On the other hand, the reaction of 1-ethyl derivatives 2a,b with excess hydrazine or phenylhydrazine in
the presence of conc. HCl proceeds rather readily to give bicyclic pyrimidinones 3a,d.
The lack of reactivity of 1a is likely related to the acidic proton N(1)H and the tendency of this compound
to undergo amide-imidol tautomerization.
1
The H NMR spectra were taken on a Varian Mercury VX-200 spectrometer at 200 MHz in DMSO-d6
using TMS as the internal standard. The IR spectra were taken on a Specord-75 IR spectrometer for KBr pellets.
The mass spectra were taken on an Agillent mass spectrometer.
Pyrimidinones 1a,b, 2a,b were obtained according to our previous procedure [6].
Pyrimidinones 3a-d (General Method). A solution of 1(N)-alkyl derivative 2 (1.16 mmol),
corresponding hydrazine (11.6 mmol), and four drops of concentrated hydrochloric acid in ethanol (3 ml) was
heated at reflux for 3 h and left for 15-20 h. The crystalline precipitate was filtered off and washed thrice with
3-ml portions of 10:20:1 ethanol–water–piperidine.
7-Ethyl-3-methyl-4-phenyl-3a,4,5,6,7,7a-hexahydro-1H-pyrazolo[4,5-d]pyrimidin-6-one (3a). Yield
1
32%; mp 183-185°C (ethanol). IR spectrum, ν, cm-1: 1682, 2930, 3080, 3216, 3370. H NMR spectrum, δ, ppm
(J, Hz): 7.22 (1H, m, H-7a); 7.10-7.35 (5H, m, C6H5); 6.70 (1H, s, H-4); 6.0 (1H, br. s, N(1)H); 5.92 (1H, br. s,
N(5)H); 5.32 (1H, d, J = 3.2, H-3a); 3.28-3.62 (2H, m, CH2); 1.75 (3H, s, 3-CH3); 1.07 (3H, t, J = 7, CH2CH3).
Found, %: N 21.90. C14H18N4O. Calculated, %: N, 21.69.
7-Ethyl-3,7a-dimethyl-4-phenyl-3a,4,5,6,7,7a-hexahydro-1H-pyrazolo[4,5-d]pyrimidin-6-one (3b).
1
Yield 44%; mp 216-218°C (ethanol). IR spectrum, ν, cm-1: 1582, 1622, 2970. H NMR spectrum, δ, ppm
(J, Hz): 12.0 (1H, br. s, N(1)H); 7.09-7.5 (5H, m, C6H5); 6.34 (1H, d, J = 8.2, H-4); 5.86 (1H, d, J = 8.2, N(5)H);
5.77-5.95 (1H, m, H-3a); 2.90-3.15 (2H, m, CH2); 1.93 (3H, s, 3-CH3); 1.93 (3H, s, 7a-CH3); 0.98 (3H, t, J = 7,
CH2CH3). Mass spectrum (electron impact, 70 eV), m/z (Irel, %): 273 [M+1] (100), 203 (10). Found, %: N 20.92.
C15H20N4O. Calculated, %: N 20.57.
7-Ethyl-3-methyl-1,4-diphenyl-3a,4,5,6,7,7a-hexahydro-1H-pyrazolo[4,5-d]pyrimidin-6-one (3c).
1
Yield 22%; mp 185-187°C (ethanol). IR spectrum, ν, cm-1: 1602, 1682, 3080, 3223. H NMR spectrum, δ, ppm
(J, Hz): 8.89 (1H, s, N(5)H); 7.40-7.45 (1H, m, ArH); 7.25-7.35 (4H, m, ArH); 7.18 (1H, t, J = 6.4, ArH); 7.13
(2H, t, J = 7.6, ArH); 6.98 (2H, d, J = 7.6, ArH); 6.89 (1H, s, H-7a); 6.66 (1H, t, J = 7.2, H-4); 5.51 (1H, d,
J = 2.8, H-3a); 3.40-3.65 (2H, m, CH2); 1.98 (3H, s, 3-CH3); 1.14 (3H, t, J = 6.8, CH2CH3). Found, %: N 17.01.
C20H22N4O. Calculated. %: N, 16.75.
7-Ethyl-3,7a-dimethyl-1,4-diphenyl-3a,4,5,6,7,7a-hexahydro-1H-pyrazolo[4,5-d]pyrimidin-6-one (3d).
1
Yield 33%; mp 168-170°C (ethanol). IR spectrum, ν, cm-1: 1600, 1669, 2923, 3196. H NMR spectrum, δ, ppm
(J, Hz): 8.83 (1H, s, N(5)H); 6.93-7.38 (10H, m, ArH); 6.66 (1H, t, J = 7.0, H-4); 5.13 (1H, d, J = 2.4, H-3a);
3.3-3.9 (2H, m, CH2); 2.05 (3H, s, 3-CH3); 1.88 (3H, s, 7a-CH3); 1.05 (3H, t, J = 7.0, CH2CH3). Found, %:
N 16.33. C21H24N4O. Calculated, %: N 16.08.
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