Synthesis of Industrially Relevant Carbamates towards Isocyanates using Carbon Dioxide and Organotin(IV) Alkoxides

A straightforward phosgene‐free synthesis of aromatic isocyanates and diisocyanates is disclosed. Theoretical investigations suggested that the insertion of carbon dioxide (CO2) by dialkyltin(IV) dialkoxides could be used to convert aromatic amines into aromatic mono‐ and dicarbamates. Here we show, that methyl phenylcarbamate (MPC) from aniline using organotin(IV) dimethoxide and CO2 can be formed in high yield of up to 92 %, experimentally corroborating the predictions of density functional theory (DFT) calculations. MPC was then separated from the tin oxide residues and converted into phenyl isocyanate. Furthermore, organotin(IV) alkoxides could be regenerated from the tin oxide residues and reused, paving the way for a continuous industrial process. Extension of the scope to the synthesis of diurethanes from toluene 2,4‐diamine and 4,4′‐methylenedianiline could potentially allow the efficient production of industrially relevant diisocyanates. Out of tin air: Straightforward access to isocyanates, precursors to polyurethanes, is achieved from carbon dioxide (CO2) and primary amine and tin alkoxides. The first step involves the synthesis of carbamates, which can be cleaved in situ to afford isocyanates. The active tin species can eventually be regenerated to produce more carbamate. The strategy can be extended to the preparation of diurethanes in good yields.