Contrasting Reactivity of CS₂ with Cyclic vs. Acyclic Amidines

Abstract

Abstract The interaction between carbon dioxide (CO 2 ) and amidines such as 1,8‐diazabicyclo[5.4.0]undecane (DBU) has been extensively studied, but the reaction of isovalent CS 2 with such bases has been largely ignored, apart from a single crystallography report. Acyclic acetamidines are cleaved by CS 2 at room temperature to give an isothiocyanate and a thioacetamide. Because the pathway to that cleavage involves a rotation that is difficult for cyclic amidines, the reaction of CS 2 with cyclic amidines produces an entirely different product: a cyclic carbamic carboxylic trithioanhydride structure. The path to that product involves sp 3 C‐H activation leading to the formation of a new C–C bond at a carbon α to the central carbon of the amidine group. Alkylation and ring‐opening of the cyclic carbamic carboxylic trithioanhydride has also been demonstrated under ambient conditions.