Studies in sigmatropic rearrangement: Regioselective synthesis of thieno[2,3-b]-thiochromen-4-one derivatives

Thermal rearrangement of a number of 2-(4'-aryloxybut-2'-ynylthio)-thiochromen-4-ones in refluxing chlorobenzene in the presence of catalytic amounts of 4-toluenesulfonic acid afforded 3-aryloxymethyl-2-methylthieno[2,3-b]thiochromen-4-ones in 55-62% yields.