Simple and efficient method for obtaining fluorene and spirobifluorene bromide derivatives

Article abstract of DOI:10.1080/00397910801997439

A mild, simple, and efficient synthetic procedure for the preparation of 2-monobromo-, 2,7-dibromo-, and 2,2′,7,7′-tetrabromo-substituted spirobifluorene derivatives and their key intermediates, 2-monobromo- and 2,7-dibromo-substituted fluorene compounds, has been developed. The oxidative bromination of fluorene and spirobifluorene was achieved using NaBr/H2O2 as the bromine source. High conversion of the starting materials was achieved together with good selectivities under optimized reaction conditions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910801997439

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Simple and Efficient Method
for Obtaining Fluorene and
Spirobifluorene Bromide
Derivatives
Wen-Feng Jiang a , Hui-Long Wang a , An-Gang Wang
a & Zhe-Qi Li b
a Department of Chemistry, Dalian University of
Technology, Dalian, China
b Environmental Science and Engineering Institute,
Dalian Jiaotong University, Dalian, China
Published online: 12 Jun 2008.
To cite this article: Wen-Feng Jiang , Hui-Long Wang , An-Gang Wang & Zhe-Qi
Li (2008) Simple and Efficient Method for Obtaining Fluorene and Spirobifluorene
Bromide Derivatives, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 38:12, 1888-1895, DOI:
10.1080/00397910801997439
To link to this article: http://dx.doi.org/10.1080/00397910801997439
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Synthetic Communications1, 38: 1888–1895, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801997439
Simple and Efficient Method for
Obtaining Fluorene and Spirobifluorene
Bromide Derivatives
Wen-Feng Jiang,1 Hui-Long Wang,1 An-Gang Wang,1 and
Zhe-Qi Li2
1Department of Chemistry, Dalian University of Technology, Dalian, China
2Environmental Science and Engineering Institute,
Dalian Jiaotong University, Dalian, China
Abstract: A mild, simple, and efficient synthetic procedure for the preparation
of 2-monobromo-, 2,7-dibromo-, and 2,20,7,70-tetrabromo-substituted spirobi-
fluorene derivatives and their key intermediates, 2-monobromo- and 2,7-
dibromo-substituted fluorene compounds, has been developed. The oxidative
bromination of fluorene and spirobifluorene was achieved using NaBr=H2O2 as
the bromine source. High conversion of the starting materials was achieved
together with good selectivities under optimized reaction conditions.
Keywords: Fluorene bromide derivatives; Oxidative bromination; Spirobifluorene
bromide derivatives
INTRODUCTION
Brominated fluorene and spirobifluorene compounds are a useful class of
intermediates and precursors for the synthesis of spiro-linked molecules,
which can be used widely for the design of a broad range of functional
materials.[1–4] The direct bromination of fluorene and spirobifluo-
rene employing toxic, corrosive Br2 not only generates large amounts
of HBr, which causes serious environmental pollution and low atom
efficiency in terms of bromine consumption, but also leads to a mixture
of the main products with various multiple brominated by-products,
Received in the USA September 8, 2007
Address correspondence to Hui-Long Wang, Department of Chemistry, Dalian
University of Technology, Dalian 116023, China. E-mail: hlwang@dlut.edu.cn
1888

Fluorene and Spirobifluorene Bromide Derivatives
1889
which could not be separated simply in final purification because of the
similar polarity of these brominated compounds.[1,5] To overcome this
problem, various methods for the bromination of fluorene and spirobi-
fluorene by employing new brominating systems or designing new syn-
thetic routes have been developed.[3,6–10] However, some of these
methods suffer from harsh reaction conditions or expensive brominating
agents. In view of this, a mild, efficient, economically attractive, and
highly regioselective method for the synthesis of fluorene and spirobi-
fluorene bromide derivatives is desirable.
The system operating for the oxidative bromination of various
organic compounds is widely explored. Oxidative bromination avoids
the hazardous and expensive Br2 by replacing it in most cases with a bro-
mide salt in the presence of an oxidant agent under acidic conditions. The
oxidizing equivalents are mostly provided by peroxides in the pro-
cesses.[11–13] Oxidative bromination using activated molecular oxygen,[14]
ceric ammonium nitrate (CAN),[15] and NaIO4
as oxidiant agents in
[16]
some instances has also been reported. In this communication, we
describe an efficient and simple method for the oxidative bromination
of fluorene and spirobifluorene compounds using NaBr=H2O2 as the bro-
mine source. Thus, fluorene and 9,90-spirobifluorene were subjected to
bromination in the presence of H2O2, NaBr, and H2SO4 in ethylene
dichloride (EDC) at room temperature to furnish the corresponding
9,90-spirobifluorene bromide derivatives and their key intermediates,
fluorene bromide compounds.
RESULTS AND DISCUSSION
The purpose of this study was to develop mild, simple, and efficient pro-
cedures for the preparation of fluorene and 9,90-spirobifluorene bromide
derivatives starting from fluorene and fluorenone, which are commer-
cially available. The synthetic approach to the fluorene bromide deriva-
tives is outlined in Scheme 1. Treatment of fluorine=NaBr=H2O2 with
Scheme 1. Synthesis of 2-bromofluorene (1) and 2,7-dibromofluorene (2).

1890
W.-F. Jiang et al.
the addition of 10% H2SO4 solution in ethylene dichloride (EDC) as
solvent at room temperature resulted in fluorene bromide derivatives,
2-bromofluorene (1) and 2,7-dibromofluorene (2). Conversion of 82%
and selectivity of 94.3% for the monobrominated product along with
5.7% for 2,7-dibromofluorene could be achieved by keeping good control
of fluorene, NaBr, H2O2, and H2SO4 in a molar ratio of 1:1.2:1.4:1.0 and
reaction time of 10 h. The dibrominated product can be obtained with a
good dibromo selectivity (99%) at 100% conversion by reacting a
1:2.6:2.6:1.8 molar ratio of fluorene, NaBr, H2O2, and H2SO4 in EDC
for the appropriate reaction time (6 h).
Scheme 2 shows the synthesis of 9,90-spirobifluorene bromide deriva-
tives starting from fluorenone, 2-bromofluorene 1, and 2,7-dibromofluor-
ene 2. The oxidation of 1 and 2 with K2Cr2O7 in acetic acid afforded
the corresponding fluorenone bromide compounds. The yields are 92%
and 95% for the 2-bromofluorenone (5) and 2,7-dibromofluorenone
(6), respectively. Compound 5, compound 6, and fluorenone are used
further to prepare spirobifluorene bromide derivatives. The 9,90-spirobi-
fluorene bromide derivatives, namely 2-bromo-9,90-spirobifluorene (7)
and 2,7-dibromo-9,90-spirobifluorene (8), were prepared through the
addition of 2-biphenylmagnesium bromide to 5 and 6, respectively, to
yield the tertiary alcohol followed by dehydration cyclization in the
presence of hydrochloric and acetic acid. This approach yielded very pure
7 and 8 without impurities. 2,20,7,70-Tetrabromo-9,90-spirobifluorene (4)
was prepared through oxidative bromination of 9,90-spirobifluorene (3)
followed by the same procedure for the synthesis of compounds 1 and
2. Fluorenone was employed to afford compound 3 through the same
procedure as 7 and 8. The oxidative bromination of 3 led to a 100%
Scheme 2. Synthetic route to 9,90-spirobifluorene bromide derivatives.

Fluorene and Spirobifluorene Bromide Derivatives
1891
conversion along with 95.1% of 2,20,7,70-tetrabromospirobifluorene after
48 h at room temperature by using a 1:8:6:6 molar ratio of compound 3,
NaBr, H2O2, and H2SO4 in EDC.
The MS and NMR spectra provided unambiguous proof of the
structures for the corresponding compounds synthesized.
It was possible to obtain 2-bromo-,2,7-dibromofluorene and 2-
bromo-, 2,7-dibromo-, 2,20,7,70-tetrabromospirobifluorene with good
selectivity at reasonable conversion using commercially available fluo-
rene and fluorenone as raw materials and NaBr=H2O2 as a bromine
source. These compounds play an important role in the design and syn-
thesis of spiro-based functional materials as key starting intermediates
and precursors.
EXPERIMENTAL
Melting points (in Celsius degrees) were determined on a X-4 microscopic
1
digital melting-point apparatus and are uncorrected. H and 13C NMR
were recorded on a Varian Inova 400 spectrometer at ambient tempera-
ture in CDCl3 (TMS as internal standard). Chemical shifts are reported
as d values in parts per million (ppm) related to the residual solvent peak.
Mass spectra were performed on a Q-Tof Micro spectrometer under EI.
2-Bromofluorene (1)
In a four-necked flask equipped with mechanical stirrer, dropping fun-
nel, thermometer, and condenser, 1.66 g (10 mmol) of fluorene, 1.24 g
(12 mmol) of NaBr, 9.80 g (10 mmol) of 10% H2SO4 solution, and
10 mL of EDC were mixed. While vigorously stirring, 1.59 g (14 mmol)
of 30% H2O2 aqueous solution was added dropwise. After complete
addition, stirring at room temperature continued for 10 h. Afterward,
the organic phase was collected and dried over Na2SO4. After the solvent
was removed, recrystallization of the residue from petroleum ether gave
the pure product. Yield: 33% (0.81 g). Mp: 110–111ꢀC. EI-MS (m=z):
1
246, 244 (Mþ, 28); 165 (100). H NMR (CDCl3, 400 MHz) d: 7.72–7.28
(7H, m, Ar–H), 3.83 (2H, s, ArCH2Ar). 13C NMR (CDCl3, 100 MHz)
d: 145.4, 143.0, 140.9, 130.0, 128.4, 127.3, 127.1, 125.2, 121.3, 120.7,
120.1, 36.9.
2,7-Dibromofluorene (2)
To a mixture of fluorene (1.66 g, 10 mmol), NaBr (2.68 g, 26 mmol), 10%
H2SO4 solution (17.64 g, 18 mmol) and 10 mL of EDC, 30% H2O2

1892
W.-F. Jiang et al.
aqueous solution (2.95 g, 26 mmol) was added and stirred for 6 h at room
temperature. The mixture was then filtered, and the solid was washed
with 5 mL of EDC and 20 mL of water. A white solid was obtained.
Yield: 85% (2.76 g). Mp: 162–164ꢀC. EI-MS (m=z): 324 (56), 243 (100),
1
82 (44). H NMR (CDCl3, 400 MHz) d: 7.66 (2H, s, Ar-H), 7.58–7.60
(2H, d, J ¼ 7.8 Hz, Ar-H), 7.49–7.50 (2H, d, J ¼ 8.0 Hz, Ar-H), 3.85
(s, 2H, ArCH2Ar).
9,90-Spirobifluorene (3)
Under N2 atmosphere,
a solution of 2-bromobiphenyl (23.30 g,
100 mmol) in 50 mL of tetrahydrofuran (THF) was added to the initially
charged magnesium turnings (2.64 g, 110 mmol) to initiate the Grignard
reaction. After the reacton initiated, the solution was added dropwise
in such a way that the solution gently refluxed, and the reaction mixture
was then refluxed for 3 h to complete the reaction. Afterward, a solution
of fluorenone (18 g, 100 mmol) in THF was slowly added to the Grignard
solution, and the mixture was refluxed for 3 h. After cooling to room tem-
perature, the mixture was then filtered and washed with THF. The yellow
magnesium complex was collected and dissolved in 5% hydrochloric
acid (100 mL) with stirring for 2 h. Then, the mixture was filtered, and
a white solid of 9-(2-biphenyly)-9-fluorene alcohol was obtained. The
obtained fluorene alcohol was then dissolved in acetic acid (100 mL)
and refluxed for 40 min. After cooling to room temperature, the 9,90-
spirobifluorene was filtered off and washed with acetic acid. A total of
26.00 g of the product was obtained (yield: 80%). EI-MS (m=z): 316
1
(Mþ, 100). H NMR (CDCl3, 400 MHz) d: 7.79–7.81 (4H, d, J ¼ 7.6
Hz, Ar-H), 7.28–7.32 (4H, t, J ¼ 7.6 Hz, Ar-H), 7.02–7.06 (4H, t,
J ¼ 7.6 Hz, Ar-H), 6.69–6.71 (4H, d, J ¼ 7.6 Hz, Ar-H). 13C NMR
(CDCl3, 100 MHz) d: 148.9, 141.9, 128.0, 127.9, 124.2, 120.1, 66.1.
2,20,7,70-Tetrabromo-9,90-spirobifluorene (4)
To a mixture of 3 (3.16 g, 10 mmol), NaBr (16.20 g, 80 mmol), 10%
H2SO4 solution (58.80 g, 60 mmol), and 20 mL of EDC, a 30% H2O2
aqueous solution (6.80 g, 60 mmol) was added and stirred for 48 h at
room temperature. The mixture was then filtered, and the solid was
washed with 5 mL of EDC and 20 mL of water. A white solid was
obtained. Yield: 80% (5.06 g). Mp: >320 ꢀC. EI-MS (m=z): 636 (18),
634 (68), 632 (Mþ, 100), 630 (66), 628 (17). 1H NMR (CDCl3,
400 MHz) d: 7.66–7.68 (4H, d, J ¼ 8.4 Hz, Ar-H), 7.52–7.54 (4H, d,

Fluorene and Spirobifluorene Bromide Derivatives
1893
J ¼ 7.6 Hz, Ar-H), 6.83 (4H, s, Ar-H). 13C NMR (CDCl3, 100 MHz) d:
149.0, 139.7, 131.9, 127.5, 123.3, 121.9, 65.3.
2-Bromofluorenone (5)
Compound 1 (2.54 g, 10 mmol) and 2.94 g (10 mmol) of K2Cr2O7 were
stirred in 30 mL of acetic acid for 6 h at reflux temperature. After cooling
to room temperature, the reaction solution was filtered. The filter cake
was washed successively with acetic acid (20 mL), water (50 mL), and
5% hydrochloric acid to remove impurities. A yellow solid was obtained.
Yield: 92% (2.38 g). Mp: 145–147 ꢀC. EI-MS (m=z): 260, 258 (Mþ, 100).
1H NMR (CDCl3, 400 MHz) d: 7.75 (1H, s, Ar-H), 7.59–7.66 (2H, m,
Ar-H), 7.49–7.50 (1H, d, J ¼ 1.1 Hz, Ar-H), 7.37–7.39 (1H, d, J ¼ 8.0 Hz,
Hz, Ar-H), 7.30–7.34 (1H, m, Ar-H). 13C NMR (CDCl3,100 MHz) d:
192.3, 143.6, 143.0, 137.1, 135.7, 135.1, 133.7, 129.5, 127.5, 124.6,
123.0, 121.8, 120.5.
2,7-Dibromofluorenone (6)
This compound was prepared according to the procedure described for
2-bromofluorenone (5) utilizing 2 (3.24 g, 10 mmol), K2Cr2O7 (2.94 g,
10 mmol), and acetic acid (30 mL). A total of 3.21 g of the yellow solid
was obtained (yield: 95%). Mp: 204–205 ꢀC. EI-MS (m=z): 340 (51),
1
338 (Mþ, 100), 336 (50). H NMR (CDCl3, 400 MHz) d: 7.73 (2H, s,
Ar-H), 7.60 (2H, s, Ar-H ), 7.35 (2H, s, Ar-H ). 13C NMR (CDCl3,
100 MHz) d: 191.0, 142.4, 137.6, 135.4, 128.0, 123.5, 122.0.
2-Bromo-9,90-spirobifluorene (7)
This compound was prepared according to the procedure described for
9,90-spirobifluorene (3) utilizing magnesium (0.288 g, 12 mmol), 2-bromo-
biphenyl (2.80 g, 12 mmol), and compound 5 (2.59 g, 12 mmol) in THF. A
white solid was obtained. Yield: 68% (2.69 g). EI-MS (m=z): 396, 394
1
(Mþ, 64); 315 (100). H NMR (CDCl3, 400 MHz) d: 7.77–7.84 (3H, m,
Ar-H), 7.66–7.68 (1H, d, J ¼ 8.0 Hz, Ar-H), 7.45–7.47 (1H, dd,
J ¼ 1.6 Hz, J ¼ 8.0 Hz, Ar-H), 7.31–7.37 (3H, m, Ar-H), 7.07–7.11 (3H,
m, Ar-H), 6.85 (1H, s, Ar-H), 6.69–6.72 (3H, m, Ar-H ). 13C NMR
(CDCl3, 100 MHz) d: 151.0, 148.7, 148.0, 141.9, 140.9, 140.8, 131.1,
128.4, 128.2, 128.1, 128.1, 128.1, 127.4, 124.3, 124.2, 121.6, 121.5,
120.3, 120.2, 66.0.

1894
W.-F. Jiang et al.
2,7-Dibromo-9,90-spirobifluorene (8)
This compound was prepared according to the procedure described for
9,90-spirobifluorene (3) utilizing magnesium (0.288 g, 12 mmol), 2-bromo-
biphenyl (2.80 g, 12 mmol), and compound 6 (3.38 g, 10 mmol) in THF. A
white solid was obtained. Yield: 74% (3.51 g). EI-MS (m=z): 476 (50), 474
1
(Mþ, 100), 472 (49). H NMR (CDCl3, 400 MHz) d: 7.84–7.86 (2H, d,
J ¼ 7.6 Hz, Ar-H), 7.65–7.68 (2H, d, J ¼ 8.0 Hz, Ar-H), 7.47–7.50 (2H,
dd, J ¼ 1.6 Hz, J ¼ 8.0 Hz, Ar-H), 7.38–7.42 (2H, td, J ¼ 1.2 Hz,
J ¼ 7.6 Hz, Ar-H), 7.12–7.17 (2H, td, J ¼ 1.2 Hz, J ¼ 7.6 Hz, Ar-H),
6.83–6.84 (2H, td, J ¼ 1.6 Hz, Ar-H), 6.71–6.73 (2H, d, J ¼ 7.6 Hz,
Ar-H). 13C NMR (CDCl3, 100 MHz) d: 150.7, 147.3, 141.9, 139.8,
131.3, 128.5, 128.3, 127.5, 124.2, 122.1, 121.6, 120.5, 65.9.
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