Abstract
Seven selected chiral mono-, di-, and tridentate amines supported on insoluble polymer were effectively prepared from corresponding primary amines or secondary amino alcohols and Merrifield resin. The reaction of the polymer-supported amines with excess n-butyllithium gave the corresponding lithium amide bases, which were tested in the aldol reactions of tropinone with benzaldehyde. The deprotonation reactions were carried out with or without separation of the lithium enolate from polymer-supported reagents. Using the procedure with separation of lithium enolate from supported chiral reagent different results were obtained with or without the addition of LiCl despite the fact that aggregate formation of Merrifield resin supported Li-amides is hindered. Without the additive, the aldol products were obtained in low diastereoselectivity and enantioselectivity, whereas the addition of LiCl resulted in a significant increase of de and ee even when LiCl was added after the deprotonation step and separation of the chiral amine.
Keywords: Amine immobilization, chiral lithium amide, enolate separation, deprotonation, aldol reaction, stereoselective synthesis, benzaldehyde.
Graphical Abstract
b) O’Brien, P. Recent advances in asymmetric synthesis using chiral lithium amide bases. J. Chem. Soc., Perkin Trans., 1998, 1, 1439-1458.
[http://dx.doi.org/10.1039/a705961e]
c) Pettersen, D.; Amedjkouh, M.; Ahlberg, P. Chiral lithium amides in asymmetric synthesis. Chem. Organolithium Compounds, 2006, 2, 411-477.
[http://dx.doi.org/10.1002/0470023236.ch6]
d) Eames, J. Recent developments in enantioselective deprotonation mediated by sub-stoichiometric quantities of chiral bases. Eur. J. Org. Chem., 2002, 2002, 393-401.
[http://dx.doi.org/10.1002/1099-0690(20022)2002:3<393::AIDEJOC393>3.0.CO;2-F]
e) Harrison-Marchand, A.; Maddaluno, J. Advances in the chemistry of chiral lithium amides. Lithium Compounds Org. Synthesis, 2014, 297-328.
[http://dx.doi.org/10.1002/9783527667512.ch10]
b) Majewski, M. Enantioselective deprotonation of cyclic ketones. Advances in Asymmetric Synthesis., 1998, vol. 3, 39-76.
[http://dx.doi.org/10.1016/j.tetlet.2009.10.045]
b) Majewski, M.; Zheng, G-Z. Enantioselective deprotonation of tropinone and reactions of tropinone lithium enolate. Synlett, 1991, 173-175.
[http://dx.doi.org/10.1055/s-1991-20667]
c) Majewski, M.; Lazny, R. Stereoselective synthesis of tropane alkaloids: Physoperuvine and dihydroxytropanes. Synlett, 1996, 785-786.
[http://dx.doi.org/10.1055/s-1996-5532]
d) Simpkins, N.S.; Weller, M.D. Asymmetric deprotonations using chiral lithium amide bases. Stereochemical Aspects Organolithium Compounds, 2010, 26, 1-52.
[http://dx.doi.org/10.1002/9783906390628.ch1]
e) Lazny, R.; Wolosewicz, K.; Zielinska, P.; Urbanczyk-Lipkowska, Z.; Kalicki, P. Diastereo- and enantioselective aldol reaction of granatanone (pseudopelletierine). Tetrahedron, 2011, 67, 9433-9439.
[http://dx.doi.org/10.1016/j.tet.2011.09.096]
[http://dx.doi.org/10.1016/0040-4039(96)01681-4]
[http://dx.doi.org/10.1002/anie.198816241]
b) Juaristi, E.; Beck, A.K.; Hansen, J.; Matt, T.; Mukhopadhyay, T.; Simson, M.; Seebach, D. Enantioselective aldol and michael additions of achiral enolates in the presence of chiral lithium amides and amines. Synthesis, 1993, 1271-1290.
[http://dx.doi.org/10.1055/s-1993-26041]
c) Seebach, D.B.A.K.; Studer, A. Some effects of lithium salts, of strong bases, and of the cosolvent DMPU in peptide chemistry, and elsewhere. Modern Synthetic Methods, 1995, 1995, 1-178.
d) Braun, M. Modern Enolate Chemistry: From Preparation to Applications in Asymmetric Synthesis; John Wiley & Sons, 2016.
e) Braun, M. Lithium enolates: ‘Capricious’ structures - Reliable reagents for synthesis. Helv. Chim. Acta, 2015, 98, 1-31.
[http://dx.doi.org/10.1002/hlca.201400288]
[http://dx.doi.org/10.1021/ja802114j] [PMID: 18693723]
[http://dx.doi.org/10.1016/00404-0399(50)1056N-]
[http://dx.doi.org/10.1021/jo00123a018]
b) Bunn, B.J.; Simpkins, N.S. An enhancement of enantioselectivity in chiral lithium amide deprotonations due to lithium chloride. J. Org. Chem., 1993, 58, 533-534.
[http://dx.doi.org/10.1021/jo00055a001]
[http://dx.doi.org/10.1351/pac199466071487]
b) Lazny, R.; Sienkiewicz, M.; Olenski, T.; Urbanczyk-Lipkowska, Z.; Kalicki, P. Approaches to the enantioselective synthesis of ferrugine and its analogues. Tetrahedron, 2012, 68, 8236-8244.
[http://dx.doi.org/10.1016/j.tet.2012.07.061]
[http://dx.doi.org/10.5059/yukigoseikyokaishi.54.188]
b) Asami, M. An asymmetric transformation of cyclohexene oxide to (S)-2-cyclohexen-1-ol by chiral lithium amides. Chem. Lett., 1984, 13, 829-832.
[http://dx.doi.org/10.1246/cl.1984.829]
[http://dx.doi.org/10.1139/v06-006]
b) Majewski, M.; Ulaczyk, A.; Wang, F. Chiral lithium amides on solid support: synthesis and applications in enantioselective deprotonation of cyclic ketones. Tetrahedron Lett., 1999, 40, 8755-8758.
[http://dx.doi.org/10.1016/S0040-4039(99)01882-1]
[http://dx.doi.org/10.1055/s-2002-34879]
[http://dx.doi.org/10.1016/j.tetasy.2006.11.011] [PMID: 18026563]
[http://dx.doi.org/10.1007/978-3-642-85055-4]
[http://dx.doi.org/10.1016/0040-4039(96)00652-1]
[http://dx.doi.org/10.1248/cpb.42.690]
[http://dx.doi.org/10.1021/jo00065a020]
[http://dx.doi.org/10.1016/S0040-4020(01)00495-1]
[http://dx.doi.org/10.1016/j.tetlet.2012.12.067]
[http://dx.doi.org/10.1016/S0040-4039(00)73063-2]
b) Bunn, B.J.; Simpkins, N.S.; Spavold, Z.; Crimmin, M.J. The effect of added salts on enantioselective transformations of cyclic ketones by chiral lithium amide bases. J. Chem. Soc., Perkin Trans. 1, 1993, 3113-3116.
[http://dx.doi.org/10.1039/p19930003113]
[http://dx.doi.org/10.1016/S0040-4039(96)02373-8]
[http://dx.doi.org/10.1016/j.tetlet.2012.08.070]
[http://dx.doi.org/10.1055/s-2003-42483]