Study of the reactions of four indolic 1-azadienes with a few enoic, ynoic, and azo dienophiles

Article abstract of DOI:10.1081/SCC-120005999

Four indolic 1-azadienes (1a-c, 2) underwent Diels-Alder reaction, dienophile-catalysed addition-elimination reaction, Michael reaction or hydrolysis with three enoic, two ynoic and one azo dienophiles, leading to a γ-carboline, various 3-cyanoindoles, 3-formylindole and several nitrones.

Full text of DOI:10.1081/SCC-120005999

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STUDY OF THE REACTIONS OF FOUR INDOLIC 1-
AZADIENES WITH A FEW ENOIC, YNOIC, AND AZO
DIENOPHILES
Manas Chakrabarty a , Sandipan Sarkar a , Shampa Khasnobis b , Yoshiihiro Harigaya c , Noriko
Sato c & Shiho Arima c
a Department of Chemistry, Bose Institute, 93/1, A.P.C. Road, Calcutta, 700 009, India
b Acharya J.C. Bose College, Calcutta, 700 020, India
c School of Pharmaceutical Sciences, Kitasato University, Minato-ku, Tokyo, 108, Japan
Version of record first published: 16 Aug 2006.
To cite this article: Manas Chakrabarty , Sandipan Sarkar , Shampa Khasnobis , Yoshiihiro Harigaya , Noriko Sato & Shiho
Arima (2002): STUDY OF THE REACTIONS OF FOUR INDOLIC 1-AZADIENES WITH A FEW ENOIC, YNOIC, AND AZO DIENOPHILES,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 32:15,
2295-2306
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 15, pp. 2295–2306, 2002
STUDY OF THE REACTIONS OF FOUR
INDOLIC 1-AZADIENES WITH A FEW
ENOIC, YNOIC, AND AZO DIENOPHILES
Manas Chakrabarty,1, Sandipan Sarkar,1
*
Shampa Khasnobis,2 Yoshihiro Harigaya,3
3
Noriko Sato,3 andShiho Arima
1Department of Chemistry, Bose Institute,
93/1, A.P.C. Road, Calcutta-700 009, India
2Acharya J.C. Bose College, Calcutta-700 020, India
3School of Pharmaceutical Sciences,
Kitasato University, Minato-ku, Tokyo 108, Japan
ABSTRACT
Four indolic 1-azadienes (1a–c, 2) underwent Diels–Alder
reaction, dienophile-catalysed addition–elimination reaction,
Michael reaction or hydrolysis with three enoic, two ynoic
and one azo dienophiles, leading to a g-carboline, various
3-cyanoindoles, 3-formylindole and several nitrones.
Key Words: 1-Azadienes; Hetero D.-A. reaction; g-
Carboline; Nitrones
Hetero Diels–Alder reactions constitute a powerful tool for the con-
struction of six-membered heterocycles.[1,2] Of the various dienes used, aza-
dienes represent a significant class. Of the two possible types of 1-azadienes,
*Corresponding author. E-mail: manas@boseinst.ac.in
2295
DOI: 10.1081/SCC-120005999
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2296
CHAKRABARTY ET AL.
Figure 1.
1-aza-1,3-dienes, although usually considered as poor 4ꢀ-components, have
been studied extensively and reviewed recently.[3] We were interested in the
D.–A. reactions of 1-azadienes in which the C¼C bond is a part of a hetero-
arene. Despite an early success,[4] several subsequent attempts towards the
D.–A. reactions of azadienes of this type were thwarted.[5–8] Later, however,
Kusurkar and we were the first to accomplish the [4ꢀ þ 2ꢀ] cycloaddition of
furfuraldoxime[9] and the N,N-dimethylhydrazone (NNDMH) of 1-ethoxy-
carbonylindole-3-carboxaldehyde (1a)[10] (Figure 1), respectively.
In continuation of our interest, we wanted to study the reaction of 1a,
its N-benzoyl analogue 1b, the parent unacylated NNDMH 1c and indole-
3-carboxaldehyde oxime (2) with a few enoic, ynoic and azo dienophiles.
FMO considerations, based on ꢀ-VE-SCF-MO calculations[11] on the
1-methoxycarbonyl analogue of 1a, predicted that (i) the azadiene system
is nearly co-planar, (ii) its EHOMO is sufficiently high to permit a normal
electron-demand D.–A. reaction with conventional electron-deficient dieno-
philes, and (iii) the very high ꢀ-electron density and the resulting highest
nucleophilicity at the dimethylamino nitrogen may trigger dienophile-
catalysed addition-elimination reactions, leading to nitriles. Although
FMO calculations were not carried out on 2, the reported previous success
with furfuraldoxime[9] induced us to use this azadiene as well. Accordingly,
the targeted reactions were carried out and the results have been briefly
presented in this communication.
We had earlier achieved the cycloaddition of 1a with N-methylmale-
imide (NMM), furnishing the g-carboline 3a (3b, R¼CO2Et).[10] When 1b
was similarly refluxed with NMM in xylene containing catalytic amount of
para-toluene sulphonic acid (PTS), the new annulated g-carboline 3b was
formed in low yield (Scheme 1). In all likelihood, a [4ꢀ þ 2ꢀ] cycloaddition,
followed by elimination of dimethylamine and dehydrogenation, resulted in
3b. Since no reaction took place in absence of PTS, the latter may be
considered as promoting both D.-A. reaction and elimination. The known
tendency of cyclic enamines to undergo decomposition and the thermal
instability of 3b are largely responsible for the observed low yield.
When 1a was similarly treated with diethyl azodicarboxylate (DEAZD)
without the use of any catalyst (Scheme 2), almost equal amounts of the

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FOUR INDOLIC 1-AZADIENES
2297
Scheme 1.
Scheme 2.
Scheme 3.
corresponding 3-cyanoindole 4a and N,N0-diethoxycarbonylhydrazine (5)
were formed in moderate overall yield (49%). The azadiene 1b reacted simi-
larly with DEAZD to furnish 4b and 5 in a lower overall yield (34%).
The compound 5 had previously been reported as a by-product of the
reaction of DEAZD with two ketone phenylhydrazones[12] and with the
NNDMH’s of two araldehyde oximes.[7] Neither of these reports contained
NMR and mass spectral data in support of the derived structure 5, nor did
they provide any literature reference to it. This situation necessitated a
complete spectral identification of 5, which we have carried out (vide
Experimental). Moreover, the mechanism of the formation of 5 was not
suggested in any of these reports. We like to explain the genesis of both
4a/b and 5 together in the following manner (Scheme 3).

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2298
CHAKRABARTY ET AL.
Scheme 4.
Scheme 5.
The cyanoindoles 4a and 4b were most likely formed by a dienophile-
catalysed addition-elimination reaction, depicted below, just as the formation
of certain 2-cyanoarenes from the reaction of dimethyl acetylenedicarbox-
ylate (DMAD) with the NNDMH’s of the respective 2-formylarenes was
explained.[6] The initially formed, unisolated intermediate 50 is likely to have
undergone thermal elimination of N-methylformaldimine to give 5 as the
stable product. The liberated aldimine may have polymerised in a manner
similar to the trimerisation of acetaldimine.
In contrast, the unacylated azadiene 1c did not react with DEAZD or
diethyl acetylenedicarboxylate (DEAD) in refluxing xylene, even in presence
of PTS or Montmorillonite K10 clay. However, in the reaction of 1c with
DEAZD in acetonitrile solution at 60ꢀ in presence of PTS, the regeneration
of 3-formylindole in good yield was observed (Scheme 4).
Because of the very high resonance energy of 1c, its C(2)¼C(3) bond
cannot behave as an olefin. In other words, the C(2)¼C(3)–CH¼N system
of 1c does not have sufficient azadiene character to permit its participation
in D.–A. reaction. This is the reason, we believe, for the observed failure.
Both 1a and 1b reacted with methyl propiolate (MP) in acetonitrile
solution at 60ꢀ to furnish once again the respective 3-cyanoindoles 4a and 4b
(Scheme 5). The presence of PTS was not found to be essential for the
conversion of 1a to 4a, but it appeared to enhance the rate of the reaction
(not detailed in the Experimental). PTS was found to be ineffective for the
conversion of 1b to 4b, but the catalytic presence of M. K10 clay appeared
to be necessary.
The parent azadiene 1c reacted fast with MP in acetonitrile to furnish
two products, of which 3-cyanoindole (4c) was the major one (Scheme 6).
While trying to arrive at the individual 1H and 13C NMR assignments of 4c by
analysing its HMQC and GHMBC spectra (CDCl3), a 3-bond 13C–1H
HMBC correlation was recorded between a carbon at ꢁ 87.6 and H-2 (ꢁ 7.74),

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FOUR INDOLIC 1-AZADIENES
2299
Scheme 6.
Scheme 7.
which suggested the former to be the 3-cyano carbon. But a perusal of the 13
C
chemical shifts of various nitriles[13] strongly advocated that another chemical
shift at ꢁ 115.7 be assigned to CN, thereby ascribing ꢁ 87.6 to C-3 of the indole
ring. These values reasonably agreed with those, viz. ꢁ 116.0 and ꢁ 84.6 (d6-
DMSO), respectively, retrieved from an online search.[14] The referred corre-
lation thus transpired to be a two-bond 13C–1H correlation.
The minor product was identified as the new 3-cyanoindole 6, which
clearly stemmed from both dienophile-catalysed addition-elimination reac-
tion and Michael addition of MP at N-1 of the indole nucleus. The place-
ment of the 3-substituted methacrylate moiety at N-1 of 3-cyanoindole was
deduced from the combined 1D and 2D NMR experiments and the nOe’s of
H-7 (ꢁ 7.66) and H-20 (ꢁ 6.15) signals, observed when H-30 (ꢁ 8.22) and H-2
(ꢁ 7.90), respectively were irradiated.
The simultaneous formation of both 4c and 6 suggested that
elimination was the first step (leading to 4c), followed by Michael reaction,
leading to 6. When 4c was similarly treated with MP, 6 was formed, but the
reaction took conspicuously long time (23 h) for completion (Scheme 7).
This suggested that both elimination and Michael reaction were taking
place simultaneously, with the former taking place at a much faster rate.
In view of the successful D.–A. reaction of furfuraldoxime,[9] we
studied the reaction of the indolic oxime 2 with acrylonitrile (AN),
acrylamide (AA), DMAD, MP and DEAZD. As apprehended, the targeted
D.–A. reaction did not take place with any of these dienophiles. Instead, the
reaction took different courses for the enoic and the ynoic dienophiles.
Thus, the reaction of 2 with AN and AA in refluxing benzene furnished
the respective nitrones 7a and 7b (Scheme 8), whose structures received
1
support from their following characteristic H NMR data: ꢁ 4.18/4.10 and

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2300
CHAKRABARTY ET AL.
Scheme 8.
Scheme 9.
ꢁ 3.12/2.70 (2H, t each, J 6.5/7 Hz) for CH2Nþ and CH2R groups, respec-
tively. These nitrones are expected to have resulted from a formal Michael
addition via the nitrogen lone pair (1,3-azaprotio cyclotransfer)[15] to the
activated alkenes, as shown above.
Similar nitrones have recently been reported to be formed by the
reaction of 2 with methyl acrylate, methyl vinyl ketone and NMM.[16]
The reaction of 2 with DMAD, MP and DEAZD, carried out in
acetonitrile at 60ꢀ, furnished two products in each case, 3-formylindole
being the common product. The second product from each of DMAD
and MP was 3-cyanoindole (4c) (Scheme 9).
We propose to explain the formation of 3-formylindole and 4c as
follows. Any oxime, e.g., 2 is known to exist in equilibrium with the corre-
sponding NH nitrone, 20 in this case, generated by 1,2-prototropy
(Scheme 10).[17] Alternatively, the oxime may experience a formal Michael
addition through the lone pair of its oxime nitrogen to the ynoic dienophiles,
leading to the nitrone 200. Water present in the LR grade acetonitrile used in
the reaction brings about the hydrolysis of either of the nitrones, 20 and 200,
to furnish 3-formylindole. When the oxime itself was stirred in acetonitrile
at 60ꢀ for 12 h, no reaction took place. This rules out the possibility of the
hydrolysis of the NH-nitrone 20, thereby pointing to the hydrolysis of 200 as
the possible pathway. As in the case of the NNDMH’s 1a–c, a dienophile-
catalysed addition-elimination reaction of 2 is likely to have led to the
formation of 4c.
The second product of the reaction of 2 with DEAZD was identified as
the hydrazine 5 (Scheme 11), which may have been formed in a manner

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FOUR INDOLIC 1-AZADIENES
2301
Scheme 10.
Scheme 11.
stated in the reaction of 1a/b with DEAZD. We were, however, baffled by
the lack of formation of 3-cyanoindole as one of the products.
In fine, both the predictions from ꢀ-VE-SCF-MO calculations came
partly true. Thus, 1b (and previously 1a) underwent Diels–Alder reaction
with only NMM, while 1a, 1b, 2 and partly 1c displayed dienophile-
catalysed addition-elimination reactions, furnishing the related
3-cyanoindoles with the ynoic and the azo dienophiles. The formation of
5 from the reactions with DEAZD and that of nitrones from the reactions of
2 have precedence in the case of other azadienes. To our knowledge, the
present communication is the first record of the formation of a product
resulting from both addition-elimination reaction and Michael addition
occurring at different sites of the same substrate.
EXPERIMENTAL
Uncorrected Melting points (in Celsius) were determined on a
Toshniwal apparatus. IR spectra (KBr) were recorded on a Nicolet
Impact 410, Shimadzu 408, JAFCO 410 or Perkin Elmer 1600 spectropho-
tometers, electron impact mass spectra on AEI MS 3074 (LR) or JEOL-JMS
1
AX505H (LR, HR) instruments, and H and 13C NMR spectra, both 1D
and 2D, on Bruker AM 300L, Varian XL-400 or Bruker DRX 500 NMR
1
spectrometers. Complete H and 13C NMR assignments, whenever stated,
1
were derived from H, 13C, spin decoupling, nOe, HMQC and GHMBC
spectra. Microanalyses were carried out on a Dr. Hans Hoesli Analyser at
the Department of Pure Chemistry, University of Calcutta, Calcutta.
Analytical and preparative TLC’s were carried out on silica gel G plates

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2302
CHAKRABARTY ET AL.
(Merck, India). Spots were identified by iodine vapour and 0.5% KMnO4 in
aq. 1(N) NaOH. All the dienophiles, NH2NMe2, NH2OHꢁHCl and
Montmorillonite K10 clay were procured commercially. For reactions
with methyl propiolate, a stock solution (1 mL in 49 mL CH3CN) was
used. Petrol refers to petroleum ether, b.p. 60–80ꢀ. The NNDMH’s 1a[10]
,
1b,[10] 1c[10] and 3-formylindole[18] were prepared by literature procedures.
The unreported spectral data of 2 have been presented here.
Preparation of 2: An aq. solution (1 mL) of NH2OH.HCl (105 mg) was
neutralised with 50% aq. NaOH, added to a solution of 3-formylindole
(145 mg; 1 mM) in ethanol (4 mL) and refluxed for 0.5 h. The solution at rt
was diluted with water and neutralised with 1 : 1 aq. AcOH. The resulting
precipitate was filtered, washed, dried and crystallised from rectified spirit to
furnish pure 2: colourless needles, m.p. 196–198ꢀ (Lit.[19] m.p. 197–198ꢀ);
yield: 0.146 g (91%); IR: 3384, 3164, 1642, 753 cmꢂ1; MS: m/z 160 (Mþ;
1
20%), 142 (100), 115 (50); H NMR (500 MHz; d6-DMSO): ꢁ11.51 & 11.21
(1H, s each, NH & OH), 8.18 (1H, d, J 2.5 Hz, CH¼N), 7.81 & 7.40 (1H, d
each, J 8 Hz, H-4 & 7, respectively), 7.74 (1H, s, H-2), 7.12 & 7.06 (1H, t each,
J 7.5 Hz, H-6 & 5, respectively); 13C NMR (125 MHz): ꢁ 135.7 (C-7a), 127.1
(C-3a), 107.2 (C-3), 139.2, 131.3, 122.7, 120.7, 119.0, 112.6 (all Ar–CH).
Reaction of 1b with NMM: A solution of 1b (90 mg; 0.3 mM) and
NMM (83 mg; 0.75 mM) in dry xylene (10 mL) containing PTS (5 mg) was
refluxed under nitrogen blanket for 12 h. Xylene was distilled off under
reduced pressure, the residue dissolved in little CHCl3 and diluted with
excess petrol. The resulting ppt. (49 mg) was purified by prep. TLC in
C6H6:EtOAc (2 : 3) to furnish 3b (Rf 0.48), yellowish solid, m.p. 248–250ꢀ
(petrol–CHCl3); yield: 16 mg (15%); anal. Found: C, 70.88; H, 3.65; N,
11.80; calc. for C21H13N3O3: C, 70.98; H, 3.66; N, 11.83%; IR: 1772,
1708, 748 cmꢂ1; MS: m/z 355 (Mþ; 11%), 165 (7), 105 (100), 77 (48), 51
1
(10); H NMR (100 MHz): ꢁ 3.16 (3H, s, NMe), 7.30–7.80 (6H), 7.84–8.04
(2H) & 8.16–8.40 (1H) (all m; 9 ꢃ Ar–CH), 9.64 (1H, s, CH¼N).
Reaction of 1a with DEAZD: 1a (63 mg; 0.25 mM), dissolved in 8 mL
xylene, was treated with DEAZD (0.1 mL; 0.5 mM) and refluxed in nitrogen
atmosphere for 32 h. Xylene was distilled off under reduced pressure, and
the residue was separated into its components by PTLC in petrol–EtOAc
(13 : 7) to furnish 1a (15 mg), 4a (Rf 0.55) and 5 (Rf 0.48).
4a; Viscous mass which, when kept in fridge, solidified; m.p. 65–66ꢀ
(Lit.[10] m.p. 66ꢀ); yield: 11 mg (25%).
5: Light brown needles, m.p. 128–130ꢀ (petrol–CHCl3) (Lit.[10] m.p.
131–132ꢀ); yield: 21 mg (24%); IR: 3246, 1753, 1699 cmꢂ1; MS: m/z 176
1
(Mþ; 31%), 131 (28), 130 (17), 104 (100), 103 (58); H NMR (400 MHz): ꢁ
6.45 (1H, br, NH), 4.2 (2H, q) & 1.24 (3H, t, J 5 Hz; CO2Et); 13C NMR
(100 MHz): ꢁ 151.7 (CO2Et), 57.3 (CH2), 9.4 (CH3).

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FOUR INDOLIC 1-AZADIENES
2303
Reaction of 1b with DEAZD: A solution of 1b (88 mg; 0.3 mM) in
xylene (8 mL) was refluxed with DEAZD (0.8 mM) under nitrogen blanket
for 30 h. Removal of xylene and PTLC of the residue in petrol–EtOAc
(13 : 7) furnished 4b (Rf 0.58), 1b (19 mg) and 5 (Rf 0.48) (20 mg; 14%) in
pure state. 4b: Colourless needles, m.p. 106–108ꢀ (Lit.[10] m.p. 108–110ꢀ);
yield: 12 mg (20%).
Reaction of 1c with DEAZD: A solution of 1c (20 mg; 0.1 mM) and
PTS (5 mg) in CH3CN (3 mL) was stirred at 60ꢀ for 11 h. Removal of solvent
and purification of the residue by PTLC in petrol–EtOAc (13 : 7) furnished
3-formylindole (Rf 0.4) as buff-coloured needles, m.p. 197–198ꢀ (aq. EtOH)
(Lit.[19] m.p. 197–199ꢀ); yield: 12 mg (77%).
Reaction of 1a with MP: MP (3 mL stock soln.; 0.6 mM) was added to a
solutionof1a(0.5 mM)inCH3CN(10 mL)andstirredat60ꢀ for34 h. Asimilar
work-up and PTLC in petrol–EtOAc (13 : 7) furnished 4a (14 mg; 13%).
Reaction of 1b with MP: A solution of 1b (0.1 mM) in CH3CN (5 mL)
containing Montmorillonite K 10 clay (5 mg) and MP (0.12 mM) was stirred
at 60ꢀ for 38 h. The solution was filtered through a bed of celite and the
residue obtained by evaporation of the filtrate was purified by PTLC to give
4b in 33% yield (8 mg).
Reaction of 1c with MP: A solution of 1c (40 mg; 0.2 mM) and MP
(0.25 mM) in CH3CN (5 mL) was stirred for 3.5 h. Removal of CH3CN and
purification by PTLC in petrol–EtOAc (3 : 1) furnished pure 4c (Rf 0.5) and
6 (Rf 0.3).
4c: Fluffy, colourless needles, m.p. 178–180ꢀ (petrol–CH2Cl2) (Lit.[20]
m.p. 179–182ꢀ); yield: 16 mg (55%); IR: 3218, 2216 cmꢂ1; MS: m/z 142
1
(100%), 115 (61), 114 (28), 88 (27); H NMR (400 MHz): ꢁ 8.74 (1H, br,
NH), 7.78 (1H, m, H-4), 7.74 (1H, d, J 3 Hz, H-2), 7.48 (1H, ddd, J 8, 2,
<1 Hz, H-7), 7.34 & 7.31 (1H, dt each, J 8, 2 Hz, H-6 & 5, respectively);
13C NMR (100 MHz): ꢁ 134.8 (C-7a), 126.9 (C-3a), 115.5 (CN), 87.6 (C-3),
131.7 (CH-2), 124.3 (CH-6), 122.4 (CH-5), 119.7 (CH-4), 112.0 (CH-7).
6: Off-white flakes, m.p. 102–104ꢀ (petrol–CHCl3); yield: 12 mg (22%);
IR: 2223, 1730, 1650, 940 cmꢂ1; MS: m/z 226.0742 (C13H10N2O2; Mþ;
1
100%), 197 (20), 195.0558 (C12H7N2O; 82), H NMR (400 MHz): ꢁ 8.22
(HA) & 6.15 (HB) (1H, d each, J 16 Hz, NCHA¼CHB), 7.90 (1H, s, H-2),
7.78 and 7.65 (1H, br d each, J 8 Hz, H-4 & 7, respectively), 7.48 & 7.41 (1H,
dt each, J 8, 2 Hz, H-6 & 5, respectively); 13C NMR (100 MHz): ꢁ 166.5
(CO2), 135.1 (C-7a), 127.8 (C-3a), 114.0 (CN), 93.0 (C-3), 135.8 (N-CH¼),
130.2 (CH-2), 126.0 (CH-6), 124.3 (CH-5), 120.4 (CH-4), 110.8 (CH-7),
105.2 (¼CH–CO2).
Reaction of 4c with MP: A solution of 4c (0.2 mM) and MP (0.2 mM)
in CH3CN (5 mL) was stirred at rt for 23 h. CH3CN was then boiled off and
the residue was crystallised from CHCl3 to furnish 6 in 64% yield (29 mg).

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2304
CHAKRABARTY ET AL.
Reaction of 2 with AN: A solution of 2 (33 mg; 0.2 mM) and AN (22 mg;
0.4 mM) in dry C6H6 (5 mL) was refluxed for 12 h and then left overnight at rt.
The resulting crystals were filtered under suction and dried to furnish pure 7a:
fluffy, white needles, m.p. 176ꢀ (C6H6) (Rf 0.6) in EtOAc–MeOH (4 : 1); yield:
36 mg (85%); anal. found: C, 67.57; H, 5.18; N, 19.75; calc. for C12H11N3O:
C, 67.61; H, 5.16; N, 19.72%; IR: 3344, 2258, 1611, 749 cmꢂ1; MS: m/z 213
(Mþ; 100%), 197 (78), 173 (40); 1H NMR (500 MHz; d6-DMSO): ꢁ 11.74 (1H,
s, NH), 8.83 (1H, d, J 1.5 Hz, CH¼Nþ), 8.31 (1H, s, H-2), 7.78 & 7.45 (1H, d
each, J 8 Hz, H-4 & 7, respectively), 7.17 & 7.13 (1H, t each, J 7.5 Hz, H-6 & 5,
respectively), 4.17 & 3.12 (2H, t each, J 6.5 Hz, NþCH2 & CH2CN,
respectively); 13C NMR (125 MHz): ꢁ 136.3 (C-7a), 126.7 (C-3a), 119.5
(CN), 107.8 (C-3), 129.6, 129.3, 123.3, 120.9, 118.9, 112.9 (all CH), 59.3
(CH2Nþ), 16.8 (CH2CN).
Reaction of 2 with AA: A solution of 2 (0.4 mM) and AA (43 mg;
0.6 mM) in dry C6H6 (8 mL) was refluxed for 14 h and left overnight at rt.
The resulting solid was filtered and dried to give 7b: white needles, m.p.
216–218ꢀ (C6H6) (Rf 0.2 in EtOAc-MeOH¼4 : 1); yield: 74 mg (80%); anal.
found: C, 62.39; H, 5.65; N, 18.21; calc. for C12H13N3O2: C, 62.34; H, 5.63;
N, 18.18%; IR: 3365, 3201, 1663, 745 cmꢂ1; MS: m/z 231 (Mþ; 78%), 215
1
(100), 214 (77), 197 (25), 187 (18); H NMR (500 MHz; d6-DMSO): ꢁ 11.55
(1H, s, NH), 8.78 (1H, d, J 2.5 Hz, CH¼Nþ), 8.16 (1H, s, H-2), 7.77 & 7.43
(1H, d each, J 8 Hz, H-4 & 7, respectively), 7.16 & 7.11 (1H, t each, J 7.3 Hz,
H-6 & 5, respectively), 7.45 & 6.87 (1H, br s each, CONH2), 4.10 & 2.70
(2H, t each, J 7 Hz, CH2Nþ & CH2CO, respectively); 13C NMR (125 MHz):
ꢁ 172.6 (CO), 136.2 (C-7a), 126.6 (C-3a), 108.1 (C-3), 129.0, 128.3, 123.1,
120.7, 118.9, 112.8 (all Ar–CH), 60.5 (CH2Nþ), 33.9 (CH2CO).
Reaction of 2 with DMAD: A solution of 2 (0.5 mM) in CH3CN (5 mL)
containing DMAD (107 mg; 0.75 mM) was stirred at 60ꢀ for 12 h. The
solvent was boiled off and the residue was purified by PTLC in petrol–
EtOAc (2 : 1) to furnish 4c (Rf 0.3) (8 mg; 11%) and 3-formylindole
(Rf 0.2) (16 mg; 22%).
Reaction of 2 with MP: A solution of 2 (0.5 mM) and MP (1.5 mM) in
CH3CN (5 mL) was stirred at 60ꢀ for 12 h. The removal of solvent, followed
by PTLC of the residue in C6H6–MeOH (9 : 1) furnished 4c (Rf 0.5) (11 mg;
15%) and 3-formylindole (Rf 0.4) (15 mg; 21%).
Reaction of 2 with DEAZD: A solution of 2 (0.2 mM) and DEAZD
(0.3 mM) in CH3CN (4 mL) was stirred at 60ꢀ for 8 h. The removal of
solvent and purification of the resulting residue by PTLC in petrol–
EtOAc (13 : 7) furnished 23 mg of a solid (Rf 0.3), m.p. 115ꢀ which was
shown by 1H NMR spectrum to be a mixture of 3-formylindole and 5
(in 7 : 93 ratio), also supported by TLC in petrol–C6H6–EtOAc (1 : 1 : 3): 5
(Rf 0.6) and 3-formylindole (Rf 0.5).

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FOUR INDOLIC 1-AZADIENES
ACKNOWLEDGMENTS
2305
The authors are thankful to the Acting Director, Bose Institute for
providing laboratory facilities and to the CSIR, Gov’t of India for a fellow-
ship to S.S., to the Principal, Acharya J.C. Bose College for permitting S.K.
to pursue research, to Professor U. Pindur, University of Mainz, Germany
for the MO calculations, and to Mr. Barun Majumdar and Mr. Pranab Das
of B.I. for recording the NMR and IR spectra, respectively.
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Received in the UK May 22, 2001