Synthesis of thiadiazine, imidazothiadiazole, diazospiroundecatetraene and spirothiadiazolopyrimidinocyclohexadiene derivatives from 2,5-dithiobiureas

Article abstract of DOI:10.3184/030823408X284503

Ethenetetracarbonitrile (2, in tetrahydrofuran solution), diethyl (E)-2,3-dicyanobutenedioate (10, in tetrahydrofuran solution), and 7,7′,8,8′-tetracyanoquinodimethane (16, in pyridine solution) act on 1-substituted-2,5-dithiobiureas 1a-c, forming the derivatives of imidazothiadiazole 5a-c, thiadiazine 11a-c and 12a-c, spiro(thiadiazolopyrimidino-cyclohexadiene)malononitrile17a-c and diazospiroundecatetraene18a-c. Rationales for these conversions involving the nucleophilic addition on diycanomethylene carbon atom are presented.

Full text of DOI:10.3184/030823408X284503

JOURNAL OF CHEMICAL RESEARCH 2008
JANUARY, 9–15
RESEARCH PAPER
9
Synthesis of thiadiazine, imidazothiadiazole, diazospiroundecatetraene
and spirothiadiazolopyrimidinocyclohexadiene derivatives from
2,5-dithiobiureas
Alaa A. Hassan*, Ashraf A. Aly and Essmat M. El-Sheref
Chemistry Department, Faculty of Science, Minia University, 61519-El-Minia, A. R. Egypt
Ethenetetracarbonitrile (2, in tetrahydrofuran solution), diethyl (E)-2,3-dicyanobutenedioate (10, in tetrahydrofuran
solution), and 7,7',8,8'-tetracyanoquinodimethane (16, in pyridine solution) act on 1-substituted-2,5-dithiobiureas
1a–c, forming the derivatives of imidazothiadiazole 5a–c, thiadiazine 11a–c and 12a–c, spiro(thiadiazolopyrimidino-
cyclohexadiene)malononitrile 17a–c and diazospiroundecatetraene 18a–c. Rationales for these conversions involving
the nucleophilic addition on diycanomethylene carbon atom are presented.
Keywords: ethenetetracarbonitrile, diethyl (E)-2,3-dicyanobutenedioate and tetracyanoquinodimethane, heterocyclisation of
substituted 2,5-dithiobiureas
Ethenetetracarbonitrile (tetracyanoethylene, 2) is the simplest
of percyanoalkenes (cyanocarbons).1 It shows a great affinity
for electrons, and is thus a fairly good dehydrogenating
agent towards dihydroheteroaromatic systems.1 The general
chemistry of 2 had been reviewed with emphasis on
molecular complexes by an intermolecular charge-transfer
interaction,1-4 tricyanovinylation reactions,1 additions1 and
cycloaddition reactions5 as well as cyanation reagents.6-8
Ethenetetracarbonitrile (2) reacted with thiosemicarbazides to
give a variety of heterocyclic compounds via a single-electron
transfer mechanism.9-16
Diethyl (E)-2,3-dicyanobutenedioate have been discovered
to be a viable and versatile alternatives to tetracyanoethylene as
building blocks for the synthesis of molecule-based magnets.17
The reaction of diethyl (E)-2,3-dicyanobutenedioate (10)
with ethylenediamine, trans-1,2-diaminocyclohexane afforded
piprazinone and quinoxalinone derivatives, respectively.18
Also, diethyl (E)-2,3-dicyanobutenedioate reacted with
o-phenylenediamine and 2,3-diaminonaphthalene with the
formation of quinoxaline and quinoxalinone derivatives.19
Aminopteridine derivatives and related compounds have been
prepared during the reaction of compound 10 with uracil and
thiouracil derivatives.20
S
H
N
NC
NC
CN
CN
HN
HN
C
C
R
H
N
R'
S
1
2
S
R
N
N
CN
CN
N
N
H
N
NH
R
CN
CN
S
CN
H2N
H2N
CN
4
3
1,3 and 4
R
C6H5
R'
a
b
c
C6H5
C6H5CH2
C6H5CH2
CH2=CH-CH2 CH2=CH-CH2
Fig. 1
As well be outlined in detail below, in this paper we reported
several heterocyclisation of 1-substituted-2,5-dithiobiureas 1a–
c using ethenetetracarbonitrile (2) either as a reaction mediator
or as a building block, diethyl (E)-2,3-dicyanobutenedioate (10)
and 7,7',8,8'-tetracyanoquinodimethane (16) as p-acceptors.
Recently, we have demonstrated that 1,6-disubstituted-2,5-
dithiobiureas 1 reacted with 2 to give products 3 and 4, in
addition to disubstituted-1,3,4-thiadiazoles (Fig. 1).13
S
NC
NC
CN
CN
H
N
HN
HN
C
C
R'
R
+
H
N
S
1
2
CN
N
N
N
N
N
N
H
N
H
N
+
R
R
R
N
H
S
S
N
H
N
H
S
N
CN
6 (32-36)
5 (51-56%)
1 5
,
6
and
R
R'
a
b
c
C6H5
C6H5CH2
CH2=CH-CH2
H
H
H
Scheme 1
* Correspondent. E-mail: alaahasan2001@yahoo.com
PAPER: 07/4952

10 JOURNAL OF CHEMICAL RESEARCH 2008
The 1H NMR spectrum of 6b showed two broad signals with
Results and discussion
the ratio 1:1 centred at 6.57 and 8.87 ppm, due to hydrazine-
Addition of doubled molar amounts of 2 to solutions of 1a–c
in tetrahydrofuran (THF) with admission of air resulted in a
pink colouration of the solution which quickly turned into
brown. This behaviour may be explained as due to initial
formation of unstable charge-transfer (CT) complexes
followed by chemical reaction. Monitoring of the reaction
by visible spectroscopy failed since the reaction is fast and
also at lower concentration no significant colour changes were
observed. After concentration of the reaction mixture, the
residue was subjected to vacuum sublimation to remove any
unreacted TCNE. Chromatographic separations of the residue
gave numerous coloured zones. From the two most intense
zones, products 5a–c and 6a–c could be isolated (Scheme 1).
The structures of 5a–c are supported by characteristic IR,
1H and 13C NMR as well as mass spectral data by the following
findings: The gross formula of 5a, C12H6N6S represents a
product from one molecule of 1a and one molecule of 2
with loss of (H2S + 2HCN). The IR spectrum of 5a shows
absorption characteristic of NH, CN and C=N groups at 3380,
2215 and 1635 cm-1, respectively. The low-field NH attached
to phenyl group is present at dH = 9.76 ppm. In its 13C NMR
spectrum, C-2, C-5, C-6 and C-4a resonate at dC = 156.88,
122.24, 122.26 and 154.53 ppm, respectively. Further peaks
at 118.11 and 118.14 ppm (CN), besides the aromatic carbons
support the assigned structure.
The formations of 9 did not take place in the absence of
2 hence its presence is definitely required for the cyclisation
observed. Charge-transfer complexes may (but not
necessarily) play an intermediate role. Since the cyclisation
involves intramolecular nucleophilic attacks on either of the
thiocarbonyl groups. It is conceivable that 2 accelerates the
process through intermediates 7 and 8 (Scheme 2), activating
the respective C=S bonds toward nucleophilic addition. After
cyclisation and formation of intermediates 9, 2 is released
with liberation of H2S.
Two routes could be suggested, the first one is the tendency
of 2 to effect tetracyanoethylation the intermediate 9 followed
by the elimination two molecules of HCN and formation the
imidazothiadiazole derivatives 5a–c. The second route is the
formation of the intermediate 9˙ to give the product 6a–c
(Scheme 2). Thus, ethenetetracarbonitrile (2) may act either
as a mediator or as a building block in heterocyclisation of
compounds 1a–c.
1
NH and phenyl-NH protons. The signal around 4.61 in H
NMR and 52.58 ppm in 13C NMR spectra due to benzylic-
CH2 further supports the structure assigned to 6b. The 13C-
DEPT NMR spectrum exhibiting negative signal at d = 52.58
ppm. The decoupled carbon spectrum of 6b showed signals
at d = 155.48 and 154.21 ppm due to thiazole-C-2 and C-5,
respectively, besides the aromatic carbons. The IR spectrum
of 6b showed absorption bands at 3385–3360, 1625 and 1600
due to NH, C=N and (ArC=C) groups.
The molecular ions of 6a–c in their EI-mass spectra confirm
the molecular masses and the gross compositions. Furthermore,
the following common features of the fragmentation patterns
support the assigned structure: Loss of N2 giving intense
(M+-28) ions and loss of RNCS giving rise to the ion
m/z = 261 common in the spectra of all three compounds.
The odd electron fragments represented the three
isothiocyanates indicating that the charge during fragmentation
may remain with the isothiocyanate fragments.
We now report a convenient method for one-step synthesis
of thiadiazine 11a–c and 12a–c derivatives. This method
consists of the reaction of 1a–c with 10 (in a 1:2 molar ratio).
The weaker acceptor 10, was expected to react similarly to 2
with the donors 1a–c. The reaction was carried out in THF
at room temperature and nearly two days were required to
achieve conversion of 96% for 1a–c and medium yields of 11
and 12 were observed (Scheme 3).
Recombination of 1a–c˙ ion radical under abstraction of
two hydrogen protons by 10˙ to give the dimer A along with
10-H˙. Elimination of a molecule of S2 from the dimer A
afforded the radical 13˙. Combination of the radicals 13˙ and
10-H˙ gave the adduct 14. The resulting adduct 14 undergoes
elimination of one molecule of ethyl formate followed by
intramolecular nucleophilic attack to the ethylenic double
bond with the elimination of HCN to form the thiadiazine
derivatives 11a–c.
On the other hand, the thiadiazines 12a–c were obtained
from cyclisation of the adduct 14 via an elimination a molecule
of ethyl cyanoacetate (Scheme 4).
The IR spectrum of 11b showed absorption bands due to
NH2 and NH stretching vibration at 3350 and 3225 cm-1, an
a,b-unsaturated nitrile CN at 2225, carbonyl ester at 1685 and
C=N group at 1620 cm-1. 1H NMR spectrum of 11b in DMSO-
1
+
2
H
N
H
N
H
N
H
N
R
NH
NH
NH2
R
C
S
4
-
N
N
4
-
S
NC
NC
R
- H2S
- H2S
S
S
NH2
CN
N
S
NH2
H
NC
NC
9
CN
.
.
NC
CN
7
N
NH
NH
+ 2
8
9
5a-c
R
- 2HCN
N
H
S
+ 2
.
.
- 2HCN
9
+ 2-H
5a-c
X
2
6a-c
Scheme 2
PAPER: 07/4952

JOURNAL OF CHEMICAL RESEARCH 2008 11
NC
CO2Et
CN
cm-1. The 1H NMR spectrum of 12c shows two broad signals
at dH = 6.35 and 7.55 ppm, due to NH2 as well as allyl-NH.
Also, the 1H NMR spectrum of 12c shows one singlet and two
multiplets at dH = 4.09, 5.18–5.26 and 5.90–5.94 ppm, due
to allyl group. The decoupled carbon spectra of 12c showed
signals at dC = 14.19 (CH3), 42.88 (allyl-CH2N), 60.63
(CH2O), 116.06 (allyl-CH2=), 118.16 (CN), and 134.22 ppm,
(allyl-CH=). Also, the 13C NMR of 12c shows another signals
at dC = 158.93, 159.67 and 166.12 ppm, due to (C-2, C-5)
and (COO), respectively. The gross formula C10H13N5O2S
represents a product from one molecule of 1c and one of 10
with loss of sulfur and ethyl cyanoacetate.
1a c
-
+
EtO2C
10
N
S
NH2
CO2Et
CN
N
S
NH2
CO2Et
N
N
+
R
R
N
H
N
H
CN
11 (45-49%)
12 (36-41%)
7,7',8,8'-Tetracyanoquinodimethane (TCNQ, 16) is
well known electron acceptor molecule,21 which has been
successfully used for the preparation of electrically conducting
salts and CT-complexes.22 The interest of TCNQ has focused
on its potential applications on material rectifiers,23 non-
linear optical materials,24 organoferromagnets25 and organic
chromophores.26
Recently, it has been reported that the addition of 1,8-
diaminonaphthalene to TCNQ (16) afforded 2-(4-(1H,3H-
pyrimidin-2-ylidene)cyclohexa-2,5-dienylidene)malono-
nitrile.27 Pyridine solution of TCNQ (16) and 1a–c in a molar
ratio of 2:1 were kept at 100°C for 2 h with admission of air.
Chromatographic separation of the residue after concentration
gave numerous coloured zones, from which products 17 and
18 could be isolated (Scheme 5).
1,11 and 12
R
C6H5
C6H5CH2
CH2=CH-CH2
R'
H
H
H
a
b
c
Scheme 3
d6, revealed signals at 4.62 due to benzylic-CH2, 1.25 and
4.16 for ethoxy group (J = 7.10), two broad signals with the
ratio 2:1 centred at 6.34 and 8.89 ppm, due to exocyclic NH2
and benzylic-NH, respectively. Signals around 52.64 (CH2),
118.19 (CN), 155.92, 161.44 (C-5, C-2) and 168.81 (COO)
in the 13C NMR spectrum further support structure 11b.
The molecular formula of compounds 11a–c were obtained
and confirmed by elemental analysis and mass data.
The presence of ethoxy and benzylic groups are also evident
from the 13C-DEPT NMR spectrum exhibiting positive signals
at 14.26 and negative signals at 52.64 and 60.79 ppm.
Structural assignment of products 17a–c is based on spectral
data and on combustion analysis. The elemental analysis
of 17b supporting the gross formula C21H14N8S, and the
mass spectrum which gave a correct molecular ion at m/z =
410 (23%).
For the formation of thiadiazines 12a–c, the IR spectrum of
12c shows characteristic bands at n = 3360, 3270 (NH2 and
NH), 2220 (CN) and 1685 (COO) as well as C=N at 1610
1a-c
CT-complex
1a-c
10
10
+
+
X
2
S
NH2
H
H
N
R
R
N
C
N
N
C
EtO2C
CN
H
S
S
2
+
S
NC
CO2Et
H
N
H
N
C
C
10-H
NH2
A
- S2
S
NH2
H
N
H
R
C
N
N
C
13
+ 10-H
S
H
H
NH2
R
N
C
N
N
C
N
C
CN
NH2
CN
H
CO2Et
- HCOOEt
EtO2C
NC
N
NC
SH
CO2Et
R
N
H
14
15
- HCN
- NCCH2CO2Et
12a-c
11a-c
Scheme 4
PAPER: 07/4952

12 JOURNAL OF CHEMICAL RESEARCH 2008
NC
NC
CN
CN
1a-c
+
16
NH2
H2N
CN
S
N
CN
CN
CN
CN
H
R
N
C
N
N
S
+
N
N
R
H2N
CN
N
H
17 (55-59%)
18 (28-33%)
1,17 and 18
R
C6H5
C6H5CH2
CH2=CH-CH2
R'
H
H
a
b
c
H
Scheme 5
S
The IR spectrum of 17b showed NH2 and NH absorption bands
at n = 3395 and 3315, cyano groups at 2220 and 2215 cm-1.
The 1H NMR spectrum revealed two broad signals at d = 6.70
and 8.91 ppm, related to NH2 and benzyl-NH, respectively,
besides the aromatic and cyclohexadiene protons. The 13C
NMR spectrum of 17b confirmed its 1H NMR spectral data by
appearance of signals at 4.62, 6.30 and 6.58 due to benzylic-
CH2 and cyclohexadiene-CH. The 13C NMR spectrum of 17b
revealed signals for pyrimidine (C-6, C-5) which resonate at
d = 60.45 and 160.91 ppm, respectively are accordance with
the observed trends in the d values for C-atoms in push-pull
alkenes.28,29
NH2
- S2
H
H
N
13
1a-c
+
16
R
N
C
N
C
+
16-H
- H2S
NH
NH
C
S
N
NH2
H
N
H
R
R
C
N
N
C
CN
CN
N
H
S
N
CN
HN
C
CN
22
NC
CN
The second zone characterised by a brown colour contains
compounds spiropyridazine-cyclohexadiene derivatives 18a–c.
The IR spectrum of 18a showed characteristic absorption to the
NH2 and NH groups at 3385, 3270, 1570 (NH def. and C-N str.)
and 1358 as well as 998 cm-1, to strong vibrational coupling
of C=S and C-N entities. The 1H NMR spectrum of 18a
showed three broad signals with the ratio 2:2:1 centred at 6.49,
6.62 and 9.84 due to two exocyclic-NH2 and Ph-NH protons.
The decoupled carbon spectrum of 18a showed signals at
d = 180.19 (C=S), 60.71 (C-5), 156.67 (C-3), 160.83 (C-6) and
46.21 (q-C-4,1'). The analytical data of compound 18a could
also match for other isomers of products 19 and 20 (Fig. 2).
The alternative structures 19 and 20 could be ruled out on
the bases of 1H NMR, 13C NMR and the fragment ions in the
mass spectrum of 18a at m/z 263, 207, 197, 135, 66 and 57.
As shown in Fig. 2, structure 18a fits best to all the
spectroscopic data (see experimental section).
21
18a-c
17a-c
Scheme 6
Formation of spiro compounds 17 and 18 derivatives from
TCNQ may be rationalised as outlined in (Scheme 6).
Experimental
Melting points have been determined using open capillaries on a
Gallenkamp melting point apparatus and are uncorrected. Elemental
analysis were determined by Microanalytical Centre, Cairo
University, Egypt. The IR spetra were recorded with Shimadzue 408
instrument using potassium bromide. 500 MHz 1H and 125 MHz 13
C
Ph
Ph
S
H
N
135
C
N
S
N
H
NH2
CN
H2N
66
NC
N
57
N
HN
NC
H2N
NC
N
S
H
N
H
N
NH2
Ph
C
N
NH2
NC
CN
NC
CN
CN
20
19
1) 3-CN
18a
1) 3-CN
1) 3-CN
2) 1-NH, 2-NH2
3) q-C
2) 3-NH, 1-NH2
3) q-C
2) 1-NH, 2-NH2
3) q-C
4) C=S
4) no C=S
4) C=S
Fig. 2
PAPER: 07/4952

JOURNAL OF CHEMICAL RESEARCH 2008 13
NMR spectra on a Bruker DRX 500 spectrometer. Chemical shifts
are expressed as d [ppm] with reference to tetramethylsilane as an
internal standard, s = singlet, d = doublet, dd = doublet of doublet,
t = triplet, m = multiplet and br = broad. 13C assignments (q C = sp2
quaternary carbon atoms) were made with the aid of distortionless
enhancement by polarisation transfer (DEPT) 135/90 spectra. Mass
spectra were recorded on Varian MAT 311 instrument in EI Mode
(70 eV) ionisation energy. Preparative layer chromatography (PLC)
used air-dried 1.0 mm thick layers of slurry applied silica gel, Merck
Pf254 on 48 cm wide and 20 cm high glass plates using the solvents
listed. Zones were detected by quenching of indicator fluorescence
upon exposure to 254 nm light and eluted with acetone.
(m/z,%): 382 (M+, 21), 354 (11), 261 (34), 219 (100), 150 (92), 135
(33), 77 (62), 65 (21). C16H14N8S2 (382.47): Calcd; C, 50.25; H, 3.69;
N, 29.30; S, 16.77. Found: C, 50.44; H, 3.52; N, 29.14; S, 16.96.
1,2-Bis[5-(benzylamino)-1,3,4-thiadiazol-2-yl]hydrazine
(6b):
Pale yellow crystals (0.148 g, 36%), m.p. 262–264°C (acetonitrile).
1H NMR (DMSO-d6): d = 8.87 (br, 2H, benzyl-NH), 7.10–7.38
(m, 10H, ArH), 6.57 (br, 2H, hydrazine-NH), 4.61 (s, 2H, CH2).
13C NMR: d = 155.48 (C-2), 154.21 (C-5), 141.63 (ArC), 127.56,
128.82, 129.59 (ArCH), 52.58 (CH2). IR (KBr): 3385-3360 (NH),
1625 (C=N), 1600 (ArC=C). MS (m/z,%): 410 (M+, 16), 382 (22),
261 (46), 164 (76), 149 (81), 91 (100), 65 (36). C18H18N8S2 (410.52):
Calcd; C, 52.66; H, 4.42; N, 27.30; S, 15.62. Found: C, 52.43; H,
4.64; N, 27.53; S, 15.39.
Starting materials
1,2-Bis[5-(allylamino)-1,3,4-thiadiazol-2-yl]hydrazine
(6c):
1-Substituted-2,5-dithiobiureas 1a–c were prepared according to
published procedures, as were 1-phenyl-2,5-dithiobiurea (1a),30 1-
benzyl-2,5-dithiobiurea (1b),30,31 1-allyl-2,5-dithiobiurea (1c).30
Ethenetetracarbonitrile (2, Merck) was purified by crystallisation from
chlorobenzene and sublimed. Diethyl (E)-2,3-dicyanobutenedioate
(10) and 7,7',8,8'-tetracyanoquino-dimethane (16, TCNQ) were
purchased from Aldrich and used as purchased.
Pale yellow crystals (0.105 g, 34%), m.p. 195–197°C (acetonitrile).
1H NMR (DMSO-d6): d = 7.61 (br, 2H, allyl-NH), 5.88–5.94 (m,
2H, allyl-CH=), 5.08–5.16 (m, 4H, allyl-CH2=), 4.08 (br, 4H, allyl-
CH2N),; 13C NMR: d = 155.83 (C-2), 154.71 (C-5), 134.28 (allyl-
CH=), 115.08 (allyl-CH2=), 43.28 (allyl-CH2N). IR (KBr): 3365–
3345 (NH), 1615 (C=N). MS (m/z,%): 310 (M+, 23), 282 (14), 269
(27), 211 (16), 131 (89), 114 (46), 99 (62), 41 (100). C10H14N8S2
(310.41): Calcd; C, 38.69; H, 4.55; N, 36.10; S, 20.66. Found:
C, 38.48; H, 4.71; N, 38.88; S, 20.89.
Reactions of 1-substituted-2,5-dithiobiureas 1a–c with ethenetetra-
carbonitrile (2)
To a chilled solution of 256 mg (2.0 mmol) of 2 in 10 ml of
tetrahydrofuran (THF) a pre-cooled solution of 1a–c in 15 ml of
THF was added dropwise which caused a spontaneous change of
colour from yellow to pink. The mixture was stirred for 3 h and
allowed to warm up to room temperature. The stirring was continued
for 48 h with admission of air to complete the reaction. After
concentration, the reaction mixture to dryness, the residue sublimed
at 80°C under vacuum to remove all unreacted 2. The residue was
then separated by PLC (100 mg per plate) using a suitable solvent
mixture as aluent (cyclohexane/ethyl acetate 2:1 for the reaction of
2 with 1a and 1b; cyclohexane/ethyl acetate 3:1 for the reaction of
2 with 1c) to give numerous coloured zones. The two most intense
of which were removed and extracted. The fastest migrating one
contained imidazothiazole derivatives 5a–c, the second zone, which
quenched all indicator fluorescence upon exposure to 254 nm UV-
light, contained 1,2-bis[2-(substituted amino)-1,3,4-thiadiazol-2-
yl]hydrazine 6a–c. Extraction of the zones with acetone gave a
residue, which was rechromatographed and recrystallised to separate
the pure compounds.
2-(Phenylamino)imidazo[2,1-b][1,3,4]thiadiazole-5,6-dicarbonitrile
(5a): Reddish brown crystals (0.149 g, 56%), m.p. 302–304°C
(methanol). 1H NMR (DMSO-d6): d = 9.76 (br, 1H, phenyl-NH),
7.11–7.66 (m, 5H, ArH). 13C NMR: d = 156.88 (C-2), 154.53 (C-4a),
143.33 (ArC), 127.31, 128.82, 129.67 (ArCH), 122.24, 122.26, (C-5,
C-6), 118.11, 118.14 (CN). IR (KBr): 3380 (NH), 2215 (CN), 1635
(C=N), 1590 (ArC=C). MS (m/z,%): 266 (M+, 22), 240 (14), 214 (3),
190 (8), 135 (44), 77 (100), 65 (42). C12H6N6S (266.28): Calcd; C,
54.13; H, 2.27; N, 31.56; S, 12.04. Found: C, 53.89; H, 2.41; N, 31.78;
S, 11.81.
Reaction of 1-substituted-2,5-dithiobiureas 1a–c with diethyl (E)-2,3-
dicyanobutenedioate (10): A solution of 444 mg (2.0 mmol) of 10 in
30 ml THF was treated with a) 226 mg (1.0 mmol) of 1a, b) 240 mg
(1.0 mmol) of 1b, c) 190 mg (1.0 mmol) of 1c and stirred at 20°C for
48 h (a) and 96 h (b, c), respectively. During which time the colour
of the solution changed from yellow to light red. Concentration of
the reaction mixture to dryness, the residues was subjected to PLC
using cyclohexane/ethyl acetate (5:1) as eluent. Chromatographic
separation of the residue gave numerous coloured zones, two of
which (with high intensity) were removed and extracted. The fastest
move zone contained the thiadiazinylidene cyanoacetate derivatives
11a–c, while the slowest moving zone contained the thiadiazine
derivatives 12a–c. Extraction of the zones with acetone and
recrystallised gave the pure compounds.
Ethyl (Z)-2-[5-amino-2-(phenylamino)-6H-1,3,4-thiadiazin-6-ylidene]-
2-cyanoacetate (11a): Orange crystals (0.154 g, 49%), m.p. 225–
227°C (ethanol). 1H NMR (DMSO-d6): d = 9.81 (br, 1H, Phenyl-
NH), 6.98–7.46 (m, 5H, ArH), 6.37 (br, 2H, NH2), 4.19 (q, 2H,
J = 7.15, OCH2), 1.27 (t, 3H, J = 7.15, CH3). 13C NMR: d = 165.74
(COO), 163.42 (C-5), 161.23 (C-2), 146.65 (C-6), 144.32 (ArC),
127.63, 128.84, 129.61 (ArCH), 118.24 (CN), 115.14 (ethylenic-C),
60.76 (CH2O), 14.28 (CH3). IR (KBr): 3360, 3280 (NH2, NH), 2220
(CN), 1680 (CO), 1610 (C=N), 1580 (ArC=C). MS (m/z,%): 315
(M+, 41), 299 (14), 204 (28), 180 (11), 150 (21), 135 (12), 77 (100).
C14H13N5O2S (315.35): Calcd; C, 53.32; H, 4.16; N, 22.21; S, 10.17.
Found: C, 53.49; H, 3.98; N, 22.48; S, 10.36.
Ethyl (Z)- 2-[5-amino-2-(benzylamino)-6H-1,3,4-thiadiazin-6-ylidene]-
2-cyanoacetate (11b): Orange crystals (0.151 g, 46%), m.p. 258–
1
260°C (methanol). H NMR (DMSO-d6): d = 8.89 (br, 1H, benzyl-
2-(Benzylamino)imidazo[2,1-b][1,3,4]thiadiazole-5,6-dicarbonitrile
(5b): Reddish brown crystals (0.148 g, 53%), m.p. 325–327°C
(acetonitrile). 1H NMR (DMSO-d6): d = 8.85 (br, 1H, benzyl-NH),
7.06–7.58 (m, 5H, ArH), 4.62 (s, 2H, CH2). 13C NMR: d = 156.66 (C-2),
154.31 (C-4a), 122.22, 122.25 (C-5, C-6), 118.10, 118.13 (CN), 52.41
(CH2). IR (KBr): 3365 (NH), 2980 (Ali-CH), 2220 (CN), 1630 (C=N),
1600 (ArC=C). MS (m/z,%): 280 (M+, 19), 204 (12), 149 (72), 91 (100),
65 (28). C13H8N6S (280.31): calcd; C, 55.70; H, 2.88; N, 29.98; S,
11.44. Found: C, 55.93; H, 2.65; N, 30.16; S, 11.67.
2-(Allylamino)imidazo[2,1-b][1,3,4]thiadiazole-5,6-dicarbonitrile
(5c): Reddish brown crystals (0.117 g, 51%), m.p. 271–273°C
(ethanol). 1H NMR (DMSO-d6): d = 7.59 (br, 1H, allyl-NH),
5.90–5.93 (m, 1H, allyl-CH=), 5.01–5.18 (m, 2H, allyl-CH2=), 4.05
(br, 2H, allyl-CH2N). 13C NMR: d = 156.77 (C-2), 155.11 (C-4a),
134.21 (allyl-CH=), 122.15, 122.18 (C-5, C-6), 118.08, 118.10 (CN),
114.81 (allyl-CH2=), 43.33 (allyl-CH2N). IR (KBr): 3370 (NH), 2965
(Ali-CH), 2215 (CN), 1635 (C=N). MS (m/z,%): 230 (M+, 36), 204
(6), 154 (44), 99 (82), 41 (100). C9H6N6S (230.25): Calcd; C, 46.95;
H, 2.63; N, 36.50; S, 13.93. Found: C, 47.18; H, 2.81; N, 36.29;
S, 14.16.
NH), 7.05–7.44 (m, 5H, ArH), 6.34 (br, 2H, NH2), 4.62 (s, 2H,
PhCH2), 4.16 (q, 2H, J = 7.10, OCH2), 1.25 (t, 3H, J = 7.10, CH3).
13C NMR: d = 165.56 (COO), 163.12 (C-5), 161.44 (C-2), 146.65
(C-6), 143.61 (ArC), 127.48, 128.68, 129.14 (ArCH), 118.19 (CN),
114.99 (ethylenic-C), 60.79 (CH2O), 52.64 (Ph-CH2), 14.26 (CH3). IR
(KBr): 3350, 3225 (NH2, NH), 2225 (CN), 1685 (CO), 1620 (C=N),
1590 (ArC=C). MS (m/z,%): 329 (M+, 26), 313 (8), 303 (6), 218 (15),
180 (16), 149 (33), 91 (100), 77 (84). C15H15N5O2S (329.38): Calcd;
C, 54.70; H, 4.59; N, 21.26; S, 9.74. Found: C, 54.45; H, 4.80; N,
21.54; S, 10.02.
Ethyl(Z)-2-[5-amino-2-(allylamino)-6H-1,3,4-thiadiazin-6-ylidene]-
2-cyanoacetate (11c): Orange crystals (0.126 g, 45%), m.p. 196–
1
198°C (acetonitrile). H NMR (DMSO-d6): d = 7.61 (br, 1H, allyl-
NH), 6.40 (br, 2H, NH2), 5.88–5.91 (m, 1H, allyl-CH=), 5.16–5.22
(m, 2H, allyl-CH2=), 4.18 (q, 2H, J = 7.06, OCH2), 4.05 (br, 2H, allyl-
CH2N), 1.26 (t, 3H, J = 7.06, CH3). 13C NMR: d = 165.32 (COO),
163.22 (C-2), 161.28 (C-2), 146.55 (C-6), 134.29 (allyl-CH=), 117.96
(CN), 115.88 (allyl-CH2=), 114.15 (ethylenic-C), 60.93 (CH2O),
43.12 (allyl-CH2N), 14.26 (CH3),. IR (KBr): 3370, 3290 (NH2, NH),
2220 (CN), 1680 (CO), 1615 (C=N). MS (m/z,%): 279 (M+, 16), 263
(9), 203 (13), 180 (23), 99 (91), 41 (100). C11H13N5O2S (279.32):
Calcd; C, 47.30; H, 4.69; N, 25.07; S, 11.48. Found: C, 47.49;
H, 4.52; N, 24.87; S, 11.27.
1,2-Bis[5-(phenylamino)-1,3,4-thiadiazol-2-yl]hydrazine
(6a):
Yellow crystals (0.122 g, 32%), m.p. 240–242°C (acetonitrile).
1H NMR (DMSO-d6): d = 9.81 (br, 2H, phenyl-NH), 7.06–7.49
(m, 10H, ArH), 6.61 (br, 2H, hydrazine-NH). 13C NMR: d = 155.76
(C-2), 154.33 (C-5), 143.12 (ArC), 127.63, 128.81, 129.67 (ArCH).
IR (KBr): 3370–3340 (NH), 1620 (C=N), 1595 (ArC=C). MS
Ethyl 5-amino-6-cyano-2-(phenylamino)-6(H)-1,2,4-thiadiazine-
6-carboxylate (12a): Reddish brown crystals (0.124 g, 41%), m.p.
205–207°C (acetonitrile). 1H NMR (DMSO-d6): d = 9.84 (br, 1H,
PAPER: 07/4952

14 JOURNAL OF CHEMICAL RESEARCH 2008
phenyl-NH), 7.09–7.46 (m, 5H, ArH), 6.39 (br, 2H, NH2), 4.16
(q, 2H, J = 7.03, OCH2), 1.25 (t, 3H, J = 7.03, CH3). 13C NMR:
d = 166.14 (COO), 159.11 (C-5), 158.77 (C-2), 144.53 (ArC), 127.38,
128.82, 129.69 (ArCH), 117.97 (CN), 60.76 (CH2O), 45.18 (C-6),
14.17 (CH3). IR (KBr): 3350, 3260 (NH2, NH), 2210 (CN), 1685
(CO), 1610 (C=N). MS (m/z,%): 303 (M+, 34), 287 (8), 259 (11),
229 (9), 168 (26), 135 (74), 77 (100). C13H13N5O2S (303.34): Calcd;
C, 51.47; H, 4.32; N, 23.09; S, 10.57. Found: C, 51.69; H, 4.11;
N, 22.85; S, 10.81.
Ethyl 5-amino-6-cyano-2-(benzylamino)-6(H)-1,2,4-thiadiazine-
6-carboxylate (12b): Reddish brown crystals (0.124 g, 39%), m.p.
237–239°C (acetonitrile). 1H NMR (DMSO-d6): d = 8.91 (br, 1H,
benzyl-NH), 7.22–7.39 (m, 5H, ArH), 6.43 (br, 2H, NH2), 4.64
(s, 2H, PhCH2), 4.18 (q, 2H, J = 7.12, OCH2), 1.23 (t, 3H, J = 7.12,
CH3). 13C NMR: d = 165.76 (COO), 159.26 (C-5), 158.69 (C-2),
127.82, 127.96, 128.84 (ArCH), 118.14 (CN), 141.12 (ArC), 60.71
(CH2O), 52.61 (Ph-CH2), 44.96 (C-6), 14.22 (CH3). IR (KBr): 3365,
3280 (NH2, NH), 2220 (CN), 1690 (CO), 1620 (C=N). MS (m/z,%):
317 (M+, 29), 290 (6), 243 (16), 168 (33), 149 (52), 91 (100), 77 (62).
C14H15N5O2S (317.37): Calcd; C, 52.98; H, 4.76; N, 22.07; S, 10.10.
Found: C, 53.22; H, 4.59; N, 21.86; S, 10.36.
{5-Amino-6-cyano-2-(allylamino)spiro[1,3,4]thiadiazolo[3,2-a]
pyrimidine-7,1'-cyclohexa[2,5]dien-4'-ylidene}malononitrile (17c):
Blue crystals (0.105 g, 57%), m.p. 216–218°C (acetonitrile). 1H NMR
(DMSO-d6): d = 7.61 (br, 1H, ally-NH), 6.65 (br, 2H, NH2), 6.33,
6.61 (dd, 4H, cyclohexadiene-H), 5.88–5.92 (m, 1H, allyl-CH=),
5.20–5.24 (m, 2H, allyl-CH2=), 4.05 (br, 2H, allyl-CH2N). 13C NMR:
d = 165.98 (C-4'), 160.87 (C-5), 156.75 (C-8a), 155.57 (C-2), 134.31
(allyl-CH=), 124.72, 126.64 (cyclohexadiene-CH), 118.61 (CN),
116.14 (allyl-CH2=), 73.75 (malononitrile-C), 60.51 (C-6), 45.48
(q-C-7,1'), 42.85 (allyl-CH2N). IR: 3400, 3320 (NH2, NH), 2225,
2220 (CN), 1630 (C=N). MS (m/z,%): 360 (M+, 22), 294 (9), 163
(26), 99 (57), 41 (100). C17H12N8S (360.40): Calcd; C, 56.65; H,
3.36; N, 31.09; S, 8.90. Found: C, 56.81; H, 3.22; N, 30.89; S, 9.14.
1,4-Diamino-5-cyano-9-(dicyanomethylene)-N-phenyl-2,
3-diazospiro[5.5]undeca-1,4,7,10-tetraene-9-thioamide
(18a):
Violet crystals (0.111 g, 28%), m.p. 289–291°C (acetonitrile).
1H NMR (DMSO-d6): d = 9.84 (br, 1H, phenyl-NH), 7.09–7.70
(m, 5H, ArH), 6.62 (br, 2H, NH2), 6.49 (br, 2H, NH2), 6.29, 6.58
(dd, 4H, cyclohexadiene-H). 13C NMR: d = 180.19 (C=S), 166.41
(C-9), 160.83 (C-4), 156.67 (C-1), 141.18 (ArC), 127.86, 128.88,
129.51 (ArCH), 125.13, 126.64 (cyclohexadiene-CH), 117.97, 118.31
(CN), 74.26 (malononitrile-C), 60.71 (C-5), 46.21 (q-C-6). IR (KBr):
3385, 3270 (NH2, NH), 2225, 2215 (CN), 1610 (C=N), 1570 (NH
def. and C-N str.), 1358, 998 (C=S, C-N). MS (m/z,%): 398 (M+, 27),
263 (35), 207 (36), 197 (21), 169 (15), 150 (42), 135 (57), 77 (100),
66 (46), 57 (37). C20H14N8S (398.44): Calcd; C, 60.29; H, 3.54;
N, 28.12; S, 8.05. Found: C, 60.51; H, 3.33; N, 27.89; S, 8.31.
Ethyl 5-amino-6-cyano-2-(allylamino)-6(H)-1,2,4-thiadiazine-6-
carboxylate (12c): Reddish brown crystals (0.96 g, 36%), m.p. 181–
1
183°C (ethanol). H NMR (DMSO-d6): d = 7.55 (br, 1H, allyl-NH),
6.35 (br, 2H, NH2), 5.90–5.94 (m, 1H, allyl-CH=), 5.18–5.26 (m, 2H,
allyl-CH2=), 4.18 (q, 2H, J = 6.97, OCH2), 4.09 (br, 2H, allyl-NH2),
1.22 (t, 3H, J = 6.97, CH3). 13C NMR: d = 166.12 (COO), 159.67
(C-5), 158.93 (C-2), 134.22 (allyl-CH=), 118.16 (CN), 116.06 (allyl-
CH2=), 60.63 (CH2O), 45.03 (C-6), 42.88 (allyl-CH2N), 14.19 (CH3).
IR (KBr): 3360, 3270 (NH2, NH), 2960 (Ali-H), 2220 (CN), 1685
(CO), 1610 (C=N). MS (m/z,%): 267 (M+, 26), 193 (19), 168 (33),
165 (5), 99 (67), 41 (100). C10H13N5O2S (267.31): Calcd; C, 44.93;
H, 4.90; N, 26.20; S, 12.00. Found: C, 45.21; H, 4.72; N, 25.97;
S, 11.97.
1,4-Diamino-5-cyano-9-(dicyanomethylene)-N-benzyl-2,
3-diazospiro[5.5]undeca-1,4,7,10-tetraene-9-thioamide
(18b):
Violet crystals (0.136 g, 33%), m.p. 324–326°C (acetonitrile).
1H NMR (DMSO-d6): d = 8.91 (br, 1H, benzyl-NH), 7.16–7.53 (m,
5H, ArH), 6.54 (br, 2H, NH2), 6.46 (br, 2H, NH2), 6.25, 6.55 (dd, 4H,
cyclohexadiene-H), 4.62 (CH2). 13C NMR: d = 180.46 (C=S), 166.72
(C-9), 161.12 (C-4), 156.41 (C-1), 141.66 (ArC), 127.84, 127.96,
128.62 (ArCH), 125.06, 126.51 (cyclohexadiene-CH), 118.05,
118.27 (CN), 74.28 (malononitrile-C), 60.66 (C-5), 52.56 (CH2),
45.96 (q-C-6). IR (KBr): 3370, 3280 (NH2, NH), 2225, 2215 (CN),
1620 (C=N), 1565 (NH def. and C-N str.), 1355, 1005 (C=S, C-N).
MS (m/z,%): 412 (M+, 18), 263 (14), 207 (9), 169 (22), 164 (26),
149 (77), 91 (100), 77 (66), 66 (51), 57 (24). C21H16N8S (412.47):
Calcd; C, 61.15; H, 3.91; N, 27.17; S, 7.77. Found: C, 60.92; H, 4.08;
N, 27.41; S, 7.59.
1,4-Diamino-5-cyano-9-(dicyanomethylene)-N-allyl-2,3-diazo-
spiro[5.5]undeca-1,4,7,10-tetraene-9-thioamide (18c):Violet crystals
(0.101 g, 28%), m.p. 261–263°C (acetonitrile). 1H NMR (DMSO-d6):
d = 7.84 (br, 1H, allyl-NH), 6.57 (br, 2H, NH2), 6.48 (br, 2H, NH2),
6.28, 6.60 (dd, 4H, cyclohexadiene-H), 5.92–5.96 (m, 1H, allyl-CH=),
5.18–5.26 (m, 2H, allyl-CH2=), 4.10 (br, 2H, allyl-CH2N). 13C NMR:
d = 180.52 (C=S), 166.12 (C-9), 160.88 (C-4), 156.36 (C-1), 134.38
(allyl-CH=), 125.11, 126.49 (cyclohexadiene-CH), 118.06, 118.26
(CN), 115.96 (allyl-CH2=), 74.36 (malononitrile-C), 60.58 (C-5),
46.08 (q-C-6), 42.78 (allyl-CH2N). IR (KBr): 3345, 3270 (NH2, NH),
2220, 2210 (CN), 1560 (NH def. and C-N str.), 1355, 1015 (C=S,
C–N). MS (m/z,%): 362 (M+, 14), 263 (26), 207 (14), 197 (16), 181
(8), 169 (19), 99 (46), 66 (58), 57 (45), 41 (100). C17H14N8S (362.41):
Calcd; C, 56.34; H, 3.89; N, 30.92; S, 8.85. Found: C, 56.11; H, 4.11;
N, 31.14; S, 8.63.
Reaction of 1-substituted-2,5-dithiobiureas 1a–c with 7,7',8,8'-tetracyano-
quinodimethane (16): To a solution of 16 (416 mg, 2.0 mmol) in dry
pyridine (15 ml) a solution of 1a–c (1.0 mmol each) in (5 ml) of dry
pyridine was added dropwise over 5 minutes at room temperature
with stirring. The mixture was warmed gently to 50–60°C and kept
at this temperature with stirring and admission of air for 3 h, then
warmed to maximum 100°C for few minutes and concentrated to
dryness at 50°C. The residue was taken up several times with cold
ethanol (15 ml) and the slurry was concentrated again to remove
any residual pyridine. This operation was repeated four times.
The residue was dissolved in (5 ml) acetone. This solution in each
case was applied to five PLC plates and developed with toluene/ethyl
acetate (3:1) for the run with 1a, toluene/ethyl acetate (4:1) for the
run with 1b and 1c. Numerous zones were observed, two of which
were extracted. The fastest migrating zone contained compound 17,
the second zone contained compound 18. Extraction of the zones with
acetone gave a residue, which was rechromatographed with the same
eluent to enhance separation. Recrystallisation from suitable solvents
afforded compounds 17a–c and 18a–c.
{5-Amino-6-cyano-2-(phenylamino)spiro[1,3,4]thiadiazolo[3,
2-a]pyrimidine-7,1'-cyclohexa[2,5]dien-4'-ylidene}malononitrile
(17a): Blue crystals (0.234 g, 59%), m.p. 246–248°C (methanol).
1H NMR (DMSO-d6): d = 9.77 (br, 1H, phenyl-NH), 7.06–7.46 (m,
5H, ArH), 6.74 (br, 2H, NH2), 6.32, 6.61 (dd, 4H, cyclohexadiene-H).
13C NMR: d = 166.32 (C-4'), 161.12 (C-5), 157.12 (C-8a), 155.72
(C-2), 144.61 (ArC), 127.62, 128.83, 129.64 (ArCH), 124.71, 126.82
(cyclohexadiene-CH), 118.66 (CN), 73.84 (malononitrile-C), 60.62
(C-6), 45.77 (q-C-7,1'). IR (KBr): 3410, 3310 (NH2, NH), 2225, 2220
(CN),1630(C=N),1595(ArC=C).MS(m/z,%):396(M+,31),330(11),
190 (19), 135 (51), 77 (100). C20H12N8S (396.43): Calcd; C, 60.59; H,
3.05; N, 28.27; S, 8.09. Found: C, 60.37; H, 2.94; N, 28.51; S, 8.32.
{5-Amino-6-cyano-2-(benzylamino)spiro[1,3,4]thiadiazolo[3,
2-a]pyrimidine-7,1'-cyclohexa[2,5]dien-4'-ylidene}malononitrile
(17b): Blue crystals (0.226 g, 55%), m.p. 276–278°C (acetonitrile).
1H NMR (DMSO-d6): d = 8.91 (br, 1H, benzyl-NH), 6.98–7.35 (m,
5H, ArH), 6.70 (br, 2H, NH2), 6.30, 6.58 (dd, 4H, cyclohexadiene-
H), 4.62 (s, 2H, CH2). 13C NMR: d = 166.22 (C-4'), 160.91 (C-5),
156.88 (C-8a), 155.57 (C-2), 141.77 (ArC), 127.83, 127.91, 128.68
(ArCH), 124.79, 126.77 (cyclohexadiene-CH), 118.61 (CN), 73.69
(malononitrile-C), 60.45 (C-6), 52.61 (CH2), 45.53 (q-C-7,1'). IR
(KBr): 3395, 3315 (NH2, NH), 2220, 2215 (CN), 1625 (C=N), 1595
(ArC=C). MS (m/z,%): 410 (M+, 23), 344 (9), 204 (22), 149 (66),
91 (100), 77 (58). C21H14N8S (410.45): Calcd; C, 61.45; H, 3.44;
N, 27.30; S, 7.81. Found: C, 61.68; H, 3.65; N, 27.57; S, 7.55.
A. A. Hassan is indebted to the A. v. Humboldt-Foundation
for the donation of the Shimadzu 408 IR spectrophotometer.
Received 19 November 2007; accepted 8 January 2008
Paper 07/4952
doi: 10.3184/030823408X284503
References
1
2
3
A.J. Fataidi, Synthesis, 1986, 249.
P. Bruni and G. Tosi, Gazz Chim. Ital. 1997, 127, 435.
G. Bocelli, C.R. Cardellini, G. Demeo, A. Ricci, C. Rizzoli and G. Tosi,
J. Crystallogr. Spectrosc. Res., 1990, 20, 561.
4
5
6
7
A.J. Fatiadi, Synthesis, 1987, 749.
A.J. Fatiadi, Synthesis, 1987, 749.
D. Döpp, S. Jüschke and G. Henkel, Z. Naturforsch, 2002, 57b, 460.
D. Döpp, A.A. Hassan, A.E. Mourad, A.M. Nour El Din, K. Argermumd,
C. Krüger, C.W. Lehmann and J. Rust, Tetrahedron, 2003, 59, 5073.
A. Hassan, K.M. El-Shaieb and D. Döpp, Arkivoc, 2005, x, 139.
A.A. Hassan, Phosphorus, Sulfur, Silicon 1995, 101, 189.
8
9
10 A.A. Hassan, Y.R. Ibrahim, E.H. El-Tamany, A.A. Samida and
A.E. Mourad, Phosphorus, Sulfur, Silicon, 1995, 167.
PAPER: 07/4952

JOURNAL OF CHEMICAL RESEARCH 2008 15
11 A.A. Hassan, N.K. Mohamed, A.A. Aly and A.E. Mourad, Monatsh.
Chem., 1997, 128, 61.
12 A.A. Hassan, N.K. Mohamed, A.M. Shawky and D. Döpp, Arkivoc, 2003,
i, 118.
22 N. Martin and C. Seoane, Organic Conductive Molecules and Polymers,
ed. N.S. Nalwa, Wiley, New York, 1996.
23 R.M. Metzger, R.R. Shumaker, M.P. Cara, R.K. Laidlow, L.A. Panetta
and E. Torres, Langmuir, 1988, 4, 198.
13 A.A. Hassan, A.E. Mourad, K.M. El-Shaieb and A.H. Abou-Zied,
Z. Naturforsch, 2004, 59b, 910.
14 A.A. Hassan, A.E. Mourad, K.M. El-Shaieb, R.M. Shaker and D. Döpp,
Heteroatom Chem., 2005, 16, 12.
15 M.A.-M. Gomaa, A.A. Hassan and H.S. Shehatta, Heteroatom Chem.,
2006, 17, 261.
24 G.J. Ashwell, E. Je. Downay, A.P. Kuczynski, M. Szablewski, I.M. Sandy,
M.R. Bryce, A.M. Girainger and M. Hasan, J. Chem. Soc., Faraday
Trans., 1990, 86, 1117.
25 J.S. Miller, J.C. Calabrese, R.L. Harlow, D.A. Dixan, J.H. Zhang,
W.M. Rieff, S. Chittipeddi, M.A. Selower and A.J. Epskin, J. Am. Chem.
Soc., 1990, 112, 5496.
16 A.A. Hassan, A.E. Mourad and A.H. Abou-Zied, J. Heterocyclic Chem.,
2007, 44, 1171.
17 B.B. Kanl, W.S. Durfee and G.T. Yee, J. Am. Chem. Soc., 1999, 121,
6862.
18 Y. Yamada, H. Yasuda and M. Kasai, Heterocycles, 1999, 51, 2453.
19 Y. Yamada and H. Yasuda, J. Heterocyclic Chem., 1998, 35, 1389.
20 Y. Yamada, H. Yasuda, Y. Yoshihara and K. Yoshizawa, J. Heterocyclic
Chem., 1999, 36, 1327.
26 N.A. Zaidi, M.R. Bryce and G.H. Cross, Tetrahedron Lett., 2000, 41,
4645.
27 A.A. Aly and K.M. El-Shaieb, Teterahedron, 2004, 60, 3797.
28 H.-O. Kalinowski, S. Berger and S. Brann, 13C NMR Specyroscopic,
Thieme, Stuttgart, 1984, pp 121.
29 K. Gewald and R. Schnidler, J. Prakt. Chem., 1990, 332, 223.
30 P.V. Indukumari, C.P. Josshva and V.P. Rajan, Indian J. Chem., 1981, 20B,
384.
21 R.C. Wheland and E.L. Martin, J. Org. Chem., 1975, 40, 3101.
31 W.H. Altland and A.P. Graham, J. Heterocyclic Chem., 1978, 15, 377.
PAPER: 07/4952