Tuning Ionic Liquid-Based Catalysts for CO2 Conversion into Quinazoline-2,4(1H,3H)-diones

Carbon capture and storage (CCS) and carbon capture and utilization (CCU) are two kinds of strategies to reduce the CO₂ concentration in the atmosphere, which is emitted from the burning of fossil fuels and leads to the greenhouse effect. With the unique properties of ionic liquids (ILs), such as low vapor pressures, tunable structures, high solubilities, and high thermal and chemical stabilities, they could be used as solvents and catalysts for CO₂ capture and conversion into value-added chemicals. In this critical review, we mainly focus our attention on the tuning IL-based catalysts for CO₂ conversion into quinazoline-2,4(1H,3H)-diones from o-aminobenzonitriles during this decade (2012~2022). Due to the importance of basicity and nucleophilicity of catalysts, kinds of ILs with basic anions such as [OH], carboxylates, aprotic heterocyclic anions, etc., for conversion CO₂ and o-aminobenzonitriles into quinazoline-2,4(1H,3H)-diones via different catalytic mechanisms, including amino preferential activation, CO₂ preferential activation, and simultaneous amino and CO₂ activation, are investigated systematically. Finally, future directions and prospects for CO₂ conversion by IL-based catalysts are outlined. This review is benefit for academic researchers to obtain an overall understanding of the synthesis of quinazoline-2,4(1H,3H)-diones from CO₂ and o-aminobenzonitriles by IL-based catalysts. This work will also open a door to develop novel IL-based catalysts for the conversion of other acid gases such as SO₂ and H₂S.

The room-temperature, ambient-pressure conversion of CO2 into value-added pharmaceutical products quinazoline-2,4(1H,3H)-diones

As global warming due to CO₂ emissions has become a widely recognized concern, CO₂ capture, sequestration, neutralization, and conversion have become possible solutions to address this concern. Among these approaches, the conversion of CO₂ into fuels or value-added products has attracted considerable attention. In this work, we report the high-efficiency conversion of CO₂ to important industrial raw materials for pharmaceutical compounds, quinazoline-2,4(1H,3H)-diones, via reactions with 2-aminobenzonitriles at room temperature and under ambient pressure, with high conversion yields (91.5-99.3%). 1,8-Diazabicyclo-[5.4.0]-undec-7-ene (DBU), 1,1,3,3-tetramethylguanidine (TMG), and cholinium (Ch) ammonium-based ionic liquids (ILs) are employed as catalysts during the process. Cations with a pK_a value near 11.9 and anions with a pK_a value range of 10 to 15 are necessary for the reaction. The experimental results indicate that the ionic liquid pair [HDBU⁺][3-Cl-PhO^-] has high efficiency under very mild conditions, obtaining high product yields of 91.5% at 25 °C and 1 atm and 99.3% at 30 °C and 1 atm. More importantly, the catalysts retain high efficiency and activity after 5 consecutive cycles. To gain insightful understanding of the reaction, density functional theory (DFT) calculations were conducted to study the reaction mechanism. The computational results indicate that the catalytic process contains three stages: cyano activation, intramolecular rearrangement, and intramolecular cyclization. Of these, the rate-determining step is cyano activation, which shows an energy barrier of 24.5 kcal mol^-1. Tuning the types of ions in ILs can effectively reduce this energy barrier and allow high efficiencies.

Alcohol amine-catalyzed CO2 conversion for the synthesis of quinazoline-2,4-(1H,3H)-dione in water

The conversion of CO₂ to high value-added chemicals in water using environment-friendly and cost-effective catalysts is a very significant topic. In this work, a green method for the conversion of CO₂ catalyzed by alcohol amines has been developed. Alcohol amines showed considerable activating ability to CO₂ in the cyclization with 2-aminobenzonitrile to quinazoline-2,4(1H,3H)-dione in water. Notably, when diethanolamine (DEA) was used as the catalyst, 94% yield of quinazoline-2,4-(1H,3H)-dione could be achieved. A plausible mechanism has been proposed based on the ¹H NMR, FT-IR analysis and DFT calculation. The excellent catalytic performance is attributed to the combined effect of both the secondary amine and hydroxyl groups on alcohol amines with the assistance of water in the formation of carbamate. Water plays a bi-functional role of solvent and co-catalyst in this catalytic process. Catalysts can be easily recovered and reused five times without significant loss of activity.

DMAP-Catalyzed One-Pot Synthesis of Quinazoline-2,4-diones from 2-Aminobenzamides and Di-tert-butyl Dicarbonate

The one-pot synthesis of quinazoline-2,4-diones was developed in the presence of 4-dimethylaminopyridine (DMAP) by metal-free catalysis. The commercially available (Boc)₂O acted as a key precursor in the construction of the 2-position carbonyl of quinazolinediones. The p-methoxybenzyl (PMB)-activated heterocyclization could smoothly proceed at room temperature instead of the microwave condition. This strategy is compatible with a variety of substrates with different functional groups. Furthermore, this protocol was utilized to smoothly prepare Zenarestat with a total yield of 70%.

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

Organocatalysts promote a range of C-N bond forming reactions of amines with CO₂ . Herein, we review these reactions and attempt to identify the unifying features of the catalysts that allows them to promote a multitude of seemingly unrelated reactions. Analysis of the literature shows that these reactions predominantly proceed by carbamate salt formation in the form [BaseH][RR'NCOO]. The anion of the carbamate salt acts as a nucleophile in hydrosilane reductions of CO₂ , internal cyclization reactions or after dehydration as an electrophile in the synthesis of urea derivatives. The reactions are enhanced by polar aprotic solvents and can be either promoted or hindered by H-bonding interactions. The predominant role of all types of organic and salt catalysts (including ionic liquids, ILs) is the stabilization of the carbamate salt, mostly by acting as a base. Catalytic enhancement depends on the combination of the amine, the base strength, the solvent, steric factors, ion pairing and H-bonding. A linear relationship between the base strength and the reaction yield has been demonstrated with IL catalysts in the synthesis of formamides and quinazoline-2,4-diones. The role of organocatalysts in the reactions indicates that all bases of sufficient strength should be able to catalyze the reactions. However, a physical limit to the extent of a purely base catalyzed reaction mechanism should exist, which needs to be identified, understood and overcome by synergistic or alternative methods.

Efficient transformation of CO2 into quinazoline-2,4(1H,3H)-diones at room temperature catalyzed by a ZnI2/NEt3 system

The readily available ZnI₂/NEt₃ system promotes the efficient transformation of CO₂ and 2-aminobenzonitriles into quinazoline-2,4(1H,3H)-diones at room temperature and low CO₂ pressure.

Recent advances in nucleophile-triggered CO2-incorporated cyclization leading to heterocycles

CO₂, as a sustainable, feasible, abundant one-carbon synthon, has been utilized in carboxylative cyclization, carbonylative cyclization, and reductive cyclization.

Cyanuric Acid-Based Organocatalyst for Utilization of Carbon Dioxide at Atmospheric Pressure

A organocatalytic system based on economical and readily available cyanuric acid has been developed for the synthesis of 2-oxazolidinones and quinazoline-2,4(1H,3H)-diones from propargylamines and 2-aminobenzonitriles under atmospheric pressure carbon dioxide. Notably, a low concentration of carbon dioxide in air was directly converted into 2-oxazolidinone in excellent yields without an external base. Through mechanistic investigation by in situ FTIR spectroscopy, cyanuric acid was demonstrated to be an efficient catalyst for carbon dioxide fixation.

Two New Alkaloids from the Roots of Baphicacanthus cusia

Phytochemical investigation of the root of Baphicacanthus cusia (NEES) BREMEK afforded two new alkaloids, baphicacanthin A (1) and baphicacanthin B (2), along with 28 known compounds. The chemical structures of these compounds were elucidated on the basis of one and two dimensional (1D/2D)-NMR and high resolution (HR)-MS spectral evidence.

A mechanistic study on guanidine-catalyzed chemical fixation of CO2 with 2-aminobenzonitrile to quinazoline-2,4(1H,3H)-dione

Both basicity of TMG and acidity of the [TMGH]⁺ guanidinium are crucial for a reaction.

La–Mg mixed oxide as a highly basic water resistant catalyst for utilization of CO2 in the synthesis of quinazoline-2,4(1H,3H)-dione

Synthesis of quinazoline-2,4(1H,3H)-dione using La–Mg mixed oxide in water.