A new and direct route to 3-fluoromethyl substituted pyrazol-4-acrylates via Pd-catalyzed C–H activation
摘要:
Direct C4-H activation of 3-fluoromethyl pyrazoles followed by an oxidative coupling with acrylates, which is perhaps the most direct method for the synthesis of 3-fluoromethyl substituted pyrazol-4-aciylates of biological interest, remains challenging. Here, the first example of the straightforward olefination via Pd-catalyzed C4-H activation of both C3-CF3 and C3-CF2H substituted pyrazoles is reported. The reaction of various C3-CF3 substituted pyrazoles with acrylates proceeds smoothly in the presence of Pd(OAc)(2) and Ag2CO3, whereas olefination of C3-CF2H substituted pyrazoles requires the addition of benzoquinone. A further computational study reveals that reactivity of the pyrazolyl substrates employed are strongly impacted by the substituents of different nature on their C1 or C5 position, which is in good agreement with the experimental data. (C) 2013 Elsevier Ltd. All rights reserved.
Palladium-Catalyzed Coupling of Pyrazole Triflates with Arylboronic Acids
摘要:
A general protocol for the palladium-mediated Suzuki coupling reaction of pyrazole triflates and aryl boronic acids has been developed. The use of additional dppf ligand was determined to increase product yields allowing for the use of a broad range of reaction substrates.
Ambident polyfluoroalkyl-substituted pyrazoles in the methylation reactions
作者:Anna E. Ivanova、Yanina V. Burgart、Viktor I. Saloutin、Pavel A. Slepukhin、Sophia S. Borisevich、Sergey L. Khursan
DOI:10.1016/j.jfluchem.2017.01.009
日期:2017.3
good regioselectivity in the methylation of polyfluoroalkylpyrazoles was reached while varying the reaction conditions. Under basic conditions, methylation of such pyrazoles led to the preferred formation of 3-RF-pyrazoles, whereas the use of dimethyl sulfate in the absence of a base resulted in the predominant formation of 5-RF-pyrazoles. A proposed mechanism of methylation was discussed.
Improved Regioselectivity in Pyrazole Formation through the Use of Fluorinated Alcohols as Solvents: Synthesis and Biological Activity of Fluorinated Tebufenpyrad Analogs
作者:Santos Fustero、Raquel Román、Juan F. Sanz-Cervera、Antonio Simón-Fuentes、Ana C. Cuñat、Salvador Villanova、Marcelo Murguía
DOI:10.1021/jo800251g
日期:2008.5.1
The preparation of N-methylpyrazoles is usually accomplished through reaction of a suitable 1,3-diketone with methylhydrazine in ethanol as the solvent. This strategy, however, leads to the formation of regioisomeric mixtures of N-methylpyrazoles, which sometimes are difficult to separate. We have determined that the use of fluorinated alcohols such as 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as solvents dramatically increases the regioselectivity in the pyrazole formation, and we have used this modification in a straightforward synthesis of fluorinated analogs of Tebufenpyrad with acaricide activity.