Condensation of Indoline with Some 1,2- and 1,3-Diketones

Article abstract of DOI:10.1002/jhet.2580

Bismuth nitrate catalyzed condensation reactions of indoline with 1,2- and 1,3-diketones were investigated and were reported to proceed via different reaction pathways with the involvement of one or two of the carbonyl groups. While the reaction of indoli

Full text of DOI:10.1002/jhet.2580

Month 2015
Condensation of Indoline with Some 1,2- and 1,3-Diketones
a
Haydar Kilic,a Omer Aydin,a Sinan Bayindir,a,b and Nurullah Saracoglu
*
aDepartment of Chemistry, Faculty of Sciences, Atatürk University, Erzurum 25240, Turkey
bDepartment of Chemistry, Faculty of Sciences and Arts, Bingöl University, Bingöl 12000, Turkey
*
E-mail: nsarac@atauni.edu.tr
Additional Supporting Information may be found in the online version of this article.
Received August 18, 2015
DOI 10.1002/jhet.2580
Published online 00 Month 2015 in Wiley Online Library (wileyonlinelibrary.com).
Bismuth nitrate catalyzed condensation reactions of indoline with 1,2- and 1,3-diketones were investi-
gated and were reported to proceed via different reaction pathways with the involvement of one or two of
the carbonyl groups. While the reaction of indoline with cyclohexane-1,3-dione (4) gave solely condensation
product, the reaction between the acetylacetone (5) and indoline provided N-acetyl indoline as single prod-
ucts on retro-aldol process. In contrast to 1,3-diketones, the reaction with benzil (17) was performed under
difficult conditions and proceeded to give secondary products.
J. Heterocyclic Chem., 00, 00 (2015).
INTRODUCTION
article, Tunge et al. synthesized N-aryl-1-aminoindoles
from indolines with different nitrosobenzenes via intermo-
lecular redox amination (Scheme 1) [10]. Recently, we also
investigated the redox amination potential of both
enolizable cyclic and acyclic ketones and benzylic ketones
with indoline [11,12]. Our results showed that the forma-
tion of N-alkyl substituted indole/indoline derivatives over
competitive redox and reductive amination processes de-
pending on the reaction condition and ketones. In the con-
tinuation of our research interest on redox amination of
indoline, we next turned attention toward the effect of the
second carbonyl group and here in report the reactions of
some 1,2- and 1,3-diketones with indoline.
Indole moiety is found in many natural products, fine
chemicals, and pharmaceuticals. N-Alkyl indoles represent
a particularly interesting class and are also known to pos-
sess a wide spectrum of biological activities in numerous
natural products and pharmaceutical compounds [1–3].
However, in contrast to the much more developed C-2
and especially C-3 functionalization, the development of
new methods for functionalization at the N-position of in-
doles is still highly desirable. Recently, a redox amination
is a powerful strategy developed for the synthesis of N-
alkylation of indoles, pyrroles and N-heterocycles by N–
C bond formation [4]. Previous studies have been reported
to generate N-alkyl indoles over the redox amination pro-
cess from indolines with aryl or non-enolizable aldehydes
by Tunge, Pan, and Siedel groups (Scheme 1) [5–9]. But
the reactions used salicylaldehyde as the substrate gave
N-alkyl indolines over the reductive amination process
with intermolecular hydride transfer from indoline instead
of the usual redox amination reaction [6]. In a recent
RESULTS AND DISCUSSIONS
Our research interest on redox amination with ketones of
indoline encouraged us to ascertain the behavior of both
1,2- and 1,3-diketones against the redox amination reactions
of indoline. Cyclohexane-1,3-dione (4) and acetylacetone (5)
© 2015 HeteroCorporation

H. Kilic, O. Aydin, S. Bayindir, and N. Saracoglu
Vol 000
Scheme 1. Examples for redox amination synthesis. [Color figure can be
viewed in the online issue, which is available at wileyonlinelibrary.com].
the hydration of the conjugated double bond undergoes
carbon-carbon bond cleavage to give N-acetyl indoline
(13) and acetone. It can be hypothesized that MnO2,
DDQ or SiO2 act as a Lewis acid during the addition of
1
water to the double bond. The H NMR spectrum of 13
revealed that N-acetyl indoline exists as an 85:15 mixture
of the rotamers. Unfortunately, all oxidation attempts of
pure N-acetyl indoline 13 to prepare N-acetyl indole 16
failed. Using manganese dioxide or DDQ in CH2Cl2
yielded only unreacted starting material. This resistance
to chemical oxidation might be the result of the
electron-withdrawing character of carbonyl group, caus-
ing the five-membered ring to be electron-deficient
(Scheme 5).
as 1,3-diketone povided an opportunity to investigate the
effect of -carbonyl group on the redox amination of indoline
with ketones. The bismuth nitrate-catalyzed reaction of
indoline with cyclohexane-1,3-dione (4) in CH2Cl2 (DCM)
gave enamine product 6 in 94% yield, instead of the desired
product 11 (Schemes 2 and 3). The introduction of the second
carbonyl group into the cyclohexanone ring has a profound
effect on the dehydration step in the outcome of the reaction.
The second competing product 11, which is a possible
desired indole type-redox amination product, was not ob-
served in the case of cyclohexane-1,3-dione (4). In this case,
the presence of the second carbonyl group plays a crucial role
in the formation of conjugated enone 6, which is formed via a
1,2-addition of indoline with cyclic-1,3-diketone, followed by
dehydration through two mechanisms (Scheme 3). Probably,
no aromatization was observed, because of the conjugated
structure of the resulting cyclohexenone. Furthermore,
3-(indolin-1-yl)cyclohex-2-enone (6) was easily aromatized
with MnO2 to afford the 3-(1H-indol-1-yl)cyclohex-2-enone
(7) in 96% yield (Scheme 2).
Similarly, the reaction of indoline with benzil (17) as
1,2-diketone was also investigated under the similar reac-
tion conditions. But no reaction was observed after 2 days
at room temperature. When benzil (17) was subjected to
bismuth nitrate-catalyzed redox amination in either aceto-
nitrile or excess indoline as solvent-free in a sealed tube
at 120°C, a mixture of three unexpected separable product
(18–20) apart from indole (21) was obtained (Scheme 6).
We assume that all of products except for indole are second-
ary products, which are formed after secondary reactions of
17 under the given reaction conditions. The mechanism for
the formation of minor product 18 is shown in Scheme 7.
The first part of the mechanism is the formation of reductive
amination product 23 and indole by a hydride transfer from
indoline to iminium ion 22 resulting from condensation of
indoline and benzil. Later, the cyclization of N-alkyl indoline
23 to 4,5-diphenyl-1,2-dihydropyrrolo[3,2,1-hi]indole (18)
involves an internal Friedel-Crafts alkylation followed
by dehydration in the presence of bismuth nitrate. For
the unexpected formation of the other products in the
Bi(NO3)3·5H2O-catalyzed reaction of 1 and 17, we as-
sume that indole occurring during reductive alkylation
processes play an important role. The condensation of in-
dole with benzil probably goes through two different
channels, leading to C3-alkylation 20 and indolocarbazol
19, via the intermediate 25, as shown in Scheme 7. The
surprising intermediate 25, which can be trapped by vari-
ous nucleophiles, that is present in the reaction mixture.
The formation of C3-alkylation product 20 can be easily
envisioned with the intramolecular hydride transfer from
indoline to the intermediate 25. The trapping of 25 by
indole gives indolocarbazole 19 by a stepwise process
involving intermolecular Friedel-Crafts alkylation and de-
hydration to provide the aromatization. We assumed that
the driving force for the reaction is the formation of aza-
fulvenium ion 25, which can be more stabilized by the
carbonyl group than iminum ion 22. The 6,7-diphenyl-
5,12-dihydroindolo[3,2-a]carbazole (19) was also synthe-
sized by an independent experiment from the reaction of
indole with benzil under same conditions in 71% yield
Under the similar reaction conditions, acetylacetone (5)
readily underwent enamine formation and retro-aldol type
cleavage, probably through a six-membered cyclic mecha-
nism (Scheme 4, 5). When a mixture of indoline and 5 in
the presence of bismuth nitrate under solvent-free condi-
tion was heated in a sealed glass tube at 120°C for 1 h
1
and the resulting mixture was analyzed by H NMR, the
formation of the similar products was observed. Then the
reaction mixture was subjected to silica gel column chro-
matography to give only N-acetyl indoline 13. However,
this transformation was carried out in the presence of
SiO2 in MeCN:H2O (9:1). All attempts to obtain the prod-
ucts from the mixture were unsuccessful. Surprisingly, the
oxidation of the mixture with MnO2 or DDQ (2,3-dichloro-
5,6-dicyano-1,4-benzoquinone) also led to the formation of
N-acylated indoline instead of the expected mixture of the
corresponding indoline products (Scheme 4). Because of
the susceptibility of the double bond toward the moisture,
Scheme 2. Synthesis of 6 and 7.
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Condensation of indoline with some 1,2- and 1,3-diketones
Scheme 3. Proposed mechanism for formation of 6. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com].
(Scheme 6). One-pot method for the synthesis of
dihydroindolo[3,2-a]carbazole 19 in 62% yield by the
para-toluenesulfonic acid catalyzed condensation of indole
with benzil was previously described by Nair et al. [13]
Actually, we examined the reactions of indoline (1)
with 1,2-diketones such as 2,3-butanedione (28),
acenaphthenequinone (29), and isatin (1H-indole-2,3-
dione) (30) apart from benzil (17) under similar condi-
tions (Fig. 1). But we have not received positive results
from these diketones. The reaction of diketones 28 and
29 gave no isolable product, whereas no reaction was
observed with 30.
7 provided a separable mixture of unexpected secondary
products.
EXPERIMENTAL
3-(Indolin-1-yl)cyclohex-2-en-1-one (6): A mixture of
indoline (1; 500mg, 4.2mmol) in CH2Cl2 (10mL), cyclohex-
ane-1,3-dione (4; 471mg, 4.2mmol) and Bi(NO3)3·5H2O
(0.1 mmol) was stirred magnetically at rt for 12h. The reaction
was monitored by TLC. After the completion of the reaction,
the mixture was diluted with EtOAc (30mL) and washed
with water (3× 50mL), and organic phase was dried over
Na2SO4. 3-(Indolin-1-yl)cyclohex-2-en-1-one (6; 845 mg,
94%, orange solid, mp =81-82°C (hexane), eluent:
EtOAc/hexane (20%), Rf= 0.17 (254 nm)) was purified on
a silica gel column chromatograph with EtOAc/hexane.
3-(Indolin-1-yl)cyclohex-2-en-1-one (6) [14]. 1H NMR
(400 MHz, CDCl3): δ 7.22 (d, J=7.2Hz, =CH, 1H), 7.17-
7.12 (m, =CH, 2H), 6.95 (t, J=7.2Hz, =CH, 1H), 5.44 (s,
=CH, 1H), 3.91 (t, J=8.3Hz, CH2, 2H), 3.14 (t, J=8.3Hz,
CH2, 2H), 2.87 (t, J=6.3Hz, CH2, 2H), 2.41 (t, J=6.3Hz,
CH2, 2H), 2.10 (p, J=6.3Hz, CH2, 2H). 13C NMR
(100 MHz, CDCl3): δ 197.6, 161.0, 143.6, 133.6, 127.3,
125.7, 122.6, 114.4, 103.7, 51.2, 36.2, 28.8, 27.7, 23.1. IR
(KBr, cmÀ1) 2947, 1624, 1483, 1436, 1410, 1353, 1265,
1190, 750. Anal. Calcd. for C14H15NO: C, 78.84; H, 7.09;
N, 6.57, found: C, 78.82; H, 7.08; N, 6.53.
CONCLUSION
Finally, the redox amination potentials of indoline with
1,2- and 1,3-diketones in the presence of bismuth nitrate
catalyst were investigated, and these ketones exhibited
the different behaviors from both enolizable cyclic and
acyclic and benzylic monoketones. Cyclohexane-1,3-dione
(4) gave primarily enamine condensation product 6,
whereas acetylacetone (5) underwent an inseparable mix-
ture of enamine and retro-aldol-type cleavage products.
The enamine type product is sensitive to acid-induced
retro-aldol type cleavage to yield N-acetyl indoline as a
single product. The reaction of indoline with 1,2-diketone
Scheme 4. Reaction of indoline (1; 1 equiv.) with acetylacetone (5; 1 equiv.).
Journal of Heterocyclic Chemistry
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H. Kilic, O. Aydin, S. Bayindir, and N. Saracoglu
Vol 000
Scheme 5. Formation mechanism for 13A/B.
3-(1H-Indol-1-yl)cyclohex-2-en-1-one (7): To a solu-
tion of of 3-(indolin-1-yl)cyclohex-2-en-1-one (6; 500mg,
2.3mmol) in CH2Cl2 (10 mL) was added the active MnO2
(2.0 g, 23.0 mmol). The mixture was stirred at rt for 12h.
The reaction was monitored by TLC. After filtration, the mix-
ture was evaporated under reduced pressure, and the com-
pound 7 was purified by silica gel column chromatography
with EtOAc/hexane. 3-(1H-Indol-1-yl)cyclohex-2-en-1-one
(7) was obtained as red viscous liquid (475mg, 96%,
eluent: 20% EtOAc/hexane, Rf = 0.14 (254 nm)). 3-(1H-
was monitored by TLC. After the completion of the reac-
tion, the mixture was diluted with EtOAc (30mL) and
washed with water (3×30mL), and organic phase was dried
over Na2SO4. The crude product (907mg) was eluted on sil-
ica gel (25g) with EtOAc/hexane. 1-(Indolin-1-yl)ethan-1-
one (13A/B; ratio of rotamers: 85:15, 640mg, 94%, white
solid, mp=99-100°C (hexane), eluent: EtOAc/hexane
(15%), =0.35 (254nm)). 1-(Indolin-1-yl)ethan-1-one (13A/
B) [15–17]: 1H NMR (400MHz, CDCl3, mixture of
rotamers): δ 8.20 (d, J=7.7Hz, =CH, 1H), 7.24-7.09 (m,
=CH, 2H), 6.99 (t, J=7.7Hz, =CH, 1H), 4.15-4.08 (m,
CH2, 0.3H), 3.99 (t, J=8.4Hz, 1.7H), 3.15 (t, J=8.4Hz,
1.7H), 3.08-3.01 (m, CH2, 0.3H), 2.42 (s, CH3, 0.4H), 2.19
(s, CH3, 2.6H).13C NMR (100MHz, CDCl3, mixture of
rotamers): δ 168.9, 143.1, 131.3, 127.7, 127.5, 126.1,
124.8, 123.8, 123.3, 117.1, 114.3, 49.0, 48.2, 28.2, 27.0,
24.8, 24.4. IR (KBr, cmÀ1): 2964, 2948, 1652, 1598, 1483,
1463, 1403, 1341, 1321, 1295, 1032, 885, 805, 762, 745.
Anal. Calcd. for C10H11NO: C, 74.51; H, 6.88; N, 8.69,
found: C, 74.47; H, 6.84; N, 8.73.
1-(Indolin-1-yl)ethan-1-one (13A/B): Procedure B:
To a solution of (162 mg) of (Z or E)-4-(indolin-1-yl)
pent-3-en-2-one (12) and 1-(indolin-1-yl)ethan-1-one
(13A/B) in 20 mL MeCN:H2O (9:1) was added 50 mg of
column chromatography silica gel. After stirring for 12 h
at rt, the mixture was diluted with EtOAc (30 mL) and
washed with water (3 × 30 mL), and organic phase was
dried over Na2SO4. The crude product (150 mg) was
eluted on silica gel (25 g) with EtOAc/hexane (2:8) to
give 1-(indolin-1-yl)ethan-1-one (13A/B; 130 mg, 96%).
1
Indol-1-yl)cyclohex-2-en-1-one (7). H NMR (400 MHz,
CDCl3): δ 7.74 (d, J = 8.0 Hz, =CH, 1H), 7.63 (d,
J = 8.0 Hz, =CH, 1H), 7.33 (d, J = 2.8 Hz, =CH, 1H),
7.31-7.20 (m, =CH, 2H), 6.72 (d, J=2.8Hz, =CH, 1H), 6.41
(s, =CH, 1H), 2.97 (t, J=6.1, CH2, 2H), 2.55 (t, J=6.1,
CH2, 2H), 2.25 (p, J=6.1Hz, CH2, 2H). 13C NMR
(100MHz, CDCl3): δ 198.8, 156.3, 135.2, 131.0, 125.2,
123.7, 122.2, 121.7, 115.6, 113.4, 107.3, 36.8, 29.1, 22.3.
IR (KBr, cmÀ1) 2950, 1658, 1598, 1454, 1184, 1128, 744.
Anal. Calcd. for C14H13NO: C, 79.59; H, 6.20; N, 6.63, found:
C, 79.62; H, 6.24; N, 6.61.
1-(Indolin-1-yl)ethan-1-one (13A/B): Procedure A: A
mixture of indoline (1; 500mg, 4.2mmol), acetylacetone (5;
420mg, 4.2mmol) and Bi(NO3)3·5H2O (0.1mmol) in CH2Cl2
(10 mL) was stirred magnetically at rt for 2 h. The reaction
Scheme 6. Reaction of indoline (1; 1 equiv.) and indole (21) with benzil
(17; 1 equiv.).
1-(Indolin-1-yl)ethan-1-one (13A/B): Procedure C:
1-(Indolin-1-yl)ethan-1-one (13A/B) was obtained as white
solid (120mg, 87%) from the reaction of a mixture of (12
and 13A/B; 159mg) with MnO2 (677 mg, 8.0 mmol) in
CH2Cl2 at rt for 12h.
1-(Indolin-1-yl)ethan-1-one (13A/B): Procedure D:
1-(Indolin-1-yl)ethan-1-one (13A/B) was obtained as white
solid (129mg 95%) from the reaction of a mixture of (12
and 13A/B; 180 mg) with DDQ (190mg, 0.8 mmol) in
CH2Cl2 at rt for 12h.
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Condensation of indoline with some 1,2- and 1,3-diketones
Scheme 7. Formation mechanism for 18–20. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com].
Reaction of indoline (1) (1.0 equiv.) with benzil (17)
(1.0 equiv.): To a solution of indoline (1; 500mg,
4.2mmol) in MeCN (5mL) was added benzil (17; 882mg,
4.2mmol) and Bi(NO3)3·5H2O (0.1mmol). Reaction mixture
was stirred magnetically in a sealed tube at 120°C for 8h.
The reaction was monitored by TLC. After the completion
of the reaction, the mixture was diluted with ethylacetate
(30mL) and washed with water (2×50mL), and organic
phase was dried over Na2SO4. The crude product was pu-
rified by silica gel column chromatograph and isolated
compounds were given according to elution sequence
(EtOAc/hexane or hexane) in general.
2952, 2919, 2846, 1650, 1599, 1569, 1503, 1446, 1435,
1393, 1138, 1077, 1021, 915. Anal. Calcd. for C22H17N:
C, 89.46; H, 5.80; N, 4.74, found: C, 89.55; H, 5.74; N,
4.73. 6,7-Diphenyl-5,12-dihydroindolo[3,2-a]carbazole
(19) [13]. 552 mg, 40%, pale yellow solid (mp = 325-
326°C; hexane), eluent: EtOAc/hexane (15%), Rf = 0.52
1
(254 nm). H NMR (400 MHz, DMSO-d6): δ 11.85 (bs,
NH, 1H), 10.73 (bs, NH, 1H), 8.70 (d, J = 7.5 Hz, =CH,
1H), 7.60 (d, J = 7.7 Hz, =CH, 1H), 7.57 (d, J = 8.1 Hz,
=CH, 1H), 7.39-7.19 (m, =CH, 13H), 6.79 (ddd, J = 8.1,
7.2, 1.0 Hz, =CH, 1H), 6.52 (d, J = 7.9 Hz, =CH, 1H).
13C NMR (100 MHz, DMSO-d6): δ 140.7, 140.4, 140.0,
138.5, 138.1, 133.9, 133.5, 131.8, 131.0, 128.8, 128.6,
127.5, 127.1, 124.8, 124.3, 123.8, 122.1, 121.7, 120.8,
119.5, 119.1, 117.9, 114.2, 112.2, 111.6, 106.2. IR
(KBr, cmÀ1): 3451, 3400, 3055, 3022, 1947, 1908,
1709, 1638, 1611, 1599, 1567, 1509, 1488, 1462, 1437,
1390, 1372, 1326, 1311, 1269, 1255, 1153, 1134, 1084,
1069, 1022, 1000, 961, 916, 868, 843, 820. Anal. Calcd.
for C30H20N2: C, 88.21; H, 4.93; N, 6.86, found: C,
88.35; H, 5.04; N, 6.79. 2-(1H-Indol-3-yl)-1,2-
diphenylethan-1-one (20) [19]. 315 mg, 23%, brown vis-
cous liquid, eluent: EtOAc/hexane (15%), Rf = 0.26
4,5-Diphenyl-1,2-dihydropyrrolo[3,2,1-hi]indole (18)
[18]. 52mg, 4%, white solid (mp= 211-212°C, hexane), el-
1
uent: EtOAc/hexane (15%), Rf = 0.82, (254 nm). H NMR
(400 MHz, CDCl3): δ 7.48 (d, J = 7.9 Hz, =CH, 1H),
7.46-7.43 (m, =CH, 3H), 7.37-7.29 (m, =CH, 6H), 7.20
(ddd, J =8.3, 2.2, 1.0 Hz, =CH, 1H), 7.09-7.05 (m, =CH,
1H), 6.98 (d, J =6.7 Hz, =CH, 1H), 4.57 (t, J= 7.0 Hz,
CH2, 2H), 3.81 (t, J = 7.0 Hz, CH2, 2H). 13C NMR
(100 MHz, CDCl3): δ 148.3, 136.7, 135.5, 133.0, 129.4,
129.3, 128.8, 128.6, 127.7, 125.7, 124.9, 122.7, 120.3,
118.0, 117.4, 115.9, 50.1, 33.8. IR (KBr, cmÀ1): 3054,
1
(254 nm). H NMR (400 MHz, CDCl3): δ 8.23 (bs, NH,
1H), 8.10 (d, J = 7.4 Hz, =CH, 2H), 7.55-7.52 (m, =CH,
2H), 7.45-7.39 (m, =CH, 2H), 7.35-7.31 (m, =CH, 2H),
7.27 (t, J = 7.5 Hz, =CH, 2H), 7.20 (t, J = 7.5 Hz, =CH,
2H), 7.12 (t, J = 7.5 Hz, =CH, 2H), 6.90 (d, J = 2.8 Hz,
=CH, 1H), 6.32 (s, =CH, 1H). 13C NMR (100 MHz,
CDCl3): δ 198.9, 139.2, 137.1, 136.7, 133.3, 129.3,
129.2, 128.9, 128.8, 127.4, 126.8, 124.2, 122.6, 120.0,
119.0, 114.4, 111.7, 51.0. IR (KBr, cmÀ1): 3410, 3059,
Figure 1. Examined other 1,2-diketones 28–30.
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H. Kilic, O. Aydin, S. Bayindir, and N. Saracoglu
Vol 000
2920, 1811, 1768, 1681, 1619, 1596, 1579, 1495, 1457,
1448, 1420, 1339, 1287, 1265, 1221, 1126, 1098, 1054,
1030, 1001, 931, 858, 801. Anal. Calcd. for C22H17NO: C,
84.86; H, 5.50; N, 4.50, found: C, 84.72; H, 5.55; N, 4.48.
Indole (21): 238mg (17%), eluent: 20% EtOAc/hexane,
Rf=0.26 (254nm).
Acknowledgments. We are greatly indebted to The Scientific and
Technical Research Council of Turkey (TUBITAK, Grant no.
TBAG-112T600) for their financial support of this study.
REFERENCES AND NOTES
Reaction of indoline (1) (5.0 equiv.) with benzil (17)
(1.0 equiv.): A mixture of indoline (1; 1.5 g, 12.6mmol),
benzil (17; 529 mg, 2.5 mmol) and Bi(NO3)3·5H2O
(0.1 mmol) was stirred magnetically in a sealed tube at
120°C for 2 h under solvent-free condition. The reaction
was monitored by TLC. After the completion of the
reaction, the mixture was diluted with ethylacetate
(30 mL) and washed with water (2 × 50 mL), and organic
phase was dried over Na2SO4. The crude product was
purified by silica gel column chromatograph, and isolated
compounds were given according to elution sequence
(EtOAc/Hexane or hexane) in general. 4,5-Diphenyl-
1,2-dihydropyrrolo[3,2,1-hi]indole (18). 48 mg, 4%.
6,7-Diphenyl-5,12-dihydroindolo[3,2-a]carbazole (19):
632 mg, 56%. 2-(1H-Indol-3-yl)-1,2-diphenylethan-1-
one (20). 95 mg (8%), eluent: 15% EtOAc/hexane.
Indole (21). 282 mg, 25%. Indoline (1). 865 mg
(7.4 mmol) was recovered.
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6,7-Diphenyl-5,12-dihydroindolo[3,2-a]carbazole (19):
Bi(NO3)3·5H2O (0.1 mmol)-catalyzed reaction of indole (21;
500mg, 4.3 mmol) with benzil (17; 898mg, 4.3 mmol) was
performed at 120°C for 12h in MeCN. 6,7-Diphenyl-5,12-
dihydroindolo[3,2-a]carbazole (19; 1.23g, 71%) was
purified on a silica gel column chromatograph with
EtOAc/hexane (15%).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet