New fluorocarbon iodides†
Richard D. Chambers,* Julian A. Cooper, Elodie Copin and Graham Sandford*
University of Durham, Department of Chemistry, South Road, Durham, UK DH1 3LE.
E-mail: R.D.Chambers@durham.ac.uk; Graham.Sandford@durham.ac.uk
Received (in Cambridge, UK) 21st August 2001, Accepted 16th October 2001
First published as an Advance Article on the web 8th November 2001
A general, efficient approach for the synthesis of fluoro-
carbon iodides and di-iodides bearing hydrocarbon groups is
described and the synthetic utility of these new systems is
demonstrated in reactions with thiols.
Perfluorocarbon iodides (RFI) have been important for many
years as ‘building blocks’ for the synthesis of various organic
compounds containing fluorine.1–3 For example, they are
crucial components in the synthesis of highly efficient surfac-
tants on the industrial scale.4 Here, we report an approach to the
synthesis of fluorocarbon iodides that bear hydrocarbon end-
Scheme 2
involving ICl and IBr are regiospecific. It is surprising that these
electrophilic additions proceed so readily with electron defi-
cient double bonds but the regioselectivity is entirely consistent
with an electrophilic process. The developing carbocationic site
in intermediate 7a is stabilised by cyclohexyl and by fluorine,
whereas 7b would be strongly destabilised by the attached
trifluoromethyl group and so, consequently, we favour Route
A.
Novel iodides 5 and 6 react with thiols and di-thiols, most
likely via an SRN1 mechanism,6 giving thioethers 8a–d7 and di-
thioethers 9, mostly in high yields (Scheme 3) and oxidation of
the thioether products to the corresponding sulphones was
possible using chromium trioxide in acetic acid.
These preliminary results demonstrate that these unusual
fluorocarbon iodide ‘building blocks’ could be used for
approaches to a variety of new systems containing fluorinated
groups.
We thank EPSRC and the University of Durham (Studentship
to E. C.) and the Royal Society (University Research Fellow-
ship to G. S.).
groups and demonstrate the potential of these systems for
further synthesis of fluorinated derivatives.
We are exploring the use of the carbon–hydrogen bond as a
functional group in efficient free radical chain reactions with
fluorinated alkenes,5 e.g. formation of 1 and 2 from cyclohex-
ane,‡ and have begun to explore the chemistry of the resultant
fluorinated adducts. It has been demonstrated that stereospecific
elimination of hydrogen fluoride5 from 1 and 2 leads to
unsaturated derivatives 3 and 4 respectively. We now find that
alkene derivatives 3 and 4 react with a stoichiometric mixture of
iodine pentafluoride and iodine, that corresponds to iodine
monofluoride, giving fluorinated iodide 5 and di-iodide 6
respectively in efficient processes (Scheme 1).
The mechanism of iodine monofluoride addition is of interest
because the process is regiospecific, to the limits of detection by
19F NMR. In principle, we could envisage two possible
mechanisms for addition of I–F to 3 (Scheme 2). Route B
involves first addition of iodine to the double bond, but the next
step would then require selective replacement of iodine at the
R–CFI site by fluorine and we see no convincing reason for this
to occur. Furthermore, we have been unable to add iodine to 3
to give a di-iodide. In contrast, we find that other additions to 3
involving bromine, iodine monochloride and iodine mono-
bromide are efficient processes and moreover, additions
Notes and references
‡ Reaction of cyclohexane with two equiv. of hexafluoropropene yields a
mixture of 1,3- and 1,4- dihexafluoropropylcyclohexane adducts. However,
the trans-1,4-diadduct 2 crystallises from the diadduct mixture and can,
therefore be readily separated and purified by filtration (see ref. 5).
1 L. E. Deev, T. I. Nazarenko, K. I. Pashkevich and V. G. Ponomarev, Russ.
Chem. Rev., 1992, 61, 40.
2 N. O. Brace, J. Fluorine Chem., 1999, 93, 1.
3 N. O. Brace, J. Fluorine Chem., 2001, 108, 147.
4 N. S. Rao and B. E. Baker, in Organofluorine Chemistry. Principles and
Commercial Applications, ed. R. E. Banks, B. E. Smart and J. C. Tatlow,
Plenum, New York, 1994, p. 321.
5 R. D. Chambers, R. W. Fuss, R. C. H. Spink, M. P. Greenhall, A. M.
Kenwright, A. S. Batsanov and J. A. K. Howard, J. Chem. Soc., Perkin
Trans. 1, 2000, 1623.
6 A. E. Feiring, J. Fluorine Chem., 1984, 24, 191.
7 All compounds were characterised by elemental analysis, NMR and mass
spectrometry. For example, 8d; a yellow oil; bp 292 °C; (Found: C, 48.7;
H, 6.3. C26H38F12S2 requires C, 48.6; H, 5.9%); nmax/cm21 2857 and
2932 (C–H); dH 1.0 –2.0 (32H, m, CH2), 2.20 (2H, m, CHCF2), 2.8 (4H,
3
Scheme 1 Reagents and conditions: i, CF2NCF–CF3, (t-BuO)2, 140 °C; ii, t-
m, CH2S); dC 24.7 (t, JCF 4.2, CH2CH), 25.4 (s, CH2), 25.5 (s, CH2),
BuOK, 0 °C; iii, I2, IF5, 0 °C.
25.5 (t, 3JCF 4.2, CH2CH), 25.7 (s, CH2), 28.5 (s, C-4), 28.8 (s, C-3), 28.9
(s, C-2), 39.0 (s, CH2S), 42.4 (t, 2JCF 21.7, CHCF2), 101.4 (dm, JCF
1
242.7, CF), 120.6 (ddd, 1JCF 262.1, 1JCF 253.7, 2JCF 24, CF2), 122.3 (qd,
1JCF 287.6, 2JCF 35.2, CF3); dF 272.8 (3F, m, CF3), 2112.0 and 2112.7
(2F, AB, JAB 267.6, CF2), 2158.4 (m, CFS); m/z (EI+) 642 (M+, 1%), 409
(40), 227 (65), 143 (100).
† Electronic supplementary information (ESI) available: characterisation of
b107565a/
2428
Chem. Commun., 2001, 2428–2429
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b107565a
Chambers
