Palladium-Catalyzed Amidocarbonylation Improved by Recyclable Ionic Liquids

Abstract

Two types of ionic liquids (halide anion ionic liquids and Brønsted acidic ionic liquids) were first applied to improve the palladium-catalyzed amidocarbonylation. Both the palladium catalyst and the ionic liquids could be recycled at least five times without significant loss in catalytic activity.

Key words

amidocarbonylation - ionic liquids - amino acids - palladium - catalysis

References and Notes

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12

General Procedure and Recycling Process:
A 60-mL autoclave with a magnet-driven propeller stirrer was used for the high-pressure amidocarbonylation. Aldehyde (20 mmol), amide (22 mmol), PdBr₂ (0.2 mmol), PPh₃ (0.2 mmol), Brønsted acidic ionic liquid (2 mmol), and [emim]Br (25 mL) were transferred into the autoclave and allowed to react under 60 bar CO at 100 °C for 15 h. After the reaction the recycling process began with refluxing the reaction mixture with THF (3 × 30 mL). Then the THF phases were combined and the volatile components were removed in a rotary evaporator, and the residue was taken up in a sat. aq solution of NaHCO₃, and then washed with CHCl₃ and EtOAc. The aqueous phase was adjusted to pH 2 with phosphoric acid and extracted with EtOAc. Then the organic phases were combined and dried over MgSO₄, and the solvent was removed in vacuum. The product was purified by recrystallization with a suitable solvent mixture. The remaining ionic liquid was dried in vacuum and then poured into the autoclave reactor containing fresh aldehyde (20 mmol), amide (22 mmol) and Brønsted acidic ionic liquid (2 mmol) for the next run, but there was no need to add [emim]Br, PdBr₂ or PPh₃. Finally the reaction was restarted.
N-Benzoyl-α-cyclohexylglycine (b): white solid; mp 193-196 °C. ¹H NMR (400 MHz, DMSO-d ₆): δ = 12.56 (s, 1 H), 8.42 (d, J = 7.6 Hz, 1 H), 7.88-7.90 (m, 2 H), 7.44-7.55 (m, 3 H), 4.32 (t, J = 7.6 Hz, 1 H), 1.59-1.87 (m, 6 H), 1.08-1.18 (m, 5 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 173.2, 166.9, 134.2, 131.3, 128.2, 127.7, 57.9, 29.4, 28.8, 25.7, 25.6. MS: m/z = 105 (100), 261 [M⁺], 262 [M + 1]. IR (KBr): 3292, 2920, 2853, 1702, 1638, 1535, 1334, 1276, 932, 697 cm^-1.
N-Acetyl-α-norvaline (d): white solid; mp 111-114 °C. ¹H NMR (400 MHz, DMSO-d ₆): δ = 8.07 (d, J = 7.6 Hz, 1 H), 4.17 (q, J = 7.6 Hz, 1 H), 1.83 (s, 3 H), 1.50-1.65 (m, 2 H), 1.26-1.31 (m, 2 H), 0.83-0.87 (t, 3 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 174.0, 169.4, 51.6, 33.2, 22.3, 18.7, 13.5. MS: m/z = 72 (100), 159 [M⁺], 160 [M + 1]. IR (KBr): 3345, 2962, 2936, 2875, 2456, 1928, 1717, 1595, 1543, 1237, 997, 612 cm^-1.
N-Acetyl-α-phenylglycine (f): white solid; mp 199-201 °C. ¹H NMR (400 MHz, DMSO-d ₆): δ = 12.34 (s, 1 H), 8.65 (d, J = 7.6 Hz, 1 H), 7.32-7.42 (m, 5 H) 5.37 (d, J = 7.6 Hz, 1 H), 1.91 (s, 3 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 172.2, 169.3, 137.4, 128.7, 128.1, 127.8, 56.4, 22.4. MS:
m/z = 106 (100), 193 [M⁺], 194 [M + 1]. IR (KBr): 3342, 3032, 2484, 1922, 1716, 1602, 1544, 1258, 1179, 1003, 719, 614 cm^-1.
N-Acetyl-α-phenylalanine (h): white solid; mp 171-173 °C. ¹H NMR (400 MHz, DMSO-d ₆): δ = 12.70 (s, 1 H), 8.21 (d, J = 8.0 Hz, 1 H), 7.18-7.30 (m, 5 H), 4.39-4.45 (m, 1 H), 3.03-3.07 (q, 1 H), 2.81-2.87 (q, 1 H), 1.79 (s, 3 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 173.2, 169.3, 137.8, 129.1, 128.2, 126.5, 53.6, 36.8, 22.4. MS: m/z = 148 (100), 207 [M⁺], 208 [M + 1]. IR (KBr): 3331, 2913, 2458, 1699, 1621, 1553, 1437, 1244, 978, 908, 704 cm^-1.
N-Acetyl-α-(α-naphthyl)glycine (i): white solid; mp: 222-224 °C. ¹H NMR (400 MHz, DMSO-d ₆): δ = 8.22 (d, 1 H), 7.90-8.08 (m, 3 H), 7.49-7.61 (m, 4 H), 6.12-6.14 (m, 1 H), 1.91 (s, 3 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 172.8, 170.3, 133.9, 133.7, 131.2, 129.2, 129.1, 127.3, 126.6, 126.1, 125.9, 123.7, 53.3, 22.6. MS: m/z = 156 (100), 243 [M⁺], 244 [M + 1]. IR (KBr): 3348, 2878, 2787, 2486, 1916, 1704, 1615, 1535, 1289, 1261, 776, 663 cm^-1.