Facile Regioselective Synthesis of Benzofuran-Annulated Six-Membered Sulfur Heterocycles and the Occurrence of Thermal [1,3] Sigmatropic Rearrangement

Thio-Claisen rearrangement of a number of 3-(4-aryloxybut-2-ynlthio)benzofurans has been achieved under very mild conditions to give 2H-benzo[b]thiopyrano[2,3-d]furans. Attempts at further thio-claisen rearrangement resulted in the occurrence of thermal [1s, 3a] sigmatropic shift.