Oxidations by thionyl chloride. IV. Benzo[b]thiophenes and oxoindeno[2,3-d]benzo[b]thiophenes via sulfenyl chlorides

✍ Scribed by Arnold J. Krubsack; Tatsuo Higa

• Publisher: Elsevier Science
• Year: 1972
• Tongue: French
• Weight: 160 KB
• Volume: 13
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)94439-9

✦ Synopsis

The reaction of hot thionyl chloride, in the presence of catalytic amounts of pyridine, on 3-phenylpropanoic acids constitutes one of the most direct routes to benso[&]thiophenes.2 It was of particular interest to us to extend this reaction to a variety of propanoic acids because the method showed promise of being a one-step synthesis of 3-alkyl-or 3-aryl-substituted benzo(b]thiophenes. The preparation of 3-phenylbenzo&]thiophene-2-carboxylic acid, 3b, by this route seemed to offer a practical challenge , since the previous synthesis of ?b involved a eixstep sequence starting from 2-chloro-5-nitrobenzoic acid. 3 When 3,3_diphenylpropanoic acid, 1, was treated with an excess of thionyl ohloride in the presence of pyridine at 120-130' over a period of 3 hr, 35 was obtained in quantitative yield as a viscous yellow oil. (The infrared spectrum of this oil was identical to that of the product obtained from the mild reaction of 3b with thionyl chloride.) Oil z was converted to 3b (65X, mp3 199-200°) by heating it at reflux for 3 hr with 2.5% hydrochloric acid in aqueous tetrahydrofuran.