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

Substituted 1 H -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 1 H -2-benzothiopyrans, we investigated the ring closure of symmetrical bis(arylmethylthio)acetylenes with iodine monochloride or bromine. This facile reaction yielded 1 H -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.