Synthesis and emitting properties of the blue-light fluorophores indolizino[3,4,5-ab]isoindole derivatives

Article abstract of DOI:10.1002/ejoc.200700250

Indolizino[3,4,5-ab]isoindoles 3a-3k have been synthesized by [8+2] cycloaddition reactions of the corresponding indolizines 2a-2k with benzyne in moderate yields. Cycloadditions of pyrrolo[2,1-a]isoquinolines 4a-4c with benzyne gave the benzo[6,7]pyrrolizino[3,4,5-ab]isoquinolines 5a-5c. Compounds 7 and 9 were similarly prepared by the reactions of 6H-[1]benzopyrano[3,4-a] indolizine-6-one (6) and 6H-[1]benzopyrano[3′,4′:3,4]pyrrolo[2,1-a] isoquinolin-6-one (8) with benzyne in 93 and 62 % yields, respectively. The electronic structures of these compounds have been calculated by the DFT method at the B3LYP/6-31G level. Compounds 3a-3j fluoresce in the blue region (λ_max^F = 439-475 nm) with high quantum yields (Φ_F = 0.49-0.77 in ethanol). Compounds 5a-5c and 9 are fluorescent in the green region with quantum yields of 0.44-0.77 in ethanol and compound 7 emits blue light with a quantum yield of 0.59. The electrochemical properties of these compounds have been investigated by cyclic voltammetry. Indolizino[3,4,5-ab]isoindoles without a substituent at C-2 (compounds 3a, 3c, 3d) or with an alkyl substituent in the framework (31, 3k) undergo irreversible anodic oxidations and reversible cathodic reductions. Compounds 3e and 3g with an electron-withdrawing group at C-2, on the other hand, undergo quasi-reversible oxidations at 1.2-1.3 V (SCE) and reversible reductions at -1.5 to -1.9 V (SCE). Therefore, compounds 3e and 3g may be promising candidates to serve as blue-light emitters with both hole- and electron-transporting ability in monolayer OLED devices, while the other indolizino[3,4,5-ab]isoindoles (3a-3d, 3f, 3h-3i) are potential blue-light emitters with electron-transporting ability. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700250

FULL PAPER
DOI: 10.1002/ejoc.200700250
Synthesis and Emitting Properties of the Blue-Light Fluorophores
Indolizino[3,4,5-ab]isoindole Derivatives
Yong-Miao Shen,[a] Guenter Grampp,[b] Nararak Leesakul,[b] Hong-Wen Hu,[a] and
Jian-Hua Xu*[a]
Keywords: Indolizino[3,4,5-ab]isoindole / Fluorescence / Electrochemistry / Molecular orbitals
Indolizino[3,4,5-ab]isoindoles 3a–3k have been synthesized
by [8+2] cycloaddition reactions of the corresponding indoliz-
ines 2a–2k with benzyne in moderate yields. Cycloadditions
of pyrrolo[2,1-a]isoquinolines 4a–4c with benzyne gave the
benzo[6,7]pyrrolizino[3,4,5-ab]isoquinolines 5a–5c. Com-
pounds 7 and 9 were similarly prepared by the reactions of
6H-[1]benzopyrano[3,4-a]indolizine-6-one (6) and 6H-
[1]benzopyrano[3Ј,4Ј:3,4]pyrrolo[2,1-a]isoquinolin-6-one (8)
properties of these compounds have been investigated by cy-
clic voltammetry. Indolizino[3,4,5-ab]isoindoles without a
substituent at C-2 (compounds 3a, 3c, 3d) or with an alkyl
substituent in the framework (3i, 3k) undergo irreversible an-
odic oxidations and reversible cathodic reductions. Com-
pounds 3e and 3g with an electron-withdrawing group at C-
2, on the other hand, undergo quasi-reversible oxidations at
1.2–1.3 V (SCE) and reversible reductions at –1.5 to –1.9 V
with benzyne in 93 and 62% yields, respectively. The elec- (SCE). Therefore, compounds 3e and 3g may be promising
tronic structures of these compounds have been calculated
by the DFT method at the B3LYP/6-31G level. Compounds
3a–3j fluoresce in the blue region (λFmax = 439–475 nm) with
high quantum yields (ΦF = 0.49–0.77 in ethanol). Compounds
5a–5c and 9 are fluorescent in the green region with quan-
tum yields of 0.44–0.77 in ethanol and compound 7 emits
blue light with a quantum yield of 0.59. The electrochemical
candidates to serve as blue-light emitters with both hole- and
electron-transporting ability in monolayer OLED devices,
while the other indolizino[3,4,5-ab]isoindoles (3a–3d, 3f, 3h–
3i) are potential blue-light emitters with electron-trans-
porting ability.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
tionship and other photophysical properties that have a
bearing on their photoelectric functions is desirable. For
this purpose, general and efficient synthetic methods lead-
ing to diverse structural modifications such as the introduc-
tion of functional groups at different ring positions and fur-
ther annulation of the indolizino[3,4,5-ab]isoindole frame-
work are needed.
Indolizino[3,4,5-ab]isoindoles are presently mainly pre-
pared by the [2+12] cycloadditions of pyrido[2,1-a]isoind-
oles with electron-deficient alkynes and alkenes.[7–9,11]
Therefore, they were prepared by the cycloaddition of 6-
cyanopyrido[2,1-a]isoindoles with electron-deficient alkynes
followed by the elimination of a hydrogen cyanide mole-
cule[8a,11] or by the cycloaddition of pyrido[2,1-a]isoindoles
with electron-deficient alkenes in the presence of dehydro-
genation reagents such as chloranil, oxygen and sulfur.[7,9]
These reactions have been mainly applied to the synthesis
of 1- and 2-mono- or 1,2-disubstituted indolizino[3,4,5-ab]-
isoindole derivatives and the starting pyrido[2,1-a]isoind-
oles need to be prepared by photoinduced cyclization of
1-benzyl-2-bromopyridinium bromide followed by depro-
tonation of the formed pyrido[2,1-a]isoindolinium bromide
with sodium carbonate as base.[10] Matsumoto and Uchida
have reported that indolizino[3,4,5-ab]isoindoles and their
Introduction
Belonging to the general family of cyclazines and as N-
bridged annulenes with 10 peripheral π electrons, pyr-
rolo[2,1,5-cd]indolizines, or [2,2,3]cyclazines following the
naming system of Boekelheide[1] and Leaver[2] and their co-
workers, have been drawing continuous research interest
owing to their special electronic structures,[3] high fluores-
cence efficiency,[4] wide range of biological activity[5] and
the fact that their partially hydrogenated frameworks have
been found in several natural products.[6] In particular, their
1,2-benzannulated derivatives indolizino[3,4,5-ab]isoindoles
have recently been found to be excellent fluorophores with
high emission quantum yields and tunable colours in the
blue and green region and may have promising applications
as electroluminescence materials, sensors, etc.[7] Therefore,
further investigation of their luminescence–structure rela-
[a] Department of Chemistry, Nanjing University,
Nanjing 210093, China
Fax: +86-25-83371161
E-mail: xujh@nju.edu.cn
[b] Institute of Physical and Theoretical Chemistry, Graz Univer-
sity of Technology,
Technikerstrasse 4/I, 8010 Graz, Austria
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Blue-Light Fluorophores Indolizinoisoindole Derivatives
FULL PAPER
1,2-benzo- and 1,2:3,4-dibenzo-annulated derivatives can be ceeded smoothly at reflux temperature to afford the desired
prepared by consecutive cycloadditions of pyridinium or indolizino[3,4,5-ab]isoindoles 3a–3k, respectively, in 23–
isoquinolinium dicyanomethylide with two benzynes.[8a,11] 75% yields (Table 1).
The benzyne precursor used in these reactions was 2-(phen-
These products were fully characterized by spectral (1H
1
yliodonio)benzoate and the yields of the benzo- and di- NMR, IR and MS) and analytical data. In their H NMR
benzo-annulated indolizino[3,4,5-ab]isoindole products are spectra, all the ring protons absorb in the region of δ = 7.3–
in the range of 18–39%.[11] To the best of our knowledge, 8.6 ppm, indicating the aromatic nature of the indoliz-
there has so far been no systematic investigation into the ino[3,4,5-ab]isoindole framework. In their mass spectra, in
synthesis of indolizino[3,4,5-ab]isoindole derivatives by almost all cases except for 3j and 3k, there is a very strong
[8+2] cycloaddition reactions of benzyne with indolizines molecular ion peak which often (for 3a–3d, 3h, 3i) occurs
except for a single report in which the 1,2-benzannulated as the base peak. The yields of the products were found
indolizino[3,4,5-ab]isoindole
(benzo[1Ј,2Ј:1,2]indolizino- to be dependent on the stability of the starting indolizines.
[3,4,5-ab]isoindole) was prepared by the [12+2] cycload- Therefore, the low yield in the reaction of 2-phenylindoliz-
dition of benzyne with pyrido[2,1-a]isoindole in 6.6% yield ine (2a) is largely caused by the low stability of this com-
with bromobenzene as the benzyne precursor.[7] We envi- pound in solution upon heating. It is seen in Table 1 that
sioned that the cycloadditions of the easily accessible substi- the 3-cyanoindolizine 2j gave a much higher yield of the
tuted indolizines with benzyne generated from the 2-tri- cycloaddition product 3j than all the other indolizines (2a–
methylsilyl trifluoromethanesulfonate precursor 1,[12] would 2i, 2k) without a cyano in the 3-position. This shows that
provide a general and versatile synthesis of indolizino[3,4,5- subsequent elimination of hydrogen cyanide from the pri-
ab]isoindole derivatives with different substitution patterns mary cycloadduct A might be much more facile than the
under mild conditions. Hence, we have synthesized a series dehydrogenation of the primary cycloadduct B or its hydro-
of indolizino[3,4,5-ab]isoindole derivatives by this method gen-migrated isomer C formed in the reactions of 3-unsub-
and further investigated their fluorescence and electrochem- stituted indolizines.[14]
ical properties, as well as their electronic structure by molec-
ular orbital calculations, because of their potential applica-
tions as blue and green light-emitting fluorophores and
electroluminescent materials for OLED devices.[13]
Results and Discussion
Synthesis of Indolizino[3,4,5-ab]isoindoles (3a–3k) and
For comparison, 3b–3d were also synthesized with 1-ami-
Annulated Indolizino[3,4,5-ab]isoindoles (5, 7 and 9)
nobenzotriazole as the benzyne precursor with lead tetra-
We first investigated the reactions of indolizines 2a–2k acetate as the oxidation reagent.[15] These reactions invaria-
with 1 as the benzyne precursor in the presence of cesium bly resulted in lower yields than obtained with 1 as the
fluoride in acetonitrile and found that these reactions pro- benzyne precursor (see Table 1, yields in parentheses).
Table 1. Synthesis of indolizino[3,4,5-ab]isoindoles 3a–3k.
R1
R2
R3
R4
R5
R6
Reagent
Product
Time[a] [h]
Yield[b,c] [%]
Ph
Ph
Ph
Ph
H
H
CO2Me
CO2Et
CO2Et
CO2Me
Ph
H
Me
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
Me
Me
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
CN
H
2a
2b
2c
2d
2e
2f
2g
2h
2i
3a
3b
3c
3d
3e
3f
3g
3h
3i
12
7
8
8
7
9
9
8
8
23
49 (40)
44 (18)
55 (42)
51
50
50
37
30
75
51
CN
CO2Me
CO2Me
CO2Et
CO2Et
CO2Me
PhCO
Me
H
Me
2j
2k
3j
3k
10
8
[a] Reaction time. [b] Isolated yield. [c] Yield in parentheses was obtained by using 1-aminobenzotriazole as benzyne precursor.
Eur. J. Org. Chem. 2007, 3718–3726
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Y.-M. Shen, G. Grampp, N. Leesakul, H.-W. Hu, J.-H. Xu
FULL PAPER
Scheme 1. Synthesis of annulated indolizino[3,4,5-ab]isoindoles 7 and 9.
We then investigated the reactions of the pyrrolo[2,1-a]- cyclic compounds,[18] including some indolizino[3,4,5-ab]-
isoquinolines 4a–4c with benzyne. The starting materials isoindole derivatives.[7] We have carried out DFT calcula-
4a–4c were prepared by the 1,3-dipolar cycloadditions of tions on compounds 3, 5, 7 and 9 at the B3LYP/6-31G level.
isoquinolinium carboxymethylide with the corresponding The molecular geometry and frontier molecular orbital
alkynes.[16] Their reactions with 1 under the same condi- (FMO) properties of some representative compounds are
tions as described above for the reactions of 2a–2k with 1 given in the Supporting Information and the FMOs of
gave the corresponding benzo[6,7]pyrrolizino[3,4,5-ab]iso- compound 3a are shown in Figure 1. Regarding the molec-
quinolines 5a–5c as red solids, respectively, in 52–60% yield ular structure, the calculations on compounds 3 gave results
(Table 2).
similar to those reported for some other indolizino[3,4,5-
ab]isoindole derivatives,[7] showing that these polycyclic het-
erocycles with 14 peripheral π electrons can be viewed as
consisting of two aromatic fragments: indolizine (10π elec-
trons) and benzene (6π electrons). Compounds 5a–5c, 7 and
9 have the same structural characteristics. Therefore, in 5a–
5c, the two C–C bonds (C7a–C7b and C11a–C11b) con-
necting the pyrrolo[2,1-a]isoquinoline ring with the benzene
ring are significantly longer (1.45–1.47 Å) than normal
Table 2. Synthesis of indolizino[3,4,5-ab]isoindoles 5a–5c.
C=C bonds (1.34 Å) and are similar to the length of Csp2
–
R1
R2
Reagent
Product
Time[a] [h] Yield[b] [%]
Csp2 bonds that link two independent aromatic rings such as
the bond between the two phenyls in biphenyl (1.49 Å).[19]
Similarly, in 7 and 9, the lengths of the two corresponding
bonds linking the benzene ring with the annulated indoliz-
ine ring are 1.45–1.46 Å.
CO2Me
CN
CO2Et
H
H
CO2Et
4a
4b
4c
5a
5b
5c
8
8
8
60
52
58
[a] Reaction time. [b] yield of isolated products.
Compounds 5a–5c have strong molecular ion peaks in
their MS spectra, with 5b and 5c having this peak as the
base peak. To examine the influence of further annulation
to the indolizino[3,4,5-ab]isoindole and the effect of incor-
porating another heterocycle which is itself a good fluoro-
phore[17] into the π system, the reactions of 6H-[1]benzopyr-
ano[3,4-a]indolizin-6-one (6)[16] and 6H-[1]benzopyrano-
[3Ј,4Ј:3,4]pyrrolo[2,1-a]isoquinolin-6-one (8)[16] with 1 un-
der the same conditions as described above were investi-
gated. These reactions afforded 7 and 9, respectively, in high
yields (Scheme 1).
Figure 1. HOMO and LUMO of compound 3a at the B3LYP /6-
31G//B3LYP/6-31G level of theory.
Molecular Structures of Compounds 3, 5, 7 and 9
Absorption and Fluorescence Spectral Properties of
Compounds 3, 5, 7 and 9
DFT calculations have been shown to give structural pa-
rameters (bond lengths and angles) that well reproduce the
The indolizino[3,4,5-ab]isoindoles 3a–3k have similar
X-ray crystallographic structures of many polycyclic hetero- UV/Vis spectra, with the longest wavelength absorption
3720
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Eur. J. Org. Chem. 2007, 3718–3726

Blue-Light Fluorophores Indolizinoisoindole Derivatives
FULL PAPER
Table 3. Absorption and fluorescence spectral properties and redox potentials of compounds 3, 5, 7 and 9.
Stoke’s shift:
[a]
[a]
[b]
λmAax [nm] (ε [104 Lmol–1 cm–1])
λFmax [nm]
ΦF
τF [ns]
Eox [c] [V]
Ered [c] [V]
∆λ [nm]
3a
3b
3c
3d
3e
3f
3g
3h
3i
284 (1.36), 406 (0.38), 431 (0.68)
265 (6.35), 312 (2.30), 437 (0.71), 463 (0.88)
266 (5.53), 422 (0.66), 447 (0.81)
265 (6.77), 311 (2.72), 436 (0.84), 464 (0.98)
265 (4.62), 296 (2.19), 410 (0.56), 432 (0.63)
268 (5.69), 321 (1.55), 405 (0.64), 430 (0.81)
269 (4.01), 312 (1.72), 425 (0.94), 442 (0.92)
269 (3.96), 312 (1.68), 425 (0.87), 440 (0.8)
272 (6.84), 430 (0.43), 447 (0.42)
14
11
8
11
15
9
22
26
26
18
18
13
15
43
6
445
474
455
475
447
439
464
466
473
462
464
519
521
556
445
518
0.49
0.63
0.64
0.50
0.51
0.52
0.77
0.60
0.72
0.69
0.01
0.70
0.60
0.44
0.59
0.77
18.0Ϯ0.3
19.6Ϯ0.1
14.8Ϯ0.1
0.95
0.77
0.84
0.75
1.29/1.26
not measured
1.32/1.23
1.41
1.39
not measured
1.23
0.96
1.06
1.07
1.38
1.08
–2.03
–2.04/–2.13
–1.99/–2.13
–2.02/–2.09
–1.81/–1.88
16.7Ϯ0.2
11.5Ϯ0.1
11.7Ϯ0.1
13.0Ϯ0.1
–1.55/–1.60
–1.54/–1.61
–1.56/–1.64
3j
268 (3.44), 425 (0.74), 444 (0.68)
3k
5a
5b
5c
7
265 (3.43), 352 (0.95), 422 (1.01), 446 (1.36)
284 (5.29), 318 (5.07), 476 (1.01), 506 (1.69)
284 (3.64), 317 (2.83), 477 (0.49), 506 (0.83)
286 (4.35), 319 (1.96), 513 (0.86)
278 (4.11), 343 (1.50), 413 (0.94), 439 (1.58)
325 (4.77), 391 (2.56), 475 (0.75), 509 (1.67)
–1.74/–1.77
–1.52/–1.59
–1.44/–1.52
–1.24/–1.32
–1.65/–1.71
–1.44
28.6Ϯ0.3
30Ϯ1[d]
6.5Ϯ0.2[d]
9
9
[a] Measured in EtOH. [b] Measured in MeCN. [c] There is also a small amount of 2nd exponential decay, but evaluation is not possible.
The values given are τeff. [d] Eox and Ered were measured in MeCN with a saturated calomel electrode (SCE) as the reference electrode.
For irreversible redox processes, peak potentials are listed. For reversible and partly reversible processes, anodic and cathodic peaks are
given.
maxima in the range of 405–447 nm (Table 3 and Figure 2
for 3a; for the spectra of the other compounds, see the Sup-
porting Information). Compounds 5a–5c, which are 3,4-an-
nulated indolizino[3,4,5-ab]isoindoles, have their longest
wavelength absorption maxima red-shifted to the 506–
513 nm region (Table 3). In contrast, annulation of the in-
dolizino[3,4,5-ab]isoindoles at the 1,2-position by the cou-
marin ring resulted in no red shift of the absorption spec-
trum and compound 7 absorbs at a similar wavelength as
3a–3k, with the longest wavelength absorption at 439 nm.
In accord with this, the absorption spectrum of compound
9 displays no red shift, as compared with its unannulated
counterpart 5, and 9 has its longest λ absorption at 509 nm
(Table 3).
This different effect of the 1,2- (in compound 7) and 3,4-
(in compound 5) annulations on the absorption wavelength
may be rationalized in terms of the nature of the annulation
groups. In 5, the 3,4-positions are annulated by the elec-
tron-rich benzene ring, whose main effect is to extend the
π-conjugation system to lead to a more dense distribution
of the molecular orbitals and a decreased HOMO–LUMO
energy gap. This situation is reflected in the smaller redox
potential gaps for compounds 5a–5c (oxidation–reduction
potential gaps are 2.52, 2.54 and 2.35 eV for 5a, 5b and 5c,
respectively) than for compounds 3 (redox potential gaps in
the range 2.81–2.99 eV). In contrast, compound 7 is derived
from the annulation of the 1,2-positions of 3 by an electron-
deficient coumarin ring which causes the simultaneous low-
ering of the HOMO and LUMO energy levels (both ioniza-
tion potential and electron affinity are raised). As a result,
Figure 2. Normalized absorption and fluorescence spectra of 3a
and 5a.
the HOMO–LUMO gap in 7 is not much changed from
that in 3. In accord with this, the redox potential gap for 7
is close to those of compounds 3 (≈3 eV).
Compounds 3a–3k are fluorescent in the region 439– in ethanol. For compound 3k, the introduction of a benzoyl
475 nm (Table 3). Except for 3k, all these compounds have group at the C-2 atom resulted in a drastic decrease in fluo-
high fluorescence quantum yields in the range of 0.49–0.77 rescence efficiency, making it behave as a typical aromatic
Eur. J. Org. Chem. 2007, 3718–3726
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Y.-M. Shen, G. Grampp, N. Leesakul, H.-W. Hu, J.-H. Xu
FULL PAPER
ketone with a ΦF of 0.01. While compounds 3a–3k emit in
the blue region, the benzo[6,7]pyrrolizino[3,4,5-ab]isoquin-
olines 5a–5c fluoresce in the green region with high quan-
tum yields. Similar to the absorption spectra, compound 7
fluoresces at a similar wavelength as compounds 3a–3k de-
spite an extended π system in the former. In line with this,
compound 9 fluoresces at a similar wavelength as com-
pounds 5a–5c.
The Stoke’s shifts for most of the compounds (3a–3f, 5a–
5b, 7 and 9) are small (≈10 nm). This, together with the
good mirror-image relationship between the absorption and
fluorescence spectra, indicates that these compounds have
a rigid molecular framework that experiences only small ge-
ometry changes upon excitation. For compounds 3g–3k
and 5c, the presence of bulky and conformationally flexible
side-chains leads to a significantly larger Stoke’s shift.
Fluorescence lifetimes for compounds 3a–3c, 3e, 3g–3i,
5a, 5b and 7 have been measured and the results are given
in Table 3. Compounds 3 have singlet lifetimes in the range
Figure 3. Cyclic voltammograms for compounds 3a, 3g and 5a.
11–20 ns, similar to the fluorescence lifetimes of their ances- (–1.35 V vs. SCE).[24] The irreversibility of the reductions of
tor indolizine compounds.[20]
7 and 9 are likely the result of the irreversible reduction of
the coumarin ring which is known to cause dimerization to
give the 4,4Ј-dimeric product.[24]
The redox potentials are sensitively influenced by the na-
ture and the position of the substituents on the ring. There-
fore, electron-withdrawing groups significantly raise the oxi-
Electrochemical Properties
The oxidation and reduction potentials of the synthe- dation potential and make the reduction potential less
sized compounds have been measured by cyclic voltamme- negative, while electron-pushing groups have the reverse ef-
try to evaluate their potential as hole- and electron-trans- fect. The redox potentials are also strongly dependent on
porting species. The results are summarized in Table 3.
the position of the substituent in relation to the atomic co-
For the indolizino[3,4,5-ab]isoindoles without a substitu- efficients in different ring positions in the HOMO and
ent at the C-2 atom, for example, compounds 3a, 3c, 3d, LUMO of the parent compound 3a, as calculated by the
the oxidations are irreversible without the corresponding DFT method at the B3LYP/6-31G level (Figure 1). Intro-
radical-cation reduction peaks being observed during the duction of an electron-donating group (such as a methyl) at
cathodic scan, indicating an EC process at the anode. This a ring position that has a large atomic coefficient in the
behaviour is similar to the electrochemical oxidations of the HOMO (or LUMO) would lead to a decline in the oxi-
indolizine derivatives in which the irreversible oxidation of dation potential (or a more negative reduction potential),
the 1-unsubstituted indolizines was caused by the dimeriza- while introducing an electron-withdrawing group at such a
tion of the cation radicals to afford the 1,1Ј-biindoliz- position has the reverse effect. However, the oxidation po-
ines,[21,22] as evidenced by bulk electrolysis.[21] The oxi- tentials seem to be more sensitive than the reduction poten-
dations of 3i and 3k, which have a methyl at the C-4 atom, tials.
are also irreversible. This is probably the result of facile de-
As a general rule, introducing an alkyl group at C-2 or,
protonation of the highly acidic cation radicals, as is often to a lesser extent, at C-4, would significantly lower the oxi-
observed in methylarene cation radicals.[23] In contrast, the dation potential of the 1-phenylindolizino[3,4,5-ab]isoin-
oxidations of compounds 3e and 3g with an electron-with- doles, while placing an alkyl group at C-3 or C-5 would
drawing group at C-2 are partially reversible with discerni- efficiently cause the reduction potentials to be more nega-
ble cathodic peaks (Figure 3). In these cases, dimerization tive.
and alkyl deprotonation pathways of the cation radicals are
Compounds 5a–5c are benzannulated indolizino[3,4,5-
blocked. The reductions for most of the indolizino[3,4,5-ab]- ab]isoindoles. Comparison of the oxidation potential of 9
isoindoles are either reversible (3a, 3b and 3g) or partially with its benzannulated counterpart 5c shows that the fusion
reversible (3c, 3e, 3h, 3i and 3k), bespeaking the high sta- of a benzene ring leads to a lowering of the oxidation po-
bility of their anion radicals. The oxidations of compounds tential by 0.33 eV.
5a–5c are irreversible, but their reductions are reversible.
For compounds 7 and 9, both oxidations and reductions the 1,2-position in compound 7 results in an oxidation po-
are irreversible. tential similar to 3g and 3h. Compound 9 has a much lower
The fusion of the electron-withdrawing coumarin ring at
The reduction potentials of compounds 7 and 9 are oxidation potential than 7 because of the further benzoan-
largely decided by the coumarin structural unit and are at nulation, 9 having an E½ value similar to compounds 5a–
slightly more negative values than that of coumarin itself 5c with an electron-withdrawing group in the ring.
3722
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3718–3726

Blue-Light Fluorophores Indolizinoisoindole Derivatives
FULL PAPER
6-31G basis set. All optimized structures were found to be planar
by frequency analysis.
Conclusions
In summary, cycloadditions of indolizines and annulated
indolizines with benzyne [generated from the precursor 2-
(trimethylsilyl)phenyl triflate] provide a general and versa-
tile one-pot synthesis of the indolizino[3,4,5-ab]isoindoles
3 and their 1,2- or 3,4-annulated and 1,2:3,4-bisannulated
derivatives. By this method, 11 new indolizino[3,4,5-ab]iso-
indoles (3a–3k) and their 3,4-annulated (5a–5c), 1,2-annu-
lated (7) as well as 1,2:3,4-bisannulated (9) derivatives have
been synthesized in moderate to high yields. Compounds
3a–3i are strong blue-light fluorophores that emit in the
wavelength region of 439–475 nm with high quantum yields.
In particular, for the indolizino[3,4,5-ab]isoindoles with an
electron-withdrawing group at the C-2 atom (e.g., com-
pounds 3e and 3g), their electrochemical redox processes
are quasi-reversible or reversible in suitable potential re-
gions (Eox 1.2 to 1.3 V, Ered –1.5 to –1.9 V vs. SCE). This
advantageous combination of fluorescence and electro-
chemical properties make them favourable candidates as
blue-light emitters with both hole- and electron-trans-
porting ability in monolayer OLED devices.[13] The other
indolizino[3,4,5-ab]isoindoles (3a–3d, 3f, 3h, 3i and 7) may
be tested as blue-light emitters with electron-transporting
ability. In addition, compounds 5a–5c and 9 are highly ef-
ficient fluorophores in the green region.
General Procedure for the Preparation of Compounds 3a–3k: A mix-
ture of indolizine (2a–2k, 1.0 mmol), 2-(trimethylsilyl)phenyl tri-
fluoromethanesulfonate (1, 0.53 g, 2 mmol) and cesium fluoride
(0.64 g, 4 mmol) in MeCN (20 mL) was heated at 90 °C for 7–12 h
with magnetic stirring. The reaction was monitored by TLC. The
solvent was removed in vacuo, the residue was poured into water,
extracted with CH2Cl2 and then separated by flash chromatography
on a silica gel column with petroleum ether (b.p. 60–90 °C)/ethyl
acetate as eluent to give the product.
1-Phenylindolizino[3,4,5-ab]isoindole (3a): Yield: 61 mg (23%), yel-
low solid from petroleum ether (b.p. 60–90 °C)/ethyl acetate, m.p.
1
75–76 °C. IR (KBr): ν = 1604, 1497, 751 cm–1. H NMR (CDCl ,
˜
3
300 MHz): δ = 7.33 (s, 1 H), 7.47 (t, J = 7.4 Hz, 1 H), 7.56 (t, J =
7.6 Hz, 1 H), 7.63 (t, J = 7.6 Hz, 2 H), 7.73 (t, J = 6.9 Hz, 2 H),
8.06 (d, J = 8.3 Hz, 1 H), 8.11 (dd, J = 7.1, 1.7 Hz, 3 H), 8.43 (d,
J = 8.1 Hz, 1 H), 8.49 (d, J = 8.0 Hz, 1 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 104.3, 108.2, 115.4, 115.7, 120.0, 120.2, 123.0, 123.1,
127.8, 128.4, 129.0, 129.1, 129.4, 130.1, 131.8, 136.6 ppm. MS: m/z
(%) = 267 (100) [M]+, 191 (3), 132 (12), 94 (7). C20H13N (267.10):
calcd. C 89.86, H 4.90, N 5.24; found C 89.70, H 4.98, N 5.34.
2-Methyl-1-phenylindolizino[3,4,5-ab]isoindole (3b): Yield: 138 mg
(49%), yellow solid from petroleum ether (b.p. 60–90 °C)/ethyl ace-
tate, m.p. 97–99 °C. IR (KBr): ν = 3044, 2962, 1600, 1523, 769,
˜
742 cm–1. 1H NMR (CDCl3, 300 MHz): δ = 2.84 (s, 3 H), 7.46–
7.54 (m, 2 H), 7.62–7.72 (m, 4 H), 7.93 (dd, J = 8.2, 1.2 Hz, 2 H),
8.07 (d, J = 8.2 Hz, 1 H), 8.12 (d, J = 7.3 Hz, 1 H), 8.23 (d, J =
8.1 Hz, 1 H), 8.47 (d, J = 8.0 Hz, 1 H) ppm. MS: m/z (%) = 281
(100) [M]+, 252 (16), 204 (14), 139 (15), 114 (12), 77 (14). C21H15N
(281.12): calcd. C 89.65, H 5.37, N 4.98; found C 89.47, H 5.32, N
4.81.
Experimental Section
1
General Methods: Melting points are uncorrected. H NMR spec-
tra were measured with a Bruker DPX 300 spectrometer at
300 MHz with CDCl3 as solvent unless otherwise stated. The
chemical shifts (δ) are reported in ppm relative to the residual de-
uteriated solvent signal and coupling constants (J) are given in Hz.
13C NMR spectra were measured with a Bruker Avance 400 spec-
trometer at 100 MHz with CDCl3 as solvent. IR spectra were re-
corded with a Shimadzu IR 440 spectrometer in KBr pellets. Mass
spectra were recorded with a VG ZAB–HS spectrometer in the elec-
tron-impact ionization mode. Elemental analyses were performed
with a Perkin–Elmer 240C analyzer.
3-Methyl-1-phenylindolizino[3,4,5-ab]isoindole (3c): Yield: 127 mg
(44%), yellow solid from petroleum ether (b.p. 60–90 °C)/ethyl ace-
tate, m.p. 131–132 °C. IR (KBr): ν = 2923, 2852, 1603, 1495,
˜
1
746 cm–1. H NMR (CDCl3, 400 MHz): δ = 2.94 (s, 1 H), 7.32 (s,
1 H), 7.47 (t, J = 7.8 Hz, 2 H), 7.54 (t, J = 7.6 Hz, 1 H), 7.64 (t, J
= 7.6 Hz, 2 H), 7.70 (t, J = 7.6 Hz, 1 H), 7.97 (d, J = 7.4 Hz, 1 H),
8.12 (d, J = 7.4 Hz, 2 H), 8.42 (dd, J = 8.1, 2.7 Hz, 2 H) ppm. 13C
NMR (CDCl3, 100 MHz): δ = 17.9, 102.6, 108.0, 119.5, 119.6,
120.4, 122.2, 122.7, 125.9, 126.5, 127.3, 127.5, 128.6, 129.0, 129.3,
129.6, 130.4, 136.4 ppm. MS: m/z (%) = 281 (100) [M]+, 204 (7.6),
189 (2.4), 132 (4.9). C21H15N (281.12): calcd. C 89.65, H 5.37, N
Fluorescence and UV/Vis Spectroscopy: UV/Vis spectra were run on
a Varian Cary 50 spectrophotometer. Fluorescence measurements 4.98; found C 89.74, H 5.45, N 5.02.
were performed with a Varian Cary Elipse fluorospectrometer.
4-Methyl-1-phenylindolizino[3,4,5-ab]isoindole (3d): Yield: 154 mg
(55%), yellow solid from petroleum ether (b.p. 60–90 °C)/ethyl ace-
Quantum yields were determined by using perylene in degassed
cyclohexane as a standard (Φ = 0.94).[7] Lifetime measurements
were carried out in acetonitrile by a modulation technique with a
digital storage oscilloscope; the sample concentration was
2ϫ10–5 .
tate, m.p. 123–126 °C. IR (KBr): ν = 3060, 2909, 1603, 1514,
˜
746 cm–1. 1H NMR (CDCl3): δ = 2.84 (s, 3 H), 7.45–7.54 (m, 2 H),
7.62 (t, J = 7.5 Hz, 2 H), 7.70 (td, J = 7.6, 0.9 Hz, 2 H), 7.84 (s, 1
H), 7.93 (s, 1 H), 8.09 (dd, J = 8.3, 1.2 Hz, 2 H), 8.39 (d, J =
Cyclic Voltammetry: Cyclic voltammetry (CV) was performed with 8.2 Hz, 1 H), 8.43 (d, J = 8.0 Hz, 1 H) ppm. MS: m/z (%) = 281
a three-electrode cell in acetonitrile solution with 0.1  (nBu)4N-
ClO4 as the supporting electrolyte. The scan rate was 100 mV/s. A
Pt wire was used as the counter-electrode, glassy carbon was used
as the working electrode and a saturated calomel electrode (SCE)
was used as the reference electrode. The set-up was calibrated with
potassium ferricyanide [K3Fe(CN)6] as the reference: Epox = 0.226 V,
Epred = 0.285 V vs. SCE[25] in 1  KCl aqueous solution.
(100) [M]+, 252 (12), 207 (11), 139 (28), 113 (15), 44 (13). C21H15N
(281.12): calcd. C 89.65, H 5.37, N 4.98; found C 89.52, H 5.22, N
4.78.
4-Methylindolizino[3,4,5-ab]isoindole-2-carbonitrile (3e): Yield:
117 mg (51%), yellow solid from petroleum ether (b.p. 60–90 °C)/
ethyl acetate, m.p. 124–125 °C. IR (KBr): ν = 2928, 2853, 2206,
˜
1
1616, 1519, 727 cm–1. H NMR (CDCl3, 300 MHz): δ = 2.85 (s, 3
Computational Methods: The Gaussian 2003 series of programs[26]
was used for all calculations. All molecules were fully optimized
using the hybrid density functional B3LYP level of theory with the
H), 7.60 (t, J = 7.6 Hz, 1 H), 7.72–7.78 (m, 2 H), 7.94 (s, 1 H), 7.97
(s, 1 H), 8.15 (d, J = 8.0 Hz, 1 H), 8.35 (d, J = 7.9 Hz, 1 H) ppm.
13C NMR (CDCl3, 75 MHz): δ = 23.8, 111.7, 114.9, 115.8, 117.7,
Eur. J. Org. Chem. 2007, 3718–3726
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3723

Y.-M. Shen, G. Grampp, N. Leesakul, H.-W. Hu, J.-H. Xu
FULL PAPER
120.7, 123.2, 125.2, 129.7, 130.7, 136.1 ppm. MS: m/z (%) = 230
(24) [M]+, 204 (7), 165 (3), 149 (100), 57 (48). C16H10N2 (230.08):
calcd. C 83.46, H 4.38, N 12.17; found C 83.37, H 4.42, N 12.20.
fluoromethanesulfonate (1, 0.53 g, 2 mmol) and cesium fluoride
(0.64 g, 4 mmol) in MeCN (20 mL) was heated at 90 °C for 8 h
with magnetic stirring. The reaction was monitored by TLC. The
solvent was removed in vacuo, the residue poured into water, ex-
tracted with CH2Cl2 and then separated by flash chromatography
on a silica gel column with petroleum ether (b.p. 60–90 °C)/ethyl
acetate as eluent to give the product.
Methyl Indolizino[3,4,5-ab]isoindole-2-carboxylate (3f): Yield:
124 mg (50%), yellow solid from petroleum ether (b.p. 60–90 °C)/
ethyl acetate, m.p. 116–117 °C (ref.[7] 118–119 °C). 1H NMR
(CDCl3, 300 MHz): δ = 4.04 (s, 3 H), 7.59 (t, J = 7.6 Hz, 1 H),
7.76 (t, J = 7.2 Hz, 1 H), 7.91 (t, J = 7.8 Hz, 1 H), 8.12 (d, J =
7.6 Hz, 1 H), 8.13 (s, 1 H), 8.21 (d, J = 8.0 Hz, 1 H), 8.41 (d, J =
8.0 Hz, 1 H), 8.50 (d, J = 8.4 Hz, 1 H) ppm.
Methyl
Benzo[6,7]pyrrolizino[3,4,5-ab]isoquinoline-2-carboxylate
(5a): Yield: 179 mg (60%), red solid from petroleum ether (b.p. 60–
90 °C)/ethyl acetate, m.p. 157–159 °C. IR (KBr): ν = 2949, 1698,
˜
1
1603, 1513 cm–1. H NMR (CDCl3, 300 MHz): δ = 4.10 (s, 3 H),
Dimethyl Indolizino[3,4,5-ab]isoindole-1,2-dicarboxylate (3g): Yield:
154 mg (50%), yellow solid from petroleum ether (b.p. 60–90 °C)/
ethyl acetate, m.p. 182–184 °C (ref.[7] 182–183 °C). 1H NMR
(CDCl3, 300 MHz): δ = 4.06 (s, 3 H), 4.19 (s, 3 H), 7.65 (t, J =
7.6 Hz, 1 H), 7.78 (t, J = 7.6 Hz, 1 H), 7.90 (t, J = 7.9 Hz, 1 H),
8.09 (d, J = 7.2 Hz, 1 H), 8.37 (d, J = 7.9 Hz, 1 H), 8.45 (d, J =
7.7 Hz, 1 H), 8.47 (d, J = 8.0 Hz, 1 H) ppm.
7.61–7.76 (m, 3 H), 7.80 (t, J = 7.2 Hz, 1 H), 8.28 (t, J = 8.9 Hz,
2 H), 8.40 (s, 1 H), 8.73 (d, J = 8.1 Hz, 1 H), 8.85 (d, J = 8.8 Hz,
1 H), 8.88 (s, 1 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 51.4,
110.7, 115.6, 120.1, 120.3, 120.6, 120.8, 123.0, 123.2, 123.7, 123.8,
125.6, 127.3, 127.4, 128.4, 128.5, 128.7, 129.9, 130.0 ppm. MS: m/z
(%) = 299 (90) [M]+, 268 (48), 240 (100), 213 (23), 120 (31), 11 (38).
C20H13NO2 (299.09): calcd. C 80.25, H 4.38, N 4.68; found C
80.26, H 4.26, N 4.59.
Diethyl Indolizino[3,4,5-ab]isoindole-1,2-dicarboxylate (3h): Yield:
124 mg (37%), yellow solid from petroleum ether (b.p. 60–90 °C)/
Benzo[6,7]pyrrolizino[3,4,5-ab]isoquinoline-2-carbonitrile
(5b):
ethyl acetate, m.p. 60–61 °C. IR (KBr): ν = 3056, 2979, 2900, 1718,
˜
1690, 1494 cm–1. 1H NMR (CDCl3, 300 MHz): δ = 1.52 (t, J =
7.1 Hz, 3 H), 1.58 (t, J = 7.2 Hz, 3 H), 4.52 (q, J = 7.1 Hz, 2 H),
4.65 (q, J = 7.1 Hz, 2 H), 7.62 (t, J = 7.6 Hz, 1 H), 7.76 (t, J =
7.6 Hz, 1 H), 7.86 (t, J = 7.9 Hz, 1 H), 8.05 (d, J = 7.1 Hz, 1 H),
8.34 (d, J = 7.6 Hz, 1 H), 8.44 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR
(CDCl3, 100 MHz): δ = 14.5, 14.6, 60.4, 61.5, 109.4, 110.0, 118.5,
119.0, 122.1, 122.5, 124.2, 124.8, 125.5, 129.3, 129.6, 129.9, 130.1,
130.7, 164.0, 164.8 ppm. MS: m/z (%) = 335 (100) [M]+, 290 (26),
262 (70), 190 (40). C20H17NO4 (335.12): calcd. C 71.63, H 4.18, N
5.11; found C 70.52, H 4.69, N 4.98.
Yield: 138 mg (52%), red solid from petroleum ether (b.p. 60–
90 °C)/ethyl acetate, m.p. 170–172 °C. IR (KBr): ν = 2206, 1729,
˜
1
1514, 747 cm–1. H NMR (CDCl3, 300 MHz): δ = 7.70–7.84 (m, 3
H), 7.90 (t, J = 7.6 Hz, 1 H), 8.25 (s, 1 H), 8.35 (t, J = 9.0 Hz, 2
H), 8.68 (s, 1 H), 8.83 (d, J = 8.0 Hz, 1 H), 8.96 (d, J = 8.6 Hz, 1
H) ppm. MS: m/z (%) = 266 (100) [M]+, 238 (11), 149 (9), 133 (7).
C19H10N2 (266.08): calcd. C 85.70, H 3.79, N 10.52; found C 85.63,
H 4.06, N 10.31.
Diethyl Benzo[6,7]pyrrolizino[3,4,5-ab]isoquinoline-1,2-dicarboxyl-
ate (5c): Yield: 223 mg (58%), red solid from petroleum ether (b.p.
60–90 °C)/ethyl acetate, m.p. 130–131 °C. IR (KBr): ν = 2980, 1732,
˜
Diethyl 4-Methylindolizino[3,4,5-ab]isoindole-1,2-dicarboxylate (3i):
Yield: 105 mg (30%), yellow solid from petroleum ether (b.p. 60–
1
1704 cm–1. H NMR (CDCl3, 300 MHz): δ = 1.57 (t, J = 6.2 Hz,
3 H), 1.62 (t, J = 6.2 Hz, 3 H), 4.59 (q, J = 7.1 Hz, 2 H), 4.71 (q,
J = 7.1 Hz, 2 H), 7.68–7.88 (m, 4 H), 8.34 (d, J = 8.5 Hz, 1 H),
8.51 (d, J = 7.9 Hz, 1 H), 8.80 (d, J = 8.0 Hz, 1 H), 8.91 (d, J =
8.5 Hz, 1 H), 9.03 (s, 1 H) ppm. 13C NMR (CDCl3, 100 MHz): δ
= 14.5, 14.6, 60.5, 61.8, 109.0, 117.4, 120.8, 121.1, 121.6, 122.8,
123.5, 123.6, 123.9, 124.8, 125.8, 127.8, 128.1, 128.3, 129.1, 129.9,
130.5, 164.0, 165.0 ppm. MS: m/z (%) = 385 (100) [M]+, 313 (22),
285 (42), 240 (48). C24H19NO4 (385.13): calcd. C 74.79, H 4.97, N
3.63; found C 74.76, H 5.23, N 3.56.
90 °C)/ethyl acetate, m.p. 136–137 °C. IR (KBr): ν = 2977, 2905,
˜
1
1736, 1690, 1495 cm–1. H NMR (CDCl3, 300 MHz): δ = 1.51 (t,
J = 7.1 Hz, 3 H), 1.57 (t, J = 7.1 Hz, 3 H), 2.83 (s, 3 H), 4.51 (q,
J = 7.1 Hz, 2 H), 4.64 (q, J = 7.1 Hz, 2 H), 7.60 (t, J = 7.6 Hz, 1
H), 7.74 (t, J = 7.6 Hz, 1 H), 7.91 (s, 1 H), 8.26 (s, 1 H), 8.32 (d,
J = 7.9 Hz, 1 H), 8.43 (d, J = 8.0 Hz, 2 H) ppm. MS: m/z (%) =
349 (100) [M]+, 276 (36), 249 (20), 204 (30). C21H19NO4 (349.13):
calcd. C 72.19, H 5.48, N 4.01; found C 72.02, H 5.56, N 3.92.
Dimethyl
5-Methylindolizino[3,4,5-ab]isoindole-1,2-dicarboxylate
Preparation of Compound 7: A mixture of 6H-[1]benzopyrano[3,4-
a]indolizine-6-one (6, 1.0 mmol), 2-(trimethylsilyl)phenyl trifluoro-
methanesulfonate (1, 0.53 g, 2 mmol) and cesium fluoride (0.64 g,
4 mmol) in MeCN (20 mL) was heated at 90 °C for 5 h with mag-
netic stirring. The reaction was monitored by TLC. A yellow pre-
cipitate was collected and washed with ethyl acetate to give the
product.
(3j): Yield: 241 mg (75%), yellow solid from petroleum ether (b.p.
60–90 °C)/ethyl acetate, m.p. 128–129 °C. IR (KBr): ν = 2923, 2851,
˜
1731, 1703, 1599, 1488 cm–1. 1H NMR (CDCl3, 300 MHz): δ =
2.94 (s, 3 H), 4.06 (s, 3 H), 4.14 (s, 3 H), 7.57 (dd, J = 7.3, 0.8 Hz,
1 H), 7.63 (td, J = 7.6, 0.9 Hz, 1 H), 7.75 (td, J = 7.6, 1.0 Hz, 1
H), 7.98 (d, J = 7.3 Hz, 1 H), 8.34 (d, J = 7.9 Hz, 1 H), 8.53 (d, J
= 8.0 Hz, 1 H) ppm. MS: m/z (%) = 321 (24) [M]+, 289 (35), 271
(100), 231 (19), 204 (29), 57 (47). C19H15NO4 (321.10): calcd. C
71.02, H 4.71, N 4.36; found C 70.91, H 4.83, N 4.35.
6H-[1]Benzopyrano[3Ј,4Ј:1,2]indolizino[3,4,5-ab]isoindole-6-one (7):
Yield: 287 mg (93%), yellow solid from petroleum ether (b.p. 60–
90 °C)/ethyl acetate, m.p. 269–271 °C. IR (KBr): ν = 1716 cm–1. 1H
˜
(4-Methyl-1-phenylindolizino[3,4,5-ab]isoindol-2-yl)phenylmeth-
anone (3k): Yield: 196 mg (51%), yellow solid from petroleum ether
NMR (CDCl3, 300 MHz): δ = 7.49–7.60 (m, 3 H), 7.67 (t, J =
7.7 Hz, 1 H), 7.87 (t, J = 7.6 Hz, 1 H), 8.04 (t, J = 7.9 Hz, 1 H),
8.26 (d, J = 7.5 Hz, 1 H), 8.45–8.51 (m, 3 H), 8.63 (d, J = 8.2 Hz,
1 H) ppm. MS: m/z (%) = 309 (34) [M]+, 252 (16), 44 (100).
C21H11NO2 (309.08): calcd. C 81.54, H 3.58, N 4.53; found C
80.97, H 3.71, N 4.45.
(b.p. 60–90 °C)/ethyl acetate, m.p. 93–95 °C. IR (KBr): ν = 3055,
˜
2949, 1732, 1493, 1387 cm–1. 1H NMR (CDCl3, 300 MHz): δ =
2.82 (s, 3 H), 7.18–7.36 (m, 6 H), 7.53–7.72 (m, 6 H), 7.96 (s, 1 H),
8.12–8.14 (m, 2 H), 8.38 (d, J = 7.7 Hz, 1 H) ppm. MS: m/z (%) =
385 (2.4) [M]+, 203 (10), 163 (20), 112 (100), 85 (26). C28H19NO
(385.15): calcd. C 87.25, H 4.97, N 3.63; found C 87.05, H 5.17, N
3.56.
Preparation of Compound 9: A mixture of 6H-[1]benzopyrano-
[3Ј,4Ј:3,4]pyrrolo[2,1-a]isoquinolin-6-one (8, 1.0 mmol), 2-(trimeth-
ylsilyl)phenyl trifluoromethanesulfonate (1, 0.53 g, 2 mmol) and ce-
sium fluoride (0.64 g, 4 mmol) in MeCN (20 mL) was heated at
General Procedure for the Preparation of Compounds 5a–5c: A mix-
ture of indolizine (4a–4c, 1.0 mmol), 2-(trimethylsilyl)phenyl tri-
3724
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3718–3726

Blue-Light Fluorophores Indolizinoisoindole Derivatives
FULL PAPER
[7]
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90 °C for 8 h with magnetic stirring. The reaction was monitored
by TLC. The solvent was removed in vacuo, the residue poured
into water, extracted with CH2Cl2, the solvent removed in vacuo
and the residue separated by flash chromatography on a silica gel
column with petroleum ether (b.p. 60–90 °C)/ethyl acetate as eluent
to give the product.
6H-[1]Benzopyrano[3Ј,4Ј:1,2]benzo[6,7]pyrrolizino[3,4,5-ab]isoquinol-
ine-6-one (9): Yield: 223 mg (62%), yellow solid from petroleum
ether (b.p. 60–90 °C)/ethyl acetate, m.p. 247–248 °C. IR (KBr): ν =
˜
1727, 1610, 1400, 741 cm–1. 1H NMR (CDCl3, 300 MHz): δ = 7.53–
7.70 (m, 4 H), 7.79 (t, J = 7.9 Hz, 1 H), 7.83 (t, J = 7.8 Hz, 1 H),
7.92 (t, J = 7.4 Hz, 1 H), 8.35 (d, J = 8.3 Hz, 1 H), 8.47–8.50 (m,
2 H), 8.78 (d, J = 8.3 Hz, 1 H), 8.92 (d, J = 8.6 Hz, 1 H), 8.96 (s,
1 H) ppm. MS: m/z (%) = 359 (100) [M]+, 302 (9), 180 (1), 138 (2).
C25H13NO2 (359.09): calcd. C 83.55, H 3.65, N 3.90; found C
83.16, H 3.92, N 3.79.
[9]
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Supporting Information (see also the footnote on the first page of
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(DFT method at the B3LYP/6-31G level) for compounds 3a, 3b,
3c, 3d, 5a, 7, 9.
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This work was supported by the National Natural Science Founda-
tion of China (NSFC) (20572044). Partial support from the Austr-
ian Exchange Service (OEAD, Project: WTZ VII.B.3) and from the
Modern Analytical Center and Institute of Theoretical and Com-
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