Bortrifluorid‐katalysierte Umsetzungen von 3‐Amino‐2 H ‐azirinen mit Aminosäure‐estern und Aminen

Boron‐Trifluoride‐Catalyzed Reactions of 3‐Amino‐2 H ‐azirines with Amino‐acid Esters and Amines After activation by protonation or complexation with BF 3 , 3‐amino‐2 H ‐azirines 1 react with the amino group of α‐amino‐acid esters 3 to give 3,6‐dihydro‐5‐aminopyrazin‐2(1 H )‐ones 4 by ring enlargement ( Scheme 2, Table 1 ). The configuration of 3 is retained in the products 4 . With unsymmetrically substituted 1 (R 1 ≠ R 2 ), two diastereoisomers of 4 ( cis and trans ) are formed in a ratio of 1:1 to 2:1. With β‐amino‐acid esters 5 and 7 , only openchain α‐amino‐imidamides 6 and 8 , respectively, are formed, but none of the seven‐membered heterocycle ( Scheme 3 ). Primary amines also react with BF 3 ‐complexed 1 to yield α‐amino‐imidamides of type 9 ( Scheme 4, Table 2 ). Compound 9b is characterized chemically by its transformation into crystalline derivatives 10 and 12 with 4‐nitrobenzoyl chloride and phenyl isothiocyanate, respectively ( Scheme 5 ). The structure of 12 is established by X‐ray crystallography. Mechanisms for the reaction of activated 1 with amino groups are proposed in Schemes 6 and 7 .