Metal‐Free Synthesis of 3‐Thiocyanatobenzothiophenes by Eosin Y Photoredox‐Catalyzed Cascade Radical Annulation of 2‐Alkynylthioanisoles

Abstract

A convenient, efficient, metal‐free synthesis of 3‐thiocyanatobenzothiophenes has been developed that uses eosin Y in a visible‐light‐mediated photoredox‐catalyzed anion oxidation of the ammonium salt of thiocyanate and proceeds through the cascade radical annulation of 2‐alkynylthioanisole at room temperature. The present protocol requires visible light as a green energy source, an organic dye as the photocatalyst, and oxygen as a green oxidant to provide a mild route with a broad substrate scope for the formation of potentially bioactive 3‐substituted benzothiophene derivatives in good yields.

Recent advances in photochemical and electrochemically induced thiocyanation: a greener approach for SCN-containing compound formation

“…Kshirsagar et al designed a photoredox-catalyzed simple green synthetic technique that uses visible light as a green source in the production of 3-thiocyanatobenzothiophenes 81 with an extensive substrate capacity in good to high yields. 34 In the photoredox-catalyzed anion oxidation of the ammonium salt of a thiocyanate, they used EY and moleculer oxygen as a terminal oxidant, which incorporates the radical annulation of 2-alkynylthioanisoles 80 at room temperature ( Scheme 27 ).…”

Sustainable Synthetic Approaches Involving Thiocyanation and Sulfur- Cyanation: An Update

“…There have been very few studies devoted to the thiocyanation of alkynes. Recently, a metal-catalyzed thiocyanation of terminal alkynes (26) was reported, leading to alkynylthiocyanates (27) or α-thiocyanoketones (28) depending on the reaction conditions used (Scheme 10) [10]. Nthiocyanosuccinimide (NTS) or N-thiocyanophtalimide (NTP) were used as thiocyanating agents.…”

Sustainable Synthetic Approaches Involving Thiocyanation and Sulfur- Cyanation: An Update

“…There have been very few studies devoted to the thiocyanation of alkynes. Recently, a metal-catalyzed thiocyanation of terminal alkynes (26) was reported, leading to alkynylthiocyanates (27) or α-thiocyanoketones (28) depending on the reaction conditions used (Scheme 10) [10]. Nthiocyanosuccinimide (NTS) or N-thiocyanophtalimide (NTP) were used as thiocyanating agents.…”