title: Asymmetric synthesis of alpha,alpha-disubstituted alpha-amino acids by diastereoselective alkylation of camphor-based tricyclic iminolactone.
abstract: A novel and convenient route for the preparation of chiral tricyclic iminolactones 9 and 10 from camphorquinone has been developed. Alkylation of iminolactones 9 and 10 provided iminolactones 16 and 17 in high yields which were, in turn, alkylated again to afford the alpha,alpha-disubstituted products in good yields (70-90%) and excellent diastereoselectivities (>98%). Hydrolysis of the alkylated iminolactones furnished the desired alpha,alpha-disubstituted alpha-amino acids in good yields and high enantiomeric excesses with good recovery yields of the chiral auxiliary 12 and 13. The extremely high endo-face selectivity for alkylation is discussed using semiempirical (MOPAC 93) calculations.
authors.affiliation: State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, Gansu 730000, PRC.
authors.forename: Peng-Fei
authors.initials: PF
authors.lastname: Xu
authors.forename: Shuo
authors.initials: S
authors.lastname: Li
authors.forename: Ta-Jung
authors.initials: TJ
authors.lastname: Lu
authors.forename: Chen-Chang
authors.initials: CC
authors.lastname: Wu
authors.forename: Botao
authors.initials: B
authors.lastname: Fan
authors.forename: Georgia
authors.initials: G
authors.lastname: Golfis
mesh_terms: D000478:Alkylation; D000596:Amino Acids / Q000138:chemical synthesis*; D002164:Camphor; D006575:Heterocyclic Compounds, 3-Ring / Q000737:chemistry*; D007097:Imines; D007783:Lactones / Q000737:chemistry*; D008958:Models, Molecular; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D006575:Heterocyclic Compounds, 3-Ring; D007097:Imines; D007783:Lactones; D002164:Camphor