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Asymmetric synthesis of alpha,alpha-disubstituted alpha-amino acids using (S,S)-cyclohexane-1,2-diol as a chiral auxiliary



Asymmetric synthesis of alpha,alpha-disubstituted alpha-amino acids using (S,S)-cyclohexane-1,2-diol as a chiral auxiliary



Journal of Organic Chemistry 66(8): 2667-2673



Diastereoselective alkylation of ethyl 2-methyl- and/or 2-ethylacetoacetates using the (S,S)-cyclohexane-1,2-diol as an acetal chiral auxiliary afforded enol ethers (2a-f and 5a-f) of 92->95% de in 31-70% yields. Removal of the cyclohexane-1,2-diol with BF(3)-OEt(2) afforded beta-keto esters (3 and 6) bearing a chiral quaternary carbon. The beta-keto esters could be easily converted into optically active alpha-methylated and/or alpha-ethylated alpha,alpha-disubstituted amino acids (12 and 13) in 21-99% yields using Schmidt rearrangement.

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Accession: 045323615

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PMID: 11304185


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