Oxidative cross dehydrogenative coupling directed carbamates synthesis using Cu(II) pincer complex as active catalyst under mild reaction condition

Abstract

AbstractDevelopment of an air‐stable and cheap transition metal‐based catalyst for the formation of carbamates via the cross‐coupling reaction of various 2‐carbonyl substituted phenolic derivatives or 1,3‐diketo derivatives with N,N‐disubstituted formamides (C(sp2)O bond formation) under mild conditions is the key focus of synthetic chemists. In this context, we have developed a novel benzothiazole appended 2,6‐di picolinamide‐based Cu(II) complex for the facile generation of carbamates at a slightly elevated temperature (50°C) with a short reaction time and low catalyst loading (0.5 mol%) for the first time. The synthesized complex was well characterized by ultraviolet–visible, infrared, electron paramagnetic resonance spectroscopy, cyclic voltammetry, high‐resolution mass spectrometry (HRMS), as well as by single crystal X‐ray diffraction analysis. A wide range of aromatic carbamates was synthesized using complex 1 in good/excellent yield with decent functional group tolerance under mild conditions. Control experiments suggest that the reaction proceeds via the radical mechanism, and the formation of radical‐mediated intermediates was confirmed by the gas chromatography (GC), GCMS and HRMS. The use of low cost and environmentally benign catalysts in mild conditions along with the tolerance of a wide range of functional groups makes this an easy synthetic approach for the development of carbamates.