Regioselective reduction of 1-methylquinolium ions by tributyltin hydride and tris(trimethylsilyl)silane via photoinduced electron transfer

Thermal reduction of 1-methylquinolinium ion by tributyltin hydride occurs via a polar mechanism to yield 1-methyl-1,2-dihydroquinoline selectively, while the photoreduction of 1-methylquinolinium ion derivatives by tributyltin hydride and tris(trimethylsilyl)silane proceeds via photoinduced electron transfer from the metal hydrides to the singlet excited states of 1-methylquinolinium ion derivatives to yield the corresponding 1,4-dihydroquinolines exclusively.