Contrasting Reactivity of CS2 with Cyclic vs. Acyclic Amidines

The interaction between carbon dioxide (CO2) and amidines such as 1,8‐diazabicyclo[5.4.0]undecane (DBU) has been extensively studied, but the reaction of isovalent CS2 with such bases has been largely ignored, apart from a single crystallography report. Acyclic acetamidines are cleaved by CS2 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 CS2 with cyclic amidines produces an entirely different product: a cyclic carbamic carboxylic trithioanhydride structure. The path to that product involves sp3 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. Cyclic amidines react readily with CS2 to create new carbamic carboxylic trithioanhydride rings but acyclic amidines cleave the C=N bond and give isothiocyanates instead.