Cycloaddition Of Diazoalkanes Research Articles

One-Bond-Nucleophilicity and -Electrophilicity Parameters: An Efficient Ordering System for 1,3-Dipolar Cycloadditions.

Diazoalkanes are ambiphilic 1,3-dipoles that undergo fast Huisgen cycloadditions with both electron-rich and electron-poor dipolarophiles but react slowly with alkenes of low polarity. Frontier molecular orbital (FMO) theory considering the 3-center-4-electron π-system of the propargyl fragment of diazoalkanes is commonly applied to rationalize these reactivity trends. However, we recently found that a change in the mechanism from cycloadditions to azo couplings takes place due to the existence of a previously overlooked lower-lying unoccupied molecular orbital. We now propose an alternative approach to analyze 1,3-dipolar cycloaddition reactions, which relies on the linear free energy relationship lg k2(20 °C) = sN(N + E) (eq 1) with two solvent-dependent parameters (N, sN) to characterize nucleophiles and one parameter (E) for electrophiles. Rate constants for the cycloadditions of diazoalkanes with dipolarophiles were measured and compared with those calculated for the formation of zwitterions by eq 1. The difference between experimental and predicted Gibbs energies of activation is interpreted as the energy of concert, i.e., the stabilization of the transition states by the concerted formation of two new bonds. By linking the plot of lg k2 vs N for nucleophilic dipolarophiles with that of lg k2 vs E for electrophilic dipolarophiles, one obtains V-shaped plots which provide absolute rate constants for the stepwise reactions on the borderlines. These plots furthermore predict relative reactivities of dipolarophiles in concerted, highly asynchronous cycloadditions more precisely than the classical correlations of rate constants with FMO energies or ionization potentials. DFT calculations using the SMD solvent model confirm these interpretations.

An Overlooked Pathway in 1,3-Dipolar Cycloadditions of Diazoalkanes with Enamines.

Methyl diazoacetate reacts with 1‐(N‐pyrrolidino)cycloalkenes to give products of 1,3‐dipolar cycloadditions and azo couplings. The kinetics and mechanisms of these reactions were investigated by NMR spectroscopy and DFT calculations. Orthogonal π‐systems in the 1,3‐dipoles of the propargyl‐allenyl type allow for two separate reaction pathways for the (3+2)‐cycloadditions. The commonly considered concerted pathway is rationalized by the interaction of the enamine HOMO with LUMO+1, the lowest unoccupied orbital of the heteropropargyl anion fragment of methyl diazoacetate. We show that HOMO/LUMO(π*N=N) interactions between enamines and methyl diazoacetate open a previously unrecognized reaction path for stepwise cycloadditions through zwitterionic intermediates with barriers approximately 40 kJ mol−1 lower in energy in CHCl3 (DFT calculations) than for the concerted path.

Ein übersehener Reaktionsweg bei 1,3‐dipolaren Cycloadditionen von Diazoalkanen mit Enaminen

AbstractMethyldiazoacetat reagiert mit 1‐(N‐Pyrrolidino)‐cycloalkenen sowohl zu Produkten aus 1,3‐dipolaren Cycloadditionen als auch aus Azokupplungen. Die Kinetik und der Mechanismus dieser Reaktionen wurden durch NMR‐Spektroskopie und DFT‐Rechnungen untersucht. Die beiden orthogonalen π‐Systeme in 1,3‐Dipolen vom Propargyl‐Allenyl Typ ermöglichen zwei getrennte Reaktionswege für (3+2)‐Cycloadditionen. Der üblicherweise betrachtete konzertierte Reaktionsweg wird durch die Wechselwirkung des Enamin‐HOMOs mit dem niedrigsten unbesetzten Orbital des Heteropropargylanion‐Fragments (LUMO+1) von Methyldiazoacetat, erklärt. Wir zeigen nun, dass HOMO/LUMO(π*N=N)‐Wechselwirkungen zwischen Enaminen und Methyldiazoacetat bisher nicht beachtete Reaktionswege stufenweiser Cycloadditionen über zwitterionische Intermediate ermöglichen. Nach DFT‐Rechnungen sind deren Barrieren in CHCl3 um 40 kJ mol−1 niedriger als für den konzertierten Reaktionsweg.

Catalytic cycloaddition of diazoalkanes with heterocyclic substituents to fullerene C60

Methanofullerenes were directly synthesized under mild conditions by cycloaddition to fullerene C60 of diazoalkanes generated in situ by oxidation of ketone hydrazones containing a heterocyclic fragment with manganese(IV) oxide in the presence of the catalytic system Pd(acac)2-2 PPh3-4 Et3Al.

1,3-Dipolar cycloaddition of diazoalkanes onto dimethyl 1-(formylamino)ethylenephosphonate: a new route to 1-aminocyclopropanephosphonic acids and 3-phosphorylated pyrazoles

Diazoalkanes regiospecifically react with dimethyl 1-(formylamino)ethylenephosphonate ( 1a) to afford 5-substituted dimethyl 3-(formylamino)-4,5-dihydro-3 H-pyrazol-3-phosphonates 2 in high yields. Their thermal decomposition followed by hydrolysis provides a straightforward access to 2-substituted 1-aminocyclopropanephosphonic acids 4. Aromatization of 2 under acidic conditions leads to 3-phosphorylated pyrazoles 5.

Catalytic cycloaddition of diazoalkanes to fullerene C60

Cycloaddition to fullerene C60 of monosubstituted diazomethanes generated in situ by oxidation of aldehyde hydrazones in the presence of Pd(acac)2-2 PPh3-4 Et3Al as catalytic system resulted in selective formation of homofullerenes in which the alkyl substituent is located above the plane of the five-membered ring in C60. Under analogous conditions, unsymmetrical disubstituted diazomethanes generated from the corresponding ketone hydrazones gave rise to mixtures of stereoisomeric 5,6-open adducts.

ChemInform Abstract: 1,3-Dipolar Cycloadditions of Diazoalkanes to Pyridazine Derivatives. Thermal 1,5-Sigmatropic Rearrangement of Methyl Groups in 3,3-Dimethyl- 3H-pyrazolo(3,4-d)pyridazine Derivatives.

Thermal 1,5-sigmatropic rearrangements of one of the methyl group attached at position 3 of 3,3-dimethyl-3H-pyrazolo[3,4-d]pyridazin-4(5H)-ones 1-3 taking place either in a clock-wise or anti-clockwise direction gave N 2 -methylated products 4-6 and C 3a -methylated products 7-9. The -7(6)-one derivative 10 and -4,7(5H,6H)-dione derivative 12 gave only N 2 -methylated products 11 and 13 respectively, and 1,2-dihydro derivative 14 produced after elimination of methane, 15.

ChemInform Abstract: Stereoselective Synthesis of Pyrazoline Derivatives by 1,3-Dipolar Cycloaddition of Diazoalkanes to α,β-Unsaturated Carbonyl Derivatives of Sugars.

New pyrazoline acyclonucleosides have been prepared by 1,3-dipolar cycloaddition reactions of diazoalkanes to derivatives of d-galacto-oct-2-enonate and d-galacto-non-3-enulose. The reactions were highly regio- and stereo-selective, and single isomers were obtained in good yields. A tautomeric equilibrium between the 1- and 2-pyrazoline structures was observed for some of the isomers in solution.

Catalytic cycloaddition of diazoalkanes generated in situ to fullerene C60

Catalytic cycloaddition of diazoalkanes generated in situ to fullerene C60

2 + 3]‐Cycloadditions of Diazoalkanes with Imines of Hexafluoroacetone and Chloral.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

2+3]-Cycloadditions of diazoalkanes with imines of hexafluoroacetone and chloral

The reactions of N-arylimines 1 and 2 of hexafluoroacetone and chloral, respectively, with diazoalkanes at –60°C to room temperature led to the corresponding 4,5-dihydro-1H-[1,2,3]triazoles 4 and 5, respectively, in a regioselective [2+3]-cycloaddition. The structure of one example in each case has been established by X-ray crystallography. The thermal decomposition of these adducts yielded the corresponding aziridines, bearing two trifluoromethyl and one trichloromethyl group, respectively, at C(2).

Aza analogs of kainoids by dipolar cycloaddition

The 1,3-dipolar cycloadditions of diazoalkanes with trans-diethyl glutaconate yield 1-pyrazolines, which isomerize to 2-pyrazolines or are oxidized to pyrazoles. The 2-pyrazolines may serve as precursors to novel glutamate analogs or aza analogs of kainoids. The regioselectivity of the 1,3-dipolar cycloadditions of diazoalkanes and trans-diethyl glutaconate and isomerization of the 1-pyrazolines to 2-pyrazolines are evaluated.

A theoretical approach to the regioselectivity in 1,3‐dipolar cycloadditions of diazoalkanes, hydrazoic acid and nitrous oxide to acetylenes, phosphaalkynes and cyanides

AbstractThe 1,3‐dipolar cycloadditions of diazoalkanes (R2CNN), hydrazoic acid (HNNN) and nitrous oxide (N2O) to some simple dipolarophiles such as acetylenes, phosphaalkynes and cyanides were studied using quantum chemical calculations at the B3LYP/6–311++G(d,p) level and, in the simplest case, using also the CCSD(T) method. Along with frontier molecular orbital coefficients, the local softness being a DFT‐based reactivity criterion is established as a useful tool to predict the regioselectivity in these cycloaddition reactions. Copyright © 2003 John Wiley & Sons, Ltd.

1,3-Dipolar cycloaddition of diazoalkanes to racemic and optically active α-(diethoxyphosphoryl)vinyl p-tolyl sulfoxides: a new synthesis of 3-phosphorylpyrazoles and asymmetric synthesis of cyclopropanes

Cycloaddition of diazomethane and ethyl diazoacetate to α-(diethoxyphosphoryl)vinyl p-tolyl sulfoxide 1a and its β-substituted analogues (Me, Ph) results in the formation of 3-phosphoryl-pyrazoles in high yield. The reaction ofchiral ( S)-(+)- 1a with diphenyldiazomethane proceeds fully diastereoselectively to give the corresponding cyclopropane (+)- 6a with the ( S c, S S) configuration determined by X-ray diffraction analysis. Diazopropane reacts with ( S)-(+)- 1a to give only one diastereoisomer of the pyrazoline cycloadduct (+)- 2e which undergoes decomposition to the cyclopropane (+)- 6b with preservation of configurational integrity.

ChemInform Abstract: 1,3‐Dipolar Cycloadditions of Diazoalkanes to Pyridazines. Asymmetric 1,3‐Dipolar Cycloaddition of Azomethine Imines Derived from Diazoalkane—Pyridazine Cycloadducts

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.

1,3‐Dipolar cycloadditions of diazoalkanes to pyridazines. Asymmetric 1,3‐dipolar cycloadditon of azomethine imines derived from diazoalkane‐pyridazine cycloadducts

1,3‐Dipolar cycloadditions of diazoalkanes to pyridazines. Asymmetric 1,3‐dipolar cycloadditon of azomethine imines derived from diazoalkane‐pyridazine cycloadducts

ChemInform Abstract: Reactions of Complex Ligands. Part 78. [2 + 1] Cycloadditions of Diazoalkanes to Enol Ethers Catalyzed by Chromium Complexes — The First Direct Spectroscopic Observation of a Carbene Complex Intermediate.

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.

2+1] Cycloadditions of Diazoalkanes to Enol Ethers Catalyzed by Chromium Complexes—The First Direct Spectroscopic Observation of a Carbene Complex Intermediate

2+1] Cycloadditions of Diazoalkanes to Enol Ethers Catalyzed by Chromium Complexes—The First Direct Spectroscopic Observation of a Carbene Complex Intermediate

ChemInform Abstract: Cycloaddition of Diazoalkanes to Methyl Acetyloxyimino(cyano)acetate: Formation of Imines by (3,3)‐Sigmatropic Transposition.

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.

Stereoselective 1,3-dipolar cycloadditions of nitrile oxides to sugar olefins. Synthesis of acyclic-sugar isoxazoline C-nucleoside analogs

The cycloaddition 1,3-dipolar of nitrile oxides to sugar nitro olefins and α,β-unsaturated carbonyl olefins has been investigated. The reaction is less regioselective that the cycloaddition of diazoalkanes to the same olefins and while nitrile oxides with bulky substituents afford the sterically less hindered cycloadducts, other nitrile oxides yield a mixture of the two possible regioisomers. However, the reactions seem to be highly stereoselective and single diastereomers were obtained in all the cases studied.