Carbene-catalyzed [3 + 2 + 1] annulation via C–N radical coupling of iminyl radicals and ketyl radicals

An N-heterocyclic carbene-catalyzed cascade [3 + 2 + 1] annulation to assemble vinyl azides, aldehydes, and trihalomethyl reagents (Togni's reagent or CCl4) towards 1,3-oxazin-6-ones was reported. The cascade was triggered by an NHC-catalyzed single electron transfer (SET) between aldehydes and trihalomethyl reagents, followed by the addition of trihalomethyl radicals to vinyl azides, a denitrogenated transformation into iminyl radicals, a C-N radical coupling of iminyl radicals and ketyl radicals, and a base-controlled dehalogenative cyclization.