Aerobic Oxidation of Alkyl 2-Phenylhydrazinecarboxylates Catalyzed by CuCl and DMAP.

Recently, various fruitful organic reactions such as a catalytic Mitsunobu reaction were reported by virtue of alkyl 2-phenylazocarboxylates, however, the synthesis of alkyl 2-phenylazocarboxylates largely depended on the stoichiometric use of toxic oxidants. In this manuscript, an environment-friendly aerobic oxidative transformation of alkyl 2-phenylhydrazinecarboxylates to alkyl 2-phenylazocarboxylates is disclosed. The use of CuCl and DMAP system efficiently catalyzed the aerobic oxidation of alkyl 2-phenylhydrazinecarboxylates under mild conditions. The reaction rate of the present Cu-catalysis was much faster than that of the previously reported Fe-catalysis, and a variety of azo products were synthesized within 3 h. The present protocol was effective on larger scale. It was observed that the produced azo compound could undergo various reactions without isolation through one-pot sequential protocols.