Fluorinated allenes synthesis

Scheme 4.34 Asymmetric synthesis of fluorine-containing allenes.

Rozhkov IN, Stepanoff AA (1981) The second regular meeting of soviet-japanese fluorine chemists. Reductive coupling of fluoroolefins Synthesis of higher perfluorinated 1,3-dienes and allenes, Moscow, p 133... 

The zinc and cadmium reagents " " (R0)2P(0)CF2MBr have also proved useful as alkylation substrates for particularly reactive species, e.g. allylic, benzylic or propargylic halides with the last type, some rearrangement to allenic compounds is observed. Scheme 12 illustrates the use of such reagents in the synthesis of a-fluorinated alkylphosphonic acid derivatives. 

Oxidative fluorination of olefins, allenes, and acetylenes are reported [11,12]. The reaction of OF2 with olefinic fluorocarbons is used for the synthesis of fluoropolymers [13]. 

Liu and coworkers have recently published the synthesis of (3) and (4), as well as several other fluorinated pyrrole analogues (not shown), by aminofluorination of allenes the synthetic approach is shown in Scheme 3 [15], This strategy takes advantage of a selective, silver-catalyzed intramolecular fluorination reaction, but the approach works best with substrates that possess electron-withdrawing R -groups on the 3-position. Because of this limitation, the yield of (3) is significantly higher than (4), 80 % versus 28 %, respectively. 4-Fluoro-pyrrole-2-carboxylic acid (5a, Fig. 2), synthesized from a fluorinated proline, was explored as a potential intermediate on the route to (3), but only extensive decomposition products were observed when (5a) was subject to flash pyrolysis [16]. 

Konno T, Tanikawa M, Ishihara T, Yamanaka H. Fluorine-containing aUenylpaUadium complexes. Synthesis of optically active fluoroalkylated allenes and furan derivatives. Collect. Czech. Chem. Commun. 2002 67 1421-1435. 

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