Synthesis of heterocyclic compounds using amidines as their ene-1,1-diamine tautomers, iv: Synthesis of n-bridged heterocycles 1,2,3,4-tetrahydropyrido[1, 2-a]pyrimidin-6-ones and methyl 1,2,3,4-tetrahydropyrrolo- [1,2-a]pyrimidin-7- ylideneacetates

Article abstract of DOI:10.1080/00397911.2010.517365

2-Benzyl-1,4,5,6-tetrahydropyrimidines 1 (as ene-1,1-diamine N,C-tautomers) in diglyme reacted with ethyl benzoylacetate at 160 °C in an oil bath to give 1,2,3,4-tetrahydropyrido[ 1,2-a]pyrimidin-6-ones 3 and with dimethyl acetylenedicarboxylate in methanol at room temperature, leading to methyl 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-7- ylideneacetates 5, respectively. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.517365

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Synthetic Communications: An
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Synthesis of Heterocyclic Compounds
Using Amidines as Their Ene-1,1-
diamine Tautomers, IV: Synthesis
of N-Bridged Heterocycles
1,2,3,4-Tetrahydropyrido[1,2-
a]pyrimidin-6-ones and Methyl 1,2,3,4-
Tetrahydropyrrolo[1,2-a]pyrimidin-7-
ylideneacetates
Shogo Ihara a , Takashi Soma a , Daigo Yano a , Shunichi Aikawa a &
Yasuhiko Yoshida a
a Department of Applied Chemistry, Faculty of Science and
Engineering, and Bio-Nano Electronics Research Center, Toyo
University, Kujirai, Kawagoe, Saitama, Japan
Version of record first published: 22 Aug 2011.
To cite this article: Shogo Ihara, Takashi Soma, Daigo Yano, Shunichi Aikawa & Yasuhiko Yoshida
(2011): Synthesis of Heterocyclic Compounds Using Amidines as Their Ene-1,1-diamine Tautomers,
IV: Synthesis of N-Bridged Heterocycles 1,2,3,4-Tetrahydropyrido[1,2-a]pyrimidin-6-ones and
Methyl 1,2,3,4-Tetrahydropyrrolo[1,2-a]pyrimidin-7-ylideneacetates, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 41:24, 3600-3608
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Synthetic Communications1, 41: 3600–3608, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.517365
SYNTHESIS OF HETEROCYCLIC COMPOUNDS USING
AMIDINES AS THEIR ENE-1,1-DIAMINE TAUTOMERS,
IV: SYNTHESIS OF N-BRIDGED HETEROCYCLES
1,2,3,4-TETRAHYDROPYRIDO[1,2-a]PYRIMIDIN-6-ONES
AND METHYL 1,2,3,4-TETRAHYDROPYRROLO-
[1,2-a]PYRIMIDIN-7-YLIDENEACETATES
Shogo Ihara, Takashi Soma, Daigo Yano, Shunichi Aikawa,
and Yasuhiko Yoshida
Department of Applied Chemistry, Faculty of Science and Engineering, and
Bio-Nano Electronics Research Center, Toyo University, Kujirai, Kawagoe,
Saitama, Japan
GRAPHICAL ABSTRACT
Abstract 2-Benzyl-1,4,5,6-tetrahydropyrimidines 1 (as ene-1,1-diamine N,C-tautomers) in
diglyme reacted with ethyl benzoylacetate at 160 ꢀC in an oil bath to give 1,2,3,4-tetrahydro-
pyrido[1,2-a]pyrimidin-6-ones 3 and with dimethyl acetylenedicarboxylate in methanol
at room temperature, leading to methyl 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-7-
ylideneacetates 5, respectively.
Keywords Cyclic ene-1,1-diamine; dimethyl acetylenedicarboxylate; ethyl benzoylace-
tate; 1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-one,methyl; N-bridged heterocycles;
1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-7-ylideneacetate; a,b-unsaturated carbonyl
compound
Received September 8, 2009.
Address correspondence to Shogo Ihara, Department of Applied Chemistry, Faculty of Science
and Engineering, Toyo University, Kujirai, Kawagoe, Saitama 350-8585, Japan. E-mail: iharayh@
toyonet.toyo.ac.jp
3600

AMIDINES AS ENE-1,1-DIAMINE TAUTOMERS IV
3601
INTRODUCTION
Ene-1,1-diamines analogs of enamines are versatile reagents in the synthesis of
heterocyclic compounds. Additionally, cyclic ene-1,1-diamines lead to construction
of fused heterocyclic compounds by the reaction with bifunctional electrophiles,[1]
although ene-1,1-diamines having electron-withdrawing group at the b-carbon
reacts. For the C-alkylation of amidines (as ene-1,1-diamine N,C-tautomers), the
reaction of N-monosubstituted arylacetamidines with arylidenemalononitrile,[2] tri-
substituted amidines (2-alkylimino-N-methylpyrrolidines) with methyl acrylate,[3]
2-alkyl-4,5-dihydroimidazole with acetoacetate,[4] and arylacetamidines with a,b-
unsaturated esters[5] were reported, respectively. In a previous article, we reported
a facile synthesis for heterocycles by the reaction of amidines (via ene-1,1-diamines)
with a,b-unsaturated carbonyl compounds.[6] In the course of our investigation of
amidines (as ene-1,1-diamine N,C-tautomers), here we report the C-alkylation of
2-benzyl-1,4,5,6-tetrahydropyrimidines (1) with ethyl benzoylacetate (2) and
dimethyl acetylenedicarboxylate (4), leading to 1,2,3,4-tetrahydropyrido[1,2-a]
pyrimidin-6-ones (3) and methyl 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-7-
ylideneacetates (5), respectively.
RESULTS AND DISCUSSION
The synthesis of 1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-ones 3 was carried
out at 160 ꢀC in an oil bath by the reaction of 2-benzyl-1,4,5,6-tetrahydropyrimidines
1 with ethyl benzoylacetate 2 in diglyme. As shown in Scheme 1, cyclic amidines (as
the ene-1,1-diamine N,C-tautomers) 1 reacted with 2 followed by elimination of
water and ethanol to give condensed heterocycles 3 in 51–78% yields. The results
1
are listed in Table 1. The structure of 3 was confirmed by elemental analysis, H
NMR, and 13C NMR spectroscopic measurements. The1H NMR spectra showed
signals corresponding to 1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-ones 3. For
3a–f, the 13C NMR signals at d 161.3, 161.7, 161.4, 161.5, 161.4, and 161.6 corre-
spond to the carbonyl carbon of the amide group. These signals are revealed that
amidines, 1,4,5,6-tetrahydropyrimidines 1 (as the ene-1,1-diamine N,C-tautomers),
added to the b-carbonyl carbon of 2 followed by elimination of ethanol and water
afford condensed heterocycles 1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-ones 3.
The methyl 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-7-ylideneacetates 5 were
prepared by the reaction of 1 with dimethyl acetylenedicarboxylate 4 in methanol
at room temperature (Scheme 2, Table 2). The structures of 5 were confirmed on
Scheme 1.

3602
S. IHARA ET AL.
Table 1. 1,2,3,4-Tetrahydropyrido[1,2-a]pyrimidin-6-ones 3
Compd.
R1
R2
Temp. (ꢀC)=Time (h)
Yield (%)
3a
3b
3c
3d
3e
3f
Ph
Ph
H
160=5
160=5
160=4
160=4
160=5
160=5
63
78
53
72
51
69
Me
H
4-MePh
4-MePh
Me
H
4-MeOPh
4-MeOPh
Me
Scheme 2.
Table 2. Methyl 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-7-ylidene)
acetates 5
Compd.
R1
R2
Temp. (ꢀC)=Time (h)
Yield (%)
5a
5b
5c
5d
5e
5f
Ph
Ph
H
rt=0.5
rt=0.5
rt=0.5
rt=0.5
rt=1
43
55
44
60
37
41
Me
H
4-MePh
4-MePh
Me
H
4-MeOPh
4-MeOPh
Me
rt=1
the basis of their elemental analysis and spectral data. The result of heteronuclear
Overhauser effect spectroscopic (HOESY) analysis of 5c provided the evidence that
a proton at the a -position of the ester group was close to the carbon atom of amide
group. On the basis of this information, compound 5c was decided as the E-configur-
ation for the ester group of the acrylate moiety, and also 5a,b and 5d–f were assigned
to the same configuration as 5c.

AMIDINES AS ENE-1,1-DIAMINE TAUTOMERS IV
3603
EXPERIMENTAL
All melting points are uncorrected. Infrared (IR) spectra were recorded on a
1
Horiba FT-720 spectrometer as potassium bromide pellets. H and 13C NMR data
were obtained using a Jeol JNM-ECX500 M (500-MHz) spectrometer in CDCl3 with
tetramethylsilane (0.03%) as an internal standard. Mass spectra of compounds 1a–f
were measured using a Shimadzu GC=MS-QP5050A spectrometer at 70 eV ionization
energy using a direct-inlet system. For compounds 3 and 5, matrix-assisted laser des-
orption=ionization time-of-flight mass spectroscopic (MALDI-TOF-MS) spectra
were recorded on a Bruker AutoFlex II TOF=TOF mass spectrometer equipped with
a nitrogen laser (k ¼ 337 nm), a pulsed ion extraction, and a reflector. The operation
was performed at an accelerating potential of 20 kV for a reflector in positive ion
mode. Samples for the MALDI analysis were prepared by mixing volumes of the
matrix solution (trans-2-(2-methyl-3-phenyl-2-propylidene)malononitrile, called
MPPM, 10 mg=mL in THF), sample solution (2 mg=mL in CHCl3), and cationization
reagent solution (2 mg=mL in THF) to obtain a 20:1:8 ratio (matrix=sample=TFANa)
v=v. Elemental analysis was performed using a Perkin-Elmer 2400 II CHN Analyzer.
trans-2-(2-Methyl-3-phenyl-2-propylidene)malononitrile (MPPM) as matrix for
MALDI-TOF-MS analysis was synthesized by Knoevenagel reaction with a-methyl-
trans-cinnamaldehyde and malononitrile at 65 ꢀC for 1 h in ion-exchanged water
1
under an argon atmosphere. H NMR d 2.41 (2H, d, J ¼ 1.2 Hz), 7.14 (1H, br s),
7.46 (1H, d, J ¼ 0.9 Hz), 7.39–7.49 (5H, m); 13C NMR: d 14.9, 81.0, 112.8, 114.4,
128.8, 130.1, 130.3, 133.4, 134.5, 149.6, 164.4. Anal. calcd. for C17H18N2O3: C,
80.39; H, 5.19; N, 14.42. Found: C, 80.67; H, 5.21; N, 14.56.
Starting Materials
2-Benzyl-1,4,5,6-tetrahydropyrimidines 1a–f were prepared from the corre-
sponding 1,3-diamines and ethyl 2-arylacetimidates[7] according to literature[8] by
gently refluxing in diglyme.
2-Benzyl-1,4,5,6-tetrahydropyrimidine (1a)
This compound was obtained as white powder, 70% yield, mp 110–113 ꢀC [lit.[8]
1
mp 112–114 ꢀC]; H NMR: d 1.74 (2H, quin, J ¼ 5.7 Hz, CH2), 3.30 (4H, br s,
2 ꢁ NCH2), 3.46 (2H, s, CH2), 4.11 (1H, br s, NH), 7.23–7.28 (3H, m, Ar-H), 7.32
(2H, t, J ¼ 7.5 Hz, Ar-H); MS: (CI) m=z 175 (MHþ).
2-Benzyl-5,5-dimethyl-1,4,5,6-tetrahydropyrimidine (1b)
This compound was obtained as white prisms, 80% yield, mp 94–95 ꢀC [lit.[9]
1
mp 95–96 ꢀC]; H NMR: d 0.91 (6H, s, 2 ꢁ CH3), 2.93 (4H, br s, 2 ꢁ CH2), 3.47
(2H, s, CH2), 3.61 (1H, br s, NH), 7.24–7.29 (3H, m, Ar-H), 7.32 (2H, t, J ¼ 7.5 Hz,
Hz, Ar-H); MS: (CI) m=z 203 (MHþ).
2-(4-Methylbenzyl)-1,4,5,6-tetrahydropyrimidine (1c)
1
This compound was obtained as white powder, 65% yield, mp 114–116 ꢀC; H
NMR: d 1.73 (2H, quin, J ¼ 5.7 Hz, CH2), 2.33 (3H, s, Ar-CH3), 3.29 (4H, br s,

3604
S. IHARA ET AL.
2 ꢁ CH2), 3.42 (2H, s, CH2), 7.13 and 7.16 (each 2H, d, J ¼ 8.0 Hz, Ar-H), NH not
observed; MS: (CI) m=z 189 (MHþ).
5,5-Dimethyl-2-(4-methylbenzyl)-1,4,5,6-tetrahydropyrimidine (1d)
1
This compound was obtained as white needles, 66% yield, mp 131–133 ꢀC; H
NMR: d 0.91 (6H, s, 2 ꢁ CH3), 2.33 (3H, s, Ar-CH3), 2.94 (4H, br s, 2 ꢁ NCH2), 3.44
(2H, s, CH2), 4.36 (1H, br s, NH), 7.13 and 7.17 (each 2H, d, J ¼ 8.0 Hz, Ar-H); MS:
(CI) m=z 217 (MHþ).
2-(4-Methoxybenzyl)-1,4,5,6-tetrahydropyrimidine (1e)
1
This compound was obtained as white powder, 54% yield, mp 118–121 ꢀC; H
NMR: d 1.73 (2H, quin, J ¼ 5.7 Hz, CH2), 3.29 (4H, br s, 2 ꢁ NCH2), 3.41 (2H, s,
CH2), 3.80 (3H, s, OCH3), 6.86 and 7.19 (each 2H, d, J ¼ 8.6 Hz, Ar-H), NH not
observed; MS: (CI) m=z 205 (MHþ).
2-(4-Methoxybenzyl)-5,5-dimethyl-1,4,5,6-tetrahdropyrimidine (1f)
This compound was obtained as white plates, 66% yield, mp 126–127 ꢀC;1H
NMR: d 0.91 (6H, s, 2 ꢁ CH3), 2.92 (4H, br s, 2 ꢁ NCH2), 3.42 (2H, s, CH2), 3.80
(3H, s, OCH3), 4.18 (1H, br s, NH) 6.86 and 7.19 (each 2H, d, J ¼ 8.6 Hz, Ar-H);
MS: (CI) m=z 233 (MHþ).
Ethyl benzoylacetate 2 and dimethyl acetylenedicarboxylate 4 purchased from
Tokyo Chemical Industry Co. Ltd. were used without further purification. Other
chemicals were purchased from commercial sources.
General Procedure for the Preparation of 1,2,3,4-Tetrahydropyrido-
[1,2-a]pyrimidin-6-ones 3
In a flask equipped with a reflux condenser, a solution of 2-benzyl-1,4,5,6-
tetrahydropyrimidines 1 (30 mmol) in diglyme (15 mL) was stirred at 160 ꢀC in an
oil bath. A solution of ethyl benzoylacetate 2 was added dropwise during a period
of 1 h through a dropping funnel on the top of reflux condenser and then refluxed
for 4 or 5 h (Table 1). After removal of solvent and low boiling materials in vacuo,
residual products were filtered, washed with ethyl acetate, and recrystallized from
ethyl acetate to give 3.
Selected Data for 3a–3f
8,9-Diphenyl-1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-one (3a). This
compound was obtained as pale yellow powder, mp 210–211 ꢀC; IR: 3411,
1
1651 cmꢂ1; H NMR: d 2.08 (2H, quin, J ¼ 6.0 Hz, CH2), 3.31 (2H, td, J ¼ 6.0,
2.5 Hz, NHCH2), 4.15 (2H, t, J ¼ 6.0 Hz, NCH2), 4.83 (1H, br s, NH), 5.93 (1H, s,
CH), 7.01 and 7.05 (each 2H, d, J ¼ 8.0 Hz, Ar-H), 7.08–7.12 (3H, m, Ar-H), 7.18
(1H, t, J ¼ 7.4 Hz, Ar-H), 7.23–7.27 (2H, m, Ar-H); 13C NMR: d 20.4, 39.4, 39.9,
100.5, 103.3, 127.1, 127.5, 128.6, 128.9, 132.1, 135.3, 139.8, 147.1, 153.5, 161.3;

AMIDINES AS ENE-1,1-DIAMINE TAUTOMERS IV
3605
MS: (MALDI) m=z 302.1 (Mþ). Anal. calcd. for C20H18N2O: C, 79.44; H, 6.00; N,
9.26. Found: C, 79.52; H, 6.12; N, 9.31.
3,3-Dimethyl-8,9-diphenyl-1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-
one (3b). This compound was obtained as pale yellow powder, mp 221–223 ꢀC; IR:
3307, 1649 cmꢂ1
;
1H NMR: d 1.13 (6H, s, 2 ꢁ CH3), 2.97 (2H, d, J ¼ 2.6 Hz,
NHCH2), 3.86 (2H, s, NCH2), 4.81 (1H, br s, NH), 5.95 (1H, s, CH), 7.02–7.06
(4H, m, Ar-H), 7.09–7.13 (3H, m, Ar-H), 7.21 (1H, t, J ¼ 7.5 Hz, Ar-H), 7.26 (2H,
t, J ¼ 7.5 Hz, Ar-H); 13C NMR: d 24.4, 27.4, 51.0, 51.1, 100.2, 103.6, 127.3, 127.6,
128.8, 129.1, 132.2, 135.5, 139.8, 146.2,153.6, 161.7; MS: (MALDI) m=z 330.2
(Mþ). Anal. calcd. for C22H22N2O: C, 79.97; H, 6.71; N, 8.48. Found: C, 79.98;
H, 6.80; N, 8.52.
8-Phenyl-9-(4-methylphenyl)-1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-
6-one (3c). This compound was obtained as pale yellow powder, mp 218–220 ꢀC;
1
IR: 3278, 1653 cmꢂ1; H NMR: d 2.08 (2H, quin, J ¼ 6.0 Hz, CH2), 2.28 (3H, s,
Ar-CH3), 3.31 (2H, td, J ¼ 6.0, 2.5 Hz, NHCH2), 4.15 (2H, t, J ¼ 6.0 Hz, NCH2),
4.81 (1H, br s, NH), 5.93 (1H, s, CH), 6.93 (2H, d, J ¼ 8.0 Hz, Ar-H), 7.02–7.06
(4H, m, Ar-H), 7.11–7.13 (3H, m, Ar-H); 13C NMR: d 20.5, 21.2, 39.5, 40.0,
100.5, 103.4, 127.2, 127.6, 128.7, 129.8, 131.9, 132.1, 136.9, 140.0, 147.3, 153.6,
161.4; MS: (MALDI) m=z 316.2 (Mþ). Anal. calcd. for C21H20N2O: C, 79.72; H,
6.37; N, 8.85. Found: C, 79.44; H, 6.54; N, 8.86.
3,3-Dimethyl-8-phenyl-9-(4-methylphenyl)-1,2,3,4-tetrahydropyrido[1,
2-a]pyrimidin-6-one (3d). This compound was obtained as pale yellow powder,
1
mp 223–225 ꢀC; IR: 3248, 1655 cmꢂ1; H NMR: d 1.12 (6H, s, 2 ꢁ CH3), 2.29 (3H,
s, Ar-CH3), 2.96 (2H, d, J ¼ 2.6 Hz, NHCH2), 3.84 (2H, s, NCH2), 4.84 (1H, br s,
NH), 5.93 (1H, s, CH), 6.93 (2H, d, J ¼ 8.0 Hz, Ar-H), 7.03–7.06 (4H, m, Ar-H),
7.09–7.12 (3H, m, Ar-H); 13C NMR: d 21.2, 24.3, 27.3, 51.0, 100.1, 103.3, 127.2,
127.6, 128.7, 129.8, 131.9, 132.2, 136.9, 139.9, 146.3, 153.5, 161.5; MS: (MALDI)
m=z 344.2 (Mþ). Anal. calcd. for C23H24N2O: C, 80.20; H, 7.02; N, 8.13. Found:
C, 80.31; H, 7.20; N, 8.19.
9-(4-Methoxyphenyl)-8-phenyl-1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-
one (3e). This compound was obtained as yellow powder, mp 214–216 ꢀC; IR: 3264,
1
1649 cmꢂ1; H NMR: d 2.08 (2H, quin, J ¼ 6.0 Hz, CH2), 3.32 (2H, td, J ¼ 6.0,
2.5 Hz, NHCH2), 3.76 (3H, s, OCH3), 4.16 (2H, t, J ¼ 6.0 Hz, NCH2), 4.77 (1H,
br s, NH), 5.93 (1H, s, CH), 6.78 and 6.96 (each 2H, d, J ¼ 8.6 Hz, Ar-H), 7.02–
7.04 (2H, m, Ar-H), 7.11–7.13 (3H, m, Ar-H); 13C NMR: d 20.6, 39.5, 40.0, 55.2,
100.2, 103.4, 114.5, 127.2, 127.7, 128.7, 133.3, 140.0, 147.4, 153.8, 158.7, 161.4;
MS: (MALDI) m=z 332.2 (Mþ). Anal. calcd. for C21H20N2O2: C, 75.88; H, 6.06;
N, 8.43. Found: C, 75.80; H, 6.21; N, 8.46.
9-(4-Methoxyphenyl)-3,3-dimethyl-8-phenyl-1,2,3,4-tetrahydropyrido
[1,2-a]pyrimidin-6-one (3f). This compound was obtained as yellow powder, mp
1
217–218 ꢀC; IR: 3234, 1653 cmꢂ1; H NMR: d 1.12 (6H, s, 2 ꢁ CH3), 2.97 (2H, d,
J ¼ 2.3 Hz, NHCH2), 3.76 (3H, s, OCH3), 3.85 (2H, s, NHCH2), 4.80 (1H, br s,
NH), 5.93 (1H, s, CH), 6.79 and 6.96 (each 2H, d, J ¼ 8.6 Hz, Ar-H), 7.03–7.05
(2H, m, Ar-H), 7.10–7.13 (3H, m, Ar-H); 13C NMR: d 24.3, 27.4, 51.0 (overlapped

3606
S. IHARA ET AL.
two carbon atoms), 55.2, 99.8, 103.3, 114.5, 127.2, 127.3, 127.6, 153.7, 158.6, 161.6;
MS: (MALDI) m=z 360.2 (Mþ). Anal. calcd. for C23H24N2O2: C, 76.64; H, 6.71; N,
7.77. Found: C, 76.74; H, 6.89; N, 7.82.
General Procedure for the Preparation of Methyl 1,2,3,4-
Tetrahydropyrrolo[1,2-a]pyrimidin-7-ylideneacetates 5
A solution of dimethyl acetylenedicarboxylate 4 (45 mmol) in methanol
(15 mL) was added dropwise to a stirred solution of 2-benzyl-1,4,5,6-tetrahydropyr-
imidines 1 (30 mmol) in methanol (15 mL) at rt over 30 min. After stirring the reac-
tion mixture at rt for 1 h the precipitated material was collected by filtration, then
washed with ethyl acetate. The desired products 5 (Table 2) were of satisfactory
purity, as determined by 1H NMR spectroscopy. Samples for analysis were recrystal-
lized from ethyl acetate.
Selected Data for 5a–5f
Methyl (E)-(6-oxo-8-phenyl-1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-
7-ylidene)acetate (5a). This compound was obtained as orange powder, mp
1
193–195 ꢀC; IR: 3350, 1710, 1670 cmꢂ1; H NMR: d 2.07 (2H, quin, J ¼ 6.0 Hz,
CH2), 3.41 (2H, td, J ¼ 6.0, 2.9 Hz, NHCH2), 3.75 (3H, s, OCH3), 4.06 (2H, t,
J ¼ 6.0 Hz, NCH2), 5.97 (1H, s, CH), 6.57 (1H, br s, NH), 7.12 (1H, t, J ¼ 7.4 Hz,
Ar-H), 7.31 (2H, t, J ¼ 8.0 Hz, Ar-H), 7.36 (2H, d, J ¼ 8.3 Hz, Ar-H); 13C NMR: d
21.5, 39.2, 43.1, 51.6, 92.9, 95.8, 125.3, 127.2, 128.8, 131.5, 145.0, 162.9, 166.5,
176.6; MS: (MALDI) m=z 284.1 (MHþ). Anal. calcd. for C16H16N2O3: C, 67.59;
H, 5.67; N, 9.85. Found: C, 67.80; H, 5.71; N, 9.96.
Methyl (E)-(3,3-dimethyl-6-oxo-8-phenyl-1,2,3,4-tetrahydropyrrolo[1,2-a]-
pyrimidin-7-ylidene)acetate (5b). This compound was obtained as orange pow-
1
der, mp 233–235 ꢀC; IR: 3330, 1705, 1668 cmꢂ1; H NMR: d 1.14 (6H, s, 2 ꢁ CH3),
3.15 (2H, d, J ¼ 3.2 Hz, NHCH2), 3.76 (3H, s, OCH3), 3.82 (2H, s, NCH2), 6.05
(1H, s, CH), 6.21 (1H, br s, NH), 7.16 (1H, t, J ¼ 7.4 Hz, Ar-H), 7.36 and 7.43 (each
2H, d, J ¼ 8.3 Hz, Ar-H); 13C NMR: d 24.4, 29.6, 50.8, 51.8, 54.6, 92.7, 96.0, 125.4,
127.2, 129.1, 131.7, 145.4, 162.2, 166.6, 177.0; MS: (MALDI) m=z 312.2 (MHþ).
Anal. calcd. for C18H20N2O3: C, 69.21; H, 6.45; N, 8.97. Found: C, 69.39; H, 6.58;
N, 8.92.
Methyl (E)-(6-oxo-8-(4-methylphenyl)-1,2,3,4-tetrahydropyrrolo[1,2-a]-
pyrimidin-7-ylidene)acetate (5c). This compound was obtained as orange
1
powder, mp 202–203 ꢀC; IR: 3359, 1709, 1662 cmꢂ1; H NMR: d 2.11 (2H, quin,
J ¼ 6.0 Hz, CH2), 2.31 (3H, s, Ar-CH3), 3.44 (2H, td, J ¼ 6.0, 2.9 Hz, NHCH2),
3.75 (3H, s, OCH3), 4.09 (2H, t, J ¼ 6.0 Hz, NCH2), 6.01 (1H, s, CH), 6.30 (1H,
br s, NH), 7.15 and 7.28 (each 2H, d, J ¼ 8.2 Hz, Ar-H); 13C NMR: d 21.2, 21.6,
39.2, 43.1, 51.7, 93.1, 95.6, 127.4, 128.5, 129.5, 134.9, 145.3, 163.0, 166.8, 176.6;
MS: (MALDI) m=z 298.1 (MHþ). Anal. calcd. for C17H18N2O3: C, 68.44; H, 6.08;
N, 9.39. Found: C, 68.63; H, 6.09; N, 9.39.

AMIDINES AS ENE-1,1-DIAMINE TAUTOMERS IV
3607
Methyl (E)-(3,3-dimethyl-6-oxo-8-(methylphenyl)-1,2,3,4-tetrahydro-
pyrrolo[1,2-a]pyrimidin-7-ylidene)acetate (5d). This compound was obtained
1
as orange powder, mp 241–242 ꢀC; IR: 3327, 1713, 1664 cmꢂ1; H NMR: d 1.13
(6H, s, 2 ꢁ CH3), 2.32 (3H, s, Ar-CH3), 3.13 (2H, d, J ¼ 2.6 Hz, NHCH2), 3.75
(3H, s, OCH3), 3.80 (2H, s, NCH2), 6.03 (1H, s, CH), 6.18 (1H, br s, NH), 7.18
and 7.31 (each 2H, d, J ¼ 8.2 Hz, Ar-H); 13C NMR: d 21.3, 24.4, 29.6, 50.9, 51.8,
54.6, 92.6, 95.9, 127.2, 128.6, 129.7, 135.1, 145.5, 162.2, 166.7, 177.1; MS: (MALDI)
m=z 326.2 (MHþ). Anal. calcd. for C19H22N2O3: C, 69.92; H, 6.79; N, 8.58. Found:
C, 70.02; H, 6.82; N, 8.51.
Methyl (E)-(8-(4-methoxyphenyl)-6-oxo-1,2,3,4-tetrahydropyrrolo[1,2-a]-
pyrimidin-7-ylidene)acetate (5e). This compound was obtained as orange pow-
1
der, mp 172–174 ꢀC; IR: 1701, 1664 cmꢂ1; H NMR: d 2.12 (2H, quin, J ¼ 6.0 Hz,
CH2), 3.45 (2H, td, J ¼ 6.0, 2.9 Hz, NHCH2), 3.75 and 3.78 (each 3H, s, OCH3),
4.10 (2H, t, J ¼ 6.0 Hz, NCH2), 6.01 (1H, s, CH), 6.23 (1H, br s, NH), 6.90 and
7.30 (each 2H, d, J ¼ 8.9 Hz, Ar-H); 13C NMR: d 21.7, 39.3, 43.1, 51.7, 55.4, 92.8,
95.8, 114.5, 123.8, 128.9, 145.3, 157.5, 163.1, 166.7, 176.7; MS: (MALDI) m=z
314.1 (MHþ). Anal. calcd. for C17H18N2O4: C, 64.96; H, 5.77; N, 8.9. Found: C,
64.91; H, 5.86; N, 8.87.
Methyl
(E)-(8-(4-methoxyphenyl)-3,3-dimethyl-6-oxo-1,2,3,4-tetrahy-
was
dropyrrolo[1,2-a]pyrimidin-7-ylidene)acetate (5f). This compound
obtained as orange powder, mp 214–215 ꢀC; IR: 1701, 1664 cmꢂ1; H NMR: d 1.09
(6H, s, 2 ꢁ CH3), 3.07 (2H, s, NHCH2), 3.74 (3H, s, OCH3), 3.76 (2H, s, NCH2),
3.77 (3H, s, OCH3), 5.94 (1H, s, CH), 6.55 (1H, br s, NH), 6.87 and 7.29 (each 2H,
d, J ¼ 8.8 Hz, Ar-H); 13C NMR: d 24.3, 29.5, 50.7, 51.7, 54.4, 55.3, 92.6, 95.5,
114.4, 123.8, 128.9, 145.7, 157.5, 162.3, 166.6, 176.7; MS: (MALDI) m=z 342.2
(MHþ), 342.09. Anal. calcd. for C19H22N2O4: C, 66.65; H, 6.48; N, 8.18. Found:
C, 66.73; H, 6.45; N, 8.26.
1
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