Three‐Component Thieno[2,3‐b]indole Synthesis from Indoles, Alkenes or Alkynes and Sulfur Powder under Metal‐Free Conditions

Abstract

A Bronsted acid promoted three-component synthesis of substituted thieno[2,3-b]indole has been developed starting from indoles, alkenes or alkynes, and sulfur powder. N,N-Dimethylformamide plays an important role to convert the starting materials into the fused products. Various functional groups attached to substrates were well tolerated to afford the corresponding products in moderate to good yields under very simple reaction conditions.

Construction of 4‐(Methylthio)isochromenones Skeleton through Regioselective Intramolecular Cyclization of 2‐Alkynylbenzoate Mediated by DMSO/[D6]DMSO and SOCl2

“…Meanwhile, diverse substituents can be introduced at the 4‐position of the isochromenones , . Although C sp 2 –S bond formation had been widely reported, the preparation of 4‐sulfenylisochromenones has been less explored due to the limitation on their synthetic strategies. Larock and co‐workers reported that by treating alkynes with the electrophilic sulfenyl chloride, sulfoesterification occurred to give the corresponding 4‐(sulfenyl)isochromenones (Scheme a).…”

Recent Advances in Sulfur-Containing Heterocycle Formation via Direct C–H Sulfuration with Elemental Sulfur

“…To this end, Deng and co-workers discovered a Brønsted acid-promoted, three-component approach for the synthesis of substituted thieno[2,3-b]indoles starting from indoles, alkenes or alkynes, and sulfur powder (Scheme 14). 34 When the reaction was carried out in refluxing DMF, 2-substituted thieno[2,3-b]indoles were obtained in moderate to good yields. DMF as the solvent was indispensable and probably activated S 8 and mediates the C-H sulfuration process.…”

One-pot multicomponent synthesis of thieno[2,3-b]indoles catalyzed by a magnetic nanoparticle-supported [Urea]4[ZnCl2] deep eutectic solvent

“…Li and coworkers reported the Brønsted acid-catalyzed three-component synthesis of thieno [2,3-b]indoles starting from indoles, alkenes or alkynes, and sulfur powder. 11 Ni and coworkers demonstrated the synthesis of 3-substituted thieno [2,3-b]indoles via cascade cyclization by Brønsted acid-promoted annulation of indoles, ketones, and sulfur powder. 12 However, the low yields, narrow substrate scope, and the inability to recycle catalysts remain a crucial challenge to industrial application.…”