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Umsetzungen von 3‐(Dimethylamino)‐2,2‐dimethyl‐2 H ‐azirin mit Barbitursäure‐Derivaten

1990; Wiley; Volume: 73; Issue: 8 Linguagem: Inglês

10.1002/hlca.19900730824

1522-2675

Marlise Schläpfer‐Dähler, Heinz Heimgartner,

Chemical Reaction Mechanisms

Reactions of 3‐(Dimethylamino)‐2,2‐dimethyl‐2 H ‐azirines with Barbituric‐Acid Derivatives The reaction of 3‐(dimethylamino)‐2,2‐dimethyl‐2 H ‐azirine ( 1 ) and 5,5‐disubstituted barbituric acids 5 in i‐PrOH at ca. 70° gives 2‐[5‐(dimethylamino)‐4,4‐dimethyl‐4 H ‐imidazol‐2‐yl]alkanamides of type 6 in good yields ( Scheme 1 ). The formation of 6 proceeds with loss of CO 2 ; various reaction mechanisms with a zwitterionic 1:1 adduct B as common intermediate are discussed ( Schemes 2 and 5 ). Thermolysis of product 6 leads to 2‐alkyl‐5‐(dimethylamino)‐4,4‐dimethyl‐4 H ‐imidazoles 8 or the tautomeric 2‐alkylidene derivatives 8 ′ via elimination of HNCO ( Scheme 3 ). The latter undergoes trimerization to give 1,3,5‐triazine‐2,4,6‐trione. No reaction is observed with 1,5,5‐trisubstituted barbiturates and 1 in refluxing i‐PrOH, but an N ‐alkylation of the barbiturate occurs in the presence of morpholine ( Scheme 4 ). This astonishing reaction is explained by a mechanism via formation of the 2‐alkoxy‐2‐(dimethylamino )aziridinium ion H which undergoes ring opening to give the O ‐alkylated 2‐amino‐ N 1 , N 1 ‐dimethylisobutyramide I as alkylating reagent ( Scheme 4 ).