Synthesis of derivatives of 4,5-dihydroimidazo[1,2-a]phenanthroline [5]

Full text of DOI:10.1007/s10593-007-0107-9

Chemistry of Heterocyclic Compounds, Vol. 43, No. 5, 2007
SYNTHESIS OF DERIVATIVES OF 4,5-DIHYDRO-
IMIDAZO[1,2-a]PHENANTHROLINE
K. G. Nazarenko1, T. I. Shirokaya2, and K. V. Shvidenko1
Keywords: ω-bromoacetophenone, 4,5-dihydroimidazo[1,2-a][1,10]phenanthroline, 1,10-phenanthro-
line, 1-phenacyl-1,10-phenanthrolinium salts.
A simple and effective method for the synthesis of derivatives of a new heterocyclic system –
4,5-dihydroimidazo[1,2-a][1,10]phenanthroline – is proposed, based on the use of phenacyl-1,10-phenanthro-
linium salts (2), obtained by the alkylation of 1,10-phenathroline (1) with ω-bromoacetophenone [1-3]. It was
found that boiling these salts in the presence of excess ammonium acetate with subsequent treatment of the
reaction mixture with hydrobromic acid led to the closing of the imidazole ring to give 2-aryl-
4,5-dihydroimidazo[1,2-a][1,10]phenanthroline hydrobromides. The latter were converted into the
O
4
5
Br
3
6
2
R
7
N
1
+
N
N 10
Br
O
8
N
9
1
–
R1NH2
2a,b
R
R1
2. Et3N, DMF
N
N
1. AcONH4
+
N
5
–
6
Br
7
4
8
N
N
R
3
4a,b
1
N
9
11
2
10
3a,b
2, 3 a R = H, b R = Br; 4 a R = H, R1 = p-MeC6H4, b R = Br, R1 = p-MeC6H4
R
__________________________________________________________________________________________
1Institute of Organic Chemistry, Ukraine National Academy of Sciences, Kiev 02094; e-mail:
shved@i.com.ua. 2National Agrarian University, Kiev 03041, Ukraine; e-mail: shyrokaya@rambler.ru.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, 5, 790-792, May, 2007. Original article submitted
September 6, 2006. Revised version submitted March 20, 2007.
0009-3122/07/4305-0667©2007 Springer Science+Business Media, Inc.
667

corresponding bases 3a,b on treatment with excess triethylamine in DMF. Treatment of compounds 2 with a
two-fold excess of an aromatic amine gave quaternary salts of 2-aryl-4,5-dihydroimidazo[1,2-a][1,10]-
phenanthroline 4a,b.
All compounds were obtained in high yields (85-97%).
1H NMR spectra of DMSO-d6 with TMS as internal standard were recorded with a Varian VXR-300
(300 MHz) instrument.
2-Phenyl-4,5-dihydro-3,11,11c-triazacyclopenta[c]phenanthrene (3a). Compound 2a (7 g, 18 mmol)
and anhydrous ammonium acetate (2.8 g, 36 mmol) were boiled in glacial acetic acid (4.2 ml) for 3 h and cooled.
The precipitate was triturated with conc. HBr (10 ml) and diluted with water (200 ml). The precipitate was
filtered off, washed with water and dried. Triethylamine (20 ml) was added to a suspension of the hydrobromide
in DMF (4 ml), shaken energetically, and diluted with water (200 ml), the precipitated crystals were filtered off,
1
washed with water, dried, and recrystallized from benzene. Yield 3.8 g (95%); mp 156-157°C. H NMR
spectrum, δ, ppm (J, Hz): 3.13 (2H, t, J = 6.0, 4-CH2); 3.20 (2H, t, J = 6.0, 5-CH2); 7.24 (1H, m, C6H5); 7.41
(2H, m, C6H5); 7.60 (1H, q, J = 6.0, H-9); 7.64 (1H, d, J = 7.8, H-6); 7.84 (1H, d, J = 7.8, H-7); 7.86 (2H, m,
C6H5); 8.43 (1H, d, J = 8.1, H-8); 9.06 (1H, d, J = 3.9, H-10); 9.28 (1H, s, H-1). Found: C 80.92; H 5.14;
N 14.04. C20H15N3. Calculated, %: C 80.78; H 5.08; N 14.13.
2-(4-Bromophenyl)-4,5-dihydro-3,11,11c-triazacyclopenta[c]phenanthrene (3b) was obtained
1
analogously to compound 3a. Yield 85%; mp 128-129°C (benzene). H NMR spectrum, δ, ppm (J, Hz): 3.10
(2H, t, J = 6.0, 4-CH2); 3.20 (2H, t, J = 6.0, 5-CH2); 7.57 (2H, d, J = 8.1, C6H4); 7.60 (1H, q, J = 6.0, H-9), 7.65
(1H, d, J = 7.8, H-6); 7.81 (2H, d, J = 8.1, C6H4); 7.85 (1H, d, J = 7.8, H-7); 8.44 (1H, d, J = 8.1, H-8); 9.06 (1H,
d, J = 3.9, H-10); 9.31 (1H, s, H-1). Found: C 63.78, Br 21.36; N 11.08. C20H14BrN3. Calculated, %: C 63.85;
Br 21.24; N 11.17.
2-Phenyl-3-p-tolyl-4,5-dihydro-3,11,11c-triazacyclopenta[c]phenanthrenium
Bromide
(4a).
Compound 2a (3g, 8 mmol) and p-toluidine (1.71 g, 16 mmol) in glacial acetic acid (1.8 ml) were boiled for 3 h
and cooled. The mixture was triturated with conc. HBr (4 ml) and then diluted with water (100 ml). The
precipitated crystals were filtered off, washed with water, dried and recrystallized from a 2-propanol – ethyl
acetate mixture. Yield 3.63 g (97%); mp 283-284°C. 1H NMR spectrum, δ, ppm (J, Hz): 2.41 (3H, s, CH3); 3.22
(2H, t, J = 6.0, 5-CH2); 3.43 (2H, t, J = 6.0, 4-CH2); 7.06 (2H, d, J = 8.1, C6H5); 7.37 (2H, m, C6H5); 7.43 (3H,
m, C6H5); 7.53 (2H, d, J = 8.1, C6H5); 7.74 (1H, q, J = 4.5, H-9); 7.81 (1H, d, J = 8.1, H-6); 8.17 (1H, d, J = 8.1,
H-7); 8.63 (1H, d, J = 8.1, H-8); 9.14 (1H, d, J = 3.9, H-10); 9.68 (1H, s, H-1). Found, %: C 69.35; Br 17.17;
N 8.84. C27H22BrN3. Calculated, %: C 69.24; Br 17.06; N 8.97.
2-(4-Bromophenyl)-3-p-tolyl-4,5-dihydro-3,11,11c-triazacyclopenta[c]phenanthrenium
Bromide
(4b) was obtained analogously to compound 4a. Yield 95%, mp 255-256°C (a mixture of 2-propanol and ethyl
acetate). 1H NMR spectrum, δ, ppm (J, Hz): 2.42 (3H, s, CH3); 3.22 (2H, t, J = 6.0, 5-CH2); 3.41 (2H, t, J = 6.0,
4-CH2); 7.30 (2H, d, J = 8.1, C6H4); 7.45 (2H, d, J = 8.1, C6H4); 7.52 (2H, d, J = 8.1, C6H4); 7.66 (2H, d, J = 8.1,
C6H4); 7.74 (1H, q, J = 4.5, H-9); 7.81 (1H, d, J = 8.1, H-6); 8.17 (1H, d, J = 8.1, H-7); 8.62 (1H, d, J = 8.1,
H-8); 9.13 (1H, d, J = 3.9, H-10); 9.72 (1H, s, H-1). Found,%: C 59.16; Br 29.19; N 7.52. C27H21Br2N3.
Calculated, %: C 59.23; Br 29.25; N 7.68.
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