Asymmetric Synthesis of α,α-Disubstituted α-Amino Acids Using (<i>S</i>,<i>S</i>)-Cyclohexane-1,2-diol as a Chiral Auxiliary
作者:Masakazu Tanaka、Makoto Oba、Koichi Tamai、Hiroshi Suemune
DOI:10.1021/jo001423m
日期:2001.4.1
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-l,2-diol with BF3-OEt2 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.