Catalyst-free visible-light induced synthesis of nitrogen- and oxygen-containing heterocycles from 1,3-diketones

The synthesis of nitrogen- and oxygen-containing heterocycles has found many applications in the preparation of biomedical intermediates, yet actual synthetic procedures display limitations such as high-loading catalysts, harsh reaction conditions and tedious preparation of heterogeneous catalysts. Alternatively, photocatalysis allows to access functional products with minimum synthetic procedures and waste generation. Here, we present an efficient, simple, green protocol for the synthesis of N- and O-containing six-membered-ring compounds under mild conditions under visible blue light. Various aldehydes and 1,3-diketones can be reacted to afford eight series of corresponding 1,4-dihydropyridines and 4H-benzo[b]pyrans. This protocol has some merits such as the use of abundant and sustainable aqueous ethanol as solvent, short reaction time (within 60 min), no need of catalyst and broad functional group tolerance to afford 81 different series of target molecules in 75–96% yield under mild conditions.