Subsequent raising of the temperature to 50-60ºC leads to a spontaneous intramolecular cyclization
involving the enolic hydroxyl and the secondary amino group in the intermediate 4 to form the final compounds 3.
O
O
HO
HC
O
H2C
N
N
H
H
C
C
Ph
HN
CN
Ph
HN
CN
O
O
N
N
PhO
PhO
4b
1
4a
IR spectra were recorded on a UR-20 instrument in vaseline oil. H NMR spectra were taken on a
Mercury Plus 300 instrument (300 MHz) using CDCl3 with TMS as internal standard.
3-Oxo-2-(2-oxo-2-phenylethylidene)-1,2,3,4-tetrahydroquinoxalin-1-yl(N-cyano-O-phenyl)carbox-
imidate (3a). A solution of the N-(2-aminophenyl)-N'-cyano-O-phenylisourea (2) (1.26 g, 5 mmol) and
5-phenyl-2,3-dihydrofuran-2,3-dione (1a) (0.9 g, 5 mmol) in dioxane (30 ml) was stirred for 40 min at 50-60ºC
to give a yellow precipitate of compound 3a with mp 180-181ºC (2-propanol) in 63% yield. IR spectrum, ν,
cm-1: 1675 (C=O), 1665 (C=O), 2200 (C≡N), 3386 (NH). 1H NMR spectrum, δ, ppm: 7.05-8.10 (14H, m, C6H5);
6.90 (1H, s, =CH−); 12.28 (1H, s, NH). The spectroscopic data was closely similar to that for previously
obtained quinoxalines [3]. Found, %: C 70.9; H 4.0; N 13.6. C24H16N4O3. Calculated, %: C 70.6; H 3.9; N 13.7.
3-Oxo-2-(2-oxo-2-p-tolylethylidene)-1,2,3,4-tetrahydroquinoxalin-1-yl(N-cyano-O-phenyl)carbox-
imidate (3b) was prepared similarly from compounds 1b and 2. Yield 75%, mp 195-197ºC (2-propanol). IR
spectrum, ν, cm-1: 1670 (C=O), 1660 (C=O), 2195 (C≡N), 3380 (NH). 1H NMR spectrum, δ, ppm: 2.36 (3H, s,
CH3); 7.05-8.10 (13H, m, Ar); 6.90 (1H, s, =CH−); 12.28 (1H, s, NH). Found, %: C 71.2; H 4.1; N 13.4.
C25H18N4O3. Calculated, %: C 71.1; H 4.3; N 13.3.
This work was carried out with the support of the Russian Fund for Basic Research (project No. 08-03-
00488-a).
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