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.