Tailored Aza‐Michael Addition as Key Step in the Synthesis of 1H‐imidazo[5,1‐c][1,4]oxazine Scaffolds

A novel protocol for the efficient synthesis of 1H‐imidazo[5,1‐c][1,4]oxazines has been developed. Aza‐Michael addition of selected primary amines to 1,2‐diaza‐1,3‐dienes (DDs) combined with isothiocyanates or isocyanates in sequential 3‐CR process, affords 2‐thiohydantoins and hydantoins with suitably positioned functional groups to be used for chemoselective acid‐promoted ring‐fused formation. A new strategy has been proposed for the synthesis of an array of imidazo[5,1‐c][1,4]oxazine chemotypes by using a planned aza‐Michael addition in a 3‐CR heteroring‐forming, post‐cyclization transformation followed by an intramolecular fused‐heterocycles formation process.