Chelated 2-Formylglycinate: Aldehyde or Enol?

Abstract

¹³ C n.m.r. data are presented which are consistent with the proposal that 2-formylglycinate chelated to bis(ethane-1,2-diamine)cobalt(III) exists as an equilibrium mixture of its hydrate, 3,3-dihydroxyalaninate (c.90%), and its E-enol , (E)-2-amino-3-hydroxyacrylate (c.10%). The new structural assignment for the minor component of the mixture leads to the proposal of a new mechanism for the formation of coordinated penicilloates by reaction of this mixture with (S)-penicillamine . The new mechanism makes it possible to rationalize the remarkable stereoselectivity of this condensation reaction.