Unique charge-separated intermolecular and eight-membered intramolecular H-bonds in bis-(thio)barbiturates

Article abstract of DOI:10.1007/s13738-013-0273-x

Reaction of symmetrical and unsymmetrical (thio)barbituric acids with aldehydes in the presence of triethylamine afforded a new form of bis-(thio)barbiturate containing charge-separated inter- and eight-membered intramolecular H-bonds. The reaction produc

Full text of DOI:10.1007/s13738-013-0273-x

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0273-x
ORIGINAL PAPER
Unique charge-separated intermolecular and eight-membered
intramolecular H-bonds in bis-(thio)barbiturates
•
Nader Noroozi Pesyan Mohammad Jalilzadeh
•
•
Nasim Yalabi Torkaman Ertan S¸ahin
Received: 2 February 2013 / Accepted: 9 May 2013
Ó Iranian Chemical Society 2013
Abstract Reaction of symmetrical and unsymmetrical
(thio)barbituric acids with aldehydes in the presence of
triethylamine afforded a new form of bis-(thio)barbiturate
containing charge-separated inter- and eight-membered
intramolecular H-bonds. The reaction products were
obtained as bis-(thio)barbiturates containing eight-mem-
bered intramolecular H-bond in the presence of L-(?)-tar-
taric acid (TA). The intramolecular H-bond strength (kcal/
mol) and corresponding pKa value for 4ab0 were estimated
to be 37 kcal/mol and -1.3, respectively.
Introduction
Hydrogen bond plays a key and major role in biological
and pharmaceutical systems and remains a topic of intense
current interest. This future judged enormous continuing
amount of literature. Few selected recent articles exemplify
the general scope of the topic, ranging from the role of
H-bonding in weak interaction in gas phase [1, 2], supra-
molecular assemblies [3–6], helical structures [7], pro-
moting catalytic enantioselective reactions [8–10] and
molecular rotors [11] as well as through measurement of
H-bond acidity of organic molecules [12]. Important con-
sequences of both inter- and intramolecular H-bonding
have long been recognized in the physicochemical behav-
ior of DNA and RNA [13]. Another compound consisting
of an eight-membered intramolecular H-bond has also been
reported [14–22]. In the past decade, some quinoline and
pyridine bis-barbiturates (Scheme 1) involving anticancer
effect have been reported by Neumann et al. [23].
Keywords Barbituric acid ꢀ Negative charge-assisted
H-bonds ꢀ Resonance-assisted H-bonds ꢀ Eight-membered
intramolecular H-bond ꢀ L-(?)-Tartaric acid
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-013-0273-x) contains supplementary
material, which is available to authorized users.
A search of the literature showed no report on the
charge-separated intermolecular and eight-membered
intramolecular H-bonds in (thio)barbiturates under basic
and/or acidic conditions. Based on these concepts, herein,
we report the charge-separated intermolecular and eight-
membered intramolecular H-bonds in the reaction between
(thio)barbituric acids with aldehydes in the presence of
L-(?)-TA and/or triethylamine.
N. N. Pesyan (&)
Department of Chemistry, Faculty of Science, Urmia University,
57159 Urmia, Iran
e-mail: n.noroozi@urmia.ac.ir; nnp403@gmail.com
M. Jalilzadeh
Department of Chemistry, Faculty of Science, Islamic Azad
University, Ahar Branch, Ahar, Iran
Experimental
N. Y. Torkaman
Department of Chemistry, Faculty of Science,
Tabriz Payam-e-noor University, Tabriz, Iran
General
E. S¸ahin
Department of Chemistry, Faculty of Science, Atatu¨rk
University, 25240 Erzurum, Turkey
The drawing and nomenclature of compounds were done
by ChemBioDraw Ultra 12.0 version software. Melting
123

J IRAN CHEM SOC
Me
N
at 0 °C. The reaction mixture was stirred for 2 h at 0 °C to
room temperature. The progression of reaction was moni-
tored by thin layer chromatography (TLC). After a few
minutes, a crystalline white solid precipitate was filtered
off, washed with few milliliters of methanol and dried
(0.18 g, 90 % yield).
Me
N
H
N
H
N
O
O
O
O
O
O
O
O
N
HN
N
NH
Me
Me
O
O
O
O
N
N
5,50-((2-Nitrophenyl)methylene)bis(1,3-diethyl-6-hydroxy-
2-thioxo-2,3-dihydropyrimidin-4(1H)-one) (3ad0)
9b
9a
Colorless solid (80 %); mp = 212–214 °C. 1H NMR
(CDCl3, 300 MHz) d: 14.00 (bs, 1H, OH), 9.72, (bs, 1H,
OH), 7.51–7.60 (m, 2H, CH–ar.), 7.42 (t, 1H, J = 7.5 Hz,
CH–ar.), 7.28 (d, 1H, J = 7.5 Hz, CH–ar.), 6.11 (s, 1H,
CH-aliph.), 4.52–4.68 (m, 8H, 4 NCH2CH3), 1.27-1.40 (m,
12H, 4 CH3CH2N); 13C NMR (CDCl3, 75 MHz) d: 11.9,
32.6, 45.1, 45.4, 96.6, 124.1, 128.0, 129.5, 131.3, 132.7,
H
N
H
N
H
N
H
N
O
O
O
O
O
O
O
O
H
HN
HN
NH
NH
O
O
O
O
H
N
N
10a
12a
150.1, 162.0, 163.6, 164.4, 174.4; FT-IR (KBr, cm-1) mmax
:
3438 (OH), 3050 (CH–ar.), 2981 (CH–aliph.), 2934 (CH–
aliph.), 1691 (C=O), 1620 (C=C ar.), 1528 (NO2), 1487,
1380, 1264, 1110.
Scheme 1 Formula structure of some bis-barbiturate having antican-
cer properties [23, 25–27]
points were measured with an electrothermal digital
apparatus and uncorrected. IR spectra were determined on
a NEXUS 670 FT-IR spectrometer by preparing KBr pel-
lets. The 1H and 13C NMR spectra were recorded on Bruker
300 FT-NMR at 300 and 75 MHz, respectively (Urmia
5,50-((4-Nitrophenyl)methylene)bis(1,3-diethyl-6-hydroxy-
2-thioxo-2,3-dihydropyrimidin-4(1H)-one) (3bd0)
Colorless solid (80 %), mp = 207–210 °C. 1H NMR
(CDCl3, 300 MHz) d: 14.0 (bs, 1H), 8.20 (d, 2H,
J = 8.4 Hz, CH–ar.), 7.33 (d, 2H, J = 8.4 Hz, CH–ar.),
5.70 (s, 1H, CH-aliph.), 5.49 (bs, 1H, OH), 4.57–4.73 (m,
8H, 4 NCH2CH3), 1.39 (t, 6H, J = 6.9 Hz, 2 CH3CH2N),
1.30 (t, 6H, J = 6.9 Hz, 2 CH3CH2N); 13C NMR (CDCl3,
75 MHz) d: 12.0, 35.3, 44.7, 45.3, 96.7, 123.7, 127.4,
143.7, 162.3, 163.8, 174.6; FT-IR (KBr, cm-1) mmax: 3433
(OH), 3040 (CH–ar.), 2985 (CH–aliph.), 2934, 2877 (CH–
aliph.), 1621 (C=O), 1520 (NO2), 1430, 1380, 1348,
1264, 1107.
1
University, Urmia, Iran). H and 13C NMR spectra were
obtained on solution in DMSO-d6 and/or in CDCl3 as
solvents using TMS as internal standard. The data are
reported as (s = singlet, d = doublet, t = triplet,
q = quartet, m = multiplet or unresolved, bs = broad
singlet, coupling constant(s) in Hz, integration). All reac-
tions were monitored by TLC with silica gel-coated plates
(AcOEt:AcOH/80:20/v:v). The X-ray analysis of com-
pound 4ab0 was used for data collection on a four-circle
Rigaku R-AXIS RAPID-S diffractometer equipped with a
two-dimensional area IP detector (Department of Chemis-
try, Atatu¨rk University, Erzurum, Turkey). Compound 2e0
was synthesized in our laboratory based on reported liter-
ature [24]. Other starting materials and the solvents used
were purchased from Merck without further purification.
The physical and spectral data of the selected compounds
are as follows.
5,50-((3-Nitrophenyl)methylene)bis(1,3-diethyl-6-hydroxy-
2-thioxo-2,3-dihydropyrimidin-4(1H)-one) (3cd0)
Colorless solid (80 %), mp = 206–207 °C. 1H NMR
(CDCl3, 300 MHz) d: 14.00 (bs, 1H, OH), 8.43 (bs, 1H,
OH), 7.20 (t, 1H, J = 7.8 Hz, CH–ar.), 6.70 (d, 2H,
J = 4.8 Hz, CH–ar.), 6.64 (s, 1H, CH–ar.), 5.63 (s, 1H,
CH-aliph.), 4.58–4.70 (m, 8H, 4 NCH2CH3), 1.38 (t, 6H,
J = 6.9 Hz, 2 CH3CH2N), 1.30 (t, 6H, J = 6.9 Hz, 2
CH3CH2N); 13C NMR (CDCl3, 75 MHz) d: 12.0, 12.1,
34.8, 44.6, 45.1, 97.3, 113.6, 113.7, 118.7, 129.6, 137.7,
155.8, 162.2, 163.7, 174.5; FT-IR (KBr, cm-1) mmax
3435 (OH), 3030 (CH–ar.), 2982 (CH–aliph.), 2932
(CH–aliph.), 1620 (C=O), 1528 (NO2), 1434, 1380, 1266,
1109.
General procedure for the preparation of 3ad0
as an example
In a 10 mL tube, equipped with a magnetic stirrer, with
Teflon-faced screw cap, 0.19 g (0.96 mmol) 1,3-diethyl
thiobarbituric acid and 0.07 g (0.48 mmol) 2-nitrobenzal-
dehyde were dissolved in 10 mL methanol and then 0.15 g
(0.96 mmol) L-(?)-tartaric acid was added to the solution
:
123

J IRAN CHEM SOC
cm-1) mmax: 3444 (OH), 3028 (CH–ar.), 2978, 2933, 2873
(CH–aliph.), 1615 (C=O), 1436, 1383, 1267, 1110.
5,50-((3-Hydroxyphenyl)methylene)bis(1,3-diethyl-6-
hydroxy-2-thioxo-2,3-dihydropyrimidin-4(1H)-one) (3dd0)
1
Colorless solid (70 %), mp = 244 °C. H NMR (CDCl3,
Triethylammonium 5-((6-hydroxy-1,3-dimethyl-2,4-dioxo-
1,2,3,4-tetrahydropyrimidin-5-yl)(2-nitrophenyl)
methyl)-1,3-dimethyl-2,6-dioxo-1,2,3,6-
300 MHz) d: 14.00 (bs, 1H, OH), 8.06 (bs, 2H, 2 OH), 7.19
(t, 1H, J = 7.8 Hz, CH–ar.), 6.71 (d, 2H, J = 7.5 Hz, CH–
ar.), 6.64 (s, 1H, CH–ar.), 5.63 (s, 1H, CH-aliph.),
4.58–4.70 (m, 8H, 4 NCH2CH3), 1.38 (t, 6H, J = 6.9 Hz, 2
CH3CH2N), 1.30 (t, 6H, J = 6.9 Hz, 2 CH3CH2N); 13C
NMR (CDCl3, 75 MHz) d: 12.0, 12.1, 34.8, 44.6, 45.1,
97.3, 113.5, 113.7, 118.8, 129.6, 137.7, 155.8, 162.2,
163.7, 174.6; FT-IR (KBr, cm-1) mmax: 3458 (OH), 3020
(CH–ar.), 2982 (CH–aliph.), 2932 (CH–aliph.), 1620
(C=O), 1432, 1377, 1265, 1109.
tetrahydropyrimidin-4-olate (4ab0)
In a 10 mL tube, equipped with a magnetic stirrer, with
Teflon-faced screw cap, 0.15 g (0.96 mmol) 1,3-dimethyl
barbituric acid and 0.07 g (0.48 mmol) 2-nitrobenzaldehyde
were dissolved in 10 mL methanol and then 0.1 g (0.14 mL)
triethylamine was added to the solution at 0 °C. The reaction
mixture was stirred for 2 h at 0 °C to room temperature. The
progression of reaction was monitored by thin layer chro-
matography (TLC). After a few minutes, a crystalline white
solid precipitate was filtered off, washed with few milliliters
of methanol and dried (0.17 g, 90 % yield). Colorless solid,
5,50-((3,4,5-Trimethoxyphenyl)methylene)bis(1,3-diethyl-6-
hydroxy-2-thioxo-2,3-dihydropyrimidin-4(1H)-one) (3ed0)
1
1
Colorless solid (70 %), mp = 155 °C. H NMR (CDCl3,
mp = 308 °C (decomps.). H NMR (CDCl3, 300 MHz) d:
300 MHz) d: 13.9 (bs, 1H, OH), 12.10 (bs, 1H, OH), 6.31
(s, 2H, CH–ar.), 5.62 (s, 1H, CH-aliph.), 4.50–4.70 (m, 8H,
4 NCH2CH3), 3.84 (s, 3H, OCH3), 3.76 (s, 6H, 2 OCH3),
1.37 (t, 6H, J = 6.9 Hz, 2 CH3CH2N), 1.30 (t, 6H,
J = 6.9 Hz, 2 CH3CH2N); 13C NMR (CDCl3, 75 MHz) d:
12.0, 12.1, 34.9, 44.5, 45.2, 56.4, 60.9, 97.5, 104.1, 131.1,
16.2 (bs, 1H, OH), 9.62 (bs, 1H, NH), 7.24–7.44 (m, 4H,
(CH–ar.)), 6.40 (s, 1H, CH-aliph.), 3.36–3.51 (m, 6H, 3 –
CH2–), 3.27 (s, 12H, 4 NCH3), 1.33 (t, 9H, J = 6.9 Hz, 3
CH3CH2); 13C NMR (CDCl3, 75 MHz) d: 8.7, 28.4, 32.0,
46.3, 50.6, 91.2, 123.7, 126.5, 129.9, 131.2, 136.1, 149.9,
151.9, 156.4, 163.8; FT-IR (KBr, cm-1) mmax: 3474 (OH),
3097 (CH–ar.), 2984 (CH–aliph.), 2947 (CH–aliph.), 1688
(C=O), 1615 (C=C ar.), 1526 (NO2).
137.1, 153.2, 162.2, 163.7, 174.6; FT-IR (KBr, cm-1) mmax
:
3436 (OH), 2977 (CH–aliph.), 2934 (CH–aliph.), 1619
(C=O), 1427, 1381, 1267, 1108.
Triethylammonium 5-((1,3-diethyl-6-hydroxy-4-oxo-2-
thioxo-1,2,3,4-tetrahydropyrimidin-5-yl)
5,50-((4-Fluorophenyl)methylene)bis(1,3-diethyl-6-
hydroxy-2-thioxo-2,3-dihydropyrimidin-4(1H)-one) (3fd0)
(2-nitrophenyl)methyl)-1,3-diethyl-6-oxo-2-thioxo-1,2,3,6-
tetrahydropyrimidin-4-olate (4ad0)
Colorless solid (70 %), mp = 189–190 °C. 1H NMR
(CDCl3, 300 MHz) d: 13.90 (bs, 1H, OH), 6.99–7.10 (m,
5H), 5.63 (s, 1H, CH-aliph.), 4.57–4.73 (m, 8H, 4
NCH2CH3), 1.38 (t, 6H, J = 6.9 Hz, 2 CH3CH2N), 1.30
(t, 6H, J = 6.9 Hz, 2 CH3CH2N); 13C NMR (CDCl3,
75 MHz) d: 11.99, 12.05, 34.4, 44.6, 45.2, 97.4, 115.2,
115.5, 127.9, 128.0, 131.1, 162.2, 163.2, 163.7, 174.6; FT-
IR (KBr, cm-1) mmax: 3432 (OH), 2975, 2918, 2849 (CH–
aliph.), 1620 (C=O), 1438, 1383, 1267, 1111.
1
Yellow solid (80 %), mp = 210 °C (decomps.). H NMR
(CDCl3, 300 MHz) d: 9.70 (bs, 1H, OH), 7.30–7.50 (m,
4H, CH–ar.), 6.42 (s, 1H, CH-aliph.), 4.37–4.59 (m, 8H, 4
NCH2CH3), 3.39–3.43 (m, 6H, 3 –CH2–), 2.30 (bs, 1H),
1.38 (t, 12H, J = 7.2 Hz, 4 CH3CH2N), 1.29 (t, 9H,
J = 6.9 Hz, 3 CH3CH2); 13C NMR (CDCl3, 75 MHz) d:
8.7, 12.2, 12.4, 32.2, 43.7, 44.1, 46.3, 96.1, 121.0, 123.9,
126.8, 129.7, 131.3, 150.1, 162.3, 162.6, 175.0; FT-IR
(KBr, cm-1) mmax: 3438 (OH, NH), 3083 (CH–ar.), 2979
(CH–aliph.), 2932 (CH–aliph.), 2871 (CH–aliph.), 1640
(C=O), 1614, 1526, 1434, 1380, 1267, 1103, 781.
5,50-(Phenylmethylene)bis(1,3-diethyl-6-hydroxy-2-thioxo-
2,3-dihydropyrimidin-4(1H)-one) (3gd0)
Colorless solid (70 %), mp = 188–190 °C. 1H NMR
(CDCl3, 300 MHz) d: 13.90 (bs, 1H), 7.29–7.36 (m, 3H,
CH–ar.), 7.14 (d, 2H, J = 7.2 Hz, CH–ar.), 6.76 (bs, 1H,
OH), 5.68 (s, 1H, CH-aliph.), 4.58–4.74 (m, 8H, 4
NCH2CH3), 1.39 (t, 6H, J = 6.9 Hz, 2 CH3CH2N), 1.31 (t,
6H, J = 6.9 Hz, 2 CH3CH2N); 13C NMR (CDCl3,
75 MHz) d: 11.98, 12.06, 34.9, 44.6, 45.1, 97.4, 126.3,
126.8, 128.5, 135.0, 162.0, 163.0, 174.6; FT-IR (KBr,
Triethylammonium 5-((6-hydroxy-1-methyl-2,4-dioxo-
1,2,3,4-tetrahydropyrimidin-5-yl)(2-nitrophenyl)methyl)-1-
methyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate
(4ae0)
1
Yellow solid (70 %), mp = 318 °C (decomps). H NMR
(DMSO-d6, 300 MHz) d: 16.25 (bs, 1H, OH), 10.28 (s, 2H,
NH-BA), 8.75 (bs, 1H, NH-triethylammonium), 7.23–7.42
123

J IRAN CHEM SOC
Scheme 2 Reaction of
path a
Hb
R
O
R
N
aldehydes with (thio)barbituric
acids in the presence of L-(?)-
TA (path a) and/or
O
X
X
R
N
L-(+)-TA
MeOH,
0 oC
X
triethylamine (paths b and c)
R
R
N
N
CHO
R
N
N
r.t.
R5
R4
R1
R2
O
O
O
O
Hf
Ar
2
3ab -3eb , 3ad -3ed
and 3ae -3ee
R3
1
path b
XH
OH
HO
HX
N
R2= R3 = R4 = R5 = H, R1 = NO2 (a)
R1= R2 = R4 = R5 = H, R3 = NO2 (b)
N
L-(+)-TA
and/or Et3N
c
R1= R3 = R4 = R5 = H, R2 = NO2 ( )
N
N
1
0 oC
MeOH
r.t.
R1= R3 = R4 = R5 = H, R2 = OH (d)
e
R1= R5 = H, R2 = R3 = R4 = OMe ( )
OH
OH
Ar
R1= R2 = R4 = R5 = H, R3 = F (f)
R1= R2 = R3 = R4 = R5 = H (g)
3aa -3ea and 3ac -3ec
a
R = R = H, X = O (
R = R = Me, X = O (
R = R = H, X = S (
)
b
)
)
Hb
R''
N
c
2
R''
O
d
R = R = Et, X = S (
)
O
X
X
N
path c
Et3N, MeOH
0 oC
r.t.
e
R = H, R = Me, X = O (
)
N
N
R'
R'
O
O
Ar
NH
4ab -4eb , 4ad -4ed
, 4ae -4ee
(m, 4H, CH–ar.), 6.18 (s, 1H, CH-aliph.), 3.09 (q, 6H,
J = 7.2 Hz, 3 –CH2CH3), 3.03 (s, 6H, 2 NCH3), 1.15 (t,
9H, J = 7.2 Hz, 3 CH3CH2); 13C NMR (DMSO-d6,
75 MHz) d: 9.1, 27.2, 30.9, 46.2, 90.4, 123.6, 126.5, 130.0,
131.1, 138.0, 150.3, 151.4, 162.6, 164.4; FT-IR (KBr,
cm-1) mmax: 3450 (OH), 3068 (CH–ar.), 2993 (CH–aliph.),
1690 (C=O), 1610, 1527, 1461, 1363.
The reaction between 3-nitrobenzaldehyde (1c) and 1,3-
diethyl thiobarbituric acid (DETBA, 2d0) were afforded
Knoevenagel condensation then subsequently Michael
adducts as; 5,50-((2-nitrophenyl)methylene)bis(1,3-diethyl-
6-hydroxy-2-thioxo-2,3-dihydropyrimidin-4(1H)-one)
(3cd0) in the presence of L-(?)-TA (Scheme 2, path a). The
structure of 3cd0 was confirmed by spectroscopic data. The
1H NMR spectrum of this compound (in CDCl3) revealed
the presence of two different chemical shifts for N-ethyl
protons as two distinct triplets at d 1.30 and 1.38 ppm for
methyl groups and a multiplet for two N–CH2– groups at d
4.58–4.69 ppm, respectively. A singlet for aliphatic C1–H
proton at d 5.63 ppm and two broad singlets at d 8.43 and
14.00 ppm that corresponded to two types of exchangeable
protons (the exchangeability was examined by adding a
drop of D2O) were found. A singlet at d 6.64 (1H), a
doublet at d 6.71 (2H) and a triplet at d 7.18 ppm (1H) at
the aromatic region were observed. The 13C NMR spec-
trum of 3 cd0 showed 15 distinct peaks that confirmed the
structure of this compound (see ‘‘Experimental’’; supple-
mentary data).
Results and discussion
This paper describes the formation of charge-separated
intermolecular and eight-membered intramolecular
H-bonds in the reaction of (thio)barbituric acids with
aldehydes in the presence of triethylamine and/or L-(?)-TA
to afford a new class of stable heterocyclic bis-(thio)bar-
biturates 5,50-(arylmethylene)bis(6-hydroxy-1,3-dimethyl-
pyrimidine-2,4(1H,3H)-diones) and their sulfur analogs
5,50-(arylmethylene)bis(1,3-diethyl-6-hydroxy-2-thioxo-2,
3-dihydropyrimidin-4(1H)-ones) (3aa0–3ae0 through 3ga0
–3ge0) (Scheme 2).
123

J IRAN CHEM SOC
X
*
Y
path a
O
X
BrCN, MeOH,
X
0 o
L-(+)-TA
C
r.t.
R
O
O
R
R
O
One-pot
RCHO
N
N
O
X
X
O
Y
5
2
Y
Y
X-Y-X = R'N-(C=X)-NR
X
X
X
X
+
+
R = R = H, X = O (a )
R = R = Me, X = O (b )
R = R = H, X = S (c )
R = R = Et, X = S (d )
R = H, R = Me, X = O (e )
O
O
O
O
Br
R
7d
6
R = Alkyl, Aryl
Y
X
X
path b
O
O
BrCN, MeOH,
Et3N, 0 o
-Et3NHBr
Br
Et3NH
+
5
C
r.t.
8
Scheme 3 Reaction of (thio)barbituric acids (2a0–e0) with cyanogen
bromide and aldehydes in the presence of L-(?)-TA (path a) and
comparison with their reaction in the presence of triethylamine (path
b) [29–32]
The Michael adducts derived from N,N0-dialkylated
(thio)barbituric acids (2b0 and 2d0) and N-alkylated barbi-
turic acid (2e0) exclusively showed an eight-membered
intramolecular H-bond between the carbonyl group of one
(thio)barbituric acid ring moiety and hydroxyl group of the
enolic form of another (thio)barbituric acid ring moiety
species (this proton is denoted by Hb) (Scheme 2, path a).
Any of these types of barbiturates include amidic (–CO–
NH–) and/or thioamidic protons (–CS–NH–) and do not
show an eight-membered intramolecular H-bond. It seems
that this phenomenon arose from tautomerization of
(thio)barbituric acids (lactam–thiolactam ꢀ lactim–thio-
lactim and/or lactam ꢀ lactim forms) that occurred prior
to formation of intramolecular H-bond (Scheme 2, path b).
Therefore, among these compounds, 2b0, 2d0 and 2e0 only
show this type of intramolecular H-bonding.
Scheme 4 Tautomeric and mesomeric forms of 8a0–8e0
2,20,4,40,60(3H,30H,5H)-pentaone (5b0), 5-aryl-2,20-dithioxo-
2,20,3,30-tetrahydro-1H,10H-spiro[furo[2,3-d] pyrimidine-
6,50-pyrimidine]-4,40,60(5H)-triones (5c0) and diastereo-
meric mixtures of 10,3-dimethyl-5-aryl-1H,10H-spiro[furo
[2,3-d]pyrimidine-6,50-pyrimidine]-2,20,4,40,60(3H,30H,5H)-
pentaone (5e0) were obtained, respectively (Scheme 3) [29–
32]. Elinson et al. [35] also reported the synthesis of spiro
compounds 5 in the presence of bromine in alkali condition
(EtONa/EtOH). No spiro compounds 5 were obtained in the
absence of cyanogen bromide under the same condition.
Exceptionally, the reaction of 1,3-diethyl thiobarbituric acid
(2d0) with aldehydes (1) in the presence of cyanogen bro-
mide produced 3d0 under the same condition. No spiro
compounds 5d0 were obtained. The reason for the formation
As mentioned above, the electron-withdrawing substit-
uents on the phenyl ring in 5-arylmethylene (thio)barbituric
acids (as an a,b-unsaturated carbonyl compounds) facili-
tate the Michael addition on their b-position [28].
More recently, the reaction of various aldehydes [29–32]
and ketones [33, 34] with (thio)barbituric acids and cyan-
ogen bromide have been investigated in the presence of
triethylamine and L-(?)-TA (Scheme 3). In these reactions,
5-aryl-1H,10H-spiro[furo[2,3-d]pyrimidine-6,50-pyrimidine]
2,20,4,40,60(3H,30H,5H)-pentaone (5a0), 5-aryl-1,10,3,30-tetra-
methyl-1H,10H-spiro[furo[2,3-d]pyrimidine-6,50-pyrimidine]
123

J IRAN CHEM SOC
10.15 ppm corresponds to the OH group of the predominant
thiolactam-enol form. The 13C NMR spectrum of 7d0 shows
five distinct peaks at d 175.4, 164.4, 90.3, 45.4 and
11.9 ppm that confirm the structure [30]. Other evidences
for the formation of 7d0 (the existence of bromine atom in
this molecule) were obtained by the Beilstein test and the
wet silver nitrate test (precipitate of pale yellow silver
bromide) [36].
As mentioned above, the reaction of aldehydes with
(thio)barbituric acids in the presence of triethylamine
afforded the salts of 4 (Scheme 2, path c). One of the most
interesting phenomena in this research is the binding of
triethylammonium salt moiety to some bis-barbiturates
anion derived from 2b0, 2d0 and 2e0 by intermolecular
H-bonding in the ratio of 1:1. The crystallographic data and
1H NMR spectra confirm the binding of triethylammonium
cation moiety to the anionic form. This phenomenon is
shown for 4ab0 and 4ae0 in Fig. 1, as examples. In 4ab0, a
triplet at d 1.33 and a quartet at d 3.41 ppm correspond to
methyl and methylene protons on the ethyl groups of tri-
ethylammonium salt moiety, a singlet at d 3.27 ppm is of
four equivalent N-Me groups, a singlet at d 6.40 ppm cor-
responds to benzylic CH proton and a multiplet at d
7.24–7.44 ppm to the phenyl ring. Two broad singlets at d
9.62 and 16.2 ppm correspond to the NH group of trieth-
ylammonium salt moiety and eight-membered intramolec-
ular H-bonding, respectively (this extra deshielded proton is
denoted by Hbg in Fig. 1a and by Hb in Scheme 5b).
The 1H NMR spectra of Michael adducts containing
o-nitro substituted phenyl ring (4ab0 and 4ae0) show an
extremely low field for intramolecular H-bonded proton. In
particular, in 1H NMR spectroscopy, the proton is
increasingly deshielded with increasing hydrogen bond
1
strength, which leads to H downfield shifts that are cor-
related with the length of the hydrogen bond [37–39].
Thus, NMR shift data can be used to estimate lengths of
H-bonds [38]. For this reason, we conclude that in com-
pounds 4ab0 and 4ae0, the donor–acceptor distances (dOꢀꢀꢀO
)
´
˚
should be less than 2.50 A (judging the extremely low field
proton chemical shift values at d 16.25 ppm for Hb in
intramolecular eight-membered H-bond in 4ab0 and 4ae0).
For instance, this phenomenon is described for 4ab0 in
Scheme 6. Another reported compound consists of delo-
calized negative charge on barbiturate and the positively
charged triethylammonium cation is the triethylammonium
2,4-dinitrophenylbarbiturate [40].
1
Fig. 1 H NMR spectrum of 4ab0 (a) and 4ae0 (b)
of 3d0 in competition with the formation of 5d0 attributed to
the strong nucleophilicity of 1,3-diethyl thiobarbituric acid
2d0 (Scheme 4) [30]. The nucleophilicity of 2d0 was
stronger than that of 5-bromo-1,3-diethyl-6-hydroxy-2-
thioxo-2,3-dihydropyrimidin-4(1H)-one (7d0). Therefore,
2d0 attacked the b-carbon position of 6cd0 as Michael
addition prior to formation of 7d0. In contrast, we detected
7d0 in the reaction of 2d0 with BrCN in the absence of
We performed NMR examinations on the bis-barbiturate
of 4ae0 derived from the reaction of unsymmetric barbituric
1
acid as 1-MBA (2e0) with 1a. The H NMR spectrum of
1
aldehyde and in the presence of L-(?)-TA [30]. The H
this compound shows a triplet at d 1.15 and a quartet at d
3.09 ppm corresponding to methyl and methylene groups
of triethylammonium salt moiety, a singlet at d 3.03 ppm is
of two equivalent N-Me groups, a singlet at d 6.18 ppm
NMR spectrum of 7d0 consists of a triplet at d 1.32 and a
quartet at d 4.57 ppm corresponding to methyl and meth-
ylene protons on ethyl groups, respectively. A singlet at d
123

J IRAN CHEM SOC
Scheme 5 Tautomeric and
mesomeric forms and
intramolecular H-bond in 3cd0
(a), 4ab0 (b) and 4ae0 (c). Hb:
H-bonding, Hf: H-free)
(a)
Hb
Hb
Et
Et
Et
Et
O
O
O
O
N
N
N
N
S
S
S
S
5
5
N
N
N
N
Et
Et
Et
Et
O
O
O
O
Hf
Hf
NO2
NO2
3cd [I]
3cd [II]
(b)
Hb
Hb
Me
N
Me
N
Me
Me
O
O
O
O
O
O
O
O
N
N
N
N
N
N
Me
Me
Me
Me
O
O
O
O
NO2
NO2
H
H
N
N
4ab [I]
4ab [II]
(c)
Hb
H
Me
Me
N
Me
Me
N
O
O
O
O
O
O
N
O
H
O
N
N
H
N
N
5
5
N
1
H
N
H
H
O
NO2
O
O
O2N
O
H
N
4ae [I]
4ae [II]
corresponds to benzylic CH proton and a multiplet at d
7.23–7.42 ppm to phenyl ring. A broad singlet at d 8.80, a
singlet at d 10.28 and a broad singlet at d 16.25 ppm
correspond to the NH group of triethylammonium salt
moiety, two equivalent NH groups of bis-barbiturate moi-
ety and eight-membered intramolecular H-bonding,
respectively (Fig. 1b; Scheme 5c). The 1H NMR data
derived from 4ae0 indicated that the bis-barbiturate moiety
in this compound has symmetric structure and a fast
intramolecular mesomerization occurred. Two mesomeric
forms, 4ae0[I] and 4ae0[II], do not have a long time on the
NMR timescale. Therefore, two methyl and NH groups on
geminal bis-barbiturate have chemical shift equivalent
(Fig. 1b; Scheme 5c). Similar to 4ab0 as mentioned above,
the negative charge is delocalized in the bis-barbiturate
moiety of 4ae0.
quinolinium bis-barbiturates, respectively. The various
ammonium salts of some bis-barbiturates have also been
reported by the same authors groups [23]. In these com-
pounds, the intramolecular H-bonded proton appeared as
1
hydride bridge and this proton is not detected in their H
NMR spectra [25–27]. In contrast, in our current research,
the intramolecular H-bonded proton (Hb) in triethylam-
monium bis-barbiturates derived from 2b0 and 2e0 (4ab0
1
and 4ae0, respectively) were detected by H NMR spec-
troscopy and appeared in the ultra deshielded field (at d
16.25 ppm). This proton is delocalized between two oxy-
gen atoms of O5 and O7 (O5ꢀꢀꢀHbꢀꢀꢀO7). Instead, the neg-
ative charge delocalized and was able to resonate between
the two terminal oxygen atoms of O4 and O6 in the bis-
barbiturate moiety as shown in Scheme 6.
It is apparent that the strengthening of the homonuclear
O–HꢀꢀꢀO bond is paralleled by a transition from dissym-
metric to symmetric properties of the X1–O–HꢀꢀꢀO–X2
Previously, Jursic et al. [25–27] and Neumann et al. [23]
have reported the zwitterionic form of pyridinium and
123

J IRAN CHEM SOC
Scheme 6 Delocalization of
negative charge in 4ab0
Hb
Hb
Me
N
Me
N
Me
N
Me
O
O
O
O
O
O
O
O
N
N
N
N
N
Me
Me
Me
Me
O
O
O
O
NO2
NO2
H
H
N
N
4ab [I]
4ab [II]
Hb
Me
N
Me
N
O
O
O
O
N
N
NH
Me
Me
O
O
O2N
4ab
Fig. 3 ORTEP diagram of the molecule 4ab0. Thermal ellipsoids are
shown at the 50 % probability level. Dashed lines indicate H-bonding
geometry
fragment involved, the condition X1 = X2 included. Very
strong H-bonds are essentially three-center four-electron
covalent bonds. The strongest H-bonds are homonuclear
(X–HꢀꢀꢀX) and symmetrical as far as the distribution of
chemical groups on the two sides of the H-bond is con-
cerned, because only in this situation the two valence bond
(VB) resonance forms X–HꢀꢀꢀX$XꢀꢀꢀH–X are isoenergetic
and can mix at the greatest extent [21]. Therefore, in this
´
0
˚
Fig. 2 Correlation of d(O5ꢀꢀꢀO7) distance (2.45 A) in 4ab with
increasing pKa values of trichloroacetic (A), chloroacetic (B), 2,6-
dimethoxybenzoic (C), propionic (D), acetic (E) and formic acids
(F) [42–45] and estimation of the pKa value for 4ab0 (top). Hydrogen
bond strength (EHB) versus d(O5ꢀꢀꢀO7) distance (bottom) [46].
Estimation of the pKa and EHB (kcal/mol) values for intramolecular
H-bond of 4ab0 (ꢀꢀꢀ)
123

J IRAN CHEM SOC
research, the type of intramolecular H-bonding can be
formed as negative charge-assisted H-bonds [(-)CAHB]
and resonance-assisted H-bonds (RAHB). Based on bar
´
˚
chart of d(OꢀꢀꢀO) distances (d, A) in organic compounds,
subdivided
into
H-bond
strength
subclasses,
´
˚
2.40 B d(OꢀO) B 2.50 and 2.46 B d(OꢀꢀꢀO) B 2.65 A are
attributed to (-)CAHB and RAHB, respectively, and are of
strong H-bonds [21]. The intramolecular H-bonds in 4ab0
and 4ae0 are classified as strong, judging from the intra-
´
0
˚
molecular d(O5ꢀꢀꢀO7) distance of 2.450 A for 4ab and are
of homonuclear O–HꢀꢀꢀO bond. Instead, the intermolecular
H-bond of Et3N?6–H6ꢀꢀꢀ O6–C15 is typically heteronu-
-
clear and can be classified as positive/negative charge-
-
assisted H-bonds [( )CAHBs]. The d(N?6ꢀꢀꢀ O6) and
-
d(N?6ꢀꢀꢀ O4) distances were obtained as 2.895 and
´
˚
3.138 A, respectively. These bonds are usually indicated as
Fig. 4 Unit cell and the H-bonding geometry of the structure of 4ab0
Table 1 Intra- and intermolecular H-bond length and angles of 4ab0
‘‘salt bridges’’ in the biochemical literature and are not only
found in proteins, but also in supramolecular chemistry
[37, 41].
D–HꢀꢀꢀA
d(D–H) d(HꢀꢀꢀA) d(DꢀꢀꢀA) \(DHA) Directionality
Comparison of the strength of the H-bond in 4ab0 with
other carboxylic acids and flavone-acid compounds repor-
ted by Wallet et al. [42–44] and methyl 2,4-dimethoxysa-
licilate by Dabbagh et al. [45] allows for estimation of the
pKa of the bis-barbiturates as 4ab0. They used this method
when the experimental pKa determination was impractical.
O5–H5ꢀꢀꢀO7 0.82
N6–H6ꢀꢀꢀO6 0.91
N6–H6ꢀꢀꢀO4 0.91
O9–H9ꢀꢀꢀO3 0.82
1.70
2.20
2.46
2.08
2.450(5) 152
2.895(5) 133
3.138(6) 131
2.869(8) 162
Strong
Moderate
Weak
Moderate
Fig. 5 Inter- and eight-
membered intramolecular
˚
H-bonds and their distances (A)
in 4ab0. Views from back (a);
front (b); top (c) and bottom
side of o-nitro phenyl
substituent (d)
123

J IRAN CHEM SOC
Table 2 Selected crystallographic data of 4ab0
Table 3 Selected bond lengths (A), angles (h, °) and torsion angles
˚
(u, °) for 4ab0
Empirical formula
Crystal color
Fw
C19H18N5O8 ꢀ C6 H16 N ꢀ CH4O
Yellow
˚
Atom
Bond length (A), angles (h, °)
and torsion angles (u, °)
578.62
Crystal system
Space group
Crystal size (mm3)
Z
Monoclinic
P21/n
O5–H5A
0.8200
O6–C15
1.236 (5)
1.239 (5)
0.9100
0.3 9 0.2 9 0.1
4
O4–C10
N6–H6
˚
a (A)
10.4938 (2)
14.3340 (4)
18.6166 (4)
90.0
C7–C6
1.534 (6)
0.9800
˚
b (A)
C7–H7
˚
c (A)
C9–O5–H5A
C8–C7–C14
C8–C7–H7
C14–C7–H7
C6–C7–H7
C21–N6–H6
C8–C7–C6–C5
C8–C7–C6–C1
C14–C7–C6–C1
C8–C7–C14–C16
O1–N1–C1–C2
109.5
a (o)
b (o)
c (o)
114.7 (3)
104.5
94.503 (12)
90.0
104.5
3
˚
V (A )
2791.63 (11)
1.38
104.5
qcalcd (g cm-3
l (mm-1
)
106.2
)
0.105
-1.0 (6)
178.0 (4)
-48.5 (5)
88.1 (5)
123.3 (5)
F(000)
1232
h range (deg)
2.2–26.5
Limiting indices
-13 B h B 13
-16 B k B 17
-23 B l B 23
58850
Measured reflections
Independent reflections
Goodness of fit on F2
Final R indices [F2 [ 2r(F2)]
Data/restrains/parameters
Extinction coefficient
5727 [Rint = 0.1184]
1.016
compounds consisting of bifurcated inter- and intramolec-
ular H-bonds have also been reported [38, 47, 48].
R1 = 0.088, wR2 = 0.169
3826/0/377
0.0
An eight-membered intramolecular H-bond was also
formed between O5–H5AꢀꢀꢀO7 atoms. The inter- and
intramolecular H-bond distances were found in results of
23
˚
2.895(5) and 2.450(5) A, respectively. The corresponding
˚
Largest diff. peak and hole (A
)
0.349 and -0.375
inter- and intramolecular H-bond angles of N6–H6ꢀꢀꢀO6
and O5–H5AꢀꢀꢀO7 were 133 and 152°, respectively
(Table 1). The methanol molecule has an intermolecular
H-bonding with O3 atom of the carbonyl group on the bis-
barbiturate moiety (Fig. 4). The H-bond length and
The estimated pKa value for intramolecular H-bond of 4ab0
is equal to *-1.3 (Fig. 2, top). Based on correlation
between hydrogen bond strength (EHB) and d(OꢀꢀꢀO) dis-
tance, [46], the estimated EHB of intramolecular H-bond for
4ab0 is *37 kcal/mol (Fig. 2, bottom).
˚
d(O9ꢀꢀꢀO3) distance were found to be 2.08 and 2.869(8) A,
respectively (Table 1). The crystal structure of 4ab0 is
shown from different views of o-nitro phenyl substituent in
Fig. 5.
X-Ray analysis of compound 4ab0
A single yellow crystal of 4ab0 was obtained by slow
evaporation from methanol at room temperature. For the
crystal structure determination, the single crystal of the
compound 4ab0 was used for data collection on a four-
circle Rigaku R-AXIS RAPID-S diffractometer (equipped
with a two-dimensional area IP detector). The graphite-
For further study, an X-ray diffraction analysis of 4ab0 was
undertaken. The results of this study confirmed unambig-
uously the crystal structure of 4ab0 (Fig. 3). The crystal
packing diagram of 4ab0 is shown in Fig. 4. Triethylam-
monium salt moiety and a methanol molecule are banded
to the bis-barbiturate anion. Intermolecular bifurcated
˚
monochromatized MoKa radiation (k = 0.71073 A) and
-
H-bond was also formed between Et3N?6–H6ꢀꢀꢀ O6–C15
˚
oscillation scan technique with Dx = 5 for one image was
-
(N6–H6ꢀꢀꢀO6) and Et3N?6–H6ꢀꢀꢀ O4–C10 (N6–H6ꢀꢀꢀO4)
used for data collection. The lattice parameters were
determined by the least-squares methods on the basis of all
reflections with F2 [ 2r(F2). Integration of the intensities,
correction for Lorentz and polarization effects and cell
refinement were performed using CrystalClear (Rigaku/
MSC Inc., 2005) software [49]. The structures were solved
atoms in the molecule. The H-bond distance between
H6ꢀꢀꢀO6 is found to be little shorter than that of H6ꢀꢀꢀO4
´
˚
(Dd = 0.26 A). The N6–H6ꢀꢀꢀO6 hydrogen bond between
the asymmetric units is the main driving force for the
orientation of the triethylammonium cation. Other
123

J IRAN CHEM SOC
22. P. Gilli, V. Bertolasi, L. Pretto, V. Ferretti, G. Gilli, J. Am. Chem.
Soc. 126, 3845–3855 (2004)
by direct methods using SHELXS-97 [50] and refined by a
full-matrix least-squares procedure using the program
SHELXL-97 [50]. The crystallographic data and selected
bond lengths, angles and torsion angles are summarized in
Tables 2 and 3, respectively. Crystallographic data were
deposited at CCDC Registration Number 846864 and are
available free of charge upon request to CCDC, 12 Union
Road, Cambridge, UK (Fax: ?44-1223-336033, e-mail:
deposit@ccdc.cam.ac.uk).
23. D. Neumann, ‘‘The Design and Synthesis of Novel Barbiturates of
Pharmaceutical Interest’’. University of New Orleans Theses and
Dissertations. Paper 1040 (2004) http://scholarworks.uno.edu/td
24. A.I. Vogel, A.R. Tatchell, B.S. Furnis, A.J. Hannaford, P.W.G.
Smith, Vogel’s textbook of practical organic chemistry, 5th edn.
(Longman, UK, 1989)
25. B.S. Jursic, D.M. Neumann, K.L. Martin, E.D. Stevens, Org. Lett.
4, 811–813 (2002)
26. B.S. Jursic, D.M. Neumann, Z. Moore, E.D. Stevens, J. Org.
Chem. 67, 2372–2374 (2002)
27. B.S. Jursic, J. Heterocycl. Chem. 40, 167–170 (2003)
28. J. Adamson, B.J. Coe, H.L. Grassam, J.C. Jeffery, S.J. Coles,
M.B. Hursthouse, J. Chem. Soc. Perkin Trans. 1, 2483–2488
(1999)
Acknowledgments We gratefully acknowledge the financial sup-
port by the Research Council of Urmia University.
29. M. Jalilzadeh, N. Noroozi Pesyan, F. Rezaee, S. Rastgar, Y.
Hosseini, E. S¸ahin, Mol. Divers. 15, 721–731 (2011)
30. M. Jalilzadeh, N. Noroozi Pesyan, Bull. Korean Chem. Soc. 32,
3382–3388 (2011)
References
31. M. Jalilzadeh, N. Noroozi Pesyan, J. Korean Chem. Soc. 55,
940–951 (2011)
32. N. Noroozi Pesyan, M. Jalilzadeh, J. Chem. Sci. Tech. (JCST) 1,
1–8 (2012)
33. N. Noroozi Pesyan, S. Rastgar, Y. Hosseini, Acta Cryst. Sect E.
65, o1444 (2009)
1. M. Nishio, Tetrahedron 61, 6923–6950 (2005)
2. X.-B. Wang, H. K Woo, B. Kira, L.-S. Wang. Angew. Chem. Int.
Ed. 44, 4968–4972 (2005)
3. R.M. McKinlay, P.K. Thallapally, G.W.V. Cave, J.L. Atwood,
Angew. Chem. Int. Ed. 44, 5733–5736 (2005)
4. H. Gong, M.J. Krische, J. Am. Chem. Soc. 127, 1719–1725
(2005)
¨
34. Y. Hosseini, S. Rastgar, Z. Heren, O. Bu¨yu¨kgu¨ngor, N. Noroozi
Pesyan, J. Chin. Chem. Soc. 58, 309–318 (2011)
35. M.N. Elinson, A.N. Vereshchagin, N.O. Stepanov, P.A. Belya-
kov, G.I. Nikishin, Tetrahedron Lett. 51, 6598–6601 (2010)
36. R.L. Schriner, R.C. Fusan, D.Y. Curtin, T.C. Morrill, The sys-
tematic identification of organic compounds, 6th edn. (Wiley,
New York, 1980)
37. G. A. Jeffrey, An Introduction to Hydrogen Bonding (Oxford
University Press, Oxford, 1997)
38. T. Steiner, Angew. Chem. Int. Ed. 41, 48–76 (2002)
39. T.K. Harris, Q. Zhao, A.S. Mildvan, J. Mol. Struct. 552, 97–109
(2000)
40. D. Kalaivani, R. Malarvizhi, Acta Cryst. Sect. E. 65, o2548
(2009)
41. E.V. Anslyn, D.A. Dougherty, Modern Physical Organic
Chemistry. Sausalito, CA: University Science Books, ISBN
1-891389-31-9 (2006)
42. J.-C. Wallet, E. Molins, C. Miravitlles, J. Phys. Org. Chem. 11,
751–755 (1998)
43. J.C. Wallet, E. Molins, C. Miravitlles, Struct. Chem. 11, 319–323
(2000)
5. A. Tessa ten Cate, P.Y.W. Dankers, R.P. Sijbesma, E.W. Meijer,
J. Org. Chem. 70, 5799-5803 (2005)
6. P. Prabhakaran, V.G. Puranik, G.J. Sanjayan, J. Org. Chem. 70,
10067–10072 (2005)
7. I. Azumaya, D. Uchida, T. Kato, A. Yokoyama, A. Tanatani, H.
Takayanagi, T. Yokozawa, Angew. Chem. Int. Ed. 43,
1360–1363 (2004)
8. Y. Zhu, D.G. Drueckhammer, J. Org. Chem. 70, 7755–7760
(2005)
9. C.P. Price, A.J. Matzger, J. Org. Chem. 70, 1–6 (2005)
10. X. Zhang, H. Du, Z. Wang, Y.-D. Wu, K. Ding, J. Org. Chem. 71,
2862–2869 (2006)
11. I. Alfonso, M.I. Burguete, S.V. Luis, J. Org. Chem. 71,
2242–2250 (2006)
12. M.H. Abraham, R.J. Abraham, J. Byrne, L. Griffiths. J. Org.
Chem. 71, 3389–3394 (2006)
13. G.A. Jeffery, W. Saenger, Hydrogen bonding in biological
structures (Springer-Verlag, Berlin, Germany, 1991)
14. A.M. Asiri, S.A. Khan, S.W. Ng, Acta Cryst. Sect. E. 65, o1860–
o1861 (2009)
44. E. Espinosa, E. Molins, J.-C. Wallet, J. Phys. Org. Chem. 12,
499–502 (1999)
45. H.A. Dabbagh, N. Noroozi Pesyan, B.O. Patrick, B.R. James,
Can. J. Chem. 82, 1179–1185 (2004)
46. J. Chen, M.A. McAllister, J.K. Lee, K.N. Houk, J. Org. Chem. 63,
4611–4619 (1998)
47. N. Noroozi Pesyan, Magn. Reson. Chem. 47, 953–958 (2009)
48. P. Gregory, Dyes Pigment. 7, 45–56 (1986)
49. Rigaku/MSC, Inc., 9009 new Trails Drive, The Woodlands, TX
77381
15. Y. Zhang, C.-S. Wang, J. Comput. Chem. 30, 1251–1260 (2009)
16. Y.-D. Wu, K.W.K. Chan, D.-P. Wang, J. Am. Chem. Soc. 118,
9794–9795 (1996)
17. D. Yang, J. Qu, B. Li, F.-F. Ng, X.-C. Wang, K.-K. Cheung, D.-P.
Wang, Y.-D. Wu, J. Am. Chem. Soc. 121, 589–590 (1999)
18. A. G. J. Ligtenbarg, R. Hage, A. Meetsma, B. L. Feringa, J.
Chem. Soc., Perkin Trans. 2, 807–812 (1999)
19. C. Peter, X. Daura, W.F. van Gunsteren, J. Am. Chem. Soc. 122,
7461–7466 (2000)
20. N. Noroozi Pesyan, M. Jalilzadeh, Turk. J. Chem. 36, 788–804
(2012)
21. G. Gilli, P. Gilli, J. Mol. Struct. 552, 1–15 (2000)
¨
50. G.M. Sheldrick, SHELXS97 and SHELXL97 (University of Got-
tingen, Germany, 1997)
123