Synthesis of Perfluoroalkyl-Substituted Vinylcyclopropanes by Way of Enhanced Neighboring Group Participation

Dirhodium-Catalyzed Enantioselective Synthesis of Difluoromethylated Cyclopropanes via Enyne Cycloisomerization

(Difluoromethylated cyclopropane represents an important motif, which is widely found in bioactive and functional molecules. Despite significant progress in modern chemistry, the atom-economic and enantioselective synthesis of difluoromethylated cyclopropanes is still challenging. Herein, an Rh2 (II)-catalyzed asymmetric enyne cycloisomerization is described to construct chiral difluoromethylated cyclopropane derivatives with up to 99% yield and 99% ee in low catalyst loading (0.2 mol%), which can be easily transformed into highly functionalized difluoromethylated cyclopropanes with vicinal all-carbon quaternary stereocenters by ozonolysis. Mechanistic studies and the crystal structures of alkyne-dirhodium complexes reveal that the cooperative weak hydrogen bondings between the substrates and the dirhodium catalyst may play key roles in this reaction.).

Taming of Furfurylidenes by Chiral Bismuth-Rhodium Paddlewheel Catalysts. Preparation and Functionalization of Optically Active 1,1-Disubstituted (Trifluoromethyl)cyclopropanes

Although 2-furyl-carbenes (furfurylidenes) are prone to instantaneous electrocyclic ring opening, chiral [BiRh]-paddlewheel complexes empowered by London dispersion allow (trifluoromethyl)furfurylidene metal complexes to be generated from a bench-stable triftosylhydrazone precursor. These reactive intermediates engage in asymmetric [2+1] cycloadditions and hence open entry into valuable trifluoromethylated cyclopropane or -cyclopropene derivatives in optically active form, which are important building blocks for medicinal chemistry but difficult to make otherwise.

Alkyl sulfinates as cross-coupling partners for programmable and stereospecific installation of C(sp3) bioisosteres

In recent years, a variety of cycloalkyl groups with quaternary carbons, in particular cyclopropyl and cyclobutyl trifluoromethyl groups, have emerged as promising bioisosteres in drug-like molecules. The modular installation of such bioisosteres remains challenging to synthetic chemists. Alkyl sulfinate reagents have been developed as radical precursors to prepare functionalized heterocycles with the desired alkyl bioisosteres. However, the innate (radical) reactivity of this transformation poses reactivity and regioselectivity challenges for the functionalization of any aromatic or heteroaromatic scaffold. Here we showcase the ability of alkyl sulfinates to engage in sulfurane-mediated C(sp3)-C(sp2) cross-coupling, thereby allowing for programmable and stereospecific installation of these alkyl bioisosteres. The ability of this method to simplify retrosynthetic analysis is exemplified by the improved synthesis of multiple medicinally relevant scaffolds. Experimental studies and theoretical calculations for the mechanism of this sulfur chemistry reveal a ligand-coupling trend under alkyl Grignard activation via the sulfurane intermediate, stabilized by solvation of tetrahydrofuran.

Sustainable radical approaches for cross electrophile coupling to synthesize trifluoromethyl- and allyl-substituted tert-alcohols

Trifluoromethylated molecules have gained privileged recognition among the medicinal and pharmaceutical chemists. Sustainable photoredox- and electrochemical processes were employed to facilitate the relatively less explored radical cross-electrophile coupling to access trifluoromethyl- and allyl-substituted tert-alcohols. Reactions proceed through trifluoromethyl ketyl radical and allyl radical intermediates, which undergo challenging radical-radical cross-coupling. The developed transformations are mild and chemo-selective to give cross-coupled products and deliver a wide range of valuable trifluoromethyl- and allyl-containing tertiary alcohols. Both processes can also be applied for the synthesis of amine variant containing trifluoromethyl and allyl moiety, which is considered as amide bioisostere.

Mild and Diazo-Free Synthesis of Trifluoromethyl-Cyclopropanes Using Sulfonium Ylides

The synthesis of several 1,1-disubstituted trifluoromethyl-cyclopropanes (TFCPs), known as tert-butyl bioisosteres, has been achieved from the reaction between trifluoromethylalkenes and unstabilized sulfonium ylides in yields of ≤97%. This method offers practical access to this cyclopropyl moiety of pharmacological interest, employing a commercially available reagent at low temperatures. The synthesis of cyclopropanes bearing other electron-withdrawing groups as well as trisubstituted TFCPs was also accomplished.

Synthesis of Vinyl Cyclopropanes via Anion Relay Cyclization

A method where an allyl alcohol is formed from a Tsuji-Trost allylation between a vinyl epoxide and an acyl containing nucleophile is described. Subsequently, a retro-Claisen condensation is utilized as a means of through-space anion relay. The anion relay results in the formation of a reactive carbanion and simultaneously activates an allylic alcohol toward intramolecular Tsuji-Trost cyclopropanation. Hence, in one pot, Tsuji-Trost allylation, retro-Claisen activation, and Tsuji-Trost cyclopropanation are combined to access synthetically useful vinyl cyclopropanes from vinyl epoxides using a mild and operationally simple procedure.

Redox-Neutral Photocatalytic Cyclopropanation via Radical/Polar Crossover

A benchtop stable, bifunctional reagent for the redox-neutral cyclopropanation of olefins has been developed. Triethylammonium bis(catecholato)iodomethylsilicate can be readily prepared on multigram scale. Using this reagent in combination with an organic photocatalyst and visible light, cyclopropanation of an array of olefins, including trifluoromethyl- and pinacolatoboryl-substituted alkenes, can be accomplished in a matter of hours. The reaction is highly tolerant of traditionally reactive functional groups (carboxylic acids, basic heterocycles, alkyl halides, etc.) and permits the chemoselective cyclopropanation of polyolefinated compounds. Mechanistic interrogation revealed that the reaction proceeds via a rapid anionic 3- exo- tet ring closure, a pathway consistent with experimental and computational data.

Difluoromethylcarbene for iron-catalyzed cyclopropanation

Difluoroethylsulfonium salt, Ph₂S⁺CH₂CF₂H OTf^-, was developed into a convenient difluoromethylcarbene reagent for the iron-catalyzed cyclopropanation of terminal olefins, giving various difluoromethyl-cyclopropanes with excellent diastereoselectivities and in high yields.

Rh-Catalyzed arylation of fluorinated ketones with arylboronic acids

The Rh-catalyzed arylation of fluorinated ketones with boronic acids is reported. This efficient process allows access to fluorinated alcohols in high yields under mild conditions. Competition experiments suggest that difluoromethyl ketones are more reactive than trifluoromethyl ketones in this process, despite their decreased electronic activation, an effect we postulate to be steric in origin.

Rhodium catalyzed synthesis of difluoromethyl cyclopropanes

Difluoromethyl-substituted cyclopropanes still remain one of the most challenging class of substrates.