Phenyliodine(III) Diacetate-Mediated 1,2-ipso-Migration in Mannich Bases of Imidazo[1,2-a]pyridines: Preparation of N-Acetoxymethyl/Alkoxymethyl-N-arylimidazo[1,2-a]pyridine-3-amines.

Phenyliodine(III) diacetate -mediated 1,2-ipso-migration of an imidazo[1,2-a]pyridine ring via the formation of an aziridine intermediate in Mannich bases derived from imidazo[1,2-a]pyridines, 2-pyridylamines or arylamines, and formaldehyde is reported. The imidazo[1,2-a]pyridines bearing different substituents showed excellent migratory aptitude and resulted in corresponding N-acetoxymethyl-, N-alkoxymethyl-, and N-hydroxymethyl-N-arylimidazo[1,2-a]pyridine-3-amine derivatives in moderate to excellent (42 examples; 35-93%) yields. Radical trapping experiments confirmed the involvement of a non-radical intermediate. The developed protocol is amenable for a scale-up reaction, and synthetic utility of N-acetoxymethyl products was demonstrated by transforming them to corresponding N-(pyridin-2-yl)imidazo[1,2-a]pyridin-3-amines.