Efficient synthesis of 5-aryl-5H-pyrido[2',1':2,3]imidazo[4,5-b]indoles by double C-N coupling reactions using HKUST-1 as recyclable heterogeneous catalyst under air

Fluorescent active small compounds containing 5H-pyrido[2',1:2,3]imidazo[4,5-b]indole core could be successfully synthesized by double C-N 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 C-N coupling reaction under-going 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 spe-cies. This method may give potential applications in the pharmaceutical and fine chemical industries.(c) 2023 Elsevier Ltd. All rights reserved.