Synthesis and Characterization of Cationic Iodonium Macrocycles

Article abstract of DOI:10.1021/jo030246x

A synthetic strategy for the high-yield preparation of iodonium containing macrocycles such as rhomboids, a square, and a pentagon is described, with the long-term objective of preparing iodonium compounds for potential molecular electronics applications.

Full text of DOI:10.1021/jo030246x

Syn th esis a n d Ch a r a cter iza tion of Ca tion ic Iod on iu m Ma cr ocycles
Ukkiramapandian Radhakrishnan and Peter J . Stang*
Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112
stang@chemistry.utah.edu
Received J uly 31, 2003
A synthetic strategy for the high-yield preparation of iodonium containing macrocycles such as
rhomboids, a square, and a pentagon is described, with the long-term objective of preparing iodonium
compounds for potential molecular electronics applications. Two cationic rhomboid shaped molecules
were prepared for the first time (55-70%) by the treatment of compounds 11 and 12a or 12b with
Me3SiOTf. The reaction of dication 8 with 6 in the presence of Me3SiOTf gave an iodonium containing
molecular square in 70% yield. In addition, a pentagon-shaped macromolecule was prepared in
60% yield. These iodonium-containing charged macromolecules were characterized by multinuclear
NMR, mass spectrometry, and physical means.
CHART 1
In tr od u ction
One of the most exciting and rewarding challenges
chemists face today is to devise a wholly synthetic
macromolecular system for potential applications in
nanotechnology.1 Since the discovery of crown ethers by
Pederson, the interest in the synthesis of neutral
macrocycles such as cyclodextrins, crown ethers, and
cryptands, which can act as molecular or cationic recep-
tors has continually increased.2 In recent years, the
synthesis and investigation on the properties of cationic
macromolecules have attracted attention as well.3,4 To
date, there are two major category of charged macro-
molecular systems those containing nitrogen-carbon
bonds (1)3 and nitrogen-metal bonds (2)4 that have been
explored for their potential application in molecular
electronics4,5 and host-guest chemistry.6,7 Stoddart et al.
have utilized cationic cyclobis(paraquat-p-phenylene) 1
as a basic entity in a number of electrochemically
switchable molecular and supramolecular systems such
as catenanes and rotaxanes (Chart 1).3,8 The catenanes
and rotaxanes are important structural units for the
construction of artificial nanomolecular machines.9
Most of the work in this area has been guided and
governed by the synthetic availability, stability, fatigue
resistance, and toxicity of a given molecular architecture
to be used as a basis for complex design. It is well-known
that polyvalent iodonium compounds are widely available
and meet all of these basic requirements.10 Furthermore,
the Martin-Arduengo formalism predicts the likely
formation of macrocyclic tetraiodonium salts 3 and 4
using 8-I-2 monocationic iodonium salts that have ex-
perimentally proven T-shaped geometry with a 90° bond
angle (Chart 2).11,12 Despite the importance of charged
(1) Frontiers in Supramolecular Organic Chemistry and Photochem-
istry; Schneider, H.-J ., Durr, H., Eds.; VCH: Weinheim, Germany,
1991. (b) Lehn, J .-M. Angew. Chem., Int. Ed. Engl. 1988, 27, 89.
(2) (a) Pederson, C. J . J . Am. Chem. Soc. 1967, 89, 2495. (b)
Pederson, C. J . Aldrichim. Acta, 1971, 4, 1. (c) Synthetic Multidentate
Macrocyclic Compounds; Izatt, R. M., Christensen, J . J ., Eds.; Academic
Press: New York, 1978.
(3) (a) Pease, A. R.; J eppensen, J . O.; Stoddart, J . F.; Luo, Y.; Collier,
C. P.; Heath, J . R. Acc. Chem. Res. 2001, 34, 611. (b) Amabilino, D. B.;
Stoddart, J . F. Chem. Rev. 1995, 95, 2725.
(4) (a) Leininger, S.; Olenyuk, B.; Stang, P. J . Chem. Rev. 2000, 100,
853. (b) Olenyuk, B.; Whiteford, J . A.; Fechtenkotter, A.; Stang, P. J .
Nature 1999, 398, 796. (c) Stang, P. J .; Olenyuk, B. Acc. Chem. Res.
1997, 30, 502. (d) Fujita, M. Chem. Soc. Rev. 1998, 27, 417. (e) Fujita,
M.; Ogura, K. Coord. Chem. Rev. 1996, 148, 249.
(5) (a) Sauvage, J .-P. Acc. Chem. Res. 1998, 31, 611. (b) Nanosystems,
Molecular Machinery, Manufacturing and Computation; Drexler, K.,
Ed.; Wiley: New York, 1992. (c) Molecular Electronic Devices; Carter,
F. E., Ed.; Marcel Dekker: New York, 1987.
(6) (a) Host-Guest Complex Chemistry/ Macrocycles; Vo¨gtle, F.,
Webber, E., Eds.; Springer-Verlag: Berlin, 1985. (b) Inclusion Phe-
nomena and Molecular Recognition; Atwood, J . L., Ed.; Plenum: New
York, 1990.
(8) (a) Bissell, R. A.; Cordova, E.; Kaifer, A. E.; Stoddart, J . F. Nature
1994, 369, 133. (b) Balzani, V.; Gomez-Lopez, M.; Stoddart, J . F., Acc.
Chem. Res. 1998, 31, 405.
(9) (a) Collier, J . P.; Matterstei, G.; Wong, E. W.; Luo, Y.; Beverly,
K.; Sampaio, J .; Raymo, F. M.; Stoddart, J . F. Science 2000, 289, 1172.
(b) Molecular Catenanes, Rotaxanes and Knots; Sauvage, J.-P., Bucheck-
er, D., Eds.; Wiley-VCH: Weinheim, 1999. (c) Schill, G. Catenanes,
Rotaxanes and Knots; Academic Press: New York, 1971.
(10) (a) Stang, P. J .; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123;
2002, 102, 2523. (b) Varvoglis, A. Hypervalent Iodine in Organic
Synthesis; Academic Press: London, 1997. (c) Wirth, T.; Hirt, U. H.
Synthesis 1999, 1271.
(11) Stang, P. J . Angew. Chem., Int. Ed. Engl. 1992, 31, 274. (b)
Stang, P. J .; Arif, A. M.; Crittell, C. M. Angew. Chem., Int. Ed. Engl.
1990, 29, 281.
(7) (a) Bradley, D. Science 1993, 259, 890. (b) Amato, I. Science 1993,
260, 753. (c) Lehn, J .-M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304.
(12) Perkins, C. W.; Martin, J . C.; Arduengo, A. J .; III; Alegria, A.;
Kochi, J . K. J . Am. Chem. Soc. 1980, 102, 7753.
10.1021/jo030246x CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/30/2003
J . Org. Chem. 2003, 68, 9209-9213
9209

Radhakrishnan and Stang
CHART 2
SCHEME 2
SCHEME 1
SCHEME 3
Angular building block 11 was prepared as a stable
white solid by the oxidation of compound 9 with CF3-
CO3H, followed by hydrolysis with toluenesulfonic acid
(Scheme 2).
macromolecules and a significant amount of information
available on the properties of iodonium compounds,
surprisingly only one example on the practical synthesis
of a charged iodonium containing macromolecule has
been described to date.13 Presented here is a versatile
method for the construction of cationic macromolecules
such as rhomboids, a square, and a pentagon in high yield
using T-shaped iodonium compounds as the shape-
defining corner units. The structures of these macrocycles
were confirmed by physical means and multinuclear
NMR and mass spectrometry.
Ca tion ic Molecu la r Rh om boid s. The simplest and
smallest iodonium-containing rhomboid shaped macro-
molecule can be prepared by the reaction of one ∼109°
iodonium angular building block with another angular
trimethylsilyl derivative. Compound 11 corresponds well
with the geometrical requirement for the angular iodo-
nium building block. The counterpart, trimethylsilyl
derivative 12a (R ) Me), was prepared from the corre-
sponding iodo compound by lithiation, followed by quench-
ing with chlorotrimethylsilane.16 The reaction of com-
pounds 11 and 12a in CH2Cl2, in the presence of
Me3SiOTf, gave a pale yellow solid after evaporation of
the solvent. When this solid was dissolved in methanol,
the addition of diethyl ether resulted in the precipitation
of rhomboid 13a (70% isolated yield) as a stable, micro-
crystalline solid (Scheme 3). We have also studied the
reactions of compounds 11 and 12a in the presence of
other Lewis acids such as BF3‚Et2O and CF3CO2H and
found that the yields of rhomboids were lower.
Resu lts a n d Discu ssion
Syn th esis of Bu ild in g Un its. An efficient method for
the synthesis of unsymmetrical diaryliodonium com-
pounds involves the known reaction of [bis(trifluro-
acetoxy)iodo]arenes or [hydroxy(sulfonyloxy)iodo] arenes
with trimethylsilyl-substituted aromatic compounds in
the presence of Lewis acids.14 Syntheses of angular and
linear building blocks for the stepwise construction of
iodonium-containing macrocycles were carried out via
these methods.
Similarly, addition of Me3SiOTf to a mixture of 11 and
12b (R ) H) in CH2Cl2 at -78 °C and stirring at room
temperature for 3-4 h resulted in the formation of
unsymmetrical rhomboid 13b in 55% yield (Scheme 3).
Both of these macrocycles are very stable at room
temperature and soluble in methanol but insoluble in
chloroform, methylene chloride, and nitromethane.
Ca tion ic Molecu la r Squ a r e. The synthesis of a
square can be achieved by the coupling of two linear
iodonium compounds with two linear trimethylsilyl de-
rivatives either in one step or multiple steps. Initially,
we attempted to construct a square-shaped macromol-
Compound 8 was prepared as outlined in Scheme 1.
Oxidation of commercially available 4,4′-diiodobiphenyl
5 with CF3CO3H [prepared from (CF3CO)2O and 80%
H2O2] gave 6 in 77% yield.15 Reaction of 6 with 2 equiv
of 7 and Me3SiOTf gave bisiodonium triflate salt 8 in 90%
isolated yield. Dication 8 is an off-white stable compound,
soluble in methanol but insoluble in CHCl3, CH2Cl2, and
hexanes.
(13) Stang, P. J .; Zhdankin, V. V. J . Am. Chem. Soc. 1993, 115, 9808.
(14) (a) Gallop, P. M.; Paz, M. A.; Fluckiger, R.; Stang, P. J .;
Zhdankin, V. V.; Tykwinski, R. R. J . Am. Chem. Soc. 1993, 115, 11702.
(b) Kuehl, C. J .; Bolz, J . T.; Zhdankin, V. V. Synthesis 1994, 312.
(15) Yagupolskii, L. M.; Maletina, I. I.; Kondratenko, N. V.; Orda,
V. V. Synthesis 1978, 835.
(16) Habich, D.; Effenberger, F. Synthesis 1979, 841.
9210 J . Org. Chem., Vol. 68, No. 24, 2003

Synthesis and Characterization of Cationic Iodonium Macrocycles
SCHEME 4
SCHEME 5
SCHEME 6
ecule in a single step. The reaction of linear compound 6
with 7 in the presence of Me3SiOTf gave molecular square
4 as a minor product (15%) with oligomers as major
products. We hypothesized that the reaction sequence
involves the formation of 8 as an intermediate, which in
turn reacted with one more iodonium compound to give
macrocycle 4 (Scheme 4).
In contrast, stepwise formation of 4 via treatment of 8
with iodonium trifluroacetate 6 in the presence of Me3-
SiOTf resulted in the formation of 4 in 70% yield (Scheme
5).
Ca tion ic Molecu la r P en ta gon . It was envisaged
that a pentagon-shaped molecule might be prepared via
the coupling of dication 8 with the angular diiodonium
species 11. As expected, the reaction of 11 with dication
8 and Me3SiOTf in CH2Cl2 at -78 °C gave pentagon 14
in 60% yield (Scheme 6).
Tem plate-Assisted Syn th esis. Template-assisted syn-
thesis is one of the more efficient methods for the
selective preparation of macrocycles and molecular recep-
tors.17 The template effect not only speeds up the reaction
rates, but it also leads to much higher yields of products.17
A recent report described the template-assisted synthesis
of tetracationic macromolecules using dimethoxybenzene
(DMB) as a neutral guest.18 The DMB formed a weak
complex with the dication and acts as a good template
for the cyclization reaction. Hence, we investigated the
possibility of using a neutral guest (DMB) as a template
to improve the yield of the final cyclization reaction. The
reaction of 8 with 6 and Me3SiOTf in the presence of
DMB gave 4 in 70% isolated yield (Scheme 7), indicating
that there is no template effect and the neutral guest,
DMB, does not enhance this reaction.
NMR Sp ectr oscop ic An a lysis. The new macrocycles
were characterized by NMR (1H, 13C, 19F), mass spec-
trometry, and elemental analysis. In all macrocycles (4,
13a , 13b, and 14), the protons attached to the carbons
ortho to the iodines were observed downfield compared
to the meta protons. The ortho and meta hydrogens were
magnetically coupled to each other with a coupling
constant of 8.4-9.0 Hz. The 1H NMR showed two
multiplets at 8.06 ppm (ortho) and 7.41 ppm (meta) for
rhomboid 13a and two multiplets at 8.05 ppm (ortho) and
7.56 ppm (meta) for the aromatic protons of square (4),
indicative of highly symmetrical structures.
The 1H NMR of the unsymmetrical rhomboid 13b
consists of two multiplets for the ortho and meta protons
of the aromatic structural units. In the case of pentagon
1
14, the H NMR showed two multiplets for the ortho and
meta protons of the linear biphenyl units at 8.14 and 7.64
ppm; it also contained two doublets at 7.95 and 7.19 ppm
for the ortho and meta protons of the angular diphenyl
units. The hydrogens of the methyl group in 14 were
observed at 1.56 ppm as a singlet. The presence of the
counterion (CF3SO3-) in all of these compounds was
confirmed by the signal at -78 ppm in 19F NMR. The
13C{H} NMR data for these macrocycles were consistent
with the structural formulations.
Ma ss Sp ectr oscop ic An a lysis. The molecular com-
position of these macrocycles was established by mass
spectrometry. Fast atom bombardment (FAB) and elec-
trospray ionization (ESI) mass spectrometry provided
charge state information and isotopic resolution for
(17) Templated Organic Synthesis; Diederich, F., Stang, P. J ., Eds.;
Wiley-VCH: Weinheim, Germany, 2000.
(18) Philp, D.; Stoddart, J . F. Synlett 1991, 445.
J . Org. Chem, Vol. 68, No. 24, 2003 9211

Radhakrishnan and Stang
SCHEME 7
molecular ions corresponding to the macrocycles. The
peak at m/z ) 790 was isotopically resolved (m/z spacing
of 1) allowing direct charge state assignment as +1
charge state. The calculated molecular weight of an intact
macromolecule minus one triflate is 791.04 and the
experimental molecular weight is 790.9, in excellent
agreement.
nm, while the distance between the two parallel biphenyl
rings is about 1.1 nm.
Con clu sion
In summary, we have described an efficient method
for the synthesis of iodonium-containing macrocycles
such as rhomboids, a square, and a pentagon in high
yield. Syntheses of these macromolecules were carried
out by the reaction of [bis(trifluroacetoxy)iodo]arenes or
[hydroxy(sulfonyloxy)iodo] with trimethylsilyl-substitut-
ed aromatic compounds in the presence of Me3SiOTf. In
addition, an attempt was made to improve the yield of
square using dimethoxybenzene (DMB) as a template and
found that DMB does not increase the yield of square.
The structures of these macrocycles were established
using elemental analysis, NMR and mass spectrometry.
These iodonium-containing macromolecules may find
potential application in nanotechnology.
FAB analysis of 13b gave a peak at m/z ) 763 due to
the loss of one triflate (M-OTf)+ as well as a peak at 615
for (M - 2OTf + H+)+ in agreement with the composition
of macrocycle 13b. The FAB mass spectrum of 4 has a
peak at m/z ) 1564 that corresponds to the molecular
ion of the cationic portion (M - OTf)+ of 4. Likewise, the
peak at 707 corresponds to the doubly charged cation (M
- 2OTf)2+ of 4. Electrospray ionization mass spectrom-
etry (ESI/MS) was used to identify the composition of
pentagon 14. In the mass spectrum of 14, the +1 species
resulting from the loss of one triflate with a mass-to-
charge ratio m/z ) 1605 and a peak at m/z ) 728.03
attributable to the loss of two triflates were observed.
Exp er im en ta l Section
Molecu la r Mod elin g. As suitable X-ray quality crys-
tals could not be obtained, the square-shaped macrocycle
was structurally minimized.19 Figure 1 displays the
minimized CPK space-filling model of macrocycle 4. The
calculated distance between diagonal iodine atoms is 1.5
All experiments were performed under an inert atmosphere
of nitrogen using standard Schlenk technique. The solvents
used in the reactions were reagent or HPLC grade and purified
in the following manner: methylene chloride was distilled from
calcium hydride, diethyl ether was distilled from sodium/
benzophenone, and CH3CN was distilled from calcium hydride.
Trifluroacetates 6, 10,15 and Me3SiOTf 20 were prepared using
a modified literature procedure. The trimethylsilyl derivatives
(7, 12a , and 12b) were prepared from the corresponding
iodides using BuLi/TMSCl.16
P r ep a r a tion of 8. In a Schlenk flask (25 mL) equipped with
a magnetic stir bar were placed 6 (0.426 g, 0.5 mmol), 7 (0.294
g, 1 mmol), and CH2Cl2 (15 mL) under a N2 atmosphere. To
this mixture was added Me3SiOTf (0.6 mL) at -78 °C, and
the mixture was allowed to warm to room temperature. After
4 h, the solvent was evaporated and the residue was dissolved
in a methanol/CH2Cl2 (2:1) mixture to remove any oligomers.
The solvent was evaporated again, and the residue was washed
with ether to yield 8 (0.52 g, 90%): 1H NMR (DMSO-d6/CDCl3,
300 MHz) δ 8.05 (d, 4H, J ) 8.2 Hz), 8.00 (d, 4H, J ) 8.3 Hz),
7.6-7.45 (m, 16H), 0.21 (s, 18H); 19F NMR (DMSO-d6/CDCl3)
-78.13; FAB/MS m/z 1005 (M - OTf), 428 (M - 2OTf). Anal.
(19) Hyperchem 5.1, Hypercube, Inc., 1997.
(20) Demuth, M.; Mikhail, G. Synthesis 1982, 827.
F IGURE 1.
9212 J . Org. Chem., Vol. 68, No. 24, 2003

Synthesis and Characterization of Cationic Iodonium Macrocycles
Calcd for C44H42S2Si2I2O6F6: C, 45.76; H, 3.67. Found: C,
45.43; H, 3.55.
FAB/MS m/z 763 (M - OTf), 615.1 (M - OTf + H+). Anal.
Calcd for C30H24F6I2O6S2: C, 39.49; H, 2.65; S, 7.03. Found:
C, 39.51; H, 3.04; S, 6.73.
P r ep a r a tion of 11. To a stirred solution of trifluroacetate
10 (2.05 g, 2.3 mmol) in CH3CN was added TsOH‚H2O (0.513
g, 2.7 mmol) at 0 °C. The mixture was warmed to room
temperature and stirred until the formation of a white
crystalline precipitate. The product was filtered, washed with
dry CH2Cl2 (10 mL), and dried in vacuo to give 11 (1.12 g,
60%): 1H NMR (DMSO-d6/CDCl3, 300 MHz) δ 8.15 (d, 4H, J
) 8.4 Hz), 7.51 (d, 4H, J ) 8.7 Hz), 7.42 (d, 4H, J ) 8.4 Hz),
7.16 (d, 4H, J ) 8.7 Hz), 2.24 (s, 6H), 1.83 (s, 6H); 13C NMR
(CD3OD, 75 MHz) δ 157.1, 143.1, 141.9, 137.2, 131.4, 129.9,
126.9, 119.8, 48.1, 45.3, 30.5, 21.3; ESI/MS m/z 481.1 (M -
2OTs), 447.9 [M - (2OTs + 2OH)].
P r ep a r a tion of Ma cr ocycle 4. In a Schlenk flask (25 mL)
equipped with a magnetic stir bar were placed 6 (0.212 g, 0.25
mmol), 8 (0.25 g, 0.25 mmol), and CH2Cl2 (10 mL) under an
N2 atmosphere. To this mixture was added Me3SiOTf (0.6 mL)
at -78 °C, and the solution was allowed to warm to room
temperature and stirred for 4 h. Workup was done as above:
1
yield (0.275 g, 71%); H NMR (CD3OD, 300 MHz) δ 8.29 (d,
16H, J ) 8.7 Hz), 7.77 (d, 16H, J ) 8.7 Hz); 13C NMR (DMSO-
d6/CDCl3, 75 MHz) δ 141.6 (Ci-I), 135.9 (Co-I), 130.2 (Cm-I),
116.2 (Cp-I), 120.8 (q, J ) 319 Hz); 19F NMR (CD3OD) -78.13;
FAB/MS m/z 1564 (M - OTf), 1415 (M - 2OTf + H+), 707 (M
- 2OTf). Anal. Calcd for C52H32F12I4O12S4: C, 36.47; H, 1.88;
S, 7.49. Found: C, 36.09; H, 2.19; S, 7.29.
P r ep a r a tion of 13a . To a mixture of 11 (0.21 g, 0.25 mmol)
and 12a (0.085 g, 0.25 mmol) in CH2Cl2 (10 mL) at -78 °C
was added Me3SiOTf (0.6 mL). The reaction mixture was
allowed to warm to room temperature. After 4 h, the solvent
was evaporated and the residue was dissolved in a methanol/
CH2Cl2 (2:1) mixture to remove any oligomers. The solvent was
evaporated, and the residue was washed with ether to yield
P r ep a r a tion of Ma cr ocycle 14. To a mixture of 8 (0.25 g,
0.25 mmol) and 11 (0.205 g, 0.25 mmol) in CH2Cl2 (10 mL) at
-78 °C was added Me3SiOTf (0.6 mL). The reaction mixture
was allowed to warm to room temperature and stirred for 4
1
h. Workup was done as above: yield (60%, 0.26 g); H NMR
1
13a : yield (70%, 0.16 g); H NMR (CD3OD, 300 MHz) δ 8.06
(DMSO-d6/CDCl3, 300 MHz) δ 8.14 (m, 12H), 7.95 (d, 4H, J )
8.7 Hz), 7.64 (m, 12H), 7.19 (d, 4H, J ) 8.4 Hz) 1.56 (s, 6H);
13C NMR (CD3OD, 75 MHz) δ 155.9, 144.3, 137.3, 137.2, 136.5,
131.9, 131.6 (all Ar), 129.1 (q, J ) 319 Hz) 116.1 (Ci-Ar), 113.4
(d, 8H, J ) 9.0 Hz), 7.41 (d, 8H, J ) 8.7 Hz), 1.63 (s, 12H); 13
C
NMR (CD3OD, 75 MHz) δ 153.0 (Ci-I), 134.2 (Co-I), 129.6
(Cm-I), 111.5 (Cp-I), 120.8 (q, J ) 319 Hz), 42.9 (Ci-Me), 29.1
(Me); 19F NMR (CD3OD) -78.13; FAB/MS m/z 790 (M - OTf),
642 (M - 2OTf + H+). Anal. Calcd for C32H28F6I2O6S2: C,
40.87; H, 3.00; S, 6.82. Found: C, 41.04; H, 3.24; S, 6.44.
P r ep a r a tion of Ma cr ocycle 13b. To a mixture of 11 (0.205
g, 0.25 mmol) and 12b (0.078 g, 0.25 mmol) in CH2Cl2 (10 mL)
at -78 °C was added Me3SiOTf (0.6 mL). The reaction mixture
was allowed to warm to room temperature and stirred for 4
19
(Ci-Ar), 44.9 (Ci-Me), 30.4 (Me); F NMR (CD3OD) -78.13;
ESI/MS m/z 1605 (M - OTf), 728.03 (M - 2OTf). Anal. Calcd
for C55H38F12I4O12S4: C, 37.65; H, 2.18; S, 7.31. Found: C,
37.55; H, 2.51; S, 7.39.
Ack n ow led gm en t. We thank the National Institute
of Health (GM-57052) for financial support.
1
h. Workup was done as above: yield (55%, 0.125 g); H NMR
Su p p or tin g In for m a tion Ava ila ble: Proton and mass
spectra for compounds 4, 13a , 13b, and 14. This material is
available free of charge via the Internet at http://pubs.acs.org.
(CD3OD, 300 MHz) δ 8.04 (m, 8H), 7.31 (d, 8H, J ) 8.4 Hz),
4.04 (s, 2H), 1.63 (s, 6H); 13C NMR (CD3OD, 75 MHz) δ 155.2,
146.1, 137.8, 136.2, 135.7, 133.1, 131.1, 129.2, 128.1 (q) 44.2
(-CH2-), 41.0 (Ci-Me), 29.8 (Me); 19 F NMR (CD3OD) -78.13;
J O030246X
J . Org. Chem, Vol. 68, No. 24, 2003 9213