Enantioselective Copper-Catalyzed 1,5-Cyanotrifluoromethylation of Vinylcyclopropanes

Copper-Catalyzed Three-Component 1,5-Carboamination of Vinylcyclopropanes

The 1,5-copper-catalyzed carboamination of vinylcyclopropanes is presented. A carbon-centered radical, formed upon reduction of an alkyl halide by Cu(I), adds across the alkene of a vinylcyclopropane, triggering ring opening to generate a benzylic radical, which, finally, undergoes copper-mediated amination to afford a homoallylic amine. The reaction occurs with outstanding regio- and good to very good diastereoselectivities. The scope of the reaction is demonstrated with respect to all three components: alkyl halide, vinylcyclopropane, and amine nucleophile. A total of 38 examples are presented with an average yield of 60%.

Ruthenium-Catalyzed Difunctionalization of Vinyl Cyclopropanes for Double m-C(sp2)-H/C-5(sp3)-H Functionalization

With in-depth research on 1,2-difunctionalization, remote difunctionalization has garnered widespread attention for achieving multifunctionality. Herein, we report a strategy for achieving remote difunctionalization under mild conditions. This strategy exhibited good substrate suitability and functional group tolerance. In addition, the significance of this method is further evidenced by its successful application in scaling up and conducting additional transformations of target compounds. Mechanistic studies showed that a radical might be involved in this process.

Three-Component Photochemical 1,2,5-Trifunctionalizations of Alkenes toward Densely Functionalized Lynchpins

Radical remote 1,n-difunctionalization reactions (n > 2) of alkenes are powerful tools to efficiently introduce functional groups with selected distances into target molecules. Among these reactions, 1,5-difunctionalizations are an important subclass, leading to sought-after scaffolds, but typically suffer from tailored starting materials and strict limitations for the formed functional group in 2-position. Seeking to address these issues and to make radical 1,5-difunctionalizations of alkenes more applicable, we report a novel three-component 1,2,5-trifunctionalization reaction between imine-based bifunctional reagents and two distinct alkenes, driven by visible light energy transfer-catalysis. Key to achieving this selective one-step installation of three different functional groups via the choreographed formation of four bonds was the utilization of a 1,2-boron shift and the rigorous capitalization of radical polarities and stabilities. Thorough mechanistic studies were carried out, and the synthetic utility of the obtained products was demonstrated by various downstream modifications. Notably, in addition to the functionalization of individual functional groups, their interplay gave rise to a unique array of cyclic products.

Remote Radical 1,3-, 1,4-, 1,5-, 1,6- and 1,7-Difunctionalization Reactions

Radical transformations are powerful in organic synthesis for the construction of molecular scaffolds and introduction of functional groups. In radical difunctionalization reactions, the radicals in the first functionalized intermediates can be relocated through resonance, hydrogen atom or group transfer, and ring opening. The resulting radical intermediates can undertake the following paths for the second functionalization: (1) couple with other radical groups, (2) oxidize to cations and then react with nucleophiles, (3) reduce to anions and then react with electrophiles, (4) couple with metal-complexes. The rearrangements of radicals provide the opportunity for the synthesis of 1,3-, 1,4-, 1,5-, 1,6-, and 1,7-difunctionalization products. Multiple ways to initiate the radical reaction coupling with intermediate radical rearrangements make the radical reactions good for difunctionalization at the remote positions. These reactions offer the advantages of synthetic efficiency, operation simplicity, and product diversity.

Metal-free, visible-light induced enantioselective three-component dicarbofunctionalization and oxytrifluoromethylation of enamines via chiral phosphoric acid catalysis

Using diverse carbon-centered radical precursors and electron-rich (hetero)aromatics and alcohols as nucleophiles, a visible-light driven chiral phosphoric acid (CPA) catalyzed asymmetric intermolecular, three-component radical-initiated dicarbofunctionalization and oxytrifluoromethylation of enamines was developed, which provides a straightforward access to chiral arylmethylamines, aza-hemiacetals and γ-amino acid derivatives with excellent enantioselectivity. As far as we know, this is the first example of constructing a chiral C–O bond using simple alcohols via visible-light photocatalysis. Chiral phosphoric acid played multiple roles in the reaction, including controlling the reaction stereoselectivity and promoting the generation of radical intermediates by activating Togni's reagent. Mechanistic studies also suggested the importance of the N–H bond of the enamine and indole for the reactions.

We have developed a metal-free, visible-light driven chiral phosphoric acid catalyzed asymmetric intermolecular, three-component radical-initiated dicarbofunctionalization and oxytrifluoromethylation of enamines.

Recent Advances on the Halo- and Cyano-Trifluoromethylation of Alkenes and Alkynes

Incorporation of fluorine into organic molecules is a well-established strategy in the design of advanced materials, agrochemicals, and pharmaceuticals. Among numerous modern synthetic approaches, functionalization of unsaturated bonds with simultaneous addition of trifluoromethyl group along with other substituents is currently one of the most attractive methods undergoing wide-ranging development. In this review article, we discuss the most significant contributions made in this area during the last decade (2012−2021). The reactions reviewed in this work include chloro-, bromo-, iodo-, fluoro- and cyano-trifluoromethylation of alkenes and alkynes.

Metal-to-Ligand Ratio-Dependent Chemodivergent Asymmetric Synthesis

Chemodivergent asymmetric synthesis was achieved by tuning the metal-to-ligand ratio in an organometallic catalytic system. Using N-(aroyloxy)phthalimide as the precursor of either an oxygen-centered aroyloxy radical or a nitrogen-centered phthalimidyl radical, enantioselective oxocyanation or aminocyanation of alkenes was achieved separately through a dual photoredox and copper catalysis. The metal-to-ligand ratio can exert chemoselective control while retaining the high enantiopurity of divergent products. Both reactions proceed efficiently with catalyst loading as low as 0.2 mol % and can be performed on a gram scale without loss of chemoselectivity or enantioselectivity. Chemodivergent asymmetric 1,5-aminocyanation or 1,5-oxocyanation of vinylcyclopropane can also be realized by this protocol. Mechanistic investigations involving electron paramagnetic resonance (EPR) experiments were performed to shed light on the stereochemical and chemodivergent results.

Copper-Catalyzed Enantioselective Arylation via Radical-Mediated C-C Bond Cleavage: Synthesis of Chiral ω,ω-Diaryl Alkyl Nitriles

The first example of copper-catalyzed ring-opening, enantioselective arylation of cyclic ketoxime esters to access ω,ω-diaryl alkyl nitriles has been developed in high yield (up to 92% yield) with excellent enantioselectivity (up to 91% ee). Side-arm bis(oxazoline) ligand plays a significant role in this asymmetric catalytic transformation, which provides an efficient route to construct diverse chiral ω,ω-diaryl alkyl nitriles. Synthetic utility has also been demonstrated in the further derivatization of the ω,ω-diaryl alkyl nitrile to the corresponding amide.

Radical 1,5-Chloropentafluorosulfanylation of Unactivated Vinylcyclopropanes and Transformation into α-SF5 Ketones

The radical 1,5-chloropentafluorosulfanylation of vinyl cyclopropanes (VCPs) initiated by Et₃B/O₂ affords allylic pentafluorosulfanyl/homoallylic chloride products through the ring-strain release of the cyclopropane. The VCP substitution pattern was investigated. The utility of this reaction was illustrated in post-transformation of the C═C bond by ozonolysis, giving access to valuable α-SF₅ carbonyl compounds.

Rh(III)-Catalyzed Csp2-Csp3 σ-Bond Enolation of α-Indolyl Alcohols

A Rh(III)-catalyzed Csp²-Csp³ σ-bond carbenoid functionalization of α-(2-indolyl)alcohols with acceptor/acceptor diazo compounds has been developed. This transformation provides an efficient strategy to assemble stable C2-enolated indole skeletons via Csp²-Csp³ σ-bond cleavage.

Regio- and enantioselective ring-opening reaction of vinylcyclopropanes with indoles under cooperative catalysis

The title reaction has been established under the cooperative bimetallic catalysis of iridium and copper catalysts, which afforded indole C3-allylation products with branched selectivity in moderate yields and good enantioselectivities.

Fe-catalyzed three-component dicarbofunctionalization of unactivated alkenes with alkyl halides and Grignard reagents

A highly chemoselective iron-catalyzed three-component dicarbofunctionalization of unactivated olefins with alkyl halides (iodides and bromides) and sp2-hybridized Grignard reagents is reported. The reaction operates under fast turnover frequency and tolerates a diverse range of sp2-hybridized nucleophiles (electron-rich and electron-deficient (hetero)aryl and alkenyl Grignard reagents), alkyl halides (tertiary alkyl iodides/bromides and perfluorinated bromides), and unactivated olefins bearing diverse functional groups including tethered alkenes, ethers, protected alcohols, aldehydes, and amines to yield the desired 1,2-alkylarylated products with high regiocontrol. Further, we demonstrate that this protocol is amenable for the synthesis of new (hetero)carbocycles including tetrahydrofurans and pyrrolidines via a three-component radical cascade cyclization/arylation that forges three new C-C bonds.

Copper-Catalyzed Annulation-Cyanotrifluoromethylation of 1,6-Enynes Toward 1-Indanones via a Radical Process

A new Cu(II)-catalyzed annulation-cyanotrifluoromethylation of 1,6-enynes with Togni's reagent and trimethylsilyl cyanide (TMSCN) has been established, enabling the direct construction of trifluoromethylated 1-indanones with an all-carbon quaternary center in good yields. This reaction was performed by using low-cost Cu(OTf)₂ as the catalyst and Togni's reagent as both the radical initiator and a CF₃ source, providing an efficient protocol for building up an 1-indanone framework with wide functional group compatibility. The reaction mechanism was proposed through a radical triggered addition/5-exo-dig cyclization/oxidation/nucleophilic cascade.

Organocatalytic 1,5-trifluoromethylthio-sulfonylation of vinylcyclopropane mediated by visible light in the water phase

1,2-Difunctionalization has developed into a robust tool for the preparation of complex organic molecules, and remote difunctionalization has also aroused widespread interest to achieve pluripotency of difunctionalization.