Experimental Identification of Enamines in Organocatalysis

In what can be regarded as the earliest evidence for the participation of enamines in a proline-catalyzed aldol reaction and its in situ detection was provided by Metzeger and coworker. A combination of high-resolution MS/MS and ESI-MS methods could detect the condensahon product between prohne and acetone [9]. Furthermore, the evidence was strongly in favor of enamine as compared to the isomeric oxazolidinone. In a subsequent study, Seebach and coworkers using NMR and IR studies proposed that an oxazolidinone intermediate plays a vital role in asymmetric organocatalytic Michael reactions. Evidence for participation of bicychc as well as spirocyclic oxazolidinones in proline-catalyzed reachons was presented [10]. 

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