Photoinduced Hydrogenative Dearomatization With Homocoupling of Quinolines to Construct Octahydro‐4,4'‐biquinolines

Dearomative functionalization of heteroaromatics has greatly contributed to drug discovery owing to nitrogen-containing three-dimensional (3D) sp³-rich frameworks. However, conventional dearomative functionalization of quinolines affords limited types of tetrahydroquinoline (THQ)-based polycycles. Herein, we present a chemoselective dearomative hydrogenative dearomatization with homocoupling of quinolines into 1,1',2,2',3,3',4,4'-octahydro-4,4'-biquinoline (OHBQ) without any photocatalyst, through boron-mediated photoexcitation using HB(pin) and KOtBu. Experimental and computational mechanistic studies revealed that the thermally induced dearomative hydroboration functionalization proceeds initially, and subsequently the photoexcited boron complex enables an unprecedented homocoupling of 1,2,3,4-THQs, which is challenging in the ground state, to yield the desired OHBQ.