Asymmetric synthesis of alpha,alpha-disubstituted alpha-amino acids by diastereoselective alkylation of camphor-based tricyclic iminolactone.
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.
Xu
Peng-Fei
PF
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, Gansu 730000, PRC.
Li
Shuo
S
Lu
Ta-Jung
TJ
Wu
Chen-Chang
CC
Fan
Botao
B
Golfis
Georgia
G
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
D000596:Amino Acids; D006575:Heterocyclic Compounds, 3-Ring; D007097:Imines; D007783:Lactones; D002164:Camphor