Reactions of 3-(Dimethylamino)-2,2-dimethyl-2H-azirines with Barbituric-Acid Derivatives

Article abstract of DOI:10.1002/hlca.19900730824

The reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine (1) and 5,5-disubstituted barbituric acids 5 in i-PrOH at ca. 70 deg gives 2-<5-(dimethylamino)-4,4-dimethyl-4H-imidazol-2-yl>alkanamides of type 6 in good yields (Scheme 1).The formation of 6 proceeds with loss of CO2; 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-4H-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-N¹,N¹-dimethylisobutyramide I as alkylating reagent (Scheme 4).