Synthesis of π-expanded BODIPYs and their fluorescent properties in the visible-near-infrared region

Article abstract of DOI:10.1016/j.tet.2010.06.045

A series of π-expanded boron-dipyrromethenes (BODIPYs) fused with aromatic rings at β,β-positions, such as benzene, acenaphthylene, and benzofluoranthene were prepared by the reaction of BF₃· OEt₂ with bicyclo[2.2.2]octadiene-fused dipyrromethene and the subsequent retro Diels-Alder reaction. These BODIPYs exhibited the absorptions and the fluorescence emissions over wide range of visible-near-infrared region at 500-800 nm. BODIPYs composed of two fluorantho[8,9-f]isoindoles absorbed and emitted at red-region over 750 nm with absolute fluorescence quantum yield (Φ_f) of ca. 0.3, although they are unstable under air in room light. BODIPY composed fluorantho[8,9-f]isoindole and acenaphtho[1,2-c]pyrrole was stable and showed a bright fluorescence emission at 695 nm with high Φ_f of 0.70.

Full text of DOI:10.1016/j.tet.2010.06.045

Tetrahedron 66 (2010) 6895e6900
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of
p
-expanded BODIPYs and their fluorescent properties
in the visibleeneareinfrared region
*
Tetsuo Okujima , Yuya Tomimori, Jun Nakamura, Hiroko Yamada, Hidemitsu Uno, Noboru Ono
Department of Chemistry and Biology, Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 May 2010
Received in revised form 16 June 2010
Accepted 17 June 2010
Available online 22 June 2010
A series of
p-expanded boronedipyrromethenes (BODIPYs) fused with aromatic rings at b,b-positions,
such as benzene, acenaphthylene, and benzofluoranthene were prepared by the reaction of BF3$OEt2
with bicyclo[2.2.2]octadiene-fused dipyrromethene and the subsequent retro DielseAlder reaction.
These BODIPYs exhibited the absorptions and the fluorescence emissions over wide range of visiblee
neareinfrared region at 500e800 nm. BODIPYs composed of two fluorantho[8,9-f]isoindoles absorbed
and emitted at red-region over 750 nm with absolute fluorescence quantum yield (Ff) of ca. 0.3, although
they are unstable under air in room light. BODIPY composed fluorantho[8,9-f]isoindole and acenaphtho
[1,2-c]pyrrole was stable and showed a bright fluorescence emission at 695 nm with high Ff of 0.70.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Dyesepigments
Boron
Dipyrromethene
Fluorescent dye
Fluoranthene
1. Introduction
preparation of BODIPYs composed of isoindoles or acenaphtho[1,2-
c]pyrroles by the retro DielseAlder strategy.10bed The benzene- or
Boronedipyrromethene (BODIPY) derivatives have attracted
much attention as fluorescent dyes because of their stability, sharp
absorption and emission spectra, and high fluorescence quantum
yield. Thus, extensive studies have been reported for the applica-
tion of this dye to chemosensors, biological probes, organic light-
emitting diodes, and dye-sensitized solar cells.1e5 The BODIPY
properties can be easily modified by the substituents. Synthetic
methods of BODIPY derivatives have been developed in order to
tune the absorption and emission wavelength since the end of
1980s. These methods enable us to access a variety of BODIPY
acenaphthyleneefused BODIPYs show the absorptions at
560e657 nm. Thus, the -expanded pyrrole component was
expected to afford the BODIPYs with absorption and emission at
over 700 nm. In this paper, we described the synthesis of a series of
p
linearly
p-expanded BODIPYs 1e4 with exocyclic rings at b,b-po-
sitions and their photochemical properties.
Ph
Ph
Ph
R
B
derivatives.5e12
p-Expanded BODIPYs show red-shifted absorp-
Ph
Ph
tions and emissions. However, most of them with absorptions at
over 650 nm are relatively unstable and show emission with low
quantum yields. Little is known about long-wavelength fluorescent
BODIPYs with high quantum yield over 0.50.
Recently, we have reported the synthesis of benzofluoranthene-
fused porphyrins by the retro DielseAlder reaction of the bicyclo
[2.2.2]octadiene(BCOD)-fused precursors.13 These porphyrins were
stable and exhibited intense absorptions and emissions at
700e800 nm with the absolute quantum yield (Ff) of 0.1e0.3
Ph
N
N
F
F
1a: R = Ph
1b: R = Me
2: R = Et
3: R, R =
R
R
N
N
4: R, R =
B
F
F
although linearly
p-expanded porphyrins are usually unstable,
such as tetraanthra[2,3-b]porphyrin.14 We have also reported the
2. Results and discussion
The synthesis of BCOD-fused BODIPYs is shown in Scheme 1.
BCOD-fused BODIPYs 6e9 were synthesized and converted into
* Corresponding author. Tel./fax: þ81 89 927 9615; e-mail address: tetsuo@chem.
sci.ehime-u.ac.jp (T. Okujima).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.06.045

6896
T. Okujima et al. / Tetrahedron 66 (2010) 6895e6900
Ph
Ph
1. PhCHO, TFA
2. DDQ
Ph
Ph
R
R
B
3. Et N, BF ·OEt (for 6a)
290 °C
3
3
2
1
NH
Ph
Ph
1. AcCl
N
N
2. Et N
3
3. BF ·OEt (for 6b)
3
2
F
F
5a: R = CO Et
5b: R = Me
H
O
2
6a: R = Ph
LiAlH
4
N
6b: R = Me
Ph
R
R
, POCl
1.
3
R
2. (i-Pr) NEt
2
290 °C
1. AcNMe , POCl
2
R
Ph
3. BF ·OEt (for 7 and 8)
3
2-4
3
2
N
N
2. NaOAc
B
F
F
Ph
NH
, POCl
7: R = Et
9: R, R =
8: R, R =
1.
2. (i-Pr) NEt
3
210 °C
NH
10: R, R =
2
3. BF ·OEt (for 9)
3
2
O
Ph
5c
Scheme 1.
symmetrical
p-expanded BODIPYs 1 and unsymmetrical ones
2e4 and 10 by the retro DielseAlder reaction in order to com-
pare their photochemical properties depending on the structure
of the BODIPYs. Pyrrole 5a was prepared from BCOD-fused
pyrrole according to the literature procedure.13,15
a-Methyl-
pyrrole 5b was obtained by the reduction of 5a with LiAlH4. The
subsequent reaction of 5b with benzaldehyde in the presence of
TFA followed by treatment with DDQ, BF3$OEt2, and Et3N gave
BCOD-fused BODIPY 6a in a 37% yield from 5a. meso-Methyl-
bodipy 6b was also prepared by the similar reaction of 5b with
acetyl chloride. Unsymmetrical BODIPYs 7 and 8 were obtained
by the reaction of 5b with a-acetyl-b a-acetyl-b-
-diethyl-16 and
BCODpyrroles10c,d in the presence of POCl3, followed by treat-
ment with (i-Pr)2NEt and BF3$OEt2. The VilsmeiereHaack-type
reaction of 5b with N,N-dimethylacetamide gave 5c in a 39%
yield from 5a, which reacted with
a-methylacenaphtho[1,2-c]
pyrrole10c,17 followed by treatment with (i-Pr)2NEt and BF3$OEt2
to give 9 in a 5% yield.
The crystal structure of 6a and 7 was determined by X-ray
diffraction analysis.18 Single crystals for the X-ray structural
determination were obtained by recrystallization from
MeOHeCHCl3 for 6a and 7. The crystallographic data are sum-
marized in Table S1. BODIPY 6a was crystallized with two mol-
ecules of CHCl3 in a monoclinic cell, space group C2/c, and Z¼4.
The BODIPY molecule occupied the C2 axis of C2/c. Boron and
meso-carbon were found in the C2 axis. The ORTEP drawing of 6a
is shown in Figure 1. Three phenyl groups at the meso-position of
BODIPY core and 7-positions of the fluoranthene moiety were
treated as a disordered structure. The stereochemistry of two
fluoranthenes is anti. The dihedral angles between BODIPY core
and fluoranthene moieties are 111.21ꢀ. The single crystals of anti-
6a were selectively precipitated by recrystallization, while 6a
was obtained as a 1:1 mixture of diastereomers in the reaction of
5b with benzaldehyde. The BODIPY core was slightly distorted
and the dihedral angle of two pyrrole moieties was 11.43ꢀ. On the
other hand, 7 was crystallized in a triclinic cell and the dihedral
angle of pyrrole moieties was 6.03ꢀ. The dihedral angles between
BODIPY core and fluoranthene moieties are slightly large
(130.34ꢀ) compared that of 6a. In the molecular packing, 7 adopts
a parallelogram-shaped configuration with two molecules as
shown in Figure 2. The distance between fluoranthene moieties
Figure 1. ORTEP drawing of 6a. Solvent, hydrogen and disordered (less popular) atoms
are omitted for clarity.
Thermogravimetric analysis (TGA) of 6e9 was carried out in
order to estimate the temperature of the retro DielseAlder
reaction. TGA curve of 8 showed the stepwise weight loss corre-
sponding to removal of two ethylene molecules at around 200 ꢀC
and 300 ꢀC (Fig. 3). The weight loss of the other BODIPYs started at
270 ꢀC and ceased after 310 ꢀC. The reaction temperature of inner
BCOD moiety of 8 was expected to be around 300 ꢀC while that of
another BCOD was around 200 ꢀC. BCOD-fused pyrrole moiety of 8
was converted into isoindole to give 10 in a nearly quantitative
yield by heating at 210 ꢀC. When the BODIPYs 6e9 were heated as
a
solid at 290 ꢀC for 2 h under reduced pressure, benzo-
fluorantheneefused BODIPYs 1e4 were formed with change of the
color in nearly quantitative yields without purification. The BODI-
PYs 2, 4, and 6e10 are stable and fully characterized by physical and
spectral methods including the X-ray crystallographic analysis in
ꢀ
is 4.497 A.

T. Okujima et al. / Tetrahedron 66 (2010) 6895e6900
6897
The UVevis absorption spectra of the BODIPYs 1a, 2e4, 6a, and
7e10 are shown in Figure 4. Preparation of the solutions of 1 and 3
was carried out under a N2 atmosphere in a glove box. Their ab-
sorption bands were observed over wide range of visibleeneareIR
region. The BODIPYs without
p-conjugation 6e8 showed sharp
absorptions around 530 nm similar to those of typical BODIPYs.
Absorptions of BODIPYs with acenaphtho[1,2-c]pyrrole 9 and iso-
indole 10 were consistent with the reported values of another
acenaphthoBODIPYs.10c
Benzofluorantheneefused
BODIPYs
showed a remarkable bathochromic shift after heating the BCOD-
fused precursors. An absorption band of 1a was observed at
765 nm, which was red-shifted by 230 nm compared to that of the
corresponding precursor 6a. Among the air-stable BODIPYs, 4
showed the most red-shifted absorption with broadening at
658 nm.
Figure 2. (a) Molecular packing and (b) side view of 7. Hydrogen atoms are omitted for
clarity.
Figure 4. Normalized UVevis absorption spectra of 7, 8, 6a, 10, 9, 2, 4, 3, and 1a (from
left to right).
Absorption and fluorescence emission data, absolute fluores-
cence quantum yields, and fluorescence lifetime (sf) are summa-
rized in Table 1, and the fluorescence emission spectra are shown in
Figure 5. The fluorescence emission peaks appeared at
547e783 nm. Their fluorescence lifetimes are determined to be
4e5 ns. No difference was observed owing to their
p-conjugation
structures. BCODefused BODIPYs 6, 7, 8, and 10 showed a strong
and sharp emission peak at 550e570 nm with high Ff values of
0.8e1.0. The emission peaks of these BODIPYs are observed in
a similar region to the parent BODIPYs because they have a similar
Figure 3. TGA of 6a (red), 7 (blue), 8 (black), and 9 (green line).
the case of 6a and 7. However, 1 and 3 are unstable under air in
room light to give decomposed products.
p
-conjugation, a BODIPY core or a BODIPY core fused with a ben-
zene ring. BODIPY 4 showed a bright red fluorescence emission at
In order to identify the decomposed product, a solution of 1b in
CHCl3 was irradiated by using a Xe lamp at 762 nm under air. The
color of the solution was changed from red to yellow. In UVevis
absorption of this green-fluorescent solution (Fig. S1 in
Supplementary data), three absorptions at 436, 464, and 499 nm
appeared and the strong absorption at 761 nm disappeared. The
MALDIeTOF MS showed a strong peak at m/z 986 corresponding to
the molecular ion peak of 1b and small peaks with the difference of
ca. 16 at m/z 1000e1050. These results indicated that 1b was oxi-
Table 1
Absorbance, Fluorescence, Absolute Quantum Yields, and Fluorescence Lifetimes of
BODIPYs
labs/nma (log
3
)
lem/nmb
Ffb
(
lex/nm)
s
f/nsc,d
7
8
6b
6a
10
9
2
4
3
1b
1a
526 (4.91)
529 (4.86)
531 (4.92)
535 (4.92)
552 (4.86)
593 (4.96)
629 (4.89)
658 (4.90)
681 (4.96)
761 (5.22)
765 (5.30)
547
546
547
557
573
613
652
695
697
777
783
0.96 (492)
0.83 (495)
0.87 (505)
0.92 (501)
1.00 (513)
0.76 (552)
0.70 (586)
0.70 (610)
0.36 (627)
0.35 (695)
0.32 (700)
5.0
5.0
4.6
5.0
4.6
4.7
4.4
3.8
de
de
de
dized under air in room light to give the BODIPY without
p-ex-
pansion. The photoreaction was performed in CDCl3 in an NMR
tube under an O2 atmosphere (Fig. S2 in Supplementary data).
During the irradiation of the light of 762 nm, two signals at 5.5 and
6.0 ppm, which were assigned to bridge head protons in a bicyclic
ring, were observed. After 4 h, the signals of 1b disappeared com-
pletely. On the other hand,1b was stable under an O2 atmosphere in
a shaded vessel. Thus, these results suggested that the endoper-
oxide or further oxidized structure was formed by the photoreac-
tion of benzofluoranthene moieties with 1O2 although the structure
of the products was not determined, yet.
In CH2Cl2 at 10ꢁ6 M.
In CH2Cl2 at 10ꢁ7 M.
In toluene.
a
b
c
d
e
Excited at 532 nm.
Fluorescence lifetimes of 1 and 3 could not be measured due to their instability.

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T. Okujima et al. / Tetrahedron 66 (2010) 6895e6900
4.2. Synthesis
4.2.1. General procedure for the synthesis of 5b. To a solution of 5a
(3.0 mmol) in dry THF (70 ml) was added slowly LiAlH4 (15 mmol)
at 0 ꢀC under an Ar atmosphere. The resulting mixture was refluxed
for 6 h. After slow addition of water at 0 ꢀC, the mixture was
filtrated with Celite. The filtrate was extracted with CHCl3. The
organic layer was separated, washed successively with water and
brine, and dried over Na2SO4. The solvent was removed under
reduced pressure to give 5b in a nearly quantitative yield. The
obtained 5b was used without further purification: pale yellow
powder; mp 189.5e191.3 ꢀC; 1H NMR (400 MHz, CDCl3)
d
¼7.62e7.53 (m, 10H), 7.47 (m, 2H), 7.22 (m, 2H), 6.63 (d, J¼7.1 Hz,
1H), 6.59 (d, J¼7.1 Hz, 1H), 6.33 (d, J¼2.2 Hz, 1H), 4.21 (m, 2H), 2.13
(s, 3H), and 1.75e1.65 (m, 4H).
Figure 5. Normalized fluorescence emission spectra of 7, 8, 6a, 10, 9, 2, 4, 3, and 1a
(from left to right).
4.2.2. Fluorantho[8,9-f]isoindole 5c. The general procedure was
followed by using 5a (272 mg, 0.499 mmol), LiAlH4 (97 mg,
2.5 mmol), and dry THF (12.5 ml) to give 5b. POCl3 (0.06 ml) was
added dropwise to N,N-dimethylacetamide (0.04 ml) at 0 ꢀC under
an Ar atmosphere. After the mixture was stirred at the same tem-
perature for 30 min, the resulting solid was dissolved in dry CH2Cl2
(3 ml). To this solution was added dropwise a solution of 5b in dry
CH2Cl2 (1.5 ml) at 0 ꢀC. The resulting mixture was refluxed for 1 h
under an Ar atmosphere. After addition of aqueous NaOAc (336 mg/
0.9 ml) to the reaction mixture at 0 ꢀC, the mixture was refluxed for
30 min. The organic layer was separated; washed successively with
aqueous NaHCO3, water, and brine; dried over Na2SO4; and con-
centrated under reduced pressure. The residue was purified by
column chromatography on silica gel with CHCl3 to give 5c
(104 mg, 39% from 5a): yellow crystals; mp >300 ꢀC; 1H NMR
695 nm, which was red-shifted by 80 nm compared to the corre-
sponding BCOD-fused precursor 9. The Ff value (0.70) of 4 is rela-
tively high compared to those of other BODIPYs with the emission
in the same region.22 BODIPYs composed of two fluorantho[8,9-f]
isoindole moieties 1a and 1b showed fluorescence emission at 783
and 777 nm with Ff values of 0.32 and 0.35, respectively, although
they were unstable. Their Ff values were similar to the known
BODIPYs with over 750-nm emission.22bec,23
3. Conclusion
We have synthesized a series of
with aromatic rings at -positions, such as benzene, acenaph-
thylene, and benzo[k]fluoranthene by the retro DielseAlder re-
action of the corresponding BCOD-fused precursors. These BODIPYs
exhibited the absorptions and the fluorescence emissions over
wide range of visibleeneareIR region at 500e800 nm. It is well
p-expanded BODIPYs fused
b
(400 MHz, CDCl3)
d
¼8.48 (br s, 1H), 7.64e7.56 (m, 10H), 7.44
(m, 2H), 7.24 (m, 2H), 6.65 (d, J¼7.3 Hz, 1H), 6.63 (d, J¼7.1 Hz, 1H),
4.61 (m, 1H), 4.22 (m, 1H), 2.15 (s, 3H), 2.14 (s, 3H), and 1.85e1.60
(m, 4H); IR (KBr disk) nmax 3261, 3056, 2937, 2861, and 1614 cmꢁ1
;
MS (70 eV) m/z (relative intensity) 527 (Mþ, 13) and 499 (MþꢁC2H4,
100). Anal. Calcd for C11H17NO: C, 88.77; H, 5.54; N, 2.65. Found: C,
88.51; H, 5.73; N, 2.62.
known that linearly aceneefused BODIPYs at
unstable compared to those at -positions. BODIPY 4 is stable and
b-positions are
a,b
showed a bright fluorescence emission at 695 nm with high Ff
value of 0.70. BODIPYs composed of two fluorantho[8,9-f]isoindoles
1 absorbed and emitted at red-region over 750 nm with Ff value of
ca. 0.3. Therefore,
and acenaphthylene without isoindole moiety has an advantage for
the preparation of stable linearly -expanded BODIPYs with
4.2.2.1. BODIPY 6a. The general procedure was followed by
using 5a (925 mg, 1.70 mmol), LiAlH4 (327 mg, 8.62 mmol), and dry
THF (41 ml) to give 5b. To a solution of 5b in dry CH2Cl2 (90 ml)
p-expansion with the combination of benzene
were added benzaldehyde (85 ml, 0.84 mmol) and a drop of TFA at
p
room temperature under an Ar atmosphere in a shaded vessel. The
resulting mixture was stirred for 2 h. The reaction mixture was
treated with a solution of DDQ (188 mg, 0.827 mmol) in dry CH2Cl2
(18 ml) for 30 min with stirring at room temperature. After addition
of Et3N (2.60 ml) and BF3$OEt2 (2.60 ml), the mixture was stirred at
room temperature for 30 min. The reaction mixture was filtrated
with Celite. The filtrate was washed successively with satd aqueous
NaHCO3, water, and brine; dried over Na2SO4; and concentrated
under reduced pressure. The residue was purified by column
chromatography on silica gel with CHCl3 and flash column chro-
matography with 50% CHCl3ehexane followed by recrystallization
from CHCl3eMeOH to give 6a (345 mg, 37%): orange crystals; mp
a bright fluorescence emission at neareIR region. These findings
would be important for the modification of BODIPY structure.
4. Experimental section
4.1. General
Melting points were determined on a Yanaco micro melting
point apparatus MP500D and are uncorrected. DIeEI and FAB mass
spectra were measured on a JEOL JMS-700. MALDIeTOF mass
spectra were measured on an Applied Biosystems Voyager de Pro.
UVevis spectra were measured on a JASCO V-570 spectrophotom-
eter. 1H NMR spectra were recorded on a JEOL AL-400 at 400 MHz.
The fluorescence emission spectra and the Ff values were
measured on a Hamamatsu Photonics K.K. absolute PL quantum
yield measurement system C9920e03. The fluorescence decay was
measured, using a C7990-01 neareinfrared fluorescence lifetime
measurements system, consisting of a Hamamatsu Photonics K.K.
using a 1 ns (FWHM) pulse laser light at 532 nm (45 mW, 14 kHz)
from a CrsLas FTSS355ꢁQ YAG laser and a NIR region R5509-43
PMT. Elemental analyses were performed at Integrated Center for
Sciences, Ehime University.
300 ꢀC (decomp.); 1H NMR (400 MHz, CDCl3)
22H), 7.26e6.85 (m, 11H), 6.61 (m, 2H), 6.23 (m, 2H), 4.17 (m, 2H),
3.25 (m, 2H), 2.44 (s, 6H), and 1.62e1.45 (m, 8H); UVevis (CH2Cl2)
d
¼7.76e7.40 (m,
lmax, nm (log 3) 374 (4.42) and 535 (4.93); MS (FAB) m/z 1105
[MþH]þ, 1086 [MþHꢁF]þ, 1077 [MþHꢁC2H4]þ, and 1049
[MþHꢁ2C2H4]þ; HRMS calcd for C81H56N2BF2, 1105.4505; found
1105.4506.
4.2.2.2. BODIPY 6b. The general procedure was followed by
using 5a (813 mg, 1.50 mmol), LiAlH4 (285 mg, 7.51 mmol), and dry
THF (37.5 ml) to give 5b. To a solution of 5b in dry CH2Cl2 (40 ml)

T. Okujima et al. / Tetrahedron 66 (2010) 6895e6900
6899
were added acetyl chloride (0.24 ml) at room temperature under an
Ar atmosphere. The resulting mixture was refluxed for 3 h. After
evaporation, the residue was dissolved in toluene (80 ml). The
mixture was treated with Et3N (0.54 ml) for 30 min with stirring at
room temperature. After addition of BF3$OEt2 (0.70 ml), the mix-
ture was stirred at 80 ꢀC for 30 min. The reaction mixture was fil-
trated with Celite. The filtrate was washed successively with water
and brine; dried over Na2SO4; and concentrated under reduced
pressure. The residue was purified by column chromatography on
silica gel with CHCl3 followed by recrystallization from
CHCl3eMeOH to give 6b (198 mg, 25%): red crystals; mp 300 ꢀC
under an Ar atmosphere. The resulting mixture was refluxed for
13 h. The mixture was treated with (i-Pr)2EtN (0.38 ml) for 2 h with
stirring at reflux. After addition of BF3$OEt2 (0.30 ml), the mixture
was refluxed for 6 h. The reaction mixture was filtrated with Celite.
The filtrate was washed successively with satd aqueous NaHCO3,
water, and brine; dried over Na2SO4; and concentrated under
reduced pressure. The residue was purified by column chroma-
tography on silica gel with CHCl3 and flash column chromatography
with 50% CHCl3ehexane and 10% EtOAcehexane to give 9 (21 mg,
5%): dark blue crystals; mp 300 ꢀC (decomp.); 1H NMR (400 MHz,
CDCl3)
d
¼7.86 (m, 2H), 7.747e7.54 (m, 14H), 7.48 (m, 2H), 7.26 (m,
(decomp.); 1H NMR (400 MHz, CDCl3)
(m, 4H), 6.66 (m, 4H), 4.65 (m, 2H), 4.23 (m, 2H), 2.39 (s, 6H), 2.03
d¼7.74e7.41 (m, 24H), 7.25
2H), 6.69 (d, 1H, J¼7.1 Hz), 6.64 (d, 1H, J¼7.1 Hz), 4.83 (m, 1H), 4.31
(m,1H), 2.86 (s, 3H), 2.67 (s, 3H), 2.51 (s, 3H), and 19.1e1.63 (m, 4H);
(s, 3H), and 1.85e1.54 (m, 8H); UVevis (CH2Cl2) lmax, nm (log
3
) 374
UVevis (CH2Cl2) lmax, nm (log 3
) 594 (4.96); MS (FAB) m/z 762 Mþ,
(4.41) and 531 (4.92); MS (FAB) m/z 1043 [MþH]þ, 1024 [MþHꢁF]þ,
1015 [MþHꢁC2H4]þ, and 987 [MþHꢁ2C2H4]þ. Anal. Calcd for
C76H53N2BF2$H2O$CHCl3: C, 78.35; H, 4.78; N, 2.37. Found: C, 78.06;
H, 5.06; N, 2.46.
743 [MꢁF]þ, and 734 [MꢁC2H4]þ; HRMS (FAB) calcd for
C54H38N2BF2, 763.3096; found 763.3093.
4.2.3. Retro DielseAlder reaction of BCODefused BODIPYs. BODIPYs
6e9 (ca. 10 mg each) were heated at 210 ꢀC (for 10) or 290 ꢀC (for
1e4) under reduced pressure for 2 h in a glass tube to give BODIPYs
1e4 and 10 in quantitative yields.
4.2.2.3. BODIPY 7. The general procedure was followed by using
5a (820 mg, 1.51 mmol), LiAlH4 (294 mg, 7.74 mmol), and dry THF
(38 ml) to give 5b. To a solution of 5b and 2-acetyl-3,4-diethyl-5-
methylpyrrole (195 mg, 1.09 mmol) in dry CHCl3 (50 ml) was added
POCl3 (0.18 ml) under an Ar atmosphere. The resulting mixture was
refluxed for 14 h. The mixture was treated with (i-Pr)2EtN (0.80 ml)
for 1.5 h with stirring at reflux. After addition of BF3$OEt2 (0.60 ml),
the mixture was refluxed for 5 h. The reaction mixture was filtrated
with Celite. The filtrate was washed successively with satd aqueous
NaHCO3, water, and brine; dried over Na2SO4; and concentrated
under reduced pressure. The residue was purified by column chro-
matography on silica gel with CHCl3 and 50% CHCl3ehexane followed
by recrystallization from CHCl3eMeOH to give 7 (326 mg, 31%): red
4.2.3.1. BODIPY 10. Purple crystals; mp 300 ꢀC (decomp.); 1H
NMR (400 MHz, CDCl3)
d
¼7.90 (d, J¼8.3 Hz, 1H), 7.73 (d, J¼7.8 Hz,
1H), 7.69e7.56 (m, 10H), 7.49 (m, 3H), 7.32e7.22 (m, 3H), 6.68 (d,
1H, J¼7.1 Hz), 6.62 (d, 1H, J¼7.1 Hz), 4.75 (m, 1H), 4.25 (m, 1H), 2.90
(s, 3H), 2.54 (s, 3H), 2.42 (s, 3H), and 1.86e1.66 (m, 4H); UVevis
(CH2Cl2) lmax, nm (log 3) 355 (4.14), 373 (4.14), and 552 (4.84); MS
(FAB) m/z 688 Mþ, 669 [MꢁF]þ, and 660 [MꢁC2H4]þ. Anal. Calcd for
C48H35N2BF2$3e2H2O: C, 80.56; H, 5.35; N, 3.91. Found: C, 80.69; H,
5.26; N, 3.97.
crystals; mp 245.0e246.8 ꢀC; 1H NMR (400 MHz, CDCl3)
d¼7.66e7.55
4.2.3.2. BODIPY 1a. Dark purple crystals; mp >300 ꢀC; 1H NMR
(m,10H), 7.45 (m, 2H), 7.25 (m, 2H), 6.68 (d,1H, J¼7.1 Hz), 6.61 (d,1H,
J¼7.1 Hz), 4.71 (m, 1H), 4.24 (m, 1H), 2.70 (q, 2H, J¼7.5 Hz), 2.48 (s,
3H), 2.40 (s, 3H), 2.37 (m, 2H), 2.35 (s, 3H), 1.84e1.60 (m, 4H), 1.16 (t,
3H, J¼7.5 Hz), and 1.05 (t, 3H, J¼7.5 Hz); UVevis (CH2Cl2) lmax, nm
(400 MHz, CDCl3)
d
¼7.90 (s, 2H), 7.78e7.51 (m, 25H), 7.29e7.14 (m,
6H), 6.90 (m, 2H), 6.58 (s, 2H), 6.48 (d, 2H, J¼7.1 Hz), 6.18 (d, 2H,
J¼7.3 Hz), and 2.92 (s, 6H); UVevis (CH2Cl2)lmax, nm (log
3)765(5.31);
MS (FAB) m/z 1065 [MþHþ16]þ,1049 [MþH]þ, and 1030 [MþHꢁF]þ;
(log
3
) 374 (4.22) and 526 (4.91); MS (FAB) m/z 694 Mþ, 675 [MꢁF]þ,
HRMS calcd for C77H48N2BF2, 1049.3879; found 1049.3878.
and 666 [MꢁC2H4]þ. Anal. Calcd for C48H41N2BF2$H2O: C, 80.89; H,
6.08; N, 3.93. Found: C, 80.72; H, 5.98; N, 4.02.
4.2.3.3. BODIPY 1b. Dark purple crystals; mp >300 ꢀC; 1H NMR
(400 MHz, CDCl3)
d
¼8.14 (s, 2H), 7.97 (s, 2H), 7.76e7.24 (m, 28H),
4.2.2.4. BODIPY 8. The general procedure was followed by using
5a (202 mg, 0.371 mmol), LiAlH4 (77 mg, 2.0 mmol), and dry THF
(20 ml) to give 5b. To a solution of 5b and 1-acetyl-4,7-ethano-3-
methyl-4,7-dihydro-2H-isoindole (78 mg, 0.39 mmol) in dry CHCl3
(25 ml) was added POCl3 (0.05 ml) at room temperature under an Ar
atmosphere. The resulting mixture was refluxed for 12 h. The mix-
ture was treated with (i-Pr)2EtN (0.30 ml) for 2 h with stirring at
reflux. After addition of BF3$OEt2 (0.25 ml), the mixture was refluxed
for 6 h. The reaction mixture was filtrated with Celite. The filtrate
was washed successively with water and brine, dried over Na2SO4,
and concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel with CHCl3 to give 8 (95 mg,
36%). red crystals: mp 200 ꢀC (decomp.); 1H NMR (400 MHz, CDCl3)
6.62 (d, 2H, J¼7.1 Hz), 6.56 (d, 2H, J¼7.1 Hz), 2.88 (s, 6H), and 2.53
(s, 3H); UVevis (CH2Cl2) lmax, nm (log 3) 761 (5.22); MS (FAB) m/z
987 [MþH]þ; HRMS calcd for C72H46N2BF2, 987.3722; found
987.3721.
4.2.3.4. BODIPY 2. Green crystals; mp 259.7e261.5 ꢀC; 1H NMR
(400 MHz, CDCl3)
d
¼8.15 (s, 1H), 8.04 (s, 1H), 7.75e7.66 (m, 8H),
7.62e7.58 (m, 4H), 7.36e7.31 (m, 2H), 6.63 (d, 1H, J¼6.8 Hz), 6.60 (d,
1H, J¼6.8 Hz), 2.90 (s, 3H), 2.73 (q, 2H, J¼7.6 Hz), 2.57 (s, 3H), 2.46
(s, 3H), 2.38 (q, 2H, J¼7.6 Hz), 1.20 (t, 3H, J¼7.6 Hz), and 1.08 (t, 3H,
J¼7.6 Hz); UVevis (CH2Cl2) lmax, nm (log
3) 325 (4.58), 584 (4.57),
and 629 (4.89); MS (FAB) m/z 666 Mþ. Anal. Calcd for C46H37N2BF2:
C, 82.88; H, 5.59; N, 4.20. Found: C, 82.65; H, 5.69; N, 4.24.
d
¼7.67e7.55 (m, 10H), 7.48e7.43 (m, 2H), 7.27e7.22 (m, 2H), 6.68 (d,
1H, J¼7.6 Hz), 6.63 (d,1H, J¼7.6 Hz), 6.52e6.36 (m, 2H), 4.69 (m,1H),
4.2.3.5. BODIPY 3. Green crystals; mp >300 ꢀC; 1H NMR
4.32 (m,1H), 4.23 (m,1H), 3.86 (m,1H), 2.47 (s, 3H), 2.41 (s, 3H), 2.38
(400 MHz, CDCl3)
d
¼8.21 (s, 1H), 8.02 (s, 1H), 7.91 (d, 1H, J¼8.1 Hz),
(m, 3H), and 1.83e1.36 (m, 8H); UVevis (CH2Cl2) lmax, nm (log
3) 374
7.76e7.14 (m,17H), 6.64 (d,1H, J¼6.8 Hz), 6.58 (d,1H, J¼7.1 Hz), 2.92
(4.23) and 529 (4.86); MS (FAB) m/z 716 Mþ, 697 [MꢁF]þ, 688
[MꢁC2H4]þ, and 660 [Mꢁ2C2H4]þ; HRMS calcd for C50H40N2BF2,
717.3253; found 717.3254. Anal. Calcd for C50H39N2BF2$2H2O: C,
79.78; H, 5.76; N, 3.72. Found: C, 79.95; H, 5.38; N, 3.67.
(s, 3H), 2.88 (s, 3H), and 2.80 (s, 3H); UVevis (CH2Cl2) lmax, nm
(log 3)
681 (4.96); MS (FAB) m/z 660 Mþ; HRMS calcd for
C46H32N2BF2, 661.2627; found 661.2629.
4.2.3.6. BODIPY 4. Green crystals; mp >300 ꢀC; 1H NMR
4.2.2.5. BODIPY 9. To a solution of 5c (277 mg, 0.526 mmol) and
7-methyl-8H-acenaphtho[1,2-c]pyrrole (104 mg, 0.506 mmol) in
dry CHCl3 (25 ml) was added POCl3 (0.05 ml) at room temperature
(400 MHz, CDCl3)
(d, 1H, J¼7.3 Hz), 6.64 (d, 1H, J¼7.3 Hz), 2.96 (s, 3H), 2.87 (s, 3H), and
2.82 (s, 3H); UVevis (CH2Cl2) lmax, nm (log ) 610 (4.62) and 658
d
¼8.28 (s,1H), 8.10 (s,1H), 7.87e7.25 (m, 20H), 6.68
3

6900
T. Okujima et al. / Tetrahedron 66 (2010) 6895e6900
(4.90); MS (MALDIeTOF) m/z 734 Mþ and 715 [MꢁF]þ; HRMS calcd
8. (a) Umezawa, K.; Nakamura, Y.; Makino, H.; Citterio, D.; Suzuki, K. J. Am. Chem. Soc.
2008, 130, 1550e1551; (b) Umezawa, K.; Matsui, A.; Nakamura, Y.; Citterio, D.;
Suzuki, K. Chem.dEur. J. 2009, 15, 1096e1106.
for C52H34N2BF2, 735.2783; found 735.2784.
9. Chen, J.; Burghart, A.; Derecskei-Kovacs, A.; Burgess, K. J. Org. Chem. 2000, 65,
2900e2906.
Acknowledgements
10. (a) Descalzo, A. B.; Xu, H.-J.; Xue, Z.-L.; Hoffmann, K.; Shen, Z.; Weller, M. G.;
€
You, X.-Z.; Rurack, K. Org. Lett. 2008, 10, 1581e1584; (b) Shen, Z.; Rohr, H.;
The authors thank Venture Business Laboratory, Ehime University,
for assistance in obtaining the MALDIeTOF mass spectra. We used
ethyl isocyanoacetate for the preparation of the pyrroles by Bar-
toneZard reaction from the Nippon Synthetic Chem. Ind. (Osaka Ja-
pan). This work was partially supported by Grants-in-Aid for the
Rurack, K.; Uno, H.; Spieles, M.; Schulz, B.; Reck, G.; Ono, N. Chem.dEur. J. 2004,
10, 4853e4871; (c) Ono, N.; Yamamoto, T.; Shimada, N.; Kuroki, K.; Wada, M.;
Utsunomiya, R.; Yano, T.; Uno, H.; Murashima, T. Heterocycles 2003, 61,
433e447; (d) Wada, M.; Ito, S.; Uno, H.; Murashima, T.; Ono, N.; Urano, T.;
Urano, Y. Tetrahedron Lett. 2001, 42, 6711e6713.
11. (a) Harriman, A.; Mallon, L. J.; Goeb, S.; Ulrich, G.; Ziessel, R. Chem.dEur. J. 2009,
15, 4553e4564; (b) Goeb, S.; Ziessel, R. Org. Lett. 2007, 9, 737e740.
12. (a) Buyukcakir, O.; Bozdemir, O. A.; Kolemen, S.; Erbas, S.; Akkaya, E. U. Org. Lett.
2009, 11, 4644e4647; (b) Atilgan, S.; Ozdemir, T.; Akkaya, E. U. Org. Lett. 2008,
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13. Nakamura, J.; Okujima, T.; Tomimori, Y.; Komobuchi, N.; Yamada, H.; Uno, H.;
Ono, N. Heterocycles 2010, 80, 1165e1175.
Scientific Researches on Innovative Areas (No 21108517, p-Space to H.
U.) and C (No 20550047 to H.U.) from the Japanese Ministry of Edu-
cation, Culture, Sports, Science and Technology and PRESTO (Photon
on soft materials to H.Y.) from Japan Science and Technology Agency.
14. (a) Yamada, H.; Kuzuhara, D.; Takahashi, T.; Shimizu, Y.; Uota, K.; Okujima, T.;
Uno, H.; Ono, N. Org. Lett. 2008, 10, 2947e2950; (b) Kobayashi, N.; Konami, H. J.
Porphyrins Phthalocyanines 2001, 5, 233e255; (c) Mack, J.; Asano, Y.; Kobayashi,
N.; Stillman, M. J. J. Am. Chem. Soc. 2005, 127, 17697e17711.
15. Okujima, T.; Komobuchi, N.; Uno, H.; Ono, N. Heterocycles 2006, 67, 255e267.
16. Tang, J.; Verkade, J. G. J. Org. Chem. 1994, 59, 7793e7802.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2010.06.045. These data in-
clude MOL files and InChIKeys of the most important compounds
described in this article.
17. (a) Ono, N.; Hironaga, H.; Shimizu, K.; Ono, K.; Kuwano, K.; Ogawa, T. J. Chem.
Soc., Chem. Commun. 1994, 1019e1020; (b) Lash, T. D.; Novak, B. H.; Lin, Y. Tet-
rahedron Lett. 1994, 35, 2493e2494.
18. The diffraction data were processed with Crystal Clear, solved with SIR-9719 or
DIRDIF-99,20 and refined with SHELXL-97.21 The data (excluding structure
factors) for the structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre. Copies of the data can be obtained,
free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[fax: þ44 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk].
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