Asymmetric synthesis of alpha,alpha-disubstituted alpha-amino acids by diastereoselective alkylation of camphor-based tricyclic iminolactone |
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Authors: | Xu Peng-Fei Li Shuo Lu Ta-Jung Wu Chen-Chang Fan Botao Golfis Georgia |
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Affiliation: | State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, Gansu 730000, PRC. |
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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. |
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