RESUMO
A metal-free, photoinduced aerobic tandem amine dehydrogenation/Povarov cyclization/aromatization reaction between N-aryl glycine esters and indoles leads to tetracyclic 11H-indolo[3,2-c]quinolines under mild conditions and with high yields. The reaction can be performed by using molecular iodine along with visible light, or by combining an organic photoredox catalyst with a halide anion. Mechanistic studies reveal that product formation occurs through a combination of radical-mediated oxidation steps with an iminium ion or N-haloiminium ion [4+2]-cycloaddition, and the N-heterocyclic products constitute new analogues of the antiplasmodial natural alkaloid isocryptolepine.
RESUMO
We report metal-free, photoinduced aerobic tandem dehydrogenative Povarov cyclisation/Csp3-H oxygenation reactions between N-aryl glycine esters and α-substituted styrenes, which efficiently lead to 4,4-disubstituted dihydroquinoline-3-ones under mild conditions. The reactions are mediated by iodine along with visible light irradiation, which allows for the in situ generation of the essential Brønsted acid HI, to catalyse the key imine [4+2]-cycloaddition.