Synthesis and physical properties of various organic dyes derived from a single core skeleton, 1,2-dihydroindol-3-one

Article abstract of DOI:10.1016/j.tetlet.2008.10.098

Various organic dyes were synthesized from 1,2-dihydroindol-3-one analogue via Robinson ring annulation, which proceeded efficiently using DBU as a base to give the π-expanded compounds. These compounds exhibited longer Stokes shifts (over 100 nm) than the 1,2-dihydroindol-3-ones (50-80 nm). Emission peaks of the obtained materials covered the 440-640 nm range.

Full text of DOI:10.1016/j.tetlet.2008.10.098

Tetrahedron Letters 50 (2009) 111–114
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and physical properties of various organic dyes derived
from a single core skeleton, 1,2-dihydroindol-3-one
*
Shoji Matsumoto , Daisuke Samata, Motohiro Akazome, Katsuyuki Ogura
Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoicho, Inageku, Chiba 263-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Various organic dyes were synthesized from 1,2-dihydroindol-3-one analogue via Robinson ring annula-
Received 20 September 2008
Revised 17 October 2008
Accepted 21 October 2008
Available online 1 November 2008
tion, which proceeded efficiently using DBU as a base to give the
p-expanded compounds. These com-
pounds exhibited longer Stokes shifts (over 100 nm) than the 1,2-dihydroindol-3-ones (50–80 nm).
Emission peaks of the obtained materials covered the 440–640 nm range.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
1,2-Dihydroindol-3-one
Robinson ring annulation
Fluorophores
Stokes shift
The importance of organic light-emitting materials has
increased greatly in recent years. They can be used in electro-
luminescent1 and electrogenerated chemiluminescent2 materials,
chemosensors,3 environmental sensors (temperature,4 pH,5
solvent,6 and viscosity7), metal ion sensors,8 etc.9 Recently, these
types of materials have received much attention for potential bio-
logical applications in fluorescence imaging and bio-labeling.10–16
We are interested in compact structures with luminescence prop-
erties that can be introduced into various compounds causing little
structural change.16 Efficient fluorophores require the following
characteristics: (1) a good donor–acceptor relationship and (2) a ri-
gid structure to prevent nonradiative decay. In this context, cou-
marin derivatives bearing a donor–acceptor system are thought
to have an enhanced fluorescence quantum yield by introducing
a donating amino moiety into the cyclic system.17 Consequently,
we focused on a 1,2-dihydroindol-3-one structure (1). It consists
of the donor (amino group) and acceptor (carbonyl group) parts
various ranges of emission peaks by a simple reaction of the origi-
nal 1,2-dihydroindol-3-one structure.
Robinson
ring
annulation
donor
H
N
donor
H
N
2
ð1Þ
O
acceptor
O
π-expansion
acceptor
1
2
Synthesis of the basic compound, N-acetyl-1,2-dihydroindol-3-
one (3), was based on a procedure reported in a related patent20
(Scheme 1). The reaction of 3 with NaOH was examined to remove
the acetyl group, but the desired compound (4) was not obtained.
However, the enol form (40) was observed in the 1H NMR spectrum
(solvent: CDCl3). Therefore, we protected the 2-position using a
methyl group. The dimethylated derivative (5a) was obtained by
the reaction of 3 with methyl iodide, with subsequent removal of
the acetyl group. The monomethylated compound (6) was also
formed by the reaction with methyl iodide by judicious choice of
a base (KOBut) and its equivalent (1.05 equiv) in comparable yield.
After the investigation of various bases for the Robinson ring annu-
lation, we found that DBU was the best base for the reaction of 6
with methyl vinyl ketone to give 7a. The one-pot synthesis of 7a
could be achieved by the reaction of 6 with DBU, followed by reac-
tion with aq NaOH under reflux in EtOH.21
connected by a
that will enhance the fluorescence quantum yield. Structure (1)
possesses an -proton activated by a carbonyl group, which can
facilitate the expansion of the -system via a Robinson ring annu-
p-system (benzene ring); it also has a ring structure
a
p
lation at the 2-position of 1 (Eq. 1). The synthesis of 1,2-dihydroin-
dol-3-one derivatives has been examined for use as intermediates
in the synthesis of alkaloids, pharmaceutical agents, and insecti-
cides.18 Surprisingly, however, few reports describe the optical
properties of derivatives of 1.18d,19 Herein, we report the synthesis
and optical properties of 1,2-dihydroindol-3-one derivatives with
To investigate comprehensive changes by an expansion of the
p-system, methyl and phenyl substituents on nitrogen atoms as
well as a dicyanomethylene group at the carbonyl moiety were
introduced into 5a and 7a (Scheme 2).
* Corresponding author. Tel.: +81 43 290 3369; fax: +81 43 290 3401.
E-mail address: smatsumo@faculty.chiba-u.jp (S. Matsumoto).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.10.098

112
S. Matsumoto et al. / Tetrahedron Letters 50 (2009) 111–114
Ac
Me
H
N
aq Na SO
reflux, 2 h
Me
N
MeI
NaH
2
3
N
N
COOH
NaOAc
Me
O
5a
or
Me
Me
or
Ac O
2
reflux, 5 h
COOH
DMF
rt
OAc
7a
O
7b
80%
5b
94%
H
N
H
Ac
N
N
aq NaOH
PhBr
Pd(OAc)
2
Ph
t
Ph
PBu
3
N
Me
O
5a
or
t
N
O
OH
4
4'
3
Me
Me
NaOBu
O
or
or
57% (two steps)
o
-xylene
o
t
7a
KOBu (1 equiv.)
MeI (1 equiv.)
THF
NaH (3.2 equiv.)
MeI (excess.)
toluene
120 C
O
5c
96%
7c
48%
o
-40 C to rt, 12 h
Me
H
reflux, 23 h
N
N
Ac
N
5a
or
Me
Me
Me
Me
CH (CN)
2
2
Ac
N
Me
Me
Me
pyridine
reflux
5b
CN
CN
O
NC
NC
6
O
8b
8a
3'
79%
59%
29%
50%
1)
DBU
O
H
N
Me
N
2 M NaOH
EtOH
reflux, 1 h
Me
Me
CH (CN)
2
2
7a
or
K CO
2
3
EtOH
rt, 18 h
or
CN
EtOH
reflux
H
7b
N
R
CN
Me
Me
N
NC
NC
Me
9a
9b
85%
92%
O
5a
O
Scheme 2. Derivatization of 5a and 7a.
87%
R= H or Ac
O
2) 3 M NaOH
reflux, 3 h
c
a
5a
5b
5c
8a
8b
5a
H
N
Me
5b
5c
8a
8b
7a
87%
O
Scheme 1. Synthesis of 5a and 7a.
200
400
600
400
600
800
The UV–vis absorption and fluorescence spectra of the obtained
wavelength / nm
wavelength / nm
compounds were measured in CH3CN (Fig. 1). The optical data are
presented in Table 1. The compounds bearing methyl (5b and 7b)
and phenyl (5c and 7c) substituents on the nitrogen atom showed
longer absorption and emission peaks than 5a and 7a, indicating
that these groups enhanced the electron-donating ability of the
amino group. To obtain longer absorption and emission peaks, it
was efficient to change the carbonyl group to the stronger elec-
tron-withdrawing dicyanomethylene moiety. Large bathochromic
shifts were obtained in the absorption and emission spectra of 5a
versus 8a and 5b versus 8b. Enhancement of the molecular absorp-
5a
5a
5b
5c
8a
8b
5b
5c
8a
8b
b
d
tion coefficients (emax) was also observed.
200
400
600
Regarding UV–vis absorption spectra, a bathochromic shift be-
tween 5a and 7a was observed. This result is consistent with those
of various substituted compounds (5b vs 7b, 5c vs 7c, 8a vs 9a, and
8b vs 9b) accompanied by ca. 14–30 nm change. The red shift of
30 nm in the absorption peaks by the introduction of another C–
400
600
800
wavelength / nm
wavelength / nm
Figure 1. UV–vis absorption spectra of (a)
5 and 8, (b) 7 and 9 in CH3CN
(3.0 ꢀ 10ꢁ5 M), and FL spectra of (c) 5 and 8, (d) 7 and 9 in CH3CN (3.0 ꢀ 10ꢁ7 M)
excited at kmax. Black line, 5a and 7a; red line, 5b and 7b; blue line, 5c and 7c; green
line, 8a and 9a; purple line, 8b and 9b.
C double bond is well known in the estimation of a,b-unsaturated
ketones.22 Khodorkovsky and co-workers reported the introduc-
tion of two vinyl tethers in their donor–acceptor system in which
a bathochromic shift of ca. 80 nm (40 nm/one vinyl component)
was observed.23 Therefore, our system is slightly defective in the
tween 5 and 7 or 8 and 9. It is noteworthy to maintain the full
width at half maximum (fwhm) in a range of 55–80 nm even in
the bathochromic shift of the emission peaks.16c,24 Quantum yields
p-expansion in relation to absorption, possibly a result from the
torsion of the fused -conjugated ring system.
Specific changes of the emission characters were observed. The
emission peak shifted to longer wavelength (about 49–70 nm) be-
p
(
UF) of the carbonyl derivatives were maintained or decreased by
the change in the -system (5 vs 7). Interestingly, the quantum
yield increased in compounds having a dicyanomethylene moiety
p

S. Matsumoto et al. / Tetrahedron Letters 50 (2009) 111–114
113
Table 1
Physical properties of 5, 7, 8, and 9 from UV–vis absorption and FL spectra
ΦF
λ
em (nm)
5a
5b
8a
8b
7a
7b
9a
481
500
559
581
566
601
629
0.70
0.43
0.10
0.17
0.11
0.05
0.05
Compound kmax (nm) [emax
kem (nm)b [fwhm
(nm)]
UF
Stokes shiftc
(nm)
(Mꢁ1 cmꢁ1)]a
5a
7a
5b
7b
5c
7c
8a
9a
8b
9b
382.5 [4,000]
405 [8,900]
442 [54]
507 [70]
461 [55]
531 [65]
476 [80]
525 [77]
540 [61]
606 [72]
571 [66]
639 [68]
0.31d 59.5
0.06d 102
0.24d 54.5
0.18d 95
0.10d 77
0.12d 98.5
0.05e 64
0.16e 116
0.09e 53
0.15e 104
406.5 [3,500]
436 [8,200]
399 [4,900]
426.5 [10,000]
476 [12,500]
490 [20,500]
518 [13,300]
535 [20,700]
400
600
800
a
b
c
Measured in CH3CN (3.0 ꢀ 10ꢁ5 M).
wavelength / nm
Measured in CH3CN (3.0 ꢀ 10ꢁ7 M). Excited at kmax
.
Figure 3. FL spectra of 5a, 5b, 8a, 8b, 7a, 7b, and 9a in H2O/CH3CN (49:1) excited at
kmax. Quantum yields (UF) were determined with fluorescein (UF = 0.90) as a
Stokes shift = kem ꢁ kmax
.
d
Determined with quinine sulfate (UF = 0.55) as a standard (3.0 ꢀ 10ꢁ7 M in
standard (3.0 ꢀ 10ꢁ7 M in 0.1 M aq NaOH).
0.l M aq H2S04).
e
Determined with fluorescein (UF = 0.90) as a standard (3.0 ꢀ 10ꢁ7 M in 0.1 M aq
NaOH).
640 nm, which largely covers the visible region (Fig. 2). Our results
show that compounds based on 1,2-dihydroindol-3-one unit are
useful for various fluorophores. Some of them were dissolved in
H2O/CH3CN and emitted under such conditions. And it will be pos-
sible that, for the biological application, a water solubilizing moi-
ety and/or a bioconjugatable reactive group is introduced onto
the indolic nitrogen in these compounds using ‘post-synthetic
as the electron-withdrawing group (8 vs 9). Although we have no
clear explanation for this phenomenon, one of the possibilities
can be mentioned. From investigation of the solvent effects in com-
parison to cyclohexane, THF, and acetonitrile, the bathochromic
shifts were observed in the UV–vis absorption and fluorescence
spectra (See Supplementary data; Fig. S1 and Table S1). Com-
pounds having dicyanomethylene moiety (8b and 9b) showed a
considerable red shift in both absorption and emission peaks,
which suggests that the excited state has a polar structure or a
charge-transfer character. The polar excited state is stabilized,
and emission occurs efficiently when the donor and acceptor parts
are separated. This trend might be enhanced in a stronger donor–
acceptor relationship, and is a good reason to increase the quan-
tum yield of 8 versus 9.
We found that enhancement of the Stokes shift was observed in
the p-expanded compounds. Stokes shifts around 50–80 nm were
observed in the spectra of 5 and 8. On the other hand, larger Stokes
shifts over 100 nm were obtained in 7 and 9. Consequently, these
materials can cover the 440–640 nm range in emission bands
(Fig. 2).
derivatization’ strategy.25 Investigation of further
p-expansion
using Robinson ring annulation is underway to ensure the longer
emission peaks.
Supplementary data
Supplementary data (experimental procedures, spectroscopic
data for all new compounds, UV–vis absorption and FL spectra in
cyclohexane, THF, CH3CN, and H2O/CH3CN (49:1), and photographs
of all compounds discussed in this manuscript under 365 nm irra-
diation) associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.tetlet.2008.10.098.
References and notes
Finally, we preliminary investigated the fluorescent character in
water for biological applications. Compounds discussed in this Let-
ter were dissolved in H2O/CH3CN (49:1) except for 9b. Fluores-
cence spectra are presented in Figure 3 (also see Supplementary
data; Fig. S3 and Table S2). They covered the 480–630 nm range
in emission bands. The relations between the structures and the
emission characters observed in CH3CN (vide supra) were varied,
1. (a)Organic Electroluminescent Materials and Device; Miyata, S., Nalwa, H. S., Eds.;
Gordon & Breach: Amsterdam, 1997; (b) D’Andrade, B. W.; Forrest, S. R. Adv.
Mater. 2004, 16, 1585–1595; (c) Gao, M.; Richter, B.; Kirstein, S.; Möhwald, H. J.
Phys. Chem. B 1998, 102, 4096–4103; (d) Chan, L.-H.; Lee, R.-H.; Hsieh, C.-F.;
Yeh, H.-C.; Chen, C.-T. J. Am. Chem. Soc. 2002, 124, 6469–6479; (e) Xue, C.; Luo,
F.-T. Tetrahedron 2003, 59, 5193–5198; (f) Tang, S.; Liu, M.; Gu, C.; Zhao, Y.; Lu,
P.; Lu, D.; Liu, L.; Shen, F.; Yang, B.; Ma, Y. J. Org. Chem. 2008, 73, 4212–4218.
2. (a) Schaper, H.; Köstlin, H.; Schnedler, E. J. Electrochem. Soc. 1982, 129, 1289–
1294; (b) Chang, S.-C.; Yang, Y.; Pei, Q. Appl. Phys. Lett. 1999, 74, 2081–2083; (c)
Chang, S.-C.; Li, Y.; Yang, Y. J. Phys. Chem. B 2000, 104, 11650–11655; (d)
Elangovan, A.; Yang, S.-W.; Lin, J.-H.; Kao, K.-M.; Ho, T.-I. Org. Biomol. Chem.
2004, 2, 1597–1602; (e) Jiang, X.; Yang, X.; Zhao, C.; Jin, K.; Sun, L. J. Phys. Chem.
C 2007, 111, 9595–9602; (f) Sartin, M. M.; Shu, C.; Bard, A. J. J. Am. Chem. Soc.
2008, 130, 5354–5360.
3. (a) Martínez-Máñez, R.; Sancenón, F. Chem. Rev. 2003, 103, 4419–4476; (b)
Umezawa, N.; Tanaka, K.; Urano, Y.; Kikuchi, K.; Higuchi, T.; Nagano, T. Angew.
Chem., Int. Ed. 1999, 38, 2899–2901; (c) Tanaka, K.; Miura, T.; Umezawa, N.;
Urano, Y.; Kikuchi, K.; Higuchi, T.; Nagano, T. J. Am. Chem. Soc. 2001, 123, 2530–
2536; (d) Wang, Z.; Zhang, D.; Zhu, D. Tetrahedron Lett. 2005, 46, 4609–4612.
4. Shiraishi, Y.; Miyamoto, R.; Zhang, X.; Hirai, T. Org. Lett. 2007, 9, 3921–3924.
5. Koo, C.-K.; Lam, B.; Leung, S.; Lam, M. H.-W.; Wong, W.-Y. J. Am. Chem. Soc.
2006, 128, 16434–16435.
that would be caused by
conditions.
a protic character in H2O/CH3CN
In summary, we reported the synthesis and photophysical prop-
erties of 1,2-dihydroindol-3-one derivatives obtained by the sim-
ple reactions. The
p-system is easily expanded using a Robinson
ring annulation. Their emission peaks ranged from 440 nm to
6. Uchiyama, S.; Takehira, K.; Yoshihara, T.; Tobita, S.; Ohwada, T. Org. Lett. 2006,
8, 5869–5872.
7. (a) Haidekker, M. A.; Brady, T. P.; Lichlyter, D.; Theodorakis, E. A. J. Am. Chem.
Soc. 2006, 128, 398–399; (b) Kuimova, M. K.; Yahioglu, G.; Levitt, J. A.; Suhling,
K. J. Am. Chem. Soc. 2008, 130, 6672–6673.
8. (a) Mello, J. V.; Finney, N. S. J. Am. Chem. Soc. 2005, 127, 10124–10125; (b) Bok, J.
H.; Kim, H. J.; Lee, J. W.; Kim, S. K.; Choi, J. K.; Vicens, J.; Kim, J. S. Tetrahedron
Lett. 2006, 47, 1237–1240; (c) Mei, Y.; Bentley, P. A.; Wang, W. Tetrahedron Lett.
2006, 47, 2447–2449; (d) Kim, S. H.; Choi, J. K.; Kim, S. K.; Sim, W.; Kim, J. S.
Tetrahedron Lett. 2006, 47, 3737–3741; (e) Wu, J.-S.; Liu, W.-M.; Zhuang, X.-Q.;
5a
5b
7a
7b
9a
9b
Figure 2. Photographs of 5a, 5b, 7a, 7b, 9a, and 9b in CH3CN under 365 nm
irradiation.

114
S. Matsumoto et al. / Tetrahedron Letters 50 (2009) 111–114
Wang, F., ; Wang, P.-F.; Tao, S.-L.; Zhang, X.-H.; Wu, S.-K.; Lee, S.-T. Org. Lett.
19. Witkop, B. J. Am. Chem. Soc. 1950, 72, 614–620.
2007, 9, 33–36; (f) Ray, D.; Bharadwaj, P. K. Inorg. Chem. 2008, 47, 2252–
2254.
20. Taki, T.; Kisida, H.; Saito, S.; Isayama, S. Eur. Patent 567138, 1993; . Chem. Abstr.
1994, 120, 163733.
9. (a) Chung, Y. M.; Raman, B.; Kim, D.-S.; Ahn, K. H. Chem. Commun. 2006, 186–
188; (b) Lee, H. N.; Singh, N. J.; Kim, S. K.; Kwon, J. Y.; Kim, Y. Y.; Kim, K. S.;
Yoon, J. Tetrahedron Lett. 2007, 48, 169–172.
10. (a) Waggoner, A. Curr. Opin. Chem. Biol. 2006, 10, 62–66; (b) Lavis, L. D.; Raines,
R. T. ACS Chem. Biol. 2008, 3, 142–155.
11. Leevy, W. M.; Gammon, S. T.; Jiang, H.; Johnson, J. R.; Maxwell, D. J.; Jackson, E.
N.; Marquez, M.; Piwnica-Worms, D.; Smith, B. D. J. Am. Chem. Soc. 2006, 128,
16476–16477.
12. Peneva, K.; Mihov, G.; Herrmann, A.; Zarrabi, N.; Börsch, M.; Duncan, T. M.;
Müllen, K. J. Am. Chem. Soc. 2008, 130, 5398–5399.
13. Lee, Y.-J.; Datta, S.; Pellois, J.-P. J. Am. Chem. Soc. 2008, 130, 2398–2399.
14. Pires, M. M.; Chmielewski, J. Org. Lett. 2008, 10, 837–840.
15. (a) Kojima, H.; Nakatsubo, N.; Kikuchi, K.; Kawahara, S.; Kirino, Y.; Nagoshi, H.;
Hirata, Y.; Nagano, T. Anal. Chem. 1998, 70, 2446–2453; (b) Takakusa, H.;
Kikuchi, K.; Urano, Y.; Sakamoto, S.; Yamaguchi, K.; Nagano, T. J. Am. Chem. Soc.
2002, 124, 1653–1657; (c) Setsukinai, K.; Urano, Y.; Kakinuma, K.; Majima, H.
J.; Nagano, T. J. Biol. Chem. 2003, 278, 3170–3175; (d) Mineno, T.; Ueno, T.;
Urano, Y.; Kojima, H.; Nagano, T. Org. Lett. 2006, 8, 5963–5966.
16. (a) Clavé, G.; Bernardin, A.; Massonneau, M.; Renard, P.-Y.; Romieu, A.
Tetrahedron Lett. 2006, 47, 6229–6233; (b) Meyer, Y.; Richard, J.-A.;
Massonneau, M.; Renard, P.-Y.; Romieu, A. Org. Lett. 2008, 10, 1517–1520; (c)
Kim, E.; Koh, M.; Ryu, J.; Park, S. B. J. Am. Chem. Soc. 2008, 190, 12206–12207.
17. Jones, G., II.; Jackson, W. R.; Choi, C.; Bergmark, W. R. J. Phys. Chem. 1985, 89,
294–300.
18. (a) Sundberg, R. J.; Yamazaki, T. J. Org. Chem. 1967, 32, 290–294; (b) Yamaguchi,
K. Bull. Chem. Soc. Jpn. 1976, 49, 1366–1368; (c) Ardakani, M. A.; Smalley, R. K.
Tetrahedron Lett. 1979, 4769–4772; (d) Azadi-Ardakani, M. A.; Alkhader, M. A.;
Lippiatt, J. H.; Patel, D. I.; Smalley, R. K.; Higson, S. J. Chem. Soc., Perkin Trans. 1
1986, 1107–1111; (e) Liu, Y.; McWhorter, W. W., Jr. J. Org. Chem. 2003, 68,
2618–2622.
21. Preparation of 7a: To a solution of 6 (0.910 g, 4.81 mmol) in EtOH (25 mL) were
added methyl vinyl ketone (0.41 mL, 5.1 mmol) and DBU (71.9 lL,
0.481 mmol) at room temperature. The mixture was refluxed for 18 h. To the
reaction mixture was added a solution of NaOH (0.595 g, 14.9 mmol) in H2O
(5 mL). After being stirred for additional 3 h in refluxing conditions, the
mixture was neutralized with 1 M aq HCl (a few drops). To a solution was
added brine (50 mL), and the solution was extracted with EtOAc (30 mL ꢀ 3).
The combined organic layer was dried with MgSO4. After the filtration and
evaporation, the residue was subjected to column chromatography on SiO2
(hexane/EtOAc = 1:1) to give 7a (0.838 g, 4.21 mmol) in 87% yield as yellow
solid. The solid was further purified by reprecipitation from hexane and EtOAc
to give orange plate crystals: mp 153.0–154.0 °C; 1H NMR (CDCl3, 300 MHz) d
1.47 (s, 3H), 2.15 (dt, 1H, J = 6.4 and 12.5 Hz), 2.26 (ddd, 1H, J = 2.2, 5.4 and
12.6 Hz), 2.46 (ddd, 1H, J = 5.4, 12.5 and 18.3 Hz), 2.57 (ddd, 1H, J = 1.5, 6.0 and
18.2 Hz), 4.57 (br s, 1H), 6.14 (s, 1H), 6.80 (d, 1H, J = 8.0 Hz), 6.83 (t, 1H,
J = 7.5 Hz), 7.30 (dt, 1H, J = 1.2 and 8.3 Hz), 7.46 (d, 1H, J = 7.7 Hz); 13C NMR
(75 MHz, CDCl3) d 25.8, 34.1, 35.2, 63.2, 111.7, 113.8, 119.6, 122.4, 123.8, 133.8,
153.9, 168.2, 197.4; IR (KBr) 3269, 3032, 2968, 1612, 1577, 1469, 1311, 1215,
955, 850, 766, 650 cmꢁ1. Anal. Calcd for C13H13NO: C, 78.36; H, 6.58; N, 7.03.
Found: C, 78.00; H, 6.46; N, 7.04.
22. Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectrometric Identification of
Organic Compounds, 5th ed.; John Wiley & Sons: New York, 1991.
23. Moore, A. J.; Chesney, A.; Bryce, M. R.; Batsanov, A. S.; Kelly, J. F.; Howard, J. A.
K.; Perepichka, I. F.; Perepichka, D. F.; Meshulam, G.; Berkovic, G.; Kotler, Z.;
Mazor, R.; Khodorkovsky, V. Eur. J. Org. Chem. 2001, 1, 2671–2687.
24. Pohl, R.; Montes, V. A.; Shinar, J.; Anzenbacher, P., Jr. J. Org. Chem. 2004, 69,
1723–1725.
25. (a) Mazières, M. R.; Duprat, C.; Bellan, J.; Wolf, J. G. Dyes and Pigments 2007, 74,
404–409; (b) Romieu, A.; Brossard, D.; Hamon, M.; Outaabout, H.; Portal, C.;
Renard, P.-Y. Bioconjugate Chem. 2008, 19, 279–289.