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

Abstract

Carboxylation 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 (CO 2 ). 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 Nmethyl-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 CO 2 -containing species of amines. Due to such favorable interactions, carboxylation reactions seem to be more facilitated in 2-PY than in NMP.

Recent Advances in the Chemical Fixation of Carbon Dioxide: A Green Route to Carbonylated Heterocycle Synthesis

“…Authors performed a theoretical calculation to support these findings. On these bases, authors introduced 2pyrrolidone as the best solvent for this reaction [200]. In fact, it can give rise to a keto-enol Also the solvent play an important role, because it should be polar enough to stabilize anionic species, but it must not interact strongly with the base catalyst via hydrogen bonding.…”

Pivotal Role of the Basic Character of Organic and Salt Catalysts in C−N Bond Forming Reactions of Amines with CO2

“…[120] Activation of CO 2 by the formation of base-CO 2 adducts has also been hypothesized, [88,137,139,141] but in the presence of an amine direct carbamate formation appears energetically favorable. [17,27,150] Overall, base catalysts, [139] H-bond donors [146] and polar solvents [139,142] stabilize carbamate salts.Asmall effect on the dehydration of the salt is also possible. [120] However,l ow sterics [139] and base stability [145] to the reaction conditions are essential for high activity in the synthesis of urea derivatives.…”

“…Overall, base catalysts, H‐bond donors and polar solvents stabilize carbamate salts. A small effect on the dehydration of the salt is also possible .…”

“…Beneficial effects of H‐bonding has been observed in catalyst‐free reactions in 2‐pyrrolidone, where a small deuterium effect was reported and supported computationally . The non‐basic, non‐reactive H‐bonding IL 1‐butyl‐3‐methylimidazoliym hexafluorophosphate ([BMIm]PF 6 ) is also weakly active .…”

CO2 Catalysis: Mature and Multifaceted

“…Other contributions include the preparation of various types of polymers such as polyureas and pH‐ responsive non‐isocyanate‐based poly(hydroxyurethane)s (NIPUs), the preparation of cyclic ureas and the organocatalytic synthesis of α‐alkylidene carbonates . This combined overview of catalytic CO 2 transformations demonstrates the richness in catalysis technologies while upgrading this carbon feedstock into value‐added compounds.…”