Synthesis and conformational studies of newly synthesized cis-2r,6c-distyryltetrahydro thiopyran-4-one and its oxime: Comparison of experimental and theoretical NMR spectral data

Article abstract of DOI:10.1016/j.saa.2012.09.071

The cis-2r,6c-distyryltetrahydro thiopyran-4-one (4) was synthesized by the reaction of dicinnamylacetone with hydrogen sulphide. cis-2r,6c- distyryltetrahydro thiopyran-4-one oxime (5) was synthesized via oximination of 4. The synthesized compounds were

Full text of DOI:10.1016/j.saa.2012.09.071

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 8–13
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and conformational studies of newly synthesized
cis-2r,6c-distyryltetrahydro thiopyran-4-one and its oxime: Comparison
of experimental and theoretical NMR spectral data
V. Vimalraj , S. Vijayalakshmi , S. Umayaparvathi c
a,
⇑
b
a
Department of Chemistry, Madha Institute of Engineering and Technology, Chennai 600 122, India
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India
CAS in MarineBiology, Faculty of Marine Science, Annamalai University, Parangipettai 608 502, India
b
c
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
"
cis-2r,6c-Distyryltetrahydro
thiopyran-4-one and its oxime have
been synthesized.
O
O
OHC
+
2
H
H
"
Synthesis compounds have been
1
13
H
3
C
CH
3
characterized by using H, C and
S
2
D NMR spectra.
Theoretical H and 13C have been
1
"
"
H
H
calculated using DFT.
1
13
4
Theoretical H and C NMR has been
1
13
compared with observed H and
C
NMR spectra.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 July 2011
Received in revised form 9 September 2012
Accepted 22 September 2012
Available online 29 September 2012
The cis-2r,6c-distyryltetrahydro thiopyran-4-one (4) was synthesized by the reaction of dicinnamylace-
tone with hydrogen sulphide. cis-2r,6c-distyryltetrahydro thiopyran-4-one oxime (5) was synthesized
via oximination of 4. The synthesized compounds were characterized by IR, NMR spectral studies and ele-
mental analysis. The proton and carbon chemical shift values were unambiguously assigned using two
dimensional NMR ( HA H COSY, HSQC, HMBC, NOESY) spectra. H NMR and C NMR chemical shifts
of 4 were also obtained by the density functional theory (DFT) using 6-311++G(d,p) basis sets and the the-
oretical values were compared with experimental values.
1
1
1
13
Keywords:
Thiopyran-4-one
1
Ó 2012 Elsevier B.V. All rights reserved.
H NMR
C NMR
D NMR
13
2
DFT
Introduction
variety of biological activities such as metalloprotein protease
inhibitors and as pro-oxidant cancer drugs [5]. These interesting
The synthesis and biological activities of thiopyran containing
molecules stand as an ever-expanding area of research in heterocy-
clic chemistry [1,2]. The thiopyran-4-one unit present in the thi-
ochroman-4-one (1) (Fig. 1) heterocycles expresses potent
activities have stimulated chemists to develop the chemistry of
this class of compounds. Now days FT-IR and NMR spectroscopy
combined with quantum chemical computations has been recently
used as an effective tool in the vibrational analysis of drug mole-
cules [6], biological compounds [7] and natural products [8]. This
paper reports the synthesis and structural characterization of cis-
2r,6c-distyryltetrahydro thiopyran-4-one and its oxime. The struc-
tures were elucidated on the basis of spectroscopic studies (IR, ele-
biological activities [3]. Thiospiro-
(
[
a
-methylene-
2) (Fig. 1) were reported for their significant biological activities
4]. Dithiomaltol (3) (Fig. 1) (Httma) and related ligands exhibited
c-butyrolactones
1
mental analysis, and NMR). The complete assignment of the H and
⇑
Corresponding author. Tel.: +91 9865569293.
E-mail address: chemvimal@yahoo.co.in (V. Vimalraj).
1
3
1
13
C NMR signals of 4 were achieved by 1D ( H and C) and 2D-
1
386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.09.071

V. Vimalraj et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 8–13
9
H
H
O
O
H
H
O
S
O
O
S
S
OH
Ph
S
Ph
Ph
S
Ph
1
2
3
Fig. 1. Thiopyran-4-one unit containing potent biological activities heterocycles.
1
1
shift-correlated ( HA H COSY, HSQC, HMBC and NOESY) NMR
experiments. Whereas, compound 5 the assignment was made by
Results and discussion
1
13
using only H and C NMR experiments. Also the present work
deals with DFT computations and the theoretical NMR spectral
analysis of 4 are compared with experimental values.
The compounds were synthesized using the reaction shown in
Scheme 1. The numbering of carbon atoms in 4 also shown in
1.The protons are numbered accordingly. Thus, the proton on C-2
is denoted as H-2. The analytical and IR spectral data of compounds
1
13
4
and 5 are represented in Table 1. The H and C chemical shifts
Experimental details
of compounds 4 and 5 are listed in Tables 2 and 3 respectively.
cis-2r,6c-Distyryltetrahydro thiopyran-4-one (4): To a boiling
solution of sodium acetate (7.5 g), dicinnamylacetone (5 g) and
1
H NMR spectral analysis of cis-2r,6c-distyryltetrahydro thiopyran-4-
9
0% ethanol (40 mL), hydrogen sulfide gas was passed for 6–7 h.
one (4)
After completion of the reaction, the contents were cooled to 0 °C
and the resinous mass formed was removed from the supernatant
liquid by decantation. The supernatant liquid was kept at 0 °C for
In the 1H NMR spectrum of 4, Aromatic protons appeared as a
Â
À
Á
0
00
multiplet in the range 7.26–7.37 ppm 7:26 H and H ; 7:32
4
4
À
Á
À
Á
0
00
0
00
2
days and the colorless crystals of cis-2r,6c-distyryltetrahydro thi-
H
and H ; 7:27 H and H ꢁ. There are the signals at 6.15 and
3
3
2
2
opyran-4-one separated, filtered off, dried and recrystallized from
petroleum ether to get the pure compound. mp 155–156 °C.
cis-2r,6c-Distyryltetrahydro thiopyran-4-one oxime (5): To a
solution of 4 (50 mmol) and sodium acetate trihytrate (150 mmol)
in boiling ethanol, hydroxylamine hydrochloride (60 mmol) was
added. The mixture was heated under reflux for 15 min and poured
into water, filtered and dried. The separated cis-2r,6c-distyryltetra-
hydro thiopyran-4-one oxime was recrystallized from ethanol. mp
6.63 ppm [J = 15 Hz] due to the styryl protons [H and H ]. On
a
b
the basis of HOMOCOSY correlation, the signal at 6.15 ppm is due
to H proton [gives cross peak with 4.00 ppm (H-2) and 6.63 ppm
b
(H ) Table 4]. The other signal at 6.63 ppm for Ha proton. The mul-
a
tiplet at 4.00 ppm is unambiguously assigned for benzylic protons
at C-2 and C-6. This assignment is evident from the NOESY spec-
trum, where the signal shows strong NOE with the signal for meth-
ylene protons at C-3/C-5 and styryl protons. There are two double
doublet at 2.86 and 2.72 ppm (J = 5 Hz, 11.6 Hz) due to methylene
protons. Among the two signals the one at 2.86 is due to H-3a and
H-5a protons, whereas the other is due to H-3e and H-5e protons
[11,12].
1
68–169 °C.
The compounds were synthesized using the reaction shown in
Scheme 1. The FT-IR spectrum of compounds 4 and 5 were re-
ꢀ1
corded in the range of 4000–400 cm on AVATAR-330 FT-IR spec-
trophotometer (Thermo Nicolet) using KBr pellet technique at
NOE spectrum of compound 4 (Table 4), gives useful informa-
tion about the conformation of the styryl protons. The methylene
protons at C-3 and C-5 have strong NOE with one of the styryl pro-
ton at 6.15 [H ] than the other at 6.63 [H ]. Since the methylene
ꢀ
1
ꢀ1
room temperature with a scanning speed of 30 cm min and a
ꢀ1
1
13
spectral resolution of 4.0 cm . The H and C NMR spectral mea-
surements were made in CDCl
3
in 5 mm NMR tubes. 1H and
13
C
b
a
NMR spectra were recorded at ambient temperature on a Bruker
protons are close proximity to Hb proton. The styryl C@C bond
1
AMX 400 NMR spectrometer operating at 400.13 MHz for H and
has an E-configuration, which is evident from the scalar coupling
00.62 MHz for C. The theoretical and experimental 1H and
1
3
13
C
1
1
between the H-
a
and HAb protons (15 Hz). The H chemical shifts
spectra of compound 4 are shown in Fig. 2. The COSY spectrum
of 4 is shown in Fig. 3.
for the 4 are listed in Table 2.
1
3
C NMR spectral analysis of cis-2r,6c-distyryltetrahydro thiopyran-4-
one (4)
Computational details
The theoretical NMR spectra of 4 were performed with the
Gaussian 03W software package [9] by using DFT method with
B3LYP hybrid exchange–correlation functional [8,9] which have
been previously shown to perform very well both for geometry
optimizations and NMR spectra calculations [10]. The 6-
In the 13C NMR spectrum of 4 there are three signals at 207.0,
136.6 and 132.6 ppm. In the HMBC spectrum of 4, the signal at
207.0 ppm showed correlation with the axial and equatorial meth-
ylene protons only. Based on its position and the observed correla-
tion, the signal could be readily assigned to the carbonyl carbon.
The signal at 136.6 ppm showed correlation with the phenyl and
3
11++G(d,p) basis set was used for calculations. In order to express
the chemical shifts in ppm, the geometry of tetra methyl silane
TMS) molecule has been optimized and then its NMR spectrum
was calculated by using the same method and basis set. The calcu-
0
00
styryl group protons and should be due to C-1 and C-1 . The signal
at 132.6 ppm showed correlation with benzylic and phenyl group
(
protons and should be due to C
b, showed correlation with benzylic and methylene proton. The
other three signals in aromatic region 128.6, 128.1 and
a
. The signal at 126.6 ppm, due to
lated Isotropic shielding constants
r
i
were then transformed to
C
chemical shifts relative to TMS by d
i
=
r
TMS i
r .
ꢀ

1
0
V. Vimalraj et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 8–13
O
O
OHC
NaOH/EtOH
+
H
H
2
H
3
C
CH
3
H
H
H2S
EtOH/NaCooEt
O
4
H
H
3
2
5
6
/
β
β
/
//
2
2
1
/
1
/
/
//
3
4
3
S
/
/
α
1
/
α
4
H
6
/
//
H
//
6
4
/
/
/
5
5
NH OH
2
sodiumacetatetriacetate
HO
N
H
H
S
H
5
H
Scheme 1. Synthetic route of compounds.
0
00
0
00
3
1
27.3 ppm are due to meta(C-3 and C-3 ), para(C-4 and C-4 ),
for H-
a (dd) are J = 7.88 Hz; 15.7 Hz The observed vicinal coupling
0
00
00
3
ortho(C-2 and C-2 ) respectively. The signal at 49.2 ppm showed
correlation with carbonyl carbon and should be due to C-3 carbon.
The remaining signal at 45.8 is due to C-2 carbon. These assign-
ments were confirmed by the observed correlation in HSQC spec-
trum. The styryl group is shielded the
than the b-carbon (C-3 and C-5) comparing the corresponding thi-
constant for H-2 (d) is J = 15.7 Hz. Which reveals that the protons
0
00
0
H-2 and H-2 are in trans to each other and H-2 and H-2 are cis to
each other. Hence the compound 4 exists in chair conformation 4b.
a-carbon (C-2 and C-6)
1
13
H and C NMR spectral analysis of cis-2r,6c-distyryltetrahydro
thiopyran-4-one oxime (5)
opyran [13].
For compound 5, the H and 13C chemical shifts are listed in Ta-
bles 2 and 3 respectively. The observed vicinal diaxial coupling
constant J5a,6a = 14.02 Hz, and the vicinal axial–equatorial coupling
constant J5e,6a = 2.95 Hz, whereas the germinal axial–equatorial
coupling constants J3a,3e and J5a,5e are, respectively, 13.26 and
1
The assignment of H-
a and H-b protons was obtained from
HMBC spectrum as follows. The HMBC spectrum for 4 reveals
interactions between the proton resonating at 6.15 ppm with car-
bons at 45.8, 49.2 and 136.6 ppm. As the signal at 49.2 ppm is due
to the C-3carbon, the signal at 6.15 ppm can be unambiguously as-
signed to H-b. Consequently, the other proton resonating at
1
4.0 Hz (slightly varied due to the bulkier oximino group in place
6
.63 ppm can be assigned to H-
interaction between the proton at 6.63 ppm with the carbon at
5.8, 126.6 and 136.6 ppm in the HMBC spectrum. The 13C chemi-
a. This is also confirmed by the
of the carbonyl carbon). Based on the obtained coupling constant
values, normal chair conformation is proposed for compound 5
and depicted in Fig. 4. J2a,3a and J2a,3e are not resolved due to broad-
ness of H-2a signal.
4
cal shifts for the 4 are listed in Table 3.
Generally dibenzalacetones afford both cis and trans thiopyrans
when treated with hydrogen sulphide gas in the presences of so-
dium acetate in ethanol medium [14–17]. But this not the case
with dicinnamylacetone which yields exclusively cis form due to
the extended conjugation. The coupling constants reveal that the
thiopyran ring exists in chair conformation with the equatorial ori-
entation of aryl (styrene) group at C-2 and C-6. There are two pos-
sible chair conformations (4a, 4b) with respect to orientation of
protons in styrene group. The observed vicinal coupling constants
Effect of oximination
Generally in six-membered heterocycles, decrease in electro-
negativity of a particular group in the ring skeleton shields the
a-carbons and deshields the b- and c-carbons [18]. Despite the less
polar nature of the C@N than C@O bond, the electronegativity of
the C@NAOAH group must be less than that of C@O group. All
the
D
d (dthiopyran ꢀ doxime) values for the thiopyran ring carbons of

V. Vimalraj et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 8–13
11
1
13C-NMR spectrum of 4 in DFT method
H NMR spectrum of 4 in DFT method
1
Observed 13C-NMR spectrum of 4
Observed H NMR spectrum of 4
Fig. 2. Computed and observed 1H, 13C and COSY spectra of 4.
the synthesized compound 5 are represented in Table 3. A perusal
of the data in Table 3, Generally in ketoximes, the syn -carbon is
shielded than the anti- -carbon, probably the chemical shift differ-
ence between the -carbons is ( ) 7.6 ppm [19–22]. The differ-
ence in the chemical shift increases with a decrease in the
dihedral angle between the C@N and CA AH bonds. If the
hydrogen lies in the NOC- plane, the dihedral angle between
them is zero. For such oximes the value is around 7 ppm
22]. The values of 5 are not much deviated from 7.0 ppm, be-
a
a
a
Dd
a
a
a-
a
Dd
a
[
Dd
a
cause the compound 5 has appreciable possibility for the Chair
conformation.
Theoretical NMR spectra
Initially, molecular structures of the mentioned compounds are
optimized. Then, gauge-including atomic orbital (GIAO) 13C and H
chemical shift calculations of the compounds are made by using
B3LYP method in conjunction with 6-311++G(d,p) basis set. The
GIAO [23,24] method is one of the most common approaches for
calculating nuclear magnetic shielding tensors. For the same basis
set size GIAO method is often more accurate than those calculated
with other approaches [25]. The NMR spectra calculations are per-
1
Fig. 3. Observed COSY spectrum of 4.
3
formed by Gaussian 03 [9] program package. Chloroform (CDCl ) is
Table 1
Analytical data for compounds 4 and 5.
Compds.
mp (°C)
Yield (%)
IR spectral data
Elemental analysis
Calculated (%)
Found (%)
C
C
H
N
S
H
N
S
4
5
155–156
168–169
75
88
1705, 2793
1640, 2803
78.75
75.22
6.25
6.27
–
4.18
10.0
9.55
78.35
75.10
6.35
6.29
–
4.25
9.90
9.33

1
2
V. Vimalraj et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 8–13
Table 2
Computed and Observed 1H chemical shifts of 4 and 5 (with respect to TMS) (6-311++G(d,p)) (d, ppm).
Protons
4 (Experimental)
4 (Theoretical)
5 (Experimental)
H-2a
H-3a
H-3e
H-5a
H-5e
H-6a
H-b and H-b
4.00
2.72
2.86
2.72
2.86
4.00
6.15
6.63
2.91
1.71
2.24
1.71
2.24
2.91
6.96
7.17
3.91(d)
2.46(dd)
2.85(ddd)
2.11(dd)
3.80(dd)
3.86(dd)
6.16
0
0
H-a
and H-
a
6.64
Aromatic protons
NAOH
7.37(o), 7.32(m), 7.26(p)
–
7.10(o), 7.17,7.20(p), 7.26,7.35(m) 7.83(o)
–
7.24–7.49
7.57
Table 3
Computed and observed 13C chemical shifts of 4 and 5 (with respect to TMS) (6-311++G(d,p)) (d, ppm).
Carbons
4
5 (Experimental)
D
d (dthiopyran ꢀ doxime
)
Experimental
Theoretical
C-2
C-3
47.8
57.2
45.8
49.2
46.2
39.5
ꢀ0.4
9.7
C-4
C-5
C-6
C-b and C-b
233.9
57.2
47.8
140.9
207.0
49.2
45.8
126.6
157.4
31.9
44.7
126.5
49.6
17.3
1.1
0.1
0.2
0
0
C-
a
and C-
a
146.8
132.6
132.4
Ipso carbons
Aromatic carbons
145.8
136.3
136.5
ꢀ0.2
127.0, 132.0 (o),133.4 (p), 133.9, 134.9 (m)
127.3 (0), 128.6 (m), 128.1 (p)
128.6, 128.1, 127.9, 127.3
–
Table 4
1
1
H– HCOSY, HSQC, HMBC, NOESY correlation spectral data of 4 (d, ppm).
1H NMR signals
Observed correlations
1
1
H– HCOSY
HSQC
HMBC
NOESY
2
2
4
6
6
7
.72 (H3a and H5a
.86 (H3e and H5e
)
)
2.86, 4.00
2.72, 4.00
2.72, 2.86, 6.15
4.00, 6.63
6.15
49.2 (C-3)
49.2 (C-3)
45.8 (C-2)
45.8, 126.6, 207.0 (C-4)
2.86, 4.00, 6.15(S), 6.63(W)
2.72, 4.00, 6.15(S), 6.63(W)
2.72, 2.86, 6.15, 6.63
2.72(S), 2.86(W), 6.63, 7.37
2.72, 2.86, 6.15, 7.37
–
45.8, 126.6, 207.0
126.6
45.8, 49.2, 136.2 (C-1 )
45.8, 126.6, 136.2
128.6, 132.6,
.00 (H
.15 (H
2
6
and H )
0
b
)
126.6 (H
b
)
.63 (H
a
) [15 Hz]
132.6 (H )
a
À
Á
0
00
0
.26
.32
.37
H
and H
–
128.1 (C-4 )
4
0
4
00
À
À
Á
0
7
7
H
H
and H
–
–
128.6 (C-3 )
136.6, 128.1
127.3
–
3
0
3
Á
00
0
and H
127.3 (C-2 )
2.86, 6.15(S), 6.63(W)
2
2
O
O
H
H
H
H
H
/
5
4
α
6
H
3
1
2
S
H
S
H
α
H
/
β
H
β
H
H
4a
4b
Fig. 4. Possible conformation of the compound 4.
1
13
used as a solvent. Relative chemical shifts are estimated by using
the corresponding TMS shielding in advance at the same theoreti-
cal level as the reference. 13C and H isotropic magnetic shielding
experimental H and C NMR spectra chemical shifts of compound
1
are gathered in Tables 2 and 3. H atom is the smallest of all atoms
1
and mostly localized on periphery of molecules; therefore their
chemical shifts would be more susceptible to intermolecular inter-
actions in the aqueous solutions as compared to that for other hea-
(
IMS) of any X carbon (or hydrogen) atom is made according to
1
3
the value C IMS of TMS:CSx = IMSTMS ꢀ IMSx. Theoretical and

V. Vimalraj et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 8–13
13
vier atoms. Taking into account that the range of 13C NMR chemical
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. Conclusions
The synthesized compounds cis-2r,6c-distyryltetrahydro thio-
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[10] V. Vimalraj, S. Vijayalakshmi, S. Umayaparvathi, Akhil R. Krishnan,
Spectrochim. Acta A 78 (2011) 670–675.
pyran-4-one and its oxime (4 and 5) were characterized by IR,
NMR spectra and elemental analysis. All the spectral data support
and confirm the formation of the target compounds. Well-pro-
nounced oximination effect is Observed on thiopyran ring carbons
and the associated protons. The oximination effect is extended up
to ipso carbons. We have carried out DFT calculations on the struc-
ture of 4. The calculated 1H NMR and C NMR by B3LYP/6-
[
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Acknowledgments
(
2009) 385–392.
The authors are thankful to SIF, Indian Institute of science, Ban-
galore for recording the NMR spectra.
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