals (only ∼1.0 mol equiv of Bu2SnO was employed). It was also demonstrated that one might exert control over the number of protected groups, by means of appropriate tuning of reaction conditions. The feasibility of a substoichiometric (tin source) catalytic protocol was demonstrated as well.