J. Am. Chem. Soc. 1997, 119, 4775-4776
4775
Preparation, X-ray Crystal Structure, and
Chemistry of
((Arylsulfonyl)methyl)(phenyl)iodonium Triflates.
Stable Alkyliodonium Salts
Viktor V. Zhdankin,* Scott A. Erickson, and Kari J. Hanson
Department of Chemistry
UniVersity of Minnesota-Duluth
Duluth, Minnesota 55812
ReceiVed March 12, 1997
Derivatives of polyvalent iodine with an alkyl substituent at
iodine generally are highly unstable and can exist only as short-
lived reactive intermediates in the oxidation of alkyl iodides
and some other reactions.1 For example, the low-temperature
reaction of iodomethane with chlorine results in the formation
of a yellow precipitate of (dichloroiodo)methane which rapidly
decomposes above -28 °C.1b The introduction of an electron-
withdrawing substituent into the alkyl moiety may lead to
stabilization of the molecule; for example, (dichloroiodo)methyl
sulfones, ArSO2CH2ICl2,2 1-(dichloroiodo)-1H,1H-perfluoro-
alkanes, RfCH2ICl2,3 and tosylates, RfCH2I(OH)OTs,4 are
known, relatively stable compounds. Several examples of
iodonium salts, R2I+X-, with one or two aliphatic alkyl groups
were generated and investigated by NMR spectroscopy at low
temperatures, and some of them even were isolated in the form
of highly unstable crystalline products.5 The only known
example of stable derivatives of this type are polyfluoroalkyl-
(aryl)iodonium salts. These salts as chlorides were first prepared
in the 1970s by Yagupolskii and co-workers6 and later widely
applied as electrophilic polyfluoroalkylating reagents by Ume-
moto and co-workers.7
Figure 1. X-ray structure of ((p-tolylsulfonyl)methyl)(phenyl)iodonium
triflate 3b. Selected bond lengths (Å): I(1)-C(1) 2.131(3), I(1)-C(9)
2.209(3), I(1)-O(3) 2.797, I(1)-O(5) 2.999, C(1)-S(1) 1.839(3), S(1)-
C(2) 1.691(3). Selected bond angles (deg): C(1)-I(1)-C(9) 91.53-
(11), S(1)-C(1)-I(1) 113.84(14).
Table 1. Reactions of ((Arylsulfonyl)methyl)(phenyl)iodonium
Triflates (3a,b) with Organic Substrates
In this paper, we report the preparation, X-ray crystal
structure, and chemical reactivity of ((arylsulfonyl)methyl)-
iodonium triflates 3, stable alkyliodonium salts of a new
structural type.
((Arylsulfonyl)methyl)iodonium salts 3 can be conveniently
prepared in two steps starting from the readily available2
iodomethyl sulfones 1. In the first step, starting iodides 1 are
oxidized with peroxytrifluoroacetic acid to trifluoroacetates 2
in almost quantitative yield. The subsequent treatment of
trifluoroacetates 2 with benzene and trimethylsilyltriflate in
dichloromethane affords products 3 in a good yield.8 Both
iodonium salts 3a and 3b are not moisture sensitive, can be
purified by crystallization from acetonitrile, and can be stored
for several months in a refrigerator.
a All reactions were carried out in CH2Cl2, under N2, at room
1
temperature. b Yields determined by H NMR. c Isolated yields.
Products 3a,b were identified by spectral data and elemental
analyses.8 In particular, the 1H NMR displayed the characteristic
signals of methylene protons at δ ) 5.52 ppm, shifted about 1
ppm downfield compared to the starting iodomethyl sulfones
1. The structure of iodonium triflate 3b was unambiguously
established by a single-crystal X-ray analysis (Figure 1). The
structural data revealed the expected geometry for iodonium
salts with the C1-I-C9 bond angle of 91.53 (11)°. The I-C
bond distances of 2.131 and 2.209 Å are longer than a typical
bond length in diaryliodonium salts (2.0 to 2.1 Å1a). The
distance between the iodine atom and the nearest oxygen of
the triflate anion, I‚‚‚O3, is 2.797 Å. A weaker secondary
bonding between the iodine atom and the triflate anion (I‚‚‚O5
) 2.999 Å) is also present. To our knowledge, no X-ray crystal
(1) (a) Varvoglis, A. The Organic Chemistry of Polycoordinated Iodine;
VCH Publishers, Inc.: New York, 1992. Varvoglis, A. HyperValent Iodine
in Organic Synthesis; Academic Press: London, 1997. Varvoglis, A.
Tetrahedron 1997, 53, 1179. (b) Stang, P. J.; Zhdankin, V. V. Chem. ReV.
1996, 96, 1123. (c) Koser, G. F. In The Chemistry of Functional Groups,
Supplement D; Patai, S., Rappoport, Z., Eds; Wiley-Interscience: Chichester,
1983; Chapters 18 and 25, pp 721-811 and 1265-1351. (d) Moriarty, R.
M.; Vaid, R. K. Synthesis 1990, 431.
(2) Cotter, J. L.; Andrews, L. J.; Keefer, R. M. J. Am. Chem. Soc. 1962,
84, 4692.
(3) Bravo, P.; Montanari, V.; Resnati, G.; DesMarteau, D. D. J. Org.
Chem. 1994, 59, 6093.
(4) Zhdankin, V. V.; Kuehl, C. J.; Simonsen, A. J. J. Org. Chem. 1996,
61, 8272.
(5) Olah, G. A. Halonium Ions; Wiley: New York, 1975.
(6) Yagupolskii, L. M.; Maletina, I. I.; Kondratenko, N. V.; Orda, V. V.
Synthesis 1978, 835.
(7) Umemoto, T. Chem. ReV. 1996, 96, 1757.
3
structural data on polyvalent iodine species with an I-Csp bond
were previously reported in the literature.
Similarly to the known polyfluoroalkyl(aryl)iodonium salts,7
((arylsulfonyl)methyl)iodonium triflates 3 can be used as
efficient electrophilic alkylating reagents. We investigated
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