The enamine is formed through an oxazolidinone intermediate

When I think of organocatalysis, I usually think of a carbonyl compound forming an enamine intermediate, which in turn attacks an electrophile. The enamine is usually formed when the carbonyl compound reacts with a proline-derived catalyst. By using Gaussian and experimental KIE calculations, Matthew Vetticatt and co-workers at Binghamton University reported in JACS on the way that the enamine compound is formed: through an oxazolidinone intermediate.

JACS paper

 

A review article on determining the transition state structures based on KIEs.