The Increased Reactivity of the Proline Carboxylate Derived Enamine

Significance

Mayr and co-workers have performed a kinetic analysis of the reaction of proline carboxylate enamine 1a, pyrrolidine enamine 1b, and proline ester enamine 1c with electrophiles 2a-c. The superior reactivity of the proline car­boxylate 1a compared to 1b-c was interpreted as ­evidence for the operation of an alternative ­mechanistic pathway that includes anchimeric assistance of the carboxylate group in the addition to the electrophile. These data were suggested to support the formation of oxazolidinones in the ­stereogenic step of proline carboxylate catalyzed reactions (D. G. Blackmond et al. J. Am. Chem. Soc. 2010, 132, 7598), although catalytic reactions have not actually been studied.