4‐Amino‐1,5‐dihydro‐2 H ‐pyrrol‐2‐one aus Bortrifluorid‐katalysierten Umsetzungen von 3‐Amino‐2 H ‐azirinen mit Carbonsäure‐Derivaten

4‐Amino‐1,5‐dihydro‐2 H ‐pyrrol‐2‐ones from Boron Trifluoride Catalyzed Reactions of 3‐Amino‐2 H ‐azirines with Carboxylic Acid Derivatives Reaction of 3‐amino‐2 H ‐azirines 1 with ethyl 2‐nitroacetate ( 6a ) in refluxing MeCN affords 4‐amino‐1,5‐dihydro‐2 H ‐pyrrol‐2‐ones 7 and 3,6‐diamino‐2,5‐dihydropyrazines 8 , the dimerization product of 1 ( Scheme 2 ). Thus, 6a reacts with 1 as a CH‐acidic compound by CC bond formation via C ‐nucleophilic attack of deprotonated 6a onto the amidinium‐C‐atom of protonated 1 ( Scheme 5 ). The scope of this reaction seems to be rather limited as 1 and 2‐substituted 2‐nitroacetates do not give any products besides the azirine dimer 8 (see Table 1 ). Sodium enolates of carboxylic esters and carboxamides 11 react with 1 under BF 3 catalysis to give 4‐amino‐1,5‐dihydro‐2 H ‐pyrrol‐2‐ones 12 in 50–80% yield ( Scheme 3, Table 2 ). In an analogous reaction, 3‐amino‐2 H ‐pyrrole 13 is formed from 1c and the Li‐enolate of acetophenone ( Scheme 4 ). A reaction mechanism for the ring enlargement of 1 involving BF 3 catalysis is proposed in Scheme 6 .