Chain extension of amino acid skeletons: preparation of ketomethylene isosteres

Ketomethylene isosteric replacements for peptide bonds were generated through a zinc carbenoid-mediated chain extension reaction in which a variety of amino acid-derived β-keto esters are converted to γ-keto esters in a single step. The reaction tolerates a variety of protecting groups and amino acid side chains with no epimerization of the amino acid stereocenter.