Solvent-Free Synthesis of Alkylthiazolium-Based
Ionic Liquids and their Use as Catalysts in the Intramolecular Stetter
Reaction

Audrey Aupoix; Giang Vo-Thanh

doi:10.1055/s-0029-1217518

LETTER

Solvent-Free Synthesis of Alkylthiazolium-Based Ionic Liquids and their Use as Catalysts in the Intramolecular Stetter Reaction

Audrey Aupoix, Giang Vo-Thanh*
Laboratoire de Catalyse Moléculaire, Institut de Chimie Moléculaire et des Matériaux d’Orsay, UMR 8182, Université Paris-Sud 11, 91405 Orsay Cedex, France
Fax: +33(1)69154680; e-Mail: gvothanh@icmo.u-psud.fr;

Abstract

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Abstract

The first synthesis of alkylthiazolium-based ionic liquids under ‘green chemistry’ conditions is described. Thiazolium salts and triethylamine have been found to catalyze efficiently the intramolecular Stetter reaction, giving excellent yields within very short reaction times using solvent-free microwave activation conditions.

Key words

solvent-free reaction - microwave activation - ionic liquids - thiazolium salts - Stetter reaction

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Referenzen

References and Notes

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11 Ciganek E. Synthesis 1995, 1311

12

General Procedure for the Solvent-Free N-Alkylation of Thiazole under Microwave Irradiation: A mixture of thiazole 1 (85 mg, 1 mmol) and 1-iodoalkane 2 (1.5 mmol) was irradiated (CEM Discover reactor) at 150 ˚C for the appropriate time (see Table [¹] ). The reaction mixture was brought to room temperature and washed with Et₂O (2 × 10 mL). The crude product was dried under reduced pressure to afford a yellow powder which did not need further purification.
1-Butylthiazolium Iodide M.p. 101 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ = 0.99 (3 H, t, J = 7.5 Hz), 1.40-1.47 (2 H, m), 2.00-2.05 (2 H, m), 4.83 (2 H, t, J = 7.5 Hz), 8.28 (1 H, d, J = 2.6 Hz), 8.34 (1 H, d, J = 3.4 Hz), 10.95 (1 H, s). ^¹³C NMR (75 MHz, CDCl₃): δ = 13.9, 19.8, 32.9, 56.5, 127.5, 137.0, 159.6. IR (KBr): 3434, 3020, 2945, 1989, 1829, 1637, 1543, 1434, 1256, 1144, 952, 861, 639 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₇H₁₂NS: 142.0685; found: 142.0690.
1-Octylthiazolium Iodide M.p. 27 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ =0.74 (3 H, t, J = 7.2 Hz), 1.21-1.26 (10 H, m), 1.91-1.96 (2 H, m), 4.73 (2 H, t, J = 7.1 Hz), 8.4 (1 H, d, J = 3.4 Hz), 8.54 (1 H, d, J = 3.8 Hz), 10.69 (1 H, s). ^¹³C NMR (90 MHz, CDCl₃): δ = 14.0, 22.5, 26.1, 28.8, 28.9, 30.6, 31.6, 56.3, 127.8, 136.9, 158.6. IR (NaCl): 3445, 3046, 2926, 2855, 1621, 1551, 1463, 1422, 1262, 1154, 907, 833, 749, 634 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₁₁H₂₀NS: 198.1313; found: 198.1316.
1-Decylthiazolium Iodide M.p. 39 ˚C. ^¹H NMR (360 MHz, CDCl₃): δ = 0.79 (3 H, t, J = 6.1 Hz), 1.17-1.28 (14 H, m), 1.96-1.97 (2 H, m), 4.76 (2 H, t, J = 7.0 Hz), 8.42 (1 H, d, J = 1.8 Hz), 8.54 (1 H, d, J = 3.2 Hz), 10.72 (1 H, s). ^¹³C NMR (90 MHz, CDCl₃): δ = 13.7, 22.1, 25.6, 28.5, 28.7, 28.8, 28.9, 30.2, 31.3, 55.8, 127.5, 136.6, 158.2. IR (KBr): 3435, 3078, 2922, 2852, 1555, 1471, 1370, 1264, 1150, 905, 812, 630 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₁₃H₂₄NS: 226.1625; found: 226.1629.
1-Dodecylthiazolium Iodide M.p. 92 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ = 0.86 (3 H, t, J = 7.0 Hz), 1.27-1.34 (18 H, m), 1.99-2.04 (2 H, m), 4.80 (2 H, t, J = 7.5 Hz), 8.41 (1 H, d, J = 3.4 Hz), 8.47 (1 H, d, J = 3.6 Hz), 10.79 (1 H, s). ^¹³C NMR (90 MHz, CDCl₃): δ = 14.0, 22.6, 26.1, 28.9, 29.2, 29.3, 29.4, 29.5, 29.6, 30.6, 31.8, 56.3, 127.6, 136.6, 159.0. IR (KBr): 3096, 3079, 2916, 2850, 1556, 1472, 1258, 1149, 908, 811 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₁₅H₂₈NS: 254.1933; found: 254.1942.
General Procedure for Solvent-Free ‘One-Pot’ Preparation of Alkylthiazolium 4 from 1 under Microwave Irradiation: A mixture of thiazole 1 (85 mg, 1 mmol), 1-iodooctane (360 mg, 1.5 mmol) and alkaline salt MY (1.5 mmol), was irradiated (CEM Discover reactor) at 150 ˚C for 1.3 h (see Table [²] ). The reaction mixture was brought to room temperature and CH₂Cl₂ (10 mL) were added. After filtration, the solvent was evaporated. The crude product was washed with Et₂O (2 × 10 mL) and dried under reduced pressure to afford a yellow viscous oil which did not need further purification.
1-Octylthiazolium Trifluoromethanesulfonate ^¹H NMR (250 MHz, CDCl₃): δ = 0.84 (3 H, t, J = 4.8 Hz), 1.23-1.32 (10 H, m), 1.96-2.02 (2 H, m), 4.68 (2 H, t, J = 7.3 Hz), 8.29 (1 H, d, J = 3.8 Hz), 8.38 (1 H, d, J = 3.8 Hz), 10.42 (1 H, s). ^¹³C NMR (90 MHz, CDCl₃): δ = 14.0, 22.5, 26.1, 28.8, 28.9, 30.5, 31.6, 56.1, 127.1, 137.0, 158.2. IR (NaCl): 3500, 3084, 2928, 2858, 1633, 1553, 1468, 1258, 1225, 1162, 1030, 914, 836, 757, 639 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₁₁H₂₀NS: 198.1308; found: 198.1316.
1-Octylthiazolium Hexafluorophosphate
M.p. 27 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ = 0.83 (3 H, t, J = 6.0 Hz), 1.22-1.31 (10 H, m), 1.98-2.02 (2 H, m), 4.73 (2 H, t, J = 7.5 Hz), 8.36 (1 H, d, J = 2.6 Hz), 8.44 (1 H, d, J = 3.8 Hz), 10.54 (1 H, s). ^¹³C NMR (90 MHz, CDCl₃): δ = 13.9, 22.3, 25.8, 28.7, 28.8, 30.5, 31.4, 56.0, 127.6, 136.7, 158.3. IR (NaCl): 3440, 3084, 2929, 2856, 1602, 1553, 1469, 1174, 1012, 905, 750 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₁₁H₂₀NS: 198.1309; found: 198.1316. 1-Octylthiazolium Tetrafluoroborate ^¹H NMR (300 MHz, CDCl₃): δ = 0.83 (3 H, t, J = 7.1 Hz), 1.28-1.32 (10 H, m), 1.99-2.03 (2 H, m), 4.79 (2 H, t, J = 7.5 Hz), 8.42 (1 H, d, J = 3.4 Hz), 8.52 (1 H, d, J = 3.4 Hz), 10.57 (1 H, s). ^¹³C NMR (90 MHz, CDCl₃): δ = 14.3, 22.8, 26.4, 29.1, 29.2, 30.8, 31.9, 56.6, 127.2, 137.2, 158.6. IR (NaCl): 3445, 3094, 2929, 2858, 1607, 1553, 1469, 1352, 1194, 1058, 915, 740 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₁₁H₂₀NS: 198.1308; found: 198.1309.
Solvent-Free Microwave-Promoted ‘Two-Step, One-Pot Sequence’ Preparation of Octylthiazolium Bis(trifluoromethanesulfonyl)imide: A mixture of thiazole 1 (85 mg, 1 mmol) and 1-bromooctane (360 mg, 1.5 mmol) was irradiated (CEM Discover reactor) at 150 ˚C for 1.3 h. Lithium bis(tstrifluoromethanesulfonyl)imide (373 mg, 1.5 mmol) was added and the resulting mixture was then placed under MW irradiation for an additional period of 30 min at 100 ˚C. The reaction mixture was brought to room temperature and CH₂Cl₂ (10 mL) was added. After filtration, the solvent was evaporated. The crude product was washed with Et₂O (2 × 10 mL) and dried under reduced pressure to afford a yellow viscous oil (356 mg, 75%) which did not need further purification.
1-Octylthiazolium Bis(trifluoromethanesulfonyl)imide M.p. 30 ˚C. ^¹H NMR (360 MHz, CDCl₃): δ = 0.84 (3 H, t, J = 6.6 Hz), 1.25-1.35 (10 H, m), 1.97-2.05 (2 H, m), 4.73 (2 H, t, J = 7.5 Hz), 8.35 (1 H, d, J = 3.6 Hz), 8.42 (1 H, d, J = 3.6 Hz), 10.52 (1 H, s). ^¹³C NMR (90 MHz, CDCl₃): δ = 13.4, 21.9, 25.5, 28.2, 28.3, 30.1, 31.0, 55.7, 127.2, 136.4, 158.1. IR (NaCl): 3436, 3064, 2926, 2855, 1622, 1553, 1463, 1267, 1154, 906, 834 cm^-¹. HRMS (EI): m/z [M⁺] calcd for C₁₁H₂₀NS: 198.1314; found: 198.1316.

Representative Procedure for Microwave-Assisted Intramolecular Stetter Reaction: A mixture of methyl 4-(2-formylphenoxy)but-2-enoate 6 (Z = H; 0.11 g, 0.5 mmol), Et₃N (51 mg, 0.5 mmol) and octylthiazolium iodide (25 mg, 15% mol) was irradiated at 100 ˚C for 20 minutes. The reaction was quenched with 0.1 N HCl and extracted with CH₂Cl₂. The organic phase was washed with H₂O, dried over MgSO₄, filtered and concentrated in vacuum to afford a pale-orange oil 7 (107 mg, 97% yield).

Methyl 2-(3,4-Dihydro-4-oxo-2 H -chromen-3-yl)acetate ^¹H NMR (250 MHz, CDCl₃): δ = 2.42 (1 H, dd, J = 8.2, 16.8 Hz), 2.92 (1 H, dd, J = 5.1, 17.1 Hz), 3.28-3.36 (1 H, m), 3.71 (3 H, s), 4. 28 (1 H, t, J = 11.7 Hz), 4.58 (1 H, dd, J = 5.4, 11.1 Hz), 6.99 (1 H, dd, J = 8.8, 15.5 Hz), 7.46 (1 H, t, J = 8.2 Hz), 7.86 (1 H, d, J = 7.9 Hz). ^¹³C NMR (90 MHz, CDCl₃): δ = 29.9, 42.4, 51.9, 70.1, 117.7, 121.4, 135.9, 161.4, 171.7, 192.4. IR (NaCl): 3583, 2953, 1738, 1694, 1606, 1580, 1480, 1324, 1301, 1215, 1014, 870, 760 cm^-¹. HRMS (EI): m/z [M + Na⁺] calcd for C₁₂H₁₂O₄Na: 243.0627; found: 243.0633.