Ag-Mediated Radical Cyclization of 2-Alkynylthio(seleno)anisoles: Direct Synthesis of 3-Phosphinoylbenzothio(seleno)phenes

Abstract

A new method for the direct synthesis of 3-phosphinoylbenzothio­(seleno)­phenes has been achieved through an Ag-mediated radical addition–cyclization of 2-alkynylthio­(seleno)­anisoles with secondary phosphine oxides in good yields under mild conditions. In this single reaction, benzenethiophene or benzeneselenophene skeleton, C­(sp2)–P and C­(sp2)–S bonds can be constructed with the cleavage of the C­(sp3)–S bond, highlighting the efficiency and step-economics of this protocol.

Recent Advances in the Construction of Phosphorus‐Substituted Heterocycles, 2009–2019

“…Very recently, the group of Gao presented an efficient protocol for the synthesis of 3‐phosphorylbenzothio(seleno)phenes . This process was achieved through an Ag‐mediated radical cascade addition/cyclization sequence of 2‐alkynylthio(seleno)anisoles 554 with H ‐phosphine oxides 29 under an argon atmosphere at 70 °C for 7 h (Scheme ).…”

Synthesis of Seleno‐Heterocycles via Electrophilic/Radical Cyclization of Alkyne Containing Heteroatoms

“…Ag-mediated radical cyclization reactions of 2alkynylthio-(seleno)anisoles 147 with secondary phosphine oxides 148 gave the corresponding 3phosphinoylbenzothio(seleno)phene 149 in good yields under mild reaction conditions (Scheme 55). [100] The radical cyclization reactions of 2-alkynylthioanisole or selenoanisole 150 with sulfinic acid 151 and tert-butyl hydroperoxide in acetonitrile solvent at 100°C gave the corresponding 3-(arylsulfonyl)benzothiophene or -benzoselenophene 152 (Scheme 56). [101] The synthesis of benzothiophenes and benzoselenophenes 155 were obtained in moderate to good yields at ambient temperature by a photoredox-catalyzed cascade annulation reactions of methyl(2-(phenylethynyl)phenyl)sulfane and methyl(2-(phenylethynyl) phenyl)selane 153 with sulfonyl chloride 154.…”

Recent Advances in the Synthesis of Selenophenes and Their Derivatives

“…In this protocol, a mixture of TMS-(ethynyl) arene 77, arenediazonium salt 78, an Au-based catalyst and a Ru-based photocatalyst in MeOH/MeCN (3:1) as the solvent, was irradiated by visible light (21 W fluorescent light bulb) for 4 h, yielding the respective products 79 in moderate yields (Scheme 54). In 2019, a new protocol for the construction of benzo[b]selenophenes through an Ag-promoted radical cyclization between the type C precursor 72 and secondary phosphine oxides 80 was developed (Scheme 56) [156]. This protocol allowed us to extend the synthesis to a wide scope of benzoselenophene derivatives 81a-c using phosphines bearing aryl groups (Ph, 4-MeC 6 H 4 , 3,5-di-MeC 6 H 3 ) in good yields (61-72%).…”