Benzylic Ammonium Ylide Mediated Epoxidations

Abstract

A high yielding synthesis of stilbene oxides using ammonium ylides has been developed. It turned out that the amine leaving group plays a crucial role as trimethylamine gives higher yields than DABCO or quinuclidine. The amine group also influences the diastereoselectivity, and detailed DFT calculations to understand the key parameters of these reactions have been carried out.

Key words

epoxides - ylides - diastereoselectivity - DFT calculations - diazo compounds

• References and Notes


For selected reviews, see:
• 1a Aggarwal VK In Comprehensive Asymmetric Catalysis . Jacobsen EN, Pfaltz A, Yamamoto H. Springer; New York: 1999. Vol. 2 679
• 1b McGarrigle EM, Myers EL, Illa O, Shaw MA, Riches SL, Aggarwal VK. Chem. Rev. 2007; 107: 5841

For seminal work on sulfur ylides, see:
• 2a Corey EJ, Chaykovsky M. J. Am. Chem. Soc. 1962; 84: 867
• 2b Corey EJ, Chaykovsky M. J. Am. Chem. Soc. 1965; 87: 1353
• 2c Johnson AW, Lacount RB. Chem. Ind. 1958; 1440

For examples highlighting the use of sulfur ylides in epoxidation reactions, see:
• 3a Zhou Y.-G, Hou X.-L, Dai L.-X, Xia L.-J, Tang M.-H. J. Chem. Soc., Perkin Trans. 1 1999; 77
• 3b Zanardi J, Leriverend C, Aubert D, Julienne K, Metzner P. J. Org. Chem. 2001; 66: 5620
• 3c Aggarwal VK, Hynd G, Picoul W, Vasse J.-L. J. Am. Chem. Soc. 2002; 124: 9964
• 3d Aggarwal VK, Richardson J. Chem. Commun. 2003; 2644
• 3e Davoust M, Briere J.-F, Jaffres P.-A, Metzner P. J. Org. Chem. 2005; 70: 4166
• 3f Aggarwal VK, Charmant JP. H, Fuentes D, Harvey JN, Hynd G, Ohara D, Picoul W, Robiette R, Smith C, Vasse J.-L, Winn CL. J. Am. Chem. Soc. 2006; 128: 2105
• 3g Illa O, Arshad M, Ros A, McGarrigle EM, Aggarwal VK. J. Am. Chem. Soc. 2010; 132: 1828
• 3h Illa O, Namutebi M, Saha C, Ostovar M, Chen CC, Haddow MF, Nocquet-Thibault S, Lusi M, McGarrigle EM, Aggarwal VK. J. Am. Chem. Soc. 2013; 135: 11951

For ammonium ylide mediated cyclopropanations, see:
• 4a Gaunt MJ, Johansson CC. C. Chem. Rev. 2007; 107: 5596
• 4b Johansson CC. C, Bremeyer N, Ley SV, Owen DR, Smith SC, Gaunt MJ. Angew. Chem. Int. Ed. 2006; 45: 6024
• 4c Papageorgiou CD, Cubillo de Dios MA, Ley SV, Gaunt MJ. Angew. Chem. Int. Ed. 2004; 43: 4641
• 4d Bremeyer N, Smith SC, Ley SV, Gaunt MJ. Angew. Chem. Int. Ed. 2004; 43: 2681
• 4e Papageorgiou CD, Ley SV, Gaunt MJ. Angew. Chem. Int. Ed. 2003; 42: 828

For benzylic ammonium ylide mediated epoxidations, see:
• 5a Kimachi T, Kinoshita H, Kusaka K, Takeuchi Y, Aoe M, Ju-ichi M. Synlett 2005; 842
• 5b Kinoshita H, Ihoriya A, Ju-ichi M, Kimachi T. Synlett 2010; 2330
• 5c Robiette R, Conza M, Aggarwal VK. Org. Biomol. Chem. 2006; 4: 621
• 5d Xiao X, Lin D, Tong S, Mo H. Synlett 2011; 2823

For cyano-stabilized ammonium ylide mediated epoxidations, see:
• 6a Jonczyk A, Konarska A. Synlett 1999; 1085
• 6b Kowalkowska A, Sucholbiak D, Jonczyk A. Eur. J. Org. Chem. 2005; 925
• 6c Alex A, Larmanjat B, Marrot J, Couty F, David O. Chem. Commun. 2007; 2500

For amide-stabilized ammonium ylide mediated epoxidations, see:
• 7a Waser M, Herchl R, Müller N. Chem. Commun. 2011; 47: 2170
• 7b Herchl R, Stiftinger M, Waser M. Org. Biomol. Chem. 2011; 9: 7023
• 7c Pichler M, Novacek J, Robiette R, Poscher V, Himmelsbach M, Monkowius U, Müller N, Waser M. Org. Biomol. Chem. 2015; 13: 2092
• 7d Novacek, J.; Roiser, L.; Zielke, K.; Robiette, R.; Waser, M. Chem. Eur. J. 2016, DOI: 10.1002/chem.201602052.

For ammonium ylide mediated aziridinations, see:
• 8a Yadav LD. S, Kapoor R Garima Synlett 2009; 3123
• 8b Aichhorn S, Gururaja GN, Reisinger M, Waser M. RSC Adv. 2013; 3: 4552
• 9 Aggarwal VK, Harvey JN, Robiette R. Angew. Chem. Int. Ed. 2005; 44: 5468
• 10 For a recent report on selenium ylide mediated epoxidations, see: Banach A, Scianowski J, Uzarewicz-Baig M, Wojtczak A. Eur. J. Org. Chem. 2015; 3477
• 11 Ylide addition onto the aldehyde occurs without enthalpic barrier and thus no significant selectivity is expected for this step.
• 12 Winberg HE, Fawcett FS, Mochel WE, Theobald CW. J. Am. Chem. Soc. 1960; 82: 1428
• 13 Computations have been carried out at the B3LYP-D3/6-311+G(d,p)//B3LYP/6-31G* level of theory, including a continuum description of dichloromethane solvent for both the geometry optimization and the single-point energy calculation using Jaguar, version 8.5; Schrodinger, Inc.: New York, 2014. Thermal and entropic contributions to free energy were computed by performing frequency calculations at the B3LYP/6-31G (d) level of theory using the fine DFT grid within Jaguar. See ESI for full computational details and data.
• 14 In the earlier computational study (ref. 5c) only electronic energies were obtained, but no entropic and thermal contributions were included.
• 15 Betaine formation occurs without enthalpic barrier. A set of constrained geometry optimization at successively smaller values of the C–C distance showed that the interaction between reactants is uniformly attractive. The free-energy barrier of a diffusion controlled reaction can, however, be estimated at 3.7 kcal/mol in THF at 40 °C (see Supporting Information for details).
• 16 Robiette R, Trieu-Van T, Aggarwal VK, Harvey JN. J. Am. Chem. Soc. 2016; 138: 734
• 17 In contrast to DABCO, quinuclidine, or triethylammonium salts the herein used trimethylammonium salts cannot undergo Hofmann elimination reactions. A possible side reaction that sometimes occurs with all these ylides is the Stevens rearrangement: Maeda Y, Sato Y. J. Chem. Soc., Perkin Trans. 1 1997; 1491

For seminal studies, see:
• 18a Aggarwal VA, Abdel-Rahman H, Jones RV. H, Lee HY, Reid BD. J. Am. Chem. Soc. 1994; 116: 5973
• 18b Aggarwal VA, Abdel-Rahman H, Jones RV. H, Standen MC. H. Tetrahedron Lett. 1995; 36: 1731
• 18c Aggarwal VA, Abdel-Rahman H, Fan L, Jones RV. H, Standen MC. H. Chem. Eur. J. 1996; 2: 1024
• 18d Aggarwal VK, Alonso E, Bae I, Hynd G, Lydon KM, Palmer MJ, Patel M, Porcelloni M, Richardson J, Stenson RA, Studley JR, Vasse J.-L, Winn CL. J. Am. Chem. Soc. 2003; 125: 10926
• 19 Zhu S, Xing C, Pang W, Zhu S. Tetrahedron Lett. 2006; 47: 5897
• 20 General Epoxidation Procedure Ammonium salt 6 (1 equiv) was suspended in dry THF (0.05 M) and stirred at 40 °C. t-BuOK (4 equiv) was added, and the mixture was stirred vigorously. After 10 min, 2 equiv of aldehyde 2 were added, and the mixture was stirred for 3 h at 40 °C. The reaction was then quenched by addition of a half-saturated NaCl solution. After phase separation, the aqueous phase was extracted three times with CH₂Cl₂, and the combined organic phases were dried with Na₂SO₄ and evaporated to dryness. Purification by column chromatography (gradient of heptanes and EtOAc) gave the corresponding epoxides in the reported yields as a mixture of diastereomers. Compound 5a: Obtained in 93% (trans/cis = 66:34) on a 0.5 mmol scale as a white solid. Analytical data match those reported previously.^5,21 Selected Data ¹H NMR (300 MHz, δ, CDCl₃, 298 K):trans isomer: 3.94 (s, 2 H), 7.36–7.49 (m, 5 H);cis isomer: 4.42 (s, 2 H), 7.18–7.28 (m, 5 H) ppm. ESI-HRMS: m/zcalcd for C₁₄H₁₂O: 197.0961 [M + H]⁺; found: 197.0961.
• 21 Robinson MW. C, Davies AM, Buckle R, Mabbett I, Taylor SH, Graham AE. Org. Biomol. Chem. 2009; 7: 2559