presence of a fluoride ion followed by the subsequent
alkylation of the isolated salt, seemed to be the most
attractive one. However, as the intermediate tetramethylam-
monium pentafluorodithiopropanoate salt was highly hygro-
scopic, we developed a modified one-pot procedure to
prepare the starting pentafluorodithioesters 1a,b required for
this study (Scheme 2).10
Scheme 1. Reaction of Grignard Reagents with Various
Fluorodithioesters
Scheme 2. One-Pot Synthesis of Pentafluorodithioesters 1a,b
on the effect of fluorinated substituents at various sites of
the pericyclic array,7 and to date, this [3,3] sigmatropic
rearrangement is one of the most attractive reactions for the
interconversion of fluorinated substrates and the preparation
of simple and readily available fluorinated building blocks.
Whereas its sulfur variant, the thio-Claisen rearrangement,
has received considerable attention as a useful synthetic
method for the transposition of a carbon-sulfur single bond
to a carbon-carbon bond and has been used in complex
target-oriented synthesis,1,8 no studies have been considered
so far with fluorinated substrates.
n-Butyl pentafluorodithiopropanoate 1a was reacted with
an allyl Grignard reagent to evaluate the relevance of the
proposed approach. We were delighted to observe that the
reaction led directly to R-fluoro R-trifluoromethyl R-allyl
dithioester 3 isolated in 76% yield after purification on a
pad of silica gel (eluent: pentane) (Scheme 3). Dithioester
On the basis of the previously reported results which
showed that organomagnesium reagents reacted with fluori-
nated dithioesters to give the corresponding fluorinated
ketene dithioacetals via a domino “thiophilic addition-
defluorination”,4,5 we anticipated that S-allyl fluorinated
ketene dithioacetals would be easily reached either by
treatment of S-alkyl fluorinated dithioesters with allylic
Grignard reagents or by treatment of S-allyl fluorinated
dithioesters with alkyl Grignard reagents. As the thio-Claisen
rearrangement of nonfluorinated substrates occurs at ambient
temperature or by heating at 101 °C at most1,8 and as the
presence of an electron-withdrawing group on the vinylic
moiety of the six-atom backbone generally has a rate-
accelerating effect on [3,3] sigmatropic rearrangements,7,8
we expected that the thio-Claisen transposition of S-allyl
fluorinated ketene dithioacetals should be thermally facile.
Scheme 3. Reaction of Allyl or Butyl Magnesium Halide with
Butyl or Allyl Pentafluorodithioesters 1a,b
Herein, we describe our results and show that the domino
reaction, thiophilic addition of an organomagnesium reagent-
â-elimination of fluoride-[3,3] sigmatropic rearrangement,
is a versatile approach for the synthesis of various unsaturated
fluorinated dithioesters.
3, which is formally the product of substitution of an
R-fluorine atom by the allyl group, results from a domino
process involving three successive steps: thiophilic nucleo-
philic allylation-fluoride elimination-σ [3,3] rearrangement,
with the two first ones leading to the intermediate ketene
dithioacetal 2.11 This reaction pathway has been corroborated
Several synthetic methods have been published for the
preparation of perfluoroalkyl dithioesters,9 but most of them
have serious disadvantages such as the use of volatile or toxic
reactants or reagents, the requirement of special techniques,
or low yields. The synthesis reported recently by Yagupolskii
and co-workers,9f which involved the direct reaction of
perfluoroalkyltrimethylsilane with carbon disulfide in the
(9) (a) Brown, H. C.; Pater, R. J. Org. Chem. 1962, 27, 2858-2863. (b)
Middleton, W. J.; Howard, E. G.; Sharkey, W. H. J. Org. Chem. 1965, 30,
1375-1384. (c) Shermolovich, Yu. G.; Slusarenko, Y. I.; Timoshenko, V.
M.; Rozhenko, A. B.; Markovski, L. N. J. Fluorine Chem. 1991, 55, 329-
333. (d) Portella, C.; Shermolovich, Yu. G.; Tschenn, O. Bull. Soc. Chim.
Fr. 1997, 134, 697-702. (e) Laduron, F.; Nyns, C.; Janousek, Z.; Viehe,
H. G. J. Prakt. Chem. 1997, 339, 697-707. (f) Badadzhanova, L. A.; Kirij,
N. V.; Yagupolskii, Yu. L. J. Fluorine Chem. 2004, 125, 1095-1098. (g)
Timoshenko, V. M.; Tchachenko, A. V.; Shermolovich, Yu. G. J. Fluorine
Chem. 2005, 126, 361-364.
(6) For a recent review on Claisen and related rearrangements, see:
Martin Castro, A. M. Chem. ReV. 2004, 104, 2939-3002.
(7) For short reviews on [3,3] sigmatropic rearrangements of fluorinated
compounds, see: (a) Purrington, S. T.; Weeks, S. C. J. Fluorine Chem.
1992, 56, 165-173. (b) Percy, J. M.; Prime, M. E. J. Fluorine Chem. 1999,
100, 147-156.
(8) For a review on thio-Claisen rearrangement, see: Majumdar, K. C.;
Ghosh, S.; Ghosh, M. Tetrahedron 2003, 59, 7251-7271.
(10) For details, see Supporting Information.
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Org. Lett., Vol. 8, No. 19, 2006