Selective C-Acylation of 2-Aminoimidazo[1,2-<i>a</i>]pyridine: Application to the Synthesis of Imidazopyridine-Fused [1,3]Diazepinones

A series of 20 optically pure 3,4-dihydro-5H-pyrido­[1′,2′:1,2]­imidazo­[4,5-d]­[1,3]­diazepin-5-ones which form a new family of azaheterocycle-fused [1,3]­diazepines were synthesized in four steps with 17–66% overall yields. The key step consists of a selective C-acylation reaction of easily accessible 2-aminoimidazo­[1,2-a]­pyridine at C-3.