Et₃N‐Catalyzed Cycloaddition Reactions of α‐(Trifluoromethyl)styrenes with 2,2,2‐Trifluorodiazoethane to Access Bis(trifluoromethyl)‐Substituted Pyrazolines

Abstract

Main observation and conclusion A novel and practical method for the synthesis of 3,5‐bis(trifluoromethyl)‐4,5‐dihydro‐1H‐pyrazoles by [3+2] cycloaddition reactions of α‐(trifluoromethyl)styrenes with 2,2,2‐trifluorodiazoethane (CF3CHN2) has been developed. The cyclization reaction proceeds smoothly in the presence of a catalytic amount of Et3N, affording a variety of bis(trifluoromethyl)‐substituted 2‐pyrazolines in good to excellent yields. This method also exhibits a broad substrate scope and tolerates various functional groups.

Trifluoromethylated Pyrazoles via Sequential (3 + 2)-Cycloaddition of Fluorinated Nitrile Imines with Chalcones and Solvent-Dependent Deacylative Oxidation Reactions

“…It is also worth noting that the presented protocol nicely supplements previously reported methods for the synthesis of rarely reported bis-trifluoromethylated pyrazoles, which are of interest in the context of not only pharmaceutical applications but also coordination chemistry. 1b , 6d , 18 …”

Solvent-controlled base-free synthesis of bis(trifluoromethyl)-cyclopropanes and -pyrazolines via cycloaddition of 2-trifluoromethyl-1,3-enynes with 2,2,2-trifluorodiazoethane

“…Based on the above experimental results and related literature studies, 11,15–17 a plausible mechanism for the solvent-controlled cycloaddition of 2-trifluoromethyl-1,3-enyne with 2,2,2-trifluorodiazoethane is depicted in Scheme 9. In path 1, heating of 2,2,2-trifluorodiazoethane in non-polar solvents such as DCE provided 2,2,2-trifluoroethyl carbene (CF 3 CH), along with the release of nitrogen.…”

“…We used 1-methoxy-4-(3-(trifluoromethyl)but-3-en-1-yn-1-yl)benzene 1a and CF 3 CHN 2 2 as model reactants for the optimization of the cycloaddition reaction conditions, and the results are shown in Table 1. According to our previous report, 17 the Et 3 N catalyst could accelerate the cycloaddition reaction of CF 3 CHN 2 . Therefore, we initiated our studies by investigating the reactions of 1a with CF 3 CHN 2 2 in the presence of 5 mol% Et 3 N by using 1,2-dichloroethane (DCE) as the solvent.…”

“…16 More recently, we developed a practical method for the synthesis of bis(trifluoromethyl)-substituted pyrazolines by [3 + 2] cycloaddition reactions of α-(trifluoromethyl)styrenes with CF 3 CHN 2 in the presence of a catalytic amount of Et 3 N (Scheme 2e). 17 In this paper, we describe a highly efficient method for the synthesis of bis(trifluoromethyl)cyclopropanes and bis(trifluoromethyl)pyrazolines via the solvent-controlled [2 + 1] or [3 + 2] cycloaddition reaction of 2-trifluoromethyl-1,3-conjugated enynes with CF 3 CHN 2 , respectively (Scheme 2f).…”

The largest Se-4f cluster incorporated polyoxometalate with high Lewis acid–base catalytic activity

“…Therefore, 1-Eu is expected to be a good bifunctional Lewis acid–base catalyst in many catalytic reactions. 14,15 To prove this, 1-Eu was applied to synthesize pyrazoles to evaluate its Lewis acid–base catalytic properties. Pyrazoles are widely used in agricultural and pharmaceutical areas, and they are also known as classical ligands and significant kinds of heterocyclic compounds.…”