1. Xiao-Fang Liu, Xiao-Ya, Li, Chang Qiao, Liang-Nian He,* Transition-Metal-Free Catalysis for Reductive Functionalization of CO2 with Amines, Synlett 2018, DOI: 10.1055/s-0036-1591533. [link]
Abstract: Reductive functionalization of CO2 with amines and a reductant, which combines both reduction of CO2 and C-N bond formation in one-pot to produce versatile chemicals and energy-storage materials i.e. formamides, aminals and methylamines that are usually from petroleum feedstock would be appealing and promising. Herein, we give a brief review on recent development in the titled CO2 chemistry by employing transition-metal-free catalysis, which can be catalogued as below according to the diversified energy content of products, i.e. formamides, aminals and methylamines being consistent with 2-, 4- and 6-electron reduction of CO2, respectively. Notably, hierarchical reduction of CO2 with amines to afford at least two products e.g. formamides and methylamines could be realized with the same catalyst through tuning the hydrosilane type, reaction temperature or CO2 pressure. Finally, the opportunities and challenges on the reductive functionalization of CO2 with amines are also highlighted.
2. Xiao-Fang Liu, Chang Qiao, Xiao-Ya, Li, Liang-Nian He,* DMF-promoted reductive functionalization of CO2 with secondary amines and phenylsilane to methylamines, Pure Appl. Chem. 2018, DOI: 10.1515/pac-2017-0304. [link]
Abstract: An amide-promoted protocol was developed for the reductive functionalization of CO2 with amines/imine and phenylsilane to produce methylamine. Various amines including aromatic and aliphatic, primary and secondary ones as well as imine were methylated successfully to methylamines with up to 98% yield under atmospheric pressure of CO2 and 80 oC. Furthermore, a tentative mechanism involving that amide-promoted CO2 reduction to the silyl acetal species was proposed. Striking features of this metal-free protocol are selective six-electron reduction of CO2 with hydrosilane as a reductant in the presence of amine.
3. Qing-Wen Song, Ping Liu, Li-Hua Han, Kan Zhang*, Liang-Nian He*, Upgrading CO2 by incorporation into urethanes through silver-catalyzed one-pot stepwise amidation reaction Chin. J. Chem., 2018, 36, 147-152. [link]
Abstract: One-pot two-step stepwise reaction of terminal propargylic alcohols, carbon dioxide, and primary/secondary amines for the effective synthesis of various urethanes through robust silver-catalysed C-O/C-N bond formation is reported. Catalytic activities were investigated by controlling catalyst loading, reaction pressure and time, and very high turnover number (turnover frequency) was obtained: 3350 (35 h−1) with 0.01 mol% silver catalyst under 0.1 MPa, and up to 13360 (139 h−1) with 0.005 mol% silver catalyst under 2.0 MPa at room temperature. The strategy was ingeniously regulated, and synchronously afforded a wide range of β-oxopropylcarbamate and 1,3-oxazolidin-2-one motifs in excellent yields and selectivity together with unprecedented high turnover number (TON) and turnover frequency (TOF) value.
4. Chang Qiao, Yu Cao, Liang-Nian He*, Transition Metal-Catalyzed Carboxylation of Terminal Alkynes with CO2, Mini-Rev. Org. Chem., 2018, 15, Accepted.
Abstract: The coupling reaction of terminal alkynes and CO2 provides a promising way to synthesize propiolic acids. Among the existing catalytic systems, transition-metal copper and silver exhibit excellent catalytic efficiency under mild conditions probably being attributed to the activation of C-C triple bond of terminal alkynes. In this aspect, efficient strategies for activating both substrate and CO2 are often smart choices. This review summarizes the development trend of the Cu/Ag-catalyzed carboxylation reactions of terminal alkynes with CO2, and representative examples are also discussed in detail.
5. Jia-Ning Xie, Liang-Nian He*, Hong-Chen Fua, Ning Wang and Mei-Yan Wang, Sodium Acetate-Promoted Oxa-Michael-Aldol [3+2] Annulation Reactions: Facile Access to the Fused Heterocycle, Current Catal., 2018, 7, Accepted
Abstract: A highly active base-promoted system based on NaOAc•3H2O has been designed for the oxa-Michael-aldol [3+2] annulation reactions of internal alkynotes with N-hydroxyphthalimides, giving a series of pharmaceutically attractive 3a-hydroxyisoxazolo[3,2-a]isoindol-8(3aH)-ones in synthetically useful yields of up to 98%. Only 10 mol% NaOAc•3H2O is needed for the reaction at room temperature within 6 h. Besides, a plausible base-promoted intermolecular [3+2] oxa-Michael-aldol type mechanism is proposed.
6. Zhi-Hua Zhou, Shu-Mei Xia, and Liang-Nian He*, Green Catalysis for Efficient Three-Component Reaction of Carbon Dioxide, Propargylic Alcohols and Nucleophiles, Acta Phys. -Chim. Sin., 2018, 34, Accepted.
Abstract: Transformation of carbon dioxide into valuable organic molecules has attracted considerable attention over the past decades. In this regard, three-component reaction of CO2, propargylic alcohols and nucleophiles including amines, water and alcohols to prepare useful carbonyl compounds, for instance, carbamates, oxazolidinones, α-hydroxyl ketones and organic carbonates, is particularly appealing due to advantages of step and atom economy. CO2 is of thermodynamic stability and kinetic inertness, leading to the reactions involving CO2 are commonly thermodynamically unfavorable. We have developed an efficient three-component reaction of CO2, propargylic alcohols and nucleophiles to offer thermodynamically favorable ways for converting CO2 into cyclic carbonates and 2-oxazolidinones with vicinal diols or 2-aminoethanols. This review aims to summarize and discuss recent advances on three-component reaction of CO2, propargylic alcohols with nucleophiles to prepare various carbonyl compounds promoted by both metal catalysts and organocatalysts.
7. Mei-Yan Wang, Ning Wang, Xiao-Fang Liu, Chang Qiao and Liang-Nian He*, Efficient Tungstate catalysis: pressure-switched 2- and 6- electron reductive functionalization of CO2 with amines and phenylsilane, Green Chem., 2018, 20, DOI: 10.1039/C7GC03416D. [link]
Abstract: An efficient and environmentally benign tungstate catalysis for reductive functionalization of CO2 with amines and phenylsilane was developed. By simply varying the pressure, 2-electron or 6-electron reduction of CO2 successfully approached with simultaneous C-N bond formation, thus leading to the formation of formamides and methylamines, respectively. That is, secondary and primary amines furnished the corresponding methylamines or dimethylamines in excellent yields under atmospheric pressure of CO2, while various formamides were formed in yields ranging from 52% to 98% when increasing the CO2 pressure to 2 MPa. 1H NMR studies and control experiments demonstrate that the N-formylation undergoes the formation of silyl formate while the N-methylation proceeds through an aminal intermediate generated by 4-electron reduction of CO2.
8. 刘晓放，何良年，二氧化碳的高值化利用，科学, 2018, 70, 14-19.
9. Xue-Dong Li, Yu Cao, Ran Ma, Liang-Nian He*, Thermodynamically favorable protocol for the synthesis of 2-oxazolidinones via Cu(I)-catalyzed three-component reaction of propargylic alcohols, CO2 and 2-aminoethanols, J. CO2 Util., 2018, DOI: 10.1016/j.jcou.2018.01.022. [link]
Abstract: Efficient CuI/1,10-phen-catalyzed three-component cascade reaction of propargylic alcohols, CO2, and 2-aminoethanols has been firstly developed for the thermodynamically favourable preparation of 2-oxazolidinones. In the presence of commercially available CuI, 1,10-phen (1,10-phenanthroline) and t-BuOK, the cascade reaction afforded the desired products in good to excellent yields with a broad substrate scope (14 examples). The predicted copper complex Cu2I2(phen)2 in situ formed from CuI and 1,10-phen could activate the triple bond through coordination. The isolation of α-alkylidene cyclic carbonate as the reaction intermediate suggests that the carboxylative cyclization of propargylic alcohol with CO2, followed by ring-opening reaction, is involved in the one-pot three-component cascade reaction.
10. Yu Cao, Ran Ma, Ning Wang, Mei-Yan Wang, Xue-Dong Li, Liang-Nian He*, Selective hydrodeoxygenation of β-O-4 model compounds and aromatic ketones promoted by palladium chloride with acidic CO2/MeOH system, J. CO2 Util., 2018, Accepted.
Abstract: Selective hydrogenolysis is a crucial challenge for lignin valorization. A PdCl2-catalyzed hydrogenolysis of C-OH bond of various lignin β-O-4 alcohol model compounds was developed for preparation of corresponding phenethoxybenzene in 78-98% isolated yield. Notably, the introduction of low-pressure CO2 (1 MPa) remarkably improves the reaction efficiency and selectivity of phenethoxybenzene. Neither over-reduction of aromatic ring nor further debenzylation was detected. This is understandable that the in situ methylcarbonic acid generated from CO2 and methanol acts as an acidic catalyst and enhances the leaving ability of hydroxyl group of β-O-4 alcohols. Besides, the present PdCl2/CO2/MeOH catalyst system proved to be effective for reductive cleavage of C-O bonds of β-O-4 ketones, producing ethylbenzenes accompanied with phenols in high yields. Furthermore, this protocol could also be extended to selective hydrodeoxygenation of the carbonyl group to methylene in aromatic ketones. As a sound reaction medium, such in situ CO2/MeOH acidic system could be inherently neutralized by depressurizing CO2, providing feature advantages for simple post-processing and none waste disposal.
11. Yu Cao, Xing He, Ning Wang, Hong-Ru Li, and Liang-Nian He*, Photochemical and Electrochemical Carbon Dioxide Utilization with Organic Compounds, Chin. J. Chem., 2018, 36, Accepted.
Abstract: In the last few years, photochemical and electrochemical CO2 transformations have attracted increasing attention in response to topical interest in renewable energy and green chemistry. The present minireview offers an overview about the current approaches for the photochemical and electrochemical carbon dioxide fixation with organic compounds. Valuable products, including carboxylic acids and heterocyclic compounds, are accessible through carboxylation and carboxylative cyclization, respectively. In photochemical and electrochemical processes, photo- or electro-induced radical ions or other high-energy organic compounds are considered as key intermediates to react with CO2. Besides, activation of CO2 to produce radical anions has also been reported.
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