Cheap thiamine hydrochloride as efficient catalyst for…
General procedure for synthesis of 4H-benzo[b]pyrans
An equimolar (2 mmol) mixture of aromatic aldehyde (1), malononitrile (2), various
1
,3-cyclohexanediones (3, 5, or 7), and thiamine hydrochloride was vigorously
stirred at 50 °C for specific time as indicated in Tables 2, 3, and 4. The end of the
reaction was monitored by thin-layer chromatography (TLC). Then, the crude
product obtained was poured into water. The precipitated resulting solid was
purified by recrystallization from hot methanol to afford pure product 4, 6, or 8. All
products are known, and their data found to be identical with those reported
elsewhere in literature. The spectral data of selected products are given below.
2
3
1
-Amino-4-(4-chlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-
-
1
-carbonitrile (4d) IR (KBr, m, cm ): 3381, 3184, 2961, 2189, 1675, 1636, 1604,
1
516, 1490; H NMR (300 MHz, DMSO-d ) d: 1.07 (s, 3H, CH ), 1.15 (s, 3H,
6
3
CH ), 2.27 (s, 2H, CH ), 2.44 (s, 2H, CH ), 4.38 (s, 1H, CH), 7.12 (d, 2H,
3
2
2
J = 8.5 Hz, Ar–H), 7.13 (d, 2H, J = 8.5 Hz, Ar–H) ppm; HRMS EI (m/z): calcd for
C H ClN O , 328.0979; found, 328.0973.
1
8
17
2 2
2
3
1
-Amino-4-(4-methoxyphenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-
-
1
-carbonitrile (4j) IR (KBr, m, cm ): 3329, 3265, 3043, 2957, 2192, 1677, 1641,
1
602, 1511, 1463; H NMR (300 MHz, DMSO-d ) d: 1.03 (s, 3H, CH ), 1.09 (s, 3H,
6
3
CH ), 2.21 (s, 2H, CH ), 2.38 (s, 2H, CH ), 3.78 (s, 3H, OCH ), 6.83 (d, 2H,
J = 8.6 Hz, Ar–H), 7.13 (d, 2H, J = 8.6 Hz, Ar–H) ppm; HRMS EI (m/z): calcd for
C H N O , 324.1474; found, 324.1468.
3
2
2
3
1
9 20 2 3
2
-Amino-4-(4-nitrophenyl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile
-
1
1
(
6b) IR (KBr, m, cm ): 3451, 3308, 3182, 2189, 1682, 1598, 1505, 1365. H
NMR (300 MHz, DMSO-d ) d: 1.79–2.00 (m, 2H, CH ), 2.11–2.22 (m, 2H, CH ),
6
2
2
2
2
.33–2.46 (m, 2H, CH ), 6.99 (s, 2H, NH ), 4.11 (s, 1H, CH), 7.14 (d, J = 8.2 Hz,
2 2
H, ArH), 7.16 (d, J = 8.2 Hz, 2H, ArH) ppm; HRMS EI (m/z): calcd for
C H N O , 311.0906; found, 311.0901.
16 13 3 4
7
-Amino-5-(4-methylphenyl)-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrano[2,3-d]pyrim-
-
1
idine-6-carbonitrile (8h) IR (KBr, m, cm ): 3432, 3346, 3263, 3172, 3063, 2205,
1
1
722, 1681, 1674, 1588; H NMR (300 MHz, DMSO-d ) d: 2.25 (s, 3H, CH ), 4.17
6
3
(
HRMS EI (m/z): calcd for C H N O , 296.0909; found, 296.0902.
s, 1H, CH), 7.07 (m, 6H, ArH, NH ), 11.05 (s, 1H, NH), 12.06 (s, 1H, NH) ppm;
2
1
4 9 4 3
Results and discussion
We firstly examined the activity of the catalysts in condition of dimedone (2 mmol),
-bromobenzaldehyde (2 mmol), and malononitrile (2 mmol) with catalyst C1–C5
10 mol%) in EtOH–H O (95:5) at 80 °C for 6 h, obtaining yield of 58 % (C1),
4
(
2
5
3 % (C2), 61 % (C3), 79 % (C4), and 68 % (C5). We thereby selected catalyst C4
(
EtOH to H O; the results are summarized in Table 1. In presence of catalyst C4
thiamine hydrochloride, VB ) and examined the activity for different ratios of
1
2
123