Replacing phenyl ring with thiophene: An approach to longer wavelength aza-dipyrromethene boron difluoride (Aza-BODIPY) dyes

Article abstract of DOI:10.1021/jo201413b

In the orignial 1,3,5,7-tetraphenyl aza-BODIPY, replacing the phenyl rings with thiophene achieved significant bathochromic shifts. One of the target molecules, DPDTAB, emitting strong NIR fluorescence with a quantum yield of 0.46 in acetonitrile, is a very competitive NIR fluorophore.

Full text of DOI:10.1021/jo201413b

Note
pubs.acs.org/joc
Replacing Phenyl Ring with Thiophene: An Approach to Longer
Wavelength Aza-dipyrromethene Boron Difluoride (Aza-BODIPY)
Dyes
Xinfu Zhang, Haibo Yu, and Yi Xiao*
State Key Laboratory of Fine Chemicals, Dalian University of Technology, West Campus, 2 Linggong Road, Dalian 116012, China
*
S Supporting Information
ABSTRACT: In the orignial 1,3,5,7-tetraphenyl aza-BODIPY,
replacing the phenyl rings with thiophene achieved significant
bathochromic shifts. One of the target molecules, DPDTAB,
emitting strong NIR fluorescence with a quantum yield of 0.46
in acetonitrile, is a very competitive NIR fluorophore.
1
1,12
wide range of interesting optical properties.
In addition,
right prospects for near-infrared (NIR) fluorescent dyes in
electron-rich thiophene may also play a similar role as the
electron-donating phenyl substituent favoring bathochromic
shift. In fact, thiophene has been introduced into BODIPY
dyes, and they show clear red shift in both absorption and
emission. However, there has been no report that thiophenes
are introduced into aza-BODIPY.
1
B
life sciences have been recognized. These dyes will play
more and more important roles in biological sensing and
imaging, photodynamic therapy, etc. because NIR light can
penetrate biological tissues more deeply and noninvasively than
13
2
UV−vis light. The application fields call for the exploration of
a large number of NIR dyes with excitation/emission at various
wavelengths in the NIR region. Aza-dipyrromethene boron
difluoride (aza-Bodipy) dyes exhibiting favorable photo-
chemical and photophysical properties attract considerable
For this investigation, diphenyldithienyl aza-BODIPY
(
DPDTAB) and tetrathienyl aza-BODIPY (TTAB) were
designed, and the tetraphenyl aza-BODIPY (TPAB) was used
as the reference. Initially, DFT calculations were carried out for
3
−6
attention.
So far, most of these derivatives are actually
13,14
rationalizing structure−property relationships,
with part of
tetraphenyl aza-BODIPYs, having four phenyl groups directly
substituted on the 1, 3, 5, and 7 positions of the aza-BODIPY
core (unknown structure, Figure 1). The absorption and
emission maxima of the precursor tetraphenyl aza-BODIPY
the data listed in Table 1. In DPDTAB and TTAB, the torsion
angles between the thienyl rings and the aza-Bodipy core are
remarkably smaller than those counterparts between the phenyl
rings and the aza-Bodipy core in TPAB. While all three
compounds have almost the same LUMO energy, HOMO
levels of TTAB and DPDTAB are 0.28 and 0.25 eV higher than
that of TPAB, which means smaller energy transitions and
bathochromic shifts for DPDTAB and TTAB compared with
TPAB. Calculated absorption and emission shows general
trend of red shift, and these values are close to the experimental
result. Another purpose of the quantum calculation is to
estimate the lowest lying singlet excited state, which is
responsible for the emissive property of the fluorophore.
According to the quantum mechanics selection rule, emissive
properties (as well as the excitation) of a dye can be evaluated
by the symmetry and the overlapping of the molecular orbitals
(
TPAB shown in Figure 1) are below 700 nm. Generally, two
approaches are adopted to move the spectra bands into the
NIR region. One is to modify on the initial phenyl groups, such
as introducing the electro-donating group, and extending
7
,8
conjugation length. The other is to fuse the 3- and 5-phenyl
groups to the aza-BODIPY core by the formation of six-
9
,10
membered rings,
which in essence, is to decrease the steric
clash-generated torsion angles between the phenyl rings and
the plane of the central chromophore. The additional NIR
bathochromic shifts observed in these “constrained” molecules
can be ascribed to the better electron delocalization due to the
enhancement of coplanarity of the 3- and 5-phenyl groups with
the aza-BODIPY core. Obviously, the existence of torsion
angles is one of the important issues, and how to address it
becomes crucial for developing longer wavelength aza-
BODIPY. Herein, we propose replacing the common phenyl
groups by smaller five-membered rings for the sake of releasing
the steric clash (Figure 1). Thiophene is the first choice because
many materials containing thiophene in the structures exhibit a
(
(
MOs), the change of the spin state, and the oscillator strength
15−17
f) of the electronic transitions, etc.
The DFT calculation
demonstrates DPDTAB bearing higher S ←S transition
1
0
Received: July 10, 2011
Published: November 23, 2011
©
2011 American Chemical Society
669
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The Journal of Organic Chemistry
Note
Figure 1. Structures of aza-BODIPY core, TPAB, DPDTAB, and TTAB. φ −φ are torsion angles between the aromatic rings and the plane of the
1
4
central chromophore.
a
Table 1. DFT Calculation Results
b
c
c
d
φ1
φ2
φ3
φ4
λabs (nm)
λem (nm)
f
HOMO/LUMO (eV)
TPAB
24.45
24.62
2.98
29.98
40.91
22.44
39.35
6.25
33.77
24.05
26.59
614
646
710
682
696
770
0.5082
0.6230
0.4407
−5.58/−3.42
−5.34/−3.41
−5.30/−3.45
DPDTAB
TTAB
17.65
a
b
Calculations were carried out using the Turbomole program suite, employing the B3LYP functional. φ −φ stand for torsion angles between the
aromatic rings and the plane of the central chromophore. Stands for calculated absorption and emission separately. Oscillator strength of S ←S
1
4
c
d
1
0
transition.
a
Scheme 1. Synthetic Procedures for DPDTAB and TTAB
a
Reagents and conditions: (i) CH NO , NEt , MeOH, reflux 10 h; (ii) NH OAc, BuOH, reflux, 24 h; (iii) BF ·OEt , NiPr Et, CH Cl , 25 °C,
3
2
3
4
3
2
2
2
2
overnight; (iv) KCN, acetic acid, ethanol, 35 °C.
oscillator strength (f) of 0.6230 than that of TPAB (0.5082).
This means the reverse transition, that is, the S →S transition,
is also fully allowed; thus, this dye is potentially fluorescent. As
for TTAB, the lower f value (0.4407) may mean weaker
fluorescence.
TTAB were obtained, although the yield still needs to be
improved.
1
0
Single-crystal X-ray structures of DPDTAB and TTAB are
shown in Figure 2, and the data of the torsion angles were listed
in Table 2. For comparison with torsion angles of
18
dimethoxytetraphenyl aza-BODIPY, DMTPAB was cited as
Encouraged by the positive results of the DFT calculations,
we synthesized the two target compounds via different paths, as
shown in Scheme 1. Path 1 was the most often adopted
procedure to synthesize tetraphenyl aza-BODIPY derivatives,
by which DPDTAB with two thienyl groups were obtained
without problems. However, in the second step of this path,
nitrous acid will be released as a byproduct, according to the
suggested mechanism. To avoid the potential risk of oxidative
damage to the electron-rich thienyl moieties, for the synthesis
of TTAB with four thienyl groups, we decided to adopt an
alternative route which did not use or generate oxidative agents;
this route was not as commonly used as path 1 in the previous
preparation of tetraphenyl aza-BODIPY derivatives, perhaps
because of the use of toxic KCN. Through path 2, desirable
a reference. The target molecules DPDTAB and TTAB bear
much smaller torsion angles (Table 2) than DMTPAB,
agreeing with the tendency predicted by DFT calculation. In
TTAB, all the four torsion angles are smaller than 10°,
indicating TTAB’s conjugation structure are totally planar. In
DPDTAB, φ3 and φ4 are smaller than 1° which are almost
negligible. Contrastingly, in DMTPAB, φ3 and φ4 between the
phenyl groups and the central plane are as large as 39° and 34°,
respectively. It is also found that in each of the three
compounds, φ1 is quite different from φ4, and φ3 is quite
different from φ4. For example, in TTAB, φ3 is around 9°, but
φ4 is only 1°. This interesting phenomenon reveals that the
“seemingly symmetric” structures of these aza-BODIPYs are
6
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dx.doi.org/10.1021/jo201413b | J. Org. Chem. 2012, 77, 669−673

The Journal of Organic Chemistry
Note
listed in Table 3. In general, thienyl-bearing DPDTAB and
TTAB show siginificant bathochromic shifts of 60−90 nm in
both the absorption and emission, compared with those of
TPAB. When two phenyls group on the 3- and 5-positions of
TPAB are replaced by thienyl groups to form DPDTAB, a 67
nm red shift in absorption and a 58 nm shift in emission are
generated. However, further introducing two more thienyl
groups on the 1- and 7-positions to get TTAB leads to only an
extra 23 nm shift compared to DPDTAB for absorption and 24
nm for fluorescence. As a result, thiophene rings at the 3- and
5
-positions contribute more pronouncedly to the bathochromic
shifts than those on the 1- and 7-positions. A similar
phenomenon happens to previous tetraphenyl aza-BODIPY
too; that is, modifications on the 3- and 5-phenyl rings affect
the optical properties more than on the 1- and 7-phenyl rings,
which can be concluded as the o-pyrollic position inducing a
6
better delocalization. DPDTAB exhibits strong NIR emission
with a quantum yield of 0.46, which is a rather high value for
NIR dyes. It is counterintuitive that introducing a heavy atom
Figure 2. X-ray crystal structures of DPDTAB and TTAB.
(
to some extent sulfur is heavy atom) could give rise to
a
Table 2. Torsion Angles in DPDTAB, TTAB and Reference
fluorescence quantum yield increment. However, it is not easy
to rationalize the effect of the presence of thiophene groups in
the photobehavior of fluorophores since all (radiative, reactive
and nonradiative) relaxations processes can be perturbed by the
heteroatom. It is actually competing between nonradiative
deactivation processes and fluorescence emission.
better understanding of this, fluorescence lifetimes of these
three compounds were measured (Figure 4 and Table 3). Both
DPDTAB and TTAB bear longer fluorescence lifetimes
compared to TPAB, 3.56 ns for DPDTAB and 2.23 ns for
DTAB. Further, both radiative (K ) and nonradiative (K )
18
Compound DMTPAB Obtained from Crystallography
φ1
φ2
φ3
φ4
DPDTAB
TTAB
18.552
5.166
25.723
9.728
7.291
0.058
8.714
0.589
0.955
21,22
For
DMTPAB
14.426
38.758
33.857
a
DMTPAB stands for dimethoxytetraphenyl aza-BODIPY cited from
18
reference. .
actually nonsymmetric. As is reported in tertraphenyl aza-
BODIPY, phenyls at the 3- and 5-positions were restricted from
free rotation owing to the steric hindrance induced by the C−
r
nr
decay rates (in relation with Φ and τ) of DPDTAB are lower
than that of TPAB, but the K decreases more significantly. In
f
19
nr
H...F interactions. In our cases, the values of C−H···F
distance for DPDTAB and TTAB were measured. The the
average value for DPDTAB was measured as 2.47 Å, and for
TTAB, it was 2.46 Å. These values are both less than the sum
of the van der Waals radii for hydrogen and fluorine (2.62 Å),
which implies that an interaction between these atoms is likely.
The interaction will help to keep the whole molecule planar.
Subsequently, photophysical properties were measured in
solvents with different polarity. The absorption and emission
spectra in acetonitrile are recorded in Figure 3, and the data are
other words, the weight of the radiative channel in the total
decay of DPDTAB gets bigger. Therefore, the increase in
quantum of DPDTAB is related mostly to the smaller
nonradiative decay rate. However, the TTAB, with longest
absorption/emission wavelength, shows much lower fluores-
cence quantum yield of 0.12. This is also a combined effect of
K and K . In this case, the K is much smaller, and the K is
much bigger than those of TPAB, respectively. Enhanced IC
(internal conversion) by lower energy gap is one pathway for
nonradiative transition.
r
nr
r
nr
In addition, the absorption spectra showed only a small
sensitivity to solvent polarity. For example, the λabs and λem of
DPDTAB in DMSO is only red-shifted by about 10 nm when
compared to that in CH Cl (Table 4). All of the other data
2
2
hardly show any different ether. The same phenomenon
happened to TTAB. This highly favorable emission wave-
lengths and insensitivity to solvent polarity are strongly
indicative of future applications in biotechnology.
Cyclic voltammetry was used to probe the electronic effects
of different aryl substituent on the aza-BODIPY chromophore,
with data listed Table 4. All three aza-BODIPYs display one
reversible oxidation wave and two reversible reduction waves
(
Supporting Information). HOMO and LUMO values have
been evaluated and are listed in Table 5. These values share the
same tendency with the computed ones. HOMO values
increase from −6.04 eV to about −5.83 eV, and LUMO values
keep constant at about −4.23 eV. Lower band gaps are
obtained for DPDTAB and TTAB due to the introduction of
electronic donating thiophene rings.
Figure 3. Normalized absorption (solid line) and emission (dashed
line) for TPAB (green), DPDTAB (blue), and TTAB (red) in
acetonitrile.
6
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The Journal of Organic Chemistry
Note
Table 3. Photophysical Properties of TPAB, DPDTAB and TTAB in acetonitrile
a
ε (M−1 cm−1
a
b
c
Kr (10 s−1)
d
8
Knr (10 s−1)
d
8
compd
TPAB
λabs (nm)
λabs‑cal (nm)
)
λem (nm)
λem‑cal (nm)
Φf
τ (ns)
643
710
733
614
646
710
76900
108600
103100
673
732
757
682
696
770
0.22
0.46
0.11
0.78
3.56
2.23
2.56
1.29
0.54
10.26
1.52
3.95
DPDTAB
TTAB
a
b
Stands for calculated absorption and emission separately. Reported 3,5-bisp-methoxyphenyl)-1,7-bisp-bromophenyl)za-BODIPY (Φ 0.42, in
f
20 c
tolunene) was used as standard. Fluorescence lifetime was determined by using Edinburgh OB 920 Fluorescence/Phosphorescence lifetime
spectrometer. Radiative (K ) and nonradiative (K ) decay rates.
d
r
nr
Table 5. Electrochemical Data of TDAB, DPDTAB, and
−1
TTAB in CH Cl (Scan Rate 100 mV s )
2
2
a
b
c
Eg eV) Ered,1/2 (V) vs ferrocene HOMO /LUMO (eV)
TDAB
1.81
1.68
1.61
−0.85
−0.84
−0.86
−6.04/-4.23
−5.92/-4.24
−5.83/-4.22
DPDTAB
TTAB
a
Optical bandgap, E = hc/λ , h is Planck's constant, c is the speed of
g
c
b
c
light, λ is edge absorption. HOMO = −(E − LUMO). Based on
the assumption that the energy of Fc/Fc is 5.08 eV relative to
vacuum.
c
g
+
with CH Cl (2 × 50 mL), and the combined organic fractions were
2
2
dried over anhydrous magnesium sulfate. The solvent was removed,
and the resulting yellow oil product was use in next without further
1
purification (4.25 g, 95%): H NMR (400 MHz, CDCl ) δ 7.66 (d, J =
3
Figure 4. Fluorescence lifetime hyperbolic curves of TPAB (black
line), DPDTAB (red line), and TTAB (blue line) in acetonitrile.
4
4
.4 Hz, 1H), 7.61 (d, J = 5.2 Hz, 1H), 7.32−7.22 (m, 5H), 7.08 (t, J =
.0, 4.0 Hz, 1H), 4.83−4.78 (m, 1H), 4.70−4.85 (m, 1H), 4.22−4.15
13
(
1
m, 1H), 3.42−3.29 (m, 1H); C NMR (100 MHz, CDCl ) δ 189.8,
3
In conclusion, by replacing the phenyl rings with thiophene
in the original 1,3,5,7-tetraphenyl aza-BODIPY, significant
bathochromic shifts were achieved, suggesting a feasible
strategy to develop NIR dyes. The data of X-ray crystalgraphy,
DFT calculations, and electrochemical investigations ascribed
the origin of bathochromic shift to the smaller torsion angles
and higher electron donating capability of thienyl against
phenyl units introduced to aza-BODIPY core. This work also
provided a very competitive NIR fluorophore, DPDTAB, which
emits strong NIR fluorescene with a quantum yield of 0.46 in
acetonitrile. Our current work is focused on enhancing
fluorescence quantum yield by restricting the rotation of
thiophene rings and improving the water solubility for
application in biotechnology.
43.6, 138.9, 134.4, 132.4, 129.1, 128.9, 128.4, 127.9, 127.5, 42.2,
+
34.58; m/z (TOF-MS-EI) calcd [M − NO ] for C H OS 229.0687,
found 229.0692.
2
14 13
Thienyl 4-Cyano-3-phenylbutan-1-one (5). A solution of 4
(
6.6 g, 29.5 mmol) in ethanol was stirred at 35 °C. Acetic acid (1.8
mL) was added and the mixture stirred for 15 min. To the above
solution was added KCN (3.7 g, 57 mmol) in water (10 mL). After all
of the raw material was consumed, the reaction mixture was portioned
between CH Cl (100 mL) and water (100 mL). The aqueous layer
2
2
was washed with CH Cl (2 × 50 mL), and the combined organic
2
2
fractions were dried over anhydrous magnesium sulfate. The solvent
was removed, and the resulting yellow oil product was purified by
column chromatography on silica gel eluting with CH Cl and mineral
2
2
ether (v/v = 1:1). White solid was collected (2.6 g, 36%): mp 86.3−
1
8
8.0 °C; H NMR (400 MHz, CDCl ) δ 7.73 (d, J = 4.0 Hz, 1H), 7.70
3
(d, J = 4.8 Hz, 1H), 7.26 (d, J = 5.2 Hz, 1H), 7.15 (t, J = 4.0, 4.8 Hz,
1
H), 6.97 (t, J = 5.2 Hz, 1H), 4.85 (t, J = 4.0 Hz, 1H), 3.70 (dd, J = 20,
EXPERIMENTAL SECTION
13
■
8 Hz, 1H), 3.57 (dd, J = 20, 8 Hz, 1H); C NMR (100 MHz, CDCl3)
δ 187.0, 142.6, 136.7, 134.9, 132.7, 128.4, 127.2, 126.8, 126.0, 119.5,
77.4, 77.1, 76.8, 44.8, 27.3; m/z (TOF-MS-ES) calcd M+ for
C H NOS 247.0126, found 247.0133.
7
20
Reference compounds TPAB and DMTPAB and the starting
materials thienyl-3-phenylprop-2-en-1-one (1) and thienyl-3-thienyl-
2
3
prop-2-en-1-one (4) were synthesized according to literature
12
9
2
procedures.
Azadipyrromethene (3). A solution of 2 (2 g, 7.33 mmol) and
Phenyl 4-Nitro-3-thienylbutan-1-one (2). A solution of
thienyl-3-phenylprop-2-en-1-one(2b) (3.5 g, 16.4 mmol), triethyl-
amine (7 mL, 48.4 mmol), and nitromethane (3.5 mL, 65.4 mmol) in
methanol (20 mL) was heated under reflux for 8 h. The reaction was
cooled to room temperature and acidified with HCl to pH 4. The
methanol was removed, and the resulting oil was portioned between
CH Cl (50 mL) and water (50 mL). The aqueous layer was washed
ammonium acetate (8.46 g, 109.89 mmol) in butanol was heated
under reflux for 24 h. After the solution was cooled to room
temperature, the solvent was concentrated to a quarter of its original
volume and filtered, and the isolated solid was washed with ethanol to
yield a dark blue-black solid. The crude product was used in the next
step without any further purification (0.20 g, 12%): mp 281.1−284.5
1
°C; H NMR (400 MHz, CDCl ) δ 8.03 (d, J = 7.2 Hz, 4H), 7.60 (s,
2
2
3
Table 4. Effects of the Solvent Polarity on Photophysical Properties of DPDTAB
ε (M− cm−1
1
)
φ
τ (ns)
K (10 s−1)
8
Knr (108 s−1
)
sovent
λabs (nm)
λem (nm)
r
CH Cl2
717
720
717
710
727
739
741
738
732
751
114500
120700
120500
108600
112900
0.47
0.44
0.46
0.46
0.42
3.71
3.70
3.22
3.56
3.36
1.27
1.19
1.43
1.29
1.25
1.43
1.51
1.68
1.52
1.73
2
tluene
THF
aetonitrile
DMSO
6
72
dx.doi.org/10.1021/jo201413b | J. Org. Chem. 2012, 77, 669−673

The Journal of Organic Chemistry
Note
2
H), 7.50 (d, J = 4.0 Hz, 2H), 7.40 (d, J = 7.2, 4H), 7.35 (d, J = 6.8
(4) Murtagh, J.; Frimannsson, D. O.; O’Shea, D. F. Org. Lett. 2009,
11, 5386−5389.
13
Hz, 2H), 7.20 (s, 2H), 7.06 (s, 2H); C NMR (100 MHz, CDCl ) δ
1
1
3
49.8, 144.9, 137.1, 134.4, 133.99, 133.1, 133.0, 132.9, 131.5, 129.9,
́
(5) Palma, A.; Tasior, M.; Frimannsson, D. O.; Vu, T. T.; Meallet-
+
29.7, 129.4, 128.1, 116.22; m/z (TOF-MS-ES) calcd [M + H] for
Renault, R.; O’Shea, D. F. Org. Lett. 2009, 11, 3638−3641.
C H N S 462.1099, found 462.1103.
(6) Bouit, P.-A.; Kamada, K.; Feneyrou, P.; Berginc, G.; Toupet, L.;
Maury, O.; Andraud, C. Adv. Mater. 2009, 21, 1151−1154.
(7) Gorman, A.; Killoran, J.; O’Shea, C.; Kenna, T.; Gallagher, W. M.;
O’Shea, D. F. J. Am. Chem. Soc. 2004, 126, 10619−10631.
28
19
3 2
Azadipyrromethene (6). A solution of 5 (2 g, 8.10 mmol) and
ammonium acetate (8.28 g, 107.55 mmol) in butanol was heated
under reflux for 24 h. After thesolution was cooled to room
temperature, the solvent was concentrated to a quarter of its original
volume and filtered, and the isolated solid was washed with ethanol to
yield a dark blue-black solid. The crude product was used in the next
step without any further purification (95.75 mg, 5%): mp >300 °C; m/
́
(8) Bellier, Q.; Pegaz, S.; Aronica, C.; Guennic, B. L.; Andraud, C.;
Maury, O. Org. Lett. 2011, 13, 22−25.
(9) Loudet, A.; Bandichhor, R.; Burgess, K.; Palma, A.; McDonnell, S.
O.; Hall, M. J.; O’Shea., D. F. Org. Lett. 2008, 10, 4771−4774.
(10) Zhao, W.; Carreira, E. M. Chem.Eur. J. 2006, 12, 7254−7263.
(11) Christensen, L. P. Rec. Res. Dev. Phytochem. 1998, 2, 227.
+
z (TOF-MS-ES) calcd [M + H] for C H N S 474.0227, found
24
16
3 4
1
13
4
74.0229. H NMR and C NMR spectra were not available due to
the extremely poor solubility of 6 in CDCl and DMSO-d , etc.
3
6
(12) Mishra, A.; Ma, C.-Q.; Bau
13) Rihn, S.; Retailleau, P.; Bugsaliewicz, N.; Nicola, A. D.; Ziessel,
R. Tetrahedron Lett. 2009, 50, 7008−7013.
14) Han, F.; Chi, L.; Liang, X.; Ji, S.; Liu, S.; Zhou, F.; Wu, Y.; Han,
K.; Zhao, J.; James, T. D. J. Org. Chem. 2009, 74, 1333−1336.
15) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 2nd ed.;
Kluwer Academic/Plenum Publishers: New York, 1999.
16) Valeur, B. Molecular Fluorescence: Principles and Applications;
̈
erle, P. Chem. Rev. 2009, 109, 1141.
DPDTAB. A dried flask was charged with 3 (200 mg,0.43 mmol)
and flushed with nitrogen. Dry dichloromethane (200 mL) and dry
diisopropylethylamine (0.77 mL, 4.3 mmol) were then added. The
solution was stirred at 25 °C for 15 min, and then BF ·OEt (0.83 mL,
(
(
3
2
6
.5 mmol) was added. After being stirred at 25 °C for 24 h, the
(
mixture was washed with water, and the organic layer was dried over
magnesium sulfate and concentrated in vacuo to give the target
compound. Purification by column chromatography on silica gel
eluting with CH Cl provided a dark brown solid (204.90 mg, 93%):
mp >300 °C; H NMR (400 MHz, CDCl ) δ 8.38 (d, J = 3.6 Hz, 1H),
(
Wiley-VCH Verlag: Weinheim, 2001.
(17) Parson, W. W. Modern Optical Spectroscopy: With Examples from
Biophysics and Biochemistry; Springer-Verlag: Berlin, Heidelberg, 2007.
2
2
1
3
8
7
1
1
.05 (d, J = 7.2 Hz, 2H), 7.64 (d, J = 4.8 Hz, 1H), 7.48−7.38 (m, 3H),
(
18) Killoran, J.; Allen, L.; Gallagher, J. F.; Gallagher, W. M.; O’Shea,
D. F. Chem. Commun. 2002, 1862−1863.
19) Chen, J.; Reibenspies, J.; Derecskei-Kovacs, A.; Burgess, K.
13
.27 (d, J = 4.0 Hz, 1H), 7.18 (s, 1H); C NMR (100 MHz, CDCl ) δ
3
49.8, 145.6, 142.8, 134.1, 133.2, 133.1, 133.0, 132.1, 131.7, 129.8,
(
+
29.4, 129.2, 128.5, 118.6; m/z (TOF-LD) calcd M for
Chem. Commun. 1999, 2501−2502.
(20) Loudet, A.; Bandichhor, R.; Wu, L.; Burgess, K. Tetrahedron
C H N F S B 509.1003, found 509.1001.
28
18
3
2
2
TTAB. A dried flask was charged with 6 (50 mg, 0.11 mmol) and
2
(
008, 3642−3654.
21) Rouxel, C.; Charlot, M.; Mir, Y.; Frochot, C.; Mongin, O.;
Blanchard-Desce, M. New J. Chem. 2011, 35, 1771−1780.
22) Ginocchietti, G.; Galiazzo, G.; Mazzucato, U.; Spalletti, A.
Photochem. Photobiol. Sci. 2005, 4, 547−553.
23) Shibata, K.; Katsuyama, I.; Matsui, M.; Muramatsu, H. J.
Heterocycl. Chem. 1991, 28, 161−165.
flushed with argon. Dry dichloromethane and dry diisopropylethyl-
amine (0.19 mL, 1.1 mmol) were then added. The solution was stirred
at 25 °C for 15 min, and then BF ·OEt (0.83 mL, 15 equiv) was
added. After being stirred at 25 °C for 24 h, the mixture was washed
with water, and the organic layer was dried over magnesium sulfate
and concentrated in vacuo to give the target compound. Purification
by column chromatography on silica gel eluting with CH Cl provided
3
2
(
(
2
2
1
a dark brown solid (53.87 mg, 98%): mp >300 °C; H NMR (400
MHz, CDCl ) δ 8.34 (d, J = 3.6 Hz, 1H), 7.92 (d, J = 3.6 Hz, 1H),
3
7
.62 (d, J = 4.8 Hz, 1H), 7.56 (d, J = 4.8 Hz, 1H), 7.20 (t, J = 4.0, 4.8
13
Hz, 1H), 7.07 (s, 1H); C NMR (100 MHz, CDCl ) δ 144.9, 134.4,
3
1
33.9, 133.0, 131.5, 129.9, 129.7, 129.4, 128.1, 116.2; m/z (TOF-MS-
+
EI) calcd M for C H N F S B 521.0132, found 521.0134.
2
4
14
3 2 4
ASSOCIATED CONTENT
Supporting Information
■
*
S
Experimental procedures, characterization data, X-ray struc-
tures, crystal data, and computational details. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: xiaoyi@dlut.edu.cn.
ACKNOWLEDGMENTS
■
We thank the NSF of China (Nos. 20876022) and the
Fundamental Research Funds for the Central University
(DUT10ZD114) for financial support.
REFERENCES
■
(
1) Kiyose, K.; Kojima, H.; Nagano, T. Chem. Asian J. 2008, 3, 506−
515.
(
(
2) Frangioni, J. V. Curr. Opin. Chem. Biol. 2003, 7, 626−634.
3) Allik, T. H.; Hermes, R. E.; Sathyamoorthi, G.; Boyer, J. H. Proc.
SPIE-Int. Soc. Opt. Eng. 1994, 2115, 240−248.
6
73
dx.doi.org/10.1021/jo201413b | J. Org. Chem. 2012, 77, 669−673