Boron-trihalide-promoted regioselective ring-opening reactions of gem-difluorocyclopropyl ketones

Reversal of the Regioselectivity of Iron-Promoted Hydrogenation and Hydrohalogenation of gem-Difluoroalkenes

The reaction regioselectivity of gem-difluoroalkenes is dependent on the intrinsic polarity. Thus, the reversal of the regioselectivity of the addition reaction of gem-difluoroalkenes remains a formidable challenge. Herein, we described an unprecedented reversal of regioselectivity of hydrogen atom transfer (HAT) to gem-difluoroalkenes triggered by Fe-H species for the formation of difluoroalkyl radicals. Hydrogenation of the in situ generated radicals gave difluoromethylated products. Mechanism experiments and theoretical studies revealed that the kinetic effect of the irreversible HAT process resulted in the reversal of the regioselectivity of this scenario, leading to the formation of a less stable α-difluoroalkyl radical regioisomer. On basis of this new reaction of gem-difluoroalkene, the iron-promoted hydrohalogenation of gem-difluoroalkenes for the efficient synthesis of aliphatic chlorodifluoromethyl-, bromodifluoromethyl- and iododifluoromethyl-containing compounds was developed. Particularly, this novel hydrohalogenation of gem-difluoroalkenes provided an effect and large-scale access to various iododifluoromethylated compounds of high value for synthetic application.

Palladium-catalyzed stereoselective ring-opening reaction of aryl cyclopropyl ketones

Herein, we report that α,β-unsaturated ketones could be obtained by palladium-catalyzed ring-opening of mono-substituted cyclopropyl ketones efficiently and systematically. (E)-1-Arylbut-2-en-1-ones were generated from aryl cyclopropyl ketones stereoselectively in yields of 23-89% by the Pd(OAc)₂/PCy₃ catalytic system. The reaction exhibited stereoselectivity (only E products were found) and was suitable for both phenyl and heteroaryl cyclopropyl ketones.

Nucleophilic Substitution of Selenosulfonates with Me3SiCF2Br: Facile and Efficient Access to Bromodifluoromethylated Selenides under Metal-Free Conditions

A facile synthesis of bromodifluoromethylated selenides under metal-free conditions is described here. Commercially available Me₃SiCF₂Br and bench-stable selenosulfonates react smoothly to give a broad scope of alkyl- and aryl-substituted bromodifluoromethylated selenides in moderate to good yields via a difluorocarbene intermediate. This protocol features a short reaction time, the absence of toxic waste, good scalability, and successful late-stage modification of bioactive molecules. In addition, the title products can be easily converted to different fluorinated and ¹⁸F-labeled selenides.

The preparation and properties of 1,1-difluorocyclopropane derivatives

Recently, the functionalization of organic molecules with fluorine substituents has grown rapidly due to its applications in such fields as medicine, agriculture or materials sciences. The aim of this article is to review the importance of 1,1-difluorocyclopropane derivatives in synthesis. It will examine the role of the fluorine substituents in both ring-forming and ring-opening reactions, as well as methods for obtaining difluorocyclopropanes as single enantiomers. Several examples are provided to highlight the biological importance of this class of compounds.

Visible-Light-Promoted Regioselective 1,3-Fluoroallylation of gem-Difluorocyclopropanes

A strategically novel protocol for ring-opening functionalization of aryl gem-difluorocyclopropanes (F₂CPs), which allows an expedient construction of CF₃-containing architectures via visible-light-promoted F-nucleophilic attack manifold, was disclosed. Single electron oxidation of F₂CPs was ascribed as the critical step for the success of this transformation by prompting F-nucleophilic attack, as well as the ensuing C-C bond scission. The observed intriguing regioselectivity for fluoroincorporation in this reaction was rationalized by invoking the cation-stabilization property of gem-difluorine substituents and also the thermodynamic gains acquired from forming CF₃ functionality. By using cost-effective fluorination reagent and readily available substrates, a broad collection of structurally diversified α-allyl-β-trifluoromethyl ethylbenzene derivatives could be obtained in generally good yields. Further mechanistic investigations proved the engagement of a benzylic radical intermediate in this transformation.

Two-step conversion of carboxylic esters into distally fluorinated ketones via ring cleavage of cyclopropanol intermediates: application of sulfinate salts as fluoroalkylating reagents

Tertiary cyclopropanols easily available from carboxylic esters have been used in the synthesis of distally fluorinated ketones. Cyclopropane ring cleavage reactions in methanol with aqueous tert-butyl hydroperoxide in the presence of a copper(ii) acetate catalyst and sodium triflinate (Langlois reagent) afford β-trifluoromethyl ketones in 16-74% isolated yields. Sodium triflinate serves as a precursor of reactive trifluoromethyl copper species, enabling ring-opening trifluoromethylation, as evidenced by mechanistic studies. We also demonstrate here that other sulfinate salts, such as sodium 1,1-difluoroethanesulfinate, sodium 2-(4-bromophenyl)-1,1-difluoroethanesulfinate and sodium 1-(trifluoromethyl)cyclopropanesulfinate, can be used as fluoroalkylation reagents, resulting in the corresponding fluorinated ketones.

Simple access to β-trifluoromethyl-substituted ketones via copper-catalyzed ring-opening trifluoromethylation of substituted cyclopropanols

Tertiary cyclopropanols react rapidly with Togni reagent in methanol at room temperature in the presence of catalytic amounts (3 mol%) of CuCl affording β-trifluoromethyl ketones in 65-73% isolated yields. Ring opening in 1,2-dialkylsubstituted cyclopropanols gives a mixture of isomeric β-trifluoromethyl ketones in about 50% combined yield.

Visible light-induced selective hydrobromodifluoromethylation of alkenes with dibromodifluoromethane

A visible light-induced selective hydrobromodifluoromethylation of alkenes using CF2Br2 was developed. This transformation proceeded smoothly in the presence of catalytic eosin Y at room temperature to give various hydrobromodifluoromethylated compounds with broad functional group tolerance.