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Asymmetric Synthesis of α,α-Disubstituted α-Amino Acids by Diastereoselective Alkylation of Camphor-Based Tricyclic Iminolactone

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posted on 09.06.2006, 00:00 by Peng-Fei Xu, Shuo Li, Ta-Jung Lu, Chen-Chang Wu, Botao Fan, Georgia Golfis
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 α,α-disubstituted products in good yields (70−90%) and excellent diastereoselectivities (>98%). Hydrolysis of the alkylated iminolactones furnished the desired α,α-disubstituted α-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.