A Greek cross dodecaphenylene: Sparteine-mediated asymmetric synthesis of chiral D2-symmetric π-conjugated tetra-o-phenylenes

Article abstract of DOI:10.1016/S0040-4020(01)00241-1

The asymmetric synthesis of a chiral, nonracemic π-conjugated system with D₂ point group of symmetry, dodecaphenylene 4 is described. In the key step, (-)-sparteine- and Cu(II)-mediated oxidation of 2,2′-dilithio-1,1′-biaryls in ether gives the corresponding dimers, tetra-o-phenylenes, in 80% isolated yields and 50-60% ee's. X-Ray crystallography confirms the structure of rac-4 and its molecular shape of a Greek cross. The torsional angles between the benzene rings in the tetra-o-phenylene core of rac-4 are in the 56.5-71.0° range. However, CD and UV spectra of 4 in CH₂Cl₂ are consistent with significant conjugation between the four terphenyl moieties.

Full text of DOI:10.1016/S0040-4020(01)00241-1

TETRAHEDRON
Pergamon
Tetrahedron 57 -2001) 3725±3735
A Greek cross dodecaphenylene: sparteine-mediated asymmetric
synthesis of chiral D2-symmetric p-conjugated tetra-o-phenylenes
Andrzej Rajca,p Hua Wang, Pavel Bolshov and Suchada Rajca
Department of Chemistry, University of Nebraska, Lincoln, NE 68588-0304, USA
Received 5 October 2000; accepted 29 December 2000
AbstractÐThe asymmetric synthesis of a chiral, nonracemic p-conjugated system with D2 point group of symmetry, dodecaphenylene 4 is
described. In the key step, -2)-sparteine- and Cu-II)-mediated oxidation of 2,20-dilithio-1,10-biaryls in ether gives the corresponding dimers,
tetra-o-phenylenes, in 80% isolated yields and 50±60% ee's. X-Ray crystallography con®rms the structure of rac-4 and its molecular shape of
a Greek cross. The torsional angles between the benzene rings in the tetra-o-phenylene core of rac-4 are in the 56.5±71.08 range. However,
CD and UV spectra of 4 in CH2Cl2 are consistent with signi®cant conjugation between the four terphenyl moieties. q 2001 Elsevier Science
Ltd. All rights reserved.
1. Introduction
One of our approaches relies on chiral derivatives of tetra-o-
phenylene 1 -tetrabenzo[a,c,e,g]cyclooctatetraene), a saddle
shaped molecule, e.g. short p-conjugated double helices 2
and 3.5±7 Such tetra-o-phenylene-based chiral p-conjugated
molecules may possess extraordinarily high barriers for
racemization and relatively high symmetry, such as D2
point groups of symmetry in 2 and 3.5,7,8 In addition to
double helices, a different substitution pattern of 1 may
lead to molecules with the shape of Greek cross, but chiral.
A novel dodecaphenylene 4, chiral p-conjugated molecule
with D2 point group of symmetry, may be viewed as a
molecule with two perpendicularly crossed hexaphenylenes.
Compared to spiro-linked oligophenyls and tetrahedrally
linked oligo-phenylenevinylenes), which have favorable
morphology and optical properties for light emitting
diodes,9,10 4 is designed to possess chirality and p-conju-
gation between the crossed chains.
There is a growing interest in chiral p-conjugated mole-
cules, directed at the design of organic materials.1 The chir-
ality may provide not only additional electronic properties
but also allow for the control of packing and p±p inter-
actions in the solid as well.2±4 Molecular shapes and
enantiomeric excesses, ee q 0%; are important factors.
Therefore, asymmetric synthesis of novel chiral p-conju-
gated molecules is the ®rst step toward ef®cient preparation
of organic materials with interesting properties.
There are only three examples of nonracemic tetra-o-
phenylenes; they are prepared in rather low yields either
from nonracemic biaryls or via resolution of race-
mates.7,8 In this work, we describe an ef®cient asym-
metric synthesis for chiral tetra-o-phenylenes, based
upon -2)-sparteine- and CuBr2-mediated coupling of
2,20-dilithiobiaryls -Scheme 1).11,12 Two aryl±aryl CC
bonds are formed and the con®guration of four chiral
axes is set. For the tetra-o-phenylene ring to be formed,
the two chiral axes originating from the 2,20-dilithio-
biaryl must have identical con®guration -e.g., R) but oppo-
site to the two new axes -e.g., S) which are associated with
the newly formed CC bonds -Scheme 1).7
The synthesis and characterization -including X-ray crystal-
lography) of the Greek cross p-conjugated dodecaphenyl-
ene 4 are reported.
Keywords: asymmetric synthesis; biaryl; chiral; sparteine; p-conjugated.
Corresponding author. Tel.: 11-402-472-9196; fax: 11-402-472-9402;
e-mail: arajca1@unl.edu
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020-01)00241-1

3726
A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
Scheme 1. Enantioselective synthesis of tetra-o-phenylenes. Intercepted lines indicate chiral axes -R and S).
Scheme 2. Synthesis of tetra-o-phenylenes 9±11.
2. Results and discussion
compounds 6±8 in 68±77% yields. The selectivity between
C±Br vs. C±I oxidative addition is suf®cient to permit the
use of only small excess -2.5 vs 2 equiv.) iodoaryls.19 This is
especially important in the case of 6, where the greater
excess of 4-iodobiphenyl and/or inaccurate stoichimetry
of t-BuLi leads to increased contamination with nearly
insoluble p-quaterphenyl side product, complicating the
puri®cation process.
Synthesis of tetra-o-phenylenes 9±11 is outlined in Scheme
2).
Bromination of 4,40-di-tert-butylbiphenyl gives 2,20,5,50-
tetrabromo-4,40-di-tert-butylbiphenyl -5) in ,20%
yield.13,14 In 5, one would expect that Li/Br exchange at
the 2,20-sites will be favored by the ion triplet formation.15
However, treatment of 5 with t-BuLi in THF at 2788C gives
predominantly the 5,50-dilithio derivative of 5, as evidenced
by both proton and deuteron quenching experiments.16 It
may be speculated that this remarkable selectivity for
the Li/Br exchange at the 5,50-sites is caused by steric
acceleration.17,18
In the next step, 6±8 are treated with t-BuLi -4 equiv.) and
-2)-sparteine -2 equiv.) in ether/pentane at 2788C. The
reaction mixture is brie¯y -30 min) allowed to attain
2208C, and then it is cooled to 2788C. After addition of
CuBr2 -6 equiv.), the vigorously stirred reaction mixture is
allowed to attain ambient temperature overnight. Following
aqueous workup, 1H NMR analyses of the reaction mixtures
reveal that tetra-o-phenylenes 9±11 are the predominant
products -,90% yield) and only minor amounts of the
biphenylene side products 12±14 -,10% yield) are formed
Following selective Li/Br exchange at the 5,50-sites in 5 and
transmetallation with ZnCl2, the Negishi coupling with
iodoaryls gives the corresponding 5,50-diarylated
Table 1. Synthesis of tetra-o-phenenylenes 9±11 and biphenylenes 12±14
R
Procedurea
-9±11)/-12±14)b -crude)
ee -%) -crude)
ee -%) -LC)
Yield -%)c -9±11)
Yield -%)c -12±14)
4-C6H4Ph
A
B
C
D
E
A
B
A
B
8:1±3:1
3:1
7:1
1:3±4:1
1:20
8:1
2:1
7:1
4:1
49±59
±
35
8±9
±
50
±
50
±
57±64
±
±
±
±
54
±
56
±
75
40
±
±
±
86
55
81
31
6
8
±
±
40±50
3
4
3
7
Ph
4-MeOC6H4
a
Aˆpentane/ether/-2)-sparteine, 2208C, 30 min; Bˆpentane/ether -no -2)-sparteine); Cˆpentane/ether/-2)-sparteine, 2788C, 30 min; Dˆpentane/THF/
Molar ratios from 1H NMR analyses.
Isolated yields of pure compounds.
-2)-sparteine, 2208C, 30 min; Eˆpentane/THF -no -2)-sparteine).
b
c

A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
3727
Figure 1. Molecular conformation for 4 as determined by a single crystal X-ray crystallography. The disordered molecules of solvent of crystallization
-chloroform) are not shown. Top part: Ortep plot, carbon atoms are depicted with ellipsoids representing 50% probability level. Bottom part: space ®lling plot.

3728
A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
Ê
Table 2. Selected interatomic distances -A), angles -deg), and torsional angles -deg) for 4 -space group P21/n).
Hexaphenylene A
Hexaphenylene B
C-31)±C-48)
C-31)±C-37)±C-48)
C-31)±C-20)±C-48)
C-12)ÐC-67)
C-12)ÐC-1)±C-67)
C-12)ÐC-56)±C-67)
a-torsions -within the tetra-o-
phenylene moiety):a
24.3
176.5
175.9
24.2
167.3
168.0
C-18)ÐC-1)±C-56)ÐC-57)
C-2)±C-1)±C-56)ÐC-55)
b-torsions:
258.1-4)
263.5-4)
C-21)±C-20)±C-37)±C-54)
C-19)±C-20)±C-37)±C-38)
258.6-4)
265.6-4)
C-3)±C-4)±C-5)±C-6)
C-17)ÐC-4)±C-5)±C-16)
C-72)ÐC-59)±C-60)ÐC-71)
C-58)ÐC-59)±C-60)ÐC-61)
x-torsions:
13.8-4)
15.2-4)
11.7-4)
11.0-4)
C-53)±C-40)±C-41)±C-52)
C-39)±C-40)±C-41)±C-42)
C-36)±C-23)±C-24)±C-35)
C-22)±C-23)±C-24)±C-25)
241.0-4)
240.0-4)
230.5-4)
231.0-4)
C-7)±C-8)±C-9)±C-10)
C-15)ÐC-8)±C-9)±C-14)
C-62)ÐC-63)±C-64)ÐC-65)
C-70)ÐC-63)±C-64)ÐC-69)
238.6-5)
241.2-5)
232.8-5)
232.8-5)
C-51)±C-44)±C-45)±C-50)
C-43)±C-44)±C-45)±C-46)
C-34)±C-27)±C-28)±C-33)
C-26)±C-27)±C-28)±C-29)
227.8-4)
228.3-4)
232.7-5)
±30.7-5)
a
Other torsional angles within the tetra-o-phenylene moiety are: C-1)±C-2)±C-19)±C-20)ˆ71.0-3), C-3)±C-2)±C-19)±C-36)ˆ63.5-3), C-37)±C-38)±
C-55)±C-56)ˆ66.9-4), C-39)±C-38)±C-55)±C-72)ˆ56.5-3).
-Table 1, procedure A). The ee's of about 50% are repro-
ducibly obtained. Nonracemic 9±11 are isolated in about
80% yields -Table 1, procedure A). Analogous reactions,
but without sparteine, give racemic 9±11; however, the
admixtures of 12±14 are somewhat increased but they are
still relatively minor -,15% yield) -Table 1, procedure B).
biaryls provides a practical synthesis of nonracemic tetra-
o-phenylenes in high chemical yields and moderate ee's.
Fractional crystallization of nonracemic 9 -ee 50±60%)
rt
gives optically pure 9 -[a]D ˆ1170) in 20±30% yield
from 6. Removal of tert-butyl groups from 9 -ee 0 or
100%) using AlCl3 in benzene,13 gives dodecaphenylene 4
in 60±90% yield -Eq. -2)). -Low solubility of rac-4 in
common organic solvents leads to lower isolated yields.)
The reaction conditions for synthesis of 9 and 12 are further
studied. For procedure A -Table 1), 2±3 fold increase in the
number of equivalents of t-BuLi and/or -2)-sparteine and/
or CuBr2 has no effect on ee's or yields. However, vigorous
stirring after the addition of CuBr2 is essential for high ee.
When -2)-sparteine is added and kept at 2788C, without
equilibriation at 2208C, the ee of 9 is signi®cantly
decreased -Table 1, procedure C).
Starting from the optically pure 9, nonracemic
4
rt
-[a]D ˆ162) is obtained; however, ee of 4 could not be
determined by NMR spectroscopy -see Section 4).
Change of solvent from ether/pentane to pentane/THF
affects ee and/or product distribution.20 With -2)-sparteine
-Table 1, procedure D), tetra-o-phenylene 9 is still a major
product but its ee of 8±9% is rather low. Without -2)-spar-
teine -Table 1, procedure E), biphenylene 12 becomes the
dominant product -9:12, 1:20), which is isolated in 40±50%
yield -Eq. -1)).21
ꢀ2†
NMR spectra for 4±14 show the expected numbers of reso-
nances and spin coupling patterns. For biphenylene products
12±14, the selected aromatic protons and carbons are sig-
ni®cantly up®eld-shifted compared to 9±11, as expected.21
In MS -EI), 12±14 show the expected isotopic clusters at
M1; isotopic clusters at m/z corresponding to 2M1 are either
not detected or their intensity is negligible. For 4 and 9±11,
isotopic clusters at m/z corresponding to M1 are found; only
negligible, if any, intensities of monocharged ions at the m/z
corresponding to -M/2)1 are detected. For all compounds,
4±14, high resolution MS -either EI or FAB) give the
expected exact masses for M1 -within 2.7 ppm).
ꢀ1†
Overall, -2)-sparteine mediated coupling of 2,20-dilithio-
The structure of rac-4 was con®rmed by single crystal X-ray

A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
3729
Figure 2. Crystal packing for 4 -view along a-axis). The disordered molecules of chloroform are not shown.
analysis -Fig. 1). The molecule has very approximate D2
point group of symmetry; all 72 carbon atoms are non-
equivalent. The torsion angles between benzene rings within
the tetra-o-phenylene moiety are in the -^)56.5±71.08
range, similar to that in 1.22 For the remaining benzene
rings, the torsion angles are in the -^)11.0±41.28 range.
The space ®lling plot shows that 4 has the molecular
shape of a Greek cross -Fig. 1). The two crossing p-hexa-
phenylenes are designated as A and B -Table 2). Both A and
B are about 2.4 nm long; A is more planar and less bent
compared to B -Table 2). While the out-of-plane twisting
within the tetra-o-phenylene moiety is unavoidable in each
of the p-hexaphenylenes, the four p-terphenyl arms could
adopt near planar conformations.23
The crystal of rac-4 contains 4.5 molecules of chloroform
per asymmetric unit. The crystal structure possesses large
voids ®lled with badly disordered molecules of chloroform.
The solvent accessible volume is slightly over a third -0.37)
of the total volume -Fig. 2).24
UV/vis spectra for 4, 9, and p-terphenyl in methylene
chloride are shown in Fig. 3.25 The bathochromic shifts
for 4 vs p-terphenyl vs 9 -22 and 18 nm, respectively)
are rather substantial. This suggests that conjugation
between the four p-terphenyl arms in 4 is signi®cant, con-
sidering the relatively large torsion angles between benzene
rings within the tetra-o-phenylene core. However, the
Figure 3. UV±vis spectra for 4, 9, and p-terphenyl in CH2Cl2. lmax/nm
-log-emax/L mol21 cm21)): 4, 228 -4.77), 256 -4.75), 302 -5.18); 9, 232
-4.96), 262 -5.20); p-terphenyl, 280 -4.51).

3730
A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
Figure 6. Selected exciton chiralities between the long-axis-polarized elec-
tronic transitions for the diagonal -positive) and proximate -negative)
biphenyl chromophores in 9.
presence of tert-butyl groups in 9 disrupts conjugation
between the biphenyl moieties and the tetra-o-phenylene
core. These observations are con®rmed by CD spectra of
9 and 4 -Figs. 4 and 5). For 9, one prominent positive
couplet -positive at long l and negative at short l cotton
effects) is centered at 259 nm. For 4, the long wavelength
couplet, centered at 289 nm, is negative. The exciton
coupling model would predict the same signs for the long
wavelength couplets in 4 and 9, providing that both
compounds possess identical con®gurations.26 The couplet
inversion in 4 might suggest that the exciton coupling
model, which assumes negligible interchromophoric conju-
gation, is not applicable to 4.7,8a,27
Figure 4. UV±vis -top) and CD -bottom) spectra for 9 -951% ee) in
CH2Cl2. CD, lmax/nm -Demax/L mol21 cm21): 249.5 -2149), 258.5 -0),
268.5 -155).
Assuming that biphenyl chromophores in 9 are unconju-
gated and their long-axis polarized transitions are domi-
nant,28 exciton coupling model may be used to infer
absolute con®guration of 9.26 Positive and negative exciton
chiralities, which are predicted for 9, involve either diagonal
or proximate pairs of biphenyl chromophores -Fig. 6).
-Exciton chiralities of biphenyls within the p-hexaphenyl-
enes are nil, because each two such biphenyls are alligned
parallel to each other.) As the interchromophoric distances
for the diagonal pairs are shorter, compared to the proximate
pairs, the exciton chirality of the diagonal pair of biphenyl
chromophores is expected to be dominant. Therefore, the
exciton chirality for the diagonal pair should be positive to
be consistent with the positive couplet centered at 259 nm in
the CD spectrum of 9; i.e. the absolute con®guration of 9
may tentatively be assigned as shown in Fig. 6. Also, this
would suggest selectivity of -2)-sparteine toward -R)-2,20-
dilithiobiaryls -Scheme 1).
3. Conclusion
Chiral derivatives of p-conjugated tetra-o-phenylenes are
prepared in good yields and moderate ee's via -2)-sparteine
mediated asymmetric synthesis. As p-terphenyl has excel-
lent quantum yields of ¯uorescence and its selected radical
cation salts are good electrical conductors,23,29 the Greek
cross dodecaphenylene 4, with four conjugated p-terphenyl
arms within a chiral molecule, is a promising target for
LEDs and electrical conductors.
Figure 5. UV±vis -top) and CD -bottom) spectra for 4 -undetermined ee) in
CH2Cl2. CD, the approximate concentrations are 25, 50, 75, 100, and
125 mM.

A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
3731
4. Experimental
4.1. General procedures
were added until baseline separation between the reso-
nances of the enantiomers -in equilibrium with diastereo-
meric complexes) was attained. Typical amounts of the
chiral tetra-o-phenylene derivative -9±11), Ag-fod), and
Yb-hfpc), giving the optimum trade-off between dispersion
and line width, were 3, 20, 20 mg, respectively. For samples
with ee q 0%; a small amount racemate was added to
verify the resolution of resonances for the enantiomers.
Ether and tetrahydrofuran -THF) for use on the vacuum line
were distilled from sodium/benzophenone under a nitrogen
atmosphere. CuBr2 was dried under vacuum at 708C over-
night prior to use. Ag-fod) was prepared as described by
Wenzel, Bettes, Sadlowski, and Sievers.30 ZnCl2
-99.999%, ultra dry) was obtained from Alfa -Johnson±
Mathey). tBuLi -pentane) and nBuLi -hexane) were
obtained from either Aldrich or Acros; prior to use, their
concentrations were determined by titration with N-piva-
loyl-o-toluidine.31 All other commercially available chemi-
cals, including MeOD -99.51%D), were obtained from
Aldrich. Column chromatography was carried out on TLC
grade silica gel -Aldrich), using 0±20 psig pressure.
Preparative TLC -PTLC) was carried out using Analtech
silica plates -tapered with a preadsorbent zone). Standard
techniques for synthesis under inert atmosphere, using
Schlenk glassware and gloveboxes -Mbraun and Vacuum
Atmospheres), were employed.
4.1.2. X-Ray crystallography. Colorless needles -approxi-
mate dimensions 0.25£0.05£0.01 mm3) of rac-4 were
obtained from chloroform solution by slow evaporation. A
crystal was placed onto a tip of a 0.1 mm diameter glass
capillary and mounted on a Bruker SMART Platform CCD
system for data collection at 173 -2) K. A low temperature
transfer was needed because the crystals rapidly lost
solvent.
The initial structure solution and re®nement revealed the
major sites of ®ve chloroform molecules, one of which
was disordered over an inversion center. However, the
modeling of disorder for the solvent molecules was not
successful as the minor sites could not be re®ned
-Rˆ0.19). Therefore, the data set was corrected for dis-
ordered solvent using the program platon/squeeze.33
NMR spectra were obtained using Bruker and Omega spec-
trometers -1H, 500 and 300 MHz) using CDCl3 as solvent.
The chemical shift references were as follows: H -TMS)
Ê 3
1
The total potential solvent accessible volume is 2515.5 A
0.0 ppm and 13C -CDCl3) 77.0 ppm. Typical 1D FID was
subjected to exponential multiplication with an exponent of
with 415 electrons, corresponding to 4.5 chloroform
molecules per asymmetric unit. With the understanding
that the exact amount of solvent is unknown -leading to
incorrect values of F-000), formula, formula weight, etc.),
the re®nement using the corrected data was satisfactory;
crystal data for rac-4 were as follows: C72H48, Mˆ913.10,
1
0.1 Hz -for H) and 1.0±2.0 Hz -for 13C).
IR spectra were obtained using a Nicolet Avatar 360 FT-IR
instrument, equipped with an ATR sampling accessory
-Spectra Tech). A few drops of the compound in CH2Cl2
were applied to the surface of a ZnSe ATR plate horizontal
parallelogram -458, Wilmad). After the solvent evaporated,
the spectrum was acquired -16 scans, 1 cm21 resolution).
Ê
monoclinic, aˆ13.561-1), bˆ23.301-2), cˆ21.764-2) A,
Ê 3
bˆ92.269-2), Vˆ6871.7-11) A , Tˆ173-2) K, space
Ê
group P21/n, Zˆ4, MoK -lˆ0.71073 A). Structure was
solved by direct methods and re®ned by full-matrix least-
squares on F2. Total of 12114 re¯ections was observed and
6238 re¯ections with I.2s-I) were recorded. Re®nement
statistics with 649 parameters was as follows: wRˆ0.1871
-I.2s-I)), Rˆ0.0701 -I.2s-I)), GOFˆ1.040.
UV±vis absorption spectra were recorded at ambient
temperature using the diode-array Hewlett Packard
-HP 8450A and HP 8452A) spectrophotometers. The
Lambert±Beer plots for 4, 9, and p-terphenyl in CH2Cl2
were obtained using 10-mm pathlength quartz cells -six
concentrations, Rˆ0.999).
4.1.3. 2,20,5,50-Tetrabromo-4,40-di-tert-butylbiphenyl 25)
and quenching experiments. Br2 -30.0 g, 9.7 mL,
0.188 mol, 10 equiv.) in CCl4 -7 mL) was added dropwise
to 4,40-tert-butylbiphenyl -5.0 g, 18.8 mmol, 1 equiv.) and
Fe powder -70 mg) in CCl4 -17 mL) in an ice bath. After 6 h
at 08C±ambient temperature, Na2S2O3aq was added. Extrac-
tion with chloroform -3£70 mL), drying over MgSO4, and
concentration in vacuo, gave white solid -16.0 g). After
several recrystallizations from toluene, the pure product 5
as white crystals -2.52 g, 23%) was obtained. Mp258±
2608C. 13C{1H}DEPT-1358)NMR -125 MHz, CDCl3):
149.6 -q), 139.4 -q), 137.4, 132.0, 122.4 -q), 120.9 -q),
36.7 -q), 29.5. LR/HR EIMS, m/z -ion type, % RA for m/zˆ
Concurrent UV±vis and CD spectra for 4 -at 248C) and 9 -at
268C) in CH2Cl2 were obtained using Applied Photophysics
Pistar 180 CDF Spectrometer at the University of North
Carolina Macromolecular Interactions Facility. The spectra
were obtained at 5 approximate concentrations -25, 50, 75,
100, and 125 mM), using 1-mm pathlength cells.
Optical rotations were measured with Autopol III -Rudolph
Research) at ambient temperature.
100±600, deviation for the formula): 690.20908 --M16)1,
Elemental analyses were carried out by M-H-W Labora-
tories, P.O. Box 15149, Phoenix, Arizona 85060 and
Quantitative Technologies, P.O. Box 470, Salem Industrial
Park, Bldg. 5, Whitehouse, NJ 08888.
12
63%, 0.3 ppm for
93%, 0.8 ppm for
C
C
1H2279Br181Br3), 581.8421 --M14)1,
20
12
1H2279Br281Br2), 579.8433 --M12)1,
20
1H2279Br381Br1), 577.8451 -M1,
1H2279Br4); 566.8182 --M142
12
64%, 20.5 ppm for
16%, 20.7 ppm for
C
20
12
C
20
CH3)1, 100%), 562.8221 --M2CH3)1, 17%). IR -cm21):
3001.7, 2987.7, 2970.6, 2949.2, 2868.0 -CH).
4.1.1. 1H NMRspectra with chiral shift reagents. 32 Spec-
trum for racemate -,3 mg) in CDCl3 -0.4±0.5 mL) was ®rst
obtained; then, Ag-fod) and ytterbium tris[3--hepta¯uoro-
t-BuLi -1.48 M in pentane, 0.27 mL, 0.40 mmol, 4 equiv.)
propylhydroxymethylene)--1)-camphorate]
-Yb-hfpc))

3732
A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
was added to 5 -58.2 mg, 0.100 mmol, 1 equiv.) in THF
-3 mL) at 2788C. After 2 h, the reaction mixture containing
®ne white precipitate was quenched with either MeOH or
MeOD -0.1 mL). Aqueous workupgave 44±47 mg of pale
yellow solids. MeOH quench: 1H NMR -300 MHz, CDCl3):
7.650 -d, Jˆ2 Hz, 2H), 7.367 -dd, J1ˆ8, J2ˆ2 Hz, 2H),
7.168 -d, Jˆ8 Hz, 2H), 1.357 -s, 18H). GC MS -CI): m/z,
424 --M12)1). MeOD quench: 7.652 -s, 2H), 7.170 -s, 2H),
1.359 -s, 18H). GC MS -CI): m/z, 426 --M12)1).
130.7, 130.0 -br), 127.3 -br), 126.8, 122.2 -q), 36.5 -q),
32.3. LR/HR EIMS, m/z -ion type, % RA for m/zˆ100±
580, deviation for the formula): 578.0848 --M14)1, 53%,
12
2.7 ppm for
3.7 ppm for
0.3 ppm for
C
C
1H3281Br2), 576.0873 --M12)1, 100%,
32
1H3281Br179Br1), 574.0873 -M1, 49%,
12
32
12
C
32
1H3279Br2). IR -cm21): 3060.0, 2962.8,
2953.0, 2867.4 -CH).
4.1.6. 2,20-Dibromo-5,50-bis24-methoxyphenyl)-4,40-di-
tert-butylbiphenyl 28). The procedure similar to that
described above, using 2,20,5,50-tetrabromo-4,40-di-tert-
butylbiphenyl -1.50 g, 2.58 mmol, 1 equiv.) and 4-iodo-
anisole -1.508 g, 6.44 mmol, 2.5 equiv.), afforded 1.97 g
of crude product. Filtration through a silica plug -hexane/
chloroform, 2:1, v/v) and crystallization from chloroform/
methanol -5:1, v/v) afforded 1.24 g -76%) of white powder.
Mp266±268 8C -after formation of needle crystals at 255±
2578C). 1H NMR -500 MHz, CDCl3): 7.720 -s, 2H), ,7.15
-br, 4H), 6.928 -s, 2H), 6.850 -bd, J<8 Hz, 4H), 3.832 -s,
6H), 1.202 -s, 18H). 13C{1H}DEPT-1358)NMR -125 MHz,
CDCl3): 158.5 -q), 149.5 -q), 140.7 -q), 137.8 -q), 135.9 -q),
135.6, 131.0 -br), 130.6, 122.0 -q), 112.6 -br), 55.2, 36.4 -q),
32.3. LR/HR EIMS, m/z -ion type, % RA for m/zˆ100±640,
4.1.4. 2,20-Dibromo-5,50-bis24-biphenylyl)-4,40-di-tert-
butylbiphenyl 26). The reaction was setupin a heavy-wall
Schlenk vessel equipped with an 8-mm PTFE vacuum stop-
cock -Chemglass). t-BuLi -1.83 M in pentane, 9.4 mL,
16.2 mmol, 4.0 equiv.) was added to a solution of
2,20,5,50-tetrabromo-4,40-di-tert-butylbiphenyl
-2.50 g,
4.30 mmol, 1 equiv.) in THF -110 mL) at 2788C. A large
amount of a white precipitate was formed. After the reaction
mixture was stirred for 2 h at 2788C, ZnCl2 -1.464 g,
10.7 mmol, 2.5 equiv.) was added under nitrogen gas
stream. After 10±30 min at 2788C, the reaction mixture
was allowed to attain ambient temperature. The resultant
solution -pale yellow to pale red colors) was transferred to
an argon-®lled glovebox. Following the addition of 4-iodo-
biphenyl -3.01 g, 10.7 mmol, 2.5 equiv.) and Pd-Ph3P)4
-0.298 g, 0.258 mmol, 0.06 equiv.), the reaction mixture
was kept at 1008C for 12±24 h. Subsequently, when the
ambient temperature was attained, the reaction mixture
was quenched with water. Chloroform was added
-150 mL), and then the organic layer was washed with
water -3£120 mL) and dried over MgSO4. Concentration
in vacuo afforded crude product -3.921 g). Puri®cation by
column chromatography -silica, hexane/benzene from 3:1 to
1:1) gave 2.343 g of white solid, of which 2.083 g was crys-
tallized from chloroform/hexane -1:3, v/v) to give 1.901 g
-68%) of 6 as white crystals. Mp293±295 8C. Anal. calcd
for C44H40Br2: C, 72.53; H, 5.53. Found: C, 70.66; H, 5.58.
1H NMR -500 MHz, CDCl3): 7.761 -s, 2H), 7.637 -d, Jˆ
7 Hz, 4H), 7.558 -bd, Jˆ7 Hz, 4H), 7.452 -t, Jˆ8 Hz, 4H),
7.354 -t, Jˆ7 Hz, 2H), ,7.32 -br, 4H), 6.989 -s, 2H), 1.240
-s, 18H). 13C{1H}DEPT-1358)NMR -125 MHz, CDCl3):
149.4 -q), 142.8 -q), 140.75 -q), 140.69 -q), 139.7 -q),
137.9 -q), 135.2, 130.8, 130.5 -br), 128.8, 127.3, 127.0,
125.9 -br), 122.2 -q), 36.5 -q), 32.4. LR/HR EIMS, m/z
-ion type, % RA for m/zˆ100±750, deviation for the
deviation for the formula): 636.1063 --M12)1, 100%,
12
0.0 ppm for
C
1H36O281Br179Br1), 634.1068 -M1, 48%,
34
12
22.2 ppm for
2955.5, 2833.6 -CH).
C
1H36O279Br2). IR -cm21): 3000.0,
34
4.1.7. General procedures: 2,7,10,16-tetra-tert-butyl-
3,6,11,15-tetrakis24-biphenylyl)tetra-o-phenylene 29).
Procedure A. t-BuLi -1.43 M in pentane, 0.26 mL,
0.37 mmol, 4.1 equiv.) was added dropwise to a suspension
of 6 -65.0 mg, 0.0892 mmol, 1 equiv.) in ether -8 mL) at
2788C. After 2 h at 2788C, -2)-sparteine -42 mg,
0.18 mmol, 2 equiv.) was added. After 20 min at 2788C,
the reaction mixture was kept at 2208C for 30 min. Subse-
quently, the pale yellow solution -with a negligible amount
of white precipitate) was slowly recooled to 2788C, and
then CuBr2 -125 mg, 0.536 mmol, 6 equiv.) was added.
After 2 h at 2788C, the reaction mixture was allowed to
warm to ambient temperature overnight. The resultant
purple solution with some yellow precipitate was quenched
with water. After washing the organic layer with HClaq
-15%, 4£20 mL), NaHCO3aq -sat., 2£20 mL), and water
-2£20 mL), the colorless solution was dried over MgSO4.
Filtration and concentration in vacuo gave the crude product
as a pale yellow solid -52.9 mg). 1H NMR analysis revealed
a mixture of 9 and 12 -8:1), with 55% ee for 9. For the
analogous three reactions, each starting from 130 mg of 6,
49, 51, and 59% ee were obtained; the 9:12 ratios were 3:1,
5:1, and 3:1, respectively. After NMR analyses, all four
crude mixtures were combined -311 mg). Puri®cation by
¯ash chromatography -silica, hexane/chloroform, from 5/1
to 4/1) yielded 9 -248 mg, 81, 64% ee).
formula): 730.1461 --M14)1, 55%, 20.7 ppm for
12
C
C
C
1H4081Br2), 728.1472 --M12)1, 100%, 0.6 ppm for
1H4081Br179Br1), 726.1479 -M1, 50%, 2.5 ppm for
1H4079Br2). IR -cm21): 3037.0, 2954.9, 2870.2 -CH).
44
44
44
12
12
4.1.5.
2,20-Dibromo-5,50-diphenyl-4,40-di-tert-butyl-bi-
phenyl 27). The procedure similar to that described above,
using 2,20,5,50-tetrabromo-4,40-di-tert-butylbiphenyl -1.50 g,
2.58 mmol, 1 equiv.) and iodobenzene -1.31 g, 0.72 mL,
6.44 mmol, 2.5 equiv.), afforded 1.77 g of crude product.
Filtration through a silica plug -hexane) and crystallization
from chloroform/methanol -5:2, v/v) afforded 1.144 g -77%)
of white powder. Mp 251±2528C -after formation of needle
crystals at ,2308C). Anal. calcd for C32H32Br2: C, 66.68; H,
5.60. Found: C, 66.64; H, 5.62. 1H NMR -500 MHz, CDCl3):
7.733 -s, 2H), ,7.30 -br, 8H), ,7.23 -br, 2H), 6.934 -s, 2H),
1.193 -s,18H). 13C{1H}DEPT-1358)NMR -125 MHz,
CDCl3): 149.2 -q), 143.8 -q), 141.0 -q), 137.8 -q), 135.1,
Rapid crystallization 9 -248 mg, 64% ee) from chloroform/
methanol -4/1) gave white crystals -138 mg, 74% ee).
Recrystallization from chloroform/hexane gave the crys-
tals -39 mg, 24% ee) and solid from mother liquor
rt
-94.4 mg, 31%, 951% ee). [a]D ˆ1168 -cˆ0.015,
chloroform). Mp-under argon) for enantiomer of 9 is
not well de®ned: 2708C -crystalline), 2818C -glass/wax),
341±3448C -clear).

A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
3733
Another reaction starting from 246 mg of 6 yielded 261 mg
of 9 and 12 -7:1). Puri®cation by ¯ash chromatography
-chloroform/hexane, 1/4) gave two fractions, F1 -less
polar), 12, 27.1 mg -14%) and F2 -more polar), 9, 136 mg
-71, 57% ee). Crystallization of F1 from chloroform/
methanol -4/1) yielded white crystals of 12 -11.2 mg, 6%).
Several recrystallizations of 125 mg of F2 yielded white
4.1.8. Tetra-o-phenylene 9. Calcd for C88H80: C, 92.91; H,
7.09. Found: C, 92.43; H, 7.48. 1H NMR -500 MHz, CDCl3,
COSY cross-peak): 7.657 -d, Jˆ7 Hz, 8H, 7.449), 7.568
-bd, Jˆ8 Hz, 8H, 7.4), 7.449 -t, Jˆ8 Hz, 8H, 7.657,
7.345), 7.4 -bs, 8H, 7.568), 7.388 -s, 4H, 6.970), 7.345 -t,
Jˆ7 Hz, 4H, 7.449), 6.971 -s, 4H, 7.388), 1.263 -s, 36 H);
328 K: 7.653 -d, Jˆ7 Hz, 8H), 7.566 -d, Jˆ8 Hz, 8H), 7.441
-t, Jˆ8 Hz, 8H), 7.396 -s, 4H), 7.391 -bd, J<7 Hz, 8H),
7.338 -t, Jˆ7 Hz, 4H), 6.970 -s, 4H), 1.272 -s, 36H).
13C{1H}DEPT-1358)NMR -125 MHz, CDCl3): 146.6 -q),
144.1 -q), 140.88 -q), 140.85 -q), 140.4 -q), 139.2 -q),
137.8 -q), 134.1, 130.6, 129.1, 128.7, 127.2, 127.0, 125.8,
36.4 -q), 32.9. LR EIMS, m/z -ion type, % RA for m/zˆ100±
1250): 1136.5 -M1, 100%), 1137.5 --M11)1, 95%), 1138.5
--M12)1, 45%), 1139.5 --M13)1, 15%), 568 -,5%);
calcd: 1136.626 -100%), 1137.629 -99%), 1138.633
-49%), 1139.636 -16%). LR/HR FABMS, m/z -ion type,
% RA for m/zˆ200±1500, deviation for the formula):
rt
solid of 9 -45.2 mg, 23%, 951% ee) with [a]D ˆ1171
-cˆ0.015, chloroform) and identical melting behavior, as
the sample described in the preceding paragraph.
Procedure B. t-BuLi -1.74 M in pentane, 0.97 mL,
1.69 mmol, 4.1 equiv.) was added dropwise to a suspension
of 6 -300 mg, 0.411 mmol, 1 equiv.) in ether -40 mL) at
2788C. After 2 h at 2788C, the reaction mixture was kept
at 2208C for 15 min. After the resultant yellow solution was
recooled to 2788C, CuBr2 -552 mg, 2.47 mmol, 6 equiv.)
was added. After 2 h at 2788C, the reaction mixture was
allowed to warm to ambient temperature overnight, yielding
a purple mixture. The usual aqueous workup, including
extraction with chloroform -150 mL), gave the crude
12
1
1137.6262 --M11)1, 98%, 2.7 ppm for
C
13C1 H80),
87
1136.6229 -M1, 100%, 2.7 ppm for
C
1H80), 568
12
88
-not observed). IR -cm21): 3026.8, 2958.7, 2904.5, 2868.8
-CH).
1
product as a pale yellow solid -273 mg). H NMR analysis
revealed a mixture of 9 and 12 -3:1). Puri®cation by ¯ash
chromatography -silica, hexane/benzene, from 6:1 to pure
benzene) yielded 9 -105 mg, 45%) and 12 -22.6 mg, 10%).
Recrystallizations of 9 and 12 from chloroform/methanol
-2:1 Ð 3:1) gave white solids: 93.5 mg, 40% and
18.4 mg, 8%. Mp-under argon) for rac- 9 is not well de®ned:
2508C -cubic crystal), 2658C -waxy), 3158C -clear).
4.1.9. Biphenylene 12. 1H NMR -500 MHz, CDCl3): 7.647
-d, Jˆ7 Hz, 4H), 7.562 -d, Jˆ8 Hz, 4H) 7.448 -t, Jˆ8 Hz,
4H), 7.345 -t, Jˆ7 Hz, 2H), 7.296 -d, Jˆ8 Hz, 4H), 6.972 -s,
2H), 6.301 -s, 2H), 1.161 -s, 18H). 13C{1H} NMR
-125 MHz, CDCl3): 149.8, 147.6, 146.9, 144.7, 140.80,
140.65, 139.2, 130.2, 128.8, 127.2, 127.0, 126.1, 121.7,
116.6, 37.1, 32.9. LR/HR EIMS, m/z -ion type, % RA for
m/zˆ100±1250, deviation for the formula): 569.3157
C
13C1 H40), 568.3120
43
Procedure C. t-BuLi -1.50 M in pentane, 0.49 mL,
0.735 mmol, 4.1 equiv.) was added dropwise to a suspen-
sion of 6 -130 mg, 0.178 mmol, 1 equiv.) in ether -16 mL) at
2788C. After 1.5 h at 2788C, the reaction mixture was kept
at 225±-230) 8C for 30 min. After the resultant yellow
solution was recooled to 2788C -no precipitate), -2)-spar-
teine -84 mg, 0.36 mmol, 2 equiv.) in ether -2 mL) was
added. After 2 h at 2788C, CuBr2 -250 mg, 1.08 mmol,
6 equiv.) was added. After 2 h at 2788C, the reaction
mixture was allowed to warm to ambient temperature over-
night, yielding a purple solution with yellow precipitate.
The usual aqueous workup, including extraction with
12
1
--M11)1, 56%, 1.1 ppm for
12
-M1, 100%, 1.8 ppm for
C
44
1H40), 1136 -not observed
upto 300 8C on the probe). IR -cm21): 3028.7, 2962.7,
2867.4 -CH).
4.1.10. 2,7,10,16-Tetra-tert-butyl-3,6,11,15-tetraphenyl-
tetra-o-pheny1ene 210) and 2,7-di-tert-butyl-3,6-diphenyl-
biphenylene 213). Procedure A. Starting from 40 and
400 mg of 7, crude mixtures of 10 and 13 -6:1 and 10:1),
with 50% ee for 10, were obtained. Puri®cation of the crude
mixture from the 400-mg scale reaction -328 mg) by ¯ash
chromatography -benzene/hexane, 1/5) gave two fractions,
F1 -less polar) and F2 -more polar).
1
chloroform -40 mL), gave the crude product -104 mg). H
NMR analysis revealed a mixture of 9 and 12 -7:1), with
35% ee for 9.
F1: 13, 31.3 mg. Preparative TLC -silica, chloroform/
hexane, 1/6) and crystallization -chloroform/methanol,
1/1) yielded 7.5 mg -3%) of pure 13. Mp215±216 8C.
Procedure D. This procedure is analogous to the Procedure
A, except ether is replaced with THF as a solvent. For three
reactions, each starting with 130, 130, and 65 mg of 6, the
following results were obtained: 9:12, 1:3Ð4:1 and 8±9%
ee for 9.
rt
F2: 10, 249 mg, 86%, 54% ee, [a]D ˆ170 -cˆ0.003,
chloroform), mp401±404 8C.
Procedure E. This procedure is analogous to the Procedure
B, except ether is replaced with THF as a solvent. Starting
with 130 mg of 6, mixture of 9 and 12 -pale yellow oil,
144 mg, ,1:20) was obtained. Puri®cation by ¯ash chroma-
tography -silica, chloroform/hexane, 1:6) yielded 12
-60.9 mg); recrystallization from chloroform/methanol
-3:2, v/v) gave 52.2 mg of 12 -52%, mp263±264 8C).
Another reaction on the identical scale yielded a similar
mixture of 9 and 12 -,1:20); after column chroma-
tography and recrystallization, 40.3 mg -40%) of 12 was
obtained.
Procedure B. Starting from 400 mg of 7, crude mixture of
rac-10 and 13 -423 mg, 5:1) was obtained. Puri®cation by
¯ash chromatography -benzene/hexane, 1/5) gave two
fractions, F1 -less polar) and F2 -more polar).
F1: 13, 33.5 mg -12%). Crystallization -chloroform/metha-
nol, 3:1, v/v) yielded 12.6 mg -4%) of pure 13.
F2: rac-10, 217 mg -75%). Crystallization -benzene/chloro-
form/methanol, 1:1:1, v/v) yielded 158.4 mg -55%) of
rac-10. Mp-under argon) 442±443 8C.

3734
A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
12
1
4.1.11. Tetra-o-pheny1ene 10. Anal. calcd for C64H64: C,
92.26; H, 7.74. Found: C, 91.96; H, 7.46. 1H NMR
-500 MHz, CDCl3): 7.341 -s, 4H), 7.30 -bm, 20 H), 6.893
-s, 4H), 1.206 -s, 36H). 13C{1H}DEPT-1358)NMR -125
MHz, CDCl3): 146.4 -q), 145.0 -q), 140.8 -q), 140.7 -q),
137.8 -q), 134.0, 130.2 -br), 129.0, 127.1, 126.4, 36.4 -q),
32.8. LR/HR EIMS, m/z -ion type, % RA for m/zˆ100±870,
deviation for the formula): 833.5037 --M11)1, 70%,
953.5465 --M11)1, 74%, 20.1 ppm for
C
67
13C1 H72O4),
1H72O4), 476 -not
12
952.5414 -M1, 100%, 1.7 ppm for
C
68
observed). IR -cm21): 2998.3, 2956.5, 2905.4, 2869.1,
2833.4 -CH).
4.1.15. Biphenylene 14. 1H NMR -500 MHz, CDCl3): 7.115
-d, Jˆ9 Hz, 4H), 6.919 -s, 2H), 6.849 -d, Jˆ9 Hz, 4H),
6.236 -s, 2H), 3.830 -s, 6H), 1.114 -s, 18H). 13C{1H}NMR
-125 MHz, CDCl3): 158.2, 149.7, 147.7, 146.8, 140.7,
137.9, 130.7, 122.1, 116.4, 112.8, 55.2, 37.0, 32.8. LR/HR
EIMS, m/z -ion type, % RA for m/zˆ100±1000, deviation
for the formula): 477.2737 --M11)1, 34%, 2.5 ppm for
13C1 H64), 832.5003 -M1, 100%, 0.7 ppm
12
1
0.5 ppm for
for
C
63
12
C
1H64). IR -cm21): 2953.6, 2868.4 -CH).
64
4.1.12. Biphenylene 13. 1H NMR -500 MHz, CDCl3):
7.33±7.20 -m, 10H), 6.942 -s, 2H), 6.246 -s, 2H), 1.114
-s, 18H). 13C{1H}NMR -125 MHz, CDCl3): 149.7, 147.3,
146.8, 145.6, 141.0, 129.7, 127.4, 126.4, 121.7, 116.5, 37.0,
32.8. LR/HR EIMS, m/z -ion type, % RA for m/zˆ100±900,
deviation for the formula): 417.2541 --M11)1, 34%,
12
12
1
C
C
13C1 H36O2), 476.2704 -M1, 100%, 2.4 ppm for
33
1H36O2), 952 -not observed at 758C, ,2% at 1008C
34
on the probe). IR -cm21): 2999.8, 2953.5, 2905.7, 2866.4,
2833.8 -CH).
12
1
4.1.16. 3,6,11,15-Tetrakis24-biphenylyl)tetra-o-phenyl-
ene 24). Tetra-o-pheny1ene
20.9 ppm for
20.3 ppm for
C
31
13C1 H32), 416.2505 -M1, 100%,
12
C
32
1H32), 832 -not observed upto 300 8C
9 -31 mg, 0.027 mmol,
rt
on the probe). IR -cm21): 2955.5, 2867.2 -CH).
[a]D ˆ1171) and AlCl3 -,20 mg) in dry benzene -2 mL)
were stirred at 508C for 3 h. Following the usual aqueous
workupwith chloroform -2 £15 mL), the crude product was
treated with charcoal in chloroform, and then recrystallized
from chloroform/methanol -1:1, v/v) to yield 21.9 mg -88%)
of white solid. Mp-under argon) 290 8C -crystalline appear-
4.1.13.
24-methoxyphenyl)tetra-o-phenylene 211) and 2,7-di-
tert-butyl-3,6-bis24-methoxyphenyl)biphenylene 214).
2,7,10,16-Tetra-tert-butyl-3,6,11,15-tetrakis-
Procedure A. Starting from 56.6 and 400 mg of 8, crude
mixtures of 11 and 14 -11:1 and 15:1), with 50% ee for
11, were obtained. Puri®cation of the crude mixture from
the 400-mg scale reaction -322 mg) by ¯ash chroma-
tography -chloroform/hexane, from 1/4 to 1:1) gave two
fractions, F1 -less polar) and F2 -more polar).
rt
ance), 3508C -wax), 362±3648C -clear). [a]D ˆ162 -cˆ
0.006, chloroform).
Starting from rac-9 -40 mg, 0.035 mmol), 18.8 mg -59%) of
rac-4 was obtained. Mp-under argon) 430±433 8C. Anal.
calcd for C72H48: C, 94.70; H, 5.30. Found: C, 94.40; H,
5.36.
F1: 14, 25.8 mg. Crystallization -chloroform/methanol, 1/1)
yielded 8.9 mg -3%) of pure 14 -1H NMR).
1H NMR -500 MHz, EMˆ21.2, GBˆ0.8, CDCl3, COSY
cross-peak): Ring A -1,2,4-Ph): 7.657 -dd, J1ˆ8 Hz, J2ˆ
2 Hz, 4H, 7.603, 7.384), 7.603 -d, Jˆ2 Hz, 4H, 7.657,
7.384), 7.384 -d, Jˆ8 Hz, 4H, 7.657, 7.603); Ring B -1,4-
Ph): 7.718 -d, Jˆ8 Hz, 8H, 7.657), 7.657 -d, Jˆ8 Hz, 8H,
7.718); Ring C -Ph): 7.628 -d, Jˆ8 Hz, 8H, 7.442, 7.344),
7.442 -t, Jˆ8 Hz, 8H, 7.628, 7.344), 7.344 -t, Jˆ8 Hz, 4H,
7.628, 7.442). 13C{1H}DEPT-1358)NMR -125 MHz,
CDCl3): 142.3 -q), 140.8 -q), 140.6 -q), 140.4 -q), 139.9
-q), 139.5 -q), 130.1, 128.9, 128.2, 127.63, 127.59,
127.49, 127.2, 126.2. LR/HR EIMS, m/z -ion type, % RA
for m/zˆ100±1000, deviation for the formula): 913.3789
rt
F2: 11, 242 mg, 81%, 56% ee, [a]D ˆ186 -cˆ0.004,
chloroform), mp395±402 8C -purity by 1H NMR).
Procedure B. Starting from 400 mg of 8, crude mixture of
rac-11 and 14 -421 mg, 7:1) was obtained. Puri®cation by
¯ash chromatography -chloroform/hexane, from 1/2 to 1/1)
gave two fractions, F1 -less polar) and F2 -more polar).
F1: 14, 24.6 mg. Crystallization -chloroform/methanol, 1/1)
yielded 19.5 mg -7%) of pure 14 -1H NMR). Mp218±
2198C.
--M11)1, 79%, 0.1 ppm for
C
13C1 H48), 912.3761
71
12
1
-M1, 100%, 20.6 ppm for
C
72
1H48), 456.2 -M21, 15%).
12
F2: rac-11, 217 mg, 47%. Crystallization -chloroform/
methanol, 1/1) yielded 91.5 mg, 31%) of pure rac-11 -1H
NMR). Mp-under argon) 393±394 8C.
IR -cm21): 3055.2, 3027.8 -CH).
Crystallographic data -excluding structure factors) for the
structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC 160101. Copies of the data can be
obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK -fax: 144 1223 336033 or
e-mail: deposit@ccdc.cam.ac.uk).
4.1.14. Tetra-o-phenylene 11. Anal. calcd for C68H72O4: C,
85.67; H, 7.61. Found: C, 85.38; H, 7.62. 1H NMR
-500 MHz, CDCl3): 7.326 -s, 4H), 7.213 -bd, J<6 Hz,
8H), 6.892 -s, 4H), 6.851 -bd, J<8 Hz, 8H), 3.832 -s,
12H), 1.216 -s, 36H); 328 K: 7.323 -s, 4H), 7.201 -bd,
J<8 Hz, 8H), 6.880 -s, 4H), 6.848 -d, Jˆ9 Hz, 8H), 3.835
-s, 12H), 1.218 -s, 36H). 13C{1H}DEPT-1358)NMR
-125 MHz, CDCl3): 158.2 -q), 146.7 -q), 140.7 -q), 140.3
-q), 137.8 -q), 137.2 -q), 134.5, 131.1, 129.0, 112.5, 55.2,
36.3 -q), 32.8. LR EIMS, m/z -ion type, % RA for m/zˆ100±
1250): 952.5 -100), 953.5 -75) 953.5 --M11)1, 75%), 952.5
-M1, 100%), 476 -,4%). LR/HR FABMS, m/z -ion type, %
RA for m/zˆ200±1200, deviation for the formula):
Acknowledgements
This research was supported by the National Science
Foundation -CHE-9510096 and CHE-9806954). We thank
Clayton Holcomb and Dr Lianhe Yu for their assistance

A. Rajca et al. / Tetrahedron 57 ,2001) 3725±3735
13. 2,20-Dibromo-4,40-di-tert-butylbiphenyl:
Yamato, T. J. J. Org. Chem. 1979, 44, 3037.
3735
M.;
Tashiro,
with synthesis. We thank Drs Maren Pink and Victor G.
Young, Jr. of the X-ray crystallographic laboratory at the
University of Minnesota for X-ray structure determination.
We thank Dr R. Cerny of the Nebraska Center for Mass
Spectrometry for the mass spectral determinations.
We thank Dr Ashutosh Tripathy of University of North
Carolina Macromolecular Interactions Facility -web
address: macinfac.bio.unc.edu) for his helpwith the CD
spectra.
14. 2,205,50-Tetrabromobiphenyl: Meyer, H.; Hoffmann, A.
Monatsch. 1917, 38, 141 -mp210±211 8C, acetic acid).
È
Sundstrom, G.; Hutzinger, O.; Safe, S.; Zitko, V.; Sci. Total
Environ. 1976, 6, 15 -mp143±144 8C).
15. Ion triplets: Streitwieser, A. Acc. Chem. Res. 1984, 17, 353.
16. The proton quenching product and 2,20-dibromo-4,40-di-tert-
butylbiphenyl -obtained by bromination of 4,40-di-tert-butyl-
1
biphenyl, Ref. 13) had identical H NMR spectra.
17. For steric acceleration in the reaction of aryl bromides with
tributylstannyl radicals, see: Crich, D.; Recupero, F. Chem.
Commun. 1998, 189.
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