Fluoroalkynes

Fluoroalkynes

Introduction

Fluoroalkynes are a class of dienophiles and dipoleophiles. They can be used as building blocks for the synthesis of fluorine-containing organic compounds. Fluoroalkynes can produce various metallated fluorine-containing alkenes through hydrometallation reactions. They can also synthesize organic compounds such as enamines and enesters through oxa-addition reactions or aza-addition reactions with various substrates. In addition, fluoroalkynes can also prepare a single cycloaddition product and various fluorine-containing heterocyclic compounds.

Synthesis

Fluoroalkynes are a class of structurally simple and efficient synthetic building blocks in organofluorine chemistry. They can easily and efficiently produce organic fluorides through addition reactions with metallic reagents. For example, Konno's group synthesized metallated fluorine-containing alkenes starting from various fluoroalkynes with Et₃SiH. In the presence of a catalytic amount of Co₂(CO)₈ at the reflux temperature of dichloroethane, the reaction proceeded smoothly to give the corresponding metallated fluorine-containing alkenes in good to high yields^[1].

Fig.1 Synthesis of metallated fluorine-containing alkenes form fluoroalkynes

Fluoroalkynes can also undergo oxa-addition reactions or aza-addition reactions to synthesize enesters or enamine compounds. For example, Kawatsura et al. demonstrated the highly regio- and eselective formation of trifluoromethyl-containing enesters by ruthenium-catalyzed addition of carboxylic acid to trifluoromethyl group substituted unsymmetrical internal alkynes. They used several fluoroalkynes and carboxylic acids to react and provided the desired enesters in good yield^[2]. Trofimov et al. reported the aza-nucleophilic addition reaction of fluoroalkynes and imidazole derivatives under the action of potassium hydroxide, and obtained highly selective enamine addition products in higher yields^[3].

In addition, fluoroalkynes can obtain a single cycloaddition product through the Diels-Alder reaction. For example, the Diels-Alder reaction with perfluorobenzene can introduce a tetrafluorophenyl group into the product to obtain a fluorine-containing polycyclic cycloaddition product. Fluoroalkynes can also undergo a 1,3-dipolar cycloaddition reaction to generate various fluorine-containing heterocyclic compounds such as pyrazoles, isoxazoles, triazoles, etc.

Fig.2 Synthesis of enesters from fluoroalkynes

Fig.3 Synthesis of enamine compounds from fluoroalkynes

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References

1. Konno T; et al. Remarkable access to fluoroalkylated trisubstituted alkenes via highly stereoselective cobalt-catalyzed hydrosilylation reaction of fluoroalkylated alkynes. Org. Biomol. Chem. 2009, 7(6): 1167-1170.
2. Kawatsura M; et al. Ruthenium-catalyzed regio- and stereoselective addition of carboxylic acids to aryl and trifluoromethyl group substituted unsymmetrical internal alkynes. Org. Lett. 2011, 13(12): 3285-3287.
3. Trofimov B. A.; et al. Reaction of imidazole derivatives with trifluoromethylated arylacetylenes. J. Fluorine Chem. 2016, 188: 157-163.