Heteropolyacid-Containing Ionic Liquid-Catalyzed Multicomponent Synthesis of Bridgehead Nitrogen Heterocycles: Mechanisms and Mitochondrial Staining

The current manuscript describes the use of a heteropolyacid-containing task-specific ionic liquid, supported in imidazolium-based ionic liquids, as the catalyst for an efficient multicomponent synthesis of hexahydroimidazo­[1,2-α]­pyridine derivatives. The reactions conditions were fully optimized, and the bridgehead nitrogen heterocycle derivatives could be obtained in just 1 h exclusively as a single isomer (trans). Single crystal X-ray analysis confirmed the trans derivative as the only isomer. The mechanism of the reaction was investigated by ESI­(+)-MS­(/MS), and the use of the elegant charge-tag strategy allowed a catalytic cycle to be proposed for the current transformation and revealed the possibility of at least two reaction pathways. One derivative bearing a coumarin scaffold was synthesized, and its fluorescent properties allowed it to be tested as a probe for live-cell imaging experiments with a preference for mitochondria.