The Biginelli cyclocondensation proceeds through three possible mechanistic pathways: the imine route, involving initial Schiff base condensation between the aldehyde and urea; the enamine route, involving initial condensation between the urea and ß-ketoester; and the Knoevenagel route, involving initial aldol condensation between the aldehyde and ß-ketoester . The mechanistic investigation of the Biginelli condensation has been complicated by short-lived reactive intermediates, which are difficult, if not impossible, to isolate, as well as the possibility for multiple competing mechanistic pathways. Previously, studies by Ramos and coworkers using electrospray mass spectrometry have suggested that the imine pathway is preferred when the reaction is performed with conventional ß-ketoesters .