Abstract
Fluorescent active small compounds containing 5H-pyrido[2′,1:2,3]imidazo[4,5-b]indole core could be successfully synthesized by double CN coupling reaction from 3-iodo-2-(2-bromophenyl)imidazo[1,2-a]pyridine with different amines in high yields under air atmosphere. HKUST-1 was found to be the most suitable heterogeneous catalyst for this transformation. Interestingly, HKUST-1 catalyst (∼12 mol% Cu loading for each reaction) showed highly active, robust, and recyclable properties with the tolerance of broad substrate scope. Remarkably, the mechanism for the CN coupling reaction undergoing Cu1+/ Cu3+ catalytic cycle was proposed from several observed important evidence. Cu2+ sites in the node of HKUST-1 structure could be reduced to Cu1+ which initiated the formation of radical amine species. This method may give potential applications in the pharmaceutical and fine chemical industries.
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