Selective aerobic oxidation of benzylic and allylic alcohols catalyzed by Cu(OAc)2/TEMPO/Et2NH

Abstract

Selective oxidation of benzylic and allylic alcohols to their corresponding aldehyde/ketone derivative without affecting saturated alcohols is still a challenging endeavor in organic synthesis. Various metal complexes, especially the copper complexes in the presence of TEMPO are being used very often for such transformations under aerobic conditions, but they are not selective to allylic and benzylic alcohols. The use of copper salt for oxidation of alcohols in the absence of a ligand are very scarcely studied except for the one catalyzed by CuCl/TEMPO where chloride inhibition and lack of selective oxidation have been noted upon use of CuCl₂. Herein we report a Cu(OAc)₂ catalyzed and TEMPO mediated selective aerobic oxidation of benzylic and allylic alcohols to aldehyde/ketone in the presence of Et₂NH. The method avoids pre-synthesis of the catalyst as in the case of Cu(II)/(I) complexes/TEMPO catalyzed oxidation reactions, requires low catalyst loading, employs cheaper copper salt, and gives excellent selectivity for oxidation of benzylic and allylic alcohols.