Base-promoted [4 + 2] cycloaddition of para-quinone methides (p-QMs) and 3-cyanochromones: facile access to chromeno[2,3-b]chromenes

Abstract

A K₂CO₃-promoted [4 + 2] cycloaddition between ortho-hydroxyphenyl-substituted p-QMs and 3-cyanochromones has been developed to synthesize chromeno[2,3-b]chromenes. The reaction pathway, involving sequential deprotonation, oxa-Michael addition, 1,6-addition, and protonation, has been rigorously formulated. Notably, this method exhibits excellent functional group tolerance, achieves 100% atom efficiency, and offers a superior strategy for rapidly constructing complex chromeno[2,3-b]chromene skeletons.