[3+2] cycloadditions: Part XXXIV: Further investigations of cycloadditions of C,N-diaryl- and C-aryl-N-methyl nitrones to α,β-unsaturated esters

Article abstract of DOI:10.14233/ajchem.2019.22232

Investigations of [3+2] cycloadditions of C,N-diaryl and C-aryl-N-methyl nitrones as three atom components (TAC) to substituted methyl E-cinnamates and diethyl arylidene malonates have been further investigated. [3+2] Cycloadditions of cinnamates yielded mixtures of cycloadducts, the major products being the 3,4-trans-4,5-trans-2,3,5-triaryl-4-carbomethoxy products originating from the endo-carbonyl-exo-aryl meta channel approach of the cinnamate component. [3+2] Cycloadditions to diethyl arylidene malonates furnished single cycloadducts-3,5-trans-2-methyl-3,5-diaryl-4,4-dicarbethoxy isoxazolidines by a endo-aryl meta channel approach of the 2π-component.

Full text of DOI:10.14233/ajchem.2019.22232

Asian Journal of Chemistry; Vol. 31, No. 12 (2019), 2777-2784
A
SIAN
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OURNAL OF HEMISTRY
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https://doi.org/10.14233/ajchem.2019.22232
[3+2] Cycloadditions: Part XXXIV: Further Investigations of Cycloadditions of
C,N-Diaryl- and C-Aryl-N-methyl Nitrones to α,β-Unsaturated Esters
1,3
SUMANA SENGUPTA1,2,* and AVIJIT BANERJI
1Department of Chemistry, Chandernagore College, Chandernagore, Hooghly-712136, India
2Centre ofAdvanced Studies on Natural Products including Synthesis, Department of Chemistry, University College of Science and Technology,
University of Calcutta, Kolkata-700009, India
3Central Ayurveda Research Institute for Drug Development, Kolkata-700091, India
*Corresponding author: E-mail: sngsumana@gmail.com
Received: 2 June 2019;
Accepted: 9 July 2019;
Published online: 16 November 2019;
AJC-19619
Investigations of [3+2] cycloadditions of C,N-diaryl and C-aryl-N-methyl nitrones as three atom components (TAC) to substituted methyl
E-cinnamates and diethyl arylidene malonates have been further investigated. [3+2] Cycloadditions of cinnamates yielded mixtures of
cycloadducts, the major products being the 3,4-trans-4,5-trans-2,3,5-triaryl-4-carbomethoxy products originating from the endo-carbonyl-
exo-aryl meta channel approach of the cinnamate component. [3+2] Cycloadditions to diethyl arylidene malonates furnished single
cycloadducts-3,5-trans-2-methyl-3,5-diaryl-4,4-dicarbethoxy isoxazolidines by a endo-aryl meta channel approach of the 2π-component.
Keywords: [3+2] Cycloadditions, Methyl E-Cinnamate, Diarylidene malonate, Nitrone, Isoxazolidine, XRD.
ester was reported [22,23]. We now report the 32CA of four
C,N-diaryl nitrones, with different C-aryl substituents to differ-
ently substituted methyl E-cinnamates, to assess the influence
of changing aryl substituents on regio- and stereoselectivities
of the cycloadditions. We had observed earlier in the 32CA of
nitrones to α,β-unsaturated amides, that changes in substituents
do have a small but perceptive influence on the selectivities of
the process [12]. 32CA reactions of C-aryl-N-methyl nitrones
with diethyl arylidene malonates were investigated for the first
time. We had earlier investigated the 32CA of C,N-diaryl nitrones
to arylidene malonates [19]; a remarkable increase in regio-
and stereoselectivity compared to cinnamic acid esters was
observed leading to the exclusive formation in the uncatalyzed
reactions of trans-3,5-diaryl-4,4-dicarbethoxy isoxazolidines
in nearly quantitative yields. It was of interest to us to find out
whether there would be any changes in reactivity and selectivity
if C-aryl-N-methyl nitrones were reacted.
INTRODUCTION
[3+2] Cycloadditions (32CA) of three atom components
(TAC) to olefinic substrates by [π4s + π2s] pathways form a useful
protocol for construction of different 5-membered heterocyclic
ring systems with regio- and stereochemical control [1-3]. The
literature on 32CAs of nitrones have been reviewed regarding
both experimental and theoretical aspects [4-11].
We have been carrying out systematic studies of 32CA of
acyclic and cyclic nitrones to olefinic substrates conjugated
to electron withdrawing groups viz. carboxamide, carboxylate
ester, keto- and nitro. The regio- and stereoselectivities of these
reactions have been studied and in several instances, the course
of reactions analyzed by computational studies [1,2,9,11-21].
The present communication is an extension of our earlier
studies. It was of interest to us to extend our investigations on
the 32CA of nitrones to substituted methyl E-cinnamates and
arylidene malonates to obtain a more complete picture of regio-
and stereoselectivities of these processes. We had previously
reported the 32CA of C-(4-nitrophenyl)-N-(4′-chlorophenyl)
nitrone with methyl E-cinnamates [18]. Earlier to this work,
only a single instance of 32CA of a nitrone to cinnamic acid
EXPERIMENTAL
Melting points of the isolated cycloadducts were recorded
on an electrically heated Köfler Block apparatus and are un-
corrected. Column and thin layer chomatography were carried
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2778 Sengupta et al.
Asian J. Chem.
out using neutral alumina (Qualigens), silica gel (Qualigens
60-120 mesh, Spectrochem 100-200 mesh) and silica gel G
(Merck), respectively. Spots on TLC chomatograms were visua-
lized with iodine vapour.Anhydrous sodium sulphate was used
for drying extracts. Analytical samples were routinely dried
over anhydrous CaCl2 in vacuo at room temperature.
8.4 Hz, H5), 3.70 (s, OCH3), 6.97-7.03 (m, ovl, A/H-2,4,6),
7.24 (t, J = 7.5 Hz, A/H-3,5), 7.30-7.45 (m, ovl, B,C/H-2,3,5,6);
13C NMR (75.5 MHz, CDCl3): δ 73.1 (C3), 66.2 (C4), 82.0
(C5), 52.3 (OCH3), 170.5 (CO), 150.6 (A/C-1),114.6 (A/C-
2,6), 127.9, 128.1, 128.9, 129.15, 129.05 (A/C-3,5, B,C/C-
2,6,3,5), 122.4 (A/C-4), 139.5 (B/C-1), 134.6, 133.7 (B,C/C-
4), 135.5 (C/C-1). Anal. calcd. (found) (%) for C23H19NO3Cl2:
C, 64.5 (64.2); H, 4.5 (4.3); N, 3.3 (3.1).
3,4-cis-4,5-trans-2-Phenyl-3,5-di(4′-chlorophenyl)-4-
carbmethoxy isoxazolidine (9b): From later hexane eluates,
a mixture of (9a) and (9b) were obtained, which were resolved
further by rechomatography and PTLC using benzene:hexane
(4:1) as developing solvent, with double development; pale
yellow solid, m.p. 66 °C, m.f.: C23H19NO3Cl2; yield 114 mg
(6 %). IR (KBr, νmax, cm-1): 2954, 2854, 1730 (ester CO), 1635,
1595, 1491, 1398, 1091 & 1010 (aryl Cl), 826 (1,4-disubstituted
benzene ring), 755 & 695 (mono-substituted benzene ring).
1H NMR(300 MHz, CDCl3): δ 4.98 (d, J = 10.2 Hz, H3), 3.73
(br t, J = 9.9 Hz, H4), 5.72 (d, J = 9.6 Hz, H5), 3.30 (s, OCH3),
6.94-7.01 (m, ovl, A/H-2,6), 7.20-7.28 (m, ovl, A/H-3,4,5),
7.30-7.45 (m, ovl, B,C/H-2,3,5,6); 13C NMR (75.5 MHz,
CDCl3): δ 71.2 (C3), 60.1 (C4), 79.5 (C5), 52.6 (OCH3), 168.8
(CO), 149.1 (A/C-1), 116.1 (A/C-2,6), 127.9, 128.3, 128.7,
129.4, 129.2 (A/C-3,5, B,C/C-2,6,3,5), 122.7 (A/C-4), 139.5
(B/C-1), 134.6, 134.2 (B,C/C-4), 136.1 (C/C-1). Anal. calcd.
(found) (%) for for C23H19NO3Cl2: C, 64.5 (64.3); H, 4.5 (4.6);
N, 3.3(3.1).
IR spectra were recorded in KBr discs on Perkin-Elmer
FT-IR model RX-9. UV spectra were recorded with a Hitachi
UV-vis-NIR model U 3501. 1H NMR and 13C NMR spectra were
recorded with Bruker AM-300L and Avance 300 instruments
at 300 MHz and 75.5 MHz and DRX 500 instruments at 500
MHz and 125.5 MHz respectively. Chemical shifts for NMR
1
are reported in ppm, downfield from TMS, H-1H coupling
constants are given in Hz. 13C NMR assignments were confir-
med by DEPT spectra. COSY and DQF-COSY experiments
were performed to unravel 1H-1H coupling information.
All chemicals were from Merck, India. These were purified
by recrystallization or by fractional distillation under reduced
pressure. The purities of starting materials were verified from
comparison of their melting points or boiling points with those
1
recorded in literature as well as from their IR and H NMR
spectra.
Preparation of dipolarophiles: The cinnamic acid methyl
esters (5,6,7) were prepared by esterification of the corres-
ponding acids (0.4 mol) by refluxing with anhydrous methanol
(162 mL)/concentrated sulphuric acid (6 mL) for 5 h. On
cooling crystals of methyl 4-chlorocinnamate, m.p. 74-76 °C
(yield 71.5 g, 91 %), methyl 4-nitrocinnamate, m.p. 162 °C
(yield 77.6 g, 95 %), methyl 4-methoxycinnamate, m.p. 94 °C
(yield 70.6 g, 92 %) respectively were obtained.
The arylidene malonate dipolarphiles (18,19,20) were
prepared by standard experimental procedures [24-26] from
diethyl malonates by condensation with the appropriate aromatic
aldehydes in presence of piperidine in benzene solution. The
structural integrities of the dipolarophiles were confirmed by
IR and NMR spectra.
General procedure for the cycloaddition reactions: The
[3+2] cycloadditions were carried out in refluxing dry thiophene-
free toluene with three-fold molar excess of the dipolarophile
under nitrogen atmosphere for 11-25 h, the reactions being
monitored by TLC and 1H NMR spectroscopy. The post-reaction
mixture was worked up by removing the solvent under reduced
pressure in a Büchi-type rotary evaporator, the residue was
analyzed by 1H NMR and TLC and then chromatographed over
neutral alumina to resolve the components.
Detected by 1H NMR in crude reaction mixture: Regio-
isomeric 3,4-trans-4,5-trans-2-phenyl-3,4-di(4′-chloro-
phenyl)-5-carbmethoxy isoxazolidine (9c): δ 4.81 (d, J = 7.5
Hz, H3), 4.07 (dd, J = 7.5, 8.5 Hz, H4), 4.49 (d, J=8.5 Hz,
H5).
Reaction of C-(4-nitrophenyl)-N-phenyl nitrone (2)
(0.655 g, 0.0027 mol) with methyl 4-chlorocinnamate (6)
1
(1.59 g, 3 × 0.0027 mol): Reaction time 12 h. 300 MHz H
NMR analysis revealed three products formed: total conversion
~ 92 %; ratio 10a:10b:10c = 89:7:4.
3,4-trans-4,5-trans-2-Phenyl-3-(4′-nitrophenyl)-5-
(4″-chlorophenyl)-4-carbmethoxy isoxazolidine (10a):
yellow solid, m.p. 62 °C, m.f.: C23H19N2O5Cl; yield 0.85 g (72
%), isolated from hexane eluates, Rf 0.62 (benzene). IR (KBr,
ν
max, cm-1): 3069, 2924, 2854, 1736 (ester CO), 1598, 1491,
1521 & 1346 (nitro), 1091, 1013 & 520 (aryl Cl), 825 (1,4-
disubstituted benzene ring), 755 & 692 (mono-substituted
benzene ring) cm-1. 1H NMR (300 MHz, CDCl3): δ 5.41 (d, J
= 6.0 Hz, H3), 3.54 (dd, J = 6.0, 9.0 Hz, H4), 5.45 (d, J = 9.0
Hz, H5), 3.73 (s, OCH3), 7.02-7.07 (m, ovl, A/H-2,4,6), 7.33
(br. t, J = 8.0 Hz, A/H-3,5), 7.79 (d, J = 8.7 Hz, B/H-2,6), 8.28
(d, J = 8.7 Hz, B/H-3,5), 7.28-7.49 (m, ovl, C/H-2,3,5,6); 13C
NMR(75.5 MHz, CDCl3): δ 72.7 (C3), 65.9 (C4), 82.1 (C5),
52.8 (OCH3), 170.2 (CO), 150.1 (A/C-1), 114.4 (A/C-2,6),
127.4 (A/C-3,5), 122.7 (A/C-4), 147.6 (B/C-1), 128.1 (B/C-
2,6), 124.2 (B/C-3,5), 148.5 (B/C-4), 134.8, 134.7 (C/C-1,4),
129.0, 129.2 (C/C-2,6,3,5). Anal. calcd. (found) (%) for
C23H19N2O5Cl: C, 62.9 (62.6); H, 4.4 (4.5); N, 6.4 (6.2).
Detected by 1H NMR in crude reaction mixture. 3,4-cis-
4,5-trans-2-Phenyl-3-(4′-nitrophenyl)-5-(4″-chlorophenyl)-4-
carbmethoxy isoxazolidine (10b): δ 5.14 (d, J = 9.0 Hz, H3),
Reaction of C-(4-chlorophenyl)-N-phenyl nitrone (1)
(1.02 g, 0.0044 mol) with methyl 4-chlorocinnamate (6)
1
(2.60 g, 3 × 0.0044 mol). Reaction time 11 h. 300 MHz H
NMR analysis revealed three products formed: total conversion
~ 94 %; ratio (9a), (9b), (9c) = 88:9:3.
3,4-trans-4,5-trans-2-Phenyl-3,5-di(4′-chlorophenyl)-4-
carbmethoxy isoxazolidine (9a): Yellow solid, m.p. 78 °C,
m.f.: C23H19NO3Cl2; yield 1.28 g (68 %), isolated from hexane
eluates, Rf 0.44 (benzene). IR (KBr, νmax, cm-1): 2952, 2852,
1732 (ester CO), 1637, 1596, 1489, 1400, 1091 & 1013 (aryl
Cl), 826 (1,4-disubstituted benzene ring), 758 & 695 (mono-
substituted benzene ring). 1H NMR(300 MHz, CDCl3): δ 5.19
(d, J = 6.6 Hz, H3), 3.49 (dd, J = 6.6, 8.4 Hz, H4), 5.38 (d, J =

Vol. 31, No. 12 (2019)
[3+2] Cycloadditions of C,N-Diaryl- and C-Aryl-N-methyl Nitrones to α,β-Unsaturated Esters 2779
3.70 (obs., overlapped with methoxy signals), 5.74 (d, J = 9.0
Hz, H5); 3,4-trans-4,5-trans-2-phenyl-3-(4′-nitrophenyl)-4-
(4″-chlorophenyl)-5-carbmethoxy isoxazolidine (10c): δ 4.83
(d, J = 6.0 Hz, H3), 4.07 (t, J = 6.0 Hz, H4), 4.67 (d, J = 6.0 Hz,
H5).
Reaction of C,N-diphenyl nitrone (3) (0.591 g, 0.003
mol) with methyl 4-chlorocinnamate (6) (1.77g, 3 × 0.003
mol): Reaction time 15 h. 300 MHz 1H NMR analysis revealed
three products formed: total conversion ~75 %; ratio
11a:11b:11c = 89:8:3.
carbmethoxy isoxazolidine (12b): δ 4.84 (d, J = 10.2 Hz, H3),
3.64 (br. t, J = ~9.7 Hz, H4), 5.70 (d, J = 9.3 Hz, H5); 3,4-trans-
4,5-trans-2-phenyl-3-(4′-chlorophenyl)-4-(4″-nitrophenyl)-5-
carbmethoxy isoxazolidine (12c): δ 4.64 (d, J = 6.0 Hz, H3),
4.07 (br. t, J = ~6.5 Hz, H4), 4.32 (d, J = 7.2 Hz, H5).
Reaction of C,N-diphenyl nitrone (3) (0.868 g, 0.0044 mol)
with methyl cinnamate (8) (2.14 g, 3 × 0.0044 mol): Reaction
time 16 h: 300 MHz 1H NMR analysis revealed three products
formed: total conversion ~75 %, ratio 13a:13b:13c = 91:7:2.
3,4-trans-4,5-trans-2,3,5-Triphenyl-4-carbmethoxy
isoxazolidine (13a): Pale yellow waxy solid, m.f.: C23H21NO3;
yield 0.94 g, 60 % isolated from hexane eluates, Rf 0.58 (benzene:
petroleum ether 1:1). IR (KBr, νmax, cm-1): 3062, 3029, 2952,
1720 (ester CO), 1637, 1597, 1489, 1443, 763 & 697 (mono-
substituted benzene ring).1H NMR(300 MHz, CDCl3): δ 5.16
(d, J = 6.8 Hz, H3), 3.53 (dd, J = 6.8, 8.8 Hz, H4), 5.32 (d, J =
8.8 Hz, H5), 3.71 (s, OCH3), 6.98 (d, J = 7.8 Hz, A/H-2,6),
6.87 (t, J = 7.5 Hz, A/H-3,5), 7.03 (t, J = 7.3 Hz, A/H-4), 7.15-
7.40 (m ovl, B/H-2,3,4,5,6, C/H-3,4,5), 7.49 (d, J = 7.2 Hz, C/
H-2,6); 13C NMR(75.5 MHz, CDCl3): δ 73.7 (C3), 66.0 (C4),
82.7 (C5), 51.9 (OCH3), 170.5 (CO), 150.9 (A/C-1),114.1 (A/
C-2,6), 126.6, 126.1 (A,B/C-3,5), 121.6 (A/C-4), 141.1 (B/C-
1), 128.7, 128.3, 128.7 (B/C-2,6, C/C-2,6,3,5), 127.9 (B/C-4),
137.3 (C/C-1), 128.6 (C/C-4). Anal. calcd. (found) (%) for
C23H21NO3: C 76.9 (76.6), H 5.9 (5.7), N 3.9 (3.7).
3,4-trans-4,5-trans-2,3-Diphenyl-5-(4′-chlorophenyl)-
4-carbmethoxy isoxazolidine (11a): Pale yellow waxy solid,
m.f.: C23H20NO3Cl; yield 0.70 g (60 %) isolated from hexane
eluates, Rf = 0.58 (benzene:petroleum ether 1:1). IR (KBr, νmax
,
cm-1): 3070, 3033, 2951, 1731 (ester CO), 1400, 1091, 1016
& 511 (aryl Cl), 826 (1,4-disubstituted benzene ring), 759 &
696 (mono-substituted benzene ring).1H NMR (300 MHz,
CDCl3): δ 5.11 (d, J = 6.8 Hz, H3), 3.45 (dd, J = 6.8 Hz, 8.4,
H4), 5.28 (d, J = 8.4 Hz, H5), 3.66 (s, OCH3), 6.93 (d, J = 8.8
Hz, A/H-2,6), 7.13 (t, J = 6.8 Hz, A/H-3,5), 6.85 (t, J = ~7.3
Hz, A/H-4), 7.12-7.31 (m, ovl, B,C/H-2,3,5,6); 13C NMR(75.5
MHz, CDCl3): δ 73.9 (C3), 66.3 (C4), 82.1 (C5), 52.5 (OCH3),
170.7 (CO), 150.9 (A/C-1),114.5 (A/C-2,6), 126.5 (A/C-3,5),
122.3 (A/C-4), 140.9 (B/C-1), 128.9, 128.3 (B/C-2,6,3,5), 127.9
(B/C-4), 135.7 (C/C-1), 129.0, 129.1 (C/C-2,6,3,5), 134.5 (C/
C-4). Anal. calcd. (found) (%) for C23H20NO3Cl: C 70.1 (69.8);
H 5.1 (4.9); N 3.6 (3.4).
Detected by 1H NMR in crude reaction mixture. 3,4-cis-
4,5-trans-2,3,5-Triphenyl-4-carbmethoxy isoxazolidine (13b):
δ 4.89 (d, J = 10.3, H3), 3.65 (obscured ovl, methoxy signal,
H4), 5.67 (d, J = 9.7, H5); 3,4-trans-4,5-trans-2,3,4-Triphenyl-
5-carbmethoxy isoxazolidine (13c): δ 4.72 (d, J = 6.7 Hz, H3),
4.01(br. t, J = ~7.0 Hz, H4), 4.45 (d, J = 7.5 Hz, H5).
Reaction of C-(4-nitrophenyl)-N-(4′-chlorophenyl)-
nitrone (14) (1.217 g, 0.0044 mol) with methyl cinnamate
(8) (2.14 g, 3 × 0.0044 mol): Reaction time 16 h. 300 MHz 1H
NMR analysis revealed three products formed: total conversion
~71 %, ratio 15a:15b:15c = 89:7:4.
Detected by 1H NMR in crude reaction mixture. 3,4-cis-
4,5-trans-2,3-Diphenyl-5-(4′-chlorophenyl)-4-carbmethoxy
isoxazolidine (11b): δ 4.85 (d, J = 10.4 Hz, H3), 3.68 (br. t, J
= ~9.9 Hz, H4), 5.61 (d, J = 9.6 Hz, H5); 3,4-trans-4,5-trans-
2,3-Diphenyl-4-(4′-chlorophenyl)-5-carbmethoxy isoxazolidine
(11c): δ 4.81 (d, J = 6.6 Hz, H3), 4.19 (br. t, J = ~7.0 Hz, H4),
4.51 (d, J = 7.5 Hz, H5).
Reaction of C-(4-chlorophenyl)-N-phenyl nitrone (1)
(1.02 g, 0.0044 mol) with methyl 4-nitrocinnamate (7) (2.73
g, 3 × 0.0044 mol): Reaction time 23 h. 300 MHz 1H NMR
analysis revealed three products formed: total conversion ~72
%; ratio 12a:12b:12c = 88:9:3.
3,4-trans-4,5-trans-2-Phenyl-3-(4′-chlorophenyl)-5-(4″-
nitrophenyl)-4-carbmethoxy isoxazolidine (12a): pale yellow
solid, m.p. 78 °C, m.f.: C23H19N2O5Cl; yield 1.10 g (58 %) isolated
from petroleum ether eluates, Rf 0.57 (petroleum ether:benzene
1:1). IR (KBr, νmax, cm-1): 3062, 2918, 2849, 1734 (ester CO),
1475, 1085, 1022 & 525 (aryl Cl), 809 (1,4-disubstituted
benzene ring), 762 & 683 (mono-substituted benzene ring).
1H NMR(300 MHz, CDCl3): δ 5.07 (d, J = 6.6 Hz, H3), 3.43
(br. t, J = ~7.1 Hz, H4), 5.47 (d, J = 7.6 Hz, H5), 3.76 (s,
OCH3), 6.96-7.18 (m, ovl, A,B/H-2,3,5,6), 6.94 (t, J = 7.4 Hz,
A/H-4), 7.44 (d, J = 8.4 Hz, C/H-2,6), 7.99 (d, J = 8.4 Hz, C/
H-3,5); 13C NMR (75.5 MHz, CDCl3): δ 72.9 (C3), 66.2 (C4),
80.9 (C5), 52.8 (OCH3), 170.3 (CO), 149.8 (A/C-1), 115.4 (A/
C-2,6), 127.4 (A/C-3,5), 122.4 (A/C-4), 138.7 (B/C-1), 128.8,
128.7, 128.0 (B/C-2,6,3,5, C/C-2,6), 134.0 (B/C-4), 145.4 (C/
C-1), 124.0 (C/C-3,5), 148.0 (C/C-4).Anal. calcd. (found) (%)
for C23H19N2O5Cl: C 62.9 (62.6); H 4.3 (4.3); N 6.4 (6.3).
Detected by 1H NMR in crude reaction mixture. 3,4-cis-
4,5-trans-2-Phenyl-3-(4′-chlorophenyl)-5-(4″-nitrophenyl)-4-
3,4-trans-4,5-trans-2-(4″-Chlorophenyl)-3-(4′-nitro-
phenyl)-5-phenyl-4-carbmethoxy isoxazolidine (15a): white
crystals, m.p. 128 °C, m.f.: C23H19N2O5Cl; yield 0.86 g (72
%), isolated from hexane eluates. UV: λmax 250 nm (log ε 4.22);
IR (KBr, νmax, cm-1): 2954, 2830, 1736 (ester CO), 1495, 1343
(aromatic –NO2), 1100 (aryl Cl), 825 (1,4-disubstituted benzene
ring), 749, 695 (mono-substituted benzene ring). 1H NMR(300
MHz, CDCl3): δ 5.35 (d, J = 6.1 Hz, H3), 3.53 (dd, J = 6.1, 8.5
Hz, H4), 5.45 (d, J = 8.5 Hz, H5), 3.70 (s, OCH3), 7.00 (d, J =
8.9 Hz, A/H-2,6), 7.25 (d, J = 8.9 Hz, A/H-3,5), 7.76 (d, J =
8.7 Hz, B/H-2,6), 8.26 (d, J = 8.7 Hz, B/H-3,5), 7.36-7.41 (m,
ovl, C/H-2,3,5,6,4); 13C NMR(75.5 MHz, CDCl3): δ 72.9 (C3),
65.9 (C4), 83.2 (C5), 52.8 (OCH3), 170.2 (CO), 148.9 (A/C-
1), 115.8 (A/C-2,6), 128.7 (A/C-3,5), 136.2, 136.0 (A/C-4, C/
C-1), 147.8 (B/C-1), 127.4 (B/C-2,6), 124.2 (B/C-3,5), 148.2
(B/C-4), 128.9, 129.1 (C/C-2,6,3,5), 126.7 (C/C-4).Anal. calcd.
(found) (%) for C23H19N2O5Cl: C 62.9 (62.7), H 4.4 (4.5), N
6.4 (6.2).
Detected by 1H NMR in crude reaction mixture. 3,4-cis-
4,5-trans-2-(4′-Chlorophenyl)3-(4″-nitrophenyl)-5-phenyl-4-
carbmethoxy isoxazolidine (15b): δ 5.13 (d, J = 10.1 Hz, H3),
3.66 (br. t, J = ~9.7 Hz, H4), 5.68 (d, J = 9.4 Hz, H5); 3,4- trans-

2780 Sengupta et al.
Asian J. Chem.
4,5-trans-2-(4′-Chlorophenyl)-3-(4″-nitrophenyl)-4-phenyl-5-
carbmethoxy isoxazolidine (15c): δ 4.96 (d, J = 6.1 Hz, H3),
4.12 (br. t, J = ~6.6 Hz, H4), 4.47 (d, J = 7.1 Hz, H5).
Reaction of C-(4-chlorophenyl)-N-methyl nitrone (16)
(0.746 g, 0.0044 mol) with diethyl (4-nitrophenyl) methylene
malonate (18) (3.86 g, 3 × 0.0044 mol): Reaction time 25 h.
300 MHz 1H NMR analysis revealed only one product.
3,5-trans-2-Methyl-3-(4′-chlorophenyl)-5-(4″-nitro-
phenyl)-4,4-dicarbethoxy isoxazolidine, (21): Pale yellow
crystals, m.p. 106-108 °C; m.f.: C22H23N2O7Cl; yield 1.70 g
(84 %), isolated from hexane eluates, Rf 0.59 (benzene). UV
(λmax, EtOH): 266 nm (log ε: 4.19). IR (KBr, νmax, cm-1): 2990,
1724 (ester CO), 1521 & 1346 (aromatic -NO2), 1103,1062 &
503 (aromatic Cl), 859 (1,4-disubstituted benzene ring), 750 &
benzene ring), 746 & 691(mono-substituted benzene ring).
1H NMR (300 MHz, CDCl3): δ 4.84 (s, H-3), 6.05 (s, H-5),
3.82, 3.34 (dq, J = 10.7, 7.2 Hz, CO2CH2CH3(I)), 0.67 (t, J =
6.3 Hz, CO2CH2CH3(I)), 3.75, 3.27 (dq, J = 10.7, 7.1 Hz,
CO2CH2CH3(II)), 0.71 (t, J = 6.3 Hz, CO2CH2CH3(II)), 2.74 (s,
N-CH3), 8.21(d, J = 8.8 Hz, A/H-2,6), 7.64 (d, J = 8.8 Hz,
A/H-3,5), 7.30-7.43 (m, B/H-2,6,3,5,4), 13C NMR(75.5 MHz,
CDCl3): δ 77.6 (C-3), 75.1 (C-4), 84.2 (C-5), 167.8, 167.4, (>CO
(I,II)), 61.7, 61.5 (CO2CH2CH3(I,II)), 13.3,13.1 (CO2CH2CH3(I,II)),
43.0 (N-CH3), 147.9 (A/C-1), 130.0 br. (A/C-2,6), 123.4 (A/C-
3,5), 143.8 (A/C-4), 135.5 (B/C-1), 128.7, 128.1 (B/C-2,6,3,5),
127.5 (B/C-4).Anal. calcd. (found) (%) for C22H24N2O7: C 61.7
(61.4), H 5.6 (5.4), N 6.5 (6.3).
X-ray crystallographic analysis of cycloadduct 22:
Cycloadduct 22 was recrystallized by slow evaporation from
methanol solution at room temperature to obtain single crystals.
Diffraction data were recorded on a Bruker Smart Apex II
CCD area detector diffractometer operating the Mo Kα radia-
tion (λ = 0.7107 Å) at the Department of Chemistry, University
of Calcutta. The structures were solved by direct methods
(SHELXS) and refined using isotropic, then anisotropic thermal
factors (SHELXL program) [27]. Hydrogens were gradually
introduced in the calculations and kept riding on the bonded
atom during all refinements. Figure is drawn using the PLATON
program [28].
1
692 (mono-substituted benzene ring). H NMR (500 MHz,
CDCl3): δ 4.72 (s, H3), 6.10 (s, H-5), 3.83, 3.40 (dq, J = 10.7,
7.0 Hz, CO2CH2CH3(I)), 0.70 (t, J = 7.0 Hz, CO2CH2CH3(I)),
3.78, 3.29 (dq, J = 10.7, 7.2 Hz, CO2CH2CH3(II)), 0.75 (t, J =
7.2 Hz, CO2CH2CH3(II)), 2.75 (s, N-CH3), 7.30-7.36 (close
coupled AB system, A/H-2,6,3,5), 7.60 (d, J = 8.7, B/H-2,6),
8.18 (d, J = 8.7 Hz, B/H-3,5); 13C NMR(125.5 MHz, CDCl3):
δ 78.3 (C3), 75.3 (C4), 83.2 (C5), 168.0, 167.9 (>CO (I,II)),
62.2, 62.1 (CO2CH2CH3(I,II)), 13.7, 13.6 (CO2CH2CH3(I,II)), 43.4
(N-CH3), 134.9, 134.7 (A/C-1,4), 129.0, 128.8, 129.3 (A/C-
2,6,3,5, B/C-3,5), 148.4 (B/C-1), 123.5 (B/C-2,6), 143.5 (B/
C-4).Anal. calcd. (found) (%) for C22H23N2O7Cl: C 57.1 (56.8),
H 5.0 (4.8), N 6.1 (5.9).
Crystals were orthorhombic (space group Pca21). Crystal
data and structure refinement for cycloadduct 22 is given in
Table-1. The X-ray crystallographic study showed an all trans-
configuration: H-3 and H-5 were trans-oriented, additionally
the N-lone pair was trans- to H-3. Two optical antipodes were
present in the unit cell which had a two-fold alternating axis
of symmetry.
Reaction of C-(4-chlorophenyl)-N-methyl nitrone (16)
(0.746 g, 0.0044 mol) with diethyl phenyl methylene
malonate (20) (3.27 g, 3 × 0.0044 mol): Reaction time 18 h.
300 MHz 1H NMR analysis revealed only one product.
3,5-trans-2-Methyl-3-(4′-chlorophenyl)-5-phenyl-4,4-
dicarbethoxy isoxazolidine (22): White shining crystals, m.p.
112-114 °C, m.f.: C22H24NO5Cl; yield 1.61 g (88 %), isolated
from hexane eluates, Rf 0.61 (benzene). IR (KBr, νmax, cm-1):
1728 (ester CO), 1591 (aromatic C=C), 1093, 1043 & 502
(aromatic -Cl), 861(1,4-disubstituted benzene ring), 759 &
Supplementary data contain - positional parameters (× 104)
and mean recalculated isotropic factors (× 103) for non-hydrogen
TABLE-1
CRYSTAL DATA AND STRUCTURE
REFINEMENT FOR CYCLOADDUCT 22
1
703 (mono substituted benzene ring); H NMR (300 MHz,
Formula
C22H24NO5Cl
CDCl3): δ4.64 (s, H3), 5.96 (s, H-5), 3.66, 3.17 (dq, J = 10.7, 7.2
Hz, CO2CH2CH3(I)), 0.59 (t, J = 7.2 Hz, CO2CH2CH3(I)), 3.71,
3.33 (dq, J = 10.7,7.2 Hz, CO2CH2CH3(II)), 0.67 (t, J = 7.2 Hz,
CO2CH2CH3(II)), 2.67 (s, N-CH3), 7.20-7.40 (m, A,B/H-2,6,3,5);
13C NMR (75.5 MHz, CDCl3): δ 77.9 (C-3), 74.9 (C-4), 84.1
(C-5), 168.1, 167.8 (>CO (I,II)), 61.4 (CO2CH2CH3(I,II)), 13.2,
13.1 (CO2CH2CH3(I,II)), 43.0 (N-CH3), 134.2, 134.7 (A/C-1,4),
128.1, 128.6, 128.5 (A/C-2,6,3,5, B/C-3,5), 135.8 (B/C-1),
129.9 br. (B/C-2,6), 127.5 (B/C-4). Anal. calcd. (found) (%)
for C22H24NO5Cl: C 63.2 (63.0), H 5.7 (5.5), N 3.4 (3.4).
Reaction of C-(4-nitrophenyl)-N-methyl nitrone (17)
(0.612 g, 0.0034 mol) with diethyl phenyl methylene
malonate (20) (2.57 g, 3 × 0.0034 mol): Reaction time 15 h.
300 MHz 1H NMR analysis revealed only one product.
3,5-trans-2-Methyl-3-(4′-nitrophenyl)-5-phenyl-4,4-
dicarbethoxy isoxazolidine (23): yellow crystals, m.p. 108-
110 °C, m.f.: C22H24N2O7; yield 1.25g (85 %) isolated from 10 %
benzene in petroleum ether eluates, Rf 0.48 (benzene). IR (KBr,
m.w.
Temperature
Radiation
Crystal system, space group
Cell parameters
417.87
150°(2) K
Mo Kα - 0.71073 Å
Orthorhombic, Pca21
a = 16.582(6) Å; b = 10.482(4) Å;
c = 25.442(10) Å; α = β = γ = 90°
4422(3) Å3
Volume
Z, Calculated density
Absorption coefficient
F(000)
8, 1.255 Mg/m3
0.204 mm-1
1760
0.22 × 0.16 × 0.09 mm
1.60 - 18.44°
-14<=h<=14, -9<=k<=9,
-22<=l<=22
Crystal size
θmin – θmax
Limiting indices
Reflections collected/unique
Completeness to q
Refinement method
14738/3232 [R(int) = 0.1284]
99.3 %
Full-matrix least-squares on F2
3232/530
Data/parameters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
1.032
R1 = 0.0510, wR2 = 0.1026
R1 = 0.0827, wR2 = 0.1185
0.162 and -0.172 e.A-3
ν
max, cm-1): 2983, 1726 (ester CO), 1602, 1524 & 1354 (aromatic
-NO2), 1102, 1035 & 502 (aromatic -Cl), 852 (1,4-disubstituted
Largest diff. peak and hole

Vol. 31, No. 12 (2019)
[3+2] Cycloadditions of C,N-Diaryl- and C-Aryl-N-methyl Nitrones to α,β-Unsaturated Esters 2781
atoms; positional parameters (× 103) and mean recalculated
isotropic factors (× 103) for hydrogen atoms; anisotropic thermal
parameters.
observed. The results of the other 32CA reactions are summa-
rized in Scheme-I.All the reactions gave 3,4-trans-4,5-trans-
2,3,5-triaryl-4-carbmethoxy isoxazolidine (series a) as major
products, the corresponding diastereoisomeric 3,4-cis-4,5-
trans-2,3,5-triaryl-4-carbmethoxy isoxazolidine (series b) were
obtained as minor products, the regioisomeric 3,4-trans-4,5-
trans-2,3,4-triaryl-5-carbmethoxy isoxazolidine (series c) were
obtained in even lesser quantity. All the major products (9a,
10a, 11a, 12a, 13a) were isolated by chromatography in pure
state. Of the minor compounds, only 9b could be isolated in
the pure state. The other diastereoisomeric products (10b to
13b) and regioisomeric products (9c to 13c) were detected by
1H NMR of the crude reaction mixture.All the isolated products
(9a-13a, 9b) showed IR bands (1736-1730 cm-1) characteristic
of unconjugated ester; other characteristic bands could be
assigned to substituted aromatic rings, aryl Cl and aryl nitro
substituents.
RESULTS AND DISCUSSION
32CA of C,N-diaryl nitrones to substituted methyl E-
cinnamates: The 32CA of four differently substituted nitrones
(1-4) to various substituted methyl E-cinnamates are reported
(Scheme-I). Additionally, the reaction of C-(4-nitrophenyl)-
N-(4′-chlorophenyl) nitrone (14) with 8, reported earlier [19],
was repeated to obtain further amounts of the resultant cyclo-
adducts 15a-c.
The following reactions were carried out in refluxing anhy-
drous toluene with thee-fold molar excess of the cinnamates:
(a) nitrones 1, 2, 3, 4 with 6; (b) nitrone 4 with 5; (c) nitrone 1
with 7; (d) nitrone 3 with 8; (e) nitrone 14 with 8 (repetition
of earlier work) [19].
The reactions were monitored by TLC and 300 MHz 1H
NMR analysis of aliquots taken from time to time. Work-up
involved removal of the solvent under reduced pressure in a
rotary evaporator, followed by 1H NMR analysis of the post-
reaction mixture for total overall yield and product ratios. The
post-reaction mixture was then chomatographed over neutral
alumina to isolate the products. Reactions of 4 with 5 and 6
did not proceed satisfactorily as evident from 1H NMR moni-
toring of the reaction mixtures-extensive decomposition was
Structure elucidation of the products were achieved by
spectroscopic analysis, particularly by 300 MHz 1H NMR and
75.5 MHz 13C NMR and comparison of the values with those
of the isoxazolidines generated by 32CA of nitrones to α,β-
unsaturated amides [9-12]. We reported earlier that the 32 CA
of C-(4-nitrophenyl)-N-(4′-chlorophenyl) nitrone (14) with
methyl cinnamate (8) furnished 15a as the major compound; this
on mild hydrolysis afforded the corresponding acid 15d. XRD
analysis of 15d established the structure as 3,4-trans-4,5-trans-
R1
H
CO2Me
H
C
C
Dry toluene/Reflux
11-23 h/N2
+
C
N
H
O
R2
R
(1) R =H R1=Cl
(5) R2= OMe
(6) R2= Cl
(2) R= H R1=NO2
(3) R= H R1=H
(7) R2= NO2
(8) R2= H
(4) R= H R1=OMe
(14) R= Cl R1=NO2
R2
R1
R1
H
CO2Me
H
B
C
H
N
H
B
A
R1
H
N
CO2Me
H
B
H
+
H
N
+
O
CO2Me
O
C
C
O
A
R
R
R2
H
R2
R
9a
9c
9b
(9) R =H R1=Cl R2= Cl
(10)R= H R1=NO2 R2= Cl
10c
11c
12c
13c
15c
10b
11b
12b
13b
15b
10a
11a
12a
13a
15a
(11)R= H R1=H
(12)R= H R1=Cl R2= NO2
(13)R= H R1= H R2= H
(15)R= Cl R1=NO2 R2= H
R2= Cl
15d= CO2H instead
of CO2Me
Scheme-I: 32CA of C,N-diaryl nitrones to substituted methyl cinnamates

2782 Sengupta et al.
Asian J. Chem.
TABLE-2
300 MHz 1H NMR ASSIGNMENTS OF CYCLOADDUCTS; CHEMICAL SHIFTS IN δ, COUPLING CONSTANTS IN Hz
Proton No.
H-3
9a
9b
9c
15a
15d
5.19 (d, 6.6)
3.49 (dd, 6.6, 8.4)
5.38 (d, 8.4)
4.98 (d, 10.2)
3.73 (br.t, ~9.9)
5.72 (d, 9.6)
4.81 (d, 7.5)
4.07 (dd, 7.5, 8.5)
4.49 (d, 8.5)
5.35 (d, 6.1)
3.53 (dd, 6.1, 8.5)
5.41 (d, 8.5)
5.54 (d, 8.4)
3.54 (dd, 8.4, 8.7)
5.33 (d, 8.7)
H-4
H-5
2-(4′-chlorophenyl)-3-(4″-nitrophenyl)-5-phenyl-4-carboxy
isoxazolidine. The characteristic 1H NMR and 13C NMR signals
relating to isoxazolidine ring of 15a and 15d are given in Tables
2 and 3. The chemical shifts and coupling constants of the
isomeric cycloadducts (9a, 9b, 9c) are given in Table-2.
In the diasteroisomeric series (9b-13b, 15b), the H-4 and
H-5 signals were more differentiated with respect to each other,
H-3 moving ~0.2 ppm upfield and H-5 ~0.3 ppm downfield;
H-4 shifted ~0.2 ppm downfield. All three 13C-signals moved
upfield: C-3 by ~2 ppm, C-4 by ~6 ppm and C-5 by ~2.5 ppm
in 9b compared to 9a. J3,4 and J4,5 coupling constants were
enhanced to ~9.5-10.5 Hz in this series.
The proton shifts of 9c were markedly different from those
of 9a – H-5 moved significantly upfield (~0.9 ppm) while H-
4 moved downfield by ~0.6 ppm, consequent upon the inter-
change of the substituents between C-4 and C-5. The magnitude
of J3,4 and J4,5 (7.5 and 8.5Hz) suggested a 3,4-trans-4,5-trans
configuration in 9c. In the other members of the regioisomeric
series (10c-13c,15c), the 1H- and 13C NMR characteristics of
the isoxazolidine ring carbons and protons were similar to those
of compound 9c.
32 CA of C,N-disubstituted nitrones to arylidene malo-
nates: 32CA reactions of C-aryl-N-methyl nitrones with
diethyl arylidene malonates were investigated (Scheme-II).
Studies on 32CA of N-methyl nitrones to arylidene malonates
had not been investigated earlier. Our earlier publication on
32CA of arylidene malonates involved C,N-diaryl nitrones only
[20].
TABLE-3
75.5 MHz 13C NMR ASSIGNMENTS OF
CYCLOADDUCTS, CHEMICAL SHIFTS IN δ
15d#
Carbon No.
9a
9b
15a
C-3
C-4
C-5
73.1
66.2
82.0
71.2
60.1
79.5
72.9
65.9
83.2
72.3
65.0
83.1
#In DMSO-d6
The signals in 9a were similar to the corresponding signals
of 15a with small changes attendant upon changes in aromatic
substituents which affect the 1H- and 13C NMR chemical shifts
in the benzylic 3- and 5-positions. Hence cycloadduct 9a was
3,4-trans-4,5-trans-2-phenyl-3,5-di(4′-chlorophenyl)-4-
carbomethoxy isoxazolidine belonging to series a type of cyclo-
adducts, arising out of meta-channel endo-carbonyl-exo-aryl
approach of 6 to the nitrone [2].
The positions of attachment of aryl rings at C-3 and C-5
were confirmed from COSY-LR assignments of 9a and 9b
which showed long range couplings of H-3 and H-5 with ortho-
aryl protons. 9b was therefore diastereoisomeric with 9a,
having a 3,4-cis-4,5-trans configuration arising from the meta-
channel exo-carbonyl-endo-aryl approach of 6 to the nitrone
[2]. The relative configuration of C-4 and C-5 were fixed from
the E-configuration of the starting E-methyl cinnamate.
The structure and stereochemistry of the other cyclo-
adducts of all three series were established by comparison of
the 1H- and 13C NMR characteristics of the isoxazolidine ring
carbons and protons with those of 9a, 9b and 9c, respectively.
The major series a (10a, 11a, 12a, 13a) showed H-3 in the
region δ 5.07-5.41, H-5 in the region δ 5.28-5.47, H-4 in the
region δ 3.43-3.54, J3,4 (6.0-6.8 Hz), J4,5 (7.6-9.0Hz); C-3 in
the region δ 72.7-73.9, C-4 in the region δ 65.9-66.3, C-5 in
the region δ 80.9-82.7.
The reactions carried out were (i) 16 with 18, 19, 20; (ii)
17 with 19, 20. Reactions were carried out with a three-fold
molar excess of the arylidene malonates in refluxing anhydrous
1
toluene with H NMR and TLC monitoring. Work-up was
similar to that described earlier. 1H NMR analysis of the post
reaction mixture showed the presence of a single cycloadduct;
no other products were detected within limits of NMR detec-
tion (~ 0.5 %). Conversions were nearly quantitative.
A remarkable increase in regio- and stereoselectivity com-
pared to cinnamic acid esters was observed leading to the exclu-
sive formation in the reactions of the trans-3,5-diaryl-4,4-
dicarbethoxy isoxazolidines. These were obtained by meta-
channel exo-aryl approach of the arylidene malonates to the
nitrone. NMR monitoring of reactions (both 16 and 17 with
19) showed that these reactions with arylidene malonates
bearing the electron-releasing substituent methoxy were not
R1
R1
EtO2C
CO2Et
H
N
CO2Et
CO2Et
A
H
Dry toluene/Reflux
N2/18 h
H
+
H
Me
O
N
B
O
Me
R2
R2
(18) R2= NO2
(19) R2= OMe
(20) R2= H
(21) R1 = Cl R2= NO2
(22) R1 = Cl R2 = H
(23) R1 = NO2 R2 = H
(16) R1 = Cl
(17) R1 = NO2
Scheme-II: 32CA of C-aryl-N-methyl nitrones to diethyl arylidene malonates

Vol. 31, No. 12 (2019)
[3+2] Cycloadditions of C,N-Diaryl- and C-Aryl-N-methyl Nitrones to α,β-Unsaturated Esters 2783
successful-extensive decomposition was observed. These were
not followed up.
IR spectra of the cycloadducts exhibited bands corres-
ponding to non-conjugated esters (~ 1730 cm -1), 300 MHz 1H
NMR spectra showed two singlets corresponding to H-3 and
H-5 (δ 4.64 and δ 5.96 respectively for 22), thus confirming
the regiochemistry of these cycloadducts. Both these protons
showed long range coupling with the ortho-protons of aryl
rings attached to C-3 and C-5.
Both these protons showed long range coupling with the
ortho-protons of aryl rings attached to C-3 and C-5 (Fig. 1;
DQF-COSY of 21). Two carbethoxyl groups are attached to
the diastereotopic centre C-4. Consequently the methylene
protons and the methyl protons in the ethyl ester units are
differentiated. Further, within each methylene group the two
protons are differentiated, the mutual relationships of which
were confirmed by reference to the DQF-COSY of cycloadduct
21. The relative stereochemistry of the N-methyl cycloadduct
22 and hence of the other cycloadducts was confirmed by XRD
studies. Earlier we had reported the XRD analysis of N-phenyl
cycloadduct having the same relative configuration [12].
Fig. 2. X-ray crystallographic analysis of cycloadduct 22-ORTEP projection
with high regioselectivity to give mainly 2,3,5-triaryl isoxa-
zolidine adducts; (ii) the major product belonged to the 3,4-
trans-4,5-trans series, obtained by the meta-channel, endo-
carbonyl-exo-aryl approach of the methyl cinnamate; (iii)
stereoselectivity overwhelmingly favoured the 3,4-trans-4,5-
trans adducts (meta-channel, endo-carbonyl-exo-aryl approach
of the methyl E-cinnamate) over the 3,4-cis-4,5-trans adducts
(meta-channel, exo-carbonyl-endo-aryl approach); (iv) the
regioisomeric isomers (ortho-channel) were obtained only in
slight amounts; (v) the product ratios of cycloadducts of series
a:b:c were 88-91: 7-9: 2-4; (vi) product ratios were essentially
similar even with changes of substituents on either of the reac-
tants. This is in contrast to 32CAs of α,β-unsaturated amides
to C,N-diaryl nitrones [12,16], where changes in aryl substi-
tuents affected the regioselectivities.
0
1
2
3
4
5
6
7
8
9
10
10
9
8
7
6
5
4
3
2
1
0
ppm
32CA reactions of C-aryl-N-methyl nitrones with diethyl
arylidene malonates were investigated, as these had not been
investigated earlier.A remarkable increase in regio- and stereo-
selectivity compared to cinnamic acid esters was observed
leading to the exclusive formation in the reactions of the trans-
3,5-diaryl-4,4-dicarbethoxy isoxazolidines by a endo-aryl meta
channel approach of the 2π component.
Fig. 1. 500 MHz 1H-1H DQF-COSY of cycloadduct 21 in CDCl3
Compound 22 was recrystallized from methanol to obtain
single crystals. Diffraction data were recorded on a Brucker
SmartApex II CCD area detector diffractometer operating the
MoKα radiation (λ = 0.7107 Å). Crystals were orthorhombic
(space group Pca21) with cell parameters a = 16.582(6) Å; b
= 10.482(4) Å; c = 25.442(10) Å; α = β = γ = 90°. The X-ray
crystallographic study showed an all trans-configuration: H-
3 and H-5 were trans-oriented, additionally the N-lone pair
was trans- to H-3. Two optical antipodes were present in the
unit cell which had a two-fold alternating axis of symmetry.
The ORTEP projection is shown in Fig. 2. The numberings of
structures as given in these projections are those provided in
the X-ray crystallographic analysis outputs.
ACKNOWLEDGEMENTS
One of the authors, S.S.G. thanks C.S.I.R. for providing
a Junior Research Fellowship and also to the authorities for
laboratory and computational facilities at Department of Chemistry,
Chandernagore College, Chandernagore to complete this work.
Another author, AB thanks University of Calcutta for provi-
ding laboratory infrastructure facilities before his retirement
as Professor of Chemistry. He also thanks Indian Science Congress
Association-Department of Science and Technology for the
award of SirAsutosh Mookerjee Fellowship for senior Scientists;
and the Director-General, CCRAS, for extending the facilities
of CentralAyurveda Research Institute for Drug Development,
Kolkata to avail this Fellowship.
Conclusion
The results of 32CA reactions between four differently
substituted C,N-diaryl nitrones with four methyl E-cinnamates,
bearing different aryl substituents, were investigated. The results
can be summarized as follows: (i) The reactions proceeded

2784 Sengupta et al.
CONFLICT OF INTEREST
Asian J. Chem.
14. A. Banerji, S. Dasgupta, P. Sengupta, T. Prangé and A. Neuman, Indian
J. Chem., 43B, 1925 (2004).
15. N. Acharjee and A. Banerji, Comput. Theor. Chem., 967, 50 (2011);
https://doi.org/10.1016/j.comptc.2011.03.040.
16. A. Banerji, P.K. Biswas, D. Bandyopadhyay, M. Gupta, T. Prangé and
A. Neuman, J. Heterocycl. Chem., 44, 137 (2007);
https://doi.org/10.1002/jhet.5570440122.
The authors declare that there is no conflict of interests
regarding the publication of this article.
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