The combination of VCl 3 (THF) 3 and N,N-bis(trimethylsilyl)aniline (1a) is an efficient catalyst for the [2+2+1] coupling reaction of alkynes and azobenzenes, giving multisubstituted pyrroles. A plausible reaction mechanism involves the generation of a mono(imido)vanadium(III) species as an initiation step, where 1a served as an imido source with concomitant release of 2 equiv of ClSiMe 3 , followed by a reaction with azobenzene to form a catalytically active bis(imido)vanadium(V) species via N=N bond cleavage.
Bibliographical noteFunding Information:
We thank Mr. Hibiki Ochi for the initial experiment results. K.K. thanks the financial support by the JSPS Research Fellowships for Young Scientist. H.T. acknowledges the financial support by JSPS KAKENHI Grant No. 15KK0185, a Fund for the Promotion of Joint International Research (Fostering Joint International Research), and Multidisciplinary Research Laboratory System of Graduate School of Engineering Science, Osaka University. K.M. acknowledges financial support by JSPS KAKENHI Grant Nos. 15H05808 and 15K21707 in Precisely Designed Catalysts with Customized Scaffolding (No. 2702). Financial support was provided by the National Institutes of Health (1R35GM119457) and the Alfred P. Sloan Foundation (I.A.T. is a 2017 Sloan Fellow). Equipment for the UMN Chemistry Department NMR facility was supported through a grant from the National Institutes of Health (S10OD011952) with matching funds from the University of Minnesota.
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