New protecting groups for 1,2-diols (boc- and moc-ethylidene). Cleavage of acetals with bases.

[reaction: see text] 1,2-Diols react at rt with alkyl propynoates, in the presence of 4-dimethylaminopyridine, to give cyclic acetals which are quite stable to acid-catalyzed hydrolysis or methanolysis. 1,3-Diols and 1, 4-diols do not form acetals with alkyl propynoates under the same conditions. Deprotection is accomplished with bases (via elimination and addition/elimination steps).