A Clean One-pot Synthesis of Tetrahydrobenzo[b]pyran Derivatives Catalyzed by Hexadecyltrimethyl Ammonium Bromide in Aqueous Media

Abstract

An efficient and convenient approach to the synthesis of 2-amino-3-cyano-4-aryl-7,7-dimethyl-5-oxo-4H-5,6,7,8-tetra­hydrobenzo[b]pyran derivatives using hexadecyltrimethyl ammonium bromide (HTMAB) as the catalyst (10 mol%) is described. This method provides several advantages such as neutral conditions, high yields and simple work-up procedure, in addition water was chosen as a green solvent.

Key words

tetrahydrobenzo[b]pyran - hexadecyltrimethyl ammonium bromide - aqueous media

References

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13

General Coupling Procedure: A mixture of an aromatic aldehyde (1, 1 mmol), malononitrile (2, 1 mmol), 5,5-dimethyl-1,3-cyclohexadion (3, 1 mmol) and HTMAB (10 mol%) in H₂O (20 mL) was stirred at 85-90 °C for 3 h. Then the mixture was cooled to r.t., solid was filtered off and washed with H₂O (40 mL). The crude products were purified by recrystallization with EtOH (95%). Liquid aldehydes were distilled before use. IR spectra were recorded on a Bio-Rad FTS-40 spectrometer (KBr). ¹H NMR spectra were measured on a Bruker AVANCE 400 (400 MHz) spectrometer using TMS as internal reference and CDCl₃ or DMSO as solvent. Data of some compounds are shown below:
Compound 4a. IR (KBr): ν_max = 3390, 3290, 2935, 2200, 1685, 1600 cm^-1. ¹H NMR: δ = 0.98 (3 H, s, CH₃), 1.05 (3 H, s, CH₃), 2.15 (1 H, d, J = 16.0 Hz, 8-H), 2.24 (1 H, d, J = 16.0 Hz, 8-H), 2.45-2.55 (2 H, m, 6-H), 4.32 (1 H, s, 4-H), 6.08 (2 H, s, NH₂), 7.15-7.30 (5 H, m, ArH) ppm.
Compound 4b. IR (KBr): ν_max = 3332, 3185, 2965, 2200, 1662, 1558 cm^-1. ¹H NMR: δ = 0.98 (3 H, s, CH₃), 1.04 (3 H, s, CH₃), 2.08 (1 H, d, J = 16.0 Hz, 8-H), 2.24 (1 H, d, J = 16.0 Hz, 8-H), 2.46-2.57 (2 H, m, 6-H), 4.59 (1 H, s, 4-H), 7.02 (2 H, s, NH₂), 7.15-7.36 (4 H, m, ArH) ppm.
Compound 4c. IR (KBr): ν_max = 3390, 3290, 3180, 2190, 1660, 1585 cm^-1. ¹H NMR: δ = 1.05 (3 H, s, CH₃), 1.12 (3 H, s, CH₃), 2.26 (2 H, s, 8-H), 2.46-2.49 (2 H, m, 6-H), 4.41 (1 H, s, 4-H), 4.58 (2 H, s, NH₂), 7.18-7.28 (4 H, m, ArH) ppm.
Compound 4d. IR (KBr): ν_max = 3410, 3310, 3005, 2200, 1695, 1605 cm^-1. ¹H NMR: δ = 0.95 (3 H, s, CH₃), 1.04 (3 H, s, CH₃), 2.10 (1 H, d, J = 16.0 Hz, 8-H), 2.25 (1 H, d, J = 16.0 Hz, 8-H), 2.47-2.55 (2 H, m, 6-H), 4.20 (1 H, s, 4-H), 7.08 (2 H, s, NH₂), 7.17 (2 H, d, J = 8.0 Hz, ArH), 7.35 (2 H, d, J = 8.0 Hz, ArH) ppm.
Compound 4e. IR (KBr): ν_max = 3450, 3310, 3005, 2200, 1695, 1605 cm^-1. ¹H NMR: δ = 0.97 (3 H, s, CH₃), 1.08 (3 H, s, CH₃), 2.14 (2 H, m, 8-H), 2.46 (2 H, s, 6-H), 5.05 (1 H, s, 4-H), 5.97 (2 H, s, NH₂), 7.47-7.95 (4 H, m, ArH) ppm.
Compound 4f. IR (KBr): ν_max = 3400, 3300, 3195, 2200, 1695, 1600 cm^-1. ¹H NMR: δ = 1.01 (3 H, s, CH₃), 1.06 (3 H, s, CH₃), 2.26 (2 H, s, 8-H), 2.46-2.52 (2 H, m, 6-H), 4.52 (1 H, s, 4-H), 4.98 (2 H, s, NH₂), 7.42-7.98 (4 H, m, ArH) ppm.
Compound 4g. IR (KBr): ν_max = 3400, 3300, 3190, 2200, 1690, 1600 cm^-1. ¹H NMR: δ = 1.02 (3 H, s, CH₃), 1.05 (3 H, s, CH₃), 2.26 (2 H, s, 8-H), 2.48-2.54 (2 H, m, 6-H), 4.54 (1 H, s, 4-H), 5.05 (2 H, s, NH₂), 7.45-8.05 (4 H, m, ArH) ppm.
Compound 4h. IR (KBr): ν_max = 3357, 3250, 3163, 2191, 1664, 1558 cm^-1. ¹H NMR: δ = 1.05 (3 H, s, CH₃), 1.10 (3 H, s, CH₃), 2.15-2.23 (2 H, m, 8-H), 2.44 (2 H, s, 6-H), 4.26 (1 H, s, 4-H), 5.34 (2 H, s, NH₂), 6.75-7.13 (4 H, m, ArH) ppm.
Compound 4i. IR (KBr): ν_max = 3310, 3255, 2895, 2192, 1673, 1596 cm^-1. ¹H NMR: δ = 1.04 (3 H, s, CH₃), 1.10 (3 H, s, CH₃), 2.20-2.24 (2 H, m, 8-H), 2.40 (2 H, s, 6-H), 3.88 (3 H, s, OCH₃), 4.31 (1 H, s, 4-H), 5.25 (2 H, s, NH₂), 6.59-6.78 (3 H, m, ArH), 6.85 (1 H, s, OH) ppm.
Compound 4j. IR (KBr): ν_max = 3377, 3186, 2964, 2198, 1681, 1655, 1596 cm^-1. ¹H NMR: δ = 0.95 (3 H, s, CH₃), 1.03 (3 H, s, CH₃), 2.09 (1 H, d, J = 16.0 Hz, 8-H), 2.24 (1 H, d, J = 16.0 Hz, 8-H), 2.46-2.56 (2 H, m, 6-H), 3.71 (3 H, s, OCH₃), 4.17 (1 H, s, 4-H), 6.84 (2 H, d, J = 8.0 Hz, ArH), 6.95 (2 H, s, NH₂), 7.05 (2 H, d, J = 8.0 Hz, ArH) ppm.
Compound 4k. IR (KBr): ν_max = 3390, 3300, 3180, 2200, 1690, 1600 cm^-1. ¹H NMR: δ = 1.01 (3 H, s, CH₃), 1.04 (3 H, s, CH₃), 2.25 (2 H, s, 8-H), 2.47-2.52 (2 H, m, 6-H), 2.95 (6 H, s, 2 N-CH₃), 4.42 (H, s, 14-H), 4.66 (2 H, s, NH₂), 7.14-7.25 (4 H, m, ArH) ppm.
Compound 4l. IR (KBr): ν_max = 3426, 3330, 2957, 2193, 1678, 1640, 1601 cm^-1. ¹H NMR: δ = 0.95 (3 H, s, CH₃), 1.04 (3 H, s, CH₃), 2.09 (1 H, d, J = 16.0 Hz, 8-H), 2.24 (1 H, d, J = 16.0 Hz, 8-H), 2.26 (3 H, s, CH₃), 2.45-2.56 (2 H, m, 6-H), 4.12 (1 H, s, 4-H), 6.96 (2 H, s, NH₂), 7.02 (2 H, d, J = 8.0 Hz, ArH), 7.08 (2 H, d, J = 8.0 Hz, ArH) ppm.
Compound 4m. IR (KBr): ν_max = 3372, 3203, 2935, 2204, 1654, 1608 cm^-1. ¹H NMR: δ = 0.96 (3 H, s, CH₃), 1.03 (3 H, s, CH₃), 2.12 (1 H, d, J = 16.0 Hz, 8-H), 2.24 (1 H, d, J = 16.0 Hz, 8-H), 2.46-2.57 (2 H, m, 6-H), 4.17 (1 H, s, 4-H), 5.97 (2 H, s, OCH₂O), 6.97 (2 H, s, NH₂), 7.02-7.15 (3 H, m, ArH) ppm.