Eine neue Aminoazirin‐Reaktion. Bildung von 3,6‐Dihydropyrazin‐2(1 H )‐onen

A New Aminoazirine Reaction. Formation of 3,6‐Dihydropyrazin‐2(1 H )‐ones The reaction of 3‐(dimethylamino)‐2 H ‐azirines 1 and 2‐(trifluoromethyl)‐1,3‐oxazol‐5(2 H )‐ones 5 in MeCN or THF at 50–80° leads to 5‐(dimethylamino)‐3,6‐dihydropyrazin‐2(1 H )‐ones 6 ( Scheme 3 ). Reaction mechanisms for the formation of 6 are discussed: either the oxazolones 5 react as CH‐acidic heterocycles with 1 ( Scheme 4 ), or the azirines 1 undergo a nucleophilic attack onto the carbonyl group of 5 ( Scheme 6 ). The reaction via intermediate formation of N ‐(trifluoroacetyl)dipeptide amide 8 ( Scheme 5 ) is excluded.