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Intramolecular Cyclization of Vinyldiazoacetates as a Versatile Route to Substituted Pyrazoles

Denis Drikermann, Valerie Kerndl, Helmar Görls, Ivan Vilotijevic*

*Friedrich-Schiller-University Jena, Institute of Organic and Macromolecular Chemistry, Humboldtstraße 10, 07743 Jena, Germany, Email: ivan.vilotijevicuni-jena.de

D. Drikermann, V. Kerndl, H. Görls, I. Vilotijevic, Synlett, 2020, 31, 1158-1162.

DOI: 10.1055/s-0040-1707111



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Abstract

Vinyldiazo compounds undergo a thermal electrocyclization to form pyrazoles in good yields. These catalyst-free reactions are operationally simple, use readily available starting materials, and enable the synthesis of mono-, di- and tri-substituted pyrazoles.

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Details

The document discusses the intramolecular cyclization of vinyldiazoacetates as a method to synthesize substituted pyrazoles. This process is efficient, yielding up to 95% and does not require a catalyst. The method allows for the creation of mono-, di-, and tri-substituted pyrazoles, which are valuable in various industries due to their biological activities. The study, conducted by researchers at Friedrich-Schiller-University Jena, optimized reaction conditions, finding that polar, aprotic solvents like trifluorotoluene provided the best yields. The vinyldiazoacetates were prepared via Regitz diazo transfer, and the reaction scope included various aryl and alkyl substituents. The method was effective for both electron-rich and electron-deficient substituents, although steric hindrance affected yields. The study also explored the use of different electron-withdrawing groups, finding that esters, carboxylic acids, and ketones were suitable. The research was funded by several institutions, including the Carl-Zeiss-Stiftung and the European Regional Development Fund. The findings offer a new, operationally simple route to synthesize highly substituted pyrazoles, which are significant in the chemical, agricultural, and pharmaceutical industries.


Key Words

pyrazoles, vinyldiazoacetates, vinyldiazo compounds, cyclization, electrocyclization


ID: J72-Y2020