Dearomative Photocatalytic Construction of Bridged 1,3‐Diazepanes

The construction of diverse sp3‐rich skeletal ring systems is of importance to drug discovery programmes and natural product synthesis. Herein, we report the photocatalytic construction of 2,7‐diazabicyclo[3.2.1]octanes (bridged 1,3‐diazepanes) via a reductive diversion of the Minisci reaction. The fused tricyclic product is proposed to form via radical addition to the C4 position of 4‐substituted quinoline substrates, with subsequent Hantzsch ester‐promoted reduction to a dihydropyridine intermediate which undergoes in situ two‐electron ring closure to form the bridged diazepane architecture. A wide scope of N‐arylimine and quinoline derivatives was demonstrated and good efficiency was observed in the construction of sterically congested all‐carbon quaternary centers. Computational and experimental mechanistic studies provided insights into the reaction mechanism and observed regioselectivity/diastereoselectivity. Building bridges: The reductive photocatalytic dearomatization of quinoline derivatives using N‐arylimines is described. The bridged 1,3‐diazepane architecture is constructed through the addition of an intermediary α‐amino radical to the C4‐position of a 4‐substituted quinoline and subsequent reductive cyclization.