Redrawing the Mannich‐Type Reaction through Carbonyl Umpolung Reactivity

Herein, the development of an effective 3 starting materials–5 component reaction (3SM‐5CR) strategy is reported to assemble imidazolidine motifs from 1,2‐diaza‐1,3‐dienes, amines, and formaldehyde. In comparison with the classical Mannich‐type reactions (3SM‐6CR) for the construction of hexahydropyrimidines, this approach that uses azoalkene substrate (umpolung of carbonyl compound) as a donor/acceptor C1 synthon (carbene equivalent) enables practical construction of a library of previously inaccessible, structurally diverse imidazolidine derivatives with unprecedented ease. Inexpensive and easily available Lewis acid ZnCl 2 is an effective catalyst for these transformations, making this methodology flexible for the guided introduction of the amine components into the final N ‐heterocycles.