Synthesis of 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones and their N-alkylation's under phase transfer conditions

Article abstract of DOI:10.1002/jhet.1561

5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 2 were synthesized by the cyclocondensation of 1,4-disubstituted 2-amino-3-cyanopyrrole 1 with formic acid. When comparative study of N versus O alkylation of ambident 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 2 was carried out under liquid-liquid PTC, solid-liquid PTC, and solid-liquid solvent free conditions using various alkylating agents 3, the N-alkylated product 4 were obtained selectively and exclusively.

Full text of DOI:10.1002/jhet.1561

July 2014
Synthesis of 5,7-Disubstituted 7H-Pyrrolo[2,3-d]Pyrimidin-4(3H)-ones
943
and Their N-Alkylation’s under Phase Transfer Conditions
Chaitanya G. Davea and Killol J. Patela,b
*
aOrganic Synthesis Laboratory, M. G. Science Institute, Navrangpura, Ahmedabad 380009, India
bPfizer Pharmaceutical India Pvt. Ltd, Plot no. 16, TTC MIDC area, Thane Belapur Road, K. U. Bazar post, Turbhe, Navi
Mumbai 400705, India
*
E-mail: kjp306@rediffmail.com
Received July 16, 2011
DOI 10.1002/jhet.1561
Published online 10 December 2013 in Wiley Online Library (wileyonlinelibrary.com).
.
+
.
+
O
N
O
Ph
Ph
NCH3
NH
N
-CH3CH=CH2(42)
N
N
R1
R1
m/z=321
-CH2=CH2(28)
m/z=335
.
+
O
N
N
Ph
-.H(1)
N
R1
-.CH3(15)
O
N
Ph
4e, m/z=363
R1 = 4ClC6H4
O
N
NH
Ph
NCH2CH2+
N
R1
N
m/z=320
R1
m/z=348
5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 2 were synthesized by the cyclocondensation of
1,4-disubstituted 2-amino-3-cyanopyrrole 1 with formic acid. When comparative study of N versus O
alkylation of ambident 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 2 was carried out under
liquid–liquid PTC, solid–liquid PTC, and solid–liquid solvent free conditions using various alkylating
agents 3, the N-alkylated product 4 were obtained selectively and exclusively.
J. Heterocyclic Chem., 51, 943 (2014).
INTRODUCTION
(3H)-ones 2. Therefore, in continuation of our interest in
fused pyrimidines and phase transfer catalyzed alkylation
of ambident heterocyclic system [16], it was of interest to
select compound 2, which is an ambident system. Therefore,
we wish to report herein the N versus O alkylation in ambi-
dent 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-
ones 2 under phase transfer condition in order to obtain
compound of biological interest, which were investigated for
antibacterial, CNS depressant, and anti-tubercular activities.
Pyrrolo[2,3-d]pyrimidines and their 4-oxoderivatives
deserve interest because of the presence of this moiety in
important antibiotics tubercidin [1], toyocamycin [1], and
sangivamycin [2,3], as well as for their potential antitumor
activity [4–6]. Various 6-substituted pyrrolo[2,3-d]pyrimidin-3,
4-ones were tested in vitro for mammalian xanthine oxidase
inhibitory activity; among them, 5-methyl-6-phenylpyrrolo
[2,3-d]pyrimidin-2,4-dione [7] was found to be the most
active compound. Hypoxenthine isoster pyrrolo[2,3-d]
pyrimidin-4(3H)ones have found to occur as heterocyclic
bases in a number of antibiotics [8,9]. Thus, there have
been ample precedents for the synthesis of pyrrolo[2,3-d]
pyrimidin-4(3H)ones derivatives [10,11].
RESULTS AND DISCUSSION
5,7-Disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-
ones 2 [11] required for N versus O alkylation study under
phase transfer condition were synthesized by cycloconden-
sation of 1,4-disubstituted 2-amino-3-cyanopyrrole 1 with
formic acid. During the process, the cyano group of
compound 1 was supposed to be partially hydrolyzed
A study of N versus O alkylation in various ambident
heterocyclic compounds under phase transfer conditions
[12–15] has been reported. However, there is no report of
such study in 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4
© 2013 HeteroCorporation

944
C. G. Dave and K. J. Patel
Vol 51
Scheme 2
because of the acidic nature of formic acid to give 1,4-
disubstituted 2-amino-3-carboxamidopyrrroles, which sub-
sequently cyclised on prolonged heating with formic acid
to give the 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4
(3H)-ones 2 (Scheme 1).
O
N
O
N
R
R
PTC
NH
N
R2
+ R2-X
N
N
R1
R1
Alkylation of 5,7-disubstituted 7H-pyrrolo[2,3-d]
pyrimidin-4(3H)-ones 2 (Scheme 2) was studied under
different phase transfer conditions: (i) liquid–liquid phase
transfer condition (PTC) (50% KOH, chlorobenzene); (ii)
solid–liquid PTC (solid KOH, chlorobenzene); and (iii)
solid–liquid PTC (solid KOH, solvent free condition).
Ethylation of 5-phenyl-7-(4-chlorophenyl)-7H-pyrrolo[2,3-
d]pyrimidin-4(3H)-one 2b was selected as a case study under
different phase transfer conditions. All studies provided
selectively N-alkylated product, and in no case, O-alkylated
product was obtained during the reaction. However, the
comparison between these phase transfer conditions revealed
that the highest product yield was found when solid–liquid
solvent free phase transfer condition employed (Table 1).
A study of the reaction between 5-phenyl-7-(4-
chlorophenyl)-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-one 2b and
ethyl bromide was also undertaken using solid–liquid solvent
free condition with different phase transfer catalysts: triethyl-
benzyl ammonium chloride (TEBA), tetrabutylammonium
3
4
2
4
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
R
R1
R2
C2H5
CH2CH2CH2Cl
CH2C6H5
C2H5
n-C3H7
iso-C3H7
CH2CH2CH2Cl
C2H5
n-C3H7
CH2CH2CH2Cl
C2H5
iso-C3H7
CH2CH2CH2Cl
iso-C3H7
C2H5
iso-C3H7
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
4-OCH3C6H4
4-OCH3C6H4
4-OCH3C6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
3-Cl-4-FC6H3
3-Cl-4-FC6H3
3-Cl-4-FC6H3
4-ClC6H4
4-ClC6H4
C6H5
C6H5
C6H5
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-OCH3C6H4
4-FC6H4
4-FC6H4
4-FC6H4
4-ClC6H4
3-Cl-4-FC6H3
3-Cl-4-FC6H3
3-Cl-4-FC6H3
3-Cl-4-FC6H3
CH2CH2CH2Cl
CH2CH2CH2Cl
C2H5
iso-C3H7
CH2CH2CH2Cl
CH2C6H5
s
t
u
V
bromide (TBAB), and cetyltrimethylammonium bromide
(Table 2). Ethylation of 5-phenyl-7-(4-chlorophenyl)-7H-
pyrrolo[2,3-d]pyrimidin-4(3H)-one 2b with different phase
transfer catalysts provided exclusively N-alkylated product.
O-alkylated product was not found during the experimental
conditions employed. The highest yield was found when
TEBA was used as phase transfer catalyst. In the absences
of phase transfer catalyst, the reaction was found to proceed
very slowly; after several hours, the majority of the starting
material 2b remained in the reaction mixture (TLC).
Scheme 1
O
R
R
CN
HCO2H,
H+
NH2
N
N
O
N
NH2
H
R1
R1
1
O
N
O
N
R
R
In conclusion, the solid–liquid solvent free phase trans-
fer condition using TEBA as catalyst was the best choice
and therefore, it was utilized for the N versus O alkylation
of 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-
ones 2. N versus O alkylation of compound 2 with different
alkylating agents such as ethyl bromide, n-propyl bromide,
isopropyl bromide, 1-bromo-3-chloropropane, and benzyl
chloride provide exclusively N-alkylated products. During
the alkylation reaction under solid–liquid solvent free
phase transfer condition, the excess of alkylating agent
itself worked as a solvent, and TEBA was used as a phase
transfer catalyst. At the end of reaction, alkylating agent
was recovered by distillation under vacuum to obtain the
solid alkylated product (Scheme 2).
NH2
OH
-H2O
NH
N
N
R1
R1
2
1, 2
R
C6H5
C6H5
C6H5
R1
a
b
c
d
e
f
g
h
i
4-OCH3C6H4
4-ClC6H4
4-BrC6H4
3-Cl-4-FC6H3
C6H5
4-CH3C6H4
4-OCH3C6H4
4-FC6H4
C6H5
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-BrC6H4
4-IC6H4
The IR (potassium bromide) spectra of 5,7-disubstituted 3-
alkyl-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 4 exhibited a
strong absorption band in the region 1700–1650 cm-1
indicated the presence of cyclic ketone structure. The absence
j
k
l
3-Cl-4-FC6H3
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

July 2014
Synthesis of Biological Important Compound under Phase Transfer Conditions
945
Table 1
Comparison of various phase transfer conditions for ethylation of compound 2b.
Reaction condition
Phase transfer catalyst
Yield %
Time (hours)
Temperature ꢀ
C
Liquid–liquid PTC (50% KOH, chlorobenzene),
Solid–liquid PTC (solid KOH, chlorobenzene
Solid–liquid PTC (solid KOH, solvent free condition)
TEBA 10 mole %
TEBA 10 mole %
TEBA 10 mole %
68
73
89
2.5
1.5
0.75
50–60
50–60
Reflux
1 H NMR (deuteriochloroform) spectral data of 5,7-di-
substituted 3-alkyl-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 4
are also mentioned in Table 3. The aromatic protons are
found to be resonated at d 7.0–8.2 in the form of multiplet.
Proton shift for other aliphatic protons are described in
Table 3.
Table 2
Comparison of various phase transfer catalysts for ethylation of
compound 2b.
Mole %
of catalyst
Yield
(%)
Time
(minutes)
Phase transfer catalyst
The mass spectra of 3-n-propyl-5-phenyl-7-(4-chloro-
phenyl)-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 4e exhib-
ited a molecular ion peak at m/z = 363. Hydrogen from
g position migrates to ketone functionality as a result
fragment obtained at m/z = 321, showed McLafferty
rearrangement [17,18]. Important fragments of compound
4e are depicted in Scheme 3.
TEBA
TBAB
Cetyl trimethylammonium
bromide
10
10
10
89
83
75
45
45
60
of characteristic bands for NH around 3250–3100 cm-1
confirmed N-alkylation of 5,7-disubstituted 7H-pyrrolo[2,3-d]
pyrimidin-4(3H)-ones. The absorption band because of
C=C, C=N (ring) stretching vibrations were found near
1600–1500cm-1.
EXPERIMENTAL
Melting points were determined by the electrothermal method
in an open capillary tube and are uncorrected. The IR spectra
Table 3
IR and 1H NMR spectral data for compound 4a–v.
No. IR (potassium bromide) cm-1
1H NMR (d ppm)
4a
4b
1677, 1602, 1576,1518
1678, 1578, 1540,1520
1.37–1.42 (t, J =7.2, 3H, CH3), 3.86 (s, 3H, OCH3), 4.04–4.11(q, J=7.2, 2H, CH2), 7.02–7.90(m, 11H, Ar-H)
2.24–2.39 (m, 2H, CH2), 3.38–3.56 (m, 2H, CH2Cl),3.88 (s, 3H, OCH3), 4.14–4.20 (m, 2H, NCH2),
7.10–7.93(m, 11H, Ar-H)
4c
4d
4e
1685, 1595, 1550, 1505
1685, 1580, 1515, 1505
1680, 1590, 1530, 1510
3.87 (s, 3H, OCH3), 5.34 (s, 2H, CH2), 7.23–8.13 (m, 16H, Ar-H)
1.38–1.43 (t, J = 7.2, 3H, CH3), 4.05–4.12 (q, J = 7.2, 2H, CH2), 7.22–7.92(m, 11H, Ar-H)
0.94–0.99 (t, J = 7.5, 3H, CH3), 1.75–1.87 (sextet, J = 7.2, 2H, CH2), 3.95–3.99 (t, J = 7.2, 2H, NCH2),
7.21–7.88 (m, 11H, Ar-H)
4f
1665, 1600, 1575, 1515
1660, 1600, 1580, 1510
1681, 1603, 1577, 1513
1670, 1600, 1578, 1551
1.46–1.48 (d, J = 6.7, 6H, 2CH3), 5.25–5.34 (heptet, J = 7.0, 1H, CH), 7.23–7.94 (m, 11H, Ar-H)
2.25–2.40 (m, 2H, CH2), 3.37–3.57 (m, 2H, CH2Cl), 4.16–4.22 (m, 2H, NCH2), 7.28–7.98(m, 11H, Ar-H)
1.39–1.45 (t, J = 7.3, 3H, CH3), 4.06–4.13 (q, J = 7.4, 2H, CH2), 7.20–8.05 (m, 10H, Ar-H)
0.95–0.99 (t, J = 7.4, 3H, CH3), 1.78–1.89 (sextet, J = 7.3, 2H, CH2), 3.96–4.02 (t, J = 7.5, 2H, NCH2),
7.19–8.03 (m, 10H, Ar-H)
4g
4h
4i
4j
4k
4l
4m
4n
1656, 1600, 1577, 1512
1679, 1597, 1549, 1511
1660, 1599, 1555, 1535
1678, 1578, 1552, 1513
1659, 1574, 1552, 1528
2.30–2.40 (m, 2H, CH2), 3.39–3.57 (m, 2H, CH2Cl), 4.17–4.23 (m, 2H, NCH2), 7.21–8.00 (m, 10H, Ar-H)
1.36–1.41 (t, J = 7.2, 3H, CH3), 4.03–4.09 (q, J = 7.3, 2H, CH2), 7.21–7.97(m, 11H, Ar-H)
1.45–1.47 (d, J = 6.9, 6H, 2CH3), 5.22–5.32 (heptet, J = 6.9, 1H, CH), 7.26–7.95 (m, 11H, Ar-H)
2.27–2.42 (m, 2H, CH2), 3.38–3.59 (m, 2H, CH2Cl), 4.15–4.21 (m, 2H, NCH2), 7.18–8.02 (m, 11H, Ar-H)
1.47–1.49 (d, J = 6.8, 6H, 2CH3), 3.87 (s, 3H, OCH3), 5.26–5.34 (heptet, J = 7.0, 1H, CH), 7.15–7.93
(m, 10H, Ar-H)
4o
4p
4q
4r
4s
4t
4u
4v
1681, 1575, 1551, 1519
1663, 1573, 1555, 1517
1663, 1581, 1551, 1509
1678, 1578, 1552, 1512
1693, 1583, 1555, 1515
1678, 1580, 1555, 1537
1676, 1598, 1580, 1555
1682, 1582, 1547, 1514
1.37–1.43 (t, J = 7.1, 3H, CH3), 4.05–4.11 (q, J = 7.2, 2H, CH2), 7.20–8.0 (m, 10 H, Ar-H)
1.46–1.48 (d, J = 6.6, 6H, 2CH3), 5.24–5.33 (heptet, J = 6.9, 1H, CH), 7.19–7.98 (m, 10H, Ar-H)
2.28–2.43 (m, 2H, CH2), 341–3.60 (m, 2H, CH2Cl), 4.19–4.25 (m, 2H, NCH2), 7.22–8.04 (m, 10H, Ar-H)
2.27–2.44 (m, 2H, CH2), 3.40–3.61 (m, 2H, CH2Cl), 4.18–4.24 (m, 2H, NCH2), 7.19–8.01 (m, 10H, Ar-H)
1.38–1.44 (t, J = 7.4, 3H, CH3), 4.06–4.12 (q, J = 7.5, 2H, CH2), 7.23–8.03 (m, 9H, Ar-H)
1.48–1.50 (d, J = 7.0, 6H, 2CH3), 5.26–5.35 (heptet, J = 7.2, 1H, CH), 7.24–8.06 (m, 9H, Ar-H)
2.28–2.44 (m, 2H, CH2), 3.41–3.61 (m, 2H, CH2Cl), 4.20–4.25 (m, 2H, NCH2), 7.26–8.08 (m, 9H, Ar-H)
5.36 (s, 2H, CH2), 7.30–8.16 (m, 14H, Ar-H)
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

946
C. G. Dave and K. J. Patel
Vol 51
Scheme 3
.
+
.
+
O
N
O
N
Ph
Ph
NCH3
NH
N
-CH3CH=CH2(42)
-CH2=CH2(28)
N
R1
R1
m/z=335
m/z=321
.
+
O
Ph
-.H(1)
N
N
N
-.CH3(15)
O
N
R1
Ph
4e, m/z=363
R1 = 4ClC6H4
O
N
NH
Ph
NCH2CH2+
N
R1
N
m/z=320
R1
m/z=348
Table 4
Physical and analytical data for compounds 4a–v.
Compound no.
Time (hours)
Temperature ꢀ
C
Yield %
mp ꢀ
C
Molecular formula
Analysis% calcd./found
C
H
N
4a
4b
4c
4d
4e
4f
0.75
1.5
1.0
0.75
1.0
1.0
1.5
1.0
1.0
1.5
0.75
1.0
1.5
1.5
1.0
1.5
35-40
65–70
75–80
35–40
65–70
55–60
65–70
35–40
65–70
65–70
35–40
55–60
65–70
55–60
35–40
55–60
87
88
79
89
84
82
82
83
82
81
88
83
91
82
90
88
122–123
112–113
138–139
200–201
143–144
174–175
117–118
162–163
119–120
148–149
150–151
181–182
88–89
C
21H19N3O2
73.02
73.17
67.08
67.12
76.63
76.83
68.61
68.89
69.32
69.42
69.32
69.21
63.32
63.26
65.30
65.59
66.05
66.31
60.53
60.77
68.66
68.49
69.32
69.45
63.32
63.12
67.08
67.19
65.30
65.22
66.05
5.54
5.29
5.11
5.23
5.19
5.13
4.57
4.71
4.98
4.91
4.98
4.89
4.30
4.41
4.11
4.37
4.48
4.37
3.84
3.92
4.61
4.72
4.98
4.87
4.30
4.25
5.11
5.31
4.11
4.25
4.48
12.16
12.21
10.66
10.57
10.31
10.47
12.01
12.16
11.54
11.65
11.54
11.42
10.55
10.36
11.42
11.09
11.00
11.15
10.09
10.23
12.01
12.23
11.54
11.73
10.55
10.62
10.66
10.57
11.42
11.58
11.00
C22H20ClN3O2
C26H21N3O2
C20H16ClN3O
C21H18ClN3O
C21H18ClN3O
C21H17Cl2N3O
C20H15ClFN3O
C21H17ClFN3O
C21H16Cl2FN3O
C20H16ClN3O
C21H18ClN3O
C21H17Cl2N3O
C22H20ClN3O2
C20H15ClFN3O
C21H17ClFN3O
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
134–135
153–154
115–116
(Continued)
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

July 2014
Synthesis of Biological Important Compound under Phase Transfer Conditions
947
Table 4
(Continued)
Compound no.
Time (hours)
Temperature ꢀ
C
Yield %
mp ꢀ
C
Molecular formula
Analysis% calcd./found
66.16
60.58
60.72
58.23
58.48
59.71
59.60
60.58
60.78
55.95
55.64
64.66
64.45
4.31
3.87
3.66
3.69
3.81
3.50
3.62
3.87
3.66
3.35
3.57
3.47
3.70
11.06
4q
4r
4s
4t
2.0
2.0
1.0
1.5
2.0
1.5
65–70
65–70
35–40
55–60
65–70
75–80
82
88
82
87
83
76
145–146
106–107
160–161
129–130
140–141
156–157
C21H16Cl2FN3O
C21H16Cl3N3O
C20H14Cl2FN3O
C21H16Cl2FN3O
C21H15Cl3FN3O
C25H16Cl2FN3O
10.09
10.27
9.71
9.84
10.44
10.32
10.09
10.23
9.32
9.11
9.04
9.13
4u
4v
are recorded in cm-1 and were acquire as potassium bromide pellets
on a Buck scientific spectrophotometer. The 1H NMR spectra were
recorded on Bruker AC 300 F NMR spectrometer using tetra-
methylsilane as internal standard and chemical shift are expressed
in ppm (d). The mass spectra were recorded on LKB 9000 mass
spectrometer. The purity of the compound was routinely checked
by thin-layer chromotography (TLC) using silica gel G, and the
spots were exposed to iodine vapor.
REFERENCES AND NOTES
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J Org Chem 1969, 28, 3329.
[2] Rao, K. V. J Med Chem 1968, 11, 939.
[3] Tolman, R. L.; Robins, R. K.; Townsendsx, L. B. J Am Chem
Soc 1969, 91, 2102.
[4] Nishimura, S. Jpn Kokai JP 5988848, 1984; Chem Abstr 1984,
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[5] Nishimura, S.; Nomura, H. European Patent 0079447, 1983;
Chem Abstr 1983, 99, 139963.
[6] Akimoto, H.; Nishimura, S.; Nomura, H. European Patent
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General procedure for the synthesis of 5,7-disubstituted
3-alkyl-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 4a–v. A mixture
of 5,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones
2
(0.005 mole), potassium hydroxide (0.01 mole), TEBA (0.0005 mole),
and alkylating agent 3 (15 mL) were placed in a 100-ml three-
neck round bottom flask equipped with reflux condenser and
stirrer. The reaction mixture was heated at appropriate temperature
with stirring and time given in Table 4. After completion of
reaction (TLC), the excess of alkylating agent was removed in
vacuo to obtain the crude product. The solid separated on cooling
was filtered, washed with water, cold methanol, dried, and
crystallized from ethanol.
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Acknowledgment. We wish to thank the Regional Sophisticated
Instrumentation centre, Central Drug Research Institute, Lucknow
and Regional Sophisticated Instrumentation centre, Chandigarh
for NMR and mass spectra; Management of M. G. Science
Institute, Ahmedabad for the facility to carry out this work.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet