1, 3-Dipolar cycloaddition reactions: Synthesis of 5-benzyl-1-(2',4'- dibromophenyl)-3-(4''-substituted phenyl)-3a,4,6,6a-tetrahydro-1H, 5H-pyrrolo[3,4-c]pyrazole-4,6-dione derivatives

Article abstract of DOI:10.1007/s12039-013-0526-3

1,3-Dipolar cycloaddition of nitrilimines 3 with N-benzyl maleimide 4 has provided 5-benzyl-1-(2',4'-dibromophenyl)-3-(4''-substituted phenyl)-3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-dione derivatives 5 in excellent yield as the only isomer through a concerted pathway. Indian Academy of Sciences.

Full text of DOI:10.1007/s12039-013-0526-3

c
J. Chem. Sci. Vol. 125, No. 6, November 2013, pp. 1529–1534. ꢀ Indian Academy of Sciences.
1, 3-Dipolar cycloaddition reactions: Synthesis of 5-benzyl-1-(2ꢁ,4ꢁ-
dibromophenyl)-3-(4ꢁꢁ-substituted phenyl)-3a,4,6,6a-tetrahydro-1H,
5H-pyrrolo[3,4-c]pyrazole-4,6-dione derivatives
MANPREET KAUR, BALDEV SINGH∗ and BALJIT SINGH
Department of Chemistry, Punjabi University, Patiala 147 002, India
e-mail: drbaldev.chem@gmail.com
MS received 4 May 2013; revised 29 August 2013; accepted 30 August 2013
Abstract. 1,3-Dipolar cycloaddition of nitrilimines 3 with N-benzyl maleimide 4 has provided 5-benzyl-
1-(2ꢁ,4ꢁ-dibromophenyl)-3-(4ꢁꢁ-substituted phenyl)-3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-dione
derivatives 5 in excellent yield as the only isomer through a concerted pathway.
Keywords. Nitrilimine; cycloaddition; stereo-controlled; pyrrolo pyrazole.
1. Introduction
hydrazidoyl halides15,16 with a tertiary base (table 1,
scheme 1).
1,3-Dipolar cycloaddition reaction has found an exten-
sive use as a high-yielding, efficient, regio and stereo-
controlled method for the synthesis of many heterocyclic
compounds.1–4 1,3-Dipolar cycloaddition reaction has
been described as ‘the single most important method
for the construction of heterocyclic five-membered
rings in organic chemistry’.5 These reactions proceed
through ‘conservation of orbital symmetry’.6 Nitril-
imines 3 are well-known labile intermediates which
are generated in situ in the presence of the dipo-
larophile to form cycloadducts.7 It has been reported
that the orientation during 1,3-dipolar cycloaddition
reaction observed for alkenes substituted with electron-
donor conjugating and electron acceptor substituents
provides the 5-substituted regioisomer, while on other
occasions, these cycloadditions of nitrilimines to highly
electron-deficient alkenes give 4-substituted products.8
The active dipolarophile maleimides are known to
be a class of substrates having biological importance
along with their synthetic utility.9 Besides, using chi-
ral maleimides, synthesis of pyrazoles have also been
explored.10 The nitrilimines 1,3-dipole have been synthe-
sised by various methods such as thermal decomposition
of substituted tetrazole,11 treatment of diarylhalofor-
mazans12 with tertiary amine, use of triphenylphos-
phine and carbon tetrachloride13 and treatment of aryl
hydrazone with chloramine-T,14 but more conveniently,
nitrilimines can be synthesised in situ by treating
2. Experimental
2.1 General
Melting points reported are uncorrected. IR spectra
were recorded on a Perkin Elmer RXIFT infrared
spectrophotometer using KBr pellets. 1H-Nuclear mag-
netic resonance (1H-NMR) spectra were recorded on
a 400 MHz Bruker Advance II Spectrometer using
tetramethylsilane (TMS) as internal standard. 13C-NMR
spectra were recorded on a Bruker Advance II 100
NMR Spectrometer, SAIF Punjab University, Chandi-
garh. Mass spectra were recorded on LCQ FINNI-
GAN MAT (ESI), NIPER, Mohali. Thin layer chro-
matography (TLC) plates were coated with silica gel-G
suspended in methanol–chloroform. Elemental analy-
sis was carried out using Elementar vario MICRO cube
CHN analyser.
2.2 General procedure for synthesis of N-benzyl
maleimide (4)
Equimolar quantities of benzylamine and maleic anhy-
dride were stirred in toluene at room temperature for
1 h to yield N-benzyl maleanilic acid. Maleanilic acid
thus obtained was cyclised to maleimide in acetic anhy-
dride in the presence of anhydrous sodium acetate under
reflux for 1.5 h and then the contents were poured
into ice cold water and kept over night to afford the
solid, which was filtered, washed with water and finally
∗For correspondence
1529

1530
Manpreet Kaur et al.
Table 1. Characterisation data of 5-benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(4ꢁꢁ-substituted phenyl)-3a,4,6,6a-
tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-dione derivatives.
Br
Br
2
X
Br
O
1
N
3
N
C
Br
H
C
N
6a
HBr
Et3N
3a
H
H
N
Br
N
6
X
O
O
N
4
O
5
Compounds
X
Yield (%)
Melting point (◦C)
5a
5b
5c
5d
5e
5f
5g
5h
5i
4-Cl
3-Cl
2-Cl
4-CH3
3-CH3
2-CH3
4-NO2
3-NO2
H
70
67
72
68
64
66
70
66
73
193–195
185–187
132–133
194–196
142–144
162–163
230–232
190–191
168–169
Scheme 1. Schematic diagram describing the synthesis of 5-benzyl-1-(2ꢁ,4ꢁ-dibro-
mophenyl)-3-(4ꢁꢁ-substituted phenyl)-3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,
6-dione derivatives.
recrystallized from petroleum ether to give N-benzyl phenyl hydrazine in ethanol. The product obtained after
recrystallization (0.1 mol) was dissolved in cold glacial
acetic acid (100 ml). To this solution a solution of ace-
maleimide 4.
2.3 General procedure for synthesis of substituted tous bromine (0.3 mol/30 ml glacial acetic acid) was
benzaldehyde-2ꢁ,4ꢁ-dibromophenyl hydrazonyl bromide
(2a–i)
added dropwise within 30 min. The reaction mixture was
stirred for about 2.5 h and kept for an overnight period.
On usual work-up, the reaction mixture provided crude
product which on recrystallisation from ethanol gave
2a–i.
All these compounds were prepared by reacting an
equimolar amount of corresponding benzaldehyde and

1, 3-Dipolar cycloaddition reactions
1531
2.4 General procedure for cycloadditions (5a–i)
2.4d 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(4ꢁꢁ-methyl-
phenyl)-3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]
pyrazole-4,6-dione (5d): Compound obtained as
white solid (4.0 g, 72.3%), m.p. 194–196◦C; IR (KBr
pellets): 1710, 1780 cm−1 (C=O); 1605 cm−1 (C=N);
1567 cm−1 (C=C); 1H-NMR (400 MHz, DMSO-
d6), δ 5.8 (d, 1H, J = 10.16 Hz); 5.0 (d, 1H, J =
10.16 Hz); 4.5 (s, 2H); 2.4 (s, 3H); 7.9–7.2 (m, 12H);
13C-NMR (100 MHz, CDCl3), δ 171.5, 171.2, 147.4,
144.4, 135.7–116.4, 133.7, 129, 63.2, 54.1, 43.3, 24.9;
MS(ESI): m/z 553[M]+, 554[M+1]+, 555[M+2]+,
Anal. Calc. for C25H19N3Br2O2: C, 54.25; H, 3.44; N,
7.60, Found: C, 54.05; H, 3.45; N, 7.65.
To the substituted benzaldehyde-2ꢁ,4ꢁ-dibromophenyl
hydrazonyl bromide 2a–i (0.01 mol) were added N-
benzyl maleimide 4 (0.01 mol) in tetrahydrofuran
(75 mL). To the cold mixture was added triethylamine
(0.01 mol) in tetrahydrofuran (25 mL) and the mixture
was stirred for 2–3 h and allowed to stand overnight.
The crude product that separated out was recrystallised
from ethanol to give cycloadducts 5a–i.
2.4a 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(4ꢁꢁ-chlorophenyl)-
3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-
4,6-dione (5a): Compound obtained as white solid
(3.7 g, 64.5%), m.p. 193–195◦C; IR (KBr pel-
lets): 1716, 1782 cm−1 (C=O); 1610 cm−1 (C=N);
1579 cm−1 (C=C); 1H-NMR (400 MHz, CDCl3), δ 5.8
(d, 1H, J = 10.36 Hz); 4.8 (d, 1H, J = 10.32 Hz);
4.6 (s, 2H); 8.0–7.1 (m, 12H); 13C-NMR (100 MHz,
CDCl3), δ 171.5, 171.2, 145.4, 140.6, 135.8–119.3,
131.3, 127.1, 63.3, 53.9, 43.2; MS(ESI): m/z
572[M]+, 574[M+2]+, 576[M+4]+, Anal. Calc. for
C24H16N3Br2ClO2: C, 50.21; H, 2.79; N, 7.32, Found:
C, 50.35; H, 2.77; N, 7.35.
2.4e 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(3ꢁꢁ-methyl-
phenyl)-3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]
pyrazole-4,6-dione (5e): Compound obtained as
white solid (4.2 g, 75.9%), m.p. 142–144◦C; IR (KBr
pellets): 1717, 1779 cm−1 (C=O); 1603 cm−1 (C=N);
1565 cm−1 (C=C); 1H-NMR (400 MHz, CDCl3), δ 5.8
(d, 1H, J = 10.08 Hz); 4.9 (d, 1H, J = 10.12 Hz);
4.5 (s, 2H); 2.5 (s, 3H); 7.8–7.1 (m, 12H); 13C-NMR
(100 MHz, CDCl3), δ 171.8, 171.6, 146.8, 145.4,
138.3–116.8, 131.3, 128.8, 63.2, 54.0, 43.1, 25.3;
MS(ESI): m/z 553[M]+, 554[M+1]+, 555[M+2]+,
Anal. Calc. for C25H19N3Br2O2: C, 54.25; H, 3.44; N,
7.60, Found: C, 54.10; H, 3.41; N, 7.61.
2.4b 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(3ꢁꢁ-chlorophenyl)-
3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-
4,6-dione (5b): Compound obtained as white solid
(3.9 g, 67.9%), m.p. 185–187◦C; IR (KBr pel-
lets): 1708, 1778 cm−1 (C=O); 1608 cm−1 (C=N);
1575 cm−1 (C=C); 1H-NMR (400 MHz, CDCl3), δ 5.8
(d, 1H, J = 10.40 Hz); 4.8 (d, 1H, J = 10.36 Hz);
4.6 (s, 2H); 7.9–7.1 (m, 12H); 13C-NMR (100 MHz,
CDCl3), δ 171.6, 171.4; 143.7, 142.7, 135.8–118.2,
130.5, 126.8, 62.4; 53.6, 43.1; MS(ESI): m/z
572[M]+, 574[M+2]+, 576[M+4]+, Anal. Calc. for
C24H16N3Br2ClO2: C, 50.21; H, 2.79; N, 7.32, Found:
C, 50.20; H, 2.81; N, 7.31.
2.4f 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(2ꢁꢁ-methyl-
phenyl)-3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]
pyrazole-4,6-dione (5f): Compound obtained as
white solid (3.6 g, 65%), m.p. 162–163◦C; IR (KBr
pellets): 1699, 1771 cm−1 (C=O); 1603 cm−1(C=N);
1574 cm−1 (C=C); 1H-NMR (400 MHz, CDCl3), δ 5.8
(d, 1H, J = 10.28 Hz); 4.8 (d, 1H, J = 10.24 Hz);
4.6 (s, 2H); 2.43 (s, 3H); 7.8–7.2 (m, 12H); 13C-NMR
(100 MHz, CDCl3), δ 171.7, 171.4, 146.4, 142.2,
135.3–117.1, 132.9, 128.5, 63.0, 54.1, 43.2, 25.1;
MS(ESI): m/z 553[M]+, 554[M+1]+, 555[M+2]+,
Anal. Calc. for C25H19N3Br2O2: C, 54.25; H, 3.40; N,
7.60, Found: C, 54.17; H, 3.23; N, 7.58.
2.4c 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(2ꢁꢁ-chlorophenyl)-
3a,4,6,6a-tetrahydro-1H,5H- pyrrolo[3,4-c]pyrazole-
4,6-dione (5c): Compound obtained as white solid
(3.3 g, 57.5%), m.p. 132–133◦C; IR (KBr pel-
lets): 1699, 1771 cm−1 (C=O); 1606 cm−1 (C=N);
2.4g 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(4ꢁꢁ-nitrophenyl)-
3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-
4,6-dione (5g): Compound obtained as yellow solid
(4.0 g, 68.5%), m.p. 230–232◦C; IR (KBr pellets):
1709, 1781 cm−1 (C=O); 1609 cm−1(C=N); 1562 cm−1
(C=C); 1H-NMR (400 MHz, DMSO-d6), δ 6.0 (d, 1H,
J = 10.44 Hz); 5.2 (d, 1H, J = 10.44 Hz); 4.6 (s, 2H);
8.3–7.2 (m, 12H); 13C-NMR (100 MHz, CDCl3), δ
171.2, 171, 145.9, 143.2, 136.2–116.9, 131.7, 127.3,
1
1574 cm−1 (C=C); H-NMR (400 MHz, DMSO-d6),
δ 5.9 (d, 1H, J = 10.20 Hz); 5.3 (d, 1H, J = 10.20 Hz);
4.5 (s, 2H); 7.6–7.1 (m, 12H); 13C-NMR (100 MHz,
DMSO-d6), δ 171.8, 171.6, 144.6, 141.9, 134.9–
16.2, 132.1, 127, 62.9, 55.3, 41.8; MS(ESI): m/z
572[M]+, 574[M+2]+, 576[M+4]+, Anal. Calc. for
C24H16N3Br2ClO2: C, 50.21; H, 2.79; N, 7.3, Found: C,
50.15; H, 2.78; N, 7.29.

1532
Manpreet Kaur et al.
62.7, 53.8, 42.9; MS(ESI): m/z 581[M]+, 583[M+2]+, characterised as 5-benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-
585[M+4]+, Anal. Calc. for C24H16N4Br2O4: C, 49.32; (4ꢁꢁ-substituted phenyl)-3a,4,6,6a-tetrahydro-1H,5H-
H, 2.74; N, 9.59, Found: C, 49.15; H, 2.74; N, 9.60.
pyrrolo[3,4-c]pyrazole-4,6-dione derivatives through
1
their melting point, elemental analysis, IR, H-NMR,
13C-NMR, 2D-COSY and mass spectra. All the com-
pounds gave satisfactory results for their elemental
analysis.
2.4h 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(3ꢁꢁ-nitrophenyl)-
3a,4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-
4,6-dione (5h): Compound obtained as yellow
solid (3.6 g, 61.6%), m.p. 190–191◦C; IR (KBr pel-
lets): 1700, 1775 cm−1 (C=O); 1606 cm−1 (C=N);
In their IR spectra, these derivatives display two
absorption bands in the region of 1782–1771 cm−1 and
1717–1699 cm−1, which have been assigned to two car-
bonyl groups stretching vibrations of succinimide moi-
ety. Absorption bands in the range of 1603–1609 cm−1
have been assigned to imino stretching vibrations of
pyrazole ring, while the absorption bands in the region
of 1575 cm−1 have been assigned to aromatic carbon–
carbon double bond skeletal stretching vibrations. In
their 1H-NMR spectrum, these derivatives display C3a-
H and C6a-H as doublets at δ 5.3–4.8 with J = 10.08–
10.44 Hz and δ 6.0–5.8 with J = 10.12–10.44 Hz,
respectively, on coupling with protons C6a-H and C3a-H.
C6a-H proton, appears downfield in comparison to C3a-
H proton due to electronegative nitrogen atom attached
to C6a-H. Aromatic protons appear as multiplets at δ
8.3–7.1 (equivalent to 12H). A two protons singlet at δ
4.6–4.5 has been assigned to methylene protons of ben-
zyl moiety; while a singlet at δ 2.5 has been assigned to
methyl group (5d–f).
1
1565 cm−1 (C=C); H-NMR (400 MHz, DMSO-d6),
δ 5.9 (d, 1H, J = 10.44 Hz); 5.2 (d, 1H, J =
10.44 Hz); 4.6 (s, 2H); 8.3–7.2 (m,12H); 13C-NMR
(100 MHz, CDCl3), δ 171.4, 171.1, 147.2, 144.9,
133.3–116.1, 130, 127.1, 63.5, 52.9, 43.3; MS(ESI):
m/z 581[M]+, 583[M+2]+, 585[M+4]+, Anal. Calc.
for C24H16N4Br2O4: C, 49.32; H, 2.74; N, 9.59, Found:
C, 49.45; H, 2.73; N, 9.57.
2.4i 5-Benzyl-1-(2ꢁ,4ꢁ-dibromophenyl)-3-(phenyl)-3a,
4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-
dione (5i): Compound obtained as white solid (3.5 g,
64.9%), m.p. 168–169◦C; IR (KBr pellets): 1709,
1781 cm−1 (C=O); 1605 cm−1 (C=N); 1562 cm−1
1
(C=C); H-NMR (400 MHz, CDCl3), δ 6.0 (d, 1H,
J = 10.16 Hz); 5.2 (d, 1H, J = 10.16 Hz); 4.6 (s, 2H);
8.3–7.2 (m, 12H); 13C-NMR (100 MHz, CDCl3), δ
171.7, 171.4, 145.2, 141.9, 135.7–118.8, 131.4, 128.0,
63.2, 54.1, 43.2; MS(ESI): m/z 539[M]+, 540[M+1]+,
541[M+2]+, Anal. Calc. for C24H17N3Br2O2: C,
53.43; H, 3.15; N, 7.79, Found: C, 53.60; H, 3.13;
N, 7.77.
Their 13C-NMR spectra of these 5-benzyl-1-(2ꢁ,4ꢁ-
dibromophenyl)-3-(4ꢁꢁ-substituted phenyl)-3a,4,6,6a-
tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-dione
derivatives 5 display characteristic signals in the range
of δ 171.2–171.8 and 171.0–171.6 which have been
assigned to two succinimide carbonyl carbons, signals
in the range of δ 143.7–147.4 have been assigned to
ipso carbon of substituted phenyl attached to C-3, sig-
nals in the range of δ 140.6–145.4 have been assigned
to carbon of dibromophenyl ring, signals in the range
of δ 116.1–136.2 have been assigned to carbon atom
3. Results and discussion
In the present study, a convenient and facile method of aromatic ring, signals in the range of 130.0–133.7
for the synthesis of C-aryl-N-(2ꢁ,4ꢁ-dibromophenyl)- have been assigned to C-3 of C = N, signals in the
nitrilimines17 and their 1,3-dipolar cycloaddition range of δ 127.0–129.0 have been assigned to ipso car-
with N-benzyl maleimide18 has been carried out, bon directly attached to benzylic carbon of N-benzyl
which has provided the synthesis of 5-benzyl-1-(2ꢁ,4ꢁ- moiety, signals in the range of δ 62.7–63.5 and 52.9–
dibromophenyl)-3-(4ꢁꢁ-substituted phenyl)-3a,4,6,6a- 55.3 have been assigned to C-5 pyrazoline and C-4
tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-dione pyrazoline, signals in the range of δ 41.8–43.3 have
derivatives 5 in excellent yield. The phenyl hydrazones been assigned to benzylic carbon. Signals at δ 24.9–
are treated with bromine19 in glacial acetic acid to give 25.3 have been assigned to carbon of methyl group
hydrazonyl bromide derivatives which subsequently on (5d–f).
treatment with triethyl amine in cold tetrahydrofuran
Mass spectra of all the synthesised compounds in
has given C-aryl-N-(2ꢁ,4ꢁ-dibromophenyl)-nitrilimines 5a–i display correct molecular ion peaks. As a rep-
in situ which undergo cycloaddition with activated resentative case, high resolution mass spectrum of
double bond of N-benzyl maleimide to form five- 5d is discussed which displays molecular ion peak
membered fused bicyclic heterocycles which have been at m/z 554 (100%) forming base peak, with other

1, 3-Dipolar cycloaddition reactions
1533
Figure 1. Mass fragmentation pattern of compound 5d.
isotopic ion peaks at m/z 553 (57%), 555 (48%) show- interactions in either case leads to the formation
ing the relative abundance of bromine atoms present of only cis product following cis-endo addition
in the molecule. Ion peaks at m/z 392, 393 and 394 rule.
are formed with the loss of C9H7NO2 from the parent
molecule. Presence of all these peaks shows the pres-
ence of two isotopic bromine atoms again. Peaks at
m/z 463 appears due to loss of benzyl moiety from
the parent molecular ion peak. Other prominent mass
ion peaks present in the mass spectrum are at m/z
473, 392, 302, 187, 96, etc. The probable mode of
fragmentation pattern of compound 5d is shown in
figure 1. Only one isomer has been obtained in all
cases as evidenced by TLC analysis showing single
spot in each case, thus this reaction is stereospecific
in nature. 2D-NMR (COSY) of parent compound 5d
shows mutual coupling of proton H3a with H6a with J =
10.16 Hz, which indicates that both protons are cis to
each other (figure 2).The single isomer seems to arise
through endo transition state where maximum double
bond accumulation occurs (TS, scheme 2). Since the N-
benzyl maleimide is a symmetrical molecule, it does not
matter whether the C-phenyl or N-phenyl ring of dipole
lies parallel to one of the carbonyl groups of succini-
mide moiety of dipolarophile; and the secondary
Figure 2. 400-MHz 2D-NMR COSY spectrum of 5d in
CDCl3.

1534
Manpreet Kaur et al.
Scheme 2. Transition states of 5a–i.
4. Conclusion
5. Koumbis A E and Gallos J K 2003 Curr. Org. Chem. 7
771
6. Gothelf K V 2002 Cycloaddition reactions in organic
synthesis (eds) S Kobayashi and K A Jorgensen (New
York: Wiley) chapter 6, p. 211
7. (a) Huisgen R, Seidel M, Wallbillich G and Knupfer
H 1962 Tetrahedron 17 3; (b) Huisgen R 1963 Angew.
Chem. Int. Ed. 2 565; (c) Huisgen R, Fliegl W and
Kolbeck W 1983 Chem. Ber. 116 3027
1,3-Dipolar cycloaddition reaction of nitrilimine gene-
rated in situ with N-benzyl maleimide has provided one
regioisomer following cis-endo addition rule, wherein
there is maximum accumulation of double bonds and
reaction seems to follow least non-bonding stearic inter-
actions. Besides, during bromination of hydrazone, N-
phenyl ring also gets brominated at 2ꢁ,4ꢁ- positions.
8. Huisgen R, Sustmann R and Wallbillich G 1967 Chem.
Ber. 100 1786
9. Konopikova M, Fisera L and Pronayova N 1991 Collect.
Czechoslov. Chem. Commun. 57 1521
Acknowledgements
10. Durust Y, Yildirim M, Fronczek C F and Fronczek F R
2012 Monatsh. Chem. 143 127
11. Huisgen R, Grashey R, Seidel M, Wallbillich G, Knupfer
H and Schmidt R 1962 Ann. Chem. 653 105
12. Fusco R and Romani K 1946 Gazz. Chim. Ital. 76 419
13. Hassaneen H M, Farg A M, Shawali A S and Alghasib
M S 1987 J. Het. Chem. 24 577
The authors are thankful to the University Grant Com-
mission (UGC), New Delhi, for financial assistance
and the Sophisticated Analytical Instrumentation Faci-
lity (SAIF), Panjab University, Chandigarh and NIPER,
Mohali for spectral analysis.
14. Lokanatha Rai K M and Hassner A 1989 Synth. Com-
mun. 19 2799
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