A green synthesis of thieno[2,3-c]xanthen-6-ones through the tandem photochemical sigmatropic shift and cyclization

A green and clean route for the synthesis of 5-hydroxy-4-methyl-6H-thieno[2,3-c]xanthen-6-ones (2) has been developed by the photoirradiation of 3-(prop-2-ynyloxy)-2-(thiophen-3-yl)-4H-chromen-4-ones (1). This photoreaction of the 3-propynyloxychromenones being observed for the first time is very interesting and appears to be the result of a tandem sigmatropic shift and cyclization. The structure of 2 has been determined by the spectroscopic (Fourier transform infrared [FTIR], nuclear magnetic resonance [NMR], and mass) and single crystal X-ray crystallographic studies. [GRAPHICS] .