Hafnium Triflate as a Highly Potent Catalyst for Regio- and Chemoselective­ Deprotection of Silyl Ethers

Abstract

As a Group IVB transition metal Lewis acid, hafnium triflate [Hf(OTf)4] exhibited exceptionally high potency in desilylations. Since the amounts of Hf(OTf)4 required for the deprotection of 1°, 2°, 3° alkyl and aryl tert-butyldimethylsilyl (TBS) ethers are significantly different, ranging from 0.05 mol% to 3 mol%, regioselective deprotection of TBS could be easily implemented. Moreover, chemoselective cleavage of different silyl ethers or removal of TBS in the presence of most hydroxyl protecting groups was also accomplished. NMR analyses of silyl products from TBS deprotection indicated that Hf(OTf)4-catalyzed desilylation may proceed via different mechanisms, depending on the solvent used.