A general synthetic route to chiral dihydroxy-9,9′-spirobifluorenes

Article abstract of DOI:10.1016/j.tet.2006.06.008

C₂-Symmetric 9,9′-spirobifluorenes with 2,2′-, 3,3′-, and 4,4′-dihydroxyls were conveniently prepared from 1,2-dibromobenzene. The palladium-catalyzed coupling reaction of 1,2-dibromobenzene with methoxyphenylmagnesium bromide or methoxyphenylb

Full text of DOI:10.1016/j.tet.2006.06.008

Tetrahedron 62 (2006) 8077–8082
A general synthetic route to chiral dihydroxy-9,90-spirobifluorenes
*
Xu Cheng, Shou-Fei Zhu, Xiang-Chen Qiao, Pu-Cha Yan and Qi-Lin Zhou
State Key Laboratory and Institute of Elemento-organic Chemistry, Nankai University, Tianjin 300071, China
Received 4 April 2006; revised 1 June 2006; accepted 2 June 2006
Available online 30 June 2006
Abstract—C2-Symmetric 9,90-spirobifluorenes with 2,20-, 3,30-, and 4,40-dihydroxyls were conveniently prepared from 1,2-dibromobenzene.
The palladium-catalyzed coupling reaction of 1,2-dibromobenzene with methoxyphenylmagnesium bromide or methoxyphenylboronic acid
provided methoxy substituted 2-bromobiphenyls. Lithium–bromine exchange with n-butyllithium, followed by reaction with dimethyl car-
bonate afforded di[2-(methoxyphenyl)phenyl]ketones as the key intermediates. A continuous ring-closure induced by a strong Lewis acid
and demethylation gave dihydroxy-9,90-spirobifluorenes. The racemic dihydroxy products were resolved by inclusion crystallization using
chiral resolving reagents or separated by chiral HPLC.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
directed by the methoxy group.9 Further studies revealed
that this method also allowed the synthesis of 9,90-spiro-
bifluorene structures with disubstituents at the ortho, meta,
and para positions. Here we wish to report the synthesis
and resolution of 2,20-, 3,30-, and 4,40-dihydroxy-9,90-spiro-
bifluorenes.
Compounds containing a spirobifluorene backbone have
been widely applied in molecular electronics,1 light-emitting
materials,2 enantioselective molecular recognition,3 and
other areas.4 In the spirobifluorene family, chiral dihydroxy-
spirobifluorene was an important branch because the
hydroxy group could be easily converted to other groups
using well-established protocols.5 Though the preparation
of spirobifluorene itself was realized in 1930 by Gomberg,6
synthesis of its 2,20-dihydroxy derivative was not achieved
until the 1970s.7 Both procedures used the same strategy;
the addition of biphenyl Grignard reagents to 9-fluorenone,
followed by a ring-closure to generate the spirobifluorene
skeleton. In this procedure, the position of substituents of
spirobifluorenedepended directly on that in the parent 9-fluo-
renone, which restricted its use in the synthesis of various
spirobifluorene compounds. An alternative strategy used
Friedel–Crafts acylation8 to construct disubstituted spirobi-
fluorene, but it was limited to the preparation of 2,20-disubsti-
tuted spirobifluorenes. In fact, development of a general
method for the synthesis of the spirobifluorene compounds
with 1,10-, 2,20-, 3,30-, or 4,40-disubstituents is still a chal-
lenge. Recently, we reported the synthesis and resolution of
1,10-dihydroxy-9,90-spirobifluorene. Two features of the
method are crucial: (1) dimethyl carbonate was employed
to condense with 2-bromo-biphenyl to create a diaryl ketone,
which was a key intermediate; (2) methanesulfonic acid was
used to close both rings of spirobifluorene in one step and the
ring-closure proceeded exclusively at the ‘bay’ position as
2. Result and discussion
2,20-Dihydroxy-9,90-spirobifluorene was prepared with the
protocol described below. 2-Bromo-40-methoxybiphenyl
(1) was prepared by the Kumada coupling of 1,2-dibromo-
benzene with 4-methoxyphenylmagnesium bromide cata-
lyzed by Pd(PPh3)4. The lithium–bromine exchange,
followed by reaction with dimethyl carbonate gave the key
intermediate 2 in 60% yield. Owing to the lack of an elec-
tron-donating group at the ortho or para position to the
‘bay’ carbon, the electrophilic ring-closure of compound 2
can only be accomplished at 120 ꢀC. It was found that the
demethylation of the methoxy group also took place at this tem-
perature, producing the target molecule 3 directly (Scheme
1). So, the construction of the spirobifluorene skeleton and
the deprotection of the diol were realized in one reaction,
which shortened the synthesis of 2,20-dihydroxy-9,90-spiro-
bifluorene from five steps9 to only three steps with 21% over-
all yield. The diol 3 was first resolved by Toda10 in 1988 and
11
€
its absolute configuration was determined by Lutzen.
3,30-Dihydroxy-9,90-spirobifluorene was obtained in a simi-
lar procedure by using 3-methoxyphenylmagnesium bro-
mide (Scheme 2). In the ring-closure step, though there
were two different ‘bay’ positions in molecule 5 and two dif-
ferent ring-closure products could be formed, the electro-
philic attack occurred at the carbon para to the methoxy
Keywords: Chiral spirobifluorene; Suzuki coupling; Kumada coupling;
Cyclization.
* Corresponding author. Fax: +86 22 2350 6177; e-mail: qlzhou@nankai.
edu.cn
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.06.008

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X. Cheng et al. / Tetrahedron 62 (2006) 8077–8082
MgBr
OMe
Br
Br
OH
Br
b
a
c
+
O
HO
OMe
OMe
OMe
1
2
3
Scheme 1. Reagents and conditions: (a) Pd(PPh3)4, THF, 40 ꢀC, 50%. (b) (i) n-BuLi, THF, ꢁ78 ꢀC; (ii) MeOCOOMe, THF, 60%. (c) MsOH, 120 ꢀC, 70%.
MgBr
Br
Br
Br
b
a
+
O
OMe
MeO
OMe
OMe
4
5
OH
OMe
c
d
HO
MeO
6
7
Scheme 2. Reagents and conditions: (a) (i) Pd(PPh3)4, THF, 40 ꢀC, 60%. (b) (i) n-BuLi, THF, ꢁ78 ꢀC; (ii) MeOCOOMe, THF, 75%. (c) MsOH, 35 ꢀC, 4 h, 96%.
(d) BBr3, added at ꢁ78 ꢀC, and reacted at rt 8 h, 90%.
group to give the spirobifluorene compound 6 with 100%
selectivity at 35 ꢀC. Using boron tribromide, the protecting
methyl group was removed smoothly at room temperature,
affording the product 3,30-dihydroxy-9,90-spirobifluorene
(7). The overall yield from 1,2-dibromobenzene was 39%.
the intermediate 2-bromo-20-methoxy-biphenyl (9), but
no reaction took place. Fortunately, the Suzuki coupling
reaction of 2-bromophenylboronic acid with 1,2-dibromo-
benzene catalyzed by Pd(PPh3)4 was found to be an efficient
method to give the desired coupling product 9 in 71% yield.
Following the procedure used in the synthesis of the
dihydroxy-9,90-spirobifluorenes described above, the diaryl
ketone 10 was prepared from biphenyl 9 in 65% yield. How-
ever, the ring-closure of biphenyl 9 prompted by MsOH was
sluggish at room temperature and 80 ꢀC. When the reaction
temperature was increased to 120 ꢀC, the reaction became
complicated. Alternatively, the 4,40-dimethoxy-9,90-spiro-
bifluorene (11) was successfully achieved in 79% yield when
PPA (polyphosphoric acid) was used to replace the MsOH as
ring-close reagent. Finally, the treatment of compound 11
with boron tribromide afforded 4,40-dihydroxy-9,90-spiro-
bifluorene (12) in high yield (Scheme 4).
In order to prepare the pure enantiomer of diol 7, (R,R)-
2,3-dimethoxy-N,N,N0,N0-tetracyclohexylsuccinamide (8),
which has successfully resolved 1,10- and 2,20-dihydroxy-
9,90-spirobifluorene, was chosen as inclusion resolving
reagent to recrystallize with racemic 7. As expected, (R,R)-8
could selectively recognize (ꢁ)-7 in the solution of acetone
and formed a white inclusion precipitate, which decomposed
in aqueous NaOH to release (ꢁ)-7 in 60% ee (Scheme 3). The
enantiomerically pure (ꢁ)-7 was obtained after repeating the
resolution procedure two more times. Elementary analysis of
inclusion complex showed that (R,R)-8 and (ꢁ)-7 assembled
in a 1:1 manner. Unfortunately, the crystal structure of the
inclusion complex of [(R,R)-8/(ꢁ)-7] was too complicated
to determine the absolute configuration of (ꢁ)-7. The enantio-
merically pure (+)-7 was gained by resolution with (S,S)-8.
The resolution of racemic 12 was unsuccessful by inclusion
recrystallization with chiral host molecules such as (R,R)-
2,3-dimethoxy-N,N,N0,N0-tetracyclohexylsuccinamide (8)
and N-benzylcinchonidinium chloride. We therefore turned
to the direct separation of racemic 12 in preparative chiral
HPLC. By using chiral column AD-H two enantiomers of
12 were separated. The absolute configuration of 4,40-
dihydroxy-9,90-spirobifluorene (12) was determined by chemical
correlation with (S)-(ꢁ)-1,10-dihydroxy-9,90-spirobifluorene
as illustrated in Scheme 5. The optically pure (S)-(ꢁ)-1,10-
dihydroxy-9,90-spirobifluorene (13)9 was methylated with
iodomethane to yield 14, which was brominated in the pres-
ence of sodium bromide and hydroperoxide, followed by
demethylation to give the (S)-4,40-dibromo-1,10-dihydroxy-
9,90-spirobifluorene (16) in 73% yield in three steps. The
diol 16 was converted to (S)-1,10-dihydroxy-4,40-
dimethoxy-9,90-spirobifluorene (17) by reaction with sodium
OH
O
OMe
OMe O
(R,R)-8
acetone
NCy2
[(-)-7 + (R,R)-8]
+
Cy2N
HO
7
Scheme 3.
For the synthesis of 4,40-dihydroxy-9,90-spirobifluorene (12),
the Kumada coupling of 2-methoxyphenylmagnesium bro-
midewith 1,2-dibromobenzenewas first attempted to prepare

X. Cheng et al. / Tetrahedron 62 (2006) 8077–8082
8079
B(OH)2
Br
Br
OMe
b
Br
a
+
OMe
MeO
O
OMe
9
10
MeO
HO
c
d
OMe
11
OH
12
Scheme 4. Reagents and conditions: (a) Pd(PPh3)4, dioxane, 50 ꢀC, 71%. (b) (i) n-BuLi, THF, ꢁ78 ꢀC; (ii) MeOCOOMe, THF, 70%. (c) PPA, 150 ꢀC, 79%.
(d) BBr3, CH2Cl2, ꢁ78 ꢀC to rt, 89%.
Br
c
b
b
MeO
OMe
MeO
OMe
HO
OH
Br
(S)-15
(S)-(-)-13
(S)-14
MeO
Br
MeO
d
e
f
TfO
OTf
HO
OH
HO
OH
OMe
(S)-18
Br
(S)-16
OMe
(S)-17
MeO
HO
g
OMe
OH
(S)-(+)-12
(S)-11
Scheme 5. Reagents and conditions: (a) KOH, MeI, water, rt, 4 h, 97%. (b) NaBr, H2O2, HAc, rt, 10 h, 88%. (c) BBr3, CH2Cl2, ꢁ78 ꢀC to rt, 8 h, 85%.
(d) NaOMe, CuCl, DMF, 120 ꢀC, 10 h, 59%. (e) Tf2O, Py, CH2Cl2, 0 ꢀC, 70%. (f) Pd/C/H2, K2CO3, i-PrOH, 45%. (g) BBr3, CH2Cl2, ꢁ78 ꢀC to rt, 73%.
1
methoxide catalyzed by copper(I) chloride with 59% yield.12
The esterification of compound 17 with Tf2O, followed by
palladium-catalyzed hydrogenation and demethylation with
BBr3 finally gave (S)-(+)-12 with 23% yield in three steps
(Scheme 5).
uncorrected. H, 13C and 31P NMR spectra were recorded
on Varian Mercury Vx-300 or Bruker 300 MHz spectro-
meters. Chemical shifts were reported in parts per million
down field from internal Me4Si. Optical rotations were deter-
mined using a Perkin–Elmer 341 MC polarimeter. Elemental
analyses were performed on Yanaca CDRDER MT-3 instru-
ment. Mass spectra were recorded on a VG-7070E spectro-
meter. HPLC analyses were performed on a Hewlett–Packard
Model HP 1100 Series or a Waters 600E.
3. Experimental
3.1. General
3.2. Synthesis of racemic 2,20-dihydroxy-9,90-spiro-
bifluorene
All reactions and manipulations were performed using stan-
dard Schlenk techniques. THF was distilled from sodium
benzophenone ketyl. CH2Cl2 was distilled from CaH2.
Melting points were measured on a RY-I apparatus and
3.2.1. Preparation of 2-bromo-40-methoxybiphenyl (1). A
solution of 4-methoxy-1-bromobenzene (16.6 g, 89 mmol)

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X. Cheng et al. / Tetrahedron 62 (2006) 8077–8082
in 40 mL of THF was added dropwise to the magnesium
scraps under nitrogen atmosphere at 40 ꢀC over 30 min.
The reaction mixture was refluxed for 1 h and transferred
into a nitrogen flushed flask charged with 1,2-dibromobenz-
ene (20.0 g, 92 mmol) and tetrakis(triphenylphosphine)pal-
ladium (1.5 g, 1.3 mmol) in 100 mL of THF. The mixture
was stirred for 30 h at 40 ꢀC and quenched with saturated
NH4Cl solution, diluted with Et2O, washed with 3 M HCl
and brine, dried over MgSO4. Evaporation of the solvent
under reduced pressure yielded the crude product that was
purified by chromatography on silica gel with PE/EA
(30:1, v/v). The product 1 was obtained as a colorless liquid
(11.8 g, 50%), which solidified after standing at room tem-
perature. Mp 53–54 ꢀC (lit. 55 ꢀC);13 1H NMR (CDCl3)
d 3.85 (s, 3H, Ar-OCH3), 6.96 (d, 2H, J¼9 Hz, Ar-H),
7.13–7.19 (m, 1H, Ar-H), 7.31–7.36 (m, 4H, Ar-H), 7.65
(d, 1H, J¼7.5 Hz, Ar-H).
3.2.2. Preparation of bis(40-methoxybiphenyl-2-yl)-
methanone (2). To a solution of 1 (5.9 g, 22.4 mmol) in
40 mL of THF at ꢁ78 ꢀC was added n-BuLi (13.5 mL,
27 mmol, 2.0 M in hexane), and the yellow solution was
stirred for another 0.5 h. After slow addition of dimethyl car-
bonate (0.91 g, 10.1 mmol) in 20 mL of THF, this mixture
was gradually warmed to ꢁ50 to ꢁ45 ꢀC and kept at this tem-
perature for 4 h resulting in a yellow slurry. This slurry was
warmed to room temperature and quenched with saturated
NH4Cl solution. The solvent was then removed under
reduced pressure. The residue was dissolved in CH2Cl2,
washed with 3 M HCl and brine, dried over MgSO4, concen-
trated under reduced pressure to afford a yellow solid. The
solid was washed with petroleum ether, recrystallized with
PE/EA (2:1, v/v) to give 2 as a white solid (2.3 g, 60%).
Mp 153–154 ꢀC; 1H NMR (CDCl3) d 3.76 (s, 6H, Ar-
OCH3), 6.73 (d, 4H, J¼8.7 Hz, Ar-H), 7.03 (d, 4H, J¼
8.7 Hz, Ar-H), 7.13 (d, 2H, J¼7.8 Hz, Ar-H), 7.18 (t, 2H,
J¼7.5 Hz, Ar-H), 7.32 (t, 2H, J¼7.5 Hz, Ar-H), 7.42 (d,
2H, J¼7.5 Hz, Ar-H); 13C NMR (CDCl3) d 55.3, 113.4,
126.3, 130.1, 130.6, 130.7, 133.0, 139.1, 141.2, 158.8; MS
(ESI) (m/z, %): 386 (M+H+, 100%); Anal. Calcd for
C27H22O3: C, 82.21; H, 5.62. Found: C, 82.47; H, 5.80.
Na2CO3, dried over Na2SO4, and concentrated. The crude
product was chromatographed on silica gel with PE/EA
(3:1, v/v) to afford 6 as a white solid (0.92 g, 96%). Mp
1
187–189 ꢀC; H NMR (CDCl3) d 3.88 (s, 6H, Ar-OCH3),
6.66–6.72 (m, 6H, Ar-H), 7.09 (t, 2H, J¼7.5 Hz, Ar-H),
7.32–7.37 (m, 4H, Ar-H), 7.79 (d, 2H, J¼7.5 Hz, Ar-H);
13C NMR (CDCl3) d 55.5, 64.7, 105.2, 113.9, 119.9,
123.9, 124.6, 127.5, 127.9, 140.8, 141.5, 143.0, 149.9,
159.8; MS (EI) (m/z, %): 376 (M+, 100%); Anal. Calcd for
C27H20O2: C, 86.14; H, 5.36. Found: C, 85.98; H, 5.30.
3.3.2. Preparation of 3,30-dihyroxy-9,90-spirobifluorene
(7). To a flask charged with 6 (2.9 g, 7.7 mmol) in 40 mL
of CH2Cl2 at ꢁ78 ꢀC under a nitrogen atmosphere, a solution
of BBr3 (3 mL, 32 mmol) in 10 mL of CH2Cl2 was added
dropwise with stirring. After addition, the reaction was spon-
taneously warmed to room temperature and kept at this
temperature for 8 h. The dark solution was washed with
NaHSO3 and NaHCO3. The organic phase was dried over
Na2SO4 and concentrated under reduced pressure. After
chromatography on silica gel with PE/EA (2:1, v/v) product
7 was obtained as a white solid (2.4 g, yield 90%). Mp 237–
1
241 ꢀC; H NMR (CDCl3) d 3.30 (s, 2H, Ar-OH), 6.43 (d,
2H, J¼8.4 Hz, Ar-H), 6.55 (d, 2H, J¼7.6 Hz, Ar-H), 7.03
(t, 2H, J¼7.6 Hz, Ar-H), 7.27–7.35 (m, 4H, Ar-H), 7.77
(d, 2H, J¼7.6 Hz, Ar-H); 13C NMR (CD3OD) d 64.8,
106.4, 114.9, 119.9, 123.6, 124.3, 127.4, 139.9, 141.8,
143.2, 150.3, 157.4, 127.5; MS (ESI) (m/z, %): 347
(MꢁH+, 60%); Anal. Calcd for C25H20O2: C, 86.19; H,
4.63. Found: C, 85.98; H, 5.03.
3.3.3. Resolution of 3,30-dihydroxy-9,90-spirobifluorene
(7). To a well-powdered mixture of racemic 7 (500 mg,
1.44 mmol) and (R,R)-2,3-dimethoxy-N,N,N0,N0-tetracyclo-
hexylsuccinamide (8) (755 mg, 1.50 mmol) was added
1 mL of acetone to give a clear solution. After a white precip-
itate appeared a further 1 mL of acetone was added to the
mixture and stirred at room temperature for 8 h. The mixture
was filtrated and the solid was dissolved in Et2O and washed
with 1 M NaOH three times. The organic phase was dried
over Na2SO4 and concentrated to recover the resolving
reagent 8. The aqueous phase was acidified with 12 M HCl
to pH¼3 and extracted with CH2Cl2 twice. The organic phase
was dried over Na2SO4 and concentrated to give product 7 as
a white solid (0.16 g, 30% recovery). The optical purity was
determined to be 60% ee by chiral HPLC [AD-H
(25 cmꢂ0.46 cm i.d.), hexane/2-PrOH ¼ 75:25, tR of (+)-
isomer is 8.9 min, tR of (ꢁ)-isomer is 17.7 min]. A sample
of 7 with predominant (ꢁ)-configuration was subjected to
the resolution procedure twice to give enantiomerically
pure (ꢁ)-7 in 15% total recovery. Mp 239–241 ꢀC, [a]D25
ꢁ1.82 (c 0.66, acetone).
3.2.3. Preparation of 2,20-dihyroxy-9,90-spirobifluorene
(3). Well-powdered 2 (1.05 g, 3.7 mmol) was added to
MsOH (7 mL) and heated at 120 ꢀC for 8 h. The reaction
mixture was diluted with water, extracted with EA. The
organic phase was dried over Na2SO4 and concentrated to
give a brown solid that was subjected to chromatography
on silica gel with PE/EA (1:1, v/v) to offer 3 as a white solid
(0.65 g, yield 70%). Mp 284–287 ꢀC (lit. 286–287 ꢀC);7b 1H
NMR (CDCl3) d 4.77 (s, 2H, OH), 6.17 (s, 2H, Ar-H), 6.71
(d, 2H, J¼7.8 Hz, Ar-H), 6.81 (d, 2H, J¼8.4 Hz, Ar-H), 7.04
(t, 2H, J¼7.5 Hz, Ar-H), 7.33 (t, 2H, J¼7.5 Hz, Ar-H), 7.67
(d, 2H, J¼8.4 Hz, Ar-H), 7.73 (d, 2H, J¼7.5 Hz, Ar-H).
3.4. Synthesis and resolution of 4,40-dihydroxy-9,90-
spirobifluorene
3.3. Synthesis and resolution of racemic 3,30-dihydroxy-
9,90-spirobifluorene (7)
3.4.1. Preparation of 20-bromo-2-methoxy-biphenyl (9).
To a flask charged with Pd(PPh3)4 (0.21 g, 0.19 mmol),
K2CO3 (2.75 g, 19.9 mmol) was added 6 mL of dioxane
and 1,2-dibromobenzene (2.28 g, 9.66 mmol), the mixture
was heated at 50 ꢀC and 2-methoxy-1-benzeneboronic acid
(1 g, 6.45 mmol, in 6 mL of dioxane) was added over 4 h.
The reaction was then quenched with 3 M HCl and extracted
3.3.1. Preparation of 3,30-dimethoxy-9,90-spirobifluorene
(6).14 The well-powdered 5 (1.0 g, 2.5 mmol) was added to
MsOH (30 mL) and warmed at 35 ꢀC for 3 h. The reaction
mixture was poured into ice water and extracted twice
with EA. The organic phase was washed with aqueous

X. Cheng et al. / Tetrahedron 62 (2006) 8077–8082
8081
with EA. The organic phase was dried over Na2SO4 and con-
centrated. After chromatography on silica gel with PE/EA
(30:1, v/v), 1.2 g (71% yield) white solid was obtained.
NMR (CDCl3) d 30.9, 114.8, 116.5, 123.5, 123.6, 127.0,
127.7, 128.4, 128.6, 140,7, 148,1, 151.2, 151.1; MS (ESI)
(m/z, %): 347 (MꢁH+, 30%); Anal. Calcd for C25H16O2: C,
86.10; H, 4.63. Found: C, 85.95; H, 4.69.
1
Mp 58 ꢀC; H NMR (CDCl3) d 3.79 (s, 3H, Ar-OCH3),
6.97–7.05 (m, 2H, Ar-H), 7.15–7.23 (m, 2H, Ar-H), 7.27–
7.41 (m, 3H, Ar-H), 7.65 (d, 1H, J¼8.1 Hz, Ar-H); 13C
NMR (CDCl3) d 55.6, 110.1, 120.3, 124.3, 127.0, 128.6,
129.3, 130.3, 130.8, 131.6, 132.4, 139.8, 156.6; MS (EI)
(m/z, %): 262, 264 (M+, 100%); Anal. Calcd for
C13H11BrO: C, 59.34; H, 4.21. Found: C, 59.35; H, 4.10.
3.4.5. Resolution of 4,40-dihyroxy-9,90-spirobifluorene
(12). The racemic sample of 11 was directly subjected to
HPLC resolution with a preparative Daicel AD-H column
[HPLC conditions: hexane/2-PrOH ¼ 85:15 (v/v); fluent
rate, 3 mL/min; tR of (+)-isomer is 12.9 min, tR of (ꢁ)-
isomer is 15.5 min]. The first peak corresponded to (+)-11.
Mp 125–127 ꢀC, [a]D25 +2.7 (c 1.7, acetone).
3.4.2. Preparation of bis(20-methoxybiphenyl-2-yl)-
methanone (10). To a flask charged with 9 (5 g, 19.0 mmol)
and 30 mL of THF was added n-BuLi (10 mL, 2.1 M in hex-
ane, 21 mmol) at ꢁ78 ꢀC. The mixture was stirred at ꢁ78 ꢀC
for 20 min, and a solution of dimethyl carbonate (0.727 g,
8.08 mmol) was added dropwise over 5 min. The reaction
mixture was allowed to warm to room temperature spontane-
ously and quenched with aqueous NH4Cl. After concentration
under reduced pressure the residue was dissolved in CH2Cl2
and washed with 3 M HCl. The organic phase was dried
over Na2SO4 and concentrated. The residue was washed
with PE/EA (5:1, v/v) to give a pale yellow solid (2.5 g,
70%). Mp 235–237 ꢀC; 1H NMR (CDCl3) d 3.50 (s, 6H, Ar-
OCH3), 6.69 (d, 2H, J¼7.8 Hz, Ar-H), 6.94 (t, 3H,
J¼7.5 Hz, Ar-H), 7.14–7.32 (m, 8H, Ar-H), 7.47 (t, 2H,
J¼7.5 Hz, Ar-H), 7.58 (d, 2H, J¼7.2 Hz, Ar-H); 13C NMR
(CDCl3) d 54.6, 110.2, 120.8, 126.0, 128.6, 129.9, 130.4,
130.5, 130.7, 131.3, 138.6, 139.3, 155.3; MS (EI) (m/z, %):
394 (M+, 35%); Anal. Calcd for C27H22O3: C, 82.21; H,
5.62. Found: C, 82.11; H, 5.57.
Acknowledgements
We thank the National Natural Science Foundation of China,
the Major Basic Research Development Program (Grant
G2000077506), and the Ministry of Education of China
for financial support.
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3.4.3. Preparation of 4,40-dimethoxy-9,90-spirobifluorene
(11). To a flask were added PPA (polyphosphoric acid,
20 mL) and bis(20-methoxybiphenyl-2-yl)methanone (2.0 g,
5.2 mmol). The mixture was heated at 150 ꢀC for 2 h and was
poured into ice. The aqueous slurry was extracted with EA.
The organic phase was dried over Na2SO4 and concentrated,
followed by chromatography on silica gel with PE/EA
(4:1, v/v) to afford 11 as a white solid (1.5 g, 79%). Mp
€
€
Chem. Commun. 2002, 2874; (e) Kruger, J.; Plass, R.; Gratzel,
M.; Cameron, P. J.; Peter, L. M. J. Phys. Chem. B 2003, 107,
7536; (f) Lee, J.-I.; Lee, H.; Oh, J.; Chu, H. Y.; Kim, S. H.;
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3. (a) Smith, D. K.; Diederich, F. Chem. Commun. 1998, 2501; (b)
Smith, D. K.; Zingg, A.; Diederich, F. Helv. Chim. Acta 1999,
1
212–213 ꢀC; H NMR (CDCl3) d 4.07 (s, 6H, Ar-OCH3),
ꢀ
82, 1225; (c) Tejeda, A.; Oliva, A. I.; Siman, L.; Grande, M.;
Caballero, M.-C.; Moran, J. R. Tetrahedron Lett. 2000, 41,
4563.
6.35 (d, 2H, J¼7.2 Hz, Ar-H), 6.71 (d, 2H, J¼7.5 Hz,
Ar-H), 6.87 (d, 2H, J¼8.4 Hz, Ar-H), 7.06 (t, 4H,
J¼7.8 Hz, Ar-H), 7.34 (t, 2H, J¼7.5 Hz, Ar-H), 8.18 (d,
2H, J¼7.8 Hz, Ar-H); 13C NMR (CDCl3) d 55.4, 100.0,
109.6, 116.2, 123.4, 123.7, 126.9, 127.6, 128.8, 141.0,
148.0, 150.6, 155.7; MS (EI) (m/z, %): 376 (M+, 100%);
Anal. Calcd for C27H20O2: C, 86.14; H, 5.36. Found: C,
86.08; H, 5.43.
ꢀ
4. (a) Fournier, J.-H.; Maris, T.; Wuest, J. D. J. Org. Chem. 2003,
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3.4.4. Preparation of 4,40-dihydroxy-9,90-spirobifluorene
(12). To a solution of 11 (1.4 g, 3.8 mmol) in 20 mL of
CH2Cl2 at ꢁ78 ꢀC under nitrogen atmosphere was added
BBr3 (1.4 mL, 14 mmol) in 10 mL of CH2Cl2. The mixture
was allowed to warm to ambient temperature spontaneously
and washed with aqueous NaHSO3 and NaHCO3, dried over
Na2SO4, and concentrated. The residue was subjected to
chromatography on silica gel with PE/EA (2:1, v/v) to give
12 as a pale yellow solid (1.2 g, 89%). Mp 125–127 ꢀC; 1H
NMR (CDCl3) d 5.43 (s, 2H, Ar-OH), 6.34 (d, 2H,
J¼7.5 Hz, Ar-H), 6.71–6.74 (m, 4H, Ar-H), 6.96 (t, 2H,
J¼7.8 Hz, Ar-H), 7.08 (t, 2H, J¼7.5 Hz, Ar-H), 7.36 (t,
2H, J¼7.5 Hz, Ar-H), 8.15 (d, 2H, J¼7.5 Hz, Ar-H); 13C

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14. For the syntheses of compounds 4 and 5, see Ref. 9 and its
supporting information.
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