Reactions of 2-amino-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene and 2-amino-3-cyano-4,7-diphenyl-5-methyl-4H-pyrano[2,3-c] pyrazole with phenylisocyanate, carbon disulfide, and thiourea

Article abstract of DOI:10.1002/hc.20070

2-Amino-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene 1a or 2-amino-3-cyano-4, 7-diphenyl-5-methyl-4H-pyrano[2,3-c]pyrazole 2a reacted with phenylisocyanate in dry pyridine to give 2- (3-phenylureido)-3-cyanobenzo[b] thiophene 1b or 2-disubstituted amino-3-

Full text of DOI:10.1002/hc.20070

Heteroatom Chemistry
Volume 16, Number 1, 2005
Reactions of 2-Amino-3-cyano-4,5,6,7-
tetrahydrobenzo[b]thiophene and
2-Amino-3-cyano-4,7-diphenyl-5-methyl-4H-
pyrano[2,3-c] pyrazole with Phenylisocyanate,
Carbon Disulfide, and Thiourea
Ahmed S. A. Youssef, Kamal A. Kandeel, Fouli A. Fouli,
and Wael S. I. Abou-Elmagd
Chemistry Department, Faculty of Science, Ain Shams University, Abbassia 11566, Cairo, Egypt
Received 17 December 2003; revised 7 April 2004
INTRODUCTION
ABSTRACT: 2-Amino-3-cyano-4,5,6,7-tetrahydro-
benzo[b]thiophene 1a or 2-amino-3-cyano-4,7-di-
phenyl-5-methyl-4H-pyrano[2,3-c]pyrazole 2a re-
acted with phenylisocyanate in dry pyridine to give
2-(3-phenylureido)-3-cyanobenzo[b]thiophene 1b
or 2-disubstituted amino-3-cyanopyranopyrazole 2b
derivative. However, when 1a and 2a were refluxed
with carbon disulfide in 10% ethanolic sodium hy-
droxide solution, they afforded the thieno[2,3-d]pyri-
midin-2,4-dithione derivative 5 in the former case, 2,4-
dicyano-1,3-bis(dithio carboxamino)cyclobuta-1,3-
diene 6 and pyrazolopyranopyrido[2,3-d]pyrimidin-
2,4-dithione derivative 7 in the latter one. Treatment of
2a with thiourea in refluxing ethanol in the presence
of potassium carbonate gave 2,2ꢀ-dithiobispyrimidine
derivative 9 (major) in addition to pyranopyrazole
derivative 10 and 2,2ꢀ-dithiobis ethoxypyrimidine
derivative 11 in minor amounts. The structures
of all products were evidenced by microanalytical
It has been reported [1] that 2-amino-3-cyano-
4,5,6,7-tetrahydrobenzo[b]thiophene 1a reacted
with phenylisocyanate in DMF and carbon disulfide
in pyridine to give dithienopyrimidopyrimidinone
and thienopyrimidinedithione beside dithienopy-
rimidopyrimidinethione, respectively. However,
Sukumaran and Rajasekharass [2] reported the for-
mation of thienothiazine upon treating 1a with car-
bon disulfide in pyridine.
In the present investigation, we are intended to
study the reaction of 2-amino-3-cyano-4,5,6,7-tetra-
hydrobenzo[b]thiophene 1a and 2-amino-3-cyano-
4,7-diphenyl-5-methyl-4H-pyrano[2,3-c]pyrazole
2a with phenylisocyanate, carbon disulfide, and
thiourea under different conditions. It is observed
that the obtained results are different from those
reported in the literature.
ꢁ
C
and spectral data.
2005 Wiley Periodicals, Inc.
RESULTS AND DISCUSSION
Heteroatom Chem 16:6–11, 2005; Published online in
Wiley InterScience (www.interscience.wiley.com). DOI
10.1002/hc.20070
Refluxing equimolar amounts of 1a and 2a with
phenylisocyanate in dry pyridine gave 2-(3-phenyl-
ureido)-3-cyanobenzothiophene 1b and 2-disubsti-
tuted amino-3-cyanopyranopyrazole 2b derivatives,
respectively, in addition to 1,3-diphenylurea 3 and
1,3,5-triphenylbiuret 4 as the major product in both
cases. However, treating 2a with phenylisocyanate in
Correspondence to: Ahmed S. A. Youssef; e-mail: ahmedy93@
hotmail.com.
c
ꢁ
2005 Wiley Periodicals, Inc.
6

Reactions of Thiophene and Pyranopyrazole with Phenylisocyanate, Carbon Disulfide, and Thiourea
7
refluxing dioxane yielded 3 and 4 as the only isolated
products, whereas 2a was recovered unchanged.
vative 7 as well as 4,4ꢀ-(phenylmethylene) bis
(3-methyl- 1-phenyl-1H-pyrazol-5-ol) 8.
Structures of compounds 1b and 2b were de-
duced from their microanalytical and spectral data,
whereas compounds 3 and 4 were rigidly confirmed
by mp comparison with authentic samples. The in-
frared spectra of compounds 1b and 2b show ab-
sorptions corresponding to NH, CN, and CO groups.
Moreover, the 1H-NMR spectra of compounds 1b and
2b are in accord with the proposed structures. The
EI-MS spectrum of compound 1b showed a correct
molecular ion peak. However, the EI-MS spectrum of
compound 2b did not show the molecular ion peak
but it showed a peak at m/e 404 which corresponds
The structures of compounds 5 and 8 were sub-
stantiated from their spectral data and they were
rigidly confirmed by mp comparison with that re-
ported [1,3]. However, the structures of compounds
6 and 7 were deduced spectroscopically as well as
chemically in the former one. Thus, the infrared
spectra of compounds 6 and 7 showed absorption
corresponding to NH and C S groups besides ad-
ditional absorptions correlated with SH and C N
groups for compound 6 which are in accord with
the proposed structures.
·
to [M+ -PhNCO and HNCO].
The formation of compounds 1b and 2b could
be interpreted on the basis of a nucleophilic attack
of the amino group in compounds 1a and 2a at the
isocyanato group of phenylisocyanate. On the other
hand, the formation of compounds 3 and 4 could
be explained through easy conversion of phenyliso-
cyanate; by a trace amount of water present in the
used solvent, into the unstable carbamic acid to
give aniline that then attacks either the phenyliso-
cyanate monomer to give 3 or its dimer to give 4
(Scheme 1)
Compounds 3 and 4 were the only isolated prod-
ucts upon treating 2a with phenylisocyanate in re-
fluxing dioxane or upon refluxing phenylisocyanate
in pyridine or dioxane alone that reflects the im-
portant role of pyridine in the enhancement of the
nucleophilicity of amino group.
The 1H-NMR spectra of compounds 6 and 7 were
consistent with their suggested structures. More-
over, the structures of compounds 6 and 7 get a fur-
ther support from their EI-MS spectra where they
showed correct molecular ion peaks beside some of
the abundant peaks. The fragmentation pathway of
compound 6 is shown in Scheme 2. Some stable cy-
clobutadiene derivatives are reported [4,5].
The formation of compounds 6, 7, and 8 could be
interpreted through a base catalyzed ring opening of
the pyrano ring of 2a to give the benzylidenepyra-
zolone (A) and cyanoacetamide (B). Benzylidene-
pyrazolone (A) undergoes benzylidene elimination
[6] to give benzaldehyde and pyrazolinone that at-
tacks another molecule of (A) to give 8. On the other
hand, cyanoacetamide (B) adds to carbon disulfide
to give the intermediate (C) (not isolated) that either
dimerizes to give 6 or attacks another molecule of 2a
to afford 7 as outlined (Scheme 3). The conversion
of the thiazinethione derivative (D) into the pyrimi-
dine dithione derivative (E) is well established in the
Treatment of compounds 1a or 2a with carbon
disulfide in 10% ethanolic sodium hydroxide solu-
tion afforded the thieno[2,3-d]pyrimidin-2,4-dithi-
one 5 or 2,4-dicyano-1,3-bis(dithiocarboxamino)-
cyclobuta-1,3-diene 6 and pyrazolo[4ꢀ,3ꢀ:5,6]pyrano-
[3ꢀ,2ꢀ:5,6]pyrido[2,3-d]pyrimidin-2,4-dithione deri-
SCHEME 1

8
Youssef et al.
the spectra were devoid of any signals correspond-
ing to methyl and methine protons that revealed
the absence of the pyranopyrazole moiety, but ex-
hibited absorptions characteristic for aromatic and
acidic protons as well as ethyl absorptions for com-
pound 11. A further evidence for structure 10 was
gained from its 13C-NMR spectrum (cf. Experimen-
tal). The EI-MS spectra of compounds 9 and 11
showed molecular ion peaks whereas compound 10
did not.
The formation of compounds 9–11 (Scheme 4)
could be rationalized on the basis of a base cat-
alyzed attack of the amino group of the pyranopy-
razole derivative 2a at the thiocarbonyl group of
thiourea followed by an elimination of hydrogen
sulfide to give compound 10 (route a). A base cat-
alyzed pyrano ring opening (route b) gave (D) and
the benzylidenepyrazolone (A). (A) undergoes ben-
zylidene elimination [6] to give 8 that was detected
by TLC in the reaction mixture. Compound (D) con-
denses with benzaldehyde to give (E) which either
oxidizes to give compound 9 or hydrolyzes followed
by oxidation and addition of 2 moles of ethanol to
give compound 11.
SCHEME 2 Fragmentation pathway of compounds 6.
The suggested mechanism was proved chemi-
cally by reacting equimolar amounts of cyanoac-
etamide, thiourea, and benzaldehyde under similar
conditions where compound 9 was isolated and com-
pound 11 was detected by TLC in the reaction mix-
ture. Compound 9 was identified by comparison with
an authentic sample (mp, mixed mp, and TLC).
presence of a base [2,7]. Compound 6 was proved
chemically by comparison with an authentic sample
prepared from cyanoacetamide and carbon disulfide
under similar conditions.
Thiourea reacted with 2-amino-3-cyanopyrano-
[2,3-c]pyrazole derivative 2a in refluxing ethanol in
the presence of potassium carbonate to give 2,2ꢀ
dithiobis-pyrimidine derivative 9 (major) in addition
to pyranopyrazole derivative 10 and 2,2ꢀ-dithiobis-
ethoxypyrimidine derivative 11 in minor amounts.
EXPERIMENTAL
All melting points were not corrected. Infrared spec-
tra were measured on a Unicam SP 1200 spectrom-
1
eter as KBr disks. H- and 13C-NMR spectra were
measured in DMSO-d6 or CDCl3 on a Varian Gemini
instrument at 200 and 50 MHz, respectively; in both
cases, chemical shifts were given in ppm downfield
from internal TMS. Mass spectra were recorded on
a Shimadzu GC-MS QP 1000 EX instrument operat-
ing at 70 eV. TLC was performed on Merk Kieselgel
60 F254 aluminum backed plates.
2-Amino-3-cyano-4,5,6,7-tetrahydro-benzo[b]-
thiophene 1a [8] and 2-amino-3-cyano-4,7-diphenyl-
5-methyl-4H-pyrano[2,3-c]pyrazole 2a [9] were
prepared according to the literature methods.
The structures of compounds 9–11 were deduced
from their microanalytical and spectral data. Thus,
their infrared spectra showed absorptions character-
istic for NH and CN groups. The absorption signals
in the H-NMR spectra of compounds 9 and 11 re-
flected their molecular symmetry. On the other hand,
Reactions of 1a and 2a with Phenylisocyanate
General Procedure. In Dry Pyridine. A mixture
of 1a (0.01 mole) or 2a (0.01 mole) and phenyliso-
cyanate (0.01 mole) in dry pyridine (20 mL) was re-
fluxed for 10 h. The reaction mixture was cooled
1

Reactions of Thiophene and Pyranopyrazole with Phenylisocyanate, Carbon Disulfide, and Thiourea
9
SCHEME 3
1H-NMR (DMSO-d6) δ 1.76 (br.s, 4, (CH2)2), 2.49
(br.s, 2, CH2), 2.51 (br.s, 2, CH2), 6.97–7.49 (m, 5,
ArH), 8.67 and 9.20 (each br.s, 1, NH, exchangeable)·.
and poured into ice cold HCl. The precipitated
solid was filtered off and recrystallized to give
1,3-diphenylurea 3, (40% yield), colorless crystals,
mp 232–234◦C (benzene/ethanol), lit. [10] mp 241–
242◦C; identical with an authentic sample (mp,
mixed mp, and TLC) prepared from aniline hy-
drochloride and urea [10]. The mother liquor was left
to evaporate at room temperature to give a semisolid.
Trituration with methanol (2 mL) gave a solid
which was fractionally recrystallized to give 1,3,5-
triphenylbiuret 4, (30% yield), bright yellow needles,
mp 142–144◦C (methanol), lit. [11] mp 143–145◦C;
identical with authentic sample (mp, mixed mp, and
TLC) prepared by fusion of 1,3-diphenylurea 3 with
phenylurea. The insoluble part in boiling methanol
was recrystallized from dioxane to give 1b in the case
of 1a and 2b on using 2a.
·
·
EIMS m/z (%) 299 (M+ + 2, 1), 297 (M+ ,9), 204 (M+
·
-PhNH2, 25), 180 (4), 178 (M+ -PhNCO,72), 152 (7),
151 (10), 150 (base). Anal. Calcd for C 16H15N3OS
(297.386): C, 64.62; H, 5.08; N, 14.13; S, 10.78.
Found: C, 64.39; H, 4.95; N, 13.87; S, 10.65%.
3-Cyano-4,7-diphenyl-2-(diphenylformamido)-
amino-5-methyl-4H-pyrano [2,3-c] pyrazole 2b: (5%
yield), gray crystals, mp 140–142◦C (dioxane). IR
νmax 3450, 3320 (NH), 3060 (aryl-H), 2930 (alkyl-H),
2230 (C N), 1745, 1715 (CO), 1590 (C C), 750
1
and 690 cm−1 (δ5-H). H-NMR (CDCl3) δ 1.99 (s, 3,
CH3), 3.71 (s, 1, methine H), 7.12–7.89 (m, 20, ArH),
8.95 (br.s, 2NH, exchangeable). EIMS m/z (%) 404
·
(M+ -PhNCO and HNCO, 1), 328 (32), 327 (37), 105
2-(3-Phenylureido)-2-cyano-4,5,6,7-tetrahydro-
benzo[b]thiophene 1b: (20% yield), colorless crystals,
mp 200–202◦C (dioxane). IR νmax 3325 (NH), 3027
(aryl-H), 2933 (alkyl-H), 2212 (C≡N), 1711 (CO),
1648, 1596, 1553 (C C), 752 and 696 cm−1 (δ5-H).
(23), 77 (base), 51 (31). Anal. Calcd for C34H26N6O3
(566.60): C, 72.07, H, 4.62; N, 14.83. Found: C, 71.88;
H, 4.51; N, 14.69%.
In Dry Dioxane. A mixture of 2a (0.01 mole) and
phenylisocyanate (0.01 mole) in dioxane (20 mL) was

10 Youssef et al.
SCHEME 4
refluxed for 20 h. The reaction mixture was concen-
trated and left at room temperature to give a precipi-
tate that was recrystallized from ethanol to afford 2a
(85% yield). The mother liquor was left to stand at
room temperature for 3 h to give 1,3-diphenylurea 3,
(50% yield), mp 232–234◦C (benzene/ethanol), iden-
tical in all respect with an authentic sample (mp,
mixed mp, and TLC). However, evaporation of the
mother liquor at room temperature and trituration
with methanol gave 1,3,5-triphenylbiuret 4, (30%
yield), mp 142–144◦C (methanol), identical with an
authentic sample (mp, mixed mp, and TLC).
droxide (3 g NaOH/30 mL ethanol), carbon disulfide
(10 mL) was added whereby the reaction mixture
becomes brown in color. The reaction mixture was
refluxed for 2 h.
In case of 1a, the reaction mixture was cooled
to room temperature, poured into ice cold water
and acidified with acetic acid to give 5,6,7,8-tetra-
hydrobenzo[b]thieno[2,3-d]pyrimidin-2,4-dithione
5, golden (20% yield), yellow crystals, mp 265–266◦C
(ethanol/benzene), lit. [1] mp 260–262◦C.
In case of 2a, a yellow solid was precipitated after
5 min which was filtered off while hot, dissolved
in water and acidified with acetic acid to give
2,4-dicyano-1,3-bis(dithiocarboxamino)cyclobuta-
1,3-diene 6, (20% yield), yellow crystals, mp 200–
202◦C (ethanol). IR νmax 3320, 3180 (NH), 2480
(SH), 2250 (C N), 1640 (C C), 1115 cm−1 (C S).
Reactions of 1a and 2a with Carbon Disulfide
General Procedure. To a solution of 1a (0.01
mole) or 2a (0.01 mole) in 10% alcoholic sodium hy-

Reactions of Thiophene and Pyranopyrazole with Phenylisocyanate, Carbon Disulfide, and Thiourea 11
1H-NMR (DMSO-d6) δ 9.62 (br.s, SH, exchangeable),
10.42 (br.s, NH, exchangeable). EIMS m/z (%) 286
3-cyano-2-diaminomethyleneamino-4,7-diphenyl-
5-methyl-4H-pyrano[2,3-c]pyrazole 10, (10% yield),
yellow crystals, mp 203–205◦C (ethanol). IR νmax
3430, 3360, and 3280 (NH2), 3069 (aryl-H), 2920
(alkyl-H), 2213 (C N), 1639, 1600 (C N and/or C C),
·
·
·
(M+ + 2, 4), 284 (M+ , 20), 220 (M+ -2S, 16), 174
·
(M+ -CS2 and H2S, 22), 142 (19), 109 (37), 83 (41),
82 (21), 76 (20), 66 (19), 64 (18), 60 (base). Anal.
Calcd for C8H4N4S4 (284.408): C, 33.78; H, 1.42; N,
19.70; S, 45.09. Found: C, 33.53; H, 1.34; N, 19.61;
S, 44.85%. The reaction mixture was refluxed for
further 2 h, cooled, poured into ice cold water and
acidified with acetic acid to afford 5-amino-6,9-
diphenyl-7-methylpyrazolo[4ꢀ,3ꢀ: 5,6]pyrano [3ꢀ,2ꢀ:
5,6]pyrido[2,3-d]pyrimidin-2,4-dithione 7, (20%
yield), orange crystals, mp 300–302◦C (ethanol). IR
νmax 3430 (NH), 3071 (aryl-H), 2916, 2851 (alkyl-H),
1
750, 690 cm−1 (δ5-H). H-NMR (CDCl3) δ 2.33 (s, 3,
CH3), 4.81 (s, 1, CH), 7.11–7.67 (m, 14, 10 ArH +
2NH2 exchangeable). 13C-NMR (DMSO-d6) δ 10.73
(CH3), 32.31 (C-4), 105.37 (C-3), 122.36 (CN), 126.53,
127.16, 127.63, 128.53, 129.37, 134.82 (phenylcar-
bons), 140.96 (C-5), 146.12 (C-2), 158.25 (methylene
·
carbon). EIMS m/z (%) 263 [M+ + 1 NC C C
·
N C(NH2)2, 42], 262 [M+ NC C C N C(NH2)2,
50], 185 (68), 174 (28), 91 (48). Anal. Calcd for
C21H18N6O (370.42): C, 68.09; H, 4.89; N, 22.69.
Found: C, 68.20; H, 4.78; N, 22.58%.
1638, 1586 (C N and/or C C), 1183, 1109 (C S),
1
747, 680 cm−1 (δ5-H). H-NMR (DMSO-d ) δ 2.13 (s,
6
The insoluble part in ethanol gave 2,2ꢀ-dithiobis-
(6-amino-5-cyano-4-phenylpyrimidine) 9, (25% yield),
yellow crystals, mp >300◦C (dioxane). IR νmax 3373,
3307, 3263, 3216 (NH), 3093 (aryl-H), 2218, 2188
(C N), 1643, 1563 (C N and/or C C), 747, 700 cm−1
3, CH3), 5.36 (br.s, NH2, exchangeable), 6.79 (br.s,
NH, exchangeable), 7.21–7.35 (m, 10, ArH). EIMS
·
m/z (%) 468 (M+ , 1), 465 (19), 464 (19), 217 (16), 215
(54), 91 (base), 83 (33), 67 (16), 64 (34), 51 (26). Anal.
Calcd for C24H16N6OS2 (468.548): C, 61.50; H, 3.44;
N, 17.94; S, 13.69. Found: C, 61.38; H, 3.37; N, 17.59;
S, 13.41%. On leaving the mother liquor to stand
at room temperature, it gave 4,4ꢀ-(phenylmethylene)
bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) 8, (≈5%
yield), colorless crystals, mp 162–164◦C (ethanol),
lit. [3] mp 162–164◦C, identical with an authentic
sample (mp, mixed mp, and TLC behavior) prepared
by refluxing 1-phenyl-3-methylpyrazolin-5-one and
benzaldehyde in benzene.
1
(δ5-H). H-NMR (DMSO-d6) δ 3.68 (br.s, 2, NH2, ex-
changeable), 7.35–7.55 (m, 5, ArH). EIMS m/z (%)
·
·
456 (M+ + 2, <1), 454 (M+ ,3), 228 (5), 227 (19), 169
·
(34), 161 (M+ -PhNH 2, 11), 153 (26), 151 (base). Anal.
Calcd for C22H14N8S2 (454.53): C, 58.13; H, 3.11, N,
24.65; S, 14.11. Found: C, 57.76; H, 2.98; N, 24.47; S,
13.85%.
REFERENCES
[1] Gewald, K.; Jeschke, T.; Gruner, M. J Prakt Chem
1991, 333(2), 229; Chem Abstr 1991, 115, 232166e.
[2] Sukumaran, P.; Rajasekharass K. N. Indian J Chem,
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158190c.
[3] (a) Youssef, A. S. A.; Kandeel, K. A. Afinidad LVII
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Belov, V. N. Khim Geterotsikl Soedin 1988, 7, 905–
958; Chem Abstr 1989, 110, 114777u.
Reactions of 2a with Thiourea
General Procedure. An equimolar amounts of
2a (0.01 mole), thiourea (0.01 mole), and potassium
carbonate (0.01 mole) were refluxed in ethanol
(40 mL) for 6 h. The reaction mixture was cooled,
poured into ice cold water to give 2,2ꢀ-dithiobis-
(5-cyano-4-ethoxy-6-hydroxy-4-phenyl-1,4-dihydro
pyrimidine) 11, (5% yield), green crystals, mp 210–
212◦C (ethanol). IR νmax 3446, 3425 (OH), 3323, 3218
(NH), 3080 (aryl-H), 2979, 2926 (alkyl-H), 2224,
2201 (C N), 1625, 1586, 1550 (C N and/or C C),
768, 699 cm−1 (δ5-H). 1H-NMR (DMSO-d6) δ 1.36 (t, 3,
[7] Taylor, E. C.; McKillop, A. Tetrahedron 1967, 23, 897.
[8] (a) Ertuzun, V. Commun Fac Sci Univ Ankara, Ser B,
1986, 32(12), 1–18; Chem Abstr 1988, 108, 150194d;
(b) Gewald, K.; Schinke, E.; Bottcher, H. Chem Ber
1966, 99, 94.
[9] (a) Otto, H. Arch Pharm 1974, 306(6), 444; (b)
Tacconi, G.; Gatti, G.; Dessmon, G. J Prakt Chem
1980, 322(5), 831; Chem Abstr 1981, 94, 174962w.
[10] Vogel, A. I. Practical Organic Chemistry, 3rd ed.;
Longman: London, 1957; p. 645.
CH3 CH2, J = 7.0 Hz), 4.46 (q, 2, CH CH2, J = 7.0
3
Hz), 7.51–7.61 (m, 5, Ar-H), 7.97 (br.s, 2, OH and NH
·
exchangeable). EIMS m/z (%) 548 (M+ ,1), 265 (19),
264 (88), 263 (35), 237 (19), 236 (base), 235 (25),
209 (28), 208 (27), 180 (14), 154 (12). Anal. Calcd for
C26H24N6O4S2 (548.628): C, 56.92; H, 4.41; N, 15.32.
Found: C, 56.73; H, 4.30; N, 15.18%. The aqueous
solution was cooled and acidified with concentrated
hydrochloric acid to give a yellow solid which
was fractionally crystallized from ethanol to give
[11] Fink, W. Ber 1964, 97(5), 1424; Chem Abstr 1964, 61,
3138a.