3-(Benzimidazolyl-2)-2-iminocoumarins in reactions with aromatic aldehydes

Article abstract of DOI:10.1023/A:1022605930640

Interaction of 3-(benzimidazolyl-2)-2-iminocoumarins with aromatic aldehydes in the presence of piperidine gave the corresponding 7-aryl-7H-benzo[4,5]imidazo[1,2-c]benzopyrano[3,2-e]pyrimidines. The 3-diethylamino derivatives of this series fluoresce effe

Full text of DOI:10.1023/A:1022605930640

Chemistry of Heterocyclic Compounds, Vol. 38, No. 12, 2002
3-(BENZIMIDAZOLYL-2)-
2-IMINOCOUMARINS IN REACTIONS
WITH AROMATIC ALDEHYDES
N. Yu. Gorobets and V. V. Abakumov
Interaction of 3-(benzimidazolyl-2)-2-iminocoumarins with aromatic aldehydes in the presence of
piperidine gave the corresponding 7-aryl-7H-benzo[4,5]imidazo[1,2-c]benzopyrano[3,2-e]pyrimidines.
The 3-diethylamino derivatives of this series fluoresce effectively in alcohol solutions.
Keywords: 7-aryl-7H-benzo[4,5]imidazo[1,2-c]benzopyrano[3,2-e]pyrimidines, aromatic aldehydes,
3-(benzimidazolyl-2)-2-iminocoumarins, piperidine, fluorescence.
The spectral-luminescent properties of derivatives of 3-(benzimidazolyl-2)-2-iminocoumarins 1
have attracted the interest of investigators recently [1]. With the objective of modifying the structures of
these compounds we have investigated their reactions with aromatic aldehydes 2. It is known that similar
reactions may lead to different compounds [2, 3]. We have observed that when 3-(benzimidazolyl-2)-2-
iminocoumarins 1a-c reacted with an excess of aromatic aldehydes 2a-d in the presence of a catalytic amount of
piperidine, only 7-aryl-7H-benzo[4,5]imidazo[1,2-c]benzopyrano[3,2-e]pyrimidines 3a-d are formed in good
yields.
The rate of the reaction depends considerably on the nature of the substituents of the iminocoumarin
ring and the aldehyde. 7-Diethylamino-2-iminocoumarin (1c) reacts most readily with 5-methoxysalicylaldehyde
(2c). In this case the reaction is complete after refluxing for 30 min in propanol to give compound 3d. The
formation of compounds 3b and 3c from coumarin 1c and p-chlorobenzaldehyde (2a) and anisaldehyde 2b
respectively required a reaction time of 6 h. The reaction of compound 1a with aldehyde 2d to give compound
3a required 36 h refluxing in butanol. Similar reactions occur with aliphatic aldehydes, but the corresponding
products were almost never isolated in a pure state. Similarly the reaction of 2-iminocoumarins 1a and 1c with
p-nitrobenzaldehyde 2f and p-bromobenzaldehyde 2e respectively led only to hydrolysis of the imino group
(Scheme 1).
Ethanol solutions of compounds 3b-d, containing the 3-diethylamino group, fluoresce at λmax 502 (3b),
501 (3c), and 505 nm (3d) with quantum yields of fluorescence close to 100%. In the electronic absorption
1
spectra of these compounds the longwave band shows well expressed vibrational structure. In the H NMR
spectra of compounds 3b-d the singlet of the methyne proton at position 7 (7.3 ppm) is clearly shown only for
compound 3d. In the other compounds it is overlapped by the multiplet of the aromatic protons.
So the synthesized 7-aryl-7H-benzo[4,5]imidazo[1,2-c]benzopyrano[3,2-e]pyrimidines, containing the
3-NEt2 group are of interest for further study as luminescent dyes.
__________________________________________________________________________________________
V. N. Karazin Kharkov National University, Kharkov 61077, Ukraine; e-mail: nic@univer.kharkov.ua.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, 1719-1721, December, 2002. Original article
submitted October 5, 2001.
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0009-3122/02/3812-1518$27.00©2002 Plenum Publishing Corporation

Scheme 1
N
N
R
O
N
Ar
12
11
13
N
10
N
14
1
4
5
4
AlkOH, to
R 2
9
3
N
8
6
7
N
H
ArCHO
2a–d
+
2
R
3
piperidine
7
O
N
Ar
O
NH
5
6
8
1
3a–d
1a–c
N
O
2e,f
N
H
R
O
4a,b
1 a R = H; b R = 6-MeO; c R = 7-NEt2; 2 a Ar = p-ClC6H4; b Ar = p-MeOC6H4;
c Ar = 2-OH-5-MeOC6H3; d Ar = p-Me2NC6H4; e Ar = p-BrC6H4; f Ar = p-NO2C6H4;
3 a R = H; b–d R = 3-NEt2; a Ar = p-Me2NC6H4; b Ar = p-ClC6H4; c Ar = p-MeOC6H4;
d Ar = 2-OH-5-MeOC6H3; 4 a R = H; b R = 6-MeO
EXPERIMENTAL
Electronic absorption spectra were measured with Hitachi U-3210 spectrophotometer, fluorescence
spectra with a Hitachi U-4010 spectrophotometer. IR spectra of KBr tablets were recorded with a Specord IE-75
1
spectrometer. H NMR spectra were recorded on a Varian Mercury 200 (200 MHz) in DMSO-d6 with TMS as
internal standard. Purity of all compounds was monitored by TLC on Silufol 200×200 mm sheets with 1:2 ethyl
acetate–toluene as eluent.
TABLE 1. Reaction Times, Constants, and Yields of Compounds 3a-d
Com-
pound
Empirical
formula
Reaction
time, h
Found N, %
——————
mp, °С
Yield, %
Calculated N, %
C25H20N4O
C27H23ClN4O
C28H26N4O2
C28H26N4O3
14.35
14.28
269-270
276-278
260-261
271-272
36
6
80
65
60
85
3a
3b
3c
3d
12.26
12.31
12.34
12.44
6
12.10
0.5
12.01
1519

TABLE 2. Spectral Characteristics of Compounds 3a-d
IR spectrum, ν, cm-1
Com-
pound
UV spectrum,
λmax, nm, (ε)
1Н NMR spectrum, δ, ppm
C=C
C=N
C–H
213 (57000),
255 (23300),
385 (24500)
1600, 1668
1616
2804,
2884,
3056
8.3 (1H, s,14-H); 7.8-7.6 (2H, m, 1-, 10-H);
7.5 (1H, t, 11-H); 7.3-7.0 (8H, m, 2-, 3-, 4-,
7-, 9-, 12-H, 2-, 6-HAr); 6.6 (2H, d, 3-, 5-Ar);
2.8 (6H, s, NMe2)
3a
217 (56000),
295 (11700),
443 (57500)
1608
1676
2876,
2932,
3056
8.1 (1H, s, 14-H); 7.6 (1H, d, 12-H);
7.5 (1H, d, 9-H); 7.4-7.3 (5H, m, 1-, 7-,
10-H, 2-, 6-HAr); 7.2 (1H, m, 11-H);
7.1 (2H, d, 3-, 5-HAr); 6.6 (1H, d, 2-H);
6.5 (1H, s, 4-H); 3.4 (4H, q, N(CH2CH3)2);
1.1 (6H, t, N(CH2CH3)2)
3b
218 (55100),
297 (11200),
444 (58000)
1624
1676
2840,
2972,
3056
8.1 (1H, s, 14-H); 7.6 (1H, d, 12-H);
7.5 (1H, d, 9-H); 7.3-7.0 (6H, m, 1-, 7-, 10-,
11-H, 2-, 6-HAr); 6.9 (2H, d, 3-, 5-HAr);
6.6 (1H, d, 2-H); 6.4 (1H, s, 4-H);
3.7 (3H, s, OMe); 3.4 (4H, q, N(CH2CH3)2);
1.1 (6H, t, N(CH2CH3)2)
3c
213 (53100),
298 (14000),
440 (51000)
1608, 1676
1628
2876,
2976
9.3 (1H, s, OH); 8.1 (1H, s, 14-H);
7.6 (1H, d, 12-H); 7.5 (1H, d, 9-H);
7.3 (1H, s, 7-H); 7.2-7.0 (3H, m, 1-,
10-, 11-H); 6.8-6.6 (3H, m, 3-, 4-, 6-HAr);
6.6 (1H, d, 2-H); 6.4 (1H, s, 4-H);
3.6 (3H, s, OMe); 3.4 (4H, q, N(CH2CH3)2);
1.1 (6H, t, N(CH2CH3)2)
3d
c
e
7-Aryl-7H-benzo[4,5]imidazo[1,2- ]benzopyrano[3,2- ]pyrimidines (3a-d). (General Method).
An
aromatic aldehyde (3 mmol) was added to a solution of a 3-(benzimidazolyl-2)-2-iminocoumarin 1a-c (2 mmol)
in the minimum amount of boiling propanol or butanol, and boiling was continued for the time recorded in
Table 1. The mixture was cooled, the precipitate was filtered off and recrystallized from butanol.
Physico-chemical and spectral characteristics are given in Tables 1 and 2.
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1.
A. A. Karasev, L. L. Lukatskaya, M. I. Rubtsov, E. K. Zhikol, S. N. Yarmolenko, and O. A. Ponomarev,
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C. N. O'Callaghan, J. Chem. Soc., Perkin Trans. I, 1335 (1980).
W. Kuzmierkiewicz, Liebigs Ann. Chem., 541 (1987).
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3.
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