Letter pubs.acs.org/OrgLett
Copper(II)-Catalyzed Oxidative Coupling of Anilines, Methyl Arenes, and TMSN3 via C(sp3/sp2)−H Functionalization and C−N Bond Formation Devulapally Mahesh, Vanaparthi Satheesh, Sundaravel Vivek Kumar, and Tharmalingam Punniyamurthy* Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India S Supporting Information *
ABSTRACT: Copper(II)-catalyzed cross-coupling of anilines, methyl arenes, and TMSN3 in the presence of tertbutylhydroperoxide at moderate temperature produced 2-aryl benzimidazoles via a tandem C(sp3/sp2)−H functionalization and C−N bond formations. The selectivity and multiple C−H functionalization of the simple substrates are significant practical features.
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available methyl arene C(sp3)−H bond with aniline N−H bond that can lead to diverse N-heterocycle structural scaffolds. Herein, we report a copper(II)-catalyzed amination of a methyl arene C(sp3)−H bond with aniline to provide N-benzylaniline that can be reacted in situ with TMSN3 to give medicinally significant 2-aryl benzimidazoles in the presence of tert-butylhydroperoxide at moderate temperature (Scheme 1c).7−9 The reaction conditions can be extended to the amination of xylene and mesitylene to produce selectively monoaminated products. First, the reaction was optimized using aniline 1a and toluene 2b as the model substrates employing different Cu sources, solvents, and azides (Table 1). Gratifyingly, the oxidative cross-coupling occurred to afford 2-aryl benzimidazole 3a in 69% conversion when the substrates 1a and 2a were reacted with 20 mol % Cu(OAc)2, 2 equiv of TMSN3, and 3 equiv of TBHP at 80 °C in toluene (entry 1). Subsequent screening of the solvents led to an increase in the conversion to 84% using DMSO, while CH3CN produced 45% conversion (entries 2−3). In contrast, DMF and THF were not effective (entries 4−5). In a set of Cu sources investigated, CuBr, CuCl, Cu(OAc), CuI, CuCl2, Cu(SO4)2· 5H2O, Cu(OAc)2·H2O, and Cu(OAc)2, the latter gave the best results (entries 6−12). TMSN3 was found to be superior to NaN3/ AcOH (entry 13). Decreasing the amount of the Cu source (10 mol %), TBHP (1.5 equiv), or toluene (5 equiv) led to the formation of 3a in
