Addition Of Carbanions Research Articles

Catalytic Intramolecular Addition of Metal Carbenes to Remote Furans

Diazo esters and diazo ketones linked to a furan undergo catalytic intramolecular addition of an intermediate metal carbene to the remote furan to form diendiones with ring sizes up to 17. Regioselectivity is catalyst dependent with addition to either the more or less substituted double bond. The high product yields and absence of need for high dilution suggest that this methodology is general for macrocycle preparations.

Synthesis and polymerization of vinylcyclopropanes

Vinylcyclopropanes are important synthetic intermediates in organic chemistry and are mostly synthesized by the simultaneous introduction of the cyclopropane and the vinyl unit, e. g., by the reaction of trans-1,4-dihalobutenes with β-dicarbonyl compounds or the addition of carbenes to dienes. The polymerization of vinylcyclopropane itself results in vinyl polymers with predominantly 1,2-structural units. The radical polymerization of substituted vinylcyclopropanes results in polymers with mainly 1,5-ring-opened units, whereby radical stabilizing substituents or electron-withdrawing groups increase the radical polymerizability and the ring-opening ability. The vinylcyclopropanes undergo a radical copolymerization with other vinyl monomers, such as methacrylates, and, in comparison to the polymerization of these linear vinyl monomers, the vinylcyclopropanes show a significantly lower volume shrinkage during ring-opening polymerization. Hybrid vinylcyclopropanes are polymerized step-by-step under formation of reactive polymers or polymer networks. Multifunctional cross-linking vinylcyclopropanes can be used as new low-shrinking matrix monomers for photopolymerizable materials. In addition, the sol-gel process of trialkoxysilyl-functionalized vinylcyclopropanes affords low shrinking organic-inorganic nanocomposites.

Formation of Nitrile Ylide by Addition of Carbene with Acetonitrile in a Low-Temperature Argon Matrix

After the photoirradiation of (biphenyl-4-yl)chlorodiazirine (BCD) in ca. 10 K argon (Ar) matrices, the IR spectrum of (biphenyl-4-yl)chlorocarbene (BCC) was measured because the measured bands were in fair agreement with the bands obtained by vibration analysis. The photolyses of BCD−acetonitrile (MeCN)−Ar tricomponent matrices were also carried out to study the reaction of BCC with MeCN. For [MeCN]/ [BCD] > 10, a spectrum that differed from BCC was obtained after the irradiation. The new bands are stable during the irradiation, during increasing temperature (to 45 K), and during storage. An 2-azonia-1-allenide type nitrile ylide (NY) structure was obtained in an optimization. Because the measured bands are in good agreement with those calculated using the vibration analysis for this NY structure, BCC adducts with MeCN immediately after the degradation of BCD.

Synthesis and polymerization of vinylcyclopropanes

Vinylcyclopropanes are important synthetic intermediates in organic chemistry and are mostly synthesized by the simultaneous introduction of the cyclopropane and the vinyl unit, e. g., by the reaction of trans-1,4-dihalobutenes with β-dicarbonyl compounds or the addition of carbenes to dienes. The polymerization of vinylcyclopropane itself results in vinyl polymers with predominantly 1,2-structural units. The radical polymerization of substituted vinylcyclopropanes results in polymers with mainly 1,5-ring-opened units, whereby radical stabilizing substituents or electron-withdrawing groups increase the radical polymerizability and the ring-opening ability. The vinylcyclopropanes undergo a radical copolymerization with other vinyl monomers, such as methacrylates, and, in comparison to the polymerization of these linear vinyl monomers, the vinylcyclopropanes show a significantly lower volume shrinkage during ring-opening polymerization. Hybrid vinylcyclopropanes are polymerized step-by-step under formation of reactive polymers or polymer networks. Multifunctional cross-linking vinylcyclopropanes can be used as new low-shrinking matrix monomers for photopolymerizable materials. In addition, the sol-gel process of trialkoxysilyl-functionalized vinylcyclopropanes affords low shrinking organic-inorganic nanocomposites.

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...

Tandem Cyclizations Involving Carbene as an Intermediate: Photochemical Reactions of Substituted 1,2-Diketones Conjugated with Ene-Yne

We have investigated photoreactions of a novel system in which a carbene generator and a carbene trap are contained in the same molecule for studying tandem cyclizations involving carbene. The photocyclization of 1,2-diketones conjugated with ene-yne to (2-furyl)carbene was employed as a carbene-generating system. Upon photoirradiation of 1,2-diketones possessing biphenyl and 2-acetyl-1-cyclopentenyl systems as a carbene trapping unit in aprotic solvents, we observed tandem cyclizations via a carbene intermediate to produce fluorenylfuran and bifuran derivative with nearly quantitative yield, respectively. The solvent dependency for the tandem cyclization clearly indicated that 1,2-diketone is equilibrated with (2-furyl)carbene under the steady state photoirradiation conditions. The results reported here indicated that such compounds containing a carbene generator and a trap within a molecule are extremely useful for studying the sequential carbene addition reaction.

ChemInform Abstract: Macrocyclic Cyclopropenes by Highly Enantioselective Intramolecular Addition of Metal Carbenes to Alkynes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Metal complexes of biologically important ligands, CXVI. Addition of carbanions from barbituric acid derivatives to unsaturated hydrocarbons in cationic complexes for the organometallic labelling of barbituric acid

The addition of the anion of 1,3,5-trimethyl-2-thiobarbituric acid 1 to π-bonded unsaturated hydrocarbons (olefin, cyclohexadienyl, cycloheptadienyl, cycloheptatrienyl) in cationic complexes of rhenium, iron, ruthenium and chromium provides a method for the introduction of organometallic fragments into the barbituric acid moiety. Substitution of the C-5-hydrogen atom gives the complexes 4–9. The dianions of 1,3-dimethylbarbituric acid 2 and 1,3-dimethyl-2-thiobarbituric acid 3 yield the bimetallic complexes 10–15. The structures of 10, 11 and 13 were determined by X-ray diffraction. Due to the protection of the N-atom there was no self-assembly via hydrogen bonds. The complexes may be useful as covalent markers for barbiturate drugs in carbonyl metalloimmunoassays.

Asymmetric synthesis of chiral amines by highly diastereoselective 1,2-additions of organometallic reagents to N- tert-butanesulfinyl imines

High yielding and highly diastereoselective methods for 1,2-additions of organometallic reagents to N- tert-butanesulfinyl aldimines ( 2) and N- tert-butanesulfinyl ketimines ( 3) are described. The additions of alkyl, aryl, alkenyl, and allyl carbanions to a diverse set of imines with different steric and electronic properties are demonstrated. Acidic methanolysis of the sulfinamide products ( 4 and 6) delivers highly enantioenriched α-branched and α,α-dibranched amines. Since a broad range of sulfinyl imines are easily accessible from aldehydes and ketones, a wide variety of enantioentriched amines may be prepared.

Geodesic polyarenes with exposed concave surfaces

Abstract

Macrocyclic Cyclopropenes by Highly Enantioselective Intramolecular Addition of Metal Carbenes to Alkynes.

The intramolecular addition of a diazo ester group to a triple bond in the presence of chiral dirhodium(II) carboxamidate catalysts gives macrocyclic lactones with a fused cycloproprene ring [Eq. (a)]. This efficient reaction is characterized by high enantiocontrol (up to 98% ee) and chemoselectivity.

Addition of Stabilized Carbanions to Cationic (η6-Arene)tricarbonylmanganese Complexes: Syntheses of Homo (Mn–Mn) and Hetero (Mn–Cr) Dinuclear Complexes

The reaction of secondary α-cyano or α-sulfonyl carbanions with cationic (η6-arene)tricarbonylmanganese complexes affords neutral mono- and dinuclear tricarbonyl(η5-cyclohexadienyl)manganese complexes. The X-ray analyses of three (η5-cyclohexadienyl)Mn complexes (two mononuclear and one dinuclear) obtained by addition of α-cyano carbanion to cationic (η6-arene)manganese complexes are reported. The addition of benzylic carbanions of (η6-arene)tricarbonylchromium complexes to cationic (η6-arene)manganese complexes gives rise to the formation of the corresponding heterodinuclear [(η5-cyclohexadienyl)manganese–(η6-arene)chromium] complexes.

Formation of nitrile ylides in the addition of singlet carbene to nitrile compounds—laser flash photolysis of (biphenyl-4-yl)chlorodiazirine in the presence of nitrile compounds

Formation of a nitrile ylide (NY) by addition of a singlet carbene to a nitrile compound was studied by laser flash photolysis (LFP) of (biphenyl-4-yl)chlorodiazirine (BCD) in the presence of nitrile compounds. Although the generated (biphenyl-4-yl)chlorocarbene (BCC) forms a NY by addition to a nitrile compound in an equilibrium reaction, the absorption spectrum of the NY can be measured only in the LFP of BCD in the presence of 2,4,6-trimethoxybenzonitrile. The equilibrium constants for the NY formation in the addition of BCC to propiononitrile or pivalonitrile were determined to be 0.45 and 0.37 M–1 at 295 K, respectively. The reactivity of NY towards olefins seems to be substantially lower than those of BCC. The reaction of BCC with 2,3-dimethylbut-2-ene was carried out in 2,2,4-trimethylpentane and propionitrile in the temperature range of ca. 170 to 300 K. In both solvents, the rate constants increased with decreasing temperature and the maximum value appeared at around 210 K. Using the difference in the rate constants, the free energy difference for the equilibrium constant was also estimated to be ca. 4.2 kJ mol–1.

ChemInform Abstract: A Novel Synthesis of Functionalized Aldehyde Equivalents Through Addition of Carbanions on Δ2‐Oxazolinium Cations.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Fused bicyclic vinylcyclopropanes from intramolecular alkylidene carbene-alkene additions

A double bond migration driven by the high strain energy of endocyclic methylenecyclopropane-containing fused bicyclic systems is proposed to explain the formation of azabicyclo[3.1.0]hexanes from the intramolecular addition of alkylidene carbenes to alkenes.

A novel synthesis of functionalized aldehyde equivalents through addition of carbanions on Δ2-oxazolinium cations

Bis- and mono carbanions add at C-2 of Δ 2-oxazolinium cations to furnish novel oxazolidines existing mainly as their unprecedented enamine chain tautomers.

Michael Additions of Benzotriazole-Stabilized Carbanions. A Review

The 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors is reviewed. The selectivity between 1,4- and 1,2-addition depends significantly on the electronic effect of the carbanion (usually lithium is the counterion), the type of the Michael acceptor, and steric effects. Steric hindrance of the benzotriazolyl group probably enhances the regioselectivity. Normally, 1,4-additions to α,β-unsaturated ketone or ester are observed for carbanions stabilized by a benzotriazolyl group and an electron-withdrawing group (e.g. aryl, vinyl, carbonyl). For α,β-unsaturated aldehydes as Michael acceptors, 1,2-addition is more likely, except where electronic effects are very strong. A review with 39 references.

Nucleic Acid Analogs with Constraint Conformational Flexibility in the Sugar‐Phosphate Backbone “Tricyclo‐DNA”. Part 1. Preparation of [(5′R,6′R)‐2′‐deoxy‐3′,5′‐ethano‐5′,6′‐methano‐β‐D‐ribofuranosyl]thymine and ‐adenine, and the corresponding phosphoramidites for oligonucleotide synthesis

AbstractThe synthesis of the tricyclo‐deoxynucleoside analogs 1 and 2 and of the corresponding cyanoethyl phosphoramidite building blocks 16 and 21 for oligonucleotide synthesis is described. These tricyclic deoxynucleoside analogs differ from the recently introduced bicyclo‐deoxynucleosides by an additional cyclopropane unit joined to the centers C(5′) and C(6′) of the latter (se Fig. 1), and thus represent a further member of the class of nucleoside analogs with constraint conformational flexibility. The synthesis of the tricyclo‐deoxynucleoside was achieved by a diastereoselective carbene addition to the enantiomerically pure silyl enol either 8/9 and a Vorbrüggen condensation of the tricyclic carbohydrate unit 10/11 with in situ persilylated thymine and N6‐benzoyladenine. Selective tritylation of the tertiary OHC(5′) and phosphinylation of OHC(3′) of 1 and 2 afforded the corresponding phosphoramidites 16 and 21. The ‘exo’‐configuration of the newly introduced cyclopropane ring was confirmed by 1H‐NMR‐NOE spectroscoy. The α‐D‐ and β‐D‐configuration at C(1′) of the nucleoside analogs 1 and 14 (2 and 19, resp.) was assigned by 1H‐NMR‐NOE spectroscopy and NOESY. Modeling studies of the β‐D‐anomeric nucleoside analog 1 indicate a preference for the 2′‐endo‐conformation of the furanose ring and a partial correction of the torsion angle γ to the anti‐clinal range compared to bicyclo‐deoxynucleosides.

ChemInform Abstract: Bicyclo(3.3.1)nonanes as Synthetic Intermediates. Part 23. A Breakthrough by Lanthanoid Mediation in Nucleophilic Addition of Carbanions to the inert “Fork Head” Carbonyl in Bicyclo(3.3.1)nonan‐3‐ ones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Bicyclo[3.3.1]nonanes as Synthetic Intermediates. XXIII.1 A Breakthrough by Lanthanoid Mediation in Nucleophilic Addition of Carbanions to the Inert “Fork Head” Carbonyl in Bicyclo[3.3.1]nonan-3-ones

Owing to the “backside steric hindrance”, the ‘fork head ketone’ (C-3 ketone) in bicyclo[3.3.1]nonan-3-ones is quite inactive against a nucleophilic attack of several kinds of organometallic reagents. Organocerium reagents and samarium iodide / organohalides turned out to react with the fork head ketone to afford the corresponding adducts efficiently.