Synthesis of vinyl fluorides

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The nucleophilic fluorination reagent DMPU/HF offers high acidity and is compatible with cationic metal catalysts. Gold-catalyzed mono- and dihydrofluorination of alkynes using this stable complex yields synthetically important fluoroalkenes and gem-difluoromethlylene compounds regioselectively.
O. E. Okoromoba, J. Han, G. B. Hammond, B. Xu, J. Am. Chem. Soc., 2014, 136, 14381-14384.

A Shapiro fluorination reaction enables a direct access to fluoroalkenes in good stereoselectivity in one- or two-step sequences from widely available ketones. This strategy should be useful for the preparation of fluorinated analogs of peptide-based therapeutics, many of which would be challenging to prepare by alternate strategies.
M.-H. Yang, S. S. Matikonda, R. A. Altman, Org. Lett., 2013, 15, 3894-3897.

A direct fluorination of 1-(2,2-dibromovinyl)benzene derivatives using wet tetra-n-butylammonium fluoride (TBAF·3H₂O) as either a base or a fluorine source provided (Z)-1-(2-bromo-1-fluorovinyl)benzene compounds in good yields with high regioselectivities.
M. Zhao, L. Ming, J. Tang, X. Zhao, Org. Lett., 2016, 18, 416-419.

The use of 1,3-diiodo-5,5,-dimethylhydantoin and HF-based reagents enables a regio- and stereoselective iodofluorination of internal and terminal alkynes. A facile method for a controlled regioselective double iodofluorination of terminal alkynes is also presented.
L. Pfeifer, V. Gouverneur, Org. Lett., 2018, 20, 1576-1579.

An ammonium hydrogen-bonding-assisted α-F elimination from Cu-CF₃ compounds generates R₃N·HF reagents in situ. This strategy enables a dual fluorination and trifluoromethylation of terminal alkynes in the presence of a single Cu(III)-CF₃ compound and a tertiary amine with excellent regio- and stereoselectivity.
S.-L. Zhang, J.-J. Dong, Org. Lett., 2019, 21, 6893-6896.

The collaboration of (phen)Cu^III(CF₃)₃ and CsF enables a one-step concurrent fluoro-trifluoromethylation across the triple bond of arylacetylenes in a syn mode to provide chemo-, regio-, and stereoselectively (Z)-α-fluoro-β-CF₃ styrenes. This method can be extended to achieve syn-oxy-trifluoromethylation and syn-aryl-trifluoromethylation.
S.-L. Zhang, H.-X. Wan, W.-F. Bie, Org. Lett., 2017, 19, 6372-6375.

A formal enone-α-H to F substitution provides 2-fluoroenones in a single step from ubiquitous enones in good yield. The reaction is applicable to a wide range of aromatic and alkenyl enones and is carried out at room temperature using HF-pyridine complex as the fluoride source. The reaction takes place through a rare umpolung Morita-Baylis-Hillman-type mechanism.
S. Maity, A. M. Szpilman, Org. Lett., 2023, 25, 1218-1222.

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A stereoselectiv hydrodefluorination reaction of trifluoromethylated alkenes with LiAlH₄ provides terminal monofluoroalkenes in very good yields and diastereoselectivities. Mechanistic studies suggested a hydroalumination reaction followed by a stereoselective fluoride elimination.
P. Poutrel, X. Pannecoucke, P. Jubault, T. Poisson, Org. Lett., 2020, 22, 4858-4863.

The visible light mediated coupling of α-fluoroacrylic acids with N-hydroxyphthalimide (NHPI) redox-active esters provides monofluoroalkenes under mild conditions. This decarboxylative reaction exhibited excellent functional group compatibility and delivered monofluoroalkene products with excellent Z-stereoselectivity.
X. Bai, L. Huang, P. Zhou, H. Xi, J. Hu, Z. Zuo, H. Feng, J. Org. Chem., 2022, 87, 4998-5004.

Monofluorovinyl tosylate is a practical vinyl fluoride building block to couple with various arylboronic acids in the presence of a palladium catalyst. A high stereoselectivity in the synthesis of 2-aryl-1-fluoroethene derivatives was achieved. This approach is also applicable to the synthesis of 2,2-diaryl-1-fluoroethenes in good yields.
H. Zhang, C.-B. Zhou, Q.-Y. Chen, J.-C. Xiao, R. Hong, Org. Lett., 2011, 13, 560-563.

Previously unknown halo-substituted molybdenum alkylidene species are exceptionally reactive and are able to participate in high-yielding olefin metathesis reactions that afford acyclic 1,2-disubstituted Z-alkenyl halides. Transformations are promoted by small amounts of a catalyst that is generated in situ and used with unpurified, commercially available and easy-to-handle liquid 1,2-dihaloethene reagents.
M. J. Koh, T. T. Ngyuen, H. Zhang, R. R. Schrock, A. H. Hoveyda, Nature, 2016, 531, 459-465.

A highly diastereoselective rhodium(I)-catalyzed C-F bond functionalization of gem-difluoroalkenes with arylboronic acids provides valuable monofluoroalkenes. A Rh(I)/BINAP catalytic system enables the C-F bond arylation of both trisubstituted β,β-difluorostyrenes and tetrasubstituted β,β-difluoroacrylates in >99:1 dr via a migratory insertion/β-F elimination mechanism.
H. Tan, Y. Zong, Y. Tang, G. C. Tsui, Org. Lett., 2023, 25, 877-882.

Difluoromethyl 2-pyridyl sulfone acts as a novel and efficient gem-difluoroolefination reagent for both aldehydes and ketones. A fluorinated sulfinate intermediate in the reaction is relatively stable and can be observed by ¹⁹F NMR and trapped with CH₃I.
Y. Zhao, W. Huang, L. Zhu, J. Hu, Org. Lett., 2010, 12, 1444-1447.

A robust copper-catalyzed or transition-metal-free alkylation of gem-difluoroalkenes with alkyl Grignard reagents proceeded very smoothly in the presence of 25 mol % of CuCN or under transition-metal-free conditions. Especially tertiary and secondary alkyl-substituted fluoroalkenes can be isolated in good to excellent yields with excellent Z stereoselectivity.
W. Dai, H. Shi, X. Zhao, S. Cao, Org. Lett., 2016, 18, 4284-4287.

A catalyst-induced defluorinative, alkylation or metal-free hydroalkylation of gem-difluoroalkenes provides a mild and practical approach to important and monofluoroalkenes and difluoromethylene-containing compounds under visible light irradiation with good yields.
F. Liu, Z. Zhuang, Q. Qian, X. Zhang, C. Yang, J. Org. Chem., 2022, 87, 2730-2739.

A mild and efficient zinc-mediated decarboxylative alkylation of gem-difluoroalkenes with N-hydroxyphthalimide (NHP) esters provides Z-monofluoroalkenes in good yields. The reaction tolerates a broad range of functional groups and can be easily scaled up.
L. Yu, M.-L. Tang, C.-M. Si, Z. Meng, Y. Liang, J. Han, X. Sun, Org. Lett., 2018, 20, 4579-4583.

A transition-metal-free cross-coupling of two carbene fragments proceeds through the direct nucleophilic addition of diazo compounds to difluorocarbene derived from Ruppert-Prakash reagent (TMSCF₃) or TMSCF₂Br followed by elimination of N₂. This transition-metal-free protocol efficiently affords various disubstituted 1,1-difluoroalkenes, including difluoroacrylates, diaryldifluoroolefins, as well as arylalkyldifluoroolefins.
M. Hu, C. Ni, L. Li, Y. Han, J. Hu, J. Am. Chem. Soc., 2015, 137, 14496-14501.

A Cu-catalyzed gem-difluoroolefination of diazo compounds with TMSCF₃ affords the desired 1,1-difluoroalkene products via trifluoromethylation followed by C-F bond cleavage.
M. Hu, Z. He, B. Gao, L. Li, C. Ni, J. Hu, J. Am. Chem. Soc., 2013, 135, 17302-17305.

A fast and practical cross-coupling between difluorocarbene and carbene-derived intermediates generated from diazocompounds provides hindered gem-difluoroolefins. Whereas the cross-coupling between difluorocarbene and aryl diazoacetates proceeded smoothly in the presence of a copper source, the coupling with diaryl diazomethanes occurred well under metal-free conditions.
J. Zheng, J.-H. Lin, L.-Y. Yu, Y. Wei, X. Zheng, J.-C. Xiao, Org. Lett., 2015, 17, 6126-6129.

A domino reaction of enolizable carbonyl compounds with Me₃SiCF₂Br provides α-fluoroenones and α-fluoroenals via formation of difluorocarbene and silyl enol ether, difluorocyclopropanation, desilylation, ring-opening, and defluorination. Me₃SiCF₂Br acts as not only the difluorocarbene source but also the TMS transfer agent as well as internal bromide and fluoride anion catalyst. Only a catalytic amount of n-Bu₄NBr as initiator is needed.
X. Song, J. Chang, D. Zhu, J. Li, C. Xu, Q. Liu, M. Wang, Org. Lett., 2015, 17, 1712-1715.

A highly stereoselective olefination reaction of α-fluoro-β-keto esters enables the synthesis of α-fluoro-α,β-unsaturated esters via nucleophilic addition, intramolecular nucleophilic addition, and elimination. α-Fluoro-α,β-unsaturated esters are important units in many biologically active compounds and useful precursors in a variety of functional-group transformations.
J. Qian, W. Yi, M. Lv, C. Cai, Synlett, 2015, 26, 127-132.

Phosphazene P4-tBu effectively catalyzes a nucleophilic substitution reaction of gem-difluoroalkenes with ketene silyl acetals under mild conditions to provide monofluoroalkenes possessing an alkoxycarbonylmethyl group in high yields with high Z selectivities.
A. Kondoh, K. Koda, M. Terada, Org. Lett., 2019, 21, 2277-2280.

With a suitable combination of N-heterocyclic carbene precatalyst, base, and fluorine reagent, a fluorination of alkynals proceeded smoothly to yield a wide range of α-fluoroallenoates with excellent chemoselectivity. α-Fluorinated allenoates are versatile synthetic intermediates toward other useful fluorine-containing building blocks.
X. Wang, Z. Wu, J. Wang, Org. Lett., 2016, 18, 576-579.