University of PardubiceFaculty of Chemical Technology

University

Employees
|
Students
Česky

Publication detail

A simple new hydrazine-free path leading to persubstituted 1H-pyrazole-3-carboxylates

Authors: Brož Břetislav | Šimůnek Petr

Year: 2012

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	A simple new hydrazine-free path leading to persubstituted 1H-pyrazole-3-carboxylates	Various substances containing 1H‑pyrazole moiety appear to be promising pharmacophores or pesticides. Furthermore, the synthesis of persubstituted pyrazole ring is a complex topic so far. We developed a new method of synthesis of such pyrazoles avoiding the use of appropriate hydrazines proceeding under mild conditions. A simple synthesis of methyl 1,4,5-trisubstitued-1H-pyrazole-3-carboxylates has been optimized. This unusual method is considered to be a useful expansion of known synthetic methods for preparation of this type of substances. The reaction is carried out easily starting from “push-pull“-polarized β-enaminoesters (A). The first step of postulated mechanism is a double azo-coupling with appropriate benzenediazonium-tetrafluoroborates (B). The following step is an intramolecular cyclization with releasing of nitrogen and corresponding arene as a byproduct. Overall reaction yet appears to be basic-catalyzed; selection of the base is the crucial point of the method considering both the yield of reaction and the regioselectivity. The above-mentioned observations have been yet identified as a core of the reaction mechanism, the detailed scheme, however, has yet to be described. Several new challenging persubstituted 1H‑pyrazole derivatives (C) have been prepared this way. The reaction conditions and procedures will be further discussed.	hydrazine-free; 1H-pyrazole-3-carboxylates