Addition Of Carbanions Research Articles

Endohedral Fullerene Derivatives: Tether-Directed Functionalizations and Regioisomer Preferences

Addition reactions have been performed (carbene and addition-elimination, Bingel) on Sc3N@C2nto determine the preferred mono- as well as multiple addition positions both experimentally and via computations. It has been observed that carbene additions lead to many more isomers than the corresponding addition-elimination reactions of malonates (Bingel reaction), which lead to a rather small number of regioisomers. Theory predicts well the Bingel adducts that are observed experimentally and provides a kinetic rationale for the observations.Tethered bis-additions have also been explored, especially on Lu3N@C80, and the results indicate very regioselective bis-additions, with only one bis-regioisomer observed in many cases for bis-carbene additions.These and other results will be presented and discussed within the context of single and multiple functionalization of endohedral fullerene compounds and how the properties of the products can be controlled via functionalization.

Silver(I)-promoted intramolecular addition of N-heterocyclic carbenes towards unsaturated esters in water

Silver(I)-promoted intramolecular addition reaction between N-heterocyclic carbene and unsaturated esters in water is described. The reaction leads to 1H-imidazo[1,2-a]indole derivatives in moderate to excellent yields.

Diastereoselective formation of aziridines from diazocarbonyl compounds and N-(O-pivaloylated D-galactosyl)benzylideneamines and ring-opening reactions with p-toluenethiol.

N-Galactosyl aziridines were synthesized via BF3·OEt2 promoted addition of carbenes generated from diazocarbonyl compounds with O-pivaloylated β-D-galactosylimines in good yields and high diastereoselectivity. The ring-opening reactions with p-toluenethiol of the aziridines provided enantiometrically pure β-S-substituted phenylalanine derivatives in a highly regioselective manner.

Reactivity of Chlorotrifluoromethylcarbene: Activation Parameters for Halocarbene–Alkene Addition Reactions

Activation parameters are reported for ClCCF3 additions to three alkenes (tetramethylethylene, cyclohexene, and 1-hexene). The results are compared to those for CCl2, CClF, and CF2. Activation enthalpies decrease as the carbene stability decreases and its electrophilicity increases, and also as alkene reactivity (degree of alkylation) increases. Activation entropies decrease in parallel with activation enthalpies, suggesting the operation of enthalpy-entropy compensation in these carbene additions.

NHC Organocatalytic Formal LUMO Activation of α,β‐Unsaturated Esters for Reaction with Enamides

An effective wake-up call: Stable α,β-unsaturated esters were activated by the addition of a chiral N-heterocyclic carbene (NHC) organocatalyst, and the resulting reactive Michael acceptor intermediates reacted with enamide nucleophiles to furnish optically pure products (see scheme; Ts=p-toluenesulfonyl). These products can be converted readily into bioactive δ-lactams, piperidines, and their derivatives. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Carbene Additions to Fullerenes

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTCarbene Additions to FullerenesMichio Yamada†, Takeshi Akasaka*‡, and Shigeru Nagase§View Author Information† Department of Chemistry, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan‡ Life Science Center of Tsukuba Advanced Research Alliance, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan§ Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto 606-8103, Japan*E-mail: [email protected]Cite this: Chem. Rev. 2013, 113, 9, 7209–7264Publication Date (Web):June 17, 2013Publication History Received12 December 2012Published online17 June 2013Published inissue 11 September 2013https://doi.org/10.1021/cr3004955Copyright © 2013 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views5635Altmetric-Citations113LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (21 MB) Get e-AlertsSUBJECTS:Carbene compounds,Carbon,Carbon nanomaterials,Molecular structure,Nanospheres Get e-Alerts

Highly Regioselective Addition of Adamantylidene Carbene to Yb@C2v(3)‐C80 to Afford the First Derivative of Divalent Metallofullerenes

Highly Regioselective Addition of Adamantylidene Carbene to Yb@<i>C</i>_2<i>v</i>(3)‐C₈₀ to Afford the First Derivative of Divalent Metallofullerenes

N‐Heterocyclic Carbene Catalyzed [4+2] Cycloaddition of Nitroalkenes with Oxodienes

NHC catalysis: N-heterocyclic carbenes were found to be efficient catalysts for the unprecedented [4+2] cycloaddition of nitroalkenes and oxodienes, giving the corresponding dihydropyrans in good yield with good diastereoselectivity (see scheme). Deuteration experiment reveals that the reaction is possibly initiated by the addition of N-heterocylic carbene to nitroalkenes.

Step-Efficient Access to Chiral Primary Amines

Routes to enantioenriched amines are outlined that employ reductive amination and carbanion addition methods. The strategies require either one or two reaction steps from prochiral carbonyl compounds for the synthesis of the corresponding chiral primary amines.

Intramolecular cyclization and subsequent rearrangements of alkyne-tethered N-heterocyclic carbenes

Alkyne-tethered imidazole and 1,2,4-triazole-based N-heterocyclic carbene precursors have been prepared and studies of the intramolecular reactions of carbenes are performed. Products consistent with intramolecular cyclizations and subsequent rearrangements were observed. Mechanistic studies using crossover experiments showed that the products did arise from intramolecular carbene additions. The reactions are proposed to go through vinylogous diaminocarbene intermediates similar to vinylogous dialkoxycarbenes formed during Boger cycloaddition reactions. Imidazole substituted dienes were observed to be the major products of tandem cyclization and elimination reactions that were observed for imidazole-based N-heterocyclic carbenes.

Carbenic vs. ionic mechanistic pathway in reaction of cyclohexanone with bromoform

The extensive computation study was done to elucidate the mechanism of formation dibromoepoxide from cyclohexanone and bromoform. In this reaction, the formation of dihaloepoxide 2 is postulated as a key step that determines the distribution and stereochemistry of products. Two mechanistic paths of reaction were investigated: the addition of dibromocarbene to carbonyl group of ketone, and the addition of tribromomethyl carbanion to the same (C=O) group. The mechanisms for the addition reactions of dibromocarbenes and tribromomethyl carbanions with cyclohexanone have been investigated using ab initio HF/6-311++G** and MP2/6-311+G* level of theory. Solvent effects on these reactions have been explored by calculations which included a continuum polarizable conductor model (CPCM) for the solvent (H₂O). The calculations showed that both mechanisms are possible and are exothermic, but have markedly different activation energies.

2-(3-Chloro-5,6-diphenyl-2,5-dihydro-1,2,4-triazin-5-yl)-2-methylpropanenitrile

The title compound, C19H17ClN4, was obtained from the reaction of 3-chloro-5,6-diphenyl-1,2,4-triazine with isobutyronitrile in the presence of lithium diisopropyl­amide as an unexpected product of covalent addition of isobutyronitrile carbanion to the C-5 atom of the 1,2,4-triazine ring. The 2,5-dihydro-1,2,4-triazine ring is essentially planar (r.m.s. deviation = 0.0059 Å) and the 5- and 6-phenyl substituents are inclined to its mean plane with dihedral angles of 89.97 (4) and 55.52 (5)°, respectively. Intra­molecular C—H⋯N inter­actions occur. In the crystal, mol­ecules related by a c-glide plane are linked into zigzag chains along [001] by N—H⋯N hydrogen bonds.

Synthesis, Pairing, and Cellular Uptake Properties of C(6′)-Functionalized Tricyclo-DNA

Tricyclo-DNA (tc-DNA) is a promising candidate for oligonucleotide-based therapeutic applications exhibiting increased affinity to RNA and increased resistance to nucleases. However, as many other oligonucleotide analogs, tc-DNA does not readily cross cell membranes. We wished to address this issue by preparing a prodrug of tc-DNA containing a metabolically labile group at C(6') that promotes cellular uptake. Two monomeric nucleoside building blocks bearing an ester function at C(6') (tc(ee)-T and tc(hd)-T) were synthesized starting from a known C(6') functionalized bicyclic sugar unit to which the cyclopropane ring was introduced via carbene addition. NIS-mediated nucleosidation of the corresponding glycal with in situ persilylated thymine afforded the β-iodonucleoside exclusively that was dehalogenated via radical reduction. Diversity in the ester function was obtained by hydrolysis and reesterification. The two nucleosides were subsequently incorporated into DNA or tc-DNA by standard phosphoramidite chemistry. The reactivity of the ester function during oligonucleotide deprotection was explored and the corresponding C(6') amide, carboxylic acid, or unchanged ester functions were obtained, depending on the deprotection conditions. Compared to unmodified DNA, these tc-DNA derivatives increased the stability of duplexes investigated with ΔT(m)/mod of +0.4 to +2.0 °C. The only destabilizing residue was tc(hd)-T, most likely due to self-aggregation of the lipophilic side chains in the single stranded oligonucleotide. A decamer containing five tc(hd)-T residues was readily taken up by HeLa and HEK 293T cells without the use of a transfection agent.

Nucleophilic Addition of β-Amino Carbanions to Arynes: One-Pot Synthesis of 4-Aryl-N-methyl-1,2,3,4-tetrahydroisoquinolines

A novel approach for the direct C-4 arylation of N-methyl-1,2,3,4-tetrahydroisoquinolines by nucleophilic addition of β-aminocarbanions to benzynes is described which provides a one-pot procedure for synthesis of the title compounds.

Remote stereocontrol of intramolecular rhodium carbene addition driven by a small and flexible chiral 2,4-pentanediol tether

Intramolecular rhodium carbenoid additions were studied using 2,4-pentanidiol as a chiral tether between a diazo group, a precursor of the carbene, and an aromatic group to be reacted with the carbene. The reaction was designed to perform the addition at a remote position, conserving the original high stereoselectivity appeared at additions near the tether, in addition to high regioselectivity and sufficient reaction efficiency. Substitution on the near reaction sites, the carbene carbon and aromatic group, in the reactant was effective to relegate the reaction site to a remote position. In the present study, two remote reactions, one dealing with C–H insertion and the other classified in Büchner reaction, were found to give sole products in high yields.

Reactivity of an Oxalamide-Based N-Heterocyclic Carbene

The reactivity of the oxalamide-based carbene 2 was investigated. Treatment with styrene or methylacrylate proceeded under carbene addition to yield the respective cyclopropanation products 6a,b. With elemental selenium the selenide 7 was obtained, which was characterized by X-ray diffraction. The Rh complex [(COD)RhCl(2)] (10) was also structurally characterized. From the IR spectrum of the dicarbonyl derivative [(CO)2RhCl(2)] (11) a Tolman electronic parameter of 2068 cm–1 was calculated for the diamidocarbene 2, which characterizes this ligand as the least electron donating NHC known so far. The dimerization product of carbene 2, the intensly fluorescing tetraamido ethylene 3, showed an unexpected chemical stability. Treatment of the chloro compound 1a with methanol afforded the methoxide 5a, whose structure was determined by X-ray diffraction.

Cyclization by Catalytic Ruthenium Carbene Insertion into CH Bonds

A novel tandem Ru-catalyzed carbene addition to terminal alkynes/insertion into CH bonds in alkynyl acetals, ethers, and amines has been accomplished under mild reaction conditions (see scheme; TMS=trimethylsilyl). This cascade provides an efficient approach to form complex spiro and fused bicyclic structures by 1,5- and 1,6-hydride shift/cyclization sequences from vinylcarbene Ru intermediates.

Synthesis of Endohedral Metallofullerene Glycoconjugates by Carbene Addition

Endohedral metallofullerene glycoconjugates were synthesized under mild conditions by carbene addition using appropriate glycosylidene-derived diazirine with La2@Ih-C80. NMR spectroscopic studies revealed that the glycoconjugate consists of two diastereomers of [6,6]-open mono-adducts. The electronic properties were characterized using Vis/NIR absorption spectroscopy and electrochemical measurements. This study demonstrates that glycosylidene carbene is useful to incorporate carbohydrate moieties onto endohedral metallofullerene surfaces.

ChemInform Abstract: Stereoselective Synthesis of α‐Branched Amines by Nucleophilic Addition of Unstabilized Carbanions to Imines

AbstractReview: 242 refs.

&amp;lt;italic&amp;gt;N&amp;lt;/italic&amp;gt;-heterocyclic carbene-catalyzed [4 + 2] annulation of &amp;alpha;,&amp;beta;-unsaturated acyl chlorides and nitroso compound

The <italic>N</italic>-heterocyclic carbene-catalyzed [4 + 2] annulation of α,β-unsaturated acyl chlorides with a nitroso compound was developed for the synthesis of aza-δ-lactones (2<italic>H</italic>-1,2-oxazin-6-one). It is proposed that the catalytic reaction was initiated by the nucleophilic addition of the N-heterocyclic carbene to the vinylketenes <italic>in situ</italic> generated from the acyl chloride to give a vinylenolate, followed by the [4 + 2] cycloaddition of the vinylenloate with nitroso compound to give the final aza-δ-lactones.