Arylation of gem-difluoroalkenes using a Pd/Cu Co-catalytic system that avoids β-fluoride elimination

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.

Difunctionalization of gem-difluoroalkenes for amination and heteroarylation via metal-free photocatalysis

gem-Difluoroalkenes are widely used building blocks in fluorine chemistry. Herein, a metal-free photocatalytic amination and heteroarylation method of gem-difluoroalkenes with heteroaryl carboxylic acid oxime esters as substrates is reported. This environmentally benign reaction proceeds via radical-radical cross-coupling in energy-transfer-mediated photocatalysis and can be used in the rapid construction of heteroaryl difluoroethylamine scaffolds and late-stage modification of complex pharmaceutical structures.

Chemoselective Reactions of Functionalized Sulfonyl Halides

Chemoselective transformations of functionalized sulfonyl fluorides and chlorides are surveyed comprehensively. It is shown that sulfonyl fluorides provide an excellent selectivity control in their reactions. Thus, numerous conditions are tolerated by the SO2 F group - from amide and ester formation to directed ortho-lithiation and transition-metal-catalyzed cross-couplings. Meanwhile, sulfur (VI) fluoride exchange (SuFEx) is also compatible with numerous functional groups, thus confirming its title of "another click reaction". On the contrary, with a few exceptions, most transformations of functionalized sulfonyl chlorides typically occur at the SO2 Cl moiety.

Rh(III)-catalyzed redox-neutral C-H alkenylation of benzamides with gem-difluorohomoallylic silyl ethers via β-H elimination

Fluorinated molecules are widely used in pharmaceutical and agrochemical industries. Herein we report the synthesis of 2-(3,3-difluoro-4-(silyloxy)but-1-en-1-yl)benzamides from the unprecedented rhodium(III)-catalyzed alkenylation of various benzamides with difluorohomoallylic silyl ethers. The practicability of this protocol is demonstrated by its broad substrate compatibility, good functional group tolerance, ready scalability and high regioselectivity. The oxygen in difluorohomoallylic silyl ethers makes β-H elimination feasible, which suppresses both the β-F elimination and dialkenylation of benzamides. This redox-neutral reaction proceeds efficiently via N-O bond cleavage without external oxidants and thus provides new opportunities for the synthesis of elaborate difluorinated compounds from readily available fluorinated synthons.

General Co-catalytic Hydrothiolation of gem-Difluoroalkenes

Regioselective functionalization of gem-difluoroalkenes enables convergent late-stage access to fluorinated functional groups, though most functionalization reactions proceed through defluorinative functionalization processes that deliver mono-fluorovinyl products. In contrast, fewer reactions undergo net hydrofunctionalization to generate difluorinated products. Herein, we report a photocatalytic hydrothiolation of gem-difluoroalkenes that enables access to a broad spectrum of α,α-difluoroalkylthioethers. Notably, the reaction successfully couples nonactivated substrates, which expands the scope of accessible molecules relative to previously reported reactions involving organo- or photocatalytic strategies. Further, this reaction successfully couples biologically relevant molecules under aqueous conditions, highlighting potential applications in both late-stage and biorthogonal functionalizations.

Fluorine-Retentive Strategies for the Functionalization of gem-Difluoroalkenes

gem-Difluoroalkenes are readily available fluorinated building blocks, and the fluorine-induced electronic perturbations of the alkenes enables a wide array of selective functionalization reactions. However, many reactions of gem-difluoroalkenes result in a net C─F functionalization to generate monofluorovinyl products or addition of F to generate trifluoromethyl-containing products. In contrast, fluorine-retentive strategies for the functionalization of gem-difluoroalkenes remain less generally developed, and is now becoming a rapidly developing area. This review will present the development of fluorine-retentive strategies including electrophilic, nucleophilic, radical, and transition metal catalytic strategies with an emphasis on key physical organic and mechanistic aspects that enable reactivities.

Base promoted gem-difluoroolefination of alkyl triflones

A new synthesis of gem-difluoroalkenes from readily available alkyl triflones and difluorocarbene precursors such as TMSCF₂Br has been reported. The reaction, regardless of electronic effect, gives gem-difluoroalkenes in good to excellent yields. The mechanism may involve deprotonation of triflones, nucleophilic addition, and the elimination of SO₂CF₃.