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

Abstract

Development 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.