Elemental sulfur as a sulfuration agent in the copper-catalyzed C–H bond thiolation of electron-deficient arenes

Abstract

By utilizing elemental sulfur as the thiolation agent and oxidant, a copper-catalyzed direct C-H bond thiolation of electron-deficient arenes was demonstrated. Various electron-deficient arenes were proved to be suitable for this transformation. Preliminary mechanistic studies indicated that this reaction underwent a radical pathway, in which the trisulfur radical anion (S˙) might play a vital role. Meanwhile, KIE experiments suggested that C-H bond cleavage was not involved in the rate-determining step.

Applications of trisulfide radical anion S3˙− in organic synthesis

“…In 2017, Lei and co-workers described another reaction involving S 3 ˙ − . 30 They found that found that the treatment of electron-deficient arenes 35 with a mixture of elemental sulfur S 8 and t -BuONa in DMF at 25 °C is catalysed by copper( ii ) dichloride to afford the corresponding thiols 36 through C–H bond thiolation. Elemental sulfur S 8 is the thiolation agent and oxidant for the reaction.…”

DMF as Methine Source: Copper‐Catalyzed Direct Annulation of Hydrazides to 1,3,4‐Oxadiazoles

“…[20] Besides, 1,3,4-oxadiazoles as typical electron-deficient arenes could be oxidized by elemental sulfur via copper-catalyzed direct CÀ H bond thiolation (Scheme 2c). [21] To gain insight into the mechanism of the reaction, a variety of control experiments were conducted as shown in Scheme 3. In order to confirm the source of CH is from N-methyl or formyl moiety of DMF, we use formamide and N,N-diethylformamide instead of N,N-dimethylformamide, no reaction occurred under the optimal reaction conditions (Scheme 3a, 3b).…”

“…Moreover, the direct alkynylation of 1,3,4‐oxadiazoles with alkynyl bromides under copper catalysis created the corresponding heteroaryl‐alkynyl linkage in good yield, which provided a convergent access to oxadiazole core π‐conjugated systems (Scheme b) . Besides, 1,3,4‐oxadiazoles as typical electron‐deficient arenes could be oxidized by elemental sulfur via copper‐catalyzed direct C−H bond thiolation (Scheme c) …”

Construction of 2-Arylbenzo[4,5]thieno[2,3-d]thiazole Skeleton via CuCl/S-Mediated Three-Component Reaction

“…On the basis of results from the previous literature research, − a plausible mechanism (Scheme ) is proposed for this newly discovered three-component one-pot reaction. First, in the presence of the copper catalyst, 2-(2-bromophenyl)­acetonitrile 1f was converted to intermediate A via an oxidative insertion.…”