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.