Ionophilic Imidazolium-Tagged Cinchona Ligand on LDH-Immobilized Osmium: Recyclable and Recoverable Catalytic System for Asymmetric Dihydroxylation Reaction of Olefins

Abstract

A catalytic system for the asymmetric dihydroxylation of olefins was developed by using an ionic-tagged biscinchona alkaloid ligand immobilized onto OsO₄-exchanged layered double hydroxide (LDH) as a robust recyclable homogenous–heterogeneous catalytic system. The desired products were obtained in high yield and enantioselectivity.

Key words

asymmetric dihydroxylation - immobilization - catalyst recycling - olefins - (QN)₂PHAL-[C₅mim]Br - ionic liquid

• References and Notes

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• 18 Compound 5 ¹H NMR (400 MHz, CDCl₃): δ = 1.36–1.44 (m, 2 H, NCH₂CH₂CH ₂CH₂CH₂ imidazolium), 1.48–1.53 (m, 2 H, quinuclidine H), 1.74–1.88 (m, 10 H, quinuclidine H), 1.91–1.99 (m, 4 H, N⁺CH₂CH₂CH ₂CH ₂CH₂CH₂ imidazolium), 2.04–2.13 (m, 4 H, N⁺CH₂CH ₂CH₂CH₂CH ₂CH₂ imidazolium), 2.13–2.17 (m, 2 H, quinuclidine H), 2.68–2.78 (m, 2 H, quinuclidine H), 2.80–2.91 (m, 2 H, quinuclidine H), 3.15–3.18 (m, 2 H, quinuclidine H), 3.38–3.48 (m, 2 H, quinuclidine H), 3.54 (t, 2 H, J = 6.4 Hz, N⁺CH ₂CH₂CH₂CH₂CH₂CH₂ imidazolium), 3.93 (s, 6 H, OCH₃), 4.01 (s, 3 H, NCH₃), 4.35 (t, 2 H, J = 7.4 Hz, CH₂CH ₂ imidazolium), 5.02–5.17 (m, 4 H, CH ₂=CH), 5.52–5.56 (m, 2 H, CH₂=CH), 7.28 (d, 1 H, J = 2.7 Hz, CHO), 7.30 (d, 1 H, J = 2.7 Hz, CHO), 7.31 (s, 1 H, imidazolium H), 7.32–7.39 (m, 2 H, phthalazine H), 7.45 (d, 2 H, J = 1.8 Hz, imidazolium H), 7.50–7.52 (m, 2 H, 2 x quinolyl H), 7.81–7.83 (m, 2 H, phthalazine H), 7.91–7.93 (m, 2 H, 2 × quinolyl H), 8.08 (d, 2 H, J = 8.5 Hz, 2 × quinolyl H), 8.31–8.35 (m, 2 H, quinolyl H), 8.72 (d, 1 H, J = 4.8 Hz, quinolyl H), 8.78 (d, 1 H, J = 4.6 Hz, quinolyl H). ¹³C NMR (400 MHz, CDCl₃): δ = 157.3, 145.8, 143.5, 142.7, 142.4, 136.2, 136.0, 130.1, 124.4, 122.3, 121.7, 121.3, 118.0, 116.4, 116.2, 99.1, 65.5, 65.0, 63.4, 59.1, 56.3, 55.4, 55.1, 53.7, 52.6, 43.1, 36.6, 36.0, 35.6, 29.9, 28.6, 28.2, 25.9, 25.2, 24.2, 23.7, 23.2, 21.2, 17.1. MS (ES+): m/z (%) = 945.1 (20) [M + H]⁺, 325.5 (100) [M – C₃₈H₄₈N₆O₂]⁺.
• 19 Typical Procedure for Assymetric Dihydroxylation of trans-Stilbene Using Catalyst 5 LDH-OsO₄ (0.020 g, 0.017 mmol), [(QN)₂PHAL-C₅mim]Br (5, 0.0102 g, 0.01 mmol) in [bmim]PF₆–H₂O–acetone (0.1:1:8, v/v) was stirred at 0 °C for 15–20 min. To this was added NMO (0.200 g, 5.13 mmol) and subsequently trans-stilbene (0.103g, 1.7 mmol) over a period of 10 h at r.t. After completion of reaction as indicated by TLC, the volatiles were removed under vacuum and Et₂O was added to the reaction mixture. The ether layer was separated, and the procedure was repeated thrice (3 × 10 mL). The combined ether layer was washed with water, brine, and dried over anhydrous Na₂SO₄. After evaporating the solvent, the crude product was vacuum dried. Column chromatography of the crude on silica gel (EtOAc–hexane, 2:8) gave the desired diol in 96% yield.
• 20 HPLC Analysis (Table 3) Entry 1 (diol): Daicel Chiralcel OJ, hexane–i-PrOH (4:1), flow rate 0.6 mL/min, t _R (min) = 11.7 (minor), 13.7 (major). Entry 2 (diol): Daicel Chiralcel OD-H, hexane–i-PrOH (19:1), flow rate 0.5 mL/min, t _R = 43.99 (major), t _R = 48.73 (minor). Entry 3 (diol): Daicel Chiralcel OD-H, hexane–i-PrOH (5.6:1), flow rate 1.0 mL/min, t _R (min) = 5.5 (major), 8.0 (minor). Entry 4 (diol): Daicel Chiralcel OJ, hexane–i-PrOH (5.6:1), flow rate 1.0 mL/min, t _R (min) = 6.5 (minor), 7.6 (major). Entry 5 (diol): Daicel Chiralcel OD-H, hexane–i-PrOH (7.5:2.5), flow rate 1.0 mL/min, t _R (min) = 2.5 (minor), 5.7 (major). Entry (diol): Daicel Chiralcel OD-H, hexane–i-PrOH (9.5:0.5), flow rate 1.0 mL/min, t _R (min) = 4.6 (minor), 9.3 (major).
• 21 Choi DS, Han SS, Kwueon EK, Choi HY, Hwang SH, Park YS, Choung ES. Adv. Synth. Catal. 2006; 348: 2560
• 22 Typical Procedure for Recycling of trans-Stilbene Using Catalyst 5 LDH-OsO₄ (0.01 g, 0.005 mmol) was added to the remaining catalytic system, after extraction of the product and was stirred at 0 °C for 15–20 min. To this was added fresh dose of NMO (0.200 g, 5.13 mmol) and subsequently trans-stilbene (0.103 g, 1.7 mmol) over a period of 10 h at r.t. After completion of reaction as indicated by TLC, the volatiles were removed under vacuum, and Et₂O was added to the reaction mixture. The ether layer was separated, and the procedure was repeated thrice (3 × 10 mL). The combined ether layer was washed with H₂O and brine, and dried over anhydrous Na₂SO₄. After evaporating the solvent, the crude product was vacuum dried. Column chromatography of the crude on silica gel (EtOAc–hexane, 2:8) gave the desired diol in 95.5% yield.