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General Method for the Preparation of Electron-Deficient Imidazo[1,2‑a]pyridines and Related Heterocycles

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journal contribution
posted on 18.12.2015 by Ivar M. McDonald, Kevin M. Peese
A new annulation method for the preparation of the imidazo­[1,2-a]­pyridine ring system under mild conditions is presented. Treatment of a 2-aminopyridine with a dimethylketal tosylate in acetonitrile at elevated temperature (80–140 °C) in the presence of catalytic Sc­(OTf)3 provides the imidazo­[1,2-a]­pyridine product in good yield. The annulation method is broadly applicable to electron-poor 2-aminopyridines and displays a complementary profile to the classic preparation of the imidazo­[1,2-a]­pyridine ring system by reaction of a bromoketone with electron-rich and -neutral substrates. The scope of the process and mechanistic considerations are discussed.