1H NMR spectra of DMSO-d6 solutions with TMS as internal standard were recorded with a Bruker DPX
200 (200 MHz) instrument, while IR spectra of nujol mulls were recorded on an IKS-40 spectrometer. Mass
spectra were recorded on a Varian 1200 L (70 eV) instrument. Purity of substances were tested by TLC on
Silufol UV-254 plates with 3:5 acetone–hexane eluent and developed with iodine vapor.
Indolizines 3a,b were prepared by method [1].
2-Amino-1-(2-benzimidazolyl)-3-benzoylindolizine (3a). Yield 30%; mp 249-250°C. IR spectrum,
ν, cm-1: 3488 (NH), 3308, 3166, 3132 (NH2), 1696 (CO). 1H NMR spectrum, δ, ppm (J, Hz): 11.97 (1H, s, NH);
9.57 (1H, d, J = 7.4, H-5); 8.12 (1H, d, J = 8.8, H-8); 7.37-7.58 (8H, m, Harom); 7.06-7.11 (2H, m, Harom); 6.85
(1H, t, J = 7.4, H-6); 6.39 (2H, br. s, NH2). Mass spectrum (EI), m/z (Irel,%): 352 [M]+ (100). Found, %: C 74.89;
H 4.51; N 16.00. C22H16N4O. Calculated, %: C 74.97; H 4.58; N 15.91.
2-Amino-1-(2-benzimidazolyl)-3-(4-methoxy)benzoylindolizine (3b). Yield 85%; mp. 235-237°C. IR
spectrum, ν, cm-1: 3446 (NH), 3300, 3174, 3104 (NH2), 1682 (CO). 1H NMR spectrum, δ, ppm (J, Hz): 11.95 (1H, s,
NH); 9.47 (1H, d, J = 6.9, H-5); 8.11 (1H, d, J = 8.8, H-8); 7.60 (2H, d, J = 8.6, H-2'arom,6'arom); 7.38-7.48 (3H, m, Harom);
7.02-7.11 (4H, m, Harom); 6.82 (1H, t, J = 6.9, H-6); 6.45 (2H, br. s, NH2); 3.89 (3H, s, CH3O). Mass spectrum (EI), m/z
(Irel, %): 3.82 [M+] (100). Found, %: C 72.31; H 4.67; N 14.75. C23H18N4O2. Calculated, %: C 72.22; H 4.75; N 14.66.
Preparation of Compounds 4a,b (General Method). The corresponding compound 3 (0.001 mmol) was
boiled in acetic anhydride (10 ml) for 3h. After 15-25 min a yellow precipitate began to separate from the boiling
acetic anhydride. After cooling the reaction mixture, the precipitate was filtered off, washed consecutively with acetic
acid (2×5 ml) and ethanol (2×10 ml) and dried with hexane.
1-Benzoyl-3-methylindolizino[2',1':4,5]pyrimido[1,6-a]benzimidazole (4a). Yield 95%; mp 298°C. IR
spectrum, ν, cm-1: 1662 (CO). 1H NMR spectrum, δ, ppm (J, Hz): 10.08 (1H, d, J = 6.8, H-13); 8.55 (1H, d, J = 8.5,
H-10); 8.05 (1H, d, J = 7.1, H-5); 7.78-7.89 (4H, m, Harom); 7.40-7.63 (6H, m, Harom); 2.84 (3H, s, CH3). Mass
spectrum (EI), m/z (Irel, %): 376 [M]+ (100). Found, %: C 76.49; H 4.36; N 14.80. C24H16N4O. Calculated, %:
C 76.57; H 4.29; N 14.89.
1-(4-Methoxybenzoyl)-3-methylindolizino[2',1':4,5]pyrimido[1,6-a]benzimidazole (4b). Yield 94%; mp
294-295°C. IR spectrum, ν, cm-1: 1684 (CO). 1H NMR spectrum, δ, ppm (J, Hz): 9.83 (1H, d, J = 6.5, H-13); 8.38 (1H,
d, J =8.3, H-10); 7.89-7.94 (3H, m, Harom); 7.82 (1H, d, J = 7.8, H-8); 7.63 (1H, t, J = 6.5, H-12); 7.48 (1H, t, J = 8.3, H-
11); 7.31 (2H, m, H-6,7); 7.05 (2H, d, J = 8.7, H-3'arom , 5'arom); 3.90 (3H, s, CH3O); 2.79 (3H, s, CH3). Mass spectrum
(EI), m/z (Irel, %): 406 [M]+ (100). Found, %: C 73.94; H 4.38; N 13.85. C25H18N4O2. Calculated, %: C 73.86; H 4.47;
N 13.79.
1-(4-Methoxybenzoyl)indolizino[2',1':4,5]pyrimido[1,6-a]benzimidazole (4c). Indolizine 3b (0.38 g,
0.001 mmol) was boiled in formic acid (8 ml) and acetic anhydride (2 ml) for 2 h.. On the following day the
precipitate was filtered off, washed sequentially with acetic acid (5 ml) and ethanol (2×10 ml), and dried with
1
hexane. Yield 57%; mp 284°C. IR spectrum, ν, cm-1: 1668 (CO). H NMR spectrum, δ, ppm (J, Hz): 9.90 (1H,
d, J = 7.1, H-13); 9.59 (1H, s, H-3); 8.58 (1H, d, J = 8.3, H-10); 8.25 (1H, d, J = 8.1, H-5); 7.78-7.89 (4H, m,
H
arom); 7.41-7.52 (3H, m, Harom); 7.06 (2H, d, J = 8.8, H-3'arom, 5'arom). Mass spectrum (EI), m/z (Irel,%): 392 [M]+
(100). Found, %: C 73.51; H 4.20; N 14.23. C24H16N4O2. Calculated, %: C 73.44; H 4.11; N 14.29.
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