Communications
DOI: 10.1002/anie.200907134
Hypervalent Iodine Compounds
AVersatile and Highly Reactive Polyfluorinated Hypervalent
Iodine(III) Compound**
Sascha Schꢀfer and Thomas Wirth*
Hypervalent iodine compounds[1] are frequently used
reagents that have found wide application in synthesis.[2]
They are used in a wide range of transformations as environ-
mentally friendly, mild, and highly selective electrophilic
reagents and oxidants since their application sidesteps the
issues of toxicity and the complicated ligands of many
Scheme 1. Synthesis of the l3-perfluorinated compound 3.
transition-metal-based systems commonly used for such
processes. The drawback of hypervalent iodine compounds
can be their low solubility in commonly used organic
solvents[3] as well as their potentially explosive character
(sometimes found for hyperveralent iodine(V) compounds).[4]
Commonly used hypervalent iodine(III) compounds such as
PhI(OAc)2 and PhI(OCOCF3)2 have only moderate reactivity
owing to their lower oxidation state.[5,1a] Because polyfluo-
rinated alkyl-substituted hypervalent iodine compounds[6]
to moisture.[14] The ligand-exchange reaction of 3 with para-
toluenesulfonic acid (pTsOH) in acetonitrile[7b] led to the
perfluorinated Koser-type reagent 5.[15] This colorless solid
can be stored at room temperature without any protection
from light or moisture (Scheme 2). In the a-oxytosylation
[7]
and C6F5I(OCOCF3)2 show increased reactivity and solu-
bility and are easy to recycle, we recently introduced
tetrafluorinated IBA (5,6,7,8-tetrafluoro-1-hydroxybenz-
iodoxol-3-one) and IBX (5,6,7,8-tetrafluoro-1-hydroxy-1-
oxobenziodoxol-3-one) derivatives.[8]
Herein we describe the synthesis of a highly reactive,
polyfluorinated hypervalent iodine(III) reagent, which is
readily accessible from commercially available octafluoroto-
luene (1; Scheme 1). Under basic aqueous conditions, 1 was
reduced with zinc.[9] Subsequent treatment with nBuLi and
iodine gave pure 2,3,5,6-tetrafluoro-4-trifluoromethyliodo-
benzene (2). The subsequent oxidation to the iodine(III)
derivative 3 was performed using concentrated nitric acid and
trifluoroacetic anhydride.[10] The amount of nitric acid was
critical, as an excess led to decomposition. Milder oxidants
such as H2O2·urea,[11] NaIO4,[12] or meta-chloroperbenzoic
acid[13] did not generate the iodine(III) derivative 3.
Scheme 2. Preparation of the iodosylarene 4, hydroxy-
(tosyloxy)iodoarene 5, and the iodonium salts 6 and 7.
The alkaline hydrolysis of 3 is exothermic and proceeded
quantitatively to the corresponding fluorinated l3-iodosyl-
arene 4, which was also slowly generated when 3 was exposed
reaction of propiophenone, 5 gave the desired product in 58%
yield (see the Supporting Information). Although the penta-
fluoro-substituted Koser reagent is known, its chemistry has
been hardly explored.[16,7b]
The reaction of 5 with dimedone formed a stable, colorless
but amorphous heptafluoroinated iodonium salt 6. The
reaction with anisole under acidic conditions led to iodonium
salt 7 in high yield and purity after crystallization (Scheme 2).
Single crystals suitable for X-ray diffraction were obtained
(Figure 1).[17] Despite quite different electronic structures in
[*] Dr. S. Schꢀfer, Prof. Dr. T. Wirth
School of Chemistry, Cardiff University
Park Place, Main Building, Cardiff CF10 3AT (UK)
Fax: (+44) 29-2087-6968
E-mail: wirth@cf.ac.uk
academicstaff/wirth.html
[**] We thank Dr. B. Kariuki, Cardiff University, for the X-ray analysis of 7,
Dr. R. Richardson, Cardiff University, for calculations and helpful
discussions, Prof. Dr. C. Bolm, RWTH Aachen, for valuable
suggestions, Warwick Analytical Service for the measurement of
elemental analyses. and the EPSRC National Mass Spectrometry
Service Centre, Swansea, for mass spectrometric data.
À
the aromatic moieties, both C I bonds were found to be
2.11 ꢀ long with a C-I-C angle of 89.38, which leads to an
almost orthogonal alignment of the two aromatic moieties.
The intermolecular distance between the iodine atom and one
À
of the oxygens of the SO3 moiety is around 2.55 ꢀ, which
Supporting information for this article is available on the WWW
indicates a secondary interaction between the two atoms.[18]
2786
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2010, 49, 2786 –2789