Catalyst‐Free, One‐Pot, Three‐Component Synthesis of 3‐Arylsulfonylated Thioflavones

Abstract

A one‐pot, three‐component synthesis of 3‐arylsulfonylated thioflavones has been developed. The reactions were carried out without using any catalysts or additives. The desired products were obtained through intramolecular radical cyclization. This process provides an alternative route for the synthesis of thioflavone derivatives, which have been found in various bioactive compounds.

Visible‐light‐mediated synthesis of 3‐arylsulfonylated thioflavones using an in situ activation strategy

“…To overcome the limitations of previous studies, our group recently developed a three‐component method for synthesizing 3‐arylsulfonylated thioflavones (Scheme 1, C) 7 . In this study, methylthiolated alkynones and aryl diazonium salts were used as starting materials.…”

“…We envisaged that aryl diazonium salts could be generated in situ during the reaction from aryl amines in the presence of tert ‐butylnitrite and boron trifluoride diethyl etherate 11 . In our previous study, we reported the catalyst‐free, one‐pot synthesis of 3‐arylsulfonylated thioflavones using DABSO as a sulfur dioxide surrogate 7 . Therefore, the reaction was initially carried out without the use of a catalyst.…”

“…To overcome the limitations of previous studies, our group recently developed a three-component method for synthesizing 3-arylsulfonylated thioflavones (Scheme 1, C). 7 In this study, methylthiolated alkynones and aryl diazonium salts were used as starting materials. In addition, a 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO) was used as the sulfur dioxide surrogate.…”

Recent advances in the dichalcogenation reactions of unsaturated compounds via double functionalization

“…More recently, Lee and coworkers described a similar one-pot three-component synthesis of 3-arylsulfonylated thioflavones 99c from aryl-terminated methylthiolated alkynones 99a using DABSO and aryldiazonium tetrafluoroborates 99b as the sulfonyl radical precursors (Scheme 99). 128 The reactions were performed at room temperature under catalyst-, reagent- and additive-free conditions. Noteworthily, 3-methylsulfonylated thioflavone 99d was observed as a by-product for this transformation, which suggests the involvement of an in situ formed methyl sulfonyl radical 99C arising from SO 2 insertion into a released methyl radical species.…”

Photoinduced Radical Cyclization of 2-Alkynylthioanisoles with Disulfides without an External Photocatalyst

“…Meanwhile, Wu et al disclosed a radical relay strategy for the generation of 3-(methylsulfonyl)-benzo [b]thiophenes through the reaction of methyl(2-alkynylphenyl)sulfanes with sodium metabisulfite, 7 and Lee's group reported a threecomponent synthesis of 3-(arylsulfonyl)benzo [b]thiophenes using potassium metabisulfite as a sulfur dioxide surrogate. 8 Moreover, some facile routes to 3-((trifluoromethyl)-thio)benzo [b]thiophenes and 3-methylthiobenzo [b]thiophenes via intramolecular cyclization of methyl(2-alkynylphenyl)sulfanes have also been developed (Scheme 1c). 9 Very recently, Kesharwani and co-workers reported the synthesis of 3-(methylthio)-2-phenylbenzo [b]thiophene via electrophilic cyclization reaction of o-alkynylthioanisoles with a stable dimethyl-(thiodimethyl)sulfonium tetrafluoroborate salt (Scheme 1d).…”