Polycyclic imidazo[1,2-a]pyridine analogs – synthesis via oxidative intramolecular C–H amination and optical properties†
A novel and straightforward approach to synthesize 5H-pyrido[2′,1′:2,3]imidazo[4,5-b]indoles has been developed. The key step is C–H amination of easily available 2-(2′-aminophenyl)imidazo[1,2-a]pyridines by the use of copper(II) triflate, trifluoroacetic acid and (diacetoxyiodo)benzene. The entire strategy consists of just four steps, starting from 2-aminopyridines and acetophenones, giving the target compounds in an overall yield of 20–35%. The optical properties of a library of π-expanded imidazo[1,2-a]pyridines were for the first time fully characterized, showing that these ladder-type compounds strongly absorb UV radiation and exhibit fluorescence in the 415–461 nm region.
- This article is part of the themed collection: Celebrating the 80th Birthday of Professor Ei-ichi Negishi