Stable Chiral Complexes of Ionic Liquids with Aluminium and Biaryl Ligands as Efficient Catalysts for the Synthesis of Chiral Lactones

Abstract

A new catalytic system for the asymmetric Baeyer–­Villiger oxidation of monosubstituted prochiral cyclobutanones to γ-butyrolactones with high yields (40–99%) and enantioselectivities (45–87%) is described. Aluminium complexes with biaryl ligands and ionic liquids are presented. The incorporation of an ionic liquid in the complex structure was confirmed by the observed four-coordinate nature of the aluminium.

Key words

ionic liquids - lactones - biaryl ligands - aluminium complexes - asymmetric catalysis

• References and Notes

• 1a Krow G. Org. React. (N. Y.) 1993; 43: 251
• 1b Renz M, Meunier B. Eur. J. Org. Chem. 1999; 737
• 2a Fischer T, Pietruszka J. Top. Curr. Chem. 2010; 297: 1
• 2b Ward RS. Tetrahedron 1990; 46: 5029
• 3 Mihovilovic MD, Rudroff F, Groetzl B. Curr. Org. Chem. 2004; 8: 1057
• 4 Strukul G, Varagnolo A, Pinna F. J. Mol. Catal. A. 1997; 117: 413
• 5 Bolm C, Schlingloff G, Weickhardt K. Angew. Chem. 1994; 106: 1944
• 6 Lopp M, Paju A, Kanger T, Pehk T. Tetrahedron Lett. 1996; 42: 7583
• 7 Kayser MM. Tetrahedron 2009; 65: 947
• 8a Bolm C, Frison JC, Palazzi C. Tetrahedron 2006; 62: 6700
• 8b Bolm C, Beckmann O, Palazzi C. Can. J. Chem. 2001; 79: 1593
• 8c Bolm C, Beckmann O, Kühn T, Palazzi C, Adam W, Rao PB, Saha-Möller CR. Tetrahedron: Asymmetry 2001; 12: 2441
• 8d Bolm C, Frison J, Zhang Y, Wulff WD. Synlett 2004; 1619
• 9a Olivier-Bourbigou H, Magna L, Morvan D. Appl. Catal. A 2010; 373: 1
• 9b Betz D, Altmann P, Cokoja M, Herrmann WA, Kuhn FE. Coord. Chem. Rev. 2011; 255: 1518
• 10a Baj S, Słupska R, Chrobok A, Drożdż A. J. Mol. Catal. A 2013; 376: 120
• 10b Chrobok A. Tetrahedron 2010; 66: 2940
• 10c Chrobok A. Tetrahedron 2010; 66: 6212
• 10d Baj S, Chrobok A, Słupska R. Green Chem. 2009; 11: 279
• 10e Chrobok A, Baj S, Pudło W, Jarzębski A. Appl. Catal. A 2009; 366: 22
• 11 Payagala T, Armstrong DW. Chirality 2012; 24: 17
• 12 Synthesis of the Complexes I–IV: Me₂AlCl (1 mmol), biaryl ligand (1 mmol), ionic liquid (1 mmol) and anhyd CH₂Cl₂ (1 mL) were placed in a round-bottom flask under a dry, inert atmosphere at –15 °C. The contents of the flask were stirred for 1 h. After this time, evaporation of the solvent gave complexes I–IV in high yields (90–99%). Complex II: ¹H NMR (600 MHz, DMSO): δ = 0.89 (t, J = 8.5 Hz, 3 H), 1.25 (sextet, J = 8.2 Hz, 2 H), 1.75 (p, J = 8.2 Hz, 2 H), 3.85 (s, 3 H), 4.15 (t, J = 8.2 Hz, 2 H), 6.67–6.75 (m, 4 H), 6.80–6.89 (m, 4 H), 6.90–7.02 (m, 2 H), 7.15 (s, 2 H), 7.29–7.35 (m, 1 H), 7.43–7.50 (m, 4 H), 7.61–7.71 (m, 1 H), 7.75–7.81 (m, 2 H), 8.25–8.35 (m, 2 H), 9.05 (s, 3 H, AlCH₃), 9.15 (s, 1 H). ¹³C NMR (150 MHz, DMSO): δ = 13.22, 18.73, 31.31, 35.70, 48.46, 116.17, 117.25, 119.62 (q, [(CF₃SO₂)₂N], 122.24, 123.59, 123.91, 124.81, 125.09, 126.05, 126.60, 126.89, 128.70, 133.49, 136.50, 141.13, 141.90, 151.47, 159.57. ²⁷Al NMR (400 MHz): δ = 60.13. ESI–MS: m/z = 139 ([bmim]⁺), 437 ([VANOL]^–), 280 ([(CF₃SO₂)₂N]^–).
• 13 General Procedure for the Synthesis of 3-Phenyl-γ-butyrolactones: The sequence of the reagent addition was as follows: first the ketone (0.5 mmol), then biaryl ligand (0.25 mmol), followed by the addition of ionic liquid (0.8 g) were placed in a round-bottom flask under a dry, inert atmosphere and cooled to –15 °C. After the addition of Me₂AlCl (0.25 mmol), the contents of the flask were stirred for 1 h. Next, CHP (1.5 mmol) was added at –25 °C and the reaction was allowed to warm to r.t. and left for 22 h. Yields and enantioselectivities of lactone were determined by GC.
• 14 Krepski LR, Hassner A. J. Org. Chem. 1978; 43: 2879