BENZOID–QUINOID TAUTOMERISM OF SCHIFF BASES ... LV.
377
chromene-6-carbaldehyde (VII) and 5-hydroxy-4,7-di-
methyl-2-oxo-2H-chromene-6,8-dicarbaldehyde (X)
[10], and 6,7-dihydroxy-4-methyl-2-oxo-2H-chro-
mene-8-carbaldehyde (VIII) [11] were synthesized
according to known methods.
mp 222–224°C. IR spectrum, ν, cm–1: 1730, 1600.
1H NMR spectrum (CDCl3), δ, ppm: 2.60 s (3H, CH3),
2.72 s (3H, CH3), 7.03–7.51 m (7H, Harom), 9.00 d (1H,
N=CH, JHH = 4.4 Hz), 16.51 d.d [1H, OH, JHH = 4.4,
J(H–15N) = 39.0 Hz]. Found, %: C 73.25; H 6.03;
N 5.11. C18H15NO3. Calculated, %: C 73.49; H 6.12;
N 5.10.
5,7-Dihydroxy-4-methyl-2-oxo-2H-chromene-
6,8-dicarbaldehyde (IX). A mixture of 5.76 g
(30 mmol) of 4-methyl-5,7-dihydroxycoumarin, 7.38 g
(60 mmol) of p-anisidine, and 4.5 ml of triethyl ortho-
formate was heated for 5 h at 170°C. The dark yellow
precipitate was filtered off and dissolved in 250 ml of
acetic acid, 200 ml of 15% aqueous HCl was added,
and the mixture was heated for 20 min under reflux,
cooled, and diluted with 500 ml of water. The precip-
itate was filtered off, dried, and recrystallized from
acetic acid. The product was dissolved in acetone and
purified by column chromatography on silica gel using
acetone as eluent. Yield 35%, mp 168–170°C. IR spec-
6,7-Dihydroxy-4-methyl-8-[(2,3,5,6,8,9,11,12-
octahydrobenzo[b][1,4,7,10,13]pentaoxacyclopenta-
decin-15-yl)iminomethyl]-2H-chromen-2-one (IIIa).
Yield 64%, mp 188–190°C. IR spectrum, ν, cm–1:
3300, 1700, 1630. 1H NMR spectrum (CDCl3), δ, ppm:
2.35 s (3H, CH3), 3.84–4.30 m (16H, CH2O), 6.06 s
(1H, 3-H), 6.54 br.s (1H, OH), 6.95–7.02 m (4H,
H
arom), 9.08 s (1H, N=CH), 15.75 br.s (1H, OH).
Found, %: C 61.85; H 5.29; N 2.85. C24H24NO9. Cal-
culated, %: C 61.27; H 5.14; N 2.98.
6,7-Dihydroxy-4-methyl-8-[(15N)phenylimino-
methyl]-2H-chromen-2-one (IIIb). Yield 57%,
mp 230–232°C. IR spectrum, ν, cm–1: 3300, 1710,
1640. 1H NMR spectrum (CDCl3), δ, ppm: 2.36 s (3H,
CH3), 6.07 s (1H, 3-H), 6.59 br.s (1H, OH), 7.03–
7.58 m (6H, Harom), 9.20 s (1H, N=CH), 15.25 br.s (1H,
OH). Found, %: C 68.45; H 4.29; N 4.85. C17H13NO4.
Calculated, %: C 68.92; H 4.39; N 4.73.
1
trum, ν, cm–1: 1740, 1700, 1695. H NMR spectrum
(CDCl3), δ, ppm: 2.61 s (3H, CH3), 6.05 s (1H, 3-H),
10.28 s (1H, CHO), 10.34 s (1H, CHO), 13.73 s (1H,
OH), 14.45 s (1H, OH). Found, %: C 58.15; H 3.64.
C12H8O6. Calculated, %: C 58.07; H 3.25.
Schiff bases I–V (general procedure). A mixture of
4 mmol of aldehyde VI–X and 4 mmol of amino-
benzo-15-crown-5 or (15N)aniline in propan-2-ol was
heated for 5 h under reflux. The precipitate was filtered
off and recrystallized from DMF or DMF–propan-2-ol
(1:1) (IVa, IVb, Va).
(Z,E)-4-Methyl-6,8-bis[(2,3,5,6,8,9,11,12-octa-
hydrobenzo[b][1,4,7,10,13]pentaoxacyclopenta-
decin-15-yl)aminomethylidene]-2H-chromene-
2,5,7(6H,8H)-trione (IVa). Yield 36%, mp 134–
136°C. IR spectrum, ν, cm–1: 1747, 1645, 1622, 1600.
1H NMR spectrum (DMSO-d6), δ, ppm: Z isomer:
2.49 s (3H, CH3), 3.55–4.17 m (32H, CH2O), 5.80 s
(1H, 3-H), 6.92–7.18 m (6H, Harom), 8.52 d (1H, CHN,
J = 12.6 Hz), 8.71 d (1H, CHN, J = 13.2 Hz), 13.57 d
(1H, NH, J = 13.2 Hz), 14.21 d (1H, NH, J = 12.6 Hz);
E isomer: 2.55 s (3H, CH3), 3.55–4.17 m (32H,
CH2O), 5.80 s (1H, 3-H), 6.92–7.18 m (6H, Harom),
8.43 d (1H, CHN, J = 13.0 Hz), 8.65 d (1H, CHN, J =
13.8 Hz), 13.14 d (1H, NH, J = 13.8 Hz), 13.29 d
(1H, NH, J = 13.0 Hz). Isomer ratio Z/E ~2:1. Found,
%: C 61.50; H 5.48; N 4.01. C40H46N2O14. Calculated,
%: C 61.69; H 5.95; N 3.60.
3-Hydroxy-4-[(2,3,5,6,8,9,11,12-octahydrobenzo-
[b][1,4,7,10,13]pentaoxacyclopentadecin-15-yl)-
iminomethyl]-6H-benzo[c]chromen-6-one (Ia). Yield
56%, mp 218–220°C. IR spectrum, ν, cm–1: 1738,
1
1620. H NMR spectrum (CDCl3), δ, ppm: 3.68–
4.23 m (16H, CH2O), 6.89–8.36 m (9H, Harom), 9.33 s
(1H, N=CH), 15.15 s (1H, OH). Found, %: C 76.40;
H 4.65; N 4.20. C28H27NO8. Calculated, %: C 66.53;
H 5.38; N 2.77.
5-Hydroxy-4,7-dimethyl-6-[(2,3,5,6,8,9,11,12-
octahydrobenzo[b][1,4,7,10,13]pentaoxacyclo-
pentadecin-15-yl)iminomethyl]-2H-chromen-2-one
(IIa). Yield 43%, mp 215–217°C. IR spectrum, ν,
cm–1: 1720, 1610. 1H NMR spectrum (CDCl3), δ, ppm:
2.52 s (3H, CH3), 2.71 s (3H, CH3), 3.63–4.25 m (16H,
CH2O), 6.02–6.97 m (5H, Harom), 8.71 s (1H, N=CH),
16.47 s (1H, OH). Found, %: C 64.65; H 6.35; N 2.41.
C26H29NO8. Calculated, %: C 64.59; H 6.05; N 2.90.
4-Methyl-6,8-bis{(15N)phenylamino]methyli-
dene}-2H-chromene-2,5,7(6H,8H)-trione (IVb).
Yield 45%, mp 256–258°C. IR spectrum, ν, cm–1:
1
1744, 1645, 1608. H NMR spectrum (DMSO-d6), δ,
ppm: Z isomer: 2.65 s (3H, CH3), 5.82 s (1H, 3-H),
7.19–7.50 m (10H, Harom), 8.60–8.95 m (2H, CHN),
13.59 d.d and 13.94 d.d [1H, NH, JHH = 13.0,
J(H–15N) = 89.5 Hz], 13.82 d.d and 14.17 d.d [1H,
5-Hydroxy-4,7-dimethyl-6-[(15N)phenylimino-
methyl]-2H-chromen-2-one (IIb). Yield 55%,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013