The first synthesis and characterization of both diastereomers of a di[2.2]paracyclophane: 4,4′-Bis(1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane)

Article abstract of DOI:10.1021/jo0157775

The synthesis and characterization of both diastereomers of a system comprised of two [2.2]-paracyclophane units linked through a single 4,4′ bond are described. Both the meso and d,l diastereomers of 4,4′-bis(octafluoro[2.2]paracyclophane) have been prepared via a palladium-catalyzed reductive homocoupling reaction by copper, producing a 3:2 ratio of meso and d,l diastereomers. A similar reductive homocoupling of pseudo-o-iodotrifluoromethyloctafluoro[2.21-paracyclophane gave only the analogous meso diastereomer. Single-crystal X-ray structures were obtained for all of the diparacyclophane products.

Full text of DOI:10.1021/jo0157775

J . Org. Chem. 2001, 66, 7055-7058
7055
Th e F ir st Syn th esis a n d Ch a r a cter iza tion of Both Dia ster eom er s
of a Di[2.2]p a r a cyclop h a n e:
4,4′-Bis(1,1,2,2,9,9,10,10-octa flu or o[2.2]p a r a cyclop h a n e)
A. J . Roche,† J .-X. Duan, W. R. Dolbier, J r.,* and K. A. Abboud
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200
wrd@chem.ufl.edu
Received May 21, 2001
The synthesis and characterization of both diastereomers of a system comprised of two [2.2]-
paracyclophane units linked through a single 4,4′ bond are described. Both the meso and d,l
diastereomers of 4,4′-bis(octafluoro[2.2]paracyclophane) have been prepared via a palladium-
catalyzed reductive homocoupling reaction by copper, producing a 3:2 ratio of meso and d,l
diastereomers. A similar reductive homocoupling of pseudo-o-iodotrifluoromethyloctafluoro[2.2]-
paracyclophane gave only the analogous meso diastereomer. Single-crystal X-ray structures were
obtained for all of the diparacyclophane products.
In tr od u ction
and ligands.10,11 When two paracyclophane units are
linked through a single aryl-aryl bond, such diparacy-
clophanes can exist as either meso or d,l diastereomers.
The first synthesis of the parent hydrocarbon bis[2.2]-
paracyclophane was reported in 1994,12 with the crystal
structure of the meso diastereomer appearing later.13 Not
being mentioned, it appears that the d,l diastereomer was
not formed in this reaction. Unable to reproduce the
above synthesis, Ernst and Wittkowski prepared a series
of meso and d,l diparacyclophane structures, where the
[2.2]paracyclophanyl groups are separated by various
spacer groups such as carbonyl or methylene linkages,
and the syntheses, diastereomeric ratios, separation, and
NMR assignments of these compounds were reported
along with several crystal structures.14 Structurally novel
diastereomers closely related to “dimers” of OFP were
recently reported via reaction of OFP with a trifluorom-
ethyl radical source.6
Although it has been 50 years since the first isolation
of [2.2] paracyclophane (PCP),1 the interest and scope of
cyclophane chemistry continues to expand.2 Recently,
bridge-fluorinated cyclophanes have attracted attention
with reports of the synthesis,3 chemical reactivity,4-6 and
commercial applications7 of 1,1,2,2,9,9,10,10-octafluoro-
[2.2]paracyclophane (OFP). It has been clearly demon-
strated that OFP displays not only all of the classic
[2.2]paracyclophane phenomena4,5 (e.g., thermal isomer-
ization/racemisation, transannular communication, NMR
substituent chemical shift additivity, and mass spectral
(xylylene) fragmentation), but also some unusual reactiv-
ity characteristics that are apparently unique to fluori-
nated cyclophanes.6
As a consequence of their geometry and rigid molecular
scaffold,8 paracyclophanes exhibit planar chirality,9 and
they find numerous applications as chiral building blocks
Resu lts a n d Discu ssion
† Present address: Department of Chemistry, Rutgers, The State
University of New J ersey, Camden, New J ersey 08102-1411.
(1) Reviews: (a) Vogtle, F. Cyclophane Chemistry; Wiley: New York,
1993. (b) Boekelheide, V. Cyclophanes. I. Top. Curr. Chem. 1983, 113,
87. (c) Hopf, H.; Marquard, C. Strain and Its Implications In Organic
Chemistry; Kluwer: Dordrecht, 1989.
(2) Brown, C. J .; Farthing, A. C. Nature 1949, 164, 915.
(3) (a) Dolbier, W. R., J r.; Rong, X. X.; Xu, Y.; Beach, W. F. J . Org.
Chem. 1997, 62, 7500. (b) Dolbier, W. R., J r.; Asghar, M. A.; Pan, H.-
Q.; Celewicz, L. J . Org. Chem. 1993, 58, 1827. (c) Dolbier, W. R., J r.;
Duan, J .-X.; Roche, A. J . USP 5,841,005, 1998. (d) Dolbier, W. R., J r.;
Duan, J .-X.; Roche, A. J . Org. Lett. 2000, 2(13), 1867.
Our recent studies of the reactivity of OFP and its
simple derivatives have provided building block com-
pounds that can be used to create more elaborate or exotic
systems that contain its signature bridge-fluorinated
cyclophane skeleton.4,5 One of the more versatile OFP
derivatives is the iodo derivative, and it was recognized
that reductive homocoupling of this compound could
potentially generate bis(OFP) compounds.
(4) Roche, A. J .; Dolbier, W. R., J r. J . Org. Chem. 1999, 64, 9137.
(5) Roche, A. J .; Dolbier, W. R., J r. J . Org. Chem. 2000, 65, 5282.
(6) Dolbier, W. R., J r.; Duan, J .-X.; Abboud, K.; Ameduri, B. J . Am.
Chem. Soc. 2000, 122, 12083.
(7) (a) Beach, W. F.; Lee, C.; Basset, D. R.; Austin, T. M.; Olson, A.
R. Xylylene Polymers. In Wiley Encyclopaedia of Polymer Science and
Technology; Wiley: New York, 1989; Vol. 17, p 990. (b) Majid, N.;
Dabral, S.; McDonald, J . F. J . Electron. Mater. 1989, 18, 301. (c)
Williams, K. R. J . Thermal Anal. 1997, 49, 589.
(10) Selected recent examples of chiral monosubstituted PCP ligands
include: (a) Tanji, S.; Ohno, A.; Sato, I.; Soai, K. Org. Lett. 2001, 3,
287. (b) Bolm, C.; Kuhn, T Synlett. 2000, 899. (c) Masterson, D. S.;
Glatzhofer, D. T. J . Mol. Catal. A 2000, 161, 65.
(11) Selected recent examples of chiral di-substituted PCP ligands
include: (a) Hou, X. L.; Wu, X. W.; Dai, L. X.; Cao, B. X.; Sun, J . Chem.
Commun. 2000, 1195. (b) Vetter, A. H.; Berkessel, A. Tetrahedron Lett.
1998, 39, 1741. (c) Belokon, Y.; Moscalenko, M.; Ikonnikov, N.;
Yashkina, L.; Antonov, D.; Vorontsov, E.; Rozenberg, V. Tetrahedron:
Asymmetry 1997, 8, 3245. (d) Pye, P. J .; Rossen, K.; Reamer, R. A.;
Volante, R. P.; Reider, P. J . Tetrahedron Lett. 1998, 39, 4441.
(12) Kus, P. Pol. J . Chem. 1994, 68, 1983.
(8) Hope, H.; Bernstein, J .; Trueblood, K. N. Acta Crystallogr. B
1972, 28, 1733.
(9) For a clarification of R and S for complex cyclophanes, see: Pye,
P. J .; Rossen, K. Tetrahedron: Asymmetry 1998, 9, 539. Otherwise,
see: Cahn, R. S.; Ingold, C. K.; Prelog, V. Experimentia 1956, 12, 81.
Cahn, R. S.; Ingold, C. K.; Prelog, V. Angew. Chem., Int. Ed. Engl.
1966, 5, 385. Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic
Compounds; Wiley: New York, 1994.
(13) J ones, P. G.; Kus, P. Pol. J . Chem. 1998, 72, 1106.
(14) (a) Ernst, L.; Wittkowski, L. Eur. J . Org. Chem. 1999, 1653, 3.
(b) J ones, G. J .; Ernst, L.; Dix, I.; Wittkowski, L. Acta Crystallogr. 2000,
C56, 239.
10.1021/jo0157775 CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/18/2001

7056 J . Org. Chem., Vol. 66, No. 21, 2001
Roche et al.
be found in the Supporting Information). Integration
showed the ratio of isomers to be 2:1.5:1.5. As expected,
the 19F NMR signals of the major isomer at the lower
temperature were consistent with it being the minor
diastereomer at the higher temperature. Thus, the major
structural diastereomer is able, at low temperatures, to
be detected in two different rotameric forms (which are
themselves present in a 1:1 ratio).
The assignment of meso and d,l to each compound was
made on the basis of single-crystal X-ray analysis. It is
noteworthy that this is the first time that both diaster-
eomers of a di[2.2]paracyclophane system have been
prepared, isolated, and characterized.
When an analogous homocoupling reaction was per-
formed using pseudo-o-iodotrifluoromethyl OFP, NMR
and GC analysis indicated that only one diastereomer
was produced! The GCMS data was entirely consistent
with a bis(OFP)-type structure bearing two trifluorom-
ethyl groups as indicated by the observed parent ion
(838). Furthermore, the trifluoromethyl groups were
shown to be on the “outer” layers of the structure by
observation of a fragment of mass 244, which is consis-
tent with a trifluoromethyl-substituted tetrafluoroxy-
lylene fragment.
Of the various methods employed (summarized in
Table 1), the most successful employed copper and PdCl2‚
dppf in DMF at 80 °C overnight (entry 7), which produced
bis(OFP) in 74% isolated yield; the only other fluorine-
containing product was OFP (11% isolated yield) result-
ing from reduction of the starting iodo compound. The
diastereomeric ratio was calculated as 3:2 as determined
from 19F NMR and GC analyses. The diastereomers could
not be separated from each other by column chromatog-
raphy on silica gel but could be enriched by fractional
crystallization.
By working at much higher concentrations (6×) and
temperatures (120-140 °C), it was possible to carry out
the coupling reaction in moderate yield (and at higher
scale) without the use of the Pd catalyst (Table 1, entry
10).
GC analysis of the product formed with Pd catalysis
showed two compounds in a 3:2 ratio. The GCMS analysis
of the two components produced identical spectra, with
both compounds having prominent M+ ions of mass 702
along with the fragmentation pattern expected for such
bis-cyclophane structures.
The 19F NMR of this diparacyclophane displayed the
expected eight doublets (four AB quartets) between -107
and -118 ppm, plus a trifluoromethyl signal (-59 ppm).
(the spectrum can be found in Figure 3 in the Supporting
Information.) At room temperature, again the 19F NMR
showed line broadening consistent with restricted rota-
tional motion. On warming to 50 °C, the lines sharpened
sufficiently to resolve the peaks clearly, which also
allowed the observation of the recently reported charac-
teristic through-space coupling of the trifluoromethyl
group with the proximate bridge fluorines (5J FF ) 26.8
However, the 19F NMR was more complex than antici-
pated on the basis of our previous experience with OFP
1
derivatives and their 19F and H NMR.4,5 Each diastere-
omer has eight chemically different fluorine atoms, and
since each fluorine will couple strongly with its neighbor
attached to the same carbon (2J F-F ∼ 240 Hz), it was
predicted that each diastereomer would display eight
doublets (four AB quartet patterns) in the 19F NMR.
Unexpectedly, the 19F NMR of the mixture (that by GC
showed only the presence of the two diastereomers)
exhibited more than 16 doublets, and some of the peaks
showed significant line broadening (Figure 1). This was
taken to be an indication of restricted molecular rotation,
observable on the NMR time scale. This was confirmed
by warming the NMR sample to 150 °C, whereupon all
of the lines became sharp, with 16 doublets being
observed. Through integration of the signals it was
confirmed that the two diastereomers were formed in a
3:2 ratio (which agreed well with the GC analysis).
Indeed, knowledge of this 3:2 ratio aided in the assign-
ment of peaks to one or the other diastereomer.
6
Hz and J FF ) 19.5 Hz).4,5 The question of whether this
was the meso or d,l diastereomer was answered by a
single-crystal X-ray structure of the product, and it was
shown to be the meso diastereomer.
It is interesting to note that of all the other related
diparacyclophane systems,7,12,14 none were reported to
exhibit such restricted rotational motion on the basis of
their NMR spectra. They also showed no diastereoselec-
tivity (ratio of 1:1) in their formation, except for the case
of the fluorinated radical addition “dimers”, and in this
reaction, the d,l diastereomer was reported to be the
major product in a 57:43 ratio.6
The homocoupling of iodo-OFP is only 60% diastereo-
selective, giving the meso isomer as the major product,
whereas the pseudo-o-iodotrifluoromethyl (OFP) homo-
coupling reaction gives completely selective meso isomer
formation (no d,l by NMR or GC). These observations are
consistent with the recent observation by Soai and co-
workers10a that pseudo-ortho-disubstituted PCPs give
Examination of the 19F NMR at lower temperatures
allowed the observation of both rotameric forms of the
diastereomer. As the temperature was lowered, the peak
broadening decreased and more peaks appeared, and at
-60 °C, a total of 24 doublets could be observed, indicat-
ing the presence of three bis(OFP) isomers (spectra can

4,4′-Bis(1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane)
J . Org. Chem., Vol. 66, No. 21, 2001 7057
F igu r e 1. 19F NMR of bis(OFP) mixture at room temperature (on top) and 150 °C (bottom).
Ta ble 1. P r ep a r a tion of 4,4′-Bis(1,1,2,2,9,9,10,10-octa flu or o[2.2]p a r a cyclop h a n e)
starting
material
reducing
agent
catalyst
(equiv)
solvent
(T/°C, time/h)
bis(OFP) (%)
(meso/d,l)
OFP
(%)
no.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
OFP-I
OFP-I
OFP-I
OFP-I
OFP-I
OFP-I
OFP-I
OFP-I
OFP-I
OFP-I
OFP-Br
OFP-Br
OFP-Cl
OFP-Cl
Cu
Cu
Cu
Cu
Cu
Cu
Cu
DMF (25, 24)
DMF (140, 24)
DMF (90,8)
DMF (80, 8)
DMF (80,8)
THF (65, 8)
DMF (80,8)
DMF (70, 8)
DMF (70,8)
DMF (130, 6)
DMF (80, 8)
DMF (25,8)
DMF (80, 8)
DMF (80,8)
0
4
0
90
55
50
50
0
11
23
77
55
0
PdCl2 (1.0)
PdCl2 (0.2)
PdCl2 (0.4)
PdCl2 (0.5)
PdCl2‚dppf (0.2)
Ni(Ph3P)4 (1.0)
NiCl2(PPH3)2 (0.2)
40 (3:2)
36 (3:2)
35 (3:2)
0
74 (3:2)
0
0
Cu
Cu
Cu
Zn
Cu
Zn
40 (1:0.8)
PdCl2‚dppf (0.1)
PdCl2‚dppf (0.3)
PdCl2‚dppf (0.1)
PdCl2‚dppf (0.1)
0
0
0
3
96
0
94
much higher enantioselectivities when used as chiral
ligands, when compared to similar monosubstituted PCP
derivatives. In light of the impressive diastereoselectivity
displayed by the pseudo-ortho-disubstituted OFP deriva-
tive in this coupling reaction, it indicates that ap-
propriately substituted bridge fluorinated paracyclo-
phanes should be ideal candidates for chiral ligands,
especially since it has already been demonstrated that
the bridge fluorines prevents racemization (via bibenzyl
radicals) up to temperatures of over 300 °C.5 Work to
prepare and test such compounds is currently in progress.
Con clu sion s
For the first time, the synthesis and characterization
of both diastereomers of a system consisting of two [2.2]
PCP units linked through a single 4,4′ bond are reported.
The 3:2 ratio of meso/d,l bis(OFP) diastereomers was
calculated directly from GC and 19F NMR analyses of the
crude products. Moreover, the meso diastereomer was
shown to exist in two rotameric forms, which could be
resolved at -50 °C by 19F NMR. Crystal structures of the
d,l and both rotamers of the meso compound are pre-

7058 J . Org. Chem., Vol. 66, No. 21, 2001
Roche et al.
239.62 Hz, 1F), -115.995 (d, 2J ) 239.62 Hz, 1F), -116.101
(d, 2J ) 239.62 Hz, 1F), -118.015 (d, 2J ) 239.62 Hz, 1F),
sented. When an analogous reductive homocoupling
reaction of pseudo-o-iodotrifluoromethyl OFP was per-
formed, only one diastereomer was produced. This also
exhibited restricted rotational motion in its 19F NMR
spectrum at room temperature, and a crystal structure
confirmed it to be the meso diastereomer.
2
-119.110 (d, J ) 239.62 Hz, 1F).
d ,l-4,4′-Bis(1,1,2,2,9,9,10,10-oct a flu or o[2.2]p a r a cyclo-
1
p h a n e): 150 °C, DMSO-d6; H NMR δ 7.763 (s, 1H), 7.566-
3
7.500 (m, 5H), 7.418 (d, 1/2 AB, J ) 8.40 Hz, 1H); 19F NMR
2
2
δ -105.017 (d, J ) 242.16 Hz, 1F), -110.210 (d, J ) 242.16
2
2
Hz, 1F), -114.353 (d, J ) 239.62 Hz, 1F), -115.596 (d, J )
237.36 Hz, 1F), -115.680 (d, 2J ) 239.90 Hz, 1F), -116.523
(d, 2J ) 237.36 Hz, 1F), -116.980 (d, 2J ) 239.90 Hz, 1F),
Exp er im en ta l Section
All NMR spectra were obtained on a Varian 300 MHz
Gemini at the specified temperature with a variable-temper-
ature control module. Deuterated acetone was used unless
indicated otherwise, and TMS and CFCl3 were used as
references for 1H and 19F, respectively. All reagents, unless
otherwise specified, were used as purchased from Aldrich or
Fisher. Column chromatography was performed using chro-
matographic silica gel 200-425 mesh, as supplied by Fisher.
Melting points are uncorrected. Mass spectrometric analyses
were obtained at an ionizing potential of 70 eV.
X-r a y Exp er im en ta l Da ta . meso-CF3: a ) 15.745(2) Å, b
) 8.770(1) Å, c ) 21.155(3) Å, â ) 94.572(2)°, V ) 2911.9(6)
Å3, R1 ) 3.24, wR2 ) 7.80, monoclinic P21/c, Z ) 4, T ) 173
K. Meso only: a ) 7.2046(5) Å, b ) 21.865(1) Å, c ) 17.051(1)
Å, â ) 100.848(1)°, V ) 2638.1(3) Å3, R1 ) 3.55, wR2 ) 7.55,
monoclinic Cc, Z ) 4, T ) 173 K. d/l + meso in one crystal: a
) 20.133(2) Å, b ) 12.6261(9) Å, c ) 23.175(2) Å, â ) 115.629-
(1)°, V ) 5311.4(7) Å3, R1 ) 6.81, wR2 ) 14.61, monoclinic
P21/c Z ) 8, T ) 173 K. The structures were solved by the
direct methods in SHELXTL515 and refined using full-matrix
least-squares. The non-H atoms were treated anisotropically,
whereas the hydrogen atoms were calculated in ideal positions
and were riding on their respective carbon atoms. All three
structures have disorders in some of the F atoms of the CF2
or CF3 groups. The most significant disorder is in d/ l + meso
in one crystal. This is because both meso and d/l structures
crystallize where one-half of the molecule is the same in both
but the other is disordered in in a way to give both stereoiso-
mers in the same molecular position.
4,4′-B is (1,1,2,2,9,9,10,10-o c t a flu o r o [2.2]p a r a c y c lo -
p h a n e). A degassed DMF solution (2 mL) containing 4-iodo-
1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane4 (120 mg, 0.251
mmol), copper powder (50 mg, 0.78 mmol), and palladium
dichloride complex with bis(diphenylphosphinyl) ferrocene (40
mg, 0.05 mmol) was stirred vigorously at 80 °C overnight
under an atmosphere of nitrogen. The reaction was cooled to
room temperature and then added to ice-water (30 mL). The
solids thus produced were filtered and chromatographed on
silica gel (hexane/diethyl ether 9/1) to give (Rf ) 0.45)
1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane (10 mg, 11%)
and (Rf ) 0.26) 4,4′-bis(1,1,2,2,9,9,10,10-octa flu or o[2.2]-
p a r a cyclop h a n e) (65 mg, 74%): MS m/z 702 (M+, 49), 526
2
-117.804 (d, J ) 239.62 Hz, 1F).
P r ep a r a tion of Bis-OF P Dia ster eom er s w ith ou t P d
Ca ta lyst. Into a 100 mL, three-necked, round-bottomed flask
containing 20 mL of DMF was added 5 g (10.4 mmol) of iodo-
OFP and 2 g (31.2 mmol) of Cu powder. The mixture was
heated to 120-140 °C and stirred under N2 for 6 h, after which
time the reaction was cooled and 100 mL of Et2O added. The
mixture was filtered to remove solids, and the filtrate was
washed with brine (3 × 30 mL) and then dried over Na2SO4.
After removal of the solvent by rotary evaporation, the residue
was subjected to flash chromatography (silica gel) using hexan/
EtOAc (10:0.05) as eluent to obtain pure bis-OFP as a 1:0.8
mixture of meso and dl isomers, as estimated by 19F NMR.
4,4′-Bis(12-tr iflu or om eth yl-1,1,2,2,9,9,10,10-octa flu or o-
[2.2]p a r a cyclop h a n e). A degassed DMF solution (2 mL) con-
taining pseudo-o-iodotrifluoromethyl-1,1,2,2,9,9,10,10-octafluoro-
[2.2]paracyclophane5 (0.50 g, 0.92 mmol), copper powder (0.09
g, 1.4 mmol), and palladium dichloride complex with bis-
(diphenylphosphinyl)ferrocene (0.15 g, 0.18 mmol) was stirred
vigorously at 80 °C overnight under an atmosphere of nitrogen.
The reaction was cooled to room temperature and then added
to ice-water (100 mL). The solids thus produced were filtered
and chromatographed (hexane/diethyl ether, 8/2) to give (Rf
) 0.53) 4-trifluoromethyl-1,1,2,2,9,9,10,10-octafluoro[2.2]para-
cyclophane4 (0.100 g, 26%) and (Rf ) 0.17) 4,4′-bis(12-
t r iflu or om et h yl-1,1,2,2,9,9,10,10-oct a flu or o[2.2]p a r a cy-
1
clop h a n e) (0.224 g, 58%): mp >250 °C; H NMR (50 °C) δ
3
7.920 (d, ? AB, J ) 8.70 Hz, 1H), 7.835-7.866 (m, 2H), 7.675
3
(d, 1/2 AB, J ) 8.40 Hz, 1H), 7.612 (s, 1H), 7.074 (s, 1H); 19
F
NMR (50 °C) δ -59.025 (dd, 5J ) 26.81 Hz, 6J ) 19.47 Hz,
3F), -108.507 (d, 2J ) 237.36 Hz, 1F), -109.900 (d, 2J ) 237.36
2
2
Hz, 1F), -109.915 (d, J ) 242.16 Hz, 1F), -112.223 (d, J )
237.36 Hz, 1F), -113.676 (d, 2J ) 242.16 Hz, 1F), -114.281
2
5
2
(dq, J ) 242.16 Hz, J ) 26.81 Hz, 1F), -116.433 (dq, J )
6
2
237.36 Hz, J ) 19.47 Hz, 1F), -116.673 (d, J ) 242.16 Hz,
1F); MS m/z 838 (M+, 57), 594 (72), 350 (9), 281 (100), 244
(40). Anal. Calcd for C34H12F22: C, 48.69; H, 1.43. Found: C,
48.60; H, 1.26. The product was shown to be a single diaste-
reomer by GC analysis using a J &W DB-5ms column (Fisher),
and single-crystal X-ray crystallography confirmed it as the
meso diastereomer.
(23), 350 (13), 281 (100), 176 (87). Anal. Calcd for C32H14F16
C, 54.70; H, 1.99. Found: C, 54.39; H, 1.77.
:
Ack n ow led gm en t. Support of this research in part
by Alphametals, Inc., is acknowledged with thanks.
K.A.A. wishes to acknowledge the National Science
Foundation and the University of Florida for funding
of the purchase of the X-ray equipment.
GC analysis of the product using a J &W DB-5ms column
(Fisher) indicated a ratio of diastereomers of 3:2. (Retention
times of 24.0. and 26.5 min for d,l and meso, respectively.)
m eso-4,4′-Bis(1,1,2,2,9,9,10,10-oct a flu or o[2.2]p a r a cy-
3
clop h a n e): 150 °C, DMSO-d6; 1H NMR δ 7.637 (d, 1/2 AB, J
) 8.40 Hz, 1H), 7.566-7.500 (m, 2H), 7.418 (s, 1H), 7.240 (d,
Su p p or tin g In for m a tion Ava ila ble: NMR spectra (two
figures), ORTEP drawings, and X-ray crystallographic data.
This material is available free of charge via the Internet at
http://pubs.acs.org.
3
1/2 AB, J ) 8.40 Hz, 1H), 7.189-7.166 (m, 2H); 19F NMR δ
-106.602 (d, 2J ) 239.90 Hz, 1F), -109.435 (d, 2J ) 239.90
2
2
Hz, 1F), -113.721 (d, J ) 239.62 Hz, 1F), -113.910 (d, J )
(15) Sheldrick, G. M. SHELXTL5; Bruker-AXS: Madison, WI, 1998.
J O0157775