Chapter 10
Functionalized Fluorinated Allenes Gerald B . Hammond
Downloaded by EMORY UNIV on April 10, 2016 | http://pubs.acs.org Publication Date: July 21, 2005 | doi: 10.1021/bk-2005-0911.ch010
Department of Chemistry, University of Louisville, Louisville, K Y 40292
An overview of the literature of mono- and di-fluorinated allenes is presented with an emphasis on the synthesis and chemistry of silyl substituted mono- and di-fluorinated allenes and fluoroallenylphosphonates.
Introduction Functionalized aliènes are of paramount importance in organic chemistry, both as building blocks, and synthetic targets. In the last two years alone, over twenty reviews have been published on the subject.(i) The effect of fluorine substitution on the chemistry of functionalized allenylic species would be expected to impart profound changes on the biological and chemical properties of aliènes. However, to date, only a minuscule amount of research in this area has been reported. The effect of one or two fluorine atoms bonded to an sp allenic carbon on the known chemistry of aliènes has not been fully addressed, in part because these compounds are either not easily accessible, unreactive toward nucleophilic substitution, less prone to form stable metal intermediates, or more susceptible to yield regioisomers (through propargyl-allene isomerization). This review will address advances in the synthesis of functionalized fluoroallenes containing >C=C=CF2, >C=C=CFH and >C=C=CFP(0)(OEt) moieties. 2
2
Background In general, fluoroallenes are less stable than those without fluorine substituents but they still possess reasonable stability at room temperature. Incorporation of increasing number of fluorine susbtituents on aliène makes 204
© 2005 American Chemical Society
Soloshonok; Fluorine-Containing Synthons ACS Symposium Series; American Chemical Society: Washington, DC, 2005.
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these species increasingly reactive with the result that 1,1-difluoroallene (DFA) and l-monofluoroallene (MFA) must be stored in vacuo at -78°C to prevent oligomerization. 1,1,3-Trichloropropadiene is an unstable material that dimerizes in solution at room temperature, and in the pure state decomposes explosively. 1,1,3,3-Tetrafluoropropadiene, though still prone to dimerization, is a known material that hydrohalogenates readily with HF, HC1, and HBr. Partially fluorinated propadienes are more stable and amenable to further reaction. Phenyl subsitution renders unstable difluoroallenes. This observation is in agreement with the fact that some phenyl substituted haloallenes are quite prone to oligomerization. Simple fluoropropadienes have been synthesized by metal reduction of dihalofluoro-olefins. The reaction of 1-trifluoromethyl-l-alkenyl bromides with n-BuLi has been employed for the synthesis of DFA (eq 1) and l,l-difluoro-3,3dimethyl aliène (eq 2).(2)
F 3 C N = C H
F 3
-
VCH
d) KUH
g
- ^
2
F
3
°
> C H
w
