Singlet Oxygen-Mediated Regioselective Thiocyanation of Terminal Alkynes, Alkenes, Indoles, Pyrrole, Anilines, and Phenols

We have developed a singlet oxygen (1O2)-mediated regioselective thiocyanation of terminal alkynes, indoles, pyrrole, anilines, and phenols using ammonium thiocyanate (NH4SCN) as an SCN source under visible light irradiation at room temperature. The oxidative thiocyanation of terminal alkynes forms α-keto thiocyanates, while indoles, pyrrole, anilines, and phenols regioselectively form the respective thiocyanate products. Herein, thiocyanate (SCN anion) undergoes single electron transfer (SET) by transferring an electron to singlet oxygen and forms an •SCN radical, which readily reacts with substrates to form thiocyanate products. Green chemistry metrics and Eco-scale evaluations signify that the current oxidative and regioselective thiocyanation protocol is an acceptable green organic synthesis process. Moreover, this method requires a simple reaction setup and uses inexpensive NH4SCN as an SCN source, O2 as an oxidant, and low-energy visible light. Thus, the current oxidative thiocyanation process is mild, green, highly efficient, eco-friendly, and environmentally feasible.