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

✍ Scribed by Krishna C Majumdar; Paritosh Biswas

• Publisher: Elsevier Science
• Year: 1999
• Tongue: French
• Weight: 454 KB
• Volume: 55
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(98)01124-7

✦ Synopsis

Rcgiosclcctive synthesis of hitherto unreported pyrano[3,2-/]benzo [b]thiophme derivatives (Sa-f) in 90-95 % yields are reported by the application of a less studied rearrangemont of 6-(4-aryloxybut-2-ynylthio)[ 1 ]benzopyran-2-unes (fat-f) via oxidation with m-chioroparoxybenzoic acid followed by themml rearrangement and treatmerit with methanol. Substrates ~t-f are prepared by the reaction of 6-mercaptocomnarin (unstable) with l-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 diazztised 6-uminoooumarin (1) with potassium cthylxanthate followed by decomposition. Pyrano[3,thiophene derivatives (Sa-f) are easily converted to l-acetylpyrano[3,2-t]benzo[b]thiophene-7-one (12) when r~.-qluxed in acetic acid in the presence of catalytic amount of cone. sulfuric acid for 4 h.