Synthesis of bioactive heterocycles: One pot regioselective synthesis of pyrano[3,2-f]benzo[b]thiophene derivatives

Article abstract of DOI:10.1016/S0040-4020(98)01124-7

Regioselective synthesis of hitherto unreported pyrano[3,2- f]benzo[b]thiophene derivatives (8a-f) in 90-95% yields are reported by the application of a less studied rearrangement of 6-(4-aryloxybut-2- ynylthio)[1]benzopyran-2-ones (5a-f) via oxidation with m-chloroperoxybenzoic acid followed by thermal rearrangement and treatment with methanol. Substrates 5a-fare prepared by the reaction of 6-mercaptocoumarin (unstable) with 1-aryloxy-4-chlorobut-2-ynes (4) in refluxing acetone in the presence of anhydrous potassium carbonate and sodium iodide. 6-Mercaptocoumarin (3) is in turn prepared by the zinc-acid reduction of the disulfide (2) obtained by the reaction of the diazotised 6-aminocoumarin (1) with potassium othylxanthate followed by decomposition. Pyrano[3,2-f]-benzo[b]thiophene derivatives (8a- f) are easily converted to 1-acetylpyrano[3,2-f]benzo[b]thiophene-7-one (12) when refluxed in acetic acid in the presence of catalytic amount of cone, sulfuric acid for 4 h.