Xue-Dong Li

Efficient chemical fixation of CO2 promoted by a bifunctional Ag2WO4/Ph3P system

An efficient heterogeneous silver-catalyzed reaction for construction of the α-methylene cyclic carbonate motif was developed through carboxylative assembly of propargyl alcohols and CO2. Such a CO2 fixation protocol proceeded smoothly with only 1 mol% of Ag2WO4 and 2 mol% of PPh3 as well as atmospheric CO2 at room temperature under solvent-free conditions, in an environmentally benign and low energy manner along with an easy operating procedure. Notably, up to 98% isolated yields of carbonates could be attained with exclusive chemo-selectivity. In addition, the dual activation capacity of Ag2WO4 towards both the propargylic substrate and CO2 is based on which cooperative catalytic mechanism by the silver cation and the tungstate anion is proposed. Recycling trials on carboxylative cyclization of propargyl alcohols and CO2 illustrate that the catalyst can be reused at least 4 times with retention of high catalytic activity and selectivity. Especially, it allows the direct and effective application in the one-pot synthesis of various oxazolidinones bearing exocyclic alkenes and carbamates in moderate to high yields upon the alternative introduction of primary or secondary amines.

Reduction of sulfoxides and pyridine-N-oxides over iron powder with water as hydrogen source promoted by carbon dioxide

A green process was developed for efficient reduction of sulfoxides and pyridine-N-oxides using the iron powder in the presence of H2O–CO2 to sulfides and pyridines, respectively. Notably, H2O is employed as the terminal hydrogen source, and CO2 could enhance hydrogen generation through in situ formation of carbonic acid. Thus carbonic acid offers simple neutralization by depressurizing CO2 and the system can eliminate unwanted byproducts. The high generality and chemo-selectivity of this protocol were demonstrated by the scope of substrates, in which chlorine, vinyl group and benzene ring can be tolerated.

An in situ acidic carbon dioxide/glycol system for aerobic oxidative iodination of electron-rich aromatics catalyzed by Fe(NO3)3·9H2O

An environmentally benign CO2/glycol reversible acidic system was developed for the iron(III)-catalyzed aerobic oxidative iodination of electron-rich aromatics without the need for any conventional acid additive or organic solvent. Notably, moderate to high isolated yields (up to 97%) of the aryl iodides were attained with comparable regioselectivity when ferric nitrate nonahydrate was used as the catalyst with molecular iodine under 1 MPa of CO2.

PEG400-enhanced synthesis of gem-dichloroaziridines and gem-dichlorocyclopropanes via in situ generated dichlorocarbene

PEG400 is employed as an efficient phase transfer catalyst for the cycloaddition reaction of imines with dichlorocarbene, which is generated in situ from chloroform and sodium hydroxide, to give gem-dichloroaziridines in moderate to excellent yields at ambient temperature. This protocol is also extended to the synthesis of cyclopropanes from a variety of alkenes. In this study, PEG400 behaves as a phase transfer reagent thanks to its ability to coordinate with alkali metal cations. Notably, the one-pot synthesis of gem-dichloroaziridines from benzaldehyde and aromatic amines has also been successfully performed. The in situ generated acid, derived from CO2 and H2O, can also be effectively applied to promote the amide synthesis via the gem-dichloroaziridine pathway. The application of the gem-dichlorocyclopropane as a platform chemical is also briefly demonstrated, to afford the 2-phenylacrylaldehyde derivative via a ring-opening reaction.

AgI/TMG‐Promoted Cascade Reaction of Propargyl Alcohols, Carbon Dioxide, and 2‐Aminoethanols to 2‐Oxazolidinones

Chemical valorization of CO2 to access various value-added compounds has been a long-term and challenging objective from the viewpoint of sustainable chemistry. Herein, a one-pot three-component reaction of terminal propargyl alcohols, CO2 , and 2-aminoethanols was developed for the synthesis of 2-oxazolidinones and an equal amount of α-hydroxyl ketones promoted by Ag2 O/TMG (1,1,3,3-tetramethylguanidine) with a TON (turnover number) of up to 1260. By addition of terminal propargyl alcohol, the thermodynamic disadvantage of the conventional 2-aminoethanol/CO2 coupling was ameliorated. Mechanistic investigations including control experiments, DFT calculation, kinetic and NMR studies suggest that the reaction proceeds through a cascade pathway and TMG could activate propargyl alcohol and 2-aminoethanol through the formation of hydrogen bonds and also activate CO2 .

Copper catalysis: ligand-controlled selective N-methylation or N-formylation of amines with CO2 and phenylsilane

Cupric subcarbonate (Cu2(OH)2CO3) was found to be effective for the reductive functionalization of CO2 to produce formamides and methylamines with phenylsilane as reductant. Interestingly, N-formylation and N-methylation were switched on/off by subtly choosing the ligand: DPPB (1,4-bis(diphenylphosphino)butane) promoted N-methylation whereas Ph2CyP (diphenylcyclohexylphosphine) favored for N-formylation.