COMMUNICATION
DOI: 10.1002/chem.201202292
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C F Bond Activation with an Apparently Benign Ethynyl Dithiocarbamate,
and Subsequent Fluoride Transfer Reactions
Gaꢀl Ung[a, b] and Guy Bertrand*[a, b]
A recent trend in the activation of small molecules and
enthalpically strong bonds is the use of non-metal activa-
tors.[1] In contrast to work on singlet carbenes[2] or heavier
analogues,[3] which are very basic, or on the so-called frus-
trated Lewis pairs,[4] which require strong Lewis acids, our
research has recently shown that the simple and mild ethyn-
yl dithiocarbamate 1 was able to activate a variety of en-
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Scheme 2. Selective C F bond activation with ethynyl dithiocarbamate 1.
a: E=N; b: E=CCF3.
thalpically strong bonds such as N H, P H, B H, and S S
bonds.[5] The activation process, which is accompanied by a
ring-closure, is due to the cooperative effect of the electro-
philic and nucleophilic centers of 1 (Scheme 1). To test the
tra showed three inequivalent isopropyl groups for the 2,4,6-
triisopropylphenyl substituent, indicating the presence of a
stereogenic center. Additionally, a new doublet in the
13C NMR spectrum (d=136.4 ppm, JCÀF =274 Hz) was ob-
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served, consistent with a fluorine directly bound to a carbon
atom. In the 19F NMR spectrum, a new singlet at d=
À37 ppm was observed, as well as two new multiplets at d=
À91 and À140 ppm. These data are consistent with the se-
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lective activation of the C F bond at the para-position of
pentafluoropyridine and the formation of adduct 2a. Inter-
estingly, in contrast to the results previously reported with
strong nucleophiles,[6e,9] the substituted fluoride ends up co-
valently bonded to the activator.
Scheme 1. Activation of small molecules with ethynyl dithiocarbamate 1.
R2N=1-piperidinyl; Tipp=2,4,6-triisopropylphenyl; pin=pinacolato.
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limits of our activator, we targeted C F bonds, which are
Although the reaction in benzene proceeded cleanly, a
long reaction time (18 h) was required. We found that more
polar solvents significantly enhanced the rate of the activa-
tion process, as shown with experiments performed in THF,
1,4-dioxane, and 1,2-dimethoxyethane (3 to 4 h; Table 1).
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even significantly stronger than C H bonds, but more polar-
ized; their activation usually requires transition metals[6,7] or
strong Lewis acids.[8] We found that fluorinated adducts, re-
sulting from the activation process with 1, can be used as
non-ionic and anhydrous fluorinating agents.
The addition of 1 to a benzene solution of pentafluoropyr-
idine, a reagent known to react with strong nucleophiles,[6e,9]
proceeded cleanly (Scheme 2). The multinuclear NMR spec-
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Table 1. Solvent optimization for C F bond activation of pentafluoropyr-
idine.
Entry
Solvent
t [h]
Conv. [%][a]
1
2
3
4
benzene
THF
1,4-dioxane
1,2-dimethoxyethane
18
4
3
100
100
100
100
[a] G. Ung, Prof. G. Bertrand
UCR-CNRS Joint Research Chemistry Laboratory (UMI 2957)
Department of Chemistry
University of California Riverside
Riverside, CA 92521-0403 (USA)
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[a] Determined by 19F NMR spectroscopy using fluorobenzene as an in-
ternal standard.
[b] G. Ung, Prof. G. Bertrand
Using these optimized conditions, we tested the activation
Present address:
UCSD-CNRS Joint Research Chemistry Laboratory (UMI 3555)
Department of Chemistry and Biochemistry
University of California San Diego
La Jolla, CA 92093-0343 (USA)
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of other aromatic C F bonds. Octafluorotoluene was suc-
cessfully cleaved under the same conditions, and the selec-
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tive activation of the C F bond in para position was also ob-
served (2b). Ethynyl dithiocarbamate 1 was however unable
to activate hexafluorobenzene, which was ascribed to the
lack of polarity of the latter.
Supporting information for this article is available on the WWW
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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