Regioselectivity in the multicomponent reaction of 5-aminopyrazoles, cyclic 1,3-diketones and dimethylformamide dimethylacetal under controlled microwave heating

Article abstract of DOI:10.3762/bjoc.8.3

The multicomponent reaction of 5-aminopyrazole derivatives with cyclic 1,3-dicarbonyl compounds and dimethylformamide dimethylacetal (DMFDMA) in DMF at 150 °C under controlled microwave heating afforded regioselectively 8,9-dihydropyrazolo[1,5-a]quinazoli

Full text of DOI:10.3762/bjoc.8.3

Regioselectivity in the multicomponent reaction of
5-aminopyrazoles, cyclic 1,3-diketones and dimethyl-
formamide dimethylacetal under controlled
microwave heating
Kamal Usef Sadek*1, Ramadan Ahmed Mekheimer1,2,
Tahany Mahmoud Mohamed1, Moustafa Sherief Moustafa*3
and Mohamed Hilmy Elnagdi3
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2012, 8, 18–24.
1Chemistry Department, Faculty of Science, El-Minia University,
El-Minia 61519, Egypt, 2Department of Chemistry, Faculty of Science
for Girls, King Abdul-Aziz University, Jeddah, P.O. Box 50918,
Jeddah 21533, Kingdom of Saudi Arabia and 3Chemistry Department,
Faculty of Science, Kuwait University, PO Box 5969, Safat, 13060
Kuwait
doi:10.3762/bjoc.8.3
Received: 05 October 2011
Accepted: 13 December 2011
Published: 04 January 2012
This article is part of the Thematic Series "Multicomponent reactions".
Guest Editor: T. J. J. Müller
Email:
Kamal Usef Sadek* - Kusadek@yahoo.com;
Moustafa Sherief Moustafa* - mostafa_msm@hotmail.com
© 2012 Sadek et al; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
Keywords:
aminopyrazoles; dimedone; DMFDMA; regioselectivity
Abstract
The multicomponent reaction of 5-aminopyrazole derivatives with cyclic 1,3-dicarbonyl compounds and dimethylformamide
dimethylacetal (DMFDMA) in DMF at 150 °C under controlled microwave heating afforded regioselectively 8,9-
dihydropyrazolo[1,5-a]quinazolin-6(7H)-ones 6 rather than the corresponding dihydropyrazolo[5,1-b]quinazolin-8(5H)-ones 4.
Introduction
Several naturally occurring and synthetic compounds containing possessing a wide range of biological activities [3,4]. Multicom-
quinazoline derivatives are of considerable interest in fields ponent reactions (MCR) occupy an interesting position in
related to the organic and medicinal chemistry of natural prod- organic synthesis because of their atom economy, simple pro-
ucts [1,2]. The quinazoline ring system represents the core cedures and convergent character [5-7]. An unresolved issue in
skeleton of an important class of heterocyclic compounds multicomponent reactions is whether their selectivity is chemo-
18

Beilstein J. Org. Chem. 2012, 8, 18–24.
or regioselectivity, or both, due to the several possible parallel A one-pot three component reaction of 5-amino-1H-pyrazole-4-
reaction pathways, which result in the formation of different carbonitrile, dimedone and triethylorthoesters in toluene under
products [8-10]. Many factors modulate the selectivity of syn- reflux was recently reported to afford the corresponding pyra-
thetic transformations, such as temperature, pressure, solvent, zolo[1,5-a]-quinazolin-6-one derivatives [21]. Although it is
catalyst and type of reaction control, i.e., either kinetic or ther- well established that 5-amino-pyrazoles have nonequivalent
modynamic [11-13]. It has been reported that the use of nucleophilic reaction centres in the aminopyrazole scaffold (N1,
microwave or ultrasound irradiation provides an additional C4, NH2), which can lead to the formation of several different
parameter for synthetic selectivity [14-17].
tricyclic reaction products, no general basis on which to deter-
mine the preferred tautomeric form of the final product has been
established.
Results and Discussion
The multicomponent reaction of 5-aminopyrazoles, dimedone
and aromatic aldehydes was reported to afford several different In continuation of our studies in which we performed multicom-
tricyclic products. Thus, in an early report [18], the reaction of ponent reactions using controlled microwave heating [22-24],
the three components in ethanol under conventional heating we report herein the results of our investigation concerning the
afforded mainly the corresponding pyrazolo[3,4-b]quinolin-5- regioselectivity in multicomponent reactions of 5-aminopyra-
ones. This finding was later supported by other authors [19]. zoles, cyclic 1,3-diketones and dimethylformamide dimethylac-
Recently, the results of an interesting study dealing with such etal (DMFDMA) under controlled microwave heating.
reactions were described by Chebanov et al. [20] Specifically,
these researchers performed the reaction at 150 °C in the pres- We began this study by treating 5-amino-3-methylpyrazole (1a)
ence of triethylamine by employing a sealed vessel under and dimedone (2a) with DMFDMA (3) in DMF under
microwave or conventional heating, and which thus afforded microwave heating at 150 °C for 15 min. After being cooled to
pyrazoloquinolinones (Hantzsch-type dihydropyridines). On the room temperature, the precipitated solid product was isolated in
other hand, the use of sonication at room temperature under 88% yield (Table 1). The mass spectrum of the reaction pro-
neutral conditions favours the formation of isomeric duct showed a molecular ion peak m/z = 229.12 (100%). The 1H
pyrazolo[5,1-b]quinazolin-8(4H)-ones (Biginelli-type dihydro- NMR revealed a singlet signal at δ = 6.70 ppm integrated for
pyrimidines) [9]. Employing more nucleophilic bases to one proton, which was assigned to the pyrazoloquinazolone C3
catalyse the reaction afforded the corresponding pyrazolo[4,3- proton, and which indicates the lack of involvement of such a
c]quinazolin-9-ones [20]. It was concluded that, under ambient proton in the condensation leading to the tricyclic system.
and neutral conditions, the reaction proceeds under kinetic Although, it was previously reported [20] that, due to reduced
control, and the Biginelli-type dihydropyrimidines are the steric hindrance, the multicomponent reaction of 5-amino-3-
predominant isomers. Increasing the reaction temperature in the methyl-pyrazole, aromatic aldehydes and dimedone under
presence of triethylamine as base produces the more thermody- controlled microwave irradiation at 150 °C involves the partici-
namically stable dihydropyridine (Hantzsch-type product). In pation of C3-H of the pyrazole ring in such a cyclocondensa-
addition, the nature of the catalyst plays an important role [20]. tion reaction, this is not favoured in our case. In addition two
Table 1: Microwave-assisted synthesis of 4 and 6.
entry
compound
5-aminopyrazole, 1;
cyclic 1,3-diketone, 2;
2a; R2 = CH3
2b; R2 = H
product
6a
yield (%)
88
1
2
3
4
5
6
7
1a
1a
1b
1c
1d
1e
1f
R = CH3,
R1 = H
R = CH3,
R1 = H
6b
85
R = NH2,
R1 = CO2Et
2b; R2 = H
6c
89
R = CH3,
R1 = C6H5
2a; R2 = CH3
2b; R2 = H
6d
83
R = C6H5,
R1 = H
6e
82
R = C6H5,
R1 = H
2a; R2 = CH3
2a; R2 = CH3
6f
83
R = OH,
6g
84
R1 = C6H5N=N–
19

Beilstein J. Org. Chem. 2012, 8, 18–24.
Figure 1: ORTEP diagram of compound 6a.
Scheme 1: Microwave-assisted synthesis of 4 and 6.
Figure 2: ORTEP diagram of compound 5.
signals were assigned to two CH2 groups and three methyl func-
tions, and a singlet at δ = 8.75 ppm corresponding to one proton
at C5. The pyrazolo[1,5-a]-quinazolin-8(5H)-one 6a was estab-
lished as the reaction product, and 13C NMR was in agreement
with the proposed structure, rather than with isomeric 4a, which
was prepared by first reacting 1a with dimedone (2a) in DMF
under microwave heating at 150 °C for 10 min to afford 5.
Subsequently, treating compound 5 with DMFDMA (3), under
the same experimental conditions, gave compound 6a in excel-
lent yield (Scheme 1 and Table 1). Furthermore, the structures
of compounds 5 and 6a were unambiguously confirmed by
single-crystal X-ray diffraction [25,26] (Figure 1, Figure 2 and
Table 1, Table 2, Table 3).
Compound 6g was also obtained by an alternative route: Com-
pound 8 was prepared by reacting enaminone 7 with
5-aminopyrazole derivative 1f in DMF under microwave
heating at 150 °C for 2 min (Table 1). When this compound was
refluxed in DMF under microwave heating for 13 min it under-
Table 2: Selected bond lengths and bond angles for compound 6a.
bond lengths
bond angles
atom
numbers
geometric
parameter
(Å)
atom
numbers
geometric
parameter (°)
N1–C8
N1–C7
N2–C10
N3–C8
N3–C1
N1–C6
N6–C7
1.372 (3)
1.309(3)
1.344 (3)
1.397 (3)
1.490 (3)
1.377 (3)
1.421 (3)
C7–N1–C8
N2–N3–C1
C1–N3–C8
N3–C1–C6
116.15 (19)
125.03 (16)
122.51 (18)
116.10 (17)
With this result in hand, we went on to study the scope of such
multicomponent reactions with several substituted 5-aminopy-
razoles and cyclic 1,3-diketones. Thus, the reaction of 1b–f with
2a,b and 3, under the same experimental conditions, afforded
the corresponding pyrazolo[5,1-b]quinazolin-8(5H)-ones 6b–g,
respectively. The structures of 6b–g were deduced from their
1H NMR, 13C NMR, mass spectra and elemental analyses.
C8–C9–C10 106.29 (17)
C1–C6–C5
N1–C7–C6
N1–C8–C9
119.42 (19)
124.5 (3)
133.29 (19)
N3–N2–C10 103.65 (17)
N2–N3–C8
N1–C8–N3
112.41(16)
121.56 (18)
20

Beilstein J. Org. Chem. 2012, 8, 18–24.
Table 3: Selected bond lengths and bond angles for compound 6e.
bond lengths bond angles
geometric
Table 4: Selected bond lengths and bond angles for compound 6g.
bond lengths
bond angles
geometric
atoms
geometric
parameter
(Å)
atom
atoms
geometric
parameter
(Å)
atom
numbers
numbers
parameter (°)
numbers
numbers
parameter (°)
N3–C9
N3–C8
N1–C1
N2–C9
N2–C2
C2–C7
C7–C8
1.360 (3)
1.3147(3)
1.346 (3)
1.396 (3)
1.364 (3)
1.363 (3)
1.428 (3)
C8–N3–C9
N1–N2–C2
N2–C1–C3
N2–C2–C7
C1–C10–C9 120.9 (17)
C2–C7–C8
N3–C8–C7
116.10 (19)
124.94 (19)
124.71 (18)
116.23 (18)
N3–C4
N3–C3
N1–C6
N2–C4
N2–C1
C1–C7
C1–C2
1.330 (2)
1.321(19)
1.343 (17)
1.393 (18)
1.343 (19)
1.491 (2)
1.394 (2)
C3–N3–C4
N1–N2–C1
C1–N2–C4
N2–C1–C2
C4–C5–C6
116.18 (10)
124.04 (12)
121.41 (12)
116.52 (13)
105.52 (13)
124.7 (2)
105.78 (17)
C1–C2–C10 119.58 (13)
N3–C3–C2
N3–C4–C5
N2–N1–C6
N1–N2–C4
N2–C4–N3
123.90 (14)
132.56 (14)
104.27 (11)
114.50(11)
123.02 (13)
N3–C9–C10 133.37 (19)
N2–N1–C1
N1–N2–C9
N2–C9–N3
103.94 (14)
112.01(15)
120.99 (18)
went cyclization to give 6g (Scheme 1). Moreover, the struc- A proposed mechanism to account for the formation of prod-
ture of compounds 6b–g was unequivocally established by ucts 6 is illustrated in Scheme 2. The base-catalyzed reaction of
single-crystal X-ray diffraction of compounds 6e,g (Figure 3, cyclic 1,3-diketones 2 with DMFDMA 3 gave the enaminone 7,
Figure 4 and Table 3, Table 4) [27,28].
which subsequently reacted with 5-aminopyrazole 1 at the
Figure 3: ORTEP diagram of compound 6e.
Scheme 2: A proposed mechanism to account for the formation of
products 6. The factors that determine the nature of the end product
are, however, at present unclear.
Figure 4: ORTEP diagram of compound 6g.
21

Beilstein J. Org. Chem. 2012, 8, 18–24.
exocyclic amino function, followed by cyclization through 13C NMR (100 MHz, DMSO-d6) δ 14.55, 27.89, 32.36, 36.46,
water loss to give 6 (route A). Formation of isomeric product 4, 38.87, 50.08, 98.04, 112.39, 146.03, 149.34, 152.21, 157.52,
which would be formed by route B, was ruled out based on 194.82; EIMS m/z: 229.1 (M+), 214, 173, calcd. for C13H15N3O
spectral and X-ray diffraction data.
229.28; Anal. calcd for C13H15N3O: C, 68.1; H, 6.59; N, 18.33;
found: C, 68.22; H, 6.62; N, 18.35%.
From the data of the X-ray crystal structure it can be concluded
that the bridged head nitrogen has bond angles closer to those of 2-Methyl-8,9-dihydropyrazolo[5,1-b]quinazolin-6(7H)-one
sp3 nitrogen. One may thus conclude that the lone pair on this (6b): Yellow plates, 170 mg (85% yield); mp 154–155 °C; 1H
nitrogen atom does not contribute much to the actual state of the NMR (400 MHz, DMSO-d6) δ 2.21–2.27 (m, 2H, CH2 at C-8),
molecule and that charge-separated ions also do not contribute 2.66 (t, J = 6.8 Hz, 2H, CH2 at C-9), 3.40 (t, J = 6.4 Hz, 2H,
significantly; although, the pyrazolo[5,1-b]quinazolin ring is CH2 at C-7), 6.71 (s,1H, CH at C-3), 8.77 (s, 1H, CH at C-5);
almost planar.
13C NMR (100 MHz, DMSO-d6) δ 14.53, 19.95, 33.37, 36.54,
97.91, 113.3, 146.3, 149.0, 153.9, 157.42, 194.81; EIMS m/z
201.12 (M+), calcd for C11H11N3O 201.22; Anal. calcd for
Conclusion
In summary, we can reveal that the reaction of substituted C11H11N3O: C, 65.66; H, 5.51; N, 20.88; found: C, 65.68; H,
5-aminopyrazoles, cyclic 1,3-diketones and dimethyformamide 5.49; N, 20.67%.
dimethylacetal (DMFDMA, 3) proceeds by initial attack of the
exocyclic amino function. Although an attack by the ring Ethyl 2-amino-6-oxo-6,7,8,9-tetrahydropyrazolo[5,1-
nitrogen has been proposed for the reaction of 5-aminopyra- b]quinazolin-3-carboxylate (6c): Yellow crystals, 243 mg
zoles with acrylonitrile [29], here steric factors hinder such an (89% yield); mp 184–185 °C; 1H NMR (400 MHz, DMSO-d6)
attack and the reaction occurs exclusively, in every case δ 1.31 (t, J = 7.2 Hz, 3H, CH3), 2.10–2.20 (m, 2H, CH2 at C-8),
studied, at the amino function.
2.63 (t, J = 6.8 Hz, 2H, CH2 at C-9), 3.25 (t, J = 6.8 Hz, 2H,
CH2 at C-7), 4.31 (q, J = 6.8 Hz, 2H, CH2), 6.7 (br s, 2H, NH2),
8.82 (s, 1H, CH at C-5); EIMS m/z 274.1 (M+), 228, 174.1,
Experimental
General information. All the reactions were carried out in a calcd for C13H14N4O3 274.28; Anal. calcd for C13H14N4O3: C,
Milestone START Microwave Labstation (temperature control 56.93; H, 5.14; 20.43; found: C, 57.12; H, 5.23; N, 20.45%
by IR sensor). 1H NMR (400 MHz) and 13C NMR (100 MHz)
spectra were measured on a Bruker DPX instrument by using 2,8,8-Trimethyl-3-phenyl-8,9-dihydropyrazolo[5,1-b]quina-
DMSO-d6 as solvent and TMS as internal standard. Chemical zolin-6(7H)-one (6d): Pale yellow crystals, 253 mg (83%
shifts are expressed as δ in ppm. Coupling constants (J) are yield); mp 279–280 °C; 1H NMR (400 MHz, DMSO-d6) δ 1.15
given in Hertz (Hz). The melting points were measured in a (s, 6H, 2 CH3), 2.49 (s, 2H, CH2 at C-9), 2.58 (s, 3H, CH3 at
Gallenkamp melting-point apparatus and are not corrected. C-2), 2.63 (s, 2H, CH2 at C-7), 7.13–7.55 (m, 5H, Ph-H), 8.83
Mass spectra were measured by using VG Autospec Q MS 30 (s, 1H, CH at C-5); 13C NMR (100 MHz, DMSO-d6) δ 14.41,
and MS 9 (AEI) spectrometer with the EI (70 eV) mode.
24.42, 27.90, 36.42, 38.87, 50.15, 112.99, 119.22, 125.88,
126.67, 128.30, 129.20, 132.43, 140.64, 144.52, 159.05,
194.70; EIMS m/z 305.2 (M+), 299, 179.1, calcd for
C19H19N3O 305.37; Anal. calcd for C19H19N3O: C, 74.73; H,
General procedure for the synthesis of pyra-
zoloquinazolinones (6a–g)
A solution of 5-aminopyrazole derivative 1a–f (1 mmol), cyclic 6.27; N, 13.76; found: C, 74.66; H, 6.35, N, 13.82%.
1,3-diketones (2a,b) (1 mmol) and dimethylformamide
dimethylacetal (DMFDMA, 3) (1 mmol) in DMF (10 mL) was 2-Phenyl-8,9-dihydropyrazolo[1,5-a]quinazolin-6(7H)-one
heated under reflux in a Milestone Microwave Labstation at 150 (6e): Pale yellow crystals, 215 mg (82% yield); mp 197–198
°C for 15 min. After concentration and cooling to room °C; 1H NMR (400 MHz, DMSO-d6) δ 2.25 (m, 2H, CH2 at
temperature, the resulting solid product so formed was collected C-8), 2.64 (t, J = 5.6 Hz, 2H, CH2 at C-9), 3.41 (t, J = 5.6 Hz,
by filtration, washed well with EtOH, dried and recrystallized 2H, CH2 at C-7), 7.39 (br s, 1H, CH at C-3), 7.48 (m, 3H,
from EtOH.
Ph-H), 8.08 (d, J = 7.2 Hz, 2H, Ph-H), 8.78 (s, 1H, CH at C-5);
13C NMR (100 MHz, DMSO-d6) δ 19.97, 23.46, 36.63, 79.19,
2,8,8-Trimethyl-8,9-dihydropyrazolo[5,1-b]quinazolin- 95.49, 114.10, 126.44, 129.0, 129.69, 131.85, 146.77, 149.69,
6(7H)-one (6a): Greenish yellow plates, 201 mg (88% yield); 154.39, 157.60, 162.32, 194.84; EIMS m/z 263.1 (M+), 235.1,
mp 134–135 °C; 1H NMR (400 MHz, DMSO-d6) δ 1.12 (s, 6H, 152.1, calcd. for C16H13N3O 263.11; Anal. calcd for
2CH3), 2.48 (s, 3H, CH3), 2.56 (s, 2H, CH2 at C-9), 3.32 (s, 2H, C16H13N3O: C, 72.99; H, 4.98; N, 15.96; found: C, 72.94; H,
CH2 at C-7), 6.70 (s, 1H, CH at C-3), 8.75 (s, 1H, CH at C-5); 5.18; N, 16.32%.
22

Beilstein J. Org. Chem. 2012, 8, 18–24.
8,8-Dimethyl-2-phenyl-8,9-dihydropyrazolo[1,5-a]quina- Alternative synthesis of 6g: Synthesis of 2-((3-hydroxy-4-
zolin-6(7H)-one (6f): Pale yellow crystals, 242 mg (83% (phenyldiazenyl)-1H-pyrazol-5-ylamino)methylene)-5,5-
yield); mp 244–245 °C; 1H NMR (400 MHz, DMSO-d6) δ 1.18 dimethylcyclohexane-1,3-dione (8): A solution of 1f (1
(s, 6H, 2 CH3), 2.59 (s, 2H, CH2 at C-9), 3.44 (s, 2H, CH2 at mmol), enaminone 7 (1 mmol) in DMF (10 mL) was heated
C-7), 7.34 (s, 1H, CH at C-3), 7.50 (m, 3H, Ph-H), 8.09 (m, 2H, under reflux in a Milestone Microwave Labstation at 150 °C for
Ph-H), 8.81 (s, 1H, CH at C-5); 13C NMR (100 MHz, DMSO- 2 min. After concentration and cooling to room temperature, the
d6) δ 28.47, 32.73, 37.17, 50.86, 95.94, 113.79, 127.02, 129.29, precipitated product was collected by filtration, washed well
129.97, 132.53, 146.90, 150.61, 152.87, 158.37, 194.85; Anal. with EtOH, dried and recrystallized from EtOH to give a pure
calcd for C18H17N3O: C, 74.20; H, 5.88; N, 14.42; found: C, sample of 8 as orange crystals, 303 mg (88% yield); mp
74.32; H, 5.91; N, 14.44%.
255–256 °C; 1H NMR (400 MHz, DMSO-d6) δ 1.01 (s, 6H, 2
CH3), 2.40 (s, 2H, CH2), 3.26 (s, 2H, CH2), 7.24–7.85 (m, 6H,
2-Hydroxy-8,8-dimethyl-3-(phenyldiazenyl)-8,9-dihydropy- 5 Ph-H and CH-NH), 11.76 (s, 1H, NH), 12.59 (s, 1H, pyrazole
razolo[1,5-a]quina-zolin-6(7H)-one (6g): Orange crystals, 295 NH); 13C NMR (100 MHz, DMSO-d6) δ 27.95, 30.70, 50.12,
mg (88% yield); mp 254–255 °C; 1H NMR (400 MHz, DMSO- 109.66, 115.16, 115.74, 121.31, 126.16, 129.32, 129.64, 129.80,
d6) δ 1.14 (s, 6H, 2 CH3), 2.66 (s, 2H, CH2 at C-9), 3.26 (s, 2H, 144.34, 148.97, 152.57, 158.40, 194.23, 195.33; EIMS m/z
CH2 at C-7), 7.45 (t, J = 7.2 Hz, 1H, Ph-H), 7.55 (t, J = 7.6 Hz, 353.2 (M+), 335.1, 242.1, calcd. for C18H19N5O3 353.15; Anal.
2H, Ph-H), 7.85 (d, J = 7.6 Hz, 2H, Ph-H), 8.95 (s, 1H, CH at calcd for C18H19N5O3: C, 61.18; H, 5.42; N, 19.82; found: C,
C-5); 13C NMR (100 MHz, DMSO-d6) δ 27.96, 32.25, 36.44, 61.23; H, 5.45; N, 19.92%.
50.14, 79.20, 115.14, 115.74, 121.33, 129.34, 129.80, 144.26,
148.99, 151.95, 152.61, 162.10, 194.3; EIMS m/z 335.1 (M+), Cyclization of 8. A solution of 8 (1 mmol) in DMF (10 ml) was
307.1, 258.1, calcd for C18H17N5O2 335.14; Anal. calcd for heated under reflux in a Milestone Microwave Labstation at 150
C18H17N5O2: C, 64.47; 5.11; 20.88; found: C, 64.43; 5.33; °C for 13 min. The reaction mixture was evaporated to dryness
20.95%.
in vacuo. The precipitated solid product was filtered off,
washed with a small amount of EtOH, dried and recrystallized
from EtOH to give an analytical pure sample of 6g (identical
with an authentic sample, MS, 1H NMR and 13C NMR).
Synthesis of (Z)-5,5-dimethyl-3-[(3-methyl-
1H-pyrazol-5-yl)amino]cyclohexanone (5)
A solution of 1a (1 mmol) and 2a (1 mmol) in DMF (10 mL)
was heated under reflux in a Milestone Microwave Labstation Acknowledgements
at 150 °C for 10 min. After concentration and cooling to room K. U. Sadek is grateful to the Alexander von Humboldt Founda-
temperature, the resulting solid product so formed was collected tion for donation of a Milestone START Microwave Labstation,
by filtration, washed well with EtOH, dried and recrystallized which was of great help in finishing this work. M. H. Elnagdi
from EtOH to afford a pure sample of compound 5 as yellow and Moustafa Sherief Moustafa are grateful to Kuwait Univer-
crystals, 186 mg (85% yield); mp 233–235 °C.
sity Research Administration for the financial support of project
SC1/10, and the analytical facilities provided by SAF projects
Synthesis of 4a: A solution of 1a (1 mmol) and 2a (1 mmol) in No. GS 03/08 (Single crystal X-ray crystallography-Rigaku
DMF (10 mL) was heated under reflux in a Milestone Rapid II) & GS 01/01 & GS 01/03 & GS 01/05 are greatly
Microwave Labstation at 150 °C for 10 min. After concentra- appreciated.
tion and cooling to room temperature, the resulting solid pro-
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Reaction of 5 with dimethylformamide dimethylacetal
(DMFDMA, 3): A solution of 5 (1 mmol) and DMFDMA (3)
(1 mmol) in DMF (10 mL) was heated under reflux in a Mile-
stone Microwave Labstation at 150 °C for 10 min. After evap-
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25.CCDC 825123 contains the supplementary crystallographic data for
compound 6a. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk
26.CCDC 833076 contains the supplementary crystallographic data for
compound 5. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk
27.CCDC 827653 contains the supplementary crystallographic data for
compound 6e. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk
28.CCDC 826742 contains the supplementary crystallographic data for
compound 6g. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk
24