AlCl3/PCC-SiO2-promoted oxidation of azaindoles and indoles

Article abstract of DOI:10.1080/00397911.2011.584008

A simple and efficient method is described for the oxidation of 7-azaindoles and indoles to 7-azaisatins and isatins using pyridinium chlorochromate-silica gel (PCC-SiO₂) with the aid of Lewis acid catalyst aluminium chloride (AlCl₃) in dichloroethane. Simplicity of the reaction conditions, easy workup procedure, and good yields are the key features of this protocol.

Full text of DOI:10.1080/00397911.2011.584008

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AlCl3/PCC-SiO2-Promoted Oxidation of
Azaindoles and Indoles
Rekulapally Sriram a b , Chebolu Naga Sesha Sai Pavan Kumar a
,
Nerella Raghunandan b , Vadla Ramesh a , Manda Sarangapani b
Vaidya Jayathirtha Rao a
&
a Organic Chemistry Division II, Indian Institute of Chemical
Technology, Tarnaka, Hyderabad, India
b University College of Pharmaceutical Sciences, Kakatiya University,
Warangal, India
Accepted author version posted online: 11 Nov 2011.Version of
record first published: 02 Aug 2012.
To cite this article: Rekulapally Sriram , Chebolu Naga Sesha Sai Pavan Kumar , Nerella Raghunandan ,
Vadla Ramesh , Manda Sarangapani & Vaidya Jayathirtha Rao (2012): AlCl3/PCC-SiO2-Promoted
Oxidation of Azaindoles and Indoles, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 42:23, 3419-3428
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Synthetic Communications1, 42: 3419–3428, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.584008
AlCl3/PCC-SiO2-PROMOTED OXIDATION OF
AZAINDOLES AND INDOLES
Rekulapally Sriram,1,2 Chebolu Naga Sesha Sai Pavan
Kumar,1 Nerella Raghunandan,2 Vadla Ramesh,1
Manda Sarangapani,2 and Vaidya Jayathirtha Rao1
1Organic Chemistry Division II, Indian Institute of Chemical Technology,
Tarnaka, Hyderabad, India
2University College of Pharmaceutical Sciences, Kakatiya University,
Warangal, India
GRAPHICAL ABSTRACT
Abstract A simple and efficient method is described for the oxidation of 7-azaindoles and
indoles to 7-azaisatins and isatins using pyridinium chlorochromate–silica gel (PCC-SiO2)
with the aid of Lewis acid catalyst aluminium chloride (AlCl3) in dichloroethane.
Simplicity of the reaction conditions, easy workup procedure, and good yields are the
key features of this protocol.
Keywords Aluminium chloride (AlCl3); azaindoles; azaisatins; indoles; isatins; oxidation;
pyridinium chlorochromate (PCC)
INTRODUCTION
Isatins and its derivatives display diverse biological properties, including
antimalarial,[1] anticancer,[2] anticonvulsant,[3] anti-inflammatory,[4] antiviral,[5] and
antineoplastic[6] activities. In recent years, 7-azaisatins have received considerable
interest in view of their potential relationship to pharmacologically important
indoles and the purine nucleus and also because of their interesting biological
activities. In contrast to isatins, only a few 7-azaisatins are known (viz., 7-azaisatin,
5-bromo-7-azaisatin, and N-alkyl-7-azaisatins).[7] Various 7-azaisatins are synthesized
Received March 31, 2011.
Address correspondence to Manda Sarangapani, University College of Pharmaceutical
Sciences, Kakatiya University, Warangal 506001, India, or Vaidya Jayathirtha Rao, Organic Chemistry
Division II, Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500607, India. E-mail:
sarangapanimanda@gmail.com; jrao@iict.res.in
3419

3420
R. SRIRAM ET AL.
for the development of pharmaceuticals such as 7-azaindirubin-3-oxime[8] and
3-arylidene-7-azaoxindoles (Figure 1).[9] The first one showed significant antiproli-
ferative activity against 57 cancer cell lines and also inhibitory activity against a series
of kinases,[8] and the other one exhibited TrkA kinase inhibitory activity in pancreatic
ductal adenocarcinoma.[9]
RESULTS AND DISCUSSION
On the basis of the activity of isatin and its derivatives, we envisaged the
synthesis of new 7-azaisatins and their derivatives bearing a heterocyclic nitrogen
atom at position 7. Kagi first synthesized 7-azaisatin from 7-azaoxindole with
nitrous acid and subsequent hydrolysis of the intermediate oxime.[10] Another route
for the preparation of 7-azaisatin from 7-azaindole in five steps was reported by
Parrick et al.[11] in 1989. Marfat and Carta[12] reported the synthesis of 7-azaoxin-
doles by the oxidation of indoles with pyridinium bromide perbromide. 5-Bromo-7-
azaisatin, an intermediate of 5-bromo-7-azaoxindole derivative, which was the first
nonpeptide antagonist of bombesin, was synthesized by oxidation of 7-azaindole
with CrO3 as oxidant in the presence of bromine.[13] Tatsugi et al.[14] reported a
one-pot synthesis of 1-alkyl-7-azaisatins via 1-alkyl-7-azaindoles using
N-bromosuccinimide (NBS) in dimethylsulfoxide (DMSO) solvent. Yadav et al.[15]
used an IBX-InCl3 combination for the oxidation of azaindole to azaisatin, but
much importance was given to indoles rather than azaindoles. Unfortunately, many
Table 1. Oxidation of 7-azaindole (0.1 mol) to 7-azaisatin with PCC-SiO2
using different acid catalysts
S. no.
Catalysta
Time (h)
Isolated yield (%)
1
2
3
4
5
AlCl3
BF3
3
4
76
45
FeCl3
lnCl3
CeCl3
7
30
20
10
12
Trace
aCatalyst 1.3 mol%.
Scheme 1. Oxidation of 7-azaindole to 7-azaisatin with PCC-SiO2 and AlCl3.

OXIDATION OF AZAINDOLES AND INDOLES
3421
Table 2. Oxidation of 7-azaindoles and indoles using PCC-SiO2 and AlCl3
S. no.
Substrate
Product
Time (h)
Isolated yield (%)
1
3
76
2
2.5
80
3
4
2.5
80
81
2
5
6
2
83
83
1.5
7
8
1
1
84
85
(Continued )

3422
R. SRIRAM ET AL.
Table 2. Continued
S. no.
Substrate
Product
Time (h)
Isolated yield (%)
9
0.5
87
10
1.5
83
11
12
1.5
88
84
2
13
14
15
2.5
2.5
2
85
85
81
of these methods suffer from limitations such as harsh reaction conditions, poor to
moderate yields, long reaction times, tedious workup procedures and co-occurrence
of several side products. Zong et al.[16] recently reported all the attempts to prepare
7-azaisatin by the oxidation of commercially available 7-azaindole under a variety of
conditions were unsuccessful. All the attempts have taken into consideration, and we
developed a convenient method for the efficient oxidation of 7-azaindoles.
Herein, we report for the first time pyridium chlorochromate (PCC)–SiO2 as
oxidizing agent for the oxidation of various 7-azaindoles to 7-azaisatins. To enhance
the yield and shorten the reaction times, we have catalyzed the reaction with AlCl3 as

OXIDATION OF AZAINDOLES AND INDOLES
3423
Figure 1. Biologically important azaisatin derivatives.
a Lewis acid catalyst. PCC is milder and less acidic and promotes fewer side
reactions that are due to overoxidation. PCC is easier to prepare, shelf stable, and
more efficient, but PCC oxidations are characterized by the formation of tarry
reduced chromium by-products, which will entrain the desired products and compli-
cate the purification procedure. In PCC-SiO2-promoted oxidation, the chromium
by-products obtained are adsorbed on the silica gel, forming a microgranular solid
that can be easily removed by filtration. PCC-SiO2 is a well-known oxidizing agent
for the oxidation of alcohols to aldehydes or ketones with high efficiency.[17]
Recently, our group reported polyaniline catalyst (PANI)=PCC combination
for the oxidation of indoles to isatins.[18] Presently we need azaisatins for the prep-
aration and bioevaluation studies of new heterocylces. In continuation of our
research work, in this study we have used PCC–silica gel with AlCl3 combination
for the synthesis of various 7-azaisatins from 7-azaindoles in an efficient manner.
We have effectively utilized this protocol not only for the milligram level but also
on a gram-scale level for the preparation of 7-azaisatins, which was difficult in all
other procedures. To evaluate the efficiency of the method, oxidation of 7-azaindole
was carried out with PCC-SiO2 using different acid catalysts BF3, FeCl3, InCl3,
CeCl3, and AlCl3 at 80 ꢀC in dichloroethane (DCE). Greater yield and short reaction
times were obtained with the use of AlCl3 as the catalyst compared to other catalysts
(Table 1).
To determine the versatility of the PCC-SiO2 and AlCl3 system, 7-azaindole
(0.1 mol) and N-alkylated-7-azaindoles[14] (0.1 mol) (prepared from alkylation with
different alkyl halides using sodium hydride in THF) were subjected to oxidation
by PCC (0.25 mol)–SiO2 with AlCl3(15 wt%=1.3 mol% with respect to the indole
derivative) in dichloroethane (DCE) at 80 ꢀC, and the reactions occurred smoothly
without formation of any side products (Scheme 1). We observed that as the alkyl
chain increases, the yield of the product increases (Table 2). To study the scope of
the method, the reaction was extended to oxidation of simple indoles. Indoles and
its derivatives (1k–1o) underwent smooth oxidation to their corresponding isatins
(2k–2o) in excellent yields (Table 2), comparable to the PANI=PCC procedure.
CONCLUSION
In conclusion, we have described an efficient protocol for the preparation of
7-azaisatins by the oxidation of 7-azaindoles using PCC-SiO2 catalyzed by AlCl3
for the first time. The advantages of the PCC-SiO2 and AlCl3 system are greater

3424
R. SRIRAM ET AL.
efficiency, low cost, versatility, gram-level preparative scale, and simple workup
procedure. Application of this strategy to the preparation of 7-azaisatins and its
derivatives toward investigation for biological activity is currently being pursued.
EXPERIMENTAL
All the chemicals used were of reagent grade and obtained from local suppliers,
Aldrich, and Fluka. PCC was freshly prepared from chromium trioxide according to
the earlier reported procedure.[19] All reactions were performed in oven-dried glass-
ware under an inert atmosphere. Analytical thin-layer chromatography (TLC) was
performed on silica-gel plates, and TLC visualization was carried out with ultraviolet
(UV) light. Melting points were determined on a Mettlers-Temp instrument and are
uncorrected. Infrared (IR) spectra were recorded using a Perkin-Elmer-1600 Fourier
1
transform (FT)–IR spectrometer; n in cmꢁ1. H and 13C NMR spectra [CDCl3=
dimethylsulfoxide (DMSO-d6)] were recorded with Gemini-200 and Bruker-Avance-
300 instruments; chemical shifts d are in parts per million (ppm) relative to SiMe4 as
an internal standard, and couplings are in hertz (Hz). High-resolution mass spec-
trometry (HRMS, ESI) data were recorded on a QSTAR XL high-resolution mass
spectrometer in m=z (rel. %).
General Experimental Procedure for the Preparation of
Compounds 2a–2o
PCC (53.7 g, 0.25 mol) was ground with silica gel (53.7 g, 70–230 mesh) and
transferred to a 1-L round-bottom flask containing DCE (400 mL). To the resulting
orange suspension was added a solution of N-butyl-7-azaindole (17.4 g, 0.1 mol) in
DCE (50 mL) while stirring at room temperature. To this, AlCl3 (15 wt%=1.3 mol%
with respect to the N-butyl-7-azaindole) was added, and the reaction mixture was stir-
red at 80 ꢀC. Completion of the reaction was monitored by TLC. After completion of
the reaction, the solvent was removed under reduced pressure and the black solid was
diluted with 500 ml of n-hexane–ethyl acetate (4:1) and filtered under suction through
a sintered funnel layered with silica gel (5 cm, 70–230 mesh). The filtrate was evapo-
rated to furnish N-butyl-7-azaisatin as yellow solid (16.93 g, 83%). A similar procedure
was adopted for the preparation of other isatins, and the authenticity of the products
was confirmed by 1H NMR, 13C NMR, IR, mass, and HRMS spectral data.[18,20]
Spectral Data of Synthesized Compounds
1H-Pyrrolo[2,3-b]pyridine-2,3-dione (2a)[10]. Yellow solid; yield 76%; mp
1
168–170. H NMR (300 MHz, CDCl3): d 11.61 (s, 1H), 8.38 (d, 1H, J ¼ 4.5 Hz),
7.86 (d, 1H, J ¼ 7.1 Hz), 7.10 (t, 1H, J ¼ 5.2 Hz). 13C NMR (75 MHz, CDCl3):
182.9, 163.9, 159.9, 155.2, 132.5, 118.9, 112.8. IR (KBr): 3291, 1743, 1604, 1592,
1458. ESI-MS: m=z 171 [M þ Na]þ. HRMS calcd. for C7H4N2O2Na 171.0168; found
171.0170.
1-Methyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2b)[14]. Yellow solid; yield
1
80%; mp 160–161. H NMR (300 MHz, CDCl3): d 8.42 (d, 1H, J ¼ 4.5 Hz), 7.79

OXIDATION OF AZAINDOLES AND INDOLES
3425
(d, 1H, J ¼ 6.7 Hz), 7.06 (t, 1H, J ¼ 6.7 Hz), 3.33 (s, 3H). 13C NMR (75 MHz,
CDCl3): 181.9, 163.8, 158.3, 155.8, 132.8, 119.6, 112.0, 25.0. IR (KBr): 1750, 1607,
1594, 1458. ESI-MS: m=z 163 [M þ H]þ. HRMS calcd. for C8H6N2O2 162.0428;
found 162.049.
1-Ethyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2c)[14]. Yellow solid; yield
1
80%; mp 127–128. H NMR (300 MHz, CDCl3): d 8.40 (d, 1H, J ¼ 5.8 Hz), 7.79
(d, 1H, J ¼ 6.6 Hz), 7.07 (t, 1H, J ¼ 5.8 Hz), 3.89 (dd, 2H, J ¼ 7.5, 6.7 Hz), 1.35 (t,
3H, J ¼ 7.5 Hz). 13C NMR (75 MHz, CDCl3): 182.1, 163.6, 157.9, 155.6, 132.8,
119.4, 112.0, 34.1, 12.8. IR (KBr): 1742, 1607, 1593, 1358. ESI-MS: m=z 176
[M þ H]þ. HRMS calcd. for C9H8N2O2 176.0585; found 176.0561.
1-Isopropyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2d). Yellow solid; yield
1
81%; mp 152–154. H NMR (300 MHz, CDCl3): d 8.39 (d, 1H, J ¼ 5.2 Hz), 7.79
(d, 1H, J ¼ 4.5 Hz), 7.02 (t, 1H, J ¼ 4.5 Hz), 4.66–4.78 (m, 1H), 1.52–1.56 (m, 6H).
13C NMR (75 MHz, CDCl3): 182.3, 163.2, 158.1, 154.3, 132.2, 118.7, 112.5, 43.1,
18.9. IR (KBr): 1742, 1603, 1592, 1443. ESI-MS: m=z 191 [M þ H]þ. HRMS calcd.
for C10H11N2O2 191.0816; found 191.0820.
1-Butyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2e). Yellow solid; yield 83%;
1
mp 104–105. H NMR (300 MHz, CDCl3): d 8.41 (d, 1H, J ¼ 7.1 Hz), 7.78 (d, 1H,
J ¼ 6.6 Hz), 7.05 (t, 1H, J ¼ 6.7 Hz), 3.82 (t, 2H, J ¼ 6.4 Hz), 1.73 (dd, 2H, J ¼ 7.9,
6.7 Hz), 1.43 (dd, 2H, J ¼ 7.1, 6.6 Hz), 0.99 (t, 3H, J ¼ 6.4 Hz). 13C NMR (75 MHz,
CDCl3): 181.8, 163.0, 158.6, 154.6, 132.2, 119.1, 112.6, 38.0, 29.0, 19.4, 13.4. IR
(KBr): 1743, 1621, 1590, 1489. ESI-MS: m=z 227 [M þ Na]þ. HRMS calcd. for
C7H4N2O2Na 227.0789; found 227.0796.
1-Hexyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2f). Yellow solid; yield 83%;
1
mp 102–104. H NMR (300 MHz, CDCl3): d 8.40 (d, 1H, J ¼ 6.7 Hz), 7.78 (d, 1H,
J ¼ 5.2 Hz), 7.04 (t, 1H, J ¼ 5.2 Hz), 3.81 (t, 2H, J ¼ 7.5 Hz), 1.73 (dd, 2H, J ¼ 7.5,
6.7 Hz), 1.31–1.41 (m, 6H), 0.89 (t, 3H, J ¼ 6.7 Hz). 13C NMR (75 MHz, CDCl3):
181.9, 163.0, 158.6, 154.6, 132.3, 119.1, 112.6, 38.4, 30.8, 26.9, 25.8, 21.9, 13.8. IR
(KBr): 1745, 1619, 1589, 1483. ESI-MS: 233 [M þ H]þ. HRMS calcd. for
C13H17N2O2 233.1293; found 233.1290.
1-Heptyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2g). Orange solid; yield
1
84%; mp 95–97. H NMR (300 MHz, CDCl3): d 8.41 (d, 1H, J ¼ 5.2 Hz), 7.76 (d,
1H, J ¼ 6.7 Hz), 7.03 (t, 1H, J ¼ 5.2 Hz), 3.81 (t, 2H, J ¼ 7.5 Hz), 1.72 (dd, 2H,
J ¼ 7.5, 6.7 Hz), 1.29–1.42 (m, 8H), 0.88 (t, 3H, J ¼ 6.7 Hz). 13C NMR (75 MHz,
CDCl3): 181.4, 163.0, 158.5, 154.6, 132.1, 119.1, 112.6, 38.3, 31.3, 28.8, 26.9, 26.2,
22.0, 13.9. IR (KBr): 1742, 1619, 1589, 1483. ESI-MS: 247 [M þ H]þ. HRMS calcd.
for C14H18N2O2 247.1510; found 247.1504.
1-Octyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2h). Yellow solid; yield 85%;
1
mp 87–88. H NMR (300 MHz, CDCl3): d 8.39 (d, 1H, J ¼ 5.2 Hz), 7.79 (d, 1H,
J ¼ 6.7 Hz), 7.03 (t, 1H, J ¼ 5.2 Hz), 3.81 (t, 2H, J ¼ 7.5 Hz), 1.73 (dd, 2H, J ¼ 7.5,
6.7 Hz), 1.26–1.37 (m, 10H), 0.88 (t, 3H, J ¼ 6.7 Hz). 13C NMR (75 MHz, CDCl3):
181.8, 163.0, 158.6, 154.6, 132.2, 119.1, 112.6, 38.3, 37.8, 31.1, 28.5, 26.9, 26.2,
22.0, 13.8. IR (KBr): 1741, 1609, 1591, 1451. ESI-MS: 261 [M þ H]þ. HRMS calcd.
for C15H21N2O2 261.1610; found 261.1603.

3426
R. SRIRAM ET AL.
1-Decyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2i). Yellow solid; yield 87%;
1
mp 88–90. H NMR (300 MHz, CDCl3): d 8.39 (d, 1H, J ¼ 5.2 Hz), 7.78 (d, 1H,
J ¼ 6.7 Hz), 7.03 (t, 1H, J ¼ 5.2 Hz), 3.81 (t, 2H, J ¼ 7.5 Hz), 1.73 (dd, 2H,
J ¼ 7.5 Hz), 1.25–1.38 (m, 14H), 0.88 (t, 3H, J ¼ 6.7 Hz). 13C NMR (75 MHz,
CDCl3): 181.8, 163.0, 158.6, 154.6, 132.2, 119.1, 112.6, 38.3, 31.2, 28.8, 28.6, 26.9,
26.2, 22.0, 13.9. IR (KBr): 1744, 1609, 1598, 1449. ESI-MS: 289 [M þ H]þ. HRMS
calcd. for C17H25N2O2 289.1929; found 289.1916.
1-Benzyl-1H-pyrrolo[2,3-b]pyridine-2,3-dione (2j)[14]. Yellow solid; yield
1
83%; mp 187–189. H NMR (300 MHz, CDCl3): d 8.41 (d, 1H, J ¼ 5.2 Hz), 7.77
(d, 1H, J ¼ 7.7 Hz), 7.46 (d, 2H, J ¼ 6.9 Hz), 7.27–7.31 (m, 3H), 7.04 (dd, 1H,
J ¼ 5.2, 1.8 Hz), 4.98 (s, 2H). 13C NMR (75 MHz, CDCl3): 181.8, 163.5, 158.1,
155.7, 135.4, 132.9, 128.8, 128.7, 128.1, 119.6, 112.1, 42.7. IR (KBr): 1742, 1603,
1592, 1443. ESI-MS: 239 [M þ H]þ. HRMS calcd. for C14H11N2O2 239.0865; found
239.0820.
1H-Indole-2,3-dione (2k)[18]. Orange-red solid; yield 88%; mp 192–194.
1H NMR (300 MHz, CDCl3 þ DMSO-d6): d 10.92 (s, 1H), 7.42–7.53 (m, 2H), 7.05
(t, 1H, J ¼ 8.1 Hz), 6.90 (d, 1H, J ¼ 8.1 Hz). IR (KBr): 2923, 2855, 1732, 1608,
1462, 1343, 1081, 1002, 857. GC-MS: (m=z) 147 [Mþ].
5-Chloroindoline2,3-dione (2l)[18]. Yellow-brownish solid; yield 84%; mp
249–251. 1H NMR (300 MHz, CDCl3 þ DMSO-d6): d 11.02 (s, 1H), 7.55–7.48
(m, 2H), 6.95 (d, 1H, J ¼ 9.1 Hz). GC-MS: (m=z) 181 [Mþ].
1-Butyl-5-chloroindoline-2,3-dione (2m)[18]. Orange solid; yield 85%; mp
62–63. 1H NMR (300 MHz, CDCl3): d 7.49 (m, 2H, J ¼ 8.0 Hz), 6.80 (d, 1H,
J ¼ 8.0 Hz), 3.7 (t, 2H, J ¼ 7.3 Hz), 1.67 (q, 2H, J ¼ 7.3 Hz), 1.43 (m, 2H, J ¼ 7.3 Hz),
), 0.98 (t, 3H, J ¼ 7.3 Hz). 13C NMR (75 MHz, CDCl3): 182.5, 157.6, 149.4, 137.5,
129.3, 125.1, 118.3, 111.8, 40.07, 29.08, 20.0, 13.5. IR (KBr): 3089, 2953, 1737,
1606, 1448, 1339, 1185, 1116, 844, 720. ESI-MS: 238 [M þ Hþ]. HRMS calcd. for
C12H13NClO2 238.0634; found 238.0630.
5-Nitroindoline-2,3-dione (2n)[18]. Pale-yellow solid; yield 85%; mp 251–
253. 1H NMR (300 MHz, CDCl3 þ DMSO-d6): d 11.65 (s, 1H), 8.58 (dd, 1H,
J ¼ 8.8, 2.2 Hz), 8.38 (d, 1H, J ¼ 2.2 Hz), 7.10 (d, 1H, J ¼ 8.8 Hz). GC-MS: (m=z)
192 [Mþ].
1-Methyl-5-nitroindoline-2,3-dione (2o)[18]. Yellowish-orange solid; yield
1
81%; mp 203–204. H NMR (300 MHz, CDCl3): d 8.47 (dd, 1H, J ¼ 8.8, 2.9 Hz),
8.34 (d, 1H, J ¼ 2.9 Hz), 7.06 (d, 1H, J ¼ 8.8 Hz), 3.29 (s, 3H). 13C NMR (75 MHz,
CDCl3): 182.1, 157.3, 150.3, 140.5, 128.0, 118.3, 116.7, 111.5, 26.2. IR (KBr): 2924,
1743, 1610, 1465, 1331, 1289, 1109, 1074, 845, 747, 710, 600. GC-MS: m=z 206
[Mþ]. Anal. calc. for C9H6N2O4; C, 52.44; H, 2.93; N, 13.59; Found: C, 52.40; H,
2.78; N, 13.42.
ACKNOWLEDGMENTS
The authors at the Indian Institute of Chemical Technology (IICT) thank the
director, IICT, and the head of the Division Organic II for encouragement. The

OXIDATION OF AZAINDOLES AND INDOLES
3427
authors at Kakatiya University (KU) thank the dean and BOS of the University Col-
lege of Pharmaceutical Sciences, Kakatiya University. C. H. N. S. S. P. and V. R.
thank the council of Scientific and Industrial Research and the University Grants
Commission, New Delhi, and R. S. thanks the Department of Science and Technology
(Inspire), New Delhi, for fellowships. This is main laboratory project work of IICT.
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