Transition-metal-free tandem cyclization by radical NHC catalysis: Rapid access to indolo[2,1‑a]isoquinolines

A diverse array of functionalized indolo[2,1-a]isoquinolines are constructed through an NHC-catalyzed transition-metal-, and oxidant-free radical tandem cyclization from readily accessible 2-aryl N-methacryloyl indoles and α-bromo esters. This redox-neutral protocol exhibits a wide substrate scope, excellent functional group tolerance, and can be scaled up to 2.0 mmol with parallel efficiency. Mechanistic studies suggest that a single electron transfer radical process is likely involved.