Odorless and Air-Stable Thionating Reagent for Broad Scope Thioamide Synthesis without H2S Emission

Abstract

A novel thionating reagent, 7-phenyl-2,4,6,8,9-pentathia-1,3,5-triphosphaadamantane 1,3,5-trisulfide (1), bearing an S–P adamantane framework, has been developed as a practical and environmentally benign alternative to conventional thionating reagents. Unlike Lawesson's reagent and P₄S₁₀, compound 1 is air- and thermally stable, odorless, and does not release detectable H₂S under ambient storage conditions. It enables efficient thionation of a broad range of amides─including primary, secondary, tertiary, aliphatic, and aromatic─into the corresponding thioamides in moderate to excellent yields. The reagent exhibits excellent chemoselectivity and functional group tolerance, allowing late-stage thionation of complex molecules, such as pharmaceuticals and natural product derivatives. It is also recyclable and retains reactivity after storage or heating. Moreover, a postreaction H₂S-trapping protocol ensures odorless and safe operation. These features establish compound 1 as a next-generation thionating reagent that addresses the critical drawbacks of existing reagents, offering a green and scalable platform for thioamide synthesis.