Copper-Catalyzed Alkynylation/Cyclization/Isomerization Cascade for Synthesis of 1,2-Dihydrobenzofuro[3,2-b]pyridines and Benzofuro[3,2-b]pyridines.

An efficient copper-catalyzed cascade alkynylation/cyclization/isomerization reaction of aurone-derived azadienes with terminal alkynes has been developed, giving a series of 1,2-dihydrobenzofuro[3,2-b]pyridines with excellent yields. The obtained 1,2-dihydrobenzofuro[3,2-b]pyridines can be conveniently transformed into the corresponding benzofuro[3,2-b]pyridines under basic conditions. Additionally, benzofuro[3,2-b]pyridines can also be prepared from azadienes and terminal alkynes in a one-pot reaction. The synthetic utility was demonstrated by the synthesis of three bioactive molecules with potent topoisomerase inhibition in high yields. This strategy provides a facile approach to 1,2-dihydrobenzofuro[3,2-b]pyridines and benzofuro[3,2-b]pyridines.