AN UNEXPECTED REACTION OF A 3-AMINO-2H-AZIRINE WITH 1,3-BENZOXAZIN-2,4-DIONE

The reaction of 3-dimethylamino-2,2-dimethyl-2H-azirine (1) with 1,3-benzoxazin-2,4-dione (3) in refluxing 2-propanol led not to the formation of a medium sized heterocycle but to the formation of the imidazo[2.1-b]-1,3-benzoxazin-5-one 4 and the imidazolin-2-one 5 in 33% and 74% yield, respectively. The structure of 4 has been confirmed by X-ray crystallographic analysis while 5 has been identified by comparison with an independently synthesized material (cf. Scheme 2). In Scheme 3 a reaction mechanism for the formation of 4 and 5 is suggested