A double Suzuki approach for synthesis of substituted diarylmethylidenefluorenes

Article abstract of DOI:10.1055/s-2006-958407

A convenient synthesis of substituted diarylmethylidenefluorene derivatives, using a double Suzuki reaction, is reported. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-958407

LETTER
127
A Double Suzuki Approach for Synthesis of Substituted Diarylmethylidene-
fluorenes
Double Suzuki
A
.
pproach to S
V
ubstituted Diarylm
.
ethylidenefl
R
uorenes amana,* Bonthu K. Kishore Reddy, Challa Nageswara Reddy, Rajesh G. Gonnade, Mukund K. Gurjar
National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
Fax +91(20)25902629; E-mail: vr.chepuri@ncl.res.in
Received 28 September 2006
Abstract: A convenient synthesis of substituted diarylmethylidene-
fluorene derivatives, using a double Suzuki reaction, is reported.
Br
Br
HO
OH
R
R
B
Key words: diarylmethylidenefluorene, dibromomethylidenefluo-
rene, Suzuki reaction, arylboronic acids, Pd-mediated coupling
R
+
2
3
1
There is great current interest in the chemistry of
Figure 1 Double Suzuki approach to substituted diarylmethyl-
fluorenes and their polymers as electroluminescent com-
positions,1 and the alkylidene fluorene liquid crystalline
semi-conducting polymers2 as organic field effect transis-
tor devices. Diarylmethylidenefluorenes in general, and
the dications3 or radical anions4 derived from them in
particular, are subjects of extensive physical studies. The
studies are related to anti-aromaticity or electron-spin
distribution/conformation, and are evaluated by means of
either magnetic criteria focusing on the consequences of
the existence of a ring current, or ESR and ENDOR spec-
tra. While there appears to be a great deal of discussion
about the derived transient intermediates by theoretical
and experimental calculations, little has focused on the
synthesis of these diarylmethylidenefluorene derivatives.
idenefluorenes
the stereoselective formation of (Z)-1-aryl- or (Z)-alke-
nyl-1-bromo-1-alkenes.10 Because a variety of organo-
boronic acid derivatives are now readily available, we
examined the feasibility of a double Suzuki reaction with
the known dibromomethylidenefluorene (2)11 to synthe-
size symmetric diarylmethylidenefluorene derivatives.
Our initial attempts to optimize the reaction conditions
were carried out with simple phenylboronic acid (3a).
After a careful examination of various reaction condi-
tions, such as reaction temperature, reaction time, base,
solvent, and amount of phenylboronic acid, we concluded
that the best results for the intended double Suzuki reac-
tion were achieved by using a suspension of benzene–eth-
anol–water as a solvent, sodium carbonate as a base,
conducting the reaction at 70–80 °C and addition of the
catalyst Pd(PPh3)2Cl2 (7.5 mol%) and phenylboronic acid
(1.5 equiv) twice to the reaction mixture with a ten-hour
interval.
Substituted diarylmethylidenefluorene derivatives are
generally synthesized by addition of fluorenylidene
anions to benzophenone and subsequent dehydration4,5
and very recently using Peterson olefination.3a There are a
few reports in which the addition of diazofluorene to a
thioketone,6 Wittig olefination,7 [2+2] addition of fluor-
enylidene stannene8 to a benzophenone and subsequent
[2+2] decomposition have been described. In many of
these approaches, the use of strong bases to generate the
requisite benzylic anion and strong acids to dehydrate the
intermediate alcohol limits the variation of the substitu-
ents on aromatic rings, especially the lack of a protocol
compatible with base-sensitive groups. Herein we wish to
report a facile synthesis of diarylmethylidenefluorenes by
means of Suzuki coupling of dibromomethylidene-
fluorene (2) with arylboronic acids 3 (Figure 1).
Thus, the reaction of 2 with differently substituted aryl
boronic acids 3b–i following the above conditions led to
the previously known and a couple of unknown diaryl-
methylidenefluorene derivatives 1b–i (Scheme 1). In
general, the reactions with electron-deficient boronic
acids were facile and good yields were obtained. For the
boronic acids with an electron-donating group, the reac-
tions were sluggish and resulted in low yields. The physi-
cal data of all the known compounds are in agreement
with those of the reported data. All the new compounds
were characterized by their spectral and analytical data
and a single-crystal X-ray structure for compound 1h.12
The Suzuki reaction, consisting of a palladium-mediated
cross-coupling of organoboronic acids with alkenyl or
aryl halides, is a great tool in synthetic organic chemistry.9
The Suzuki reaction of 1,1-dibromo-1-alkenes with alke-
nyl or arylboronic acids is well known and well used in the
synthesis of tri- and tetrasubstituted olefins and also for
In conclusion, a simple method for the synthesis of sym-
metric and substituted diarylmethylidenefluorenes has
been reported using a double Suzuki reaction. Work in the
direction of stepwise coupling of different boronic acids
to address the synthesis of unsymmetric derivatives is in
progress.
SYNLETT 2007, No. 1, pp 0127–0128
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4.
0
1.
2
0
0
7
Advanced online publication: 20.12.2006
DOI: 10.1055/s-2006-958407; Art ID: G29506ST
© Georg Thieme Verlag Stuttgart · New York

128
C. V. Ramana et al.
LETTER
(9) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
Br
Br
HO
+
OH
R
(b) Suzuki, A. J. Organomet. Chem. 1999, 576, 147.
(c) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002,
58, 9633.
R
B
Pd(PPh3)2Cl2,
Na2CO3
C6H6,
(10) (a) Soderquist, J. A.; Leon, G.; Colberg, J. C.; Martinez, I.
Tetrahedron Lett. 1995, 36, 3119. (b) Shen, W. Synlett
2000, 737. (c) Bauer, A.; Miller, M. W.; Vice, S. F.;
McCombie, S. W. Synlett 2001, 254. (d) Oh, C. H.; Lim, Y.
M. Bull. Korean Chem. Soc. 2002, 23, 663. (e) Barluenga,
J.; Moriel, P.; Aznar, F.; Valdès, C. Adv. Synth. Catal. 2006,
348, 347.
(11) (a) Neidlein, R.; Winter, M. Synthesis 1998, 1362.
(b) Ramirez, F.; Desai, N. B.; McKelvie, N. J. Am. Chem.
Soc. 1962, 84, 1745. (c) Corey, E. J.; Fuchs, P. L.
Tetrahedron Lett. 1972, 13, 3769.
EtOH–H2O
70–80 °C
R
2
3a–i
1a–i
a R = H
61%
f R = 3-NO2
79%
b R = 4-Me
c R = 4-Cl
67%
81%
g R = 3,4-di(OMe) 44%
h R = 4-COMe
i R = 3-COMe
88%
81%
d R = 4-NMe2 69%
e R = 3-OMe 73%
Scheme 1 Double Suzuki coupling reaction with dibromomethyl-
idenefluorene (2)
(12) Selected Experimental Procedure: Under an argon
atmosphere, a solution of dibromide 2 (200 mg, 0.6 mmol)
in benzene (15 mL) was treated with solid Na2CO3 (154 mg,
1.5 mmol), Pd(PPh3)2Cl2 (40 mg, 0.06 mmol) and boronic
acid 3h (145 mg, 0.9 mmol) and the contents were degassed
for 5 min. To this, EtOH (0.5 mL) and H2O (0.5 mL) were
added and the reaction mixture was heated at 80 °C for 10 h.
The reaction mixture was cooled, the catalyst (40 mg, 0.06
mmol) and boronic acid 3h (145 mg, 0.9 mmol) were
introduced and the heating at 80 °C was continued for an
additional 10 h. In general, the reactions are light-sensitive
and covering the reaction vessel with aluminum foil is
recommended. The reaction mixture was concentrated under
reduced pressure and diluted with EtOAc (30 mL) and
washed with H2O. The organic layer was separated, dried
(Na2SO4), concentrated and purified by silica gel column
chromatography (10% EtOAc–PE). Recrystallization from
toluene gave 1h (217 mg, 88%) as yellow colored crystals
suitable for single-crystal X-ray diffraction studies.13
Spectral Data of Compound 1h: mp 231–233 °C (toluene).
IR (CHCl3): 3019, 1682, 1601, 1446, 1403, 1360, 1266,
1215, 1075, 958, 849 cm–1. 1H NMR (200 MHz, CDCl3):
d = 2.65 (s, 6 H), 6.61 (br dt, J = 0.83, 8.0 Hz, 2 H), 6.92 (dt,
J = 1.2, 7.4, 8.0 Hz, 2 H), 7.26 (dt, J = 1.0, 7.4 Hz, 2 H), 7.48
(br dt, J = 1.6, 8.1 Hz, 4 H), 7.65–7.74 (m, 2 H), 8.64 (br dt,
J = 1.8, 8.1 Hz, 4 H). 13C NMR (50 MHz, CDCl3): d = 26.6
(q), 119.4 (d), 124.8 (d), 126.6 (d), 128.4 (d), 128.9 (d),
129.9 (d), 135.7 (s), 136.6 (s), 137.8 (s), 140.7 (s), 141.9 (s),
146.9 (s), 197.5 (s). Anal. Calcd for C30H22O2: C, 86.93; H,
5.35. Found: C, 86.97; H, 5.59.
Acknowledgment
C.N.R. thanks UGC (New Delhi) for the financial support in the
form of a research fellowship.
References and Notes
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(13) The crystallographic data for 1h has been deposited with the
Cambridge Crystallographic Data Centre with deposition
no. CCDC 625077. Copies of the data can be obtained free
of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: +44(1223)336033; e-mail:
deposit@ccdc.cam.ac.uk].
(7) Johnson, A. W.; LaCount, R. B. Tetrahedron 1960, 9, 130.
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