Synthesis of Densely Functionalized Pyrroles via Photoinduced C-Insertion into N-Alkylenamines: Sequential C(sp2)-H/C(sp3)-H Activation with Bromine Radicals

Abstract

Photoinduced C_sp³-Br bond homolysis of ArCOCF₂Br using triethylamine as the halogen bonding (XB) acceptor was a key step for the [2 + 2 + 1] cyclization. An unprecedented strategy for assembling privileged pyrroles and their fused scaffolds via metal-, oxidant-free C-incorporation into N-alkylenamines through a triple-cleavage process has been disclosed. This method uses readily available alkyl amines, alkynes, or CF₃-containing N-benzylenamines as the starting material and features two consecutive C-C-forming reactions with ArCOCF₂Br as the carbon source. The transformation exploits the dual reactivity of bromine radicals─hydrogen-atom transfer (HAT) and reversible radical addition (RRA)─to coactivate the N-alkylenamines, and the resulting open-shell intermediates are then intercepted by in situ-generated difluoroalkyl radicals to deliver the target heterocycles.