Pyridine-boryl radical mediated synthesis of quinolines via α-amino radical formation and intramolecular alkenyl sulfone trapping

Abstract

This study demonstrates that catalytic amounts of functionalized pyridines, in the presence of B₂nep₂ as a diboron reagent, can react with imines to form α-amino radicals. These α-amino radicals can be intramolecularly trapped by alkenyl sulfones through a 6-endo-trig process. According to our experiments and DFT calculations, the sulfonyl moiety plays a crucial role in the cyclization and aromatization processes, which occur in two steps: elimination of the sulfonyl radical and hydrogen atom abstraction, facilitating both aromatization and regeneration of the pyridine–boryl radical. The approach represents a useful application of radical-based methodologies for heterocycle synthesis under mild and catalytic conditions.