Hydrofluorination, alkynes

In accordance with the Markovnikov rule, terminal alkynes are converted to 2-halo-l-alkenes. The reagents prepared in the reaction of anhydrous HF with organic bases and used in hydrofluorination of alkenes can add to the carbon-carbon triple bond producing Markovnikov products.94-96,98 99 However, 1-bromo-l-alkenes and... 

Hydrofluorination of alkynes.1 The reagent adds to alkynes activated by CN, COOCH3, COR, or CHO groups to form fluoroalkenes. 

Olah and Li2 have prepared a solid form of this reagent by reaction of anhydrous HF with cross-linked poly-4-vinylpyridine. It is comparable to pyridinium poly (hydrogen fluoride) for hydrofluorination of alkenes and alkynes and fluorination of alcohols, but is easier to handle. Work-up of reactions requires only a simple filtration, and the spent reagent can be regenerated with HF for further use. 

Alkynes can be hydrofluorinated with the hydrogen fluoride/pyridine reagent. - Tetra-hydrofuran is a highly convenient solvent for this reaction. The reaction products are difluorides with Markovnikov orientation, e.g. 2. ... 

Table 43. Hydrofluorination of Electrophilic Alkynes with CsF/H20/DMF546...

Olah GA, Nojima M, Kerekes I (1973) Synthetic methods and reactions. II. Hydrofluorination of alkenes, cyclopropane, and alkynes with poly-hydrogen fluoride pyridine (trialkylamine) reagents. Synthesis 1973 (12) 779-780... 

HF-pyridine reagent, however, can also be used for the hy-drofluorination of alkenes,7 alkynes,7 cyclopropanes,7 and diazo compounds,8 the halofluorination of alkenes,9 the preparation of fluoroformates from carbamates,10 the preparation of a-fluorocarboxylic acids from a-amino acids,11 and as a deprotecting reagent in peptide chemistry.12 Examples of the hydrofluorination of alkenes with HF-pyridine are given in Table II. 

To the best of our knowledge, until today there is only one reported example where it appears to be clear that the tuning of the electronic properties of the ancillary NHC ligand resulted only in an improvement of the obtained yields of the desired products. Sadighi and coworkers reported this example. In their studies of the gold-catalyzed hydrofluorination of alkynes (see Scheme 9.22), they foimd that in this reaction the fluorinated vinyl-gold species is in... 

Abstract Recent developments in the stereoselective synthesis of fluoroalkenes, which include hydrofluorination of alkyne, fluorination of alkenylmetal, condensation methods, dehydrofluorination of cm-difluoro compounds, and a cross-coupling reaction using fluorohaloalkenes or fluoroalkenylmetal, are described in this chapter. 

Scheme 3 Regioselective hydrofluorination of alkyne having a directing group...

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