Singlet-oxygen-driven stereoselective iodothiocyanation and iodoselenocyanation of alkynes

Abstract

We present here a series of low-energy visible-light-induced metal-free C–I, C–S, and C–Se cross-coupling reactions for the formation of iodo-vinyl-thiocyanates (IVTs) and iodo-vinyl-selenocyanates (IVSs) using alkynes, iodine and ammonium thiocyanate (NH₄SCN)/potassium selenocyanate (KSeCN) in the presence of oxygen at room temperature. Upon photo-irradiation, iodine, molecular oxygen, and NH₄SCN synergistically generate iodine radical, singlet oxygen (¹O₂), and ˙SCN/˙SeCN radicals, respectively, and selectively react with alkyne to form stereoselective E-configured IVTs and IVSs. Iodine plays a significant role as I₂ acts as a photoactive species, undergoing homolytic cleavage to form iodine radicals, while singlet oxygen is produced via energy transfer (ET), and thiocyanate/selenocyanate radicals via single-electron transfer (SET) process. Moreover, green chemistry metrics and Eco-Scale evaluations highlight that the current stereoselective oxidative C–I, C–S, and C–Se coupling protocol aligns well with sustainable principles, establishing it as a viable and environmentally benign approach to organic synthesis.