Fluorinated alkynes

Fluorinated alkynes are readily prepared by treatment of the mtermediate formed by acylation with a second equivalent of ylide followed by pyrolysis [63. 64, 65] (equation 57)... 

Fuchigami and co-workers utilized the regioselective anodic fluorination of aryl propargyl sulfides 301 for the preparation of fluorinated alkyne intermediates, which were subsequently isomerized by sodium ethoxide to furnish 1-fluoro-l-arylthioallenes 302 (Scheme 8.80) [166]. 

One of the very few examples of a four-membered heterocycle with sulfur atoms substituted 1,2 was reported by Dupont workers (60JA1515,61JA3434). Its synthesis involves the high temperature reaction of fluorinated alkynes and elemental sulfur, probably via a diradical intermediate (Scheme 102). The chemistry of these 1,2-dithietenes has been reviewed (76RCR639). As discussed later, these dithietenes form complexes with a number of transition metals. 

Only a few fluorinated alkynes are described in the literature (e.g., see ref 4, p37, and Table ), but no toxic data have been given to date. 

Under flash vacuum thermolysis (FVT) the 1,2,3-triazine (32) was readily thermolyzed to an alkyne, a nitrile, and nitrogen in high yields. For unsymmetrically substituted 1,2,3-triazines as FVT substrates, fragmentation proceeded selectively a bulky substituent at C-4(6) made the adjacent C—N bond break more easily than the opposite C—N bond. The FVT method was applied to the synthesis of the fluorinated alkynes, perfluoro-3-methyl-l-butyne and difluoroethyne [(33), R = (CF3)2CF, F] (Equation (1)) (89CC1657, 91CC456). It has been claimed, however, that tris(dimethylamino)-1,2,3-triazine forms the monocyclic azete. 

Fluorinated alkynes are usually prepared from the corresponding alkenes, but a twofold didechlorination of the corresponding alkane has also been applied. Alkynes bearing a fluorine atom on the triple bond are extremely reactive and hence special precautions have to be taken in their preparation under ordinary conditions, this fluorine atom is lost to afford a non-halogenated triple bond. Perfluoroalkynes with an internal triple bond can even be prepared using zinc. Examples of dehalogenations of fluorinated compounds to provide fluoroalkynes are listed in Table 3. 

The FVT method can be applied for the synthesis of the fluorinated alkynes, perfluoro-3-methyl-l-butyne and difluoroethyne 40 (R = (CF3)2CF, F) (Scheme 3) <1989CC1657, 1991CC456>. It has been claimed, however, that tris (dimethylamino)-l,2,3-triazine forms the monocyclic azete. 

Radical Addition to Fluorinated Alkynes with Hydrogen Transfer... 

Fluorinated cyclobutenes synthesized from the cycloaddition of fluoroalkenes with non-fluorinated alkynes (vide supra) undergo pyrolysis to give fluorinated butadienes, e.g. the pyrolysis of 3,3.4,4-tetrafluorocyclobut-l-ene gives l,1,4,4-tctrafluorobuta-l,3-diene (15) almost quantitatively. Tetrafluorodienes of this type undergo [2-F 2]-cycloaddition reactions with alkenes to give fluorinated cyclobutancs. ... 

Thermal elimination of nitrogen presents a route to fluorinated alkyne derivatives [270] (Figure 9.112). 

Various insertion reactions occur when metal thiolate complexes are treated with fluorinated alkynes under different reaction conditions. The manganese thiolate complexes of type 381 (R = Cp3, QFj) react with hexafluorobut-2-yne at 20°C in pentane to give an insertion product acting... 

A perfluoroacetylenephosphonate was prepared that can provide access to a number offluoroalkylated and phosphonylated quinolines (Scheme 55). The reaction combines ort/zo-aminoarylketones with perfluoroacetylene-phosphonates in a regioselective manner and is very sensitive to changes in temperature, solvent polarity, and the base used. The reaction failed to proceed in the presence of any of the typical Tewis acids employed in quinoline syntheses. Lower polarity and lower temperatures seemed to be favored for high isolable yields. When the fluorinated alkyne is varied, it appears that... 

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