Efficient Non‐Catalytic Carboxylation of Diamines to Cyclic Ureas Using 2‐Pyrrolidone as a Solvent and a Promoter

Abstract

AbstractCarboxylation reactions of diamines were found to proceed rapidly and non‐catalytically, producing corresponding cyclic ureas in excellent yields and selectivities when 2‐pyrrolidone (2‐PY) was used as a solvent. A similar promoting effect with 2‐PY was also observed for the carboxylation of monoamines by carbon dioxide (CO2). Most notably, the carboxylation reactions of mono‐ and diamines conducted in 2‐PY afforded 2–4 times higher yields of corresponding dialkyl ureas and cyclic ureas compared with those in N‐methyl‐2‐pyrrolidone (NMP). Such a dramatic promoting effect using 2‐PY is believed to be associated with the multiple hydrogen bonding interactions between 2‐PY and the CO2‐containing species of amines. Due to such favorable interactions, carboxylation reactions seem to be more facilitated in 2‐PY than in NMP.magnified image