Elemental Sulfur‐Promoted [2+3+1] Annulation for Synthesis of Functionalized Thiochromeno[2,3‐b]indoles from Indole Derivatives

Abstract

An intermolecular [2 + 3 + 1] annulation between indole and 2-bromobenzylaldehyde derivatives was successfully achieved by utilizing elemental sulfur as the promoter and coupling partner. This direct and operationally simple procedure provided a rapid and reliable approach to synthesize functionalized thiochromeno [2,3-b] indoles. Preliminary mechanistic studies indicated that elemental sulfur enhanced the nucleophilicity of the 3position of indole to attack an aldehyde group, and CÀ H cleavage of indole was not involved in the rate-determining step.

Elemental-Sulfur-Incorporated Cyclizations of Pyrrolidines Leading to Thienopyrroles

“…Furthermore, elemental sulfur is a promising oxidant and electrophile owing to its numerous oxidation states . Motivated by these promising advancements in the synthesis of S-containing compounds, − we explored the possibility of synthesizing thieno­[3,2- b ]­pyrroles by incorporating elemental sulfur and pyrrolidine. The first step involved the synthesis of thiophene via oxidative annulation using elemental sulfur as the oxidant.…”