Synthesis and spectral studies of some 4H-pyran derivatives: Crystal and molecular structure of isobutyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran-3- carboxylate

Article abstract of DOI:10.1016/j.molstruc.2012.11.057

A series of isobutyl 6-amino-4-aryl-5-cyano-2-methyl-4H-pyran-3- carboxylates (1-9) have been synthesized by the multicomponent reaction (MCR) between isobutyl ethylacetoacetate, aryl aldehydes and malononitrile using BF₃:OEt₂ as catalyst. The derived compounds have been analyzed by IR and NMR (1D and 2D) spectra. Single crystal X-ray structural analysis of 1, evidences the flattened-boat conformation of pyran ring.

Full text of DOI:10.1016/j.molstruc.2012.11.057

Journal of Molecular Structure 1036 (2013) 257–266
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and spectral studies of some 4H-pyran derivatives: Crystal and
molecular structure of isobutyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran
-3-carboxylate
⇑
C. Udhaya Kumar, A. Sethukumar, B. Arul Prakasam
Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, India
h i g h l i g h t s
"
"
"
BF3:OEt2 catalyzed synthesis of 4H-pyrans. MCR between isobutyl ethylacetoacetate, aryl aldehydes and malononitrile.
Spectral characterization by IR, 1D and 2D NMR.
Single crystal XRD analysis of isobutyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran-3-carboxylate.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 October 2012
Received in revised form 24 November 2012
Accepted 26 November 2012
Available online 5 December 2012
A series of isobutyl 6-amino-4-aryl-5-cyano-2-methyl-4H-pyran-3-carboxylates (1–9) have been synthe-
sized by the multicomponent reaction (MCR) between isobutyl ethylacetoacetate, aryl aldehydes and
malononitrile using BF3:OEt2 as catalyst. The derived compounds have been analyzed by IR and NMR
(1D and 2D) spectra. Single crystal X-ray structural analysis of 1, evidences the flattened-boat conforma-
tion of pyran ring.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
MCR
BF3:OEt2
HSQC
HMBC
XRD
1. Introduction
vital for enhancing quality of life [7]. The development of efficient
chemical processes for the preparation of new biologically active
Development of environmentally benign and clean synthetic
procedures has become the goal of present day organic synthesis
[1]. Multi-step reactions usually produce significant amount of
waste, principally due to a series of complex isolation procedures
which often involves hazardous and expensive solvents after each
step. Multicomponent domino reactions (MDRs), have become an
increasingly useful tool for the synthesis of chemically and biolog-
ically important compounds because of their convergence atom
economy and other suitable characteristics form the point of view
of green chemistry [2–6].
and structurally captivating molecules constitutes a major chal-
lenge for chemists in organic synthesis. Significant advances have
been made in the chemical processes to achieve the ultimate goal
of hazard-free, waste-free and energy-efficient synthesis [8]. In this
context, multicomponent reactions have played an important role
in these processes [9,10]. MCR is the well-known concept [11,12]
and has been used extensively in both liquid-phase and
solid-phase [13] chemistry for the rapid assembly of complex
heterocyclic structures of therapeutic importance [14]. Pyran
based heterocyclic compounds are having an important place due
to their distinct structures and great potential for further transfor-
mations. Some novel methods for the synthesis of pyrans via MCR’s
have been reported. Several catalysts like CTACl [15], Baker’s yeast
Heterocyclic compounds occur very widely in nature and are
essential to life. Oxygen containing heterocyclic molecules consti-
tutes the significant portion of chemical entities, which are part of
many natural products and biologically active pharmaceuticals
[16], L-proline [17], NaBr [18], phenylboronic acid [19], piperidine
[20,21], KF-montmorillonite [22], Ru [23], imidazole [24], NiCl2
[25], nano-ZnO [26,27], S-proline [28], SiO2 NPs [29], DMAP [30]
and NEt3 [31] have been utilized for this transformations. However,
⇑
Corresponding author. Tel.: +91 9443583619.
E-mail address: arul7777@yahoo.com (B. Arul Prakasam).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.11.057

258
C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
up procedure, which hampers their applications and leaves room
for further upgradation.
A careful survey of literature reveals that there is a need for
general method of the synthesis of structurally diverse isobutyl
6-amino-4-aryl-5-cyano-2-methyl-4H-pyran-3-carboxylates. In this
paper, we report the synthesis of a series of isobutyl 6-amino-4-
aryl-5-cyano-2-methyl-4H-pyran-3-carboxylates using BF3:OEt2
as a catalyst.
2. Experimental
Starting materials obtained from commercially available analyt-
ical grade materials were used as supplied, without further purifi-
cation. IR spectra were recorded on Avatar Nicolet FT-IR
spectrophotometer (range 4000–400 cmꢀ1) as KBr pellets. Proton
NMR spectra were recorded at room temperature (298 K) on Bru-
ker AMX-400 spectrometer operating at 400.23 MHz using TMS
as internal reference. 13C NMR spectra were recorded in proton
decoupled mode on Bruker AMX-400 spectrometer operating at
100.63 MHz. CDCl3 was used as solvent for NMR spectral studies.
2.1. General procedure for the synthesis of compounds 1–9
A mixture of aromatic aldehyde (1.0 mmol), malononitrile
(1.0 mmol), isobutyl ethylacetoacetate (1.0 mmol), and BF3:OEt2
(0.04 mmol) was stirred magnetically in 25 ml of absolute ethanol
at 80 °C (Scheme 1) for required period of time (ꢁ80 min). The pro-
gress of the reaction was monitored by TLC. After completion of the
reaction, the reaction mixture was allowed to cool to room temper-
ature and the solvent was evaporated. The solid thus appeared was
Scheme 1.
in this era, when green methods are warranted, many of these
methods are not satisfactory as they involve the use of halogenated
solvents, drastic reaction conditions, low yields and tedious work
Scheme 2.

C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
259
Table 1
collected and washed with cold water and finally recrystallized
from ethanol to get the pure product. The proposed mechanism
of the reaction is given in Scheme 2.
Structure and yield for compounds 1–9.
Compound nos.
Aldehyde
Product
Yield (%)
1
92
87
89
O
O
O
H
H
H
2.1.1. Isobutyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran-3-
carboxylate 1
O
O
Yellow solid, yield: 92%. m.p. 158–160 °C; IR (KBr, cmꢀ1) 3408,
3332, 2963, 2191, 1696, 1380, 1263, 1061; 1H NMR (d): 7.31–7.18
(m, 5H, ArAH), 4.47 (s, 2H, NH2), 4.44 (s, 1H, H-4), 3.76 (m, 2H, H-8),
2.4 (s, 3H, H-12), 1.74 (m, 1H, H-9), 0.76 (d, J = 8 Hz, 3H, H-10),
0.73 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d): 166.0, 157.4, 157.2,
143.7, 128.6, 127.3, 127.2, 119.0, 107.7, 70.9, 62.5, 38.7, 27.5,
19.0, 19.0, 18.5; Anal. Calcd. (%) for C18H20N2O3: C, 69.21; H, 6.45;
N, 8.97. Found (%): C, 69.01; H, 6.34; N, 8.25; HRMS (ESI): m/z 312.8.
NC
O
O
H2N
O
2
3
Cl
Cl
NC
H2N
O
Cl
2.1.2. Isobutyl 6-amino-4-(2-chlorophenyl)-5-cyano-2-methyl-4H-
pyran-3-carboxylate 2
Yellow solid, yield: 87%. m.p. 145–147 °C; IR (KBr, cmꢀ1) 3423,
3329, 2962, 2195, 1691, 1377, 1264, 1060; 1H NMR (d): 7.34–7.12
(m, 4H, ArAH), 5.06 (s, 1H, H-4), 4.49 (s, 2H, NH2), 3.75 (m, 2H, H-
8), 2.43 (s, 3H, H-12), 1.77 (m, 1H, H-9), 0.75 (d, J = 6.8 Hz, 3H, H-
10), 0.67 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d): 166.7, 158.2,
157.6, 141.1, 133.0, 129.9, 129.5, 128.3, 127.3, 118.5, 106.8, 71.1,
61.3, 35.2, 27.5, 18.9, 18.9, 18.5; Anal. Calcd. (%) for C18H19ClN2O3:
C, 62.34; H, 5.52; N, 8.08. Found (%): C, 62.02; H, 5.32; N, 7.92;
HRMS (ESI): m/z 346.7.
O
O
NC
O
O
Cl
H2N
Br
O
4
5
90
88
O
O
H
H
NC
Br
H2N
O
F
2.1.3. Isobutyl 6-amino-4-(4-chlorophenyl)-5-cyano-2-methyl-4H-
pyran-3-carboxylate 3
Yellow solid, yield: 89%. m.p. 139–140 °C; IR (KBr, cmꢀ1) 3403,
3330, 2963, 2196, 1694, 1339, 1268, 1062; 1H NMR (d): 7.28–7.08
(m, 4H, ArAH), 4.52 (s, 2H, NH2), 4.46 (s, 1H, H-4), 3.76 (m, 2H, H-
8), 2.39 (s, 3H, H-12), 1.77 (m, 1H, H-9), 0.79 (d, J = 6.4 Hz, 3H, H-
10), 0.76 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d): 166.0, 157.4,
157.3, 132.9, 129.6, 129.6, 129.1, 119.0, 107.9, 70.9, 66.2, 38.3,
27.5, 19.0, 19.0, 18.6; Anal. Calcd. (%) for C18H19ClN2O3: C, 62.34;
H, 5.52; N, 8.08. Found (%): C, 62.10; H, 5.38; N, 7.84; HRMS
(ESI): m/z 346.4.
O
O
NC
O
O
F
H2N
O
O
O
6
91
O
O
H
H3C
NC
2.1.4. Isobutyl 6-amino-4-(3-bromophenyl)-5-cyano-2-methyl-4H-
pyran-3-carboxylate 4
CH3
H
H2N
Yellow solid, yield: 90%. m.p. 142–144 °C; IR (KBr, cmꢀ1) 3405,
3326, 2958, 2190, 1695, 1379, 1263, 1060; 1H NMR (d): 7.34–7.14
(m, 4H, ArAH), 4.54 (s, 2H, NH2), 4.40 (s, 1H, H-4), 3.78 (m, 2H, H-
8), 2.41 (s, 3H, H-12), 1.78 (m, 1H, H-9), 0.79 (d, J = 6.8 Hz, 3H, H-
10), 0.76 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d): 165.6, 157.7,
157.5, 146.1, 130.4, 130.3, 130.2, 126.2, 122.8, 118.6, 107.2, 71.1,
61.9, 38.5, 27.5, 19.0, 19.0, 18.6; Anal. Calcd. (%) for C18H19BrN2O3:
C, 55.26; H, 4.89; N, 7.16. Found (%): C, 55.12; H, 4.52; N, 7.02;
HRMS (ESI): m/z 390.9.
7
92
H3CO
O
O
NC
O
O
OCH3
H
H2N
8
9
86
86
O
O
O
2.1.5. Isobutyl 6-amino-5-cyano-4-(4-fluorophenyl)-2-methyl-4H-
pyran-3-carboxylate 5
NC
Yellow solid, yield: 88%. m.p. 147–149 °C; IR (KBr, cmꢀ1) 3410,
3335, 2963, 2197, 1688, 1378, 1266, 1063; 1H NMR (d): 7.18–6.96
(m, 4H, ArAH), 4.55 (s, 2H, NH2), 4.43 (s, 1H, H-4), 3.77 (m, 2H, H-
8), 2.39 (s, 3H, H-12), 1.77 (m, 1H, H-9), 0.78 (d, J = 6.8 Hz, 3H, H-
10), 0.75 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d): 165.9, 157.4,
157.2, 139.6, 128.9, 128.8, 118.9, 116.4, 115.6, 115.4, 107.6, 71.3,
62.2, 38.1, 27.5, 19.2, 18.8, 18.5; Anal. Calcd. (%) for C18H19FN2O3:
C, 65.44; H, 5.80; N, 8.48. Found (%): C, 65.02; H, 5.49; N, 8.20;
HRMS (ESI): m/z 330.8.
H2N
O
O
H
Cl
Cl
O
Cl
NC
O
Cl
H2N
O

260
C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
Fig. 1. IR spectrum of compound 4.
2.1.6. Isobutyl 6-amino-5-cyano-2-methyl-4-(4-methylphenyl)-4H-
pyran-3-carboxylate 6
J = 2.8 Hz, 3H, H-10), 0.85 (d, J = 2.8 Hz, 3H, H-11); 13C NMR (d):
165.7, 158.5, 158.1, 155.2, 141.9, 118.8, 110.4, 105.7, 105.6, 71.1,
59.4, 32.3, 30.9, 27.6, 19.0, 18.5; Anal. Calcd. (%) for C16H18N2O4:
C, 63.56; H, 6.00; N, 9.27. Found (%): C, 63.21; H, 5.89; N, 9.14;
HRMS (ESI): m/z 302.9.
Yellow solid, yield: 91%. m.p. 137–139 °C; IR (KBr, cmꢀ1) 3407,
3330, 2962, 2198, 1690, 1379, 1266, 1060; 1H NMR (d): 7.20–7.08
(m, 4H, ArAH), 4.47 (s, 2H, NH2), 4.40 (s, 1H, H-4), 3.76 (m,
J = 6.4 Hz, 2H, H-8), 2.38 (s, 3H, H-12), 1.78 (m, 1H, H-9), 0.79 (d,
J = 6.8 Hz, 3H, H-10), 0.76 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d):
166.0, 157.3, 156.9, 140.8, 136.7, 129.3, 127.1, 119.0, 107.9, 70.9,
62.8, 38.3, 27.5, 21.0, 19.0, 19.0, 18.5; Anal. Calcd. (%) for
2.1.9. Isobutyl 6-amino-5-cyano-4-(2,4-dichlorophenyl)-2-methyl-
4H-pyran-3-carboxylate 9
Yellow solid, yield: 86%. m.p. 144–146 °C; IR (KBr, cmꢀ1) 3414,
3329, 3260, 2961, 2195, 1709, 1315, 1260, 1065; 1H NMR (d): 7.36–
7.08 (m, 3H, ArAH), 5.01 (s, 1H, H-4), 4.57 (s, 2H, NH2), 3.76 (m, 2H,
H-8), 2.42 (s, 3H, H-12), 1.78 (m, 1H, H-9), 0.93 (d, J = 6.8 Hz, 3H, H-
10), 0.78 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d): 165.5, 158.5, 157.7,
139.9, 133.7, 133.4, 129.6, 127.7, 118.3, 106.4, 71.2, 60.7, 35.0, 27.5,
19.1, 18.9, 18.9, 18.6 Anal. Calcd. (%) for C18H18Cl2N2O3: C, 56.71; H,
4.76; N, 7.35. Found (%): C, 56.54; H, 4.52; N, 7.21; HRMS (ESI): m/z
380.8.
C19H22N2O3: C, 69.92; H, 6.79; N, 8.58. Found (%): C, 69.52; H,
6.38; N, 8.02; HRMS (ESI): m/z 326.4.
2.1.7. Isobutyl 6-amino-5-cyano-4-(4-methoxyphenyl)-2-methyl-4H-
pyran-3-carboxylate 7
Yellow solid, yield: 92%. m.p. 135–137 °C; IR (KBr, cmꢀ1) 3404,
3330, 2962, 2192, 1691, 1378, 1260, 1062; 1H NMR (d): 7.26–6.81
(m, 4H, ArAH), 4.41 (s, 2H, NH2), 4.40 (s, 1H, H-4), 3.77 (m, 2H, H-
8), 2.38 (s, 3H, H-12), 1.78 (m, 1H, H-9), 0.80 (d, J = 6.8 Hz, 3H, H-
10), 0.77 (d, J = 6.8 Hz, 3H, H-11); 13C NMR (d): 166.1, 158.7,
157.2, 156.7, 136.0, 128.4, 119.0, 114.0, 108.0, 70.9, 62.9, 55.3,
37.9, 27.5, 19.0, 19.0, 18.5; Anal. Calcd. (%) for C19H22N2O4: C,
66.65; H, 6.48; N, 8.18. Found (%): C, 66.25; H, 6.39; N, 7.92; HRMS
(ESI): m/z 342.7.
2.2. X-ray crystallography
Crystal was grown by slow evaporation technique using ethanol
as solvent. Diffraction data were collected on a Bruker, 2004 APEX
2 diffractometer using graphite-monochromated Mo K
a radiation
(k = 0.71073 Å) at 293 K with crystal size of 0.30 ꢂ 0.30 ꢂ
0.30 mm. The structure was solved by direct methods and succes-
sive Fourier difference syntheses (SHELXS-97) [32] and refined by
full matrix least square procedure on F2 with anisotropic thermal
parameters. All non-hydrogen atoms were refined (SHELXL-97)
[33] and placed at chemically acceptable positions. A total of 269
parameters were refined with 3023 unique reflections which
2.1.8. Isobutyl 6-amino-5-cyano- 4-(furan-2-yl)-2-methyl-4H-pyran-
3-carboxylate 8
Yellow solid, yield: 86%. m.p. 132–134 °C; IR (KBr, cmꢀ1) 3409,
3331, 3267, 2969, 2192, 1697, 1332, 1263, 1061; 1H NMR (d):
7.29–6.08 (m, 3H, ArAH), 4.62 (s, 2H, NH2), 4.57 (s, 1H, H-4),
3.87 (m, 2H, H-8), 2.37 (s, 3H, H-12), 1.87 (m, 1H, H-9), 0.86 (d,

C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
261
Fig. 2. 1H NMR spectrum of compound 4.
Fig. 3. 13C NMR spectrum of compound 4.

262
C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
Fig. 4. HSQC spectrum of compound 4.
Fig. 5. HMBC spectrum of compound 4.

C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
263
Table 2
Correlations in the HSQC and HMBC spectra of compound 4.
Signals
Correlations in HSQC
146.1–122.8
Correlations in HMBC
7.36–7.14 (ArAH)
H20: 130.2 (
H30: 130.3 (
H40: 130.2 (
H60: 146.1 (
a), 130.4 (b), 146.1 (
a), 146.1 (b), 122.8 (
a), 130.3 (b), 146.1 (
a), 130.3 (b), 130.2 (
a), 122.8 (b), 38.5 (b)
c
c
c
), 130.4 (
)
a
), 126.2 (b), 38.5 (
c
)
), 126.2 (
a
), 130.4 (b), 38.5 (b)
), 61.9 ( ), 157.5 (b), 107.2 (a), 157.7 (b), 165.6 (b)
4.40 (Benzylic proton)
2.4 (CH3)
3.82–3.74 (OACH2)
1.83–1.73 (Isobutyl CH)
0.80–0.79 (Isobutyl CH3)
0.77–0.75 (Isobutyl CH3)
38.5
18.6
71.1
27.5
19.03
19.01
146.1 (
157.7 (
a
a
), 130.3 (b), 130.2 (
), 107.2 (b), 165.6 (
c
c
), 122.8 (b), 126.2 (
c
a
), 157.5 (
c
)
27.5 (
a
), 19.03 (b), 19.01 (b), 165.6 (b)
), 19.03 ( ), 71.1 (
), 19.01 ( ), 71.1 (b)
), 19.03 (b), 71.1 (b)
19.01 (
a
a
a)
27.5 (
27.5 (
a
a
a
Fig. 6. Mass spectrum of 1.
covered the residuals to R1 = 0.0566. Crystallographic data have
been deposited with the Cambridge Crystallographic Data
Centre as supplementary publications number CCDC 901850 for
1. Copies of the data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: +44 1223 336 033: or e-mail: deposit@ccdc.cam.ac.uk.
same reaction was carried out with substituted aryl aldehydes in
ethanol using BF3:OEt2 as catalyst and the corresponding isobutyl
6-amino-4-aryl-5-cyano-2-methyl-4H-pyran-3-carboxylates were
obtained in high yield (86–92%). The results are summarized in
Table 1.
3.1. IR spectral analysis of compounds 1–9
3. Results and discussion
Characteristic absorption of the 4H-pyran derivatives (1–9) are
due to mC@O, mC„N, mNAH stretching modes. The observed maxima in
Initially, the reaction between benzaldehyde, malononitrile and
isobutyl ethylacetoacetate was selected as a model reaction. The
the region of 1714–1688 cmꢀ1 are characteristic of carbonyl (C@O)
stretching frequency of ester function. The observed bands around

264
C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
Fig. 7. ORTEP diagram of 1.
Fig. 8. Packing diagram of 1.

C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
265
Table 3
3.2. NMR spectra
Crystal data and structure refinement details for 1.
3.2.1. 1H NMR spectral analysis of compound 4
Empirical formula
Formula weight
C18H20N2O3
312.3
For NMR spectral analysis, compound 4 was chosen as a repre-
sentative. For 4, the HSQC and HMBC NMR spectra were also re-
corded for the unambiguous assignment of signals. Proton NMR
spectrum of this compound (Fig. 2) shows the presence of a sharp
singlet at 4.40 ppm due to benzylic proton and another sharp sin-
glet appeared at 2.41 ppm is due to the presence of three methyl
protons. One sharp singlet appeared at 4.50 ppm is assigned to
two amino (NH2) protons. Two multiplets appeared around 1.83–
1.73 ppm and 3.82–3.74 ppm is assigned to C9 and C8 protons.
Methyl protons associated with C10 and C11 are appeared as two
doublets (0.79–0.76 ppm) with the small difference in chemical
shifts. Aromatic protons occur in the range of 7.36–7.14 ppm.
Three sets of signals are observed for the aromatic protons and
among the three; the multiplet in the range of 7.19–7.14 ppm is as-
signed to C30 proton. In the remaining two signals, a singlet at
7.30 ppm is assigned to C60 proton and another doublet at
7.34 ppm is due to C40 and C20 protons in the phenyl ring.
Temperature
Wavelength
Crystal system, space group
Unit cell dimension
293(2) K
0.71073 Å
Monoclinic, P21/c
a = 8.526(5) Å
a
= 90.0(5)°
b = 23.138(5) Å
b = 103.719(5)°
c = 8.949(5) Å
c
= 90.0(5)°
Volume
1715.0(14) Å3
Z, calculated density
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Limiting indices
Reflections collected/unique
Completeness to theta
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R, RW (obs, data)
4, 1.210 mg/m3
0.083 mmꢀ1
664
0.30 ꢂ 0.30 ꢂ 0.30 mm
2.46–25.0°
ꢀ6 6 h 6 10, ꢀ26 6 k 6 27, ꢀ10 6 l 6 10
15,186/3023
100.0%
Semi-empirical from equivalents
0.970 and 0.942
Full-matrix least squares on F2
3023/233/269
3.2.2. 13C NMR and 2D NMR spectral analysis of compound 4
1.034
0.0566, 0.1218
In the 13C NMR spectrum of compound 4 (Fig. 3), the most up-
filed resonances at 18.6, 19.01 and 19.03 ppm are assigned to the
methyl carbons at C10, C11 and C12 respectively. In addition, there
are three signals observed in the aliphatic region of 71.1, 38.5 and
27.5 ppm respectively. In its HSQC spectrum (Fig. 4), the carbon
signal at 71.1 ppm has a cross peak with the proton resonance at
3.80 ppm. Hence, the signal is conveniently assigned to C8 carbon.
Similarly, the carbon resonance at 38.5 ppm has a cross peak with
the singlet at 4.40 ppm, in the 1H NMR spectrum and hence it is as-
signed to the benzylic carbon (C4). The remaining signal at
27.5 ppm shows correlation with a multiplet at 1.78 ppm and
Table 4
Selected bond distances (Å) and angles (°) for 1.
Bond length
C(1)–C(2)
C(1)–C(7)
C(2)–O(3)
C(2)–C(3)
C(4)–N(2)
C(4)–C(6)
C(4)–O(3)
C(5)–N(1)
1.336(2)
1.508(2)
1.391(2)
1.484(2)
1.330(2)
1.352(2)
1.361(2)
1.146(2)
1.409(2)
1.506(2)
1.203(2)
1.327(2)
1.450(2)
0.841(15)
0.866(16)
2.150(17)
2.187(17)
hence it is conveniently assigned to C9 carbon.
A peak at
165.6 ppm without correlation is owed to carbonyl carbon of the
ester moiety. Further the assignment of signals was irrefutably
confirmed from its HMBC spectrum (Fig. 5). In the HMBC spectrum
the signals from 146.1 to 122.8 ppm have correlations with phenyl
protons multiplet. However, the lower frequency resonance at
146.1 ppm has good correlation with the benzylic proton signal
C(5)–C(6)
C(6)–C(7)
C(14)–O(1)
C(14)–O(2)
C(15)–O(2)
N(2)–H(2A)
N(2)–H(2B)
H(2A)ꢃ ꢃ ꢃO(1)#1
H(2B)ꢃ ꢃ ꢃN(1)#2
at 4.40 ppm (a-correlation); this clearly indicates that the signal
is ascribed to the phenyl ipso carbon. All the HSQC and HMBC cor-
relations are listed in Table 2. HRMS of compound 1 is given in
Fig. 6.
Bond angles
C(1)–C(2)–O(3)
C(6)–C(4)–O(3)
N(1)–C(5)–C(6)
C(4)–C(6)–C(7)
C(6)–C(7)–C(1)
C(6)–C(7)–C(8)
C(1)–C(7)–C(8)
O(1)–C(14)–O(2)
O(1)–C(14)–C(1)
O(2)–C(14)–C(1)
C(14)–O(2)–C(15)
C(4)–O(3)–C(2)
N(2)–H(2A)ꢃ ꢃ ꢃO(1)#1
N(2)–H(2B)ꢃ ꢃ ꢃN(1)#2
120.95(15)
121.01(15)
178.4(2)
3.3. Single crystal X-ray structural analysis of isobutyl 6-amino-5-
cyano-2-methyl-4-phenyl-4H-pyran-3-carboxylate 1
121.92(14)
109.57(11)
111.67(8)
109.91(8)
124.13(16)
122.00(16)
113.83(14)
119.47(15)
119.96(12)
160.9(19)
165(2)
The structure and geometry of 1 in the solid state is established
by single crystal X-ray structural analysis. Compound 1 crystallizes
in a monoclinic system with P21/c space group. Four molecules are
present in the unit cell. ORTEP of 1 is shown in Fig. 7 and the pack-
ing diagram is given in Fig. 8. Crystal data, data collection and
structure refinement parameters are given in Table 3. Selected
bond distances and angles are given in Table 4.
In the pyran ring C(1)AC(2) and C(4)AC(6) bonds are dou-
ble bonded in nature [C(1)AC(2) = 1.336(2) and C(4)AC(6) =
1.352(2) Å] as indicated by the bond distances [34]. The conforma-
tion of the pyran ring can be described as flattened boat, which is
evidenced from the small puckering parameters associated with
the O(3) and C(7) atoms present at 1st and 4th positions, respec-
tively, of the pyran ring. The atoms O(3) and C(7) are displaced
by 0.141 and 0.231 Å, respectively, from the plane defined by
C(6)/C(4)/C(2)/C(1). The phenyl group is almost perpendicular to
the pyran ring with the angle of 88.35(2)° [35].
3423–3403 cmꢀ1 and 2190–2198 cmꢀ1 are due to amino and cya-
no groups respectively. The strong absorption band for CAO bond
appeared around 1260–1268 cmꢀ1 and also the CAH stretching
frequencies were observed in the region of 2962–2969 cmꢀ1. IR
spectrum of compound 4 is shown in Fig. 1.

266
C. Udhaya Kumar et al. / Journal of Molecular Structure 1036 (2013) 257–266
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[C(14)AO(1) = 1.203(2) and C(14)AO(2) = 1.327(2) Å] clearly
indicate the partial delocalization of electron density over
p
COOꢀ moiety. Similarly, the cyano group is just about linear
[C(6)AC(5)AN(1) = 178.4(2)°] and also triple bonded in nature
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4. Conclusions
A series of isobutyl 6-amino-4-aryl-5-cyano-2-methyl-4H-pyr-
an-3-carboxylates (1–9) have been synthesized by the multicom-
ponent reaction (MCR) between isobutyl ethylacetoacetate, aryl
aldehydes and malononitrile using BF3:OEt2 as catalyst. In the IR
spectra bands due to mC@O, mC„N, mNꢀH stretching modes are ob-
served clearly. 1H and 13C NMR spectral results are in line with
the proposed structure of compounds. Subsequently, the assign-
ment of signals is unambiguously confirmed from the HMBC and
HSQC spectra of the representative compound (4). Single crystal
X-ray structural analysis of 1, has also been performed and the re-
sults evidence the mean plane deviations of atoms present at 1st
and 4th positions of the pyran ring due to the ‘‘flattened-boat con-
formation’’. The packing of molecules is stabilized by homonuclear
[NAHꢃ ꢃ ꢃN] and heteronuclear [NAHꢃ ꢃ ꢃO] intermolecular hydrogen
bonds.
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References
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