A facile method to protect vic diols, 1,3 diols and other hydroxyl functions as methylene acetals is achieved by treating the relative substrates with POCl3 or SOCl2 in DMSO. The good yields obtained, the good solubility of many organic compounds in DMSO and the easy hydrolysis of the 1,3,5-trioxaepane derivatives prepared from trans vic diols make useful this protecting method.