Chemo-, regio-, and stereoselective tetrafunctionalization of fluoroalkynes enables divergent synthesis of 5-7-membered azacycles

Water-Involved 1,3-Aminoxylation of Fluoroalkenes: Chemo-, Regio-, and Stereoselective Synthesis of β-Fluoroacyl Vinylamines

Perfluoroalkyl alkenyl iodides (PFAIs) are emerging as highly reactive, storage-stable, and multifunctional fluoroalkyl-bearing reagents, facilitating the manufacture of value-added organofluorides through multi-halo-functionalization. Herein, we developed a water-involved 1,3-aminoxylation of PFAIs with sulfonamides for the chemo-, regio-, and Z-stereoselective synthesis of valuable β-fluoroacyl vinylamines. This reaction proceeded via a sequential deiodoamination and defluoroxylation process under transition-metal-free conditions, featuring a broad substrate scope and good functional group tolerance. Compared to reported methods, some drawbacks, such as multistep manipulation, harsh reaction conditions, the need for expensive catalysts, and the use of toxic/sensitive reagents, could be eliminated. Furthermore, the synthetic potential of this method was demonstrated through scale-up synthesis, postfunctionalization of complex molecules, and ready transformation of the products.

[4+2] Defluorocycloaddition of Perfluoroalkyl Alkynes and Benzylamines: Synthesis of meta-Fluoroalkylated Pyridin-4-amines

Pyridines represent privileged heterocycles, and the ability to produce fluorinated pyridines from polyfluorinated substances through selective defluorofunctionalization is a new addition to their synthesis. Herein, an unprecedented formal [4+2] defluorocycloaddition of perfluoroalkyl alkynes and benzylamines under metal-free conditions is described. By leveraging the functionalization of four C(sp3)-F bonds on two vicinal sterically hindered perfluoroalkyl carbons of perfluoroalkyl alkynes, a diverse array of meta-fluoroalkylated pyridin-4-amines were synthesized with good functional group tolerance. The mechanistic studies revealed a sequence of hydroamination, successive defluorination, 6π-electrocyclization, aromatization, and amination.

Dialkylation of Alkenes to Fluorinated δ-Lactams Enabled by Nickel-Electron-Shuttle Catalysis

The δ-lactam motif is a privileged pharmacophore in drug design and development. While these biologically relevant molecules could be assembled through two-component cyclization, a modular approach to constructing these structures via a multicomponent reaction with unactivated alkenes as starting materials is rare. Herein, we report a tandem reaction that integrates alkene-dialkylation with radical-involved ring-opening and cyclization under a single metal-electron-shuttle catalysis, which represents the most expeditious access to fluorinated δ-lactams from unactivated simple alkenes.

Synthesis of Tetrasubstituted Pyrroles via DBU-Mediated Cyclization of Unactivated Propargyl Tertiary Amines

Compared with the well-developed cyclization of functionalized propargylamines, the use of unactivated tertiary propargylamines to access pyrroles remains challenging. Herein, we report an efficient method for constructing tetrasubstituted pyrroles via a DBU-mediated intramolecular cycloaddition of N-alkyl propargylamines. This reaction employs cyclization to access dihydropyrrole intermediates, followed by oxidation to produce pyrroles in the presence of 2,3-dichloro-5,6-dicyano-p-benzoquinone. In addition, a broad substrate scope, high atom economy, high selectivity, and simple operation are also advantages of this protocol.

Perfluoroalkyl Editing of Fluoroalkynes: Chemo-, Regio-, and Stereoselective Synthesis of (E)-(2-Amino-fluoroalkenyl)pyrimidines

A chemo-, regio-, and stereoselective condensation reaction of perfluoroalkyl alkynes (PFAAs), (CH2O)n, and (NH4)2CO3 through the cleavage of five inert C(sp3)-F bonds at three distinct carbon sites, thereby establishing an unprecedented platform for synthesizing structurally unique (E)-(2-amino-fluoroalkenyl)pyrimidines, is first developed. Remarkably, this reaction features mild reaction conditions, good compatibility with various functional groups, excellent E-stereoselectivity, late-stage modification of complex molecules, scalability, and versatile synthetic transformations of the resulting heterocyclic compounds.

Three-Component Sulfonylation and Heteroannulation Enabled by 3-Fold Defluorofunctionalization of Trifluoromethyl Enones

Trifluoromethyl enone emerges as a versatile and multifaceted building block in organic synthesis. A defluorinative heterocyclization reaction of readily available β,β-ditrifluoromethylated enones and biocompatible sodium sulfinates has been developed for the modular synthesis of densely functionalized furans with regio-defined C2,4-bissulfonyl and C3-trifluoromethyl substitutions. This three-component method proceeds through a sequential sulfonylation and intramolecular O-cyclization, enabling the assembly of one furan ring, the formation of C-SO2/C-O bonds, and the cleavage of three C(sp3)-F bonds in a one-pot manner under transition metal-free conditions. Moreover, the obtained furan product can further react with a benzyne precursor to generate 1,4-epoxynaphthalene through a Diels-Alder cycloaddition. The reaction is also distinguished by its broad substrate scope, excellent functional group tolerance, and scalability.

Defluorinative Diazolation-Cyclization Relay for Synthesis of Furan-Bridged Triheterocycles and Colorimetric Sensor Application

Polyaromatics, as the assembly of diverse cyclic π-systems, exhibit unique physicochemical properties when compared to their individual constituents. In this study, we developed a strategic connection of two azacycles via a furan bridge through a defluorinative diazolation-cyclization reaction of trifluoromethyl enones and N-heterocycles. A range of modular 2,4-furan-bridged triheterocycles (FBTHs), featuring a C3-trifluoromethyl group, was synthesized with broad substrate scope and good regioselectivity under transition metal-free conditions. This three-component protocol was achieved through successive C(sp3)-F bond functionalization of one trifluoromethyl group, which is recognized for its stability and durability. Moreover, the synthetically useful functionalities such as bromide and formyl group could be easily installed on the resulting products, and the imidazole-containing FBTH could serve as a valuable ligand in the preparation of an advanced colorimetric sensor, thereby underscoring their potential applications.

Sulfinate-Promoted Defluorinative Cyclization of Polyfluoroalkyl Tetralones Enabled by Photocatalysis

A Ru-catalyzed defluorinative cyclization of polyfluoroalkyl tetralones has been developed under visible-light irradiation for the precise assembly of γ-pyrones featuring α-perfluoroalkyl and β-fluorine substituents. Selective functionalization of five C(sp3)-F bonds at three carbon sites on the perfluoroalkyl chain provides a new mode for utilizing polyfluorides as versatile synthons to access difficult-to-obtain heterocyclic scaffolds. Moreover, the sulfinate salt serves dual roles as an oxygen source for creating the carbonyl group and as a defluorinating promoter.

Defluorinative Cyclization of Enamides with Fluoroalkyl Halides Through Two Vicinal C(sp3)─F Bonds Functionalization

Introducing distinctive functional groups to expand the structural diversity and improve the intrinsic properties of parent molecules has been an essential pursuit in organic chemistry. By using perfluoroalkyl halide (PFAH) as a nontraditional, readily available, ideal 1,2-difluoroalkenyl coupling partner, a defluorinative cyclization reaction of enamides for the construction of fluoroalkenyl oxazoles is first developed. The selective and controllable two-fold cleavage of vicinal C(sp3)─F bonds in PFAH not only enables the introduction of a specific 1,2-difluoroalkenyl moiety with ease but also results in the functionalization of two C(sp2)─H bonds of enamides without the need for metal catalyst, photocatalyst, oxidant, or light. The method can be applied to the late-stage modification of complex molecules, synthesis of biological-relevant oxazole analoges, and scale-up synthesis, which all further highlight the real-world utility of this protocol. Mechanistic studies reveal that the reaction possibly proceeds through a radical perfluoroalkylation, consecutive C─F bond heterolytic cleavage, and cyclization process. In addition, the in situ formed perfluoroalkyl radical which may also serve as an essential hydrogen abstractor.

Intramolecular/Intermolecular Sequential Cyclization Accompanied by Double C-F Bond Cleavage: Access to Tricyclic Fluorine-Containing Pyrano[3,2-c]chromenes

Defluorinative cyclization of CF3-alkenes has emerged as a reliable strategy for crafting intricate polycyclic frameworks. In this study, a facile defluorinative bicyclization approach was developed for the construction of 4H,5H-pyrano[3,2-c]chromenes under mild conditions involving a sequence of intramolecular cyclization and intermolecular defluoroheterocyclization. A variety of polysubstituted 4H,5H-pyrano[3,2-c]chromenes featuring C2-fluorine could be synthesized in good yields with excellent tolerance toward various functional groups. Moreover, the introduction of a C-F bond provides additional possibilities for further modification of this skeleton. The product features aggregation-induced emission (AIE) characteristics after simple modification, which is promising for chemical and biomedical imaging.

Palladium-Catalyzed Regioselective Monofluoroallylation of Indoles with gem-Difluorocyclopropanes

We present a palladium-catalyzed ring-opening reaction that induces indoles to cross-couple with gem-difluorocyclopropanes. The reaction proceeds through a domino process of C-C bond activation and C-F bond elimination, followed by C-C(sp2) coupling to produce various 2-fluoroallylindoles. This method is characterized by its high functional group tolerance, good yields and high regioselectivity, under base-free conditions. The synthetic utility of the products is illustrated by the functionalization of the NH and C2 positions of the indole scaffold.

Silver-Promoted Three-Component Synthesis of Perfluoroalkenyl Pyrroles through Partial Defluorinative Functionalization of Perfluoroalkyl Halides

A silver-promoted three-component heterocyclization of alkynes, perfluoroalkyl halides, and 1,3-dinucleophiles was developed for the efficient synthesis of privileged (E)-perfluoroalkenyl pyrroles. The reaction proceeded through a rationally designed sequence of radical perfluoroalkylation and intramolecular defluorinative [3 + 2]-heterocyclization. The utility of perfluoroalkyl halide as a perfluoroalkenyl reagent, by selective and controllable functionalization of two inert C(sp3)-F bonds at vicinal carbon centers on the perfluoroalkyl chain, provides a new reaction mode for the synthesis of value-added organofluorides starting from the easily available and low-cost fluorinated feedstock.