Catalytic oxidative nitrene transfer from azides with the early transition metals is rare, and has not been observed without the support of redox noninnocent spectator ligands. Here, we report the formal [2+2+1] coupling of azides and alkynes via TiII/TiIV redox catalysis from simple Ti halide imido precatalysts. These reactions yield polysubstituted N-alkyl pyrroles, including N-benzyl protected pyrroles and rare examples of very electron rich pentaalkyl pyrroles. Mechanistic analysis reveals that [2+2+1] reactions with bulky azides have different mechanistic features from previously-reported reactions using azobenzene as a nitrene source.
Bibliographical noteFunding Information:
Financial support was provided by the National Institutes of Health (1R35GM119457) and the Alfred P. Sloan Foundation (Sloan Fellowship for IAT). Equipment purchases for the NMR facility were supported from the NIH (S10OD011952) with matching funds from the University of Minnesota.
© 2018 The Royal Society of Chemistry.