Versatile Route to Functionalized 1H-2-Benzothiopyrans and 1H-2-Naphthothiopyrans by Electrophilic Cyclization of Bis(arylmethylthio)acetylenes:  2-Benzo- and 2-Naphthothiopyrylium Salts

• Published in: Journal of organic chemistry Vol. 63; no. 14; pp. 4626 - 4631
• Main Authors: Klein, Thomas R, Bergemann, Marco, Yehia, Nasser A. M, Fanghänel, Egon
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10-07-1998
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo972334l

Substituted 1H-2-benzothiopyrans find applications as pharmaceutically active compounds or synthons for more complex sulfur heterocycles. However, restricted variability in their synthesis limits the application for research or industrial purposes. To develop a direct and fast route to substituted and functionalized 1H-2-benzothiopyrans, we investigated the ring closure of symmetrical bis(arylmethylthio)acetylenes with iodine monochloride or bromine. This facile reaction yielded 1H-3-halo-4-arylmethylthio-2-benzo- and 2-naphthothiopyrans via postulated vinyl cations in yields of 47−86%. Substituted 2-benzo- and 2-naphthothiopyrylium salts were prepared by hydride abstraction with triphenylcarbenium tetrafluoroborate from the products, further enhancing the synthetic potential of the found cyclization reaction.