Stereoselective C-terminal peptide elongation from Chan-Lam-Evans reaction generated isopropenyl esters

C-Terminal dipeptide isopropenyl esters were synthesised by a Cu(II)-mediated Chan-Lam-Evans enol esterification of peptide carboxylic acids and isoprenyl boroxine. These shelf stable peptide esters could be coupled stereoselectively with a variety of amino acid and dipeptide nucleophiles in high yield and purity in the presence of pyrazole/DBU as the catalyst.