Pyrazol aus Acetylen und Diazomethan

Pechmann, H. v.

doi:10.1002/cber.18980310363

Cited by 53 publications

(9 citation statements)

References 1 publication

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“…The latter is also indicated by the shorter C–C bonds compared to the C–N bonds formed in the transition states TS(1e) and TS(1f) . While the (3 + 2) cycloaddition between diazomethane and 2‐butyne ( 1f ) or related alkynes is unknown in the literature (presumably due to the high barriers), the combinations between diazomethane and 1e and 1g proceed slowly at room temperature (50 % after 2 d for 1e ) or at 0 °C (44 % after 1 h for 1g ) …”

Section: Resultsmentioning

confidence: 99%

Regioselective 1,3‐Dipolar Cycloadditions of Diazoalkanes with Heteroatom‐Substituted Alkynes: Theory and Experiment

2018

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The 1,3‐dipolar cycloadditions of diazomethane and diazoethane with methyl 3‐(diethylamino)propiolate were investigated experimentally and computationally by employing density functional theory (DFT). The experiments provided methyl 3‐(diethylamino)‐pyrazole‐4‐carboxylates as the only isolated regioisomers. The constitution of these cycloadducts was secured by independent synthesis and decarboxylation to 3‐(diethylamino)pyrazoles. The calculations fully support the experimental findings. For the preferred pathway of the diazomethane cycloaddition with the alkyne, a kinetic preference of 9.6 kJ mol–1 was calculated in Et2O solution. The computational analysis was extended to other alkynes, for instance to heteroatom‐substituted alkynes such as ethoxyethyne and (ethylthio)ethyne. Again, the calculations nicely explain the switch in regioselectivity of the 1,3‐dipolar cycloadditions of diazomethane with these two alkynes, which has been reported earlier by the group of Arens.

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Section: Resultsmentioning

confidence: 99%

Regioselective 1,3‐Dipolar Cycloadditions of Diazoalkanes with Heteroatom‐Substituted Alkynes: Theory and Experiment

2018

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“…Generated in situ from CaC 2 and water, acetylene can be successfully utilized as a starting material in various nucleophilic addition and cross-coupling reactions giving rise to vinyl ethers, vinyl sulfides, vinyl indoles, enaminones, acetylenic alcohols, and aryl- and diarylacetylenes . Besides, 1,3-dipolar cycloaddition of the calcium carbide-derived acetylene to azides, diazo compounds, and nitrile oxides is possible. Calcium carbide has a number of advantages over the gaseous acetylene, and it is more safe and convenient to handle.…”

Section: Introductionmentioning

confidence: 99%

[3 + 2]-Cycloaddition of in Situ Generated Nitrile Imines and Acetylene for Assembling of 1,3-Disubstituted Pyrazoles with Quantitative Deuterium Labeling

et al. 2018

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A novel synthetic methodology for the preparation of 1,3-disubstituted pyrazoles from in situ generated nitrile imines and acetylene is reported. The reactions are performed in a simple two-chamber reactor. One part of the reactor is loaded with hydrazonoyl chloride precursors of active nitrile imine species and a base. The other part is used to generate acetylene from CaC and water. Partitioning of the reactants improves the yields of desired pyrazoles up to 99% and simplifies their isolation to a simple procedure of solvent evaporation. The approach requires no complex equipment and utilizes inexpensive, safe, and easy to handle calcium carbide as a starting material. A model deuterium incorporation is carried out according to the developed methodology, producing a series of novel 4,5-dideuteropyrazoles with excellent deuterium enrichment. Theoretical calculations on reaction mechanism and characterization of possible intermediate structures were performed.

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“…The 1,3-dipolar cycloaddition of diazomethane and acetylenes was first reported by Pechman [24]. Subsequently, many groups have reported this reaction with symmetrical and unsymmetrical acetylenic compounds resulting in pyrazole derivatives.…”

Section: 3-dipolar Cycloaddition Of Alkynes Andmentioning

confidence: 95%

Synthesis of fluorine containing N‐benzyl‐1,2,3‐triazoles and N‐methyl‐pyrazoles from conjugated alkynes

Rao¹,

Lingaiah²,

Yadla³

et al. 2006

Journal of Heterocyclic Chem

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1, 3‐Dipolar‐cycloaddition reaction of fluoro substituted 3‐aryl‐propynenitriles 1 with benzyl azide 2 afforded the expected 3‐benzyl‐5‐aryl‐3H‐[1,2,3]triazole‐4‐carbonitrile 3 and 1‐benzyl‐5‐aryl‐1H‐[1,2,3]‐triazole‐4‐carbonitrile 4 in good yield. However, 1,3‐dipolar cycloaddition of diazomethane 5 with 3‐aryl‐propynenitriles 1 resulted in the exclusive formation of N‐methyl‐pyrazole derivatives 6 and 7.

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Pyrazol aus Acetylen und Diazomethan

Cited by 53 publications

References 1 publication

Regioselective 1,3‐Dipolar Cycloadditions of Diazoalkanes with Heteroatom‐Substituted Alkynes: Theory and Experiment

Regioselective 1,3‐Dipolar Cycloadditions of Diazoalkanes with Heteroatom‐Substituted Alkynes: Theory and Experiment

[3 + 2]-Cycloaddition of in Situ Generated Nitrile Imines and Acetylene for Assembling of 1,3-Disubstituted Pyrazoles with Quantitative Deuterium Labeling

Synthesis of fluorine containing N‐benzyl‐1,2,3‐triazoles and N‐methyl‐pyrazoles from conjugated alkynes

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