A facile approach to the synthesis of substituted dibenzofulvenes-precursors to pi-stacked poly(dibenzofulvene)s

Article abstract of DOI:10.1016/j.tet.2010.03.046

A series of novel substituted (2-methoxy, 2-nitro, 2-bromo, 2-iodo, 2-cyano, and 2-acetyl) and disubstitiuted (2-bromo-7-methoxy, 2-bromo-7-propoxy, 2-bromo-7-hexoxy, 2-nitro-7-propoxy, 2-nitro-7-hexoxy, and 2,7-di-bromo) dibenzofulvenes have been prepared from the corresponding fluorenes with fair to very good overall yields (35.7-66.7%) based on the Wittig chemistry. The new approach enjoyed much simpler experimental procedures and has the advantage of higher functional group tolerance. Preliminary results on their polymerization using solution free-radical approach are also presented.

Full text of DOI:10.1016/j.tet.2010.03.046

Tetrahedron 66 (2010) 3973–3977
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A facile approach to the synthesis of substituted dibenzofulvenes-precursors
to pi-stacked poly(dibenzofulvene)s
*
Michael Y. Wong, Louis M. Leung
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel substituted (2-methoxy, 2-nitro, 2-bromo, 2-iodo, 2-cyano, and 2-acetyl) and di-
substitiuted (2-bromo-7-methoxy, 2-bromo-7-propoxy, 2-bromo-7-hexoxy, 2-nitro-7-propoxy, 2-nitro-
7-hexoxy, and 2,7-di-bromo) dibenzofulvenes have been prepared from the corresponding fluorenes
with fair to very good overall yields (35.7–66.7%) based on the Wittig chemistry. The new approach
enjoyed much simpler experimental procedures and has the advantage of higher functional group tol-
erance. Preliminary results on their polymerization using solution free-radical approach are also
presented.
Received 14 September 2009
Received in revised form
9 March 2010
Accepted 16 March 2010
Available online 27 March 2010
Keywords:
Dibenzofulvene
Ó 2010 Elsevier Ltd. All rights reserved.
9-Fluorenyltriphenylphosphonium bromide
Wittig
1. Introduction
37.2%.1 Similarly, 2,7-di-tert-butyldibenzofulvene has been syn-
thesized via the two-step process starting from 2,7-di-tert-butyl-
It is well known that 1,1-diphenylethylene cannot be polymer-
ized due to steric hindrance, its coplanar analog dibenzofulvene
(DBF), however, can undergo addition polymerization effectively.1
The conductivity of traditional main-chain conductive polymers
fluorene with only 54.9% overall yield.7 It was necessary to
maintain strict stoichiometric balance between the lithiation
reagent and fluorene or otherwise the yield would drop signifi-
cantly.8 Another drawback to this approach has been the use of
air-sensitive organometallic reagent. Fluorenyllithium is known to
attack molecular oxygen.9 Thus the solvent used for the reaction
has to be dried thoroughly and degassed. The use of organometallic
regents also raises an issue with functional-group tolerance when
preparing substituted DBF.
derived from extensive delocalization of conjugated
p-electrons,
whereas the conductivity for poly(dibenzofulvene) (poly(DBF))
resulted from unique stacking conformation of the fluorene moie-
ties.2 The
p-stacked fluorene moieties allow efficient charge
tunneling leading to a hole mobility of 2.7ꢀ10ꢁ4 cm2 Vꢁ1 sꢁ1 at
299 K (under an electric field 7ꢀ105 V/cm),3 which is unusually
high for a side-chain polymer. Enhanced charge mobility due to
OH
p–p stacking has also been proposed as the underlying principle
KOH
n-BuLi
behind charge transport within DNA strands.4,5,6 In addition, the
solubility of side-chain polymers is general better than main-chain
(CH2O)n
conducting polymers. Optical clarity due to restricted
p-electrons
Figure 1. Synthesis of DBF via the lithiation route.
delocalization also rendered poly(DBF) a novel organic opto-
electronic materials.2
In the past, there have been two major routes for the prepara-
tion of DBF monomer. One of them involved lithiation at the
9-position of fluorene followed by hydroxymethylation using
paraformaldehyde. The carbinol was then subjected to base-
catalyzed dehydration to afford the DBF monomer (Fig. 1). DBF
has been prepared from commercially available 9-hydroxy-
methylfluorene using this route but produced a meager yield of
An alternative route to prepare DBF would be first oxidizing
fluorene to fluorenone, followed by a nucleophilic attack on the
keto group by methylmagnesium bromide to produce an alcohol.
Finally, the alcohol was subjected to acid-catalyzed dehydration to
yield the DBF monomer (Fig. 2).10 The oxidation step was carried
out typically using dichromate salts in acetic acid under slight
heating while p-toluenesulfonic acid would be used in the acid-
catalyzed dehydration reaction step. Although higher yield was
resulted, this approach again utilized air-sensitive organometallic
reagent, which greatly limited the choice of functional groups in the
* Corresponding author: Tel.: þ852 3411 7073; fax: þ852 3411 7348; e-mail
address: s20974@hkbu.edu.hk (L.M. Leung).
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.03.046

3974
M.Y. Wong, L.M. Leung / Tetrahedron 66 (2010) 3973–3977
DBF to be prepared. In addition, chromium salts bring toxicity and
waste disposal problems that need to be resolved.
R¼Me, Pr, Hex), Br. It is expected that substituents with different
electronic and steric properties would affect the optical properties
and solubility of the resulting p-stacked poly(DBF)s. The chemistry
also affected thermal stability of the resulting polymers, such as the
tendency for depolymerization or degradation.11,12
O
OH
p-TsOH
Initial trial on the synthesis of DBF (1) was attempted with
9-fluorenone as the carbonyl participant and deprotonated meth-
yltriphenylphosphonium bromide as the ylide for the Wittig
reaction. However, only trace amount of product was obtained. This
was attributed to the highly electrophilic nature of DBF in situ
formed, which was then attacked by the non-stabilized ylide.13
With this understanding in mind, the role for the carbonyl group
and ylide for the Wittig reaction was interchanged, i.e., para-
formaldehyde was used to provide the carbonyl group while
9-fluorenylphosphonium bromide was used as the ylide precursor.
As a result the yield (10–130) increased drastically. This is because
ylide from 9-fluorenylphosphonium salt was stabilized by the
strong delocalization of electron density over the planar fluorene
moiety and as a result the stabilized ylide was compatible with the
DBF products.
Indeed, protons at the 9-position of the fluorenes are particu-
larly active. It has been reported that fluorene could be easily
metalated by potassium hydroxide in ether at room temperature.14
Deprotonation of a hydrocarbon using merely potassium hydroxide
is extremely rare. It should be attributed to the efficient charge
delocalization of the resulting anion over the two aromatic rings
together with coplanar conformation. It was noted that the acidity
of fluorene (pKa: w20.5)15 is much higher than that of diphenyl-
methane (pKa: w35).16
CH3MgBr
Figure 2. Synthesis of DBF via the oxidation route.
2. Results and discussion
In this manuscript, an alternative route for the preparation of
DBF with a range of electron-donating and withdrawing sub-
stituents is reported. The methodology presented here is facile,
high yield and without using air-sensitive reagents. The underlying
chemistry is the extremely well-known Wittig reaction. As shown
in Figure 3, the first step was bromination at the 9-position of the
fluorene moiety (100–1300) followed by preparation of its phospho-
nium salt using triphenylphosphine in a one-pot manner. Details on
the preparation of the substituted fluorenes (100–1300) are given as
Supplementary data except for 400, 500, and 1300, which were
obtained commercially. The phosphonium salts offered the corre-
sponding ylides upon deprotonation and reacted with para-
formaldehyde to produce the desired DBFs. The yields for the two
reaction steps and reaction times for the second step are given in
Table 1. In general, the yields for the first reaction step were
between 50 and 70% and the reaction times for the second step
affording 70% to near quantitative yield were from 4 to 48 h
depending on the chemistry of the substituted groups.
The substituted DBFs have been fully characterized by 1H, 13C
NMR, melting point analysis, infra-red spectroscopy (spectra for 3,
6, 7, 12 are provided as Fig. 7(a–d) in Supplementary data) and
high-resolution mass spectrometry. A characteristic 1H NMR peak
for the vinyl protons at about 6.0 ppm was detected. The splitting of
this NMR peak provided further information on the chemical
structure of the resulting DBFs. For symmetrically substituted DBFs
like the parent DBF (1) and 2,7-di-bromo-DBF (13), this vinyl proton
peak appeared as a singlet (e.g., NMR spectra for (1) and (13) are
given in Fig. 6 (a) and 6 (b) in Supplementary data), whereas for the
unsymmetrically substituted DBFs (2–11) the vinyl proton peaks
were two singlets (e.g., NMR spectra for unsymmetrical 2-acetyl-
DBF (7) and 2-methoxy-DBF (2) are given in Fig. 6(c) and 6(d) in
Supplementary data). However, 2-NO2-7-HexO-DBF (12) did not
show two singlets probably because its vinyl protons were
accidentally equivalent in 1H NMR.17 The results indicated the two
vinyl protons can be non-equivalent for asymmetrically substituted
DBFs. The two vinyl proton peaks in all unsymmetrically
substituted DBFs (except 12) are barely singlets, i.e., there is no
coupling among these geminal protons.
Elucidation on the structure of the substituted 9-fluorenyl-
triphenylphosphonium bromide intermediates (10–130) was
attempted using NMR spectroscopy.18 It was, however, hampered
by the poor solubility of the phosphonium salts in deuterated
solvents. Nevertheless, the chemical structure for some of the
phosphonium salts can be implied by the yields and structures of
the final products. For example, DBF (1) as well as 2-methoxy-DBF
(2) were prepared from their corresponding phosphonium salts
with nearly quantitative yields (99.7% and 99.5%, respectively),
which implied the chemical structure as well as high purity of the
salts. Because the phosphonium salts of 10–130 were all prepared
from the corresponding substituted fluorenes via the same
side-chain bromination and SN2 displacement by triphenylphos-
phine, they therefore should possess the chemical structures as
suggested in Figure 3.
Figure 3. Synthetic scheme for the substituted DBFs from their corresponding
fluorenes.
Table 1
Summary of reaction yields and times for step 1 and step 2 employing the Wittig
approach
Entry
X
Y
Yield for
step 1
Reaction time
for step 2
(1–13) (hrs)
Yield for
step 2
(1–13) (%)
(10–130) (%)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
OMe
OPr
OHex
OPr
OHex
Br
62.0
67.0
61.8
61.0
59.2
67.2
58.9
53.8
59.3
50.7
53.3
49.5
61.5
12
4
99.7
99.5
81.4
w93a
79.5
84.1
79.6
98.8
w50a
82.0
80.3
72.2
68.8
OMe
NO2
Br
48
12
12
24
24
4
4
4
24
24
12
I
CN
Ac
Br
Br
Br
NO2
NO2
Br
9
10
11
12
13
a
Notes: Products were oil-like and some insoluble solids were obtained spon-
taneously upon solvent removal. The yield was calculated according to product
fraction which is soluble in toluene.
The new route allowed the preparation of a range of substituted
DBFs (2–13) that have not been previously reported. The sub-
stituents include X¼H, OMe, NO2, Br, I, CN, Ac, and Y¼H, OR (where
There were several precautions to achieve high yields for the
parent and substituted DBFs. Firstly, the substituted DBFs were

M.Y. Wong, L.M. Leung / Tetrahedron 66 (2010) 3973–3977
3975
rather sensitive to heat. We observed DBF (1) readily converted into
insoluble solids, probably polymers19, as the temperature of the
water bath for the rotary evaporator exceeded 40 ꢂC. A small
amount of insoluble solids was detected for some of the substituted
DBFs at temperature as low as 32 ꢂC. It is therefore suggested 30 ꢂC
should be the maximum temperature for subsequent workup
processes. Secondly, the monomers were sensitive to oxygen. It has
been reported that DBF was able to carry out solid-state
copolymerization with oxygen.20 Thirdly, the monomers might be
moisture sensitive. In one occasion, insoluble material was formed
when a DCM solution of DBF was extracted with DI water. Cho
stated that DBF had to be stored under anhydrous condition.21
Stability of substituted DBFs might also be related to their
physical states. The monomers 2-Br-7-MeO-DBF (8) and 2-Br-7-
HexO-DBF (10) remained stable in the solid state format, whereas
2-Br-7-PrO-DBF (9), which was a greenish oil, produced substantial
quantity of insoluble solids upon solvent removal and was sus-
pected to be the result of self-induced polymerization. The reasons
underlying this observation are not clear and could be related to the
stability of the monomer when exposed to ambient UV irradiation.
Table 1 indicated that DBFs with electron-withdrawing sub-
stituents, such as 2-nitro (3) and 2-cyano (6) needed a longer
reaction time to achieve high yield whereas those with electron-
donating substituents, such as 2-methoxy (2) and 2-bromo-7-
methoxy (8) accomplished excellent yields within relatively short
reaction time. This is expected as the electronic property of the
substituents affected the electron density of their ylides and thus
the rate of nucleophilic attack onto formaldehyde.
severe steric hindrance imposed at the vinylic linkages. For the
polymers 3, 6, 11, their Xn were lower than unity because the MW
was not determined using universal MW calibration. Further study
on the substituted DBF polymers, such as the electronic and steric
effects of the substituted group on the thermal, optical and electrical
properties will be reported in a paper to follow.
n
2.5 mol% AIBN
Y
X
Y
X
80oC, toluene, 20hrs
DBF monomers
poly(DBF)s
Figure 5. Polymerization scheme of substituted DBFs.
Table 2
Summary of polymerization results of substituted DBFs
c
Entry
X
Y
% Insolublea
% Solubleb
Total yield
(%)
Xn
1
2
3
4
H
H
H
H
H
H
H
H
OMe
OPr
OHex
OPr
OHex
Br
15.0
0
16.8
42.9
29.1
29.7
31.3
21.1
NA
31.8
42.9
55.2
68.1
84.4
66.7
NA
75.4
63.0
39.8
94.8
60.1
51.6
7.9
OMe
NO2
Br
11.1
0.19
4.4
4.4
0.37
NA
NA
3.8
9.3
0.82
6.8
26.1
38.4
53.1
45.6
NA
69.1
45.8
0
5
I
6
CN
Ac
Br
Br
Br
NO2
NO2
Br
7d
8
6.3
9
17.2
39.8
23.9
60.1
Trace
We have previously suggested either the traditional lithiation or
oxidation route has limited functional group tolerance. Derivatives,
such as 2-cyano (6) and 2-acetyl-DBF (7) that cannot be prepared
using the traditional routes have been accomplished here using the
methodology presented above. For example, 2-acetyl-DBF (7) was
prepared successfully with a 46.9% overall yield starting from
2-acetylfluorene, as shown in Figure 4. If either n-butyllithium or
methylmagnesium bromide was employed in the reaction, the
acetyl group would have been destroyed.
10
11
12
13
70.9
0
51.6
NA
a
Polymer yield of insoluble fraction in THF.
Yield of soluble fraction in THF.
Number-averaged number of repeating units for the soluble fraction.
Polymerization not yet carried out for this monomer.
b
c
d
3. Conclusion
The advantages of the Wittig approach presented in this report
have been its simplicity and ease of handling. Neither organome-
tallic reagents nor pre-dried solvents were required. All reactions
were carried out under ambient conditions and open atmosphere.
The purification of the substituted DBFs by column chromatogra-
phy is particularly efficient due to the excellent reaction yield and
cleanliness of the reaction. As a result, a series of novel substituted
DBFs have been prepared successfully employing the Wittig
approach with good yields. The DBF monomers prepared have been
polymerized using solution free-radical polyaddition method.
Preliminary results indicating the yield, solubility, and molecular
weights of the polymers are affected critically by the chemistry of
the substituted groups. Details on the properties of the DBF poly-
mers and relationship to the chemistry of the substituted groups
will be the subject of a forthcoming paper.
Step 1 and Step 2
O
O
7, overall: 46.9%
Figure 4. Synthesis of 2-acetyl-DBF via the Wittig route.
Free-radical initiated solution polymerizations for the
substituted DBFs (all except 7) have been attempted (see Fig. 5). The
yields and number-averaged number of repeating units (Xn) have
been summarizedinTable 2. Themolecularweights(MW)of the THF
soluble fraction have been measured by gel permeation chroma-
tography using polystyrene MW standards. As previously reported
by Nakano et al.1,2,20 both soluble and insoluble fraction were
obtained for the p-stacked DBF polymer. The insoluble fraction was
most likely higher molecular weight and crystalline materials. In
general, it was found that the overall yield increased with the ad-
dition of any substituted group in comparison to the neat monomer
1. The amount of soluble fraction increased with an increase in the
size of the solubilizing alkoxy group (e.g., 10>9>8, 12>11). The
substituted polymers became fully soluble when the mono-
substituent was methoxy (2) or one of the di-substituent was hex-
oxy (10, 12). The number-averaged number of repeating units (Xn)
was also found to be among highest for the polymers (2, 10, 12) that
were fully soluble. For DBF polymers with bulky substituted side-
group (such as Br, I, NO2), their Xn are lowered probable due to
4. Experimental section
4.1. General
All reagents and chemicals, unless otherwise stated, were pur-
chased from commercial sources and used without further purifi-
cation. N-bromosuccinimide was recrystallized from hot water,
followed by vacuum drying at about 40 ꢂC. Analytical grade
solvents were used as received. Melting points were taken on
a MEL-TEMP capillary tube apparatus and were uncorrected.
Infrared spectra were recorded using KBr pellets on the Nicolet

3976
M.Y. Wong, L.M. Leung / Tetrahedron 66 (2010) 3973–3977
Magna 550 Series II FTIR spectrometer. 1H and 13C NMR spectra
were recorded on a Bruker-AF301 AT 400 MHz spectrometer. High
resolution mass spectrometry was carried out using a Bruker
Autoflex MALDI–TOF mass spectrometer. The synthesis of the
substituted fluorenes (10–130) is reported as Supplementary data.
ArH), 7.33 (1H, t, J 7.4, ArH), 7.41–7.47 (2H, m, ArH), 7.59 (1H, d, J 7.4,
ArH), 7.66 (1H, d, J 7.4, ArH), and 7.77 (1H, d, J 1.4, ArH); dC (CDCl3)
109.03, 119.76, 120.81, 121.00, 121.01, 124.27, 127.37, 128.89, 131.45,
137.66, 138.89, 139.15, 139.82, and 142.33; HRMS (MALDI) calcd for
C14H979Br: 255.9888; found: 255.9865.
4.2. General procedures for the preparation of substituted
9-fluorenyltriphenylphosphonium bromides
4.3.5. 2-Iododibenzofulvene (2-I-DBF) (5). White solids, mp 78.8–
80.1 ꢂC; dH (CDCl3) 6.02 (1H, s, vinyl), 6.08 (1H, s, vinyl), 7.30–7.42
(3H, m ArH), 7.63–7.71 (3H, m, ArH), and 8.02 (1H, d, J 1.2, ArH);
dC (CDCl3) 92.07, 109.11, 119.89, 121.08, 121.44, 127.63, 128.95,
130.26, 137.40, 137.48, 139.27, 139.56, 140.04 and 142.27; HRMS
(MALDI) calcd for C14H9127I: 303.9749; found: 303.9762.
4.2.1. Fluorenyl-9-triphenylphosphonium bromide (10). Fluorene
(5.00 g, 30.1 mmol), N-bromosuccinimide (5.36 g, 30.1 mmol), and
benzoyl peroxide (182 mg, 0.75 mmol) in benzene (50 mL) were
refluxed for 4 h. Two additional portions of benzoyl peroxide
(182 mg, 0.75 mmol) were added at one-hour interval. The reaction
mixture was cooled to room temperature and benzene was
removed by rotary evaporator to near completion. The crude solids
obtained were washed with warm water (w100 mL) followed by
cold methanol (w20 mL) to remove all residue moisture. After
air-drying, the crude solids and triphenylphosphine (11.9 g,
45.1 mmol) were mixed in benzene (50 mL) and refluxed further
for two days. Upon cooling, the precipitates were collected, thor-
oughly washed with ether, and dried. The resulting compound is
a white solid (9.17 g, 60.2%).
4.3.6. 2-Cyanodibenzofulvene (2-CN-DBF) (6). Yellowish solids, mp
not observed up to 200 ꢂC; dH (CDCl3) 6.14 (1H, s, vinyl), 6.19 (1H, s,
vinyl), 7.39 (1H, t, J 7.4, ArH), 7.42 (1H, t, J 7.4, ArH), 7.63 (1H, dd, J 7.9
and 1.4, ArH), 7.72–7.78 (3H, m, ArH), and 7.95 (1H, d, J 1.4, ArH);
dC (CDCl3) 110.10, 110.47, 119.47, 120.31, 120.81, 121.38, 124.75,
128.85, 129.27, 132.54, 138.34, 138.37, 138.52, 141.72, and 143.98;
HRMS (MALDI) calcd for C15H9N: 203.0735; found: 203.0766; IR
(KBr pellet) 2224 cmꢁ1 (nitrile).
4.3.7. 2-Acetyldibenzofulvene (2-Ac-DBF) (7). Tan colored solids,
mp 116.7–118.0 ꢂC; dH (CDCl3) 2.65 (3H, s, COCH3), 6.19 (1H, s,
vinyl), 6.23 (1H, s, vinyl), 7.41 (1H, t, J 7.4, ArH), 7.45 (1H, t, J 7.4,
ArH), 7.77–7.81 (3H, m, ArH), 8.02 (1H, dd, J 7.9 and 1.5, ArH), and
8.35 (1H, d, J 1.5, ArH); dC (CDCl3) 26.80, 109.31, 119.58, 120.72,
120.91, 121.25, 128.33, 129.03, 129.45, 135.94, 138.14, 138.90,
139.13, 142.56, 144.39, and 197.82; HRMS (MALDI) calcd for
C16H12O: 220.0888; found: 220.0854; IR (KBr pellet) 1650 cmꢁ1
(carbonyl).
Other substituted fluorenyl-9-triphenylphosphonium bromides
(20–130) were prepared similarly. Their yields are summarized in
Table 1.
4.3. General procedures for the preparation of substituted
DBFs
4.3.1. Dibenzofulvene (DBF) (1). To a suspension of fluorenyl-9-
triphenylphosphonium bromide (1.0 g, 1.98 mmol) in untreated
THF (10 mL) was added potassium tert-butoxide (222 mg,
1.98 mmol)22 and stirred for 30 min. Paraformaldehyde (1.78 g,
59.4 mmol) was then added in a single portion, and the reaction
mixture was stirred for 12 h in a 30 ꢂC oil bath. Hexane (w25 mL)
wasthen added and thewhole reaction mixturewas filtered through
a plug of silica, followed by washing with DCM several times. The
filtrate was concentrated by rotaryevaporator and subjected to flash
column chromatography using hexane as the eluent. The compound
(351 mg, 99.7%) is a colorless oil, which crystallized upon drying
under high-vacuum. Mp 53.4–54.5 ꢂC (lit.1 50–52 ꢂC); dH (CDCl3)
6.08 (2H, s, vinyl), 7.29 (2H, t, J 7.4, ArH), 7.36 (2H, t, J 7.4, ArH), 7.68
(2H, d, J 7.4, ArH), and 7.72 (2H, d, J 7.4, ArH); dC (CDCl3) 107.76,119.73,
120.99, 127.03, 128.72, 138.00, 140.13, and 143.33; HRMS (MALDI)
calcd for C14H10: 178.0783; found: 178.0768.
4.3.8. 2-Bromo-7-methoxydibenzofulvene (2-Br-7-MeO-DBF) (8). Greenish
solids, mp 122.5–123.6 ꢂC; dH (CDCl3) 3.89 (3H, s, OCH3), 6.02 (1H, s, vi-
nyl), 6.05 (1H, s, vinyl), 6.91 (1H, dd, J 8.3 and 2.3, ArH), 7.22 (1H, d, J 2.3,
ArH), 7.40–7.44 (2H, m, ArH), 7.52 (1H, d, J 8.3, ArH), and 7.76 (1H, s, ArH);
dC (CDCl3) 55.60, 106.48, 109.00, 115.13, 119.63, 120.28, 120.68, 124.18,
131.51, 132.41, 139.11, 139.49, 139.76, 142.46, and 159.85; HRMS (MALDI)
calcd for C15H1179BrO: 285.9993; found: 285.9985.
4.3.9. 2-Bromo-7-propoxydibenzofulvene (2-Br-7-PrO-DBF) (9). Greenish
oil; dH (CDCl3) 1.10 (3H, t, J 7.4, alkyl), 1.87 (2H, m, alkyl), 4.00 (2H, t, J 6.6,
OCH2), 6.02 (1H, s, vinyl), 6.05 (1H, s, vinyl), 6.92 (1H, dd, J 8.3 and 2.3,
ArH), 7.24 (1H, d, J 2.3, ArH), 7.40 (1H, d, J 8.0, ArH), 7.44 (1H, dd, J 8.0 and
1.4, ArH), 7.51 (1H, d, J 8.0, ArH), and 7.77 (1H, d, J 1.4, ArH); dC (CDCl3)
10.63, 22.70, 69.88, 107.14, 108.94, 115.59, 119.56, 120.26, 120.67, 124.16,
131.49, 132.21, 139.20, 139.47, 139.77, 142.49, and 159.40; HRMS (MALDI)
calcd for C17H1579BrO: 314.0306; found: 314.0324.
4.3.2. 2-Methoxydibenzofulvene (2-MeO-DBF) (2). Slight greenish
solids, mp 103.5–105.1 ꢂC; dH (CDCl3) 3.85 (3H, s, OCH3), 6.00 (1H, s,
vinyl), 6.02 (1H, s, vinyl), 6.89 (1H, dd, J 8.3 and 2.4, ArH), 7.19 (1H, t,
J 7.5, ArH), 7.23 (1H, d, J 2.4, ArH), 7.30 (1H, t, J 7.5, ArH), 7.54 (1H, d, J
8.3, ArH), 7.55 (1H, d, J 7.5, ArH), and 7.65 (1H, d, J 7.5, ArH); dC
(CDCl3) 55.61, 106.47, 107.76, 114.88, 119.00, 120.57, 120.90, 125.98,
128.82, 133.38, 137.89, 139.76, 140.28, 143.41, and 159.59; HRMS
(MALDI) calcd for C15H12O: 208.0888; found: 208.0859.
4.3.10. 2-Bromo-7-hexoxydibenzofulvene (2-Br-7-HexO-DBF) (10). Greenish
solids, mp 98.5–99.7 ꢂC; dH (CDCl3) 0.88 (3H, t, J 7.4, alkyl), 1.34–1.38 (4H,
br, alkyl), 1.47–1.49 (2H, br, alkyl), 1.83 (2H, m, alkyl), 4.04 (2H, t, J 6.5,
OCH2), 6.04 (1H, s, vinyl), 6.07 (1H, s, vinyl), 6.93 (1H, dd, J 8.3 and 2.1,
ArH), 7.25 (1H, d, J 2.1, ArH), 7.39–7.49 (2H, m, ArH), 7.54 (1H, d, J 8.3,
ArH), and 7.79 (1H, s, ArH); dC (CDCl3) 14.09, 22.65, 25.77, 29.30, 31.62,
68.40, 107.16, 108.95, 115.63, 119.55, 120.27, 120.67, 124.18, 131.51, 132.21,
139.20, 139.47, 139.77, 142.52, and 159.43; HRMS (MALDI) calcd for
C20H2179BrO: 356.0776; found: 356.0759.
4.3.3. 2-Nitrodibenzofulvene (2-NO2-DBF) (3). Tan colored solids,
mp not observed up to 200 ꢂC; dH (CDCl3) 6.25 (1H, s, vinyl), 6.26
(1H, s, vinyl), 7.42–7.48 (2H, m, ArH), 7.77–7.82 (3H, m, ArH), 8.28
(1H, dd, J 8.3 and 1.9, ArH), and 8.56 (1H, d, J 1.9, ArH); dC (CDCl3)
110.93, 116.59, 119.86, 121.13, 131.46, 124.35, 129.11, 129.37, 137.95,
138.70, 139.38, 141.74, 145.71, and 147.21; HRMS (MALDI) calcd for
C14H9NO2: 223.0633; found: 223.0647; IR (KBr pellet) 1330 cmꢁ1
(NO2 sym stretch) and 1520 cmꢁ1 (NO2 asym stretch).
4.3.11. 2-Nitro-7-propoxydibenzofulvene (2-NO2-7-PrO-DBF) (11). Orange
solids, mp not observed up to 200 ꢂC; dH (CDCl3) 1.05 (3H, t, J 7.5,
alkyl), 1.84 (2H, m, alkyl), 4.00 (2H, t, J 6.6, OCH2), 6.17 (1H, s, vinyl),
6.18 (1H, s, vinyl), 6.96 (1H, dd, J 8.4 and 2.3, ArH), 7.26 (1H, d, J 2.3,
ArH), 7.61 (1H, d, J 8.4, ArH), 7.63 (1H, d, J 8.4, ArH), 8.21 (1H, dd, J
8.4 and 2.0, ArH), and 8.46 (1H, d, J 2.0, ArH); dC (CDCl3) 10.56,
22.60, 69.97, 107.04, 110.74, 116.40, 116.43, 118.79, 122.21, 124.64,
4.3.4. 2-Bromodibenzofulvene (2-Br-DBF) (4). Slightly greenish oil;
dH (CDCl3) 5.99 (1H, s, vinyl), 6.04 (1H, s, vinyl), 7.28 (1H, t, J 7.4,

M.Y. Wong, L.M. Leung / Tetrahedron 66 (2010) 3973–3977
3977
2. Nakano, T.; Yade, T.; Fukuda, Y.; Yamaguchi, T.; Okumura, S. Macromolecules
2005, 38, 8140.
3. Nakano, T.; Yade, T.; Yokoyama, M.; Nagayama, N. Chem. Lett. 2004, 33,
296.
130.92, 138.43, 141.38, 141.81, 146.14, 146.23 and 160.76; HRMS
(MALDI) calcd for C17H15NO3: 281.1052; found: 281.1044.
4. Treadway, C.-R.; Hill, M.-G.; Barton, J.-K. Chem. Phys. 2002, 2–3, 409.
5. Dohno, C.; Stemp, E.-D.-A.; Barton, J.-K. J. Am. Chem. Soc. 2003, 125, 9586.
6. Lewis, F.-D.; Miller, S.-E.; Hayes, R.-T.; Wasielewski, M.-R. J. Am. Chem. Soc. 2002,
124, 11280.
7. Yade, T.; Nakano, T. J. Polym. Sci., Part A 2006, 44, 561.
8. Stigers, D.; Koutroulis, R.; Chung, D.; Nowick, S. J. Org. Chem. 2000, 65, 3858.
9. Feng, P. Chin. J. Polym. Sci. 1995, 13, 35.
10. Nakano, T.; Kotani, A.; Gao, M.-T. Jpn. Kokai Tokkyo Koho JP 20 07,320,2729,
2007.
11. Cappelli, A.; Galeazzi, S.; Giuliani, G.; Anzini, M.; Donati, A.; Zetta, L.; Mendichi,
R.; Aggravi, M.; Giorgi, G.; Paccagnini, E.; Vomero, S. Macromolecules 2007, 40,
3005.
12. Cappelli, A.; Galeazzi, S.; Giuliani, G.; Anzini, M.; Aggravi, M.; Donati, A.;
Zetta, L.; Boccia, A.-C.; Mendichi, R.; Giorgi, G.; Paccagnini, E.; Vomero, S.
Macromolecules 2008, 41, 2324.
4.3.12. 2-Nitro-7-hexoxydibenzofulvene (2-NO2-7-HexO-DBF)
(12). Yellowish solids, mp 94.2–96.1 ꢂC; dH (CDCl3) 0.90 (3H, t, J 7.2,
alkyl), 1.33–1.40 (4H, br, alkyl), 1.41–1.52 (2H, br, alkyl), 1.81 (2H, m,
alkyl), 4.02 (2H, t, J 6.4, OCH2), 6.15 (2H, s, vinyl), 6.95 (1H, dd, J 8.4 and
2.0,ArH), 7.24(1H,d,J2.0,ArH),7.58(1H, d,J8.4,ArH),7.60(1H, d,J8.2,
ArH), 8.19 (1H, dd, J 8.2 and 2.0, ArH), and 8.43 (1H, d, J 2.0, ArH);
dC (CDCl3) 14.09, 22.64, 25.74, 29.23, 31.60, 68.47, 106.98, 110.72,
116.36, 116.39, 118.75, 122.18, 124.61, 130.87, 138.39, 141.36, 141.78,
146.12, 146.18, and 160.76; HRMS (MALDI) calcd for C20H21NO3:
323.1521; found: 323.1499; IR (KBr pellet) 1330 cmꢁ1 (NO2 sym
stretch), 1510 cmꢁ1 (NO2 asym stretch) and 2930 cmꢁ1 (alkane).
13. Mechoulam, R.; Sondheimer, F. J. Am. Chem. Soc. 1958, 80, 4386.
14. Morton, A.; Claff, E., Jr.; Kagen, P. J. Am. Chem. Soc. 1954, 76, 4556.
15. Ritchie, D.; Uschold, E. J. Am. Chem. Soc. 1967, 89, 1721.
16. Hori, Y.; Nagano, Y.; Uchiyama, H.; Yamada, Y.; Taniquchi, H. Chem. Lett. 1978,
7, 73.
17. It should be noted the vinyl protons for 12 can be resolved into two singlets when
a different deuterated solvent d-benzene was used. dH (C6D6) 0.98 (3H, t,
J 7.2, alkyl), 1.30–1.46 (6H, m, alkyl), 1.70–1.74 (2H, m, alkyl), 3.74 (2H, t, J 6.4,
OCH2), 5.61 (1H, s, vinyl), 5.77 (1H, s, vinyl), 6.94 (1H, dd, J 8.4 and 2.4, ArH), 7.04
(1 H, d, J 8.4, ArH), 7.26 (1H, d, J 2.4, ArH), 7.30 (1H, d, J 8.4, ArH), 8.08 (1H, dd, J 8.4
and 2.0, ArH), and 8.39 (1H, d, J 2.0, ArH); dC (C6D6) 14.25, 22.99, 26.07, 29.53, 31.
89, 68.31, 107.20, 110.71, 116.52, 116.68, 118.82, 122.37, 124.64, 131.38, 138.56, 141.
69, 142.00, 145.84, 146.85, and 161.09.
18. (2-bromo-7-hexoxyfluorenyl)-9-triphenylphosphoniumbromide:dH (CDCl3)0.87
(3H, t, J 7.2), 1.25–1.31 (6H, br), 1.55–1.58 (2H, br), 3.32–3.36 (1H, m), 3.64–
3.70(1H, m),6.66(1H, s),6.77(1H,dt,J8.4and 2.0),7.11(1H, d,J8.0), 7.23–7.29(3H,
m), 7.49–7.54 (6 H, br), 7.63–7.66 (3 H, m), 7.94–7.99 (6H, br), and 8.53 (1H, d, J 8.8);
dP (CDCl3) 30.54; (b) (2-nitro-7-hexoxyfluorenyl)-9-triphenylphosphonium bro-
mide: dH (CDCl3) 0.87 (3H, t, J 7.2),1.28–1.34 (6H, br), 1.58–1.63 (2H, br), 3.32–3.38
(1H, m), 3.67–3.72 (1H, m), 6.67 (1H, s), 6.77 (1H, d, J 8.4), 7.44–7.56 (9H, m),
7.66–7.69 (5H, m), 7.96–7.99 (8H, br), and 8.94 (1 H, d, J 8.2, ArH); dP (CDCl3) 30.44.
19. According to our experience, whether polymerization has occurred or not can
be accomplished by a solubility test. DBF is highly soluble in solvent like DCM
and THF, whereas its polymer is not.
4.3.13. 2,7-Dibromodibenzofulvene (2,7-di-Br-DBF) (13). White crys-
tals, mp not observed up to 200 ꢂC; dH (CDCl3) 6.08 (2H, s, vinyl),
7.49–7.54 (4H, m, ArH) and 7.84 (2H, d, J 0.8, ArH); dC (CDCl3) 110.48,
121.17, 121.29, 124.48, 131.80, 138.04, 139.55, and 141.46; HRMS
(MALDI) calcd for C14H879Br2: 335.8972; found: 335.8956.
Acknowledgements
We are grateful to the Hong Kong Research Grants Council
(HKBU 2105/06E) for financial support of this work.
Supplementary data
Supplementary data associated with this article can be found in
online version, at doi:10.1016/j.tet.2010.03.046.
20. Nakano, T.; Nakagawa, O.; Yade, T.; Okamoto, Y. Macromolecules 2003, 36, 1433.
21. Cho, P. Tetrahedron Lett. 1995, 36, 2403.
References and notes
22. It is important to keep the equivalence of potassium tert-butoxide NOT larger
than the phosphonium salts as polymerization of the products can be initiated
by this weak nucleophile even at ꢁ78 ꢂC.1
1. Nakano, T.; Takewaki, K.; Yade, T.; Okamoto, Y. J. Am. Chem. Soc. 2001, 123,
9182.