Chiral environment specifically induced by metal ion: Asymmetric α-alkylation of α-amino esters using pyridoxal derivatives having a chiral ionophore function
prepared from α-aminoesters and pyridoxalmodelshaving an ionophoric side-chain composed of a chiral glycerol structure, proceeded in the presence of Li+ or Na+ to afford α,α-dialkyl amino esters after acidic hydrolysis. Both the structure of the side chain and the metal ion were found to be in relation with the stereoselectivity, affording the highest stereoselectivity when the side-chain having a 2-naphthylmethoxy
Asymmetric α-alkylation of α-amino esters using pyridoxal model compounds with a chiral ionophore function; dependence of stereoselectivity on a chelated metal ion
Asymmetric alpha-alkylation of alpha-amino esters by use of novel pyridoxal model compounds having a chiral ionophore function is studied; the stereoselectivity is specifically induced by Na+ and the most effective asymmetric induction occurs with a combination of Na+ and an additional chiral ansa-structure.
Synthesis of Quaternary α-Methyl α-Amino Acids by Asymmetric Alkylation of Pseudoephenamine Alaninamide Pivaldimine
作者:Cedric L. Hugelshofer、Kevin T. Mellem、Andrew G. Myers
DOI:10.1021/ol401337p
日期:2013.6.21
The utility of pseudoephenamine as a chiral auxiliary for the alkylative construction of quaternary alpha-methyl alpha-amino acids Is demonstrated. The method is notable for the high diastereoselectivities of the alkylation reactions, for its versatility with respect to electrophilic substrate partners, and for its mild hydrolysis conditions, which provide alpha-amino acids without salt contaminants. Alternatively, alpha-amino esters can be obtained by direct alcoholysis.