Cyclic transformations of 5‐aryl(or benzyl)‐3‐(2‐bromoethyl‐ 1,3,4‐oxadiazol‐2(3 H )‐ones into 1‐aminoimidazolidin‐2‐one and 5,6‐dihydro‐4 H ‐1,3,4‐oxadiazine derivatives

5‐Aryl(or benzyl)‐3‐(2‐bromoethyl)‐1,3,4‐oxadiazol‐2(3 H )‐ones 3 have been prepared. They were reacted with secondary alkylamines without any change of the heterocycle to give amino derivatives 6 , but with primary alkylamines, cyclic transformation occurred to give 1‐acylamino‐3‐alkylimidazolidin‐2‐ones 7 . In the presence of sodium alcoholate, bromo compounds 3 were transformed into 2‐aryl(or benzyl)‐4‐alkoxycarbonyl‐5,6‐dihydro‐4 H ‐1,3,4‐oxadiazines 9 .