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Journal articles on the topic 'Heterocyclic Carbene'

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Author: Grafiati

Published: 6 September 2023

Last updated: 18 May 2024

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1

Longevial, Jean-François, Mamadou Lo, Aurélien Lebrun, Danielle Laurencin, Sébastien Clément, and Sébastien Richeter. "Molecular complexes and main-chain organometallic polymers based on Janus bis(carbenes) fused to metalloporphyrins." Dalton Transactions 49, no. 21 (2020): 7005–14. http://dx.doi.org/10.1039/d0dt00594k.

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Janus bis(N-heterocyclic carbenes) composed of a porphyrin core with two N-heterocyclic carbene (NHC) heads fused to opposite pyrroles were used as bridging ligands for the preparation of metal complexes.

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2

Zhu, Yannan, and You Huang. "Organocatalyzed [3+3] Annulations for the Construction of Heterocycles." Synthesis 52, no. 08 (February 5, 2020): 1181–202. http://dx.doi.org/10.1055/s-0039-1690810.

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Six-membered heterocyclic systems are widely distributed in many natural products and pharmaceuticals, and the construction of highly functionalized six-membered heterocyclic compounds is an important topic in modern organic synthesis. Organocatalyzed [3+3] annulations represents an important method for assembling a substantial variety of six-membered cycles that contain one or more heteroatoms. This review describes the development of organocatalyzed [3+3] annulations for the synthesis of six-membered heterocycles, including organocatalysis using secondary amines, tertiary amines, phosphines, chiral phosphoric acids and N-heterocyclic carbenes.1 Introduction2 Secondary Amine Catalyzed [3+3] Annulations2.1 Synthesis of Nitrogen Heterocycles2.2 Synthesis of Oxygen Heterocycles2.3 Synthesis of Sulfur Heterocycles3 Tertiary Amine Catalyzed [3+3] Annulations3.1 Catalysis through Multiple Hydrogen-Bonding Interactions3.2 Catalysis of Tertiary Amines as Lewis Bases4 Phosphine-Catalyzed [3+3] Annulations4.1 Synthesis of Nitrogen Heterocycles4.2 Synthesis of Oxygen Heterocycles4.3 Synthesis of Heterocycles Containing Two or More Heteroatoms5 Chiral Phosphoric Acid Catalyzed [3+3] Annulations5.1 Synthesis of Nitrogen Heterocycles5.2 Synthesis of Heterocycles Containing Two or More Heteroatoms6 N-Heterocyclic Carbene Catalyzed [3+3] Annulations6.1 Synthesis of Nitrogen Heterocycles6.2 Synthesis of Oxygen Heterocycles6.3 Synthesis of Heterocycles Containing Two or More Heteroatoms7 Conclusion and Outlook

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3

Fernando, Jared, Alison Levens, Daniel Moock, and David Lupton. "N-Heterocyclic Carbene Catalyzed Transformylation." Synthesis 49, no. 15 (June 12, 2017): 3505–10. http://dx.doi.org/10.1055/s-0036-1588449.

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The N-heterocyclic carbene (NHC) catalyzed transformylation has been developed for the conversion of 1°, 2°, and 3° alcohols to the corresponding formates. The reaction employs low catalyst loadings and methyl formate as the formyl transfer reagent. The scope of the reaction is broad with 23 examples reported with good yields (59–96%). The reaction is insensitive to common nitrogen and oxygen protecting groups and can be achieved in the presence of a number of heterocycles.

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4

Leitão, Maria Inês P. S., Giulia Francescato, Clara S. B. Gomes, and Ana Petronilho. "Synthesis of Platinum(II) N-Heterocyclic Carbenes Based on Adenosine." Molecules 26, no. 17 (September 4, 2021): 5384. http://dx.doi.org/10.3390/molecules26175384.

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Organometallic derivatization of nucleosides is a highly promising strategy for the improvement of the therapeutic profile of nucleosides. Herein, a methodology for the synthesis of metalated adenosine with a deprotected ribose moiety is described. Platinum(II) N-heterocyclic carbene complexes based on adenosine were synthesized, namely N-heterocyclic carbenes bearing a protected and unprotected ribose ring. Reaction of the 8-bromo-2′,3′,5′-tri-O-acetyladenosine with Pt(PPh3)4 by C8−Br oxidative addition yielded complex 1, with a PtII centre bonded to C-8 and an unprotonated N7. Complex 1 reacted at N7 with HBF4 or methyl iodide, yielding protic carbene 2 or methyl carbene 3, respectively. Deprotection of 1 to yield 4 was achieved with NH4OH. Deprotected compound 4 reacted at N7 with HCl solutions to yield protic NHC 5 or with methyl iodide yielding methyl carbene 6. Protic N-heterocyclic carbene 5 is not stable in DMSO solutions leading to the formation of compound 7, in which a bromide was replaced by chloride. The cis-influence of complexes 1–7 was examined by 31P{1H} and 195Pt NMR. Complexes 2, 3, 5, 6 and 7 induce a decrease of 1JPt,P of more than 300 Hz, as result of the higher cis-influence of the N-heterocyclic carbene when compared to the azolato ligand in 1 and 4.

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5

Dong, Zhaowen, Cristian Pezzato, Andrzej Sienkiewicz, Rosario Scopelliti, Farzaneh Fadaei-Tirani, and Kay Severin. "SET processes in Lewis acid–base reactions: the tritylation of N-heterocyclic carbenes." Chemical Science 11, no. 29 (2020): 7615–18. http://dx.doi.org/10.1039/d0sc01278e.

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6

Fujita, Ken-ichi, Junichi Sato, and Hiroyuki Yasuda. "Tautomerization of 5-Alkylidene-2-Oxazolidinone to 2-Oxazolone by Use of an N-Heterocyclic Carbene Catalyst." Synlett 26, no. 08 (March 3, 2015): 1106–10. http://dx.doi.org/10.1055/s-0034-1380274.

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By employing an N-heterocyclic carbene as a catalyst, the tautomerization of 5-alkylidene-2-oxazolidinone proceeded to afford the corresponding 2-oxazolone. Among N-heterocyclic carbenes, 1,3-di-tert-butylimidazol-2-ylidene was the most effective catalyst for the tautomerization of 5-alkylidene-2-oxazolidinone.

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7

Zhao, Shixian, Feifei Wu, Yuyu Ma, Wanzhi Chen, Miaochang Liu, and Huayue Wu. "Enhancement of N-heterocyclic carbenes on rhodium catalyzed olefination of triazoles." Organic & Biomolecular Chemistry 14, no. 8 (2016): 2550–55. http://dx.doi.org/10.1039/c5ob02397a.

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8

Hollóczki, Oldamur. "Unveiling the peculiar hydrogen bonding behavior of solvated N-heterocyclic carbenes." Physical Chemistry Chemical Physics 18, no. 1 (2016): 126–40. http://dx.doi.org/10.1039/c5cp05369b.

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After fitting a molecular mechanical force field for imidazol-2-ylidenes, MD simulations revealed carbene–carbene and three-center hydrogen bonds of carbenes. The practical importance of these structures is also highlighted.

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9

Wu, Wenchao, Shuangli Xu, Yan Zhang, Xiu Wang, Ruotong Li, Fang Sun, Chenxia Yu, Tuanjie Li, Donghui Wei, and Changsheng Yao. "NHC-catalyzed β-specific addition of N-based nucleophiles to allenoates." Organic Chemistry Frontiers 7, no. 13 (2020): 1593–99. http://dx.doi.org/10.1039/d0qo00189a.

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N-heterocyclic carbene (NHC) catalyzed reactions of nitrogenous heterocycles or trifluoromethylated acylhydrazone with allenoates gave regiospecific β-adducts. DFT calculations rationalized the origination of regio- and E/Z selectivities.

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10

Hata, Kazuhiro, Hideto Ito, Yasutomo Segawa, and Kenichiro Itami. "Pyridylidene ligand facilitates gold-catalyzed oxidative C–H arylation of heterocycles." Beilstein Journal of Organic Chemistry 11 (December 28, 2015): 2737–46. http://dx.doi.org/10.3762/bjoc.11.295.

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Triaryl-2-pyridylidene effectively facilitates the gold-catalyzed oxidative C–H arylation of heteroarenes with arylsilanes as a unique electron-donating ligand on gold. The employment of the 2-pyridylidene ligand, which is one of the strongest electron-donating N-heterocyclic carbenes, resulted in the rate acceleration of the C–H arylation reaction of heterocycles over conventional ligands such as triphenylphosphine and a classical N-heterocyclic carbene. In situ observation and isolation of the 2-pyridylidene-gold(III) species, as well as a DFT study, indicated unusual stability of gold(III) species stabilized by strong electron donation from the 2-pyridylidene ligand. Thus, the gold(I)-to-gold(III) oxidation process is thought to be facilitated by the highly electron-donating 2-pyridylidene ligand.

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11

Graham, David C., and Brian F. Yates. "Increased Stability of NO and NS Heterocyclic Carbenes?" Australian Journal of Chemistry 57, no. 4 (2004): 359. http://dx.doi.org/10.1071/ch03248.

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Density functional theory has been used to investigate the effects of alkylation and oxidation on the stability of NO and NS heterocyclic carbenes. While O- and S-alkylation leads to a dramatic increase in stability with respect to dimerization, oxidation of the NS heterocyclic carbene to form the sulphoxide appears to have the opposite effect.

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12

Das, Tamal Kanti, and Akkattu T. Biju. "Imines as acceptors and donors in N-heterocyclic carbene (NHC) organocatalysis." Chemical Communications 56, no. 61 (2020): 8537–52. http://dx.doi.org/10.1039/d0cc03290e.

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The application of imines as electrophiles (acceptors) or as a source of nucleophiles (donors) in N-heterocyclic carbene (NHC) catalysis for the synthesis of various nitrogen heterocycles and functionalized amines is presented.

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13

Iversen, Kalon J., David J. D. Wilson, and Jason L. Dutton. "Activation of the C–N bond of N-heterocyclic carbenes by inorganic elements." Dalton Trans. 43, no. 34 (2014): 12820–23. http://dx.doi.org/10.1039/c4dt00946k.

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14

Gehrke, Sascha, and Oldamur Hollóczki. "A molecular mechanical model for N-heterocyclic carbenes." Physical Chemistry Chemical Physics 18, no. 32 (2016): 22070–80. http://dx.doi.org/10.1039/c6cp02624a.

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In this work a set of force fields for nine synthetically relevant and/or structurally interesting N-heterocyclic carbenes is presented, allowing facile substitution and the simulation of numerous carbene catalysts in solution by classical MD.

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15

Andrada, Diego M., Nicole Holzmann, Thomas Hamadi, and Gernot Frenking. "Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules." Beilstein Journal of Organic Chemistry 11 (December 24, 2015): 2727–36. http://dx.doi.org/10.3762/bjoc.11.294.

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Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X→p(π) π-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO calculations and with an energy decomposition analysis. The investigated molecules include N-heterocyclic carbenes (NHCs), the cyclic alkyl(amino)carbene (cAAC), mesoionic carbenes and ylide-stabilized carbenes. The bonding analysis suggests that the carbene centre in cAAC and in diamidocarbene have the weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation.

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16

Zhang, Zhen-Zhen, Yongna Zhang, Hui-Xin Duan, Zhuo-Fei Deng, and You-Qing Wang. "Enantioselective (3+2) cycloaddition via N-heterocyclic carbene-catalyzed addition of homoenolates to cyclic N-sulfonyl trifluoromethylated ketimines: synthesis of fused N-heterocycle γ-lactams." Chemical Communications 56, no. 10 (2020): 1553–56. http://dx.doi.org/10.1039/c9cc09269b.

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An enantioselective (3+2) cycloaddition via N-heterocyclic carbene-catalyzed homoenolate addition to cyclic N-sulfonyl trifluoromethyl ketimines is realized, affording fused N-heterocycle γ-lactams with up to >20 : 1 dr and 94–99% ee.

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17

Gao, Yafei, Qi Chen, Xuebing Leng, and Liang Deng. "Cyclometallation reactions of a three-coordinate cobalt(i) complex bearing a nonsymmetric N-heterocyclic carbene ligand." Dalton Transactions 48, no. 26 (2019): 9676–83. http://dx.doi.org/10.1039/c9dt00731h.

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18

De Vreese, Rob, and Matthias D’hooghe. "N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis." Beilstein Journal of Organic Chemistry 8 (March 14, 2012): 398–402. http://dx.doi.org/10.3762/bjoc.8.43.

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The interplay between metals and N-heterocyclic carbenes (NHCs) has provided a window of opportunities for the development of novel catalytic strategies within the past few years. The recent successful combination of Brønsted acids with NHCs has added a new dimension to the field of cooperative catalysis, enabling the stereoselective synthesis of functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyclic carbene/Brønsted acid cooperative catalysis as a new and powerful methodology in organic chemistry.

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19

Walker, James A., and Levi M. Stanley. "N-Heterocyclic carbene-catalysed intramolecular hydroacylation to form basic nitrogen-containing heterocycles." Organic & Biomolecular Chemistry 14, no. 42 (2016): 9981–84. http://dx.doi.org/10.1039/c6ob01956k.

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N-Heterocyclic carbene-catalysed intramolecular hydroacylation of N-allylimidazole-2-carboxaldehydes and N-allylbenzimidazole-2-carboxaldehydes is reported. These exo-selective hydroacylations of unactivated alkenes enable the synthesis of a variety of basic, polycyclic nitrogen heterocycles in good-to-excellent yields.

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20

Gehrke, Sascha, and Oldamur Hollóczki. "N‐Heterocyclic Carbene Organocatalysis: With or Without Carbenes?" Chemistry – A European Journal 26, no. 44 (July 23, 2020): 10140–51. http://dx.doi.org/10.1002/chem.202002656.

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21

Gehrke, Sascha, and Oldamur Hollóczki. "Are There Carbenes in N-Heterocyclic Carbene Organocatalysis?" Angewandte Chemie International Edition 56, no. 51 (November 22, 2017): 16395–98. http://dx.doi.org/10.1002/anie.201708305.

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22

Frański, Rafał, Błażej Gierczyk, Grzegorz Schroeder, Stefan Pieper, Andreas Springer, and Michael Linscheid. "Electrospray ionization mass spectrometric study of mercury complexes of N-heterocyclic carbenes derived from 1,2,4-triazolium salt precursors." Open Chemistry 5, no. 1 (March 1, 2007): 316–29. http://dx.doi.org/10.2478/s11532-006-0050-0.

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AbstractBy mixing 1,2,4-triazolium salts (precursors of N-heterocyclic carbenes 1–6) with mercury acetate, a number of complexes have been obtained under electrospray ionization condition. Carbenes 1 and 2 contain one carbene center; therefore, they are able to bond only one mercury cation. Carbenes 3–5 contain two carbene centers; therefore, they can bond two mercury cations. Mercury complexes of 1–5 always contain an acetate anion attached to a mercury cation. Carbene 6 also contains two carbene centers; however, its structure allows formation of a complex containing mercury bonded simultaneously to both centers, therefore, the complex that does not contain an acetate anion. The MS/MS spectra taken for complexes of carbenes 1–5 have shown formation of a cation corresponding to N1 substituent (adamantyl or benzyl), and those of complexes of carbenes 3–5 (doubly charged ions) have also shown the respective complementary partner ions. Mercury complex of 2 has yielded some other interesting fragmentation pathways, e.g. a loss of the HHgOOCCH3 molecule. The fragmentation pathway of the mercury complexes of 6 was found to be complicated.

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23

Al Furaiji, Khalidah H. M., Andrew Molino, Jason L. Dutton, and David J. D. Wilson. "Theoretical Investigation of Main-Group Element Hydride Insertion into Phosphorus-Heterocyclic Carbenes (PHCs)." Australian Journal of Chemistry 73, no. 8 (2020): 787. http://dx.doi.org/10.1071/ch19487.

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Initial reports of ring expansion reactions (RER) of N-heterocyclic carbenes (NHCs) with main-group element hydrides have led to several synthetic and theoretical investigations, which include reports of insertion by Be, B, Al, Si, and Zn hydrides. The RERs generally lead to insertion of the heteroatom into the endocyclic C–N bond with formation of an expanded heterocyclic ring. Following the recent isolation of a P-heterocyclic carbene (PHC), here we report results from a computational study (RI-SCS-MP2/def2-TZVP//M06–2X/def2-TZVP) of RERs with a series of PHCs for the ring-insertion of silicon (SiH4, SiH2Ph2) and boron (BH3, BH2NMe2) hydrides. In order to explore the roles of both electronic and steric effects on PHCs and their reactivity, a series of P-substituent PHCR (R=H, Me, Ph, and bulky Ar groups) were investigated. Bulky R groups serve to maximise ring planarity and the σ-donating capability of the PHC. For RER, the PHC analogues exhibit facile initial hydride transfer from the main-group hydrides to the carbene carbon, with barriers that are substantially lower than with NHCs. However, the full ring insertion mechanisms for PHCs are, in general, kinetically unfavourable due to a large barrier associated with the ring-expansion step. While bulky P-substituents maximise heterocycle planarity towards that of NHCs, the RER reactivity with bulky PHCs does not reflect that of an NHC.

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24

Nonnenmacher, Michael, Dominik M. Buck, and Doris Kunz. "Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes." Beilstein Journal of Organic Chemistry 12 (August 23, 2016): 1884–96. http://dx.doi.org/10.3762/bjoc.12.178.

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Rh(CO)2Cl(NHC) complexes of dipyrido-annelated N-heterocyclic carbenes were prepared. From the C–H coupling constant of the respective imidazolium salts and the N–C–N angle of the N-heterocyclic carbene (NHC), a weaker σ-donor character than that of typical unsaturated NHCs is expected. However, the IR stretching frequencies of their Rh(CO)2Cl complexes suggest an electron-donor character even stronger than that of saturated NHCs. We ascribe this to the extremely weak π-acceptor character of the dipyrido-annelated NHCs caused by the conjugated 14 πe− system that thus allows for an enhanced Rh–CO backbonding. This extremely low π-acceptor ability is also corroborated by the 77Se NMR chemical shift of −55.8 ppm for the respective selenourea, the lowest value ever measured for imidazole derived selenoureas. DFT-calculations of the free carbene confirm the low σ-donor character by the fact that the σ-orbital of the carbene is the HOMO−1 that lies 0.58 eV below the HOMO which is located at the π-system. Natural population analysis reveals the lowest occupation of the pπ-orbital for the saturated carbene carbon atom and the highest for the pyrido-annelated carbene. Going from the free carbene to the Rh(CO)2Cl(NHC) complexes, the increase in occupancy of the complete π-system of the carbene ligand upon coordination is lowest for the pyrido-annelated carbene and highest for the saturated carbene.

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25

Hasson, Mohammed Mujbel, Basim H. Al-Zaidi, and Ahmad H. Ismail. "Synthesis and Characterization of Ag(I) Complexes Derived from New N-Heterocyclic Carbenes." Asian Journal of Chemistry 31, no. 5 (March 28, 2019): 1149–52. http://dx.doi.org/10.14233/ajchem.2019.21877.

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Two new unsymmetrical imidazolium salts viz., [1-(4-ethylphenyl)-3-propyl-1H-imidazole-3-ium bromide] (3) and [1-(2,6-dimethylphenyl)-3-propyl-1H-imidazole-3-ium bromide] (4) have been synthesized via the reaction of propyl bromide with imidazole derivatives, [1-(4-ethylphenyl)-1Himidazole] (1) and [1-(2,6-dimethylphenyl)-1H-imidazole] (2) in absence of solvent. Then two new N-heterocyclic carbene silver complexes (5 and 6) were prepared through the reaction of imidazoluim salts (3 and 4) as a source of N-heterocyclic carbene with Ag2O by in situ method. These complexes can be used in the future as a transfer agent for preparing other transitional metal carbine complexes (NHCs) via transmetallation method. The formation of these compounds was confirmed by spectral analysis.

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26

Kelemen, Z., R. Streubel, and L. Nyulászi. "Zwitterionic carbene adducts and their carbene isomers." RSC Advances 5, no. 52 (2015): 41795–802. http://dx.doi.org/10.1039/c5ra07039b.

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27

Kassam, Karim, and John Warkentin. "Reactions of dialkoxycarbenes with tethered triple bonds to form heterocyclic compounds." Canadian Journal of Chemistry 75, no. 2 (February 1, 1997): 120–28. http://dx.doi.org/10.1139/v97-016.

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Dialkoxycarbenes with a tethered triple bond, generated from the corresponding oxadiazolines, undergo an intramolecular cyclization with the tethered alkyne moiety to give 3,3-dialkoxyvinylcarbene/1,3-dipole intermediates. The regioselectivity of the carbene cyclization is highly dependent upon the nature of the alkyne substituent. In the cases where an exocyclic vinylcarbene is generated, the vinylcarbene intermediate can undergo a synthetically useful [3 + 2] cycloaddition with either an appropriate olefin or an alkyne. This approach allows the rapid construction of some interesting heterocyclic ring systems. Keywords: carbene, dialkoxycarbene, vinylogous dialkoxycarbene, heterocycle.

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28

Dash, Chandrakanta, Animesh Das, and H. V. Rasika Dias. "Mercury(II) Complexes of Anionic N-Heterocyclic Carbene Ligands: Steric Effects of the Backbone Substituent." Molecules 25, no. 16 (August 16, 2020): 3741. http://dx.doi.org/10.3390/molecules25163741.

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Mercury(II) complexes (Me-maloNHCDipp)HgCl (1b), (t-Bu-maloNHCDipp)HgCl (2b) and (t-Bu-maloNHCDipp)HgMe (2c) supported by anionic N-heterocyclic carbenes have been obtained in good yields from the reaction of the potassium salt of N-heterocyclic carbene ligand precursors and mercury(II) salts, HgCl2 and MeHgI. These molecules have been characterized by 1H-NMR, 13C-NMR and IR spectroscopy and elemental analysis. X-ray crystal structures of 1b and 2b are also presented. Interestingly, complex 1b is polymeric {(Me-maloNHCDipp)HgCl}n in the solid state, as a result of inter-molecular Hg-O contacts, and features rare three coordinate mercury sites with a T-shaped arrangement, whereas the (t-Bu-maloNHCDipp)HgCl (2b) is monomeric and has a linear, two-coordinate mercury center. The formation of T-shaped structure and the aggregation of complex 1b is attributable to the reduced steric demand of the N-heterocyclic carbene ligand backbone substituent.

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29

Barnett, Harrison J., and Anthony F. Hill. "A Dirhoda‐Heterocyclic Carbene." Angewandte Chemie International Edition 59, no. 11 (January 29, 2020): 4274–77. http://dx.doi.org/10.1002/anie.201912650.

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30

Barnett, Harrison J., and Anthony F. Hill. "A Dirhoda‐Heterocyclic Carbene." Angewandte Chemie 132, no. 11 (March 9, 2020): 4304–7. http://dx.doi.org/10.1002/ange.201912650.

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31

Ono, Shintaro, Takashi Watanabe, Yosuke Nakamura, Hiroyasu Sato, Toru Hashimoto, and Yoshitaka Yamaguchi. "Synthesis of N -heterocyclic carbene boranes via silver N -heterocyclic carbene complexes." Polyhedron 137 (November 2017): 296–305. http://dx.doi.org/10.1016/j.poly.2017.08.045.

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32

Michalak and Kośnik. "Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis." Catalysts 9, no. 11 (October 25, 2019): 890. http://dx.doi.org/10.3390/catal9110890.

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N-Heterocyclic carbenes have found many applications in modern metal catalysis, due to the formation of stable metal complexes, and organocatalysis. Among a myriad of N-heterocyclic carbene metal complexes, gold complexes have gained a lot of attention due to their unique propensity for the activation of carbon-carbon multiple bonds, allowing many useful transformations of alkynes, allenes, and alkenes, inaccessible by other metal complexes. The present review summarizes synthetic efforts towards the preparation of chiral N-heterocyclic gold(I) complexes exhibiting C2 and C1 symmetry, as well as their applications in enantioselective catalysis. Finally, the emerging area of rare gold(III) complexes and their preliminary usage in asymmetric catalysis is also presented.

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33

Dzieszkowski, Krzysztof, and Zbigniew Rafiński. "N-Heterocyclic Carbene Catalysis under Oxidizing Conditions." Catalysts 8, no. 11 (November 16, 2018): 549. http://dx.doi.org/10.3390/catal8110549.

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N-heterocyclic carbene organocatalysis under oxidizing conditions provides a vast range of various synthetic procedures via diverse mechanisms. The available catalysts, bases, oxidants, and oxidizing methods afford numerous opportunities for developing this branch of organocatalysis. Furthermore, implementation of tandem reactions and cooperative catalysis in the described methodology significantly expands the possibilities of modern organic chemistry. This approach allows the synthesis of different structurally complex and often enantiomerically enriched substances, which can be interesting in terms of biological activity and natural product synthesis. Many esters, amides, thioesters, lactams, lactones, and other cyclic compounds obtained in oxidative or oxygenative reactions promoted by N-heterocyclic carbenes can be interesting precursors in advanced organic synthesis. Sophistication and broad applicability prove that the described synthetic approaches are exceptionally worthy of further development.

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34

Zhou, Bi-Hui, Wei-Ping He, Lin-Lin Li, Li-Mei Fan, Xiang-Rong Li, and Jie Li. "Synthesis of Novel Chiral Pyrimidone Salts and their Application in Asymmetric Diethylzinc Addition of Arylaldehydes." Current Organic Synthesis 15, no. 1 (March 20, 2018): 137–42. http://dx.doi.org/10.2174/1570179414666170830130658.

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Aims and Objectives: When compared to five-membered N-heterocyclic carbene, recent reports have demonstrated that ring expanded NHCs showed rather different properties such as increased basicity (nucleophilicity) and greater steric demand. These unique features provide an opportunity to design new chiral ligands. This study was undertaken to design and synthesize a series of novel enantiopure pyrimidone salts, the precursors of N-heterocyclic carbenes, and their activity in asymmetric diethylzinc addition of arylaldehydes was demonstrated as well. Materials and Method: Commercially available dimethylmalonic acid was treated with thionyl chloride to form dimethylmalony dichloride, followed by subsequent reaction with different chiral primary amine produced corresponding diamide. Next, conversion of diamide to monoamide was achieved by partial reduction with lithium aluminum hydride. Finally, cyclization of monoamide with triethyl orthoformate in the presence of ammonium salts provided pyrimidone salts in good yields. Results: Seven enantiopure pyrimidone salts, the precursors of N-heterocyclic carbenes, have been synthesized starting from dimethylmalonic acid. Their applicability in asymmetric diethylzinc addition of arylaldehydes has been demonstrated and the corresponding secondary alcohol was obtained with good yields and moderate enantioselectivities. Conclusion: Herein we developed an efficient route to prepare a series of novel N-heterocyclic carbene precursors, which were demonstrated as effective catalysts for asymmetric diethylzinc addition of arylaldehydes, and the corresponding secondary alcohol was obtained with good yields and moderate enantioselectivities.

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35

Boubakri, Lamia, A. Chakchouk-Mtibaa, Abdullah S. Al-Ayed, L. Mansour, Nael Abutaha, Abdel Halim Harrath, L. Mellouli, I. Özdemir, S. Yasar, and Naceur Hamdi. "Ru(ii)–N-heterocyclic carbene complexes: synthesis, characterization, transfer hydrogenation reactions and biological determination." RSC Advances 9, no. 59 (2019): 34406–20. http://dx.doi.org/10.1039/c9ra05605j.

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A series of ruthenium(ii) complexes with N-heterocyclic carbene ligands were successfully synthesized by transmetalation reactions between silver(i) N-heterocyclic carbene complexes and [RuCl₂(p-cymene)]₂ in dichloromethane under Ar conditions.

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36

Brückner, Tobias, Merle Arrowsmith, Merlin Heß, Kai Hammond, Marcel Müller, and Holger Braunschweig. "Synthesis of fused B,N-heterocycles by alkyne cleavage, NHC ring-expansion and C–H activation at a diboryne." Chemical Communications 55, no. 47 (2019): 6700–6703. http://dx.doi.org/10.1039/c9cc02657f.

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The addition of alkynes to a saturated N-heterocyclic carbene (NHC)-supported diboryne results in spontaneous cycloaddition, with complete BB and CC triple bond cleavage, NHC ring-expansion and activation of a variety of C–H bonds, leading to the formation of complex mixtures of fused B,N-heterocycles.

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37

Le, Nguyen Nhat Thu, Josefine Just, Jonathan M. Pankauski, Paul R. Rablen, and Dasan M. Thamattoor. "Ring Expansion of Alkylidenecarbenes Derived from Lactams, Lactones, and Thiolactones into Strained Heterocyclic Alkynes: A Theoretical Study." Molecules 24, no. 3 (February 7, 2019): 593. http://dx.doi.org/10.3390/molecules24030593.

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Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes—formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon—were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled. Interestingly, the C≡C bonds in the five-membered heterocycles, obtained from the rearrangement of β-lactam- and β-lactone-derived alkylidenecarbenes, displayed lengths intermediate between formal double and triple bonds. Furthermore, 2-(1-azacyclobutylidene)carbene was found to be nearly isoenergetic with its ring-expanded isomer, and 1-oxacyclopent-2-yne was notably higher in energy than its precursor carbene. In all other cases, the cycloalkynes were lower in energy than the corresponding carbenes. The transition states for ring-expansion were always lower for the 1,2-carbon shifts than for 1,2-nitrogen or oxygen shifts, but higher than for the 1,2-sulfur shifts. These predictions should be verifiable using carbenes bearing appropriate isotopic labels. Computed vibrational spectra for the carbenes, and their ring-expanded isomers, are presented and could be of value to matrix isolation experiments.

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38

Lin, Ivan JB, and Chandra Sekhar Vasam. "Review of gold(I) N-heterocyclic carbenes." Canadian Journal of Chemistry 83, no. 6-7 (June 1, 2005): 812–25. http://dx.doi.org/10.1139/v05-087.

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This review presents an overview of the work on Au(I)NHC chemistry. The efficiency of different synthetic strategies of Au(I)NHCs is discussed. Transmetallation of Ag(I)NHCs appears to be an easy method as compared with the others. The influence of aurophilicity "a traditional property of a Au(I) center" in making the supramolecular assemblies is also covered. The combination of the Au(I) center with NHCs has great potential in the fields of medicine, catalysis, liquid crystal, and optoelectronic.Key words: goldcarbenes, silvercarbenes, carbene transfer, aurophilicity.

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39

Mariconda, Annaluisa, Marco Sirignano, Rubina Troiano, Simona Russo, and Pasquale Longo. "N-heterocyclic Carbene Gold Complexes Active in Hydroamination and Hydration of Alkynes." Catalysts 12, no. 8 (July 29, 2022): 836. http://dx.doi.org/10.3390/catal12080836.

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Until the year 2000, gold compounds were considered catalytically inert. Subsequently, it was found that they are able to promote the nucleophilic attack on unsaturated substrates by forming an Au–π-system. The main limitation in the use of these catalytic systems is the ease with which they decompose, which is avoided by stabilization with an ancillary ligand. N-heterocyclic carbenes (NHCs), having interesting s-donor capacities, are able to stabilize the gold complexes (Au (I/III) NHC), favoring the exploration of their catalytic activity. This review reports the state of the art (years 2007–2022) in the nucleophilic addition of amines (hydroamination) and water (hydration) to the terminal and internal alkynes catalyzed by N-heterocyclic carbene gold (I/III) complexes. These reactions are particularly interesting both because they are environmentally sustainable and because they lead to the production of important intermediates in the chemical and pharmaceutical industry. In fact, they have an atom economy of 100%, and lead to the formation of imines and enamines, as well as the formation of ketones and enols, all important scaffolds in the synthesis of bioactive molecules, drugs, heterocycles, polymers, and bulk and fine chemicals.

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40

Azizi, Zahra, Mehdi Ghambarian, Mohammad A. Rezaei, and Mohammad Ghashghaee. "Saturated N,X-Heterocyclic Carbenes (X=N, O, S, P, Si, C, and B): Stability, Nucleophilicity, and Basicity." Australian Journal of Chemistry 68, no. 9 (2015): 1438. http://dx.doi.org/10.1071/ch14715.

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Various saturated five-membered N,X-heterocyclic carbenes (X = N, O, S, P, Si, C, and B) have been studied by ab initio and density functional theory (DFT) methods. The substitutions alter the properties of the reference carbene from the viewpoint of electronic structure, stability, nucleophilicity, and basicity. Our study shows that the oxygen containing carbene (X = O) induces the highest HOMO–LUMO energy gap (ΔEHOMO–LUMO), while carbene with X = N has the widest singlet–triplet energy difference (ΔEs–t). The nucleophilicity of the carbene derivatives increased upon replacement of C, Si, and B, with the effect of the boron substituent being more pronounced. In addition, the basicity of the structure increased for the carbene derivatives with X = C and B with the latter substitution imposing a remarkably higher effect. Moreover, the substitution of boron at the α-position of the carbene increased the nucleophilicity and basicity, while inducing a reduction in the values of ΔEs–t and ΔEHOMO–LUMO.

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41

Ho, Peter C., Hilary A. Jenkins, James F. Britten, and Ignacio Vargas-Baca. "Building new discrete supramolecular assemblies through the interaction of iso-tellurazole N-oxides with Lewis acids and bases." Faraday Discussions 203 (2017): 187–99. http://dx.doi.org/10.1039/c7fd00075h.

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The supramolecular macrocycles spontaneously assembled by iso-tellurazole N-oxides are stable towards Lewis bases as strong as N-heterocyclic carbenes (NHC) but readily react with Lewis acids such as BR₃ (R = Ph, F). The electron acceptor ability of the tellurium atom is greatly enhanced in the resulting O-bonded adducts, which consequently enables binding to a variety of Lewis bases that includes acetonitrile, 4-dimethylaminopyridine, 4,4′-bipyridine, triphenyl phosphine, a N-heterocyclic carbene and a second molecule of iso-tellurazole N-oxide.

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42

Groso, Emilia, and Corinna Schindler. "Recent Advances in the Application of Ring-Closing Metathesis for the Synthesis of Unsaturated Nitrogen Heterocycles." Synthesis 51, no. 05 (February 8, 2019): 1100–1114. http://dx.doi.org/10.1055/s-0037-1611651.

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This short review summarizes recent advances relating to the application of ring-closing olefin-olefin and carbonyl-olefin metathesis reactions towards the synthesis of unsaturated five- and six-membered nitrogen heterocycles. These developments include catalyst modifications and reaction designs that will enable access to more complex nitrogen heterocycles.1 Introduction2 Expansion of Ring-Closing Metathesis Methods3 Evaluation of Catalyst Design4 Indenylidene Catalysts5 Unsymmetrical N-Heterocyclic Carbene Ligands6 Carbonyl-Olefin Metathesis7 Conclusions

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Xu, Xinfang, and Michael P. Doyle. "Recent Developments in the Synthetic Uses of Silyl-protected Enoldiazoacetates for Heterocyclic Syntheses." Australian Journal of Chemistry 67, no. 3 (2014): 365. http://dx.doi.org/10.1071/ch13576.

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Diazo compounds have been used as precursors to a wide variety of heterocyclic compounds that represent the core structural subunits in many biologically active compounds. Various methodologies have been established for their synthesis via metal-catalyzed carbene transformations. Although the advantages of vinyldiazoacetates have been known for many years, realization of the synthetic use of enoldiazoacetates has been more recent. This review covers advances in the utility of silyl-protected enoldiazoacetates in heterocycle syntheses that include X–H insertion reactions, ylide rearrangements, formal [3+3]- and [4+3]-cycloaddition reactions, and other traditional and unusual metal carbene transformations.

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44

Jandl, Christian, and Alexander Pöthig. "A hybrid carbocyclic/N-heterocyclic carbene ligand." Chemical Communications 53, no. 13 (2017): 2098–101. http://dx.doi.org/10.1039/c6cc08468k.

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45

Ritleng, Vincent, and Christophe Michon. "Bidentate Donor-Functionalized N-Heterocyclic Carbenes: Valuable Ligands for Ruthenium-Catalyzed Transfer Hydrogenation." Molecules 27, no. 15 (July 23, 2022): 4703. http://dx.doi.org/10.3390/molecules27154703.

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Ruthenium complexes are by far the most studied compounds that catalyze hydrogen transfer reactions. In this review, we describe the use in this field of ruthenium complexes bearing bidentate donor-functionalized N-heterocyclic carbene ligands. The review specifically covers the application in transfer hydrogenations of (κ2-CNHC,Y)-ruthenacyclic compounds where the Y donor atom is a N, P, O, or S atom, and where the N-heterocyclic carbene ligand is a classical imidazol-2-ylidene, a benzimidazol-2-ylidene, a mesoionic 1,2,3-triazolylidene, or an imidazol-4-ylidene ligand. Tridentate donor-functionalized N-heterocyclic carbene complexes thus fall outside the scope of the review. Applications in (asymmetric) transfer hydrogenation of ketones, aldehydes, imines, alkenes, and nitrobenzene are discussed.

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46

Šegina, Jan, Luka Ciber, Helena Brodnik, Franc Požgan, Jurij Svete, Bogdan Štefane, and Uroš Grošelj. "Synthesis of Six-Membered N-Heterocyclic Carbene Precursors Based on Camphor." Molecules 28, no. 24 (December 6, 2023): 7973. http://dx.doi.org/10.3390/molecules28247973.

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The endo- and exo-N-heterocyclic carbene precursors based on camphor were prepared diastereoselectively in five synthetic steps starting from (1S)-(+)-ketopinic acid. The obtained N-heterocyclic carbene precursors were investigated in an asymmetric benzoin reaction. All new compounds were fully characterized, and the absolute configurations were determined via X-ray diffraction and NOESY measurements.

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47

Tang, Xiang-Ting, Fan Yang, Ting-Ting Zhang, Yi-Fan Liu, Si-Yu Liu, Tong-Fu Su, Dong-Can Lv, and Wen-Bo Shen. "Recent Progress in N-Heterocyclic Carbene Gold-Catalyzed Reactions of Alkynes Involving Oxidation/Amination/Cycloaddition." Catalysts 10, no. 3 (March 20, 2020): 350. http://dx.doi.org/10.3390/catal10030350.

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Recent rapid development in homogeneous gold catalysis affords an alternative and particularly thriving strategy for the generation of gold carbenes through gold-catalyzed oxidation/amination/cycloaddition of alkynes, while it avoids the employment of hazardous and potentially explosive diazo compounds as starting materials for carbene generation. In addition to facile and secure operation, gold carbenes generated in this strategy display good chemoselectivity distinct from other metal carbenes produced from the related diazo approach. N-heterocyclic carbene (NHC) gold is a special metal complex that can be used as ancillary ligands, which provides enhanced stability and can also act as an efficient chiral directing group. In this review, we will present an overview of these recent advances in alkyne oxidation/amination/cycloaddition by highlighting their specificity and applicability, aiming to facilitate progress in this very exciting area of research.

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48

Ojha, Minita, Shweta Choudhary, and Raj K. Bansal. "3-Benzylbenzothiazolylidene Carbene Catalyzed Isomerization of Dimethyl Maleate to Dimethyl Fumarate: Experimental and Theoretical Results." Current Organocatalysis 7, no. 2 (July 2, 2020): 108–17. http://dx.doi.org/10.2174/2213337206666191018111354.

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Background: N-Heterocyclic Carbenes (NHCs) have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. Since Arduengo and co-workers first isolated a bottlable NHC, namely imidazol-2-ylidene derivative, these nucleophilic species have attained a prominent place in synthetic organic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a really fruitful area of research in recent years. Methods and Results: The quantitative aspects of the experimental and theoretical investigation of isomerization of dimethyl maleate to dimethyl fumarate catalyzed by an N-heterocyclic carbene (NHC), namely 3-benzylbenzothiazolylidene are being reported for the first time. Dimethyl maleate on treating with 3-benzylbenzothiazolylidene carbene (10 mol%), generated in situ from the reaction of 3- benzylbenzothiazolium bromide with triethylamine in diethyl ether at room temperature under nitrogen atmosphere isomerizes quantitatively to dimethyl fumarate. Theoretical investigation of a model reaction scheme at the wB97XD/6-31+G(d) level reveals that initial attack of the carbene, which is the ratedetermining step, is followed by rotation about the C-C bond in preference to a higher activation free energy path involving proton abstraction. The species so formed splits off the carbene to yield dimethyl fumarate. Eyring equation has been used to rationalize the effect of temperature on the isomerization rate. Conclusions and Perspective: 3-Benzylbenzothiazolylidene carbene catalyzes the isomerization of dimethyl maleate to its trans-isomer. This carbene can be used in other catalytic reactions, such as acyloin condensation and Stetter reaction.

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49

Hongfa, Chayanant, Haw-Lih Su, Hassan S. Bazzi, and David E. Bergbreiter. "Polyisobutylene-AnchoredN-Heterocyclic Carbene Ligands." Organic Letters 11, no. 3 (February 5, 2009): 665–67. http://dx.doi.org/10.1021/ol802728t.

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50

Maki, Brooks E., Audrey Chan, Eric M. Phillips, and Karl A. Scheidt. "N-Heterocyclic carbene-catalyzed oxidations." Tetrahedron 65, no. 16 (April 2009): 3102–9. http://dx.doi.org/10.1016/j.tet.2008.10.033.

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