Month 2018
Regioselectivity in the Reaction of 2-Aminobenzoylthiazoles and 2-
Aminobenzimidazoles with Enaminonitriles and Enaminones
An alternative route to 6a,b and 9 was found in reacting
7a,b with malononitrile or ethyl cyanoacetate in DMF
(10 mL) in the presence of catalytic amount of
anhydrous K2CO3 (10 mol%). The reaction mixture was
1H, J = 7.6 Hz, Ar–H), 7.55–7.48 (m, 2H, Ar–H),
7.42–7.34 (m, 3H, Ar–H), 7.27–7.19 (m, 2H, Ar–H).
Anal. Calc. for C16H11N3S (277.34): C, 69.29; H, 4.00;
N, 15.15; S, 11.56. Found: C, 69.33; H, 4.11; N, 14.84;
S, 11.52.
heated under reflux for
3 h. After cooling and
evaporation to dryness in vacuo, the remaining product
was triturated with ethanol, and the crude product
obtained was collected by filtration and crystallizes from
the proper solvent to afford analytically pure samples
identical with 6a,b and 9.
4-Iminopyrimido[2,1-b]benzothiazol-3-carbonitrile 6a.
Crystals from ethanol, m.p. 188–190°C. Yield 80%, EST-
MS: m/z = 226.0 (M+, 100%). IR max/cmꢀ1: 3246 (imine
NH), 2221 (CN), 1622 (C═N). 1H NMR (DMSO-d6,
δ ppm) = 9.41 (br s, 1H, NH), 8.21 (s, 1H, H-2), 8.15–
8.077 (m, 2H, Ar–H), 7.64–7.55 (m, 2H, Ar–H). 13C NMR
(DMSO-d6, δ ppm) = 94.01, 115.54, 120.77, 122.77,
124.08, 126.81, 127.10, 136.51, 153.32, 153.73, 166.86.
Anal. Calc. for C11H6N4S (226.26): C, 58.39; H, 2.67; N,
3-Phenyl-2H-benzo[d]pyrimido[2,1-b][1,3]thiazol-2-one
13. Crystals from benzene, m.p. 259–267°C. Yield 75%,
EST-MS: m/z = 270 (M+, 90%). IR max/cmꢀ1: 1676
(C═O). 1H NMR (DMSO-d6, δ ppm) = 9.04 (t, 1H,
J = 5.2 Hz, Ar–H), 8.27 (s, 1H, H-4), 8.11 (t, 1H,
J = 5.2 Hz, Ar–H), 7.77 (d, 2H, J = 7.6 Hz, Ar–H),
7.62 (t, 2H, J = 7.6 Hz, Ar–H), 7.49 (t, 2H, Ar–H),
7.43–7.39 (m. 1H, Ar–H). 13C NMR (DMSO-d6,
δ ppm) = 119.74, 120.81, 123.54, 124.98, 127.34,
127.70, 128.21, 128.68, 129.08, 133.84, 136.50, 150.25,
160.17, 161.39. Anal. Calc. for C16H10N2OS (278.33):
C, 69.05; H, 3.62; N, 10.06; S, 11.52. Found: C, 69.21;
H, 3.76; N, 10.26; S, 11.40.
3-Phenyl-1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidin-2-
one 14. Crystals from dioxane, m.p. 278–280°C. Yield
24.76; S, 14.17. Found: C, 58.33; H, 2.63; N, 24.66; S, 14.15.
4-Aminopyrimido[1,2-a]benzimidazole-3-carbonitrile 6b.
76%, EST-MS: m/z = 261.10 (M+, 24.3%). IR max/cmꢀ1
:
3170 (NH), 1643 (C═O). 1H NMR (DMSO-d6,
δ ppm) = 10.53 (br s, 1H, NH), 8.53 (d, 1H, J = 8.4 Hz,
Ar–H), 8.22 (s, 1H, H-4), 7.76–7.73 (m, 2H, Ar–H),
7.53–7.44 (m, 6H, Ar–H). Anal. Calc. for C16H11N3O
(261.20): C, 73.55; H, 4.24; N, 16.08. Found: C, 73.60;
H, 4.20; N, 16.18.
Crystals from dioxane, m.p. > 300°C. Yield 75%, EST-
MS: m/z = 209.0 (M+, 100%). IR max/cmꢀ1: 3313 (NH2),
2220 (CN), 1648 (C═N). 1H NMR (DMSO-d6,
δ ppm) = 8.75 (br s, 2H, NH2), 8.57–8.52 (m, 2H, Ar–H),
7.77 (s, 1H, H-2), 7.54–7.52 (m, 1H, Ar–H), 7.41–7.35 (m,
1H, Ar–H). Anal. Calc. for C11H7N5 (209.21): C, 63.15; H,
3.37; N, 33.48. Found: C, 63.22; H, 3.35; N, 33.52.
2H-Benzo[d]pyrimido[2,1-b][1,3]thiazol-2-one
15.
Ethyl 3-(benzo[d]thiazol-2-ylamino)-2-cyanoacrylate 8.
Crystals from ethanol, m.p. 164–165°C. Yield 83%,
EST-MS: m/z = 273.0 (M+, 76%). IR max/cmꢀ1: 3202
(NH), 2223 (CN), 1716 (ester C═O) 1686 (C═N). 1H
NMR (DMSO-d6, δ ppm) = 12.4 (br s, 1H, NH), 8.85 (s,
1H, ylidene C–H), 7.98 (d, 1H, J = 7.6 Hz Ar–H), 7.79 (d,
1H, J = 8 Hz Ar–H),7.48–7.44 (m, 1H, Ar–H), 7.35–7.31
(m, 1H, Ar–H), 4.26 (q, 2H, J = 7.2 Hz OCH2), 1.27 (t,
3H, J = 7.2 Hz CH3). Anal. Calc. for C13H11N3O2S
(273.05): C, 57.13; H, 4.06; N, 15.37; S, 11.73. Found: C,
57.21; H, 4.07; N, 15.42; S, 11.66.
Crystals from benzene, m.p. 128–131°C. Yield 76%, EST-
MS: m/z = 202 (M+, 15%). IR max/cmꢀ1: 1637 (C═O). 1H
NMR (DMSO-d6, δ ppm) = 7.64 (d, 1H, J = 7.3 Hz, H-4),
7.42–6.84 (m, 4H, Ar–H), 6.97 (d, 1H J = 7.3 Hz, H-3).
Anal. Calc. for C10H6N2OS (202.23): C, 59.39; H, 2.99; N,
13.85; S, 15.85. Found: C, 59.45; H, 3.02; N, 13.77; S, 15.74.
Benzo[4,5]imidazo[1,2-a]pyrimidin-2-ylamine
16.
Crystals from ethanol, m.p. 293–295°C. Yield 82%, EST-
MS: m/z = 185 (M+, 100%). IR max/cmꢀ1: 3430 (NH2),
1
1682 (C═N). H NMR (DMSO-d6, δ ppm) = 12.8 + 8.42
(two s, 2H, NH2), 7.95 (d, 1H, J = 6.9 Hz, H-4), 7.55–
7.28 (m, 4H, Ar–H), 5.95 (d, 1H, J = 6.9 Hz, H-3). Anal.
Calc. for C10H8N4 (184.20): C, 65.20; H, 4.38; N, 30.42.
4-Oxo-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-
carbonitrile 9.
Crystals from benzene, m.p. > 300°C.
Yield 83%, EST-MS: m/z = 209.0 (M+, 76%). IR
max/cmꢀ1: 3104 (NH), 2221 (CN), 1664 (C═O). 1H
NMR (DMSO-d6, δ ppm) = 8.58 (s, 1H, H-2), 8.43 (br s,
1H, NH), 8.43 (d, J = 7 Hz, 1H, NH), 7.62–7.58 (m, 2H,
Ar–H), 7.55–7.48 (m, 2H, Ar–H). Anal. Calc. for
C11H6N4O (209.19): C, 63.16; H, 2.41; N, 26.78. Found:
C, 62.90; H, 2.45; N, 26.55.
Found: C, 64.70; H, 4.42; N, 30.11.
2-Amino-4-phenylbenzo[4,5]imidazo[1,2-a]pyrimidine-3-
carbonitrile 21. Crystals from ethanol, m.p. 220–222°C.
Yield 74%, EST-MS: m/z = 285 (M+, 17%). IR
1
max/cmꢀ1: 3423 (NH2), 2220 (CN). H NMR (DMSO-
d6, δ ppm) = 8.53 (s, 2H, NH2), 7.96–7.93 (m, 4H, Ar–
H), 7.71–7.58 (m, 5H, Ar–H). Anal. Calc. for C17H11N5
(285.31): C, 71.57; H, 3.89; N, 24.55. Found: C, 71.55;
H, 3.78; N, 24.65.
3-(Benzo[d]thiazol-2-ylamino)-2-phenylacrylonitrile 11.
Crystals from ethanol, m.p. 168–177°C. Yield 79%,
EST-MS: m/z = 277.0 (M+, 90%). IR max/cmꢀ1: 3395
Benzo[4,5]imidazo[1,2-a]pyrimidine 22.
Crystals from
1
ethanol, m.p. > 300°C. Yield 78%, EST-MS: m/z = 169
(NH), 2223 (CN). H NMR (DMSO-d6, δ ppm) = 11.5
1
(M+, 100%). H NMR (DMSO-d6, δ ppm) = 9.52–6.87
(d, 1H, J = 11.6 Hz, NH), 8.35 (d, 1H, J = 11.6 Hz
ylidene C–H), 7.85 (d, 1H, J = 7.6 Hz, Ar–H), 7.64 (d,
(m, 7H, Ar–H, H-2, H-3 and H-4). Anal. Calc. for
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet