New accelerated strategy for the synthesis of poly(ether ketone) dendrons

Article abstract of DOI:10.1021/jo015805j

A new AB₄-type hypermonomer with four activated aromatic fluorines was prepared and converted to hyperbranched poly(ether ketones) by nucleophilic aromatic substitution of these fluorine atoms with phenolates. The preparation and application of the AB₄ hypermonomer for the accelerated synthesis of a family of poly(ether ketone) dendrons G2-G4 in good yield are described.

Full text of DOI:10.1021/jo015805j

1004
J . Org. Chem. 2002, 67, 1004-1007
New Acceler a ted Str a tegy for th e Syn th esis
of P oly(Eth er Keton e) Den d r on s
Michael A. Abramov,† Ramesh Shukla,†
David B. Amabilino,‡ and Wim Dehaen*,†
Department of Chemistry, University of Leuven, Heverlee
(Leuven), B-3001, Belgium, and Institut de Cie`nciade
Materials de Barcelona (CSIC), 08193 Bellaterra, Spain
wim.dehaen@chem.kuleuven.ac.be
Received May 30, 2001
Abstr a ct: A new AB4-type hypermonomer with four acti-
vated aromatic fluorines was prepared and converted to
hyperbranched poly(ether ketones) by nucleophilic aromatic
substitution of these fluorine atoms with phenolates. The
preparation and application of the AB4 hypermonomer for
the accelerated synthesis of a family of poly(ether ketone)
dendrons G2-G4 in good yield are described.
F igu r e 1. Hypermonomer 1.
Sch em e 1. Acceler a ted Str a tegy for th e Syn th esis
of P oly(Eth er Keton e) Den d r on s
The convergent synthesis of dendritic poly(ether ke-
tones), based on AB2 monomers, has been developed by
Morikawa1 and successfully used by his and other groups
to construct monodisperse macromolecules.2 Also, hyper-
branched polymers have been prepared using the same
chemistry and building blocks.3 The drawback of the
method, however, is that the buildup of the dendritic
wedges is time consuming and the increasing steric
hindrance, which occurs at the focal functional group
with dendron growth, may inhibit its anchoring to a
center core.
Our approach to accelerate the dendrimer growth
consists of using an appropriate AB4 hypermonomer 1
in the assembly of higher-generation poly(ether ketone)
dendrons. Such a synthetic strategy was successfully
applied in our group for the accelerated synthesis of
benzylic polyether dendrons.4
from 5-methoxyisophthaloyl chloride5 2 and prepared 3
by the reported procedure1a from 2 and fluorobenzene in
the presence of AlCl3. Alternatively, we used monomer
3 obtained from 2 and 4-fluorophenylmagnesium bromide
in THF in 60-65% yield. As a side product, 3-(4-
fluorobenzoyl)-5-methoxybenzoic acid 3a was isolated in
30% yield. The separation of 3 and 3a was straight-
forward.
To deactivate the fluorine atoms of 3 for the controlled
synthesis of 1, we decided to reduce the ketone groups.
We tried reduction procedures with hydrazine and so-
dium cyanoborohydrate, but only hydrogenation on Pd-C
was successful; we obtained 3,5-bis(4-fluorobenzyl)anisole
4 as a colorless oil in 96% yield and used it in the next
step without purification. Treatment of 4 with 1 N BBr3
dichloromethane solution gave phenol 5 in 97% yield, 2
equiv of which were condensed with monomer 3 in a
DMF-toluene mixture at 150 °C in the presence of
potassium carbonate, resulting in anisole 6 in 82% yield.
To reactivate the four fluorine atoms at the aromatic
rings, we had to oxidize the methylene groups to ketone
functions. Oxidation with pyridinium chlorochromate did
not lead to compound 1, and reaction of 6 with potassium
permanganate at room temperature in acetone was very
slow and did not reach completion after 30 days. Finally,
oxidation of 6 with potassium permanganate in the
presence of tetrabutylammonium bromide as a phase
transfer catalyst gave 1 in a satisfying yield of 70%.
The AB4-type hypermonomer 1 was used for the
preparation of dendritic poly(ether ketone) by nucleo-
philic aromatic substitution of the activated fluorine
atoms with phenolate generated in the presence of
potassium carbonate (Scheme 3). The substitution pro-
ceeded at 120-150 °C in a mixture of toluene and DMF.
Herein, we describe the preparation of a new AB4-type
hypermonomer 1 (Figure 1) and its application for the
accelerated synthesis of a family of poly(ether ketone)
dendrons (Scheme 1).
Syn th esis. Hypermonomer 1 used for this investiga-
tion was obtained in accordance to Scheme 2. We started
† University of Leuven.
‡ Institut de Cie`nciade Materials de Barcelona (CSIC).
(1) (a) Morikawa, A.; Kakimoto, M.-A.; Imai, Y. Macromolecules
1993, 26, 6324. (b) Morikawa, A. Macromolecules 1998, 31, 5999. (c)
Morikawa, A.; Ono, K. Macromolecules 1999, 32, 1062. (d) Miller, T.
M.; Neenan, T. H.; Kwock, E. W.; Stein, S. M. J . Am. Chem. Soc. 1993,
115, 356.
(2) Selected references: (a) Hawker, C. J .; Chu, F. K. Macromol-
ecules 1996, 29, 4370. (b) Shu, C. F.; Leu, C. M.; Huang, F. Y. Polymer
J . 1999, 40, 6591. (c) Shu, C. F.; Leu, C. M. Macromolecules 1999, 32,
100. (d) Morikawa, A.; Ono, K. Polymer J . 2000, 32, 234. (e) Morikawa,
A.; Ono, K. Polymer J . 2000, 32, 255.
(3) Selected references: (a) Bhatnagar, A.; Mani, R. S.; King, B.;
Mohanty, D. K. Macromol. Chem. and Phys. 1996, 197, 315. (b) Ding,
Y.; Hay, A. S. Macromolecules 1996, 29, 3090. (c) Selampinar, F.;
Akbulut, U.; Yildiz, E.; Gungor, A.; Toppare, L. Synth. Met. 1997, 89,
111. (d) Zhang, S. J .; Zheng, Y. B.; Wu, Z. W.; Tian, M. W.; Yang, D.
C.; Yosomiya, R. Liq. Cryst. 1998, 24, 311. (e) Baxter, I.; Colquhoun,
H. M.; Hodge, P.; Kohnke, F. H.; Lewis, D. F.; Williams, D. J .; J . Mater.
Chem. 2000, 10, 309. (f) Fitch, J . W.; Reddy, V. S.; Youngman, P. W.;
Wohlfahrt, G. A.; Cassidy, P. E. Polymer 2000, 41, 2301.
(4) L’abbe´, G.; Forier, B.; Dehaen, W. J . Chem. Soc., Chem. Commun.
1996, 2143.
(5) Hwang, Y.-S.; Matsui, M. Agr. Biol. Chem. 1971, 35, 1812.
10.1021/jo015805j CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/15/2002

Notes
J . Org. Chem., Vol. 67, No. 3, 2002 1005
Sch em e 2. Gen er a l Syn th esis of Hyp er m on om er
1
Sch em e 3. Gen er a l Syn th esis of G-1 a n d G-2
P h en ols 8 a n d 10
spectra were recorded on a KRATOS ANALYTICAL (Manches-
ter, U.K.) KOMPACT MALDI-2 K-PROBE instrument in posi-
tive high (20 kV) mode, which uses a 3 ns pulse from a nitrogen
laser (λ ) 337 nm) at a target area of 100 µm in diameter and
pulse extracts the ions down a linear flight tube (2 m), employing
dithranol as a matrix. Melting points were determined using a
Reichert Thermovar apparatus. DMF was dried on molecular
sieves 4 Å, and THF was freshly distilled from sodium diphenyl
ketyl solution. 5-Methoxyisophthaloyl chloride was prepared by
the method described.5
Thus, the G-1 dendron 7 was prepared from monomer
3 and 4-tert-butylphenol in 87% yield and converted to
the corresponding phenol 8 (92%) with BBr3 solution. The
G-2 dendron 9 was obtained from hypermonomer 1 and
4-tert-butylphenol in 88% yield and converted to the G-2
phenol 10 in 83% yield (Scheme 2).
G-3 11 and G-4 12 dendritic poly(ether ketones) were
prepared in one step in 68 and 54% yields, respectively,
from hypermonomer 1 and poly(ether ketone)phenols 8
and 10 (Scheme 4).
In conclusion, we developed a new AB4 hypermonomer
on the basis of (1) a reduction/oxidation strategy for
protection/deprotection and (2) the nucleophilic substitu-
tion reaction. The latter reaction is then used in an
accelerated synthesis of poly(ether ketone) dendrons,
starting from the hypermonomer.
3,5-Bis{4-[3.5-b is(4-flu or ob en zoyl)p h en oxy]b en zoyl}-
a n isole 1. To a solution of 3,5-bis[3.5bis(4-fluorobenzyl)phenyl-
oxybenzoyl]anisole 6 (350 mg, 0.38 mmol) and tetrabutylammo-
nium bromide (300 mg) in dichloromethane (10 mL) was added
potassium permanganate (1.0 g), and the deeply colored reaction
mixture was stirred under reflux for 3 days. The reaction was
monitored with TLC. When the starting compound disappeared,
the reaction mixture was allowed to cool to room temperature
and MeOH was added dropwise. After the solution became
colorless, the black precipitate was filtered off and washed with
dichloromethane and the solvent was removed under reduced
pressure. The product was purified by silica gel column chro-
matography with dichloromethane/EtOAc (20:1). Yield: 250 mg
Exp er im en ta l Section
1
Ma ter ia ls a n d Meth od s. NMR spectra were acquired on
commercial instruments (Bruker Avance 300 MHz or Bruker
AMX 400 MHz), and chemical shifts are reported in parts per
million (δ) referenced to internal residual solvent protons (1H)
or the carbon signal of deuterated solvents (13C). Mass spec-
trometry data were obtained with an HP MS apparatus 5989A
(electron impact (EI), 70 eV; chemical ionization (CI), CH4) or a
Micromass Quattro II apparatus (electrospray ionization (ESI),
solvent mixture: CH2Cl2/MeOH + NH4OAc). MALDI-TOF mass
(67%). H NMR (CDCl3, δ, ppm): 3.92 s (3H), 7.12 m (4H), 7.17
m (8H), 7.51 d (2H), 7.69 s (1H), 7.69 d (4H), 7.88 m (14H). 13C
NMR (CDCl3, δ, ppm): 55.8, 115, 9 (d, J ) 22 Hz), 117.9, 118.5,
123.1, 124.0, 126.4, 132.5, 132.67 (d, J ) 7 Hz), 132.73, 132.75,
139.1, 139.8, 156.0, 159.6, 160.4, 165.7 (d, J ) 256 Hz), 193.1,
194.0. MS (ESI): m/z 989. Found, %: C, 73.82; H, 3.64. Anal.
Calcd for C61H34F4O9, %: C, 74.09; H, 3.67. M 989.
3.5-Bis(4-flu or oben zoyl)a n isole 3. To a solution of 5-meth-
oxyisophthaloyl dichloride 2 (16.3 g, 0.07 mmol) at -78 °C in

1006 J . Org. Chem., Vol. 67, No. 3, 2002
Sch em e 4. Gen er a l Syn th esis of G-3 11 a n d G-4 12 Den d r itic P oly(Eth er Keton es)
Notes
THF (150 mL) was added dropwise over a period of about 30
min a solution of the Grignard reagent obtained from Mg (3.9
g, 0.16 mol) and 4-fluorophenyl bromide (28 g, 0.16 mmol) in
THF (100 mL). The reaction mixture was allowed to reach room
temperature under stirring for 1 h. After addition of water (300
mL), the organic layer was extracted with ether, washed with 1
N NaOH and water, and dried over MgSO4. Evaporation afforded
the residue, which after purification by silica gel column
chromatography with dichloromethane/ethyl acetate (6:1) gave
14.8 g (60%) of anisole 3, mp 100-101 °C.1a
The next fraction gave 8.2 g (30%) of white solid with an mp
) 152-3 °C, which was identified as 3-(4-fluorobenzyl)-5-
methoxybenzoic acid 3a . 1H NMR (DMSO-d6, δ, ppm): 3.89 s
(3H), 7.41 m (2H), 7.47 m (1H), 7.70 m (1H), 7.78 m (1H), 7.86
m (2H), 13.0 v br s (1H). 13C NMR (DMSO-d6, δ, ppm): 55.7,
115.7 (d, J ) 22 Hz), 118.1, 118.7, 122.4, 132.5, 132.5 (d, J ) 9
Hz), 138.6, 159.3, 164.5 (d, J ) 254 Hz), 166.3, 193.4.
3.5-Bis(4-flu or oben zyl)p h en ol 5. To a solution of 3.5-bis-
(4-fluorobenzyl)anisole 4 (420 mg, 1.3 mmol) in dichloromethane
(2 mL) was added 4 mL of 1 N BBr3 in dichloromethane under
argon at -78 °C, and the mixture was stirred for 1h. The
reaction mixture was allowed to warm to room temperature for
2 h, and cold water (20 mL) was added in one portion; the
mixture was stirred overnight. The white solid was filtered off,
washed with water, dried under reduced pressure, and purified
by silica gel column chromatography with dichloromethane.
Yield: 390 mg (97%), white solid, mp 104.5-105 °C. 1H
NMR spectrum (CDCl3, δ, ppm): 3.83 s (4H), 4.71 br s (1H),
6.42 s (2H), 6.58 s (1H), 6.93 m (4H), 7.09 m (4H). 13C NMR
spectrum (CDCl3, δ, ppm): 40.8, 113.6, 115.2 (d, J ) 22 Hz),
121.9, 130.2 and 130.3 (d, J ) 9 Hz), 136.3, 142.9, 155.8, 160.4
(d, J ) 254 Hz). MS (EI): m/z M+ 310. Found, %: C, 77.11; H,
5.16. Anal. Calcd for C20H16F2O, %: C, 77.40; H, 5.20. M
310.
3,5-Bis{4-[3.5-b is(4-flu or ob e n zyl)p h e n oxy]b e n zoyl}-
a n isole 6. To a solution of 3.5-bis(4-fluorobenzoyl)anisole 3 (176
mg, 0.5 mmol) and 3.5-bis(4-fluorobenzyl)phenol 5 (325 mg, 1.05
mmol) in a mixture of toluene (1 mL) and DMF (2 mL) was added
K2CO3 (150 mg, 1.09 mmol), and the reaction mixture was
stirred under reflux for 3 h in an argon atmosphere. The reaction
mixture was diluted with water and extracted with dichlo-
romethane, and the organic layer was washed with water, dried
over MgSO4, and evaporated under reduced pressure. The
residue was purified by silica gel column chromatography with
dichloromethane/ether (20:1). Yield: 410 mg (82%), colorless
3.5-Bis(4-flu or oben zyl)a n isole 4. A slurry of 3.5-bis(4-
fluorobenzoyl)anisole 3 (352 mg, 1 mmol), EtOH (20 mL), 36%
HCl (0.5 mL), and 5% Pd/C (200 mg) was hydrogenated at room
temperature and atmosphere pressure with stirring for 40 h.
The catalyst was filtered off and washed with EtOH. The
combined ethanolic solutions were boiled with charcoal and
filtered, and the filtrate was evaporated under reduced pressure.
The viscous residue was dried under vacuum to a constant
weight. Yield: 310 mg (96%), colorless oil. 1H NMR (CDCl3, δ,
ppm): 3.68 s (3H), 3.84 s (4H), 6.53 s (2H), 6.58 s (1H), 6.93 m
(4H), 7.09 m (4H). 13C NMR (CDCl3, δ, ppm): 41.0, 55.0, 112.3,
115.1 (d, J ) 22 Hz), 121.9, 130.1 (d, J ) 9 Hz), 136.53, 142.56,
160.0, 160.4 (d, J ) 254 Hz). MS (EI): m/z 324. Anal. Calcd for
C21H18F2O: M 324. The product was used in the next stage
without purification.
1
glass. H NMR (CDCl3, δ, ppm): 3.88 s (8H), 3.92 s (3H), 6.72 s
(4H), 6.83 s (2H), 6.97 m (12H), 7.11 m (12H), 7.49 s (2H), 7.67
(1H). MS (EI): m/z 933. Found, %: C, 78.36; H, 4.89. Anal. Calcd
for C61H44F4O5, %: C, 78.53; H, 4.75. M 933.

Notes
3.5-Bis{4-[4-(ter t-bu tyl)ph en oxy]ben zoyl}an isole 7. A mix-
J . Org. Chem., Vol. 67, No. 3, 2002 1007
gel chromatography with dichloromethane/EtOAc (25:1). Yield:
330 mg (85%). 1H NMR (CDCl3, δ, ppm): 1.33 s (36H), 6.12 br
s (1H), 7.00 m (8H), 7.02 m (8H), 7.10 m (4H), 7.40 m (8H), 7.45
d (2H), 7.66 d (4H), 7.69 t (1H), 7.81 m (8H), 7.86 m (4H), 7.89
t (2H). 13C NMR (CDCl3, δ, ppm): 31.4, 34.4, 117.0, 117.9, 119.8,
120.1, 123.7, 126.5, 126.9, 130.5, 132.3, 132.5, 132.7, 139.5, 140.2,
147.9, 152.7, 155.9, 160.7, 162.7, 193.5, 194.0. MS (ESI): m/z
ture of the monomer 3 (1.06 g, 3 mmol), tert-butylphenol (0.95
g, 6.3 mmol), potassium carbonate (0.91 g, 6.6 mmol), DMF (10
mL), and toluene (3 mL) was stirred at 130 °C for 1 h while
water was distilled off azeotropically with toluene. The reacton
temperature was raised to 150 °C, and the mixture was stirred
for 1.5 h. The solvent was removed under reduced pressure, and
the residue was washed with water, extracted with methylene
chloride, and dried over MgSO4. The product was obtained by
evaporation of the solvent and purified by silica gel column
chromatography with hexane/EtOAc (6:1). Yield: 1.6 g (87%).
1H NMR (CDCl3, δ, ppm): 1.33 s (18H), 3.90 s (3H), 7.00 m (8H),
7.40 m (4H), 7.50 d (2H), 7.67 t (1H), 7.82 m (4H). 13C NMR
(CDCl3, δ, ppm): 31.4, 34.4, 55.8, 116.9, 118.3, 119.7, 123.3,
126.9, 132.4, 139.4, 147.7, 152.8, 159.6, 162.4, 194.3. MS (EI):
m/z 612. Found, %: C, 80.34; H, 6.57. Anal. Calcd for C41H40O5,
%: C, 80.36; H, 6.58. M 612.
3.5-Bis{(4-[4-(ter t-bu tyl)p h en oxy]ben zoyl}p h en ol 8. To a
solution of anisole 7 (1.6 g, 2.6 mmol) in dichloromethane (2 mL)
was added 4 mL of 1 N BBr3 in dichloromethane under argon
at -78 °C, and the solution was was stirred for 1 h. The reaction
mixture was allowed to warm to room temperature for 2 h, and
20 mL of water was added; the mixture was stirred overnight.
The organic layer was washed with water and dried over MgSO4.
The solvent was removed under reduced pressure, and the
product was purified by silica gel column chromatography with
dichloromethane/EtOAc (10:1). Yield: 1.43 g (92%). 1H NMR
(CDCl3, δ, ppm): 1.33 s (18H), 6.31 br s (1H), 7.00 m (8H), 7.40
m (4H), 7.52 d (2H), 762 t (1H), 7.81 m (4H). 13C NMR (CDCl3,
δ, ppm): 31.4, 34.4, 116.9, 119.8, 120.0, 123.4, 126.9, 130.8,
132.6, 139.5, 147.8, 152.8, 156.1, 162.5, 194.6. MS (EI): m/z 598.
Found, %: C, 80.28; H, 6.42. Anal. Calcd for C40H38O5, %: C.
80.24; H. 6.40. M 598.
3,5-Bis[4-(3.5-b is{4-[4-(t er t -b u t yl)p h e n oxy]b e n zoyl}-
p h en oxy)ben zoyl]a n isole 9 was prepared by the same pro-
cedure as that for the synthesis of 7 from 1 (300 mg, 0.30 mmol),
tert-butylphenol (220 mg, 1.50 mmol), potassium carbonate (210
mg, 1.50 mmol), toluene (1 mL), and DMF (2 mL). The product
was purified by silica gel column chromatography with dichlo-
romethane/EtOAc (40:1). Yield: 400 mg (88%). 1H NMR (CDCl3,
δ, ppm): 1.33 s (36H), 3.91 s (3H), 7.00 m (8H), 7.02 m (8H),
7.10 m (4H), 7.40 m (8H), 7.50 d (2H), 7.67 d (4H), 7.69 t (1H),
7.81 m (8H), 7.87 m (4H), 7.89 t (2H). 13C NMR (CDCl3, δ,
ppm): 31.4, 34.4, 55.9, 117.0, 117.9, 118.5, 119.8, 123.1, 123.8,
126.5, 126.9, 130.5, 132.4, 132.5, 132.7, 139.3, 140.3, 147.9, 152.7,
155.8, 160.7, 162.7, 193.4, 194.1. MS (ESI): m/z 1509. Found,
%: C, 80.09; H, 5.73. Anal. Calcd for C101H378O61, %: C, 80.35;
H, 5.87. M 1509.
1495. Found, %: C, 80.06; H, 5.75. Anal. Calcd for C100H86O13
%: C, 80.30; H, 5.80. M 1495.
,
3,5-Bis(4-{3,5-b is[4-(3.5-b is{4-[4-(ter t-b u t yl)p h en oxy]-
ben zoyl}ph en oxy)ben zoyl]ph en oxy}ben zoyl)an isole 11 was
prepared by the same procedure as that for the synthesis of 9
from 1 (160 mg, 0.16 mmol), phenol 9 (420 mg, 0.70 mmol),
potassium carbonate (93 mg, 0.70 mmol), toluene (1 mL), and
DMF (2 mL). The product was purified by silica gel column
chromatography with dichloromethane/EtOAc (40:1). Yield: 350
mg (68%). 1H NMR (CDCl3, δ, ppm): 1.33 s (72H), 3.90 br s (3H),
7.00 m (16H), 7.02 m (16H), 7.10 m (12H), 7.40 m (16 H), 7.50
d (2H), 7.68 d (12H), 7.70 t (1H), 7.81 m (16H), 7.86 m (12H),
7.90 m (6H). 13C NMR (CDCl3, δ, ppm): 31.4, 34.4, 55.8, 116.9,
117.9, 118.5, 119.8, 123.1, 123.8, 123.9, 126.6, 126.9, 130.4, 131.7,
132.3, 132.4, 132.7, 139.2, 140.0, 140.2, 147.8, 152.6, 155.6, 155.7,
155.8, 160.5, 160.9, 172.1, 162.6, 193.1, 193.3, 194.0. MS
(MALDI-TOF): m/z 3305 [M + H]. Found, %: C, 80.21; H, 5.41.
Anal. Calcd for C221H184O29, %: C, 80.34; H, 5.61. M 3304.
3.5-Bis{4-[3,5-b is(4-{3,5-b is[4-(3.5-b is{4-[4-(ter t-b u t yl)-
p h en oxy]b en zoyl}p h en oxy)b en zoyl]p h en oxy}b en zoyl)-
p h en oxy]ben zoyl}a n isole 12 was prepared by the same
procedure as that for the synthesis of 9 from 1 (31 mg, 0.032
mmol), phenol 10 (190 mg, 0.13 mmol), potassium carbonate (20
mg, 0.14 mmol), toluene (0.5 mL), and DMF (1 mL). The product
was purified by silica gel column chromatography with dichlo-
romethane/EtOAc (20:1). Yield: 120 mg (54%). 1H NMR (CDCl3,
δ, ppm): 1.33 s (144H), 3.86 m (3H), 6.98 m (32H), 7.00 m (32H),
7.10 m (32H), 7.39 m (32 H), 7.45 m (2H), 7.67 m (24H), 7.70 m
(1H), 7.78 m (32H), 7.87 m (28H), 7.91 m (14H). 13C NMR
(CDCl3, δ, ppm): 31.4, 34.4, 55.8, 116.9, 117.9, 118.5, 119.8,
123.8, 123.9, 126.4, 126.9, 126.9, 130.4, 131.7, 131.8, 132.4, 132.7,
139.2, 139.9, 140.0, 140.2, 147.8, 152.6, 155.6, 155.7, 155.8, 156.0,
162.1, 162.6, 193.0, 193.3, 194.0. MS (MALDI-TOF): m/z 6915
[M + Na]. Found, %: C, 79.98; H, 5.50. Anal. Calcd for
C461H376O61, %: C, 80.34; H, 5.57. M 6892.
Ack n ow led gm en t. We thank the University of
Leuven, the Ministerie voor Wetenschapsbeleid, and the
FWO Vlaanderen for their continuing support. R.S.
thanks the University of Leuven for a postdoctoral
fellowship. D.B.A. thanks project BQU2000-1157 for
financial support and Prof J . Veciana for backing.
3,5-Bis[4-(3.5-b is{4-[4-(t er t -b u t yl)p h e n oxy]b e n zoyl}-
p h en oxy)ben zoyl]p h en ol 10 was prepared by the same pro-
cedure as that for the synthesis of phenol 8 from anisole 7 (400
mg, 0.26 mmol), dichloromethane (1 mL), and 4 mL of 1 N BBr3
in dichloromethane. The product was purified by column silica
J O015805J