Mild and Effective Removal of Dithioketal Protecting Groups by Triarylamine Cation Radicals as Homogeneous Electron Transfer Agents

Abstract

Abstract 1,3‐Dithianes 2 can effectively be converted in to the parent carbonyl compounds 7 by a very mild oxidative procedure using tri‐ p ‐tolylammoniumyl ( 1a +. ) or tris(4‐bromophenyl)ammoniumyl ( 1b +. ) as homogeneous electron transfer agents. The yields are equally good for the cleavage by stoichiometric amounts of the triarylammoniumyl hexachloroantimonates as well as for the indirect electrochemical procedure using catalytic amounts of the triarylamine together with electrochemical generation and regeneration of the cation radicals. In the case of 1,3‐dithiolanes 3 the application of stoichiometric amounts of tris(4‐bromophenyl)ammoniumyl hexachloroantimonate is very effective while during the indirect electrochemical procedure the deposition of polymeric sulfur compounds onto the electrode surface has to be prevented by the use of a flow‐through cell. In all cases the conditions for the cleavage are so mild that hydroxy functions and double bonds are tolerated without problems.