Phase-transfer catalyzed alkylation and cycloalkylation of 2-mercaptoquinazolin-4(3H)-one

Article abstract of DOI:10.1080/104265090929940

Solid/liquid phase-transfer catalyzed alkylation of 2-mercaptoquinazolin- 4(3H)-one at 25°C by different organohalogen compounds in the presence of tetrabutylammonium bromide as a catalyst underwent, exclusively, S-monoalkylation or S- and N-, di-, or cyc

Full text of DOI:10.1080/104265090929940

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Phase-Transfer Catalyzed
Alkylation and Cycloalkylation
of 2-Mercaptoquinazolin-4(3H)-
One
A. Kh. Khalil a
a Chemistry Department, Ain Shams University,
Abbasia, Cairo, Egypt
Version of record first published: 16 Aug 2006.
To cite this article: A. Kh. Khalil (2005): Phase-Transfer Catalyzed Alkylation and
Cycloalkylation of 2-Mercaptoquinazolin-4(3H)-One, Phosphorus, Sulfur, and Silicon
and the Related Elements, 180:11, 2533-2541
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Phosphorus, Sulfur, and Silicon, 180:2533–2541, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090929940
Phase-Transfer Catalyzed Alkylation and Cycloalkylation
of 2-Mercaptoquinazolin-4(3H)-One
A. Kh. Khalil
Chemistry Department, Ain Shams University, Abbasia, Cairo, Egypt
Solid/liquid phase-transfer catalyzed alkylation of 2-mercaptoquinazolin-4(3H)-
one at 25◦C by different organohalogen compounds in the presence of tetrabutylam-
monium bromide as a catalyst underwent, exclusively, S-monoalkylation or S- and
N-, di-, or cycloalkylation, depending on the nature of alkylating agents.
Keywords Alkylation; cycloalkylation; mercaptoquinazolinone; phase-transfer catalysis
INTRODUCTION
Phase-transfer catalysis (PTC) is one of the promising methods in or-
ganic synthesis of specialty chemicals. In the last 20 years, a steadily
increasing number of published papers and patents dealing with
PTC topics and their applications. PTC is not merely important for
substitutional reactions but, now a days, it is being applied exten-
sively in polymer chemistry, heterocyclic chemistry, organometallic
FIGURE 1
Received November 8, 2004; accepted December 10, 2004.
Address correspondence to A. Kh. Khalil, Ain Shams University, Chemistry Depart-
ment, Faculty of Science, Abbasia, Cairo, Egypt. E-mail: khalilali123@yahoo.com
2533

2534
A. Kh. Khalil
synthesis, agrochemicals, dyes, flavors, perfumes, and pharmaceutical
manufacturing.1−3
The technique of PTC has been applied extensively in the organic
synthesis via substitution, displacement, condensation, elimination,
Ylide-mediated reactions, redox, and polymerization. The biggest ad-
vantages of using the PTC technique to synthesize organic chemicals
are the enhancing the reaction rate, carrying out the reaction at moder-
ate conditions, and obtaining high selectivity of the main product with
a high conversion of the reactants.4,5
On the other hand, 4(3H)-quinazolinones are the most frequently
encountered heterocycles in medicinal chemistry with wide appli-
cations including anticonvulsant,6 antihypertensive,7 antidiabetic,8
antibacterial,9 antitumor,10 antihistaminic,11 and antiinflammatory12
activities. Recent investigations on the biological activity of heterocycles
containing a benzimidazole ring clearly show that they play an impor-
tant role as selective neuropeptide YY1 receptor antagonists,13 factor
Xa inhibitors,14 5-lipoxygenase inhibitors for use as novel antiallergic
agents,15 poly polymerase inhibitors,16 and as human cytomegalovirus
inhibitors.17
RESULTS AND DISCUSSION
The approach reported here is an extension and continuation of my
interest in alkylation of some heterocycles uender PTC conditions.18−20
This work is aiming to study the reactivity of S-versus N-alkylation
of 2-mercaptoquinazolin-4(3H)-one (1) via solid/liquid PTC conditions
by some mono- and dihologen organic reagents as an efficient recent
alkylation technique. Also, it is expected that the alkylated products
might have biological and medicinal activities in analogy to the well
known biologically active quinazolin-4(3H)-one derivatives.
2-mercaptoquinazolin-4(3H)-one (1) is existed, predomenantly, in
four toutomeric forms (Scheme 1A–D).
The position of alkylation depends on the relative acidity and nucle-
ophilicity of SH, NH, and OH.
The acidity of NH at the 3-position of structure 1B of Scheme 1 is
higher than at the 1-position, so N3 alkylation has a higher periority
than N1.
Spectral data and some reported articles19−23 proved that 2-
mercaptopyrimidinones existed, predomenantely, as 2-mercapto-
lactames such as 1A. It is expected that monoalkylation occurs exclu-
sively at S- rather than N-due to the higher SH acididty than NH,
while dialkylation occurs at S- and N3 to give the dialkylated product.

2-Mercaptoquinazolin-4(3H)-One
2535
SCHEME 1
The optimized reaction conditions of PTC alkylation are the treat-
ment of 2-mercaptoquinazolin-4(3H)-one (1) with haloorganic reagents
in dioxane/anhydrous potasstium carbonate as liquid/solid phases in
the presence of tetrabutylammonium bromide (TBAB) as catalyst with
efficient stirring for 2–4 h at 25◦C.
Treatment of 2-mercaptoquinazolin-4(3H)-one (1) with ethyl bro-
mide, allyl bromide, bromoactylacetone, and diethyl bromomalonate in
SCHEME 2

2536
A. Kh. Khalil
SCHEME 3
a 1:3 molar ratio, respectively, under the optimized PTC reaction condi-
tions afforded, exclusively, S-monoalkylation to give 2a–d, while with
methyl iodide, benzyl bromide, ω-bromo-4-methoxyacetophenone, ethyl
bromoacetate, and chloroacetyl chloride simultaneously underwent S-
and N-dialkylation to give 2e–i, respectively (Scheme 2).
On the other hand, under the same optimized PTC conditions, treat-
ment of an equimolar amount of 2-mercaptoquinazolin-4(3H)-one (1)
and dihalogen organic reagents such as 1,2-dibromoethane, 1,3-dibro-
mopropane and chloroacetyl chloride underwent S- and N-cyclo-
alkylation to give 2,3-dihydro-5H-[1,3]thiazolo[2,3-b]quinazolin-5-one
(3a), 3,4-dihydro -2H, 6H-[1,3]thiazino[2,3-b]quinazolin-6-one (3b),
and 5H-[1,3]-thiazolo-[2,3-b]quinazolin-3,5(2H)-dione (4), respectively
(Scheme 3).
CONCLUSION
The feasibility study in this work revealed that PTC alkylation of
mercaptoquinazolin-4(3H)-one (1) proceeds smoothly with a moderate
yield (60–85%) and occurs in all cases, predominantly, at S- with mono-
halogen compounds, while simultaneously with S- and N-dialkylations
of some cases. Also, PTC cycloalkylations was afforded, with dihalo-
gen, organic reagents to give annulated heterocyclic systems such as
thiazoloquinolinone and thiazinoquinolinone derivatives.
EXPERIMENTAL
Melting points are uncorrected. IR spectra were recorded on a Perkin
Elmer’s Spectrum RXIFT-IR spectrophotometer (ν in cm−1). The NMR

2-Mercaptoquinazolin-4(3H)-One
2537
spectra were recorded on a Bruker Avance DPX400 spectrometer, us-
ing TMS as internal standard (chemical shifts in δ values in ppm).
Elemental analyses were preformed using a Perkine Elmer 2400, Series
II micro analyzer. The key starting, 2-mercaptoquinazolin-4(3H)-one (1)
is an Aldrich product and was used without further purification.
General Procedure
To a solution of 2-mercaptoquinazolin-4(3H)-one (1.78 g, 0.01 mol) (1) in
dioxane (50 mL), anhydrous K2CO3 (2.7 g, 0.02 mol) and TBAB (0.9 g,
0.003 mol); the monohalogen organic reagents (0.03 mol) such as ethyl
bromide, allyl bromide, bromoacetylacetone, diethyl bromomalonate,
methyl iodide, benzyl bromide, ω-bromo-4-methoxyacetophenone, ethyl
bromoacetate; and chloroacetyl chloride or a dihalgen organic reagent
(0.01 mol) such as 1,2-dibromoethane, 1,3-dibromopropane, and
chloroacetyl chloride was added. The reaction mixture was stirred vigor-
ously at 25◦C and monitored by TLC over the reaction period. After com-
pletion of the reaction, the dioxane was separated by filtration and the
solvent was evaporated; then the residue was triturated with pet. ether
60–80◦C to release the excess of the unreacted halogen reagent; then the
residue was crystallized from the suitable solvent to give the product
2–4. The K2CO3 residue was dissolved in water (50 mL) and acidified
by hydrochloric acid (15% solution) to confirm if an acidic byproduct ex-
isted. In all cases, there is no byproduct isolated from K2CO3 residue.
2-Mercaptoquinazolin-4(3H)-one (1)
1H NMR: δ (DMSO), 7.27 (t, 1H, Ph-H), 7.39 (d, 1H, Ph-H), 7.63 (t,
1H, Ph-H), 8.02 (d, 1H, Ph-H), 11.97 (s, 1H, NH), 12.56 (s, 1H, SH);
13C NMR: δ (DMSO), 116.00 (C), 126.03 (CH), 127.12 (CH), 134.7 (CH),
135.73 (CH), 140.46 (C), 159.99 (C2), 174.35 (C4).
2-(Ethylthio)quinazolin-4(3H)-one (2a)
White crystals from ethanol; C10H10N2OS (206.71), Calcd.: C, 58.23;
H, 4.89; N, 13.5; found: C, 58.55; H, 4.82; N, 12.99; yield 64%; m.p.
147◦C; IR (KBr), 1580, 1678, 2878, 3318; 1H NMR, δ (CDCl3), 1.47
(t, 3H, CH3), 3.32 (q, 2H, S-CH2), 7.40, 7.61, 7.72, 8.26 (4H, Ar-H), 10.90
(s, 1H, NH); 13C NMR, δ (CDCl3), 14.44 (CH3), 25.25 (CH2), 119.87 (C),
125.73 (CH), 126.39 (CH), 126.60 (CH), 134.83 (CH), 149.21 (C), 154.54
(C2), 163.03 (C4).
2-(Allylthio)quinazolin-4(3H)-one (2b)
White crystals from pet. ether 60–80◦C; C11H10N2OS (218.28),
Calcd.: C, 60.53; H, 4.62; N, 12.83; found: C, 60.47; H, 4.58; N, 12.77;

2538
A. Kh. Khalil
yield 58%; m.p. 154◦C; IR (KBr), 1581, 1668, 2871, 3310; 1H NMR,
δ (CDCl3), 4.41 (d, 2H, CH2), 5.62 (d, 1H, =CHb), 5.82 (d, 1H, =CHa),
6.45 (m, 1H, CH ), 7.83, 8.03, 8.16, 8.67 (4H, Ar-H), 11.90 (s, 1H, NH);
13C NMR, δ (CDCl3), 33.32 (CH2), 118.73 (=CH2), 120.26 (C), 124.92
(CH), 125.73 (CH), 127.55 (CH), 133.87 (CH), 135.47 (CH), 149.01 (C),
154.24 (C2), 163.03 (C4).
3-[(4-Oxo-3,4-dihydroquinazolin-2-yl)thio]pentane-
2,4-dione (2c)
Orange crystals from ethanol; C13H12N2O3S (276.32), Calcd.: C,
56.51, H, 4.38, N, 10.14; found: C, 56.46; H, 4.33; N, 10.06; yield 62%;
m.p. 208◦C; IR (KBr), 1584, 1671, 2868, 3011; 1H NMR, δ (CDCl3), 2.35
(s, 6H, 2xCH3), 4.11 (s, 1H, CH), 7.41–8.24 (4H, Ar-H), 12.53 (s, 1H,
NH); 13C NMR, δ (CDCl3), 26.94 (CH3), 64.67 (CH), 121.67 (C), 126.34
(CH), 127.18 (CH), 134.79 (CH), 147.27 (C), 154.88 (C2), 162.07 (C4),
197.13 (C=O).
Diethyl[(4-Oxo-3,4-dihydroquinazolin-2-yl)thio]malonate (2d)
Pale yellow crystals from ethanol; C15H16N2O5S (336.37), Calcd.: C,
53.56; H, 4.75; N, 8.33; found: C, 53.66; H, 4.65; N, 8.41; yield 66%; m.p.
126◦C; IR (KBr), 1658, 1747, 2881, 2982, 3321; 1H NMR, δ (CDCl3), 1.31
(txt, 6H, 2xCH3), 4.24 (qxq, 4H, 2xOCH2), 5.62 (s, 1H, CH), 7.36–8.22
(4H, Ar-H), 12.07 (s, 1H, NH); 13C NMR, δ (CDCl3), 51.82 (CH3), 60.61
(CH), 62.94 (CH2), 119.81 (C), 126.28 (CH), 126.80 (CH), 135.23 (CH),
148.57 (C), 152.73 (C2), 163.39 (C4), 165.60 (C=O).
3-Methyl-2-(methylthio)quinazolin-4(3H)-one (2e)
White crystals from pet. ether 40–60◦C; C10H10N2OS (206.27),
Calcd.: C, 58.23; H, 4.89; N, 13.58; found: C, 58.65; H, 4.82; N, 13.69;
yield 85%; m.p. 66–68◦C; IR (KBr), 1556, 1667, 2934; 1H NMR, δ
(CDCl3), 2.65 (s, 3H, S CH3), 3.60 (s, 3H, N CH3), 7.35, 7.52, 7.65,
8.19 (4H, Ar-H); 13C NMR, δ (CDCl3), 14.45 (S CH3), 30.84 (N CH3),
118.89 (C), 124.65 (CH), 126.27 (CH), 127.65 (CH), 134.86 (CH), 147.39
(C), 157.48 (C2), 161.81 (C4).
3-Benzyl-2-(bezylthio)quinazolin-4(3H)-one (2f)
White crystals from pet. ether 60–80◦C; C22H18N2OS (358.47),
Calcd.: C, 73.72; H, 5.06; N, 7.81; found: C, 73.68; H, 5.12; N, 7.89;
1
yield 73%; m.p. 95–97◦C; IR (KBr), 1565, 1691, 2938, 3032; H NMR,
δ (CDCl3), 4.50 (s, 2H, S CH2), 5.35 (s, 2H, N CH2), 7.23 (m, 10H,
2xC6H5), 7.40, 7.57, 7.65, 8.22 (4H, Ar-H); 13C NMR, δ (CDCl3), 37.24
(S CH2), 47.77 (N CH2), 119.67 (C), 126.48 (CH), 127.88 (CH), 129.06

2-Mercaptoquinazolin-4(3H)-One
2539
(CH), 129.80 (CH), 134.93 (CH), 135.94 (C), 136.79 (C), 147.85 (C),
156.84 (C2), 162.45 (C4).
3-[2-(4-Methoxyphenyl)-2-oxoethyl]-2-{[2-(4-methoxyphenyl)-
2-oxoethyl]thio}quinazolin-4(3H)-one (2g)
White crystals from ethanol; C26H22N2O5S (474.54), Calcd.: C, 65.81;
H, 4.67; N, 5.90; found: C, 65.92; H, 4.59; N, 6.01; yield 54%; m. p. 169◦C;
1
IR (KBr), 1597, 1680, 2909; H NMR, δ (CDCl3), 3.85 (s, 3H, O-CH3),
3.97 (s, 3H, O CH3), 4.97 (s, 2H, S CH2), 5.72 (s, 2H, N CH2), 7.23–
8.25 (12H, Ar-H); 13C NMR, δ (CDCl3), 39.63 (S-CH2), 49.70 (N CH2),
55.55 (OCH3), 114.72 (CH), 115.19 (CH), 120.02 (C), 126.45 (CH), 127.63
(CH), 129.37 (C), 130.32 (CH), 134.68 (CH), 146.28 (C), 155.48 (C2),
159.23 (C4), 164.12 (C), 164.52 (C), 186.38 (C=O), 190.93 (C=O).
Ethyl{[3-(2-ethoxy-2-oxoethyl)-4-oxo-3,4-dihydroquinazolin-
2-yl]thio}acetate (2h)
White crystals from ethanol; C16H18N2O5S (350.40), Calcd.: C, 54.85;
H, 5.18; N, 7.99; found: C, 54.69; H, 5.19; N, 8.05; yield 75%; m.p. 249◦C;
1
IR (KBr), 1557, 1680, 1741, 2927, 2983; H NMR, δ (CDCl3), 1.34 (txt,
6H, 2xCH3), 4.11 (s, 2H, S CH2), 4.32 (qxq, 4H, 2xO CH2), 4.98 (s, 2H,
N CH2), 7.45, 7.57, 7.76, 8.25, (4H, Ar-H); 13C NMR, δ (CDCl3), 14.08
(CH3), 14.18 (CH3), 34.63 (S CH2), 44.98 (N CH2), 61.96(OCH2), 62.09
(OCH2), 118.99 (C), 126.15 (CH), 127.12 (CH), 134.67 (CH), 147.13 (C),
154.38 (C2), 161.36 (C4), 166.76 (C=O), 168.19 (C=O).
S-[3-(Chloroacetyl)-4-oxo-3,4-dihydroquinazolin-
2-yl]chloroethanethioate (2i)
White crystals from ethanol; C12H8Cl2N2O3S (331.18), Calcd.: C,
43.52; H, 2.43; N, 8.46; found: C, 43.66; H, 2.55; N, 8.41; yield 78%;
1
m.p. 215◦C; IR (KBr), 1572, 1701, 3074; H NMR, δ (CDCl3), 2.57 (s,
2H, NCOCH2), 3.20 (s, 2H, SCOCH2), 7.43, 7.60, 7.78, 8.29, (4H, Ar-H);
13C NMR, δ (CDCl3), 43.98 (NCOCH2), 46.12 (SCOCH2), 118.67 (C),
125.13 (CH), 127.96 (CH), 128.77 (CH), 148.75 (C), 157.90 (C2), 158.67
(C4), 164.34 (NCO), 191.58 (SCO).
2,3-Dihydro-5H-[1,3]thiazolo[2,3-b]quinazolin-5-one (3a)
White crystals from pet. ether 60–80◦C; C10H8N2OS (204.25), Calcd.:
C, 58.81; H, 3.95; N, 13.72; found: C, 58.76, H, 4.09, N, 13.91; yield 63%;
1
m.p. 63–65◦C; IR (KBr), 1566, 1626, 1690, 3075; H NMR, δ (CDCl3),
3.45 (txt, 2H, S CH2), 4.43 (txt, 2H, N CH2), 7.24, 7.38, 7.54, 8.01, (4H,
Ar-H); 13C NMR, δ (CDCl3), 26.32 (S CH2), 48.57 (N CH2), 119.97 (C),
126.23 (CH), 127.39 (CH), 127.88 (CH), 134.75 (CH), 149.13 (C), 159.62
(C), 161.14 (C=O).

2540
A. Kh. Khalil
3,4-Dihydro-2H, 6H-[1,3]thiazino[2,3-b]quinazolin-5-one (3b)
White crystals from pet. ether 60–80◦C; C11H10N2OS (218.28),
Calcd.: C, 60.53; H, 4.62; N, 12.83; found: C, 60.59; H, 4.65; N, 12.89;
yield 83%; m.p. 90–92◦C; IR (KBr), 1607, 1676, 2934; 1H NMR, δ
(CDCl3), 2.33(m, 2H, CH2), 3.23 (t, 2H, S CH2), 4.21 (t, 2H, N CH2),
7.36, 7.51, 7.69, 8.18 (4H, Ar-H); 13C NMR, δ (CDCl3), 23.14 (CH2), 27.91
(S CH2), 41.73 (N CH2), 119.38 (C), 125.63 (CH), 125.74 (CH), 126.92
(CH), 134.61 (CH), 147.34 (C), 153.94 (C), 161.48 (C=O).
5H-[1,3]Thiazolo[2,3-b]quinazolin-3,5(2H)-dione (4)
Yellow crystals from ethanol; C10H6N2O2S (218.24), Calcd.: C, 55.04,
H, 2.77, N, 12.84; found: C, 55.14; H, 2.66; N, 12.92; yield 51%; m.p.
1
251◦C (dec.); IR (KBr), 1581, 1683, 1692, 2971; H NMR, δ (Aceton-
d6), 4.11(s, 2H, CH2), 7.42–8.13 (4H, Ar-H); 13C NMR, δ (CDCl3), 34.64
(CH2), 121.73 (C), 125.12 (CH), 127.87 (CH), 135.23 (CH), 147.29 (C),
159.41 (C), 161.54 (C), 170.74 (C=O).
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