Síntese de benzo[b]tiofenos funcionalizados com organocalcogênios usando selectfluor® como agente oxidante

Abstract

In the present work, two methodologies were developed for obtaining benzo[b]thiophene derivatives containing organochalcogens as substituents from the electrophilic cyclization of alkynes using diorganoyl dichalcogenides as a source of chalcogen. For both procedures, F-TEDA was used, known commercially as Selectfluor®, a safe, stable, non-toxic and non-hygroscopic oxidizing agent. Based on results obtained by our group, it was found that this oxidizing agent promotes the cleavage of the chalcogen-chalcogen bond of diorganoyl dichalcogenides, generating active chalcogen species. The first part of this work reports the synthesis of 23 compounds derived from 2-organyl-3-organochalcogenyl-benzo[b]thiophenes in yields of 42% to 94%, obtained from the cyclization of 2-alkynyl-thioanisoles. This methodology also proved efficient for obtaining a 3-organochalcogenyl-benzo[b]selenophene derivative in 78% yield. Next, the reactivity of the terminal alkyne ethyl(2-ethynylphenyl)sulfane towards diorganoyl dichalcogenides and Selectfluor® was studied, and it was possible to obtain mono- or disubstituted benzo[b]thiophenes by varying the reaction conditions. From this substrate, eight 3-organochalcogenyl-benzo[b]thiophene derivatives were obtained in yields ranging from 35% to 80%, and four 2,3-bis(organochalcogenyl)benzo[b]thiophene derivatives in yields ranging from 42 to 70%. The 37 compounds obtained in this work were characterized by nuclear magnetic resonance spectroscopy of hydrogen (1H), carbon (13C) and in some cases selenium (77Se), high-resolution mass spectroscopy (HRMS), melting point and single-crystal X-ray diffraction, when necessary. The methodologies described allow benzo[b]thiophene derivatives to be obtained under mild conditions, using Selectfluor® as a safe oxidizer and without the need for heating or an inert system.