Divergent Synthesis of Chelating Aziridines and Cyclic(Alkyl)(Amino)Carbenes (CAACs) from Pyridyl-Tethered Robust...

Azomethine ylides are typically in situ generated synthons for making N-heterocycles through cycloaddition reactions. But an offbeat aspect about them is the isomeric nature of aldiminium-based azomethine ylides and (alkyl/aryl)(amino)carbenes, interconvertible by a formal 1,3-H⁺ transfer. Herein, two thermally robust azomethine ylides with a N-appended picolyl sidearm are isolated, which cyclize to ^py aziridines at 80 °C but unprecedentedly result ^N-pico CAAC-CuCl (CAAC=cyclic(alkyl)(amino)carbene) complexes when heated with CuCl at merely 60 °C. The pendant N_py , as revealed by computational analysis, plays a crucial role in this unusual 1,3-H⁺ shift using a deprotonation-protonation sequence, as well as in placing the CuCl at the carbenic site in tandem. The softer nature of Cu^(I) is also critical. Chelating CAACs are rare and one with a N-tethered additional donor is priorly unknown. Both ^N-pico CAAC and ^py aziridine are bidentate chelators giving highly active cationic Rh^(I) catalysts for hydrosilylating unactivated olefins by Et₃ SiH. Notably, the ^py aziridine-Rh^(I) is superior than the ^N-pico CAAC-Rh^(I) catalyst.