Acetal functions are tolerant under neutral and basic conditions. Acidic conditions are usually used for their deprotection, and under these conditions, ketals (acetals from ketone functions) are usually deprotected more easily than the acetals (acetals from aldehyde functions) due to the stability of the cation intermediates. We present a new method1), which can selectively deprotect acetals, not ketals. Thus, the use of combinations of triethyltriflate (TESOTf)-2,6-lutidine or 2,4,6-collidine can selectively deprotect acetals in the presence of ketals. Another advantage of the method is that the compounds with acid-sensitive functional groups can also be well adapted because the reactions proceed under basic condition. Furthermore, we have found that the structures of the intermediates are pyridinium salts.
