Addition Of Carbanions Research Articles

Copper‐Catalyzed Bis(methoxycarbonyl)carbene Reactions of α,β‐Unsaturated Carboxamides

AbstractThe [Cu(acac)2]‐catalyzed reactions of α,β‐unsaturated carboxamides with dimethyl diazomalonate yielded dihydrofuran derivatives by a 1,5‐electrocyclic reaction at C(β), and butadiene derivatives by carbene addition reaction at C(α) (Schemes 4 and 5; Table). Phenyl substituents at the N‐atom of the amides seem to be effective on the reaction pathways (Table).

Interaction of β-Lactam Carbenes with 3,6-Diphenyltetrazines: A Five-Step Cascade Reaction for the Direct Construction of Indeno[2,1-b]pyrrol-2-ones

A study of the nucleophilic addition of β-lactam carbenes to 3,6-diphenyltetrazines is reported. Instead of the formation of pyrazole derivatives like most reactions between nucleophilic or ambiphilic carbenes and 3,6-disubstituted tetrazines, β-lactam carbenes reacted with 3,6-diphenyltetrazines to produce indeno[2,1-b]pyrrol-2-ones in good yields. The reaction proceeds most probably through a five-step cascade process. This work has not only provided a one-pot operation for the efficient construction of mutisubstituted indeno[2,1-b]pyrrol-2-ones but also revealed the nucleophilicity of β-lactam carbenes.

N-Heterocyclic Carbenes and Charge Separation in Heterometallic s-Block Silylamides

Addition of the N-heterocyclic carbene (NHC), 1,3-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene (IPr), to equimolar quantities of group 1 and group 2 bis(trimethylsilyl)amides results in the isolation of charge separated species, [M(IPr)(2)](+)[M'{N(SiMe(3))(2)}(3)](-) (M = Li, Na, K; M' = Mg, Ca, Sr, Ba). Although these systems were found to be prone to the separation of oily, most likely liquid clathrate, materials, either slow cooling or careful diffusion of the less polar solvent hexane into toluene solutions yielded nine crystalline heterobimetallic complexes in which the coordination sphere of the cationic group 1 center was found by X-ray diffraction analysis to be provided by two IPr ligands. These derivatives are the first examples of any compounds in which coordination at the central alkali metal cation is provided exclusively by NHC ligands and, for the cases where M = Na, are the first instances of any type in which an NHC ligand is bound to sodium. The anionic group 2-containing component of each compound was found to comprise three bis(trimethylsilyl)amido ligands coordinated in an approximately trigonal array about the divalent metal center. The bonding within the unusual cationic components of the compounds has been investigated by density functional theoretical (DFT) methods. Natural Bond Orbital (NBO) analyses have revealed that the coordination is provided by donation of the sp-hydridized IPr lone pair into the valence s-orbital of the alkali metal cation and are consistent with weaker binding, and consequently more labile solution behavior, as group 1 is descended.

Synthesis and characterization of chiral mono N-heterocyclic carbene-substituted rhodium complexes and their catalytic properties in hydrosilylation reactions

Different chiral mono-substituted N-heterocyclic carbene complexes of rhodium were prepared, starting from [Rh(COD)Cl] 2 (COD = cyclooctadiene) by addition of free N-heterocyclic carbenes (NHC), or an in-situ deprotonation of the corresponding iminium salt. All new complexes were characterized by spectroscopy methods. In addition, the structures of chloro( η 4-1,5-cyclooctadiene)(1,3-di-[(1 R,2 R,3 R,5 S)-2,6,6-trimethylbicyclo[3.1.1]hept-3-yl] imidazolin-2-ylidene)rhodium(I) ( 5a), chloro( η 4-1,5-cyclooctadiene)(1,3-di-[(1 R,2 S,5 R)-2-isopropyl-5-menthylcyclohex-1-yl]imidazol-2-ylidene)rhodium(I) ( 5b) and chloro( η 4-1,5-cyclooctadiene)(1,3-di-[(2 R,4 S,5 S)-2-methyl-4-phenyl-1,3-dioxacyclohex-5-yl]imidazolin-2-ylidene)rhodium(I) ( 5i) were analyzed by DFT-calculations. The enantioselective hydrosilylation of acetophenone, ethylpyruvate and n-propylpyruvate with diphenylsilane and hydrolysis was carried out with chiral C 2-symmetrical mono-substituted N-heterocyclic carbene rhodium complexes giving for the first time an enantioselective excess of up to 74% ee in the case of the n-propylpyruvate.

Regioselective Bis-functionalization of Endohedral Dimetallofullerene, La2@C80: Extremal La–La Distance

Bis-functionalization of endohedral metallofullerene La(2)@C(80) by carbene addition is reported herein. Adducts were characterized using spectroscopic and single-crystal X-ray structure analyses. Crystallographic data for bisadduct La(2)@C(80)(CClPh)Ad (3, Ad = adamantylidene) revealed that both carbene additions occur at the 6,6-bond junction on the C(80) cage with ring cleavages and that La atoms are positioned collinearly with spiro carbons. It is noteworthy that the La-La distance in 3 is highly elongated by carbene bis-functionalization compared to the distance in pristine La(2)@C(80) and reported functionalized derivatives. The metal positions were confirmed through density functional calculations.

ChemInform Abstract: Intramolecular Regioselective Addition of Radicals and Carbanions to Ynol Ethers. A Strategy for the Synthesis of Exocyclic Enol Ethers.

AbstractTwo new strategies to synthesize exocyclic enol ethers are presented.

Addition of N-Heterocyclic Carbenes to a Ruthenium(VI) Nitrido Polyoxometalate: a New Route to Cyclic Guanidines

The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW(11)O(39)Ru(VI)N](4-) has been extended to the N-heterocyclic carbene {CH(2)(Mes)N}(2)C and the coupling product {CH(2)(Mes)N}(2)CNH(2)(+) characterized by (1)H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes. In the course of the reaction, the ruthenium(III)-containing polyoxometallic intermediate [PW(11)O(39)Ru(III){NC{N(Mes)CH(2)}(2)}](5-) has been thoroughly characterized by continuous-wave and pulsed electron paramagnetic resonance, which nicely confirms the presence of the organic moiety on the polyoxometallic framework, Ru K-edge X-ray absorption near-edge structure, and electrochemistry.

Covalently Assembled Gold Nanoparticle-Carbon Nanotube Hybrids via a Photoinitiated Carbene Addition Reaction

A nanohybrid consisting of monolayer protected gold nanoparticles (AuNPs) covalently attached to multiwalled carbon nanotubes (CNT) was prepared using a photoinitiated carbene addition approach. Photolysis of 3-aryl-3-(trifluoromethyl)diazirine-modified gold nanoparticles (Diaz-AuNPs) of two core sizes (3.9 ± 0.9 nm and 1.8 ± 0.3 nm in diameter) resulted in the generation of reactive carbene intermediates on the monolayer of the AuNPs. In the presence of untreated CNT the reactive carbenes undergo an addition reaction with the π-conjugated carbon skeleton. The AuNPs are well dispersed on the sidewall of the CNT and the hybrids are robust enough to survive vigorous washing in a variety of solvents. In the absence of photolysis no covalent attachment occurs with the same AuNP. The nanohybrid AuNP-CNTs were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman, and UV−visible spectroscopy. All of the characterization studies confirm the presence of the AuNPs. This methodo...

Addition of Dissimilar Carbenes across an Unsymmetrically Substituted Alkyne: Regio- and Stereoselective Synthesis of Trisubstituted 1,3-Dienes

The formal addition of dissimilar carbenes across an unsymmetrically substituted alkyne has been achieved for the first time by a two-step sequence in which a cobalt−alkyne complex undergoes reaction with a carbene addend (CHR1) to give a metallacyclobutene complex, followed by reaction with a second carbene addend (CHR2) to give a mixture of diene complexes. In situ treatment of the diene mixture with fluoride leads to desilylation and conversion to a single cobalt−diene complex with a high degree of regio- and stereoselectivity.

ChemInform Abstract: Cp*RuCl(COD) in Catalysis: A Unique Role in the Addition of Diazoalkane Carbene to Alkynes

AbstractReview: 123 refs.

ChemInform Abstract: Synthesis of Alkyl‐ and Cycloalkylamines by Addition of Carbanions to Azomethines

AbstractReview: 211 refs.

Intramolecular regioselective addition of radicals and carbanions to ynol ethers. A strategy for the synthesis of exocyclic enol ethers

The scope and limitations of radical and anionic cyclization reactions involving halo ynol ethers have been investigated. 5- exo and 6- exo radical cyclizations of 6-iodo and 7-iodo ynol ethers proceeded well when the oxygen of the ynol ether was bearing an ethyl group. Exocyclic iodoenol ethers resulting from these cyclizations were highly unstable and decomposed rapidly. Li–I exchange of iodo ynol ethers proceeded smoothly at −78 °C. 6-Alkoxy-5-hexynyllithiums underwent regiospecific 5- exo-dig anionic cyclization to produce five-membered rings bearing an exocyclic enol ether moiety. The cyclized vinyllithium intermediate was successfully trapped with electrophiles to afford functionalized cycloalkoxyalkylidene derivatives in modest to good yields. 7-Alkoxy-6-heptynyllithiums did not cyclize via a 6- exo anionic process.

ChemInform Abstract: Fluorinated Cyclopropanecarboxylic Acids and Their Derivatives.

Abstract The addition of halofluorocarbenes such as :CF 2 , :CClF or :CBrF, generated from the appropriate halofluoromethanes with bases, to butadiene or isoprene gives the corresponding l-vinyl substituted halofluorocyclopropanes in moderate to good yield. The vinyl group facilitates the carbene addition and permits a subsequent wide derivatisation. Several transformations including hydroboration, oxidation and Curtius degradation are presented. Furthermore, replacement of the chlorine atom in 2-chloro-2-fluorocyclopropanecarboxylic acid derivatives by hydrogen is achieved catalytically with Raney nickel. This sequence provides a convenient route to mono-fluorine substituted cyclopropane carboxylic acids.

ChemInform Abstract: Reductive Transformations. Part 14. Regioselective Addition of Carbanions to the “Aromatic” Pyrene Isomer Dicyclopenta(ef,kl) heptalene (I).

ChemInform Abstract: Reductive Transformations. Part 14. Regioselective Addition of Carbanions to the “Aromatic” Pyrene Isomer Dicyclopenta(ef,kl) heptalene (I).

ChemInform Abstract: Carbanion Addition to Acetylenes: An Efficient Stereoselective Route to α-Methylene γ-Lactams.

Abstract Intramolecular addition of carbanions, derived from the acetylenic amides (5b,d) , (7) and (9) has been shown to be highly stereoselective leading to the α-methylene-γ-lactam derivatives (6a,b) , (8a,b) and (10) .

ChemInform Abstract: Synthesis and Reaction of Novel Sulfur-Containing Heterocyclic Systems.

Abstract The strained alkylidene episulfides were synthesized by carbene and alkylidene carbene additions to thiocarbonyl compounds. Thermal, photochemical, and acid catalyzed reactions have been extensively investigated, and and the transition metal-promoted reaction results in the first isolation of thioallyl iron tricarbonyl complex. Germylene and zirconocene also reacted with thioketene to give metallic analogue of alkylidene episulfides, which are excellent synthetic source of a variety of cyclogermanes and stable enethiolizable thioaldehyde. Thermal sulfurization of some 1,2,3-butatriene derivatives and 1,2,3-selenadiazoles with elemental sulfur has been examined to give a variety of novel cyclic polysulfides having an unique structure. Reactive silicon and germanium species also reacted with elemental sulfur and selenium to afford cyclic metallachalcogenides.

ChemInform Abstract: Michael Reactions of Allylic Sulfones with Nitroolefins. Regio- and Stereochemical Control.

Abstract Michael addition of allylsulfone carbanions to nitroolefins where shown to be sensitive to substitution in both the donor and the acceptor. While sulfone 10 gave predominantly products of γ-addition with aromatic nitroolefins, addition to aliphatic nitroolefins produced almost exclusively α-adducts. In the presence of an OH function in the sulfone (see 13) only (Z) γ-adducts were observed, while a bromine substituent reversed the regiochemistry.

ChemInform Abstract: Pyrolysis of Quinoline-3,4-dicarboxylic Anhydrides Bearing 2-Phenyl, 2- Benzyl and 2-o-Tolyl Substituents: Formation of Products of Carbene Insertion and Addition.

Abstract Flash vacuum pyrolysis of 2-phenylquinoline-3,4-dicarboxylic anhydride at 800°/0.06 mm gave indeno[1,2- b ]indole (30–40%), which readily added nucleophiles Y − at C-10 to give 5,10-dihydro derivatives (Y  H, Me, Ph, NEt 2 , OMe, CH(COOMe) 2 and CMe 2 NO 2 ). Similar pyrolysis of the 2-benzylquinoline anhydride gave a 1:2 mixture of the (expected) linear 5 H -benzo[ b ]carbazole and the (unexpected) angular 7 H -benzo[ c ]carbazole. The isomeric 2- o -tolylquinoline anhydride on similar pyrolysis gave mainly 11 H -benzo[ a ]carbazole (85%), isomeric benzocarbazoles (4%) and 11 H -indeno[1,2- b ]quinoline (2.6%). Most of these products are probably derived from exocyclic carbenes formed by aryne - carbene equilibration, but the last compound may be formed by direct aryne - methyl interaction.

Origin of the regioselectivity in an intramolecular nucleophilic addition to arene chromium tricarbonyl complexes

The source of the regioselectivity in the intramolecular nucleophilic addition of nitrile-stabilized carbanions to arene chromium tricarbonyl complexes was investigated for seven different substitution patterns on the arenes. All of the arenes are 1,4-dioxygenated and the substitution varies in the oxygen substituent and in the substituents of the arene carbons (hydrogen and alkyl). The regioselectivity is correlated with the preferred conformations of the chromium tricarbonyl group which in turn was determined by solution and solid-state 13C NMR spectroscopy, 1H NMR spectroscopy in solution as well as X-ray diffraction. In the four complexes analyzed by X-ray diffraction and the three complexes analyzed by solid-state 13C NMR spectroscopy, there was only one complex where it was found that the preferred conformation of the –Cr(CO) 3 is different in solution than it is in the solid-state.

ChemInform Abstract: A Hard-Soft Acid-Base and DFT Analysis of Singlet-Triplet Gaps and the Addition of Singlet Carbenes to Alkenes.

The electronic structures of sixteen carbenes and four alkenes calculated at the B3LYP/6-31G* level were used to carry out a hard−soft acid−base investigation of carbene singlet−triplet gaps and of the addition of carbenes to alkenes. The carbenes chosen include examples where the ground state varies from triplet to singlet state and examples that have been characterized as nucleophilic, electrophilic, or ambiphilic based on their reactivity with alkenes having varying electron demands. We confirmed that singlet−triplet gaps calculated by DFT methods with the B3LYP functional correlate well with experimentally known values of carbenes spanning over 70 kcal/mol. Correlations between electron-density-based parameters and singlet−triplet gaps, or with carbene−alkene reactivity, were analyzed to gain insight into the electronic structure of the carbenes and their acid−base tendencies. A good correlation was found between the singlet−triplet energy gap and the condensed softness for electrophilic attack at the...