ChemInform Abstract: An Exceedingly Mild and Efficient CAN-Mediated Method for the Deprotection of Acetals.

Abstract

. Carbon-carbon and carbon-heteroatom bond forming reactions mediated by CAN have attracted much attention recently.l-4 In the context of our recent investigations in this area, we were intrigued by the possibility of CAN mediated oxidative addition of acetals to alkenes. With this objective, benzaldehyde acetal was treated with styrene and CAN in methanol. In the event the expected reaction did not take place; the acetal, however, was dismantled and the styrene was transformed to ffi-methoxyacetophenone . Although the expected reaction did not occur, the facility with which the acetal underwent fragmenta~ tion was impressive and therefore we decided to explore the process from the vantage point of devising a synthetically useful deprotection method. It is worth noting that although CAN has been used for the oxidative removal of a variety of protecting groups6 including thioacetals, t_Boc, THP ethers and TBDMSgroups, there has not been any report on its use for the deprotection of acetals. Against the background given above, our investigation of the deprotection of acetals was initiated with the treatment of ethylidene acetal of benzaldehyde with CAN in aqueous methanol. A rapid and complete deacetalization leading to benzaldehyde in 90 % yield was observed (Scheme I) The reaction was found to be applicable to cyclic and acyclic acetals derived from a variety of carbonyl compounds and in all cases the products were obtained in high yields. The results are summarized in