Condensation of nitrobenzaldehydes 3 and α-[o-(p-methoxybenzylthio) benzoyl] sulfoxide 4 gave α-sulfinyl enones 5. Treatment of 5 with formic acid caused cyclization followed by debenzylation to afford 3-(methylsulfinyl) thioflavanones 6. Double-bond formation with elimination of methanesulfenic acid was performed by refluxing 6 in benzene, and, finally, the nitro group of 2-phenyl-4H-1-benzothiopyran-4-one (thioflavones) 7 was reduced with ...
