Removal of Thioacetal Protecting Groups by Cerium (IV) Ammonium Nitrate - Hydrolysis of 1,3-Dithiannes

Abstract

In the course of our work on umpolung of α,β-ethylenic ketones and aldehydes¹, the use of thioacetalised γ-ketophosphonium salts and ylids led us to investigate the hydrolysis of 1,3-dithianes. Among the known methods of removal of thioacetal protecting groups², the one using cerium (IV) ammonium nitrate (CAN) has the advantages of a fast reaction with easy work-up and good to very good yields³. This method has been widely applied for preparative purposes using four equivalents of the cerium salt. However it does not seem that a theoretical explanation has been brought for the use of such a quantity of CAN. The only one proposed⁴ deals with a mechanism similar to the one involving mercury (II) salts, where indeed, four equivalents of metallic salt are not necessary⁵.