Visible‐Light Cercosporin Catalyzed Sulfenylation of Electron‐Rich Compounds with Thiols under Transition‐Metal‐Free Conditions

Abstract

In the present study, an efficient visible-light and cercosporin catalyzed direct sulfenylation of electron rich aromatic compounds such as indoles, active methylenes, and phenols with thiols through a photoredox catalyzed process has been reported through the cleavage of a CÀ H/SÀ H bond at room temperature under transition-metal-free conditions. The reported methodology gives a direct way in the formation of CÀ S bonds with broad functional group compatibility, which produces 3-sulfenylated indoles, α-sulfenylated carbonyl compounds and diaryl sulfides in moderate to good yields. The advantage of the reaction is that it meets the criteria of green and sustainable synthetic chemistry and can be used widely in the fields of organic synthesis and pharmaceutical chemistry.

Recent Advances in Visible‐Light‐Driven C−S Bond Formation

“…Aromatic thioethers are common existed in pharmaceutical and bioactive natural products such as Thymitaq, Axitinib and Albendazole. Barman and co‐workers recently reported a protocol for the sulfenylation of electron‐rich arenes and nitrogen based heterocycles (including indole 8.1 , Scheme 8) by aromatic thiols under transition‐metal‐free conditions [35] . In the, described mechanism, Cercosporin (CS) is promoted to the excited state (CS*), which then monoelectronically reduces 8.1 to form, after deprotonation of the radical cation 8.3 , radical 8.4 , along with radical cation CS •+ .…”

“…Subsequently, CS •+ oxidizes thiol and the resulting radical cation 8.4 deprotonates to 8.5 , which coupling with 8.3 affords the desired product. An analogous approach has been applied also to the functionalization of 1,3‐diketones [35] …”

“…Barman and co-workers recently reported a protocol for the sulfenylation of electron-rich arenes and nitrogen based heterocycles (including indole 8.1, Scheme 8) by aromatic thiols under transition-metalfree conditions. [35] In the, described mechanism, Cercosporin (CS) is promoted to the excited state (CS*), which then monoelectronically reduces 8.1 to form, after deprotonation of the radical cation 8.3, radical 8.4, along with radical cation CS * + . Subsequently, CS * + oxidizes thiol and the resulting radical cation 8.4 deprotonates to 8.5, which coupling with 8.3 affords the desired product.…”

“…An analogous approach has been applied also to the functionalization of 1,3diketones. [35] Among the nitrogen containing heterocycles, indolizine derivatives found a large variety of application, ranging from biology (due to the different biological activities) to material chemistry. [36] A set of variously substituted 3-sulfanylindolizines 9.3 (Scheme 9a) have been isolated in moderate to good yields via the Eosin Y (EY) photoredox catalyzed oxidative coupling reaction of 2-arylindolizines 9.1 and aromatic thiols 9.2 under air atmosphere.…”

Recent Advances in Synthesis of 3-Sulfenylated Indoles

“…反应以硫酚作为硫源, 化学 染料玫瑰红(Rose bengal)作为光敏剂, 在 415 nm 光照射 下, 通过氧气的协同作用首先生成芳基硫自由基, 进一 步经历了与吲哚化合物的自由基加成以及氧化、去质子 化历程, 最终实现温和条件下吲哚-3-硫醚的高效构建. 2020 年, Barman 课题组 [18] 报道了一种可见光催化下富 电子芳香族化合物与硫醇(酚)的 C-H/C-S 键交叉偶联 反应(Eq. 9).…”