Metal-Free Synthesis of Guanidines from Thioureas in Water Reactions Mediated by Visible Light

Abstract Metal-free synthesis of guanidines from thioureas under visible-light irradiation in water was successfully developed. Using 1–5 mol% of inexpensive and commercially available phenazine ethosulfate as a photocatalyst in the presence of 1 wt% cetyltrimethylammonium bromide (CTAB) as surfactant with K2CO3 as an additive base, transformations of a variety of thioureas into the corresponding guanidines under visible-light irradiation were achieved in moderate to high yields. The advantages of this reaction include the use of a metal-free photocatalyst, water as a nontoxic solvent, and ease of operating at room temperature in an open-flask manner.