May-Jun 2007
Synthesis and reactivity of pyrazolo[3',4':4,5]pyrimido[1,6-a]benzoimidazolo-5-one
705
of piperidine (3 drops) was boiled under relux for 2 hrs. The
resulting solid was collected and recrystallized from N,N-
dimethylformamide to give 10 (Tables 1 and 2).
razolo[3,4-d]-pyrimidine-3-carboxylate (19). Its
mass spectrum showed peaks m/z at = 380 (3.3%,
M+2), 379 (23.3%, M+1), 378 (100%, M), 306
(17%), 254 (39.2%), 182 (17.5%) and 90 (16.8%).
Synthesis of Benzimidazolo[1'',2'':1',6']pyrimidino[4',5':
4,3]-pyrazolo[1,5-a]pyrimidine derivatives 14, 15, 17and 19.
Diazonium chloride 13 (which was prepared via addition sodium
nitrite solution (0.35g, (5 mmol), 10 mL water) to a mixture of 3
(2.15 g, 5 mmol), acetic acid (1 mL) and hydrochloric acid (3 mL,
6 M)) at 0°C) was added dropwise to a cold solution of each of
2,4-pentandione, ethyl 3-oxobutanoate, malononitrile or ethyl
cyanoacetate (5 mmol each), sodium acetate (1 g) in ethanol (50
mL) while stirring at 0-5°C. The reaction mixture was stirred 3 hrs
the resulting solid was collected and recrystallized from acetic
acid to give 14, 15, 17 and 19, respectively (Tables 1 and 2).
EXPERIMENTAL
All melting points were determined on an electrothermal
apparatus and are uncorrected. IR spectra were recorded (KBr
1
discs) on a Shimadzu FT-IR 8201 PC spectrophotometer. H
NMR spectra were recorded in CDCl3 or (CD3)2SO solutions on
a Varian Gemini 300 MHz spectrometer and chemical shifts are
expressed in ꢀ units using TMS as an internal reference. Mass
spectra were recorded on a GC-MS QP1000 EX Shimadzu.
Elemental analyses were carried out at the Microanalytical
Center of the Cairo University
REFERENCES AND NOTES
Synthesis of 2-methyl-3-(methylsulfanyl)-1-oxo-1,2-
dihydroyrimido[1,6-a]benzimidazo-4-carbonitrile (2). A
mixture of 2-(1-ethoxycarbonoyl)benzimidazolylacetonitrile,
methyl isothiocyanate, potassium hydroxide (5 mmol each) in
N,N-dimethylformamide (15 mL) was stirred for 6 hrs.
Iodomethane (0.72 g, 5 mmol) was added while stirring and the
reaction mixture was stirred for 2 hrs. The resulting solid was
collected and recrystallized from N,N-dimethylformamide to
give 2 (Tables 1 and 2).
Synthesis of 1-amino-4-methyl-3,4-dihydro-5H-pyrazolo-
[3',4':4,5]pyrimido[1,6-a]benzoimidazolo-5-one (3). A mixture
of 2 (2.18 g, 5 mmol) and hydrazine hydrate (1 mL, 99%) in
ethanol (20 mL) was boiled under reflux for 4 hrs. The resulting
solid was collected and recrystallized from acetic acid to give 3
(Tables 1, 2).
Synthesis of 4, 6 and 7. Equimolar amounts aminopyrazole 3
and the appropriate 2,4-pentandione, ethyl acetoacetate (or aceto-
acetanilide) or ethyl benzoylacetate (or benzoylacetanilide) (5
mmol) in acetic acid (20 mL) were heated under reflux for 3 hrs.
The resulting solid was collected and recrystallized from N,N-
dimethylformamide to give 4, 6 and 7, respectively (Tables 1 and 2).
Synthesis of 9 and 12. Equimolar amounts of aminopyrazole 3
and the appropriate ꢁ-substituted cinnamonitrile (5 mmol each) in
ethanol (20 mL) containing catalytical amount of piperidine (3
drops) was boiled under reflux for 2 hrs. The resulting solid was
collected and recrystallized from N,N-dimethylformamide to give
9 and 12, respectively (Tables 1 and 2).
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5-(1-Aza-2-phenylvinyl)-2-methyl-2,10b-dihydrobenzimi-
dazolo[1,2-e]pyrazolo[4,3-d]pyridine-1-one (10). Equimolar
amounts of aminopyrazole 3 and the appropriate benzaldehyde
(5 mmol each) in ethanol (20 mL) containing catalytical amount