Photocatalytic Synthesis of 1,2-Dihydroquinolines via SET-Desilylation-Triggered Vinyl Radical Cyclization of N -(α-Silyl)glycinates

Abstract

Visible-light-induced photocyclization of N-(α-trimethylsilyl)-N-phenylglycinates with the electron-deficient alkyne dimethyl acetylenedicarboxylate (DMAD) was developed using methylene blue (MB) as an organic photocatalyst. Sequential single-electron transfer (SET) oxidation by the excited MB and desilylation of the resulting amine radical cations generate α-amino radicals, which added to DMAD to form vinyl radical intermediates. Subsequent intramolecular cyclization onto the arene and oxidative rearomatization afforded 1,2-dihydroquinoline derivatives in moderate to high yields. Control experiments revealed that both the α-trimethylsilyl group and electron-withdrawing N-substituents are essential for productive radical generation and addition. This strategy enables vinyl radical-mediated N-heterocycle synthesis from readily accessible α-silylglycinates under mild, metal-free photocatalytic conditions.