Journal articles: 'Carbenes (Methylene compounds)'

1

Kidonakis, Marios, and Manolis Stratakis. "Reduction of the Diazo Functionality of α-Diazocarbonyl Compounds into a Methylene Group by NH3BH3 or NaBH4 Catalyzed by Au Nanoparticles." Nanomaterials 11, no. 1 (January 18, 2021): 248. http://dx.doi.org/10.3390/nano11010248.

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Supported Au nanoparticles on TiO2 (1 mol%) are capable of catalyzing the reduction of the carbene-like diazo functionality of α-diazocarbonyl compounds into a methylene group [C=(N2) → CH2] by NH3BH3 or NaBH4 in methanol as solvent. The Au-catalyzed reduction that occurs within a few minutes at room temperature formally requires one hydride equivalent (B-H) and one proton that originates from the protic solvent. This pathway is in contrast to the Pt/CeO2-catalyzed reaction of α-diazocarbonyl compounds with NH3BH3 in methanol, which leads to the corresponding hydrazones instead. Under our stoichiometric Au-catalyzed reaction conditions, the ketone-type carbonyls remain intact, which is in contrast to the uncatalyzed conditions where they are selectively reduced by the boron hydride reagent. It is proposed that the transformation occurs via the formation of chemisorbed carbenes on Au nanoparticles, having proximally activated the boron hydride reagent. This protocol is the first general example of catalytic transfer hydrogenation of the carbene-like α -ketodiazo functionality.

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Mbuvi, Harun M., Erik R. Klobukowski, Gina M. Roberts, and L. Keith Woo. "O-H insertion and tandem N-H insertion/cyclization reactions using an iron porphyrin as catalyst with diazo compounds as carbene sources." Journal of Porphyrins and Phthalocyanines 14, no. 03 (March 2010): 284–92. http://dx.doi.org/10.1142/s1088424610001982.

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Iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl , efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols, with yields generally above 80%. Although the analogous N-H insertions are rapid at room temperature, the O-H insertion reactions are slower and required heating in refluxing methylene chloride for about 8 hours using 1.0 mol.% catalyst. Fe(TPP)Cl was also found to be effective for tandem N-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents to give piperazinones and morpholinones and related analogs such as quinoxalinones and benzoxazin-2-ones. This approach provides a new one-pot route for synthesizing these classes of heterocyclic compounds.

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3

Zoghbi, Michel, and John Warkentin. "Azetinone formation is not competitive with intermolecular reactions of a β-lactam-4-ylidene." Canadian Journal of Chemistry 70, no. 11 (November 1, 1992): 2792–97. http://dx.doi.org/10.1139/v92-355.

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3-Phenoxy-1-phenyl-2-azetidinon-4-ylidene (β-lactam-4-ylidene) 2a, was generated by thermolysis of a spiro-fused β-lactam oxadiazoline precursor (1). Fast 1,2-H migration, a characteristic reaction of singlet carbenes that would convert 2a to 3-phenoxy-1-phenyl-3-azetin-2-one (4a) could not be demonstrated. Added 1, 3-diphenylisobenzofuran (6) did not afford the [4 + 2] cycloadduct (7) expected from 4a but, instead, the isomeric E- and Z-4-[1-(2-benzoylphenyl)-1-phenyl]-methylene-3-phenoxy-1-phenylazetidin-2-ones (9). Those compounds can be rationalized as the products of rearrangement of first-formed [2 + 1] adducts of 6 and the ylidene. The structure of the Z isomer of 9 was established by means of single crystal X-ray diffraction. Generation of 2a in methanol-d4, either neat or 3.3 M in benzene, afforded the isomeric products of carbene insertion into the OD bond of methanol-d4. Structural isomers expected from addition of methanol-d4 to 4a could not be detected. The results suggest that 1,2-H migration in 2a is relatively slow, with kH ≤ 1.4 × 106 s−1 at 100 °C, which is slower than analogous rearrangement of benzylchlorocarbene by 200-fold or more.

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4

Kysilka, Ondřej, Markéta Rybáčková, Martin Skalický, Magdalena Kvíčalová, Josef Cvačka, and Jaroslav Kvíčala. "HFPO Trimer-Based Alkyl Triflate, a Novel Building Block for Fluorous Chemistry. Preparation, Reactions and 19F gCOSY Analysis." Collection of Czechoslovak Chemical Communications 73, no. 12 (2008): 1799–813. http://dx.doi.org/10.1135/cccc20081799.

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Triflate 4, CF3(CF2)2O-CF(CF3)CF2O-CF(CF3)CH2-OTf (RFOCH2OTf), of the HFPO trimer-based alcohol 3 (RFOCH2OH) is a novel highly fluorinated building block for fluorous chemistry. In analogy to similar polyfluorinated triflates with methylene spacer, its reactivity is limited to strong and soft nucleophiles. Whereas reactions with cyanide anion, phenolate anion, enolate of diethyl malonate or lithium salt of benzaldehyde bis(phenylsulfanyl)acetal were unsuccessful, the corresponding imidazole 5, iodide 6 or azide 7 were prepared in good yields. Reaction of imidazole 5 with (perfluorohexyl)methyl triflate (9) afforded highly fluorinated non-crystalline imidazolium salt 8, TfO-RFOCH2-(C3H3N2)+-CH2C6F13-n, which could be employed as fluorous ionic liquid or intermediate for fluorous carbenes. Complete assignment of complex 19F NMR spectra of all compounds employed was accomplished using 19F gCOSY NMR method.

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5

Monopoli, Antonio, Pietro Cotugno, Carlo Giorgio Zambonin, Francesco Ciminale, and Angelo Nacci. "Highly selective palladium–benzothiazole carbene-catalyzed allylation of active methylene compounds under neutral conditions." Beilstein Journal of Organic Chemistry 11 (June 10, 2015): 994–99. http://dx.doi.org/10.3762/bjoc.11.111.

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The Pd–benzothiazol-2-ylidene complex I was found to be a chemoselective catalyst for the Tsuji–Trost allylation of active methylene compounds carried out under neutral conditions and using carbonates as allylating agents. The proposed protocol consists in a simplified procedure adopting an in situ prepared catalyst from Pd2dba3 and 3-methylbenzothiazolium salt V as precursors. A comparison of the performance of benzothiazole carbene with phosphanes and an analogous imidazolium carbene ligand is also proposed.

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6

Amer, Atef Mohamed, Mohamed Fouad Zayed, Ali Deeb, and Ahmed Ali. "Pyridazine derivatives and related compounds. Part 141. Photolysis of 3-diazo-4,5-diphenylpyrazolo[3,4-c]pyridazine." Journal of Chemical Research 2005, no. 10 (October 2005): 643–47. http://dx.doi.org/10.3184/030823405774663011.

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The photochemistry of 3-diazopyrazolopyridazine has been investigated. The irradiation of 3-diazo-4,5-diphenylpyrazolo[3,4-c]pyridazine in various solvents forms a carbene intermediate, which transforms into 3-substituted derivatives. For photolysis in the presence of acetylacetone or ethyl acetoacetate the coupling reactions which occur at the methylene group are faster than carbene formation, and can lead to direct cyclisation into condensed 1,2,4-triazines. Photolysis in the presence of diethyl malonate forms an acyclic hydrazone.

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7

Chetcuti, Michael J., Haithem Naghmouchi, Abdelwaheb Hamdi, and Lydia Karmazin. "Synthesis of Imidazolium Cations Linked to Para-t-Butylcalix[4]arene Frameworks and Their Use as Synthons for Nickel-NHC Complexes Tethered to Calix[4]arenes." Molecules 28, no. 15 (July 27, 2023): 5697. http://dx.doi.org/10.3390/molecules28155697.

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A series of cationic p-tert-butylcalix[4]arenes, with side-arms that are functionalized with imidazolium groups, have been synthesized in good yields. The parent tetrahydroxy para-t-butyl-calix[4]arene was dialkylated at the phenolic hydrogen atoms using α,ω-dibromo-alkanes to yield bis(mono-brominated) alkoxy-chains of variable length. The brominated side-arms in these compounds were then further alkylated with substituted imidazoles (N-methylimidazole, N-(2,4,6-trimethyl-phenyl)imidazole, or N-(2,6-di-isopropylphenyl)imidazole) to yield a series of dicationic calixarenes with two imidazolium groups tethered, via different numbers of methylene spacers (n = 2–4), to the calixarene moiety. Related tetracationic compounds, which contain four imidazolium units linked to the calix[4]arene backbone, were also prepared. In all of these compounds, the NMR data show that the calixarenes adopted a cone configuration. All molecules were characterized by NMR spectroscopy and by MS studies. Single crystal X-ray diffraction studies were attempted on many mono-crystals of these cations, but significant disorder problems, partly caused by occluded solvent in the lattice, and lack of crystallinity resulting from partial solvent loss, precluded the good resolution of most X-ray structures. Eventually, good structural data were obtained from an unusually disordered single crystal of 5a, (1,3)-Cone-5,11,17,23-tetra-t-butyl-25,27-di-hydroxy-26,28-di-[2-(N-2,6-diisopropylphenyl-imidazolium)ethoxy]calix[4]arene dibromide and its presumed structure was confirmed. The structure revealed the presence of H-bonded interactions and some evidence of π-stacking. Some of these imidazolium salts were reacted with nickelocene to form the nickel N-heterocyclic carbene (NHC) complexes 7a–7d. A bis-carbene nickel complex 8 was also isolated and its structure was established by single crystal X-ray diffraction studies. The structure was disordered and not of high quality, but the structural data corroborated the spectroscopic data.

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8

Monopoli, Antonio, Pietro Cotugno, Carlo Giorgio Zambonin, Francesco Ciminale, and Angelo Nacci. "ChemInform Abstract: Highly Selective Palladium-Benzothiazole Carbene-Catalyzed Allylation of Active Methylene Compounds under Neutral Conditions." ChemInform 46, no. 34 (August 2015): no. http://dx.doi.org/10.1002/chin.201534057.

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9

Singh, Shailesh, Jyoti Tiwari, Deepali Jaiswal, Amit Kumar Sharma, Jaya Singh, Vandana Singh, and Jagdamba Singh. "Nucleophilic Acylation with Aromatic Aldehydes to 2 Bromoacetonitrile: An Umpolung Strategy for the Synthesis of Active Methylene Compounds." Current Organic Synthesis 17, no. 7 (October 28, 2020): 518–24. http://dx.doi.org/10.2174/1570179417666200615153536.

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Background: A novel one-pot N-heterocyclic carbene (NHC)-catalysed acylation of 2- bromoacetonitrile with aromatic aldehydes is reported. The protocol involves carbonyl umpolung reactivity of aldehydes in which the carbonyl carbon attacks nucleophilically (as d1 nucleophile) on the electrophilic terminal of 2-bromoacetonitrile to afford 3-aryl-3-oxopropanenitrile. The salient features of this procedure are short reaction time, operational simplicity, ambient temperature, no by-product formation and high yields. Materials and Methods: A flame-dried round bottom flask was charged with Imidazolium salts (3a) (0.20 mmol). Aldehyde 1a (1.0 mmol), 2-bromoacetonitrile 2 (1.0 mmol), and THF / t-BuOH 5 mL; 10:1) were added at positive nitrogen pressure followed by the addition of DBU (0.15 mmol) through stirring. The resulting yellow- orange solution was stirred at room temperature for 5-6 h. After completion of the reaction (TLC monitored), the reaction mixture was concentrated under reduced pressure. The product was purified using hexane / EtOAc (10:1) as an eluent to provide analytically pure compound 4a. Physical data of representative compounds and the NMR spectroscopic data are in agreement with the literature value. Results and Discussion: The salient features of this procedure are short reaction time, operational simplicity, ambient temperature, no by-product formation and high yields. Conclusion: To sum up, we have developed a convenient, efficient and one-pot route for 3-oxo-3- phenylpropanenitrile synthesis from NHC promoted direct nucleophilic acylation of aromatic aldehydes using 2- bromoacetonitrile. This method provided a wide range of products and good yields. To best of our knowledge, this is the new report for the synthesis of 3-oxo-3-phenylpropanenitrile through NHC promoted nucleophilic acylation of aromatic aldehyde.

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10

Terada, Yukiyoshi, Mitsuhiro Arisawa, and Atsushi Nishida. "Cycloisomerization Promoted by the Combination of a Ruthenium–Carbene Catalyst and Trimethylsilyl Vinyl Ether, and its Application in The Synthesis of Heterocyclic Compounds: 3-Methylene-2,3-dihydroindoles and 3-Methylene-2,3-dihydrobenzofurans." Angewandte Chemie International Edition 43, no. 31 (August 6, 2004): 4063–67. http://dx.doi.org/10.1002/anie.200454157.

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11

Terada, Yukiyoshi, Mitsuhiro Arisawa, and Atsushi Nishida. "Cycloisomerization Promoted by the Combination of a Ruthenium–Carbene Catalyst and Trimethylsilyl Vinyl Ether, and its Application in The Synthesis of Heterocyclic Compounds: 3-Methylene-2,3-dihydroindoles and 3-Methylene-2,3-dihydrobenzofurans." Angewandte Chemie 116, no. 31 (August 6, 2004): 4155–59. http://dx.doi.org/10.1002/ange.200454157.

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12

Liu, Mingxin, and Christopher Uyeda. "Redox Approaches to Carbene Generation in Catalytic Cyclopropanation Reactions." Angewandte Chemie, May 16, 2024. http://dx.doi.org/10.1002/ange.202406218.

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Transition metal‐catalyzed carbene transfer reactions have a century‐old history in organic chemistry and are a primary method for the synthesis of cyclopropanes. Much of the work in this field has focused on the use of diazo compounds and related precursors, which can transfer a carbene fragment to a catalyst with concomitant loss of a stable byproduct. Despite the utility of this approach, there are persistent limitations in the scope of viable carbenes, most notably those lacking stabilizing substituents. By coupling carbene transfer chemistry with two‐electron redox cycles, it is possible to expand the available starting materials that can be used as carbene precursors. In this Minireview, we discuss emerging catalytic reductive cyclopropanation reactions using either gem‐dihaloalkanes or carbonyl compounds. This strategy is inspired by classic stoichiometric transformations, such as the Simmons–Smith cyclopropanation and the Clemmensen reduction, but instead entails the formation of a catalytically generated transition metal carbene or carbenoid. We also present recent efforts to generate carbenes directly from methylene (CR2H2) groups via a formal dehydrogenation. These reactions are currently restricted to substrates containing electron‐withdrawing substituents, which serve to facilitate deprotonation and subsequent oxidation of the anion.

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13

Liu, Mingxin, and Christopher Uyeda. "Redox Approaches to Carbene Generation in Catalytic Cyclopropanation Reactions." Angewandte Chemie International Edition, May 16, 2024. http://dx.doi.org/10.1002/anie.202406218.

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Transition metal‐catalyzed carbene transfer reactions have a century‐old history in organic chemistry and are a primary method for the synthesis of cyclopropanes. Much of the work in this field has focused on the use of diazo compounds and related precursors, which can transfer a carbene fragment to a catalyst with concomitant loss of a stable byproduct. Despite the utility of this approach, there are persistent limitations in the scope of viable carbenes, most notably those lacking stabilizing substituents. By coupling carbene transfer chemistry with two‐electron redox cycles, it is possible to expand the available starting materials that can be used as carbene precursors. In this Minireview, we discuss emerging catalytic reductive cyclopropanation reactions using either gem‐dihaloalkanes or carbonyl compounds. This strategy is inspired by classic stoichiometric transformations, such as the Simmons–Smith cyclopropanation and the Clemmensen reduction, but instead entails the formation of a catalytically generated transition metal carbene or carbenoid. We also present recent efforts to generate carbenes directly from methylene (CR2H2) groups via a formal dehydrogenation. These reactions are currently restricted to substrates containing electron‐withdrawing substituents, which serve to facilitate deprotonation and subsequent oxidation of the anion.

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14

Fu, Duo, and Jiaxi Xu. "Synthesis of Sulfo(xo)nium Diacylmethylides." European Journal of Organic Chemistry, April 28, 2024. http://dx.doi.org/10.1002/ejoc.202400390.

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Sulfo(xo)nium diacylmethylides (sulfur ylides) are simple, stable, readily prepared, and versatile synthons. Compared with the sulfo(xo)nium monoacylmethylides, they can be compatible with more rigorous reaction conditions and showcase unique characteristics due to their excellent stability. This concept article provides an account for the syntheses of sulfo(xo)nium diacylmethylides, including the utilization of active methylene compounds, carbene precursors, sulfo(xo)nium monoacylmethylides, and electron‐deficient alkynes as substrates, with discussions on substrate scopes, proposed mechanisms, selected product examples, and applications. Challenges for further exploration and prospect on sulfo(xo)nium diacylmethylides in the future are also suggested.

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15

Terada, Yukiyoshi, Mitsuhiro Arisawa, and Atsushi Nishida. "Cycloisomerization Promoted by the Combination of a Ruthenium-Carbene Catalyst and Trimethylsilyl Vinyl Ether, and Its Application in the Synthesis of Heterocyclic Compounds: 3-Methylene-2,3-dihydroindoles and 3-Methylene-2,3-dihydrobenzofurans." ChemInform 35, no. 46 (November 16, 2004). http://dx.doi.org/10.1002/chin.200446039.

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Journal articles on the topic 'Carbenes (Methylene compounds)'

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