A Simple and Efficient Procedure for the Synthesis of Amidoalkyl Naphthols by p-TSA in Solution or under Solvent-Free Conditions

Abstract

An efficient and direct procedure for the synthesis of amidoalkyl naphthols has been described that employs a three-component condensation reaction in one pot using aromatic aldehydes, β-naphthol and ureas or amides in the presence of p-toluene sulfonic acid in 1,2-dichloroethane at room temperature or under solvent-free conditions at elevated temperature.

Key words

amidoalkyl naphthol - one-pot reaction - condensation - β-naphthol - aryl aldehyde - solvent-free

References and Notes

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9

General Experimental Procedure (Method A).
A mixture of aromatic aldehyde (1 mmol), β-naphthol
(1 mmol), urea or amide (1.1 mmol) and p-TSA (0.1 mmol) in 1,2-dichloroethane (2 mL) at r.t. was stirred for the time as shown in Table [3] . The progress of the reaction was monitored by TLC. On completion, the reaction mixture was filtered and the precipitate washed with H₂O. The crude products were purified by recrystallization from EtOH-H₂O (1:3) and the pure products were obtained in 83-96% yields.

10

General Experimental Procedure (Method B).
A mixture of aromatic aldehyde (1 mmol), β-naphthol
(1 mmol), urea or amide (1.1 mmol) and p-TSA (0.1 mmol) was magnetically stirred at 125 °C for the appropriate time as indicated in Table [3] . The reaction was followed by TLC. After completion, the reaction mixture was washed with H₂O. The pure products were obtained by recrystallization using EtOH-H₂O (1:3) in 80-95% yields.

11

Selected Characterization Data.
Table 3, entry 1: IR (neat): ν_max = 3456, 3360, 3200-2240, 1632, 1580, 1513, 1430, 1370, 1238, 816 cm^-1. ¹H NMR (200 MHz, DMSO-d ₆): δ = 10.30 (s, 1 H), 7.88-7.71 (m, 3 H), 7.45-7.10 (m, 7 H), 6.90 (s, 2 H), 5.85 (s, 2 H). ¹³C NMR (50 MHz, DMSO-d ₆): δ = 159.4, 153.7, 144.4, 132.9, 131.2, 130.1, 129.5, 129.2, 129.0, 128.7, 128.5, 127.5, 123.4, 120.5, 119.3, 48.5. MS (EI): m/z (%) = 266 (6), 231 (14), 202 (10), 172 (18), 144 (100), 115 (57), 60 (52), 44 (70).
Table 3, entry 6: IR (neat): ν_max = 3380, 3250-2800, 1625, 1580, 1535, 1430, 1360, 1240, 815 cm^-1. ¹H NMR (200 MHz, DMSO-d ₆): δ = 10.16 (s, 1 H), 8.07-6.96 (m, 12 H), 6.43 (s, 1 H), 2.61 (d, J = 3.72 Hz, 3 H). ¹³C NMR (50 MHz, DMSO-d ₆): δ = 159.4, 153.8, 148.5, 148.0, 133.5, 132.9, 130.5, 130.4, 129.6, 129.2, 127.8, 123.5, 123.3, 122.0, 121.0, 120.1, 119.3, 49.0, 27.2. MS (EI): m/z (%) = 260 (4), 229 (17), 207 (100), 144 (23), 115 (33), 77 (40), 58 (70).
Table 3, entry 19: IR (neat): ν_max = 3390, 3300-2800, 1648, 1620, 1517, 1418, 1322, 1262, 1062, 970, 820 cm^-1. ¹H NMR (200 MHz, DMSO-d ₆): δ = 10.16 (s, 1 H), 8.80 (d, J = 7.91 Hz, 1 H), 7.91-7.78 (m, 3 H), 7.44-7.18 (m, 8 H), 6.75-6.60 (m, 1 H), 6.10 (d, J = 16.99 Hz, 1 H), 5.60 (d, J = 10.40 Hz, 1 H). ¹³C NMR (50 MHz, DMSO-d ₆): δ = 165.0, 154.2, 142.3, 133.1, 132.5, 131.7, 130.5, 129.5, 129.3, 128.9, 128.8, 127.4, 126.8, 124.0, 123.4, 119.3, 119.0, 48.5. MS (EI): m/z (%) = 339 (2) [M + 2], 337 (7) [M], 266 (40), 231 (64), 202 (54), 144 (64), 115 (54), 101 (63), 71 (25), 55 (100).