A Noncarbenoid Approach to Imidazolidines via ZnCl2-Catalyzed Annulation of 4-Alkoxycarbonyl-1,2-diaza-1,3-dienes with 1,3,5-Triazinanes

An unprecedented ZnCl2-catalyzed formal [2 + 2 + 1] annulation of 1,2-diaza-1,3-dienes (DDs) with hexahydro-1,3,5-triazines (HTs) has been accomplished, which provides imidazolidine frameworks with quaternary carbon centers. Thus, a new opportunity bypassing the use of hazardous diazo reagents is made possible by a unique carbene-like reactivity (C1 synthon) of readily available and safe 4-alkoxycarbonyl-1,2-diaza-1,3-butadienes. Besides, this noncarbenoid transformation can be implemented into a two-step three-component approach by utilizing the aromatic amine, 1,2-diaza-1,3-dienes and 1,3,5-triazines to synthesize differently substituted 1,3-diaryl imidazolidines.