Chiral epimeric carboxycyclopentylglycines from norbornane derivatives: reaction conditions and ring strain effect on stereochemical control of amino acid centers

A new synthetic approach to diastereomeric cyclopent-3-enylglycines, functionalized on the ring with a formyl group, and to cyclopentylglycine, substituted with a carboxy group, was devised by applying retro-aldol and retro-Claisen reactions, respectively, to diastereomeric 2-amino-3-ethoxycarbonyloxynorbornene-2-carboxylic acid derivatives and to diastereomeric 2-amino-3-oxo-norbornane-2-carboxylic acid derivatives. The goal of controlling the cis stereochemistry of the cyclopentyl substituents was reached . A partial control of the stereochemistry of the amino acidic carbon was achieved starting from 17 and using sodium hydrogen carbonate in acetone/DMF.