Metal-Free Synthesis of Unsymmetrical Ureas and Carbamates from CO₂ and Amines via Isocyanate Intermediates

摘要

A mild and metal-free synthesis of aryl isocyanates from arylamines under an atmosphere of CO_(2) was developed. The carbamic acid intermediate, derived from the arylamine starting material and CO_(2) in the presence of DBU, is dehydrated by activated sulfonium reagents to generate the corresponding isocyanate. The latter can be detected by in situ IR and trapped by various amines and alcohols to make unsymmetrical ureas and carbamates, respectively. Dicarbamates can also be prepared in good yields via the mild dehydration of the corresponding dicarbamic acids.