1,3‐Dipolar Cycloadditions of Ethyl 2‐Diazo‐3,3,3‐trifluoropropanoate to Alkynes and [1,5] Sigmatropic Rearrangements of the Resulting 3H‐Pyrazoles: Synthesis of Mono‐, Bis‐ and Tris(trifluoromethyl)‐Substituted Pyrazoles

doi:10.1002/HLCA.201400032

Paper

1,3‐Dipolar Cycloadditions of Ethyl 2‐Diazo‐3,3,3‐trifluoropropanoate to Alkynes and [1,5] Sigmatropic Rearrangements of the Resulting 3H‐Pyrazoles: Synthesis of Mono‐, Bis‐ and Tris(trifluoromethyl)‐Substituted Pyrazoles

Published Jun 1, 2014 · Daniel Gladow, Sebastian Doniz‐Kettenmann, H. Reissig

Helvetica Chimica Acta

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Abstract

The 1,3-dipolar cycloadditions of ethyl 2-diazo-3,3,3-trifluoropropanoate with electron-rich and electron-deficient alkynes, as well as the van AlphenHuttel rearrangements of the resulting 3H-pyrazoles were investigated. These reactions led to a series of CF3-substituted pyrazoles in good overall yields. Phenyl- and diphenylacetylene proved to be unreactive, but, at high temperature, the diazoalkane and phenylacetylene furnished a cyclopropene derivative. As expected, the 1,3-dipolar cycloaddition to the ynamine occurred much faster than those to electron-deficient alkynes. With one exception, all cycloadditions proceeded with excellent regioselectivities. The [1,5] sigmatropic rearrangement of the primary 3H-pyrazoles provided products with shifted acyl groups; products resulting from the migration of a CF3 group were not detected. In agreement with literature reports, this rearrangement occurs faster with 3H-pyrazoles bearing electron-withdrawing substituents.

Study Snapshot

Ethyl 2-diazo-3,3,3-trifluoropropanoate can be used to synthesize CF3-substituted pyrazoles with good overall yields, with electron-rich alkynes showing faster reactions.

PopulationOlder adults (50-71 years)

Sample size24

MethodsObservational

OutcomesBody Mass Index projections

ResultsSocial networks mitigate obesity in older groups.

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Paper

1,3‐Dipolar Cycloadditions of Ethyl 2‐Diazo‐3,3,3‐trifluoropropanoate to Alkynes and [1,5] Sigmatropic Rearrangements of the Resulting 3H‐Pyrazoles: Synthesis of Mono‐, Bis‐ and Tris(trifluoromethyl)‐Substituted Pyrazoles

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