Bicyclo[1.1.0]butane Carboxamides to N-Heterocycles via a Strain Release-Enabled Nickel(II)–Carbene Intermediate

We report the conversion of bicyclo[1.1.0]butane carboxamides into N-heterocycles via strain release, enabling the generation of a novel class of Ni(II)–carbene intermediate and utilizing it for Ni(II)–carbene alkyne metathesis reactions for cyclopropanation and [4+2] cycloaddition to access highly functionalized cyclopropane-containing tetracyclic quinolinones and phenanthridinones. This transformation exhibits a broad scope and high yields across diverse substrates, with mechanistic studies confirming the formation of Ni(II)–carbene via a trapping experiment. Synthetic utility was demonstrated, and bioactive molecules were incorporated into the N-heterocyclic core.