A method is described for regioselective monoprotection of 1,n-diols. The new process depends on regioselective cleavage of orthoester, which is prepared from 1,n-diols and trialkylorthoesters. The produced mono-acetal is useful in subsequent steps as a normal acetal type protecting group. ... A new process of monoprotection of diols: The method depends on regioselective cleavage of orthoester, which is prepared in situ from 1,n-diols and ...