Efficient ionic liquid-catalysed synthesis and antimicrobial studies of 4,6-diaryl- and 4,5-fused pyrimidine-2-thiones

Article abstract of DOI:10.3184/174751912X13523931169712

One-pot three-component condensation of aromatic ketones (1-tetralones, acetophenones, indane-1,3-dione), substituted aromatic aldehydes and thiourea in the presence of N-methylpyridinium tosylate under solvent free conditions at 100-110 °C for 2-4 h afforded tetrahydrobenzo[h]quinazoline-2-thiones, pyridimidine-2-thiones and indeno-pyrimidine-2-thiones in excellent yields. All synthesised thiones were screened for their antimicrobial activities.

Full text of DOI:10.3184/174751912X13523931169712

718 RESEARCH PAPER
DECEMBER, 718–721
JOURNAL OF CHEMICAL RESEARCH 2012
Efficient ionic liquid-catalysed synthesis and antimicrobial studies of
4,6-diaryl- and 4,5-fused pyrimidine-2-thiones
Richa Gupta and Ram Pal Chaudhary*
Department of Chemistry, Sant Longowal Institute of Engineering andTechnology, Longowal (Sangrur) Punjab-148106, India
One-pot three-component condensation of aromatic ketones (1-tetralones, acetophenones, indane-1,3-dione),
substituted aromatic aldehydes and thiourea in the presence of N-methylpyridinium tosylate under solvent free
conditions at 100–110 °C for 2–4 h afforded tetrahydrobenzo[h]quinazoline-2-thiones, pyridimidine-2-thiones and
indeno-pyrimidine-2-thiones in excellent yields. All synthesised thiones were screened for their antimicrobial
activities.
Keywords: N-methylpyridiniumtosylate, spectraldata, tetrahydrobenzo[h]qunazoline-2-thiones, pyrimidine-2-thiones, antimicro-
bial activities
The chemistry of sulfur-containing organic compounds has
gained importance, since it has led to a multitude of com-
pounds displaying interesting structural features and biologi-
cally active profiles. For example, organosulfur compounds
have been reported to be useful as antibacterials,1 antibiotics2
and antioxidants.3 We therefore explored the synthesis and
antimicrobial properties of some fused and substituted pyrimi-
dine thiones containing biologically active moieties such as
tetrahydronaphthalene and indanone.
The quinazoline skeleton is of great importance as it is
prevalent in many natural and synthetic biologically active
compounds which find applications in the pharmaceutical and
biochemical arenas.4 The pharmacodynamic versatility of the
quinazoline moiety has been documented not only in many of
its synthetic derivatives but also in several naturally occurring
alkaloids isolated from animals, families of plant kingdoms
and from microorganism.5,6 Quinazoline compounds are also
useful in the treatment of cancer, inflammation and epilepsy
disorders.7 Two recently reported tetrahydrobenzo[h]quinazoli
ne-2-thiones I, II (Fig. 1) are, respectively, inhibitors of
phosphodiesterase 10A8 and melanogenesis.9
We now report the efficient synthesis of fused heterocyclic
thiones using N-methylpyridinium tosylate, an ionic liquid, in
excellent yields. The method developed has the advantage of
being environmentally benign, rapid, and features an easy
work up, a recyclable catalyst and affords products in excellent
yields.
Results and discussion
Multicomponent reactions (MCRs) constitute a highly valu-
able synthetic tool for construction of heterocyclic compounds
required for drug discovery programmes.19 They provide con-
vergent and ecofriendly assembly of three or more building
blocks in practical one-pot operations.2o During the last decade
ionic liquids have emerged as green alternatives to volatile and
hazardous organic solvents. This prompted us to explore the
capability of ionic liquids in the synthesis of thiones.
In the present investigations, one-pot three-component
reactions of aromatic ketones (1-tetralones, acetophenones
and 1,3-indandiones), aromatic aldehydes and thiourea at
100–110 oC for 2–4 h in the presence of N-methylpyridinium
tosylate (prepared by a reported procedure21) afforded vari-
ously substituted tetrahydrobenzo[h]qunazoline-2-thiones 3,
pyrimidine-2-thiones 6 and indeno-pyrimidine-2-thiones 9
(Schemes 1–3) in excellent yield (80–90%). A plausible mech-
anism of the reaction is given in Scheme 4. A comparison
of reaction times and yields of conventional methods,16,23–26
microwave heating,17,26 ultrasound irradiation18 and our solvent-
free method is made in Table 1.
Pyrimidines, variously substituted, are also important
sub-structures found in a number of naturally occurring and
biologically active substances. For example, pyrimidine-2-
thiones find applications as antihypertensives e.g. SQ 32926
III (Fig. 1),1o as potential calcium channel blockers,11 anti-
bacterial,12 anti-inflammatory, antifungal,13 antibiotics14 and
antitumour agents.15
Originally, tetrahydrobenzo[h]qunazoline-2-thiones and
pyrimidine-2-thiones were prepared under thermal condi-
tions16 in two steps or in a single step by using different organic
solvents. However, in spite of their potential utility, these
methods suffer from drawbacks such as harsh reaction
conditions, unsatisfactory yields, prolonged reaction time,
cumbersome product isolation procedures, polar, volatile and
hazardous organic solvents and often expensive catalysts.
However, more recently there are reports of the synthesis of
thiones using microwave irradiations17 and ultrasonication.18
It is pertinent to note that conventional synthesis of thiones
either in one step (ketone + aldehyde + NH2CSNH2) or in two
steps (2-benzylidene derivatives of ketone + NH2CSNH2)
in presence of KOH and ethanol afforded products only after
prolonged refluxing and in a low yield. The method reported in
this paper requires only water to work up the products, was
completed in less time and afforded products in excellent
yields (Table 1). The ionic liquid was recovered after the reac-
tion and it was found suitable for two more reaction cycles
without any change in its efficiency.
Fig. 1 Structures of tetrahydrobenzo[h]quinazoline-2-thiones I, II and pyrimidine-2-thione SQ 32926 III.
* Correspondent. E-mail: rpchaudhary65@gmail.com

JOURNAL OF CHEMICAL RESEARCH 2012 719
Scheme 3
1
to the tetrahydronaphthalene ring. Similarly in the H NMR
spectrum of 6a, appearance of a multiplet at δ 5.21 is assigned
to HA and a multiplet at δ 5.30 is assigned to HB (Scheme 2).
Aromatic protons appear as multiplet at δ 7.33–7.45 and NH
protons appear at δ 6.83 and δ 7.67.
Scheme 1
Indeno-pyrimidine-2-thiones 9a–c were also prepared by
the same method as was used for 3a–g and 6a–d and also under
acidic conditions (using CH3COOH) at room temperature stir-
ring for 12–14 h which afforded thiones 9 in only moderate
yield (50–60%). As a representative case, 9a shows a singlet at
δ 5.36 assigned to HA in its 1H NMR spectrum and NH protons
appear as broad singlets at δ 9.77 and δ 11.68 (Scheme 3).
Antimicrobial studies
The 14 compounds, 3a–f, 6a–d and 9a–c, showed a varied
degree of antimicrobial activity against the test organisms
employed, most showing mild to moderate antibacterial and
antifungal activity (Tables 2 and 3). However, among this
series of compounds 3e, 6d, and 9c showed excellent activity
against the gram-positive bacteria B. Subtilis and S. aureus and
were the most active among their congeners in the antifungal
tests.
Scheme 2
The products 3a–d, f, g, and 6a, b, d are known compounds,
and were characterised by comparison of their physical and
spectroscopic data with those previously reported.16–18,23–26 The
structures of the new compounds 3e, 6c and 9a–c were deduced
from their spectroscopic data.
The structural assignment of 3f and 6a as representative
cases are discussed. The H NMR spectrum of 3f shows a
1
Conclusions
singlet at δ 5.20 readily assignable to HA (Scheme 1). Two trip-
lets at δ 2.10, 2.78 and multiplet at δ 6.68–8.10 are assigned
In conclusion, the present procedure using an ionic liquid
N-methylpyridinium tosylate, provides a very efficient and
Scheme 4 Plausible reaction mechanism for synthesis of pyrimidine thiones.

720 JOURNAL OF CHEMICAL RESEARCH 2012
Table 1 Synthesis of thiones by conventional method, microwave heating, ultrasound irradiation and solvent free method
Entry
Conventional method
Microwave heating
Ultrasound irradiation
Solvent free method
Time of
reaction/h
Yield/%
Time of
reaction/min
Yield/%
Time of
reaction/min
Yield/%
Time of
reaction/h
Yield/%
3a
3b
3c
3d
3e
3f
3g
6a
6b
6c
6d
9a
9b
9c
5.0
5.0
7216
7623
7323
7023
61
5.3
–
4617
–
–
–
–
–
2.5
2.0
2.5
3.0
3.0
3.5
2.5
3.0
2.5
3.0
2.5
3.0
3.5
2.0
85
87
80
82
84
83
81
90
85
88
86
84
85
81
5.0
–
–
–
–
5.0
5.0
–
–
–
4017
–
–
–
6.0
–
–
5.0
7524
6525
7326
6826
55
–
–
–
–
5.0
–
–
4.5
3.0
4.0
–
8126
8026
–
20
24
–
8218
7518
–
6.0
5.5
6.0
6826
60
54
58
–
–
–
–
12.0
14.0
14.0
–
–
–
–
–
–
–
–
–
–
–
overnight and the volume was reduced to half. The solid, thus obtained,
was filtered, washed well with water and finally crystallised from
suitable solvents to afford thiones 3a–g and 6a–d.
b) Thiones 3a–g and 6a–d were also obtained directly from, respec-
tively, compound 1 or 4 (0.01 mol), aromatic aldehydes (0.01 mol),
and thiourea (0.76 g, 0.01 mol) in ethanolic potash (2g KOH in 25 mL
ethanol) by refluxing for 5–6 h. The solid obtained, was filtered off,
washed well with water and finally crystallised from suitable solvents
to give thiones 3a–g and 6a–d.
c) An equimolar mixture of 1,3-indandione (1.46 g, 0.01 mol), thio-
urea (0.76 g, 0.01mol) and aromatic aldehydes (0.01 mol) in glacial
acetic acid (10 mL) was stirred at room temperature for 12–14 h.
The solid obtained was filtered off and recrystallised from suitable
solvents to obtain thiones 9a–c.
convenient methodology for the synthesis of fused and substi-
tuted pyrimidine thiones from active methylene compounds.
The significant advantages offered by this methodology are:
(a) general applicability to a large number of substrates; (b)
clean and fast reaction; (c) high isolated yield of products; (d)
reusability of catalyst and cost effectiveness; and (e) use of
ionic liquid as a catalyst as well as reaction medium avoiding
hazardous organic solvents. Some of the compounds have
shown moderate antimicrobial activity. Thus we believe that
this simple and green procedure will be an alternative to
existing procedures.
Experimental
Melting points were determined in sulfuric acid bath and are uncor-
rected. TLC was performed on silica gel G plates using pet ether-ethyl
acetate (4:1) as eluent and iodine vapours as visualising agent. IR
spectra (ν in cm−1) were recorded on an ABB FTIR spectrometer.
1H NMR spectra were recorded in DMSO-d6 on a Bruker Advance II
400 MHz NMR spectrometer using tetramethylsilane (TMS) as an
internal standard (chemical shift in δ, ppm). The elemental analysis of
compounds was performed on a Carlo Erba-1108 elemental analyser.
Solvent free synthesis of thiones 3, 6 and 9; general procedure
An equimolar mixture of compound 1, 4 or 7 (0.01 mol), thiourea
(0.76 g, 0.01 mol) and aromatic aldehydes (0.01 mol) in premolten
ionic liquid, N-methylpyridinium tosylate 2.0 g was stirred at 100–
110 °C for 2–4 h. The progress of the reaction was monitored by TLC.
After completion of the reaction the reaction mixture was poured
into ice cold water. The solid obtained was filtered off, dried and
crystallised from suitable solvents.
4-Phenyl-3,4,5,6-tetrahydro-1H-benzo[h]quinazoline-2-thione
(3a): M.p. 254–255 °C (DMF/water) [lit.16 256 oC]; IR spectrum
Synthesis of thiones 3, 6 and 9; general procedure
1
(cm−1): 1138 (C=S) 1588 (C=C) 3180 (NH); H NMR: δ 2.14 (t, H,
a) A mixture of 2-benzylidene derivatives of compound 1 or 4
(0.01 mol), and thiourea (0.76 g, 0.01 mol) in ethanolic potash (2.0 g
KOH in 25 mL ethanol) was heated under reflux for 5–6 h, and kept
CH2, J = 6.5 Hz), 2.78 (t, 2H, CH2, J = 6.2 Hz), 5.39 (s, 1H, HA),
7.23–7.50 (m, 9H, ArH), 8.10 (br, 1H, NH), 8.12 (br, 1H, NH); Anal.
Calcd for C18H16N2S: C, 73.97; H, 5.48; N, 9.59; S, 10.96. Found: C,
73.90; H, 5.41; N, 9.52; S, 10.88%.
Table 2 Antibacterial activities of variously substituted pyrimi-
dine-2-thiones 3a–g, 6a–d and 9a–c
Table 3 Antifungal activities of variously substituted pyrimi-
dine-2-thiones 3a–g, 6a–d and 9a–c
Sr. no. Entry
Zone of inhibition/mm
Gram Positive Gram Negative
B. subtilis S. aureus P. aeruginosa E. coli
Sr.no.
Entry
Zone of inhibition/mm
A. niger C. albicans A. fumigatus
1
2
3a
10
19
12
15
22
16
17
11
12
13
19
9
11
18
12
16
23
15
16
10
12
14
22
10
14
24
28
8
14
10
12
12
12
15
16
5
9
16
11
13
13
14
16
17
16
9
12
8
11
14
21
1
2
3a
8
18
11
14
20
16
15
7
7
15
12
13
19
13
14
8
11
16
20
10
14
17
25
10
17
14
15
18
16
14
9
10
11
17
11
17
19
22
3b
3b
3
3c
3
3c
4
3d
4
3d
5
3e
5
3e
6
3f
6
3f
7
3g
7
3g
8
6a
8
6a
9
6b
6c
9
6b
6c
9
10
11
12
13
14
8
10
11
12
13
14
14
21
8
12
19
24
6d
13
6
10
12
24
6d
9a
9a
9b
15
21
26
9b
9c
9c
Ampicillin
trihydrate
DMSO
Ampicillin
trihydrate
DMSO
00
00
00
00
0
0
0

JOURNAL OF CHEMICAL RESEARCH 2012 721
4-(4-Chloro-phenyl)-3,4,5,6-tetrahydro-1H-benzo[h]quinazoline-
2-thione (3b): M.p. 246–248 °C (DMF/water) [lit.23 250–251 °C]; IR
(cm−1): 1141 (C=S), 1579 (C=C), 3200 (NH); 1H NMR: δ 2.20 (t, 2H,
CH2, J = 6.8 Hz), 2.84 (t, 2H, CH2, J = 6.5 Hz), 5.43 (s, 1H, HA),
7.25–7.55 (m, 8H, ArH), 8.00 (br, 1H, NH), 8.02 (br, 1H, NH); Anal.
Calcd for C18H15N2SCl: C, 66.16; H, 4.59; N, 8.58; S, 9.80. Found: C,
66.30; H, 4.67; N, 8.63; S, 9.72%.
4-p-Tolyl-3,4,5,6-tetrahydro-1H-benzo[h]quinazoline-2-thione
(3c): M.p. 228–230 °C (DMF/water) [lit.23 230–232 °C]; IR (cm−1):
1214 (C=S), 1568 (C=C); 1H NMR: δ 2.18 (t, 2H, CH2, J = 6.9 Hz),
2.38 (s, 3H, CH3), 2.84 (t, 2H, CH2, J = 6.1 Hz), 5.36 (s, 1H, HA),
7.20–7.50 (m, 8H, ArH), 7.55 (br, 1H, NH), 7.62 (br, 1H, NH); Anal.
Calcd for C19H18N2S: C, 74.51; H, 5.88; N, 9.15; S, 10.46. Found: C,
74.57; H, 5.81; N, 9.00; S, 10.40%.
(C=C), 1674 (C=O); 1H NMR: δ 5.36 (s, 1H, HA), 7.25–7.39 (m, 8H,
ArH), 7.80–7.86 (m, 1H, ArH), 9.77 (br, 1H, NH), 11.68 (br, 1H, NH);
Anal. Calcd for C17H12N2SO: C, 69.86; H, 4.11; N, 9.59; S, 10.96.
Found: C, 69.80; H, 4.18; N, 9.51; S, 10.89%.
4-p-Tolyl-1,3,4,4a,5,9b-hexahydroindeno[1,2-d]pyrimidine-2-
thione (9b): M.p. 170–172 °C (EtOH); IR (cm−1): 1270 (C=S), 1640
(C=C), 1670 (C=O); 1H NMR: δ 2.52 (s, 3H, CH3), 5.38 (s, 1H, HA),
7.48–7.49 (m, 2H, ArH), 7.74–7.76 (m, 2H, ArH), 7.80–7.84 (m, 4H,
ArH), 8.41 (br, 1H, NH), 8.62 (br, 1H, NH); Anal. Calcd for
C18H14N2SO: C, 70.59; H, 4.58; N, 9.15; S, 10.46. Found: C, 70.51; H,
4.63; N, 9.08; S, 10.54%.
4-(4-Chlorophenyl)-1,3,4,4a,5,9b-hexahydroindeno[1,2-d]pyr-
imidine-2-thione (9c): M.p. 200–202 °C (DMF/water); IR (cm−1):
1312 (C=S), 1630 (C=C), 1680 (C=O); 1H NMR: δ 5.32 (s, 1H, HA),
7.40–7.43 (m, 2H, ArH), 7.72–7.75 (m, 2H, ArH), 7.84–7.86 (m, 4H,
ArH), 8.50 (br, 1H, NH), 8.72 (br, 1H, NH); Anal. Calcd for
C17H11N2SClO: C, 62.48; H, 3.37; N, 8.58; S, 9.80. Found: C, 62.40;
H, 3.42; N, 8.50; S, 9.88%.
4-(4-Methoxy-phenyl)-3,4,5,6-tetrahydro-1H-benzo[h]quinazo-
line-2-thione (3d): M.p. 226–228 °C (DMF/water) [lit.23 220–222 °C];
IR (cm−1): 1210 (C=S), 1611 (C=C), 3200 (NH); 1H NMR: δ 2.18 (t,
2H, CH2, J = 6.5 Hz), 2.83 (t, 2H, CH2, J = 6.4 Hz), 4.0 (s, 3H, OCH3),
5.43 (s, 1H, HA), 7.28 (m, 4H, ArH), 7.26–7.54 (m, 4H, ArH), 7.90 (br,
1H, NH), 7.98 (br, 1H, NH);Anal. Calcd for C19H18N2SO: C, 70.80; H,
5.59; N, 8.69; S, 9.94. Found: C, 70.86; H, 5.52; N, 8.65; S, 9.90%.
4-(4-Fluoro-phenyl)-3,4,5,6-tetrahydro-1H-benzo[h]quinazoline-
2-thione (3e): M.p. 228–230 °C (DMF/water); IR (cm−1): 1215 (C=S),
One of the authors (RG) thanks the authorities of Sant
Longowal Institute of Engineering and Technology, Longowal
for providing financial assistance. The facilities provided by
SLIET authorities are gratefully acknowledged.
1
1650 (C=C), 3170 (NH); H NMR: δ 2.16 (t, 2H, CH2, J = 7.0 Hz),
2.40 (t, 2H, CH2, J = 6.7 Hz), 5.40 (s, 1H, HA), 7.35–7.60 (m, 8H,
ArH), 8.12 (br, 1H, NH), 8.14 (br, 1H, NH); Anal. Calcd for
C18H15N2SF: C, 69.67; H, 4.84; N, 9.03; S, 10.32. Found: C, 69.60; H,
4.90; N, 9.10; S, 10.39%.
Received 21 September 2012; accepted 9 October 2012
Paper 1201528 doi: 10.3184/174751912X13523931169712
Published online: 5 December 2012
8-Methoxy-4-phenyl-3,4,5,6-tetrahydro-1H-benzo[h]quinazoline-
2-thione (3f): M.p. 244–246 °C (EtOH) [lit.24 248–250 °C]; IR (cm−1):
1
References
1304 (C=S), 3202 (NH); H NMR: δ, 2.10 (t, 2H, CH2, J = 7.7 Hz),
2.78 (t, 2H, CH2, J = 7.2 Hz), 3.80 (s, 3H, OCH3), 5.20 (s, 1H, HA),
6.68–8.10 (m, 8H, ArH), 8.14 (br, 1H, NH), 8.16 (br, 1H, NH); Anal.
Calcd for C19H18N2SO: C, 70.80; H, 5.59; N, 8.69; S, 9.94. Found: C,
70.88; H, 5.54; N, 8.62; S, 9.88%.
9-Methoxy-4-phenyl-3,4,5,6-tetrahydro-1H-benzo[h]quinazoline-
2-thione (3g): M.p. 232–233 °C (EtOH) [lit.25 230–235 °C]; IR (cm−1):
1315 (C=S), 1558 (C=C); 1H NMR: δ 2.12 (t, 2H, CH2, J = 6.1 Hz),
2.76 (t, 2H, CH2, J = 6.6 Hz), 3.82 (s, 3H, OCH3), 5.25 (s, 1H, HA),
6.77–8.16 (m, 8H, ArH), 8.18 (br, 1H, NH), 8.20 (br, 1H, NH); Anal.
Calcd for C19H18N2SO: C, 70.80; H, 5.59; N, 8.69; S, 9.94. Found: C,
70.86; H, 5.56; N, 8.63; S, 9.90%.
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162 °C (EtOH); IR (cm−1): 1180 (C=S), 1558 (C=C), 3171 (NH); 1H
NMR: δ 5.21 (m, 1H, HA), 5.30 (m, 1H, HB), 6.83 (br, 1H, NH), 7.33–
7.45 (m, 10H, ArH), 7.67 (br, 1H, NH); Anal. Calcd for C16H14N2S: C,
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S, 12.09%.
8
9
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1
1558 (C=C), 3202 (NH); H NMR: δ 3.78 (s, 3H, OCH3), 5.12–5.14
(m, 1H, HA), 5.18–5.20 (m, 1H, HB), 6.87–6.90 (m, 2H, ArH), 7.27–
7.30 (m, 2H, ArH), 7.34–7.38 (m, 3H, ArH), 7.48–7.50 (m, 2H, ArH),
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6-(4-Chlorophenyl)-4-phenyl-3,4-dihydro-1H-pyrimidine-2-thione
(6c): M.p. 180–182 °C (EtOH); IR (cm−1): 1234 (C=S), 1566 (C=C);
1H NMR: δ 5.19 (s, 1H, HA), 5.28 (s, 1H, HB), 7.35–7.50 (m, 5H,
ArH), 7.56 (br, 1H, NH), 7.80 (br, 1H, NH), 8.02–8.06 (m, 2H, ArH),
8.07–8.09 (m, 2H, ArH); Anal. Calcd for C16H13N2SCl: C, 63.89; H,
4.33; N, 9.32; S, 10.65. Found: C, 63.81; H, 4.39; N, 10.58; S,
9.37%.
Pharm., 2011, 68 (3), 357.
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17 B. Kaur and R.Kaur, ARKIVOC, 2007, (xv), 315.
18 J. Safaei-Ghomi and M.A. Ghasemzadeh, J. Serb. Chem. Soc., 2011,
76 (5), 679.
19 Z.L. Shen, X.P. Xu and S.J. Ji, J. Org. Chem., 2010, 75, 1162.
20 Y. Zhu, S. Huang, J. Wan, L. Yan, Y. Pan and A.Wu, Org. Lett., 2006, 8,
2599.
21 J. Kroutil and M. Budesinsky, Carbohydr. Res., 2007, 342, 147.
22 B.A. Arthington-Skaggs, M. Motley, D.W. Warnock and C.J. Morrison,
J. Clin. Microbiol., 2000, 38, 2254.
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24 R. Gupta and R.P. Chaudhary, Phosphorus, Sulfur, Silicon Relat. Elem.,
2012, 187, 735.
6-(4-Chlorophenyl)-4-(methoxyphenyl)-3,4-dihydro-1H-pyrimi-
dine-2-thione (6d): M.p. 225–226 °C (DMF/water); IR (cm−1): 1227
1
(C=S), 1566 (C=C); H NMR: δ 5.17 (s, 1H, HA), 5.30 (s, 1H, HB),
7.30–7.52 (m, 5H, ArH), 7.58 (br, 1H, NH), 7.82 (br, 1H, NH), 8.05–
8.08 (m, 2H, ArH), 8.03–8.08 (m, 2H, ArH); Anal. Calcd for
C17H15N2SClO: C, 61.72; H, 4.54; N, 8.47; S, 9.68. Found: C, 61.79;
H, 4.58; N, 8.40; S, 9.60%.
25 R. Gupta and R.P. Chaudhary, Asian J. Chem., 2012, 24(5), 2113.
26 I.T. Phucho, A. Nongpiur, R. Nongrum and R.L. Nongkhlaw, Indian J.
Chem., 2010, 49B, 346.
4-Phenyl-1,3,4,4a,5,9b-hexahydroindeno[1,2-d]pyrimidine-2-
thione (9a): M.p. 224–226 °C (EtOH); IR (cm−1): 1173 (C=S), 1636