Synthesis of 2-(trifluoromethyl)-1,2-dihydro-4H-thieno[2,3-c]chromen-4-ones and 2-(trifluoromethyl)-4H-thieno[2,3-c]chromen-4-ones from 2-trifluoromethylchromones and ethyl mercaptoacetate

The redox reaction of 2-trifluoromethylchromones with ethyl mercaptoacetate in the presence of triethylamine results in the formation of 1,2-dihydrothieno[2,3-c]chromen-4-ones and diethyl 3,4-dithiadipate in high yields. Oxidation of the first compounds with nitrogen dioxide gave 1,2-dihydrothieno[2,3-c]chromen-3,4-diones which were converted into thieno[2,3-c]chromen-4-ones.