SELECTIVE PROTECTION OF 1,2-DIOLS AND 1,3-DIOLS VIA ACYLATIVE CLEAVAGE OF CYCLIC FORMALS

An efficient two-step method for the differential functionalization of 1,2- and 1,3-diols, involving regioselective cleavage of five- and six-membered cyclic formals with acetyl chloride followed by conversion of the resulting chloromethyl ether acetate 1 to an alkoxymethyl ether acetate (2), has been developed. When applied to unsymmetrically substituted cyclic formals, the differential functionalization sequence is highly selective and produces an alkoxymethyl ether acetate having the acetate at the less hindered center and the acetal moiety at the more hindered center. Removal of either protecting group affords a selectively monoprotected diol: for the case of an unsymmetrical diol, removal of the acetate gives a product selectively protected with an acetal group at the more hindered hydroxyl.