An efficient approach toward formation of polycyclic coumarin derivatives via carbocation-initiated [4+2] cycloaddition and atom-economical photo-irradiated cyclization

Facile carbocation-initiated [4+2] cycloaddition of o-anisole-substituted propargyl silyl ethers and ynamides led to the formation of 4-vinylcoumarins. Subsequent intramolecular cyclization of 3-aryl-4-vinylcoumarins afforded polycyclic coumarin derivatives 11,12-dihydronaphtho[1,2-c] chromen-5-ones in excellent yields under mild photo-irradiated conditions established by fluorescence analysis-oriented screening.