Purines, pyrimidines, and imidazoles. Part XLIV. Syntheses of some dihydro-1,3-oxazine derivatives and related substituted uracils

Abstract

6-Methyl-1,3-oxazine-2,4(3H)-dione has been prepared from ethyl acetoacetate by reaction with NN-dimethyl- or NN-diethyl-urea in acetic acid–acetic anhydride solution, and by heating with ethyl carbamate in the presence or absence of solvent. The oxazinedione was also produced by heating ethyl N-acetoacetylcarbamate, and by heating N′-acetoacetyl-NN-dimethylurea with acetic acid–acetic anhydride or sulphuric acid. The compound was identical with material prepared from diketen and NN-dimethylurea, and its structure was confirmed by ¹H and ¹³C n.m.r. spectroscopy. Similar reactions of various β-oxo-esters, including C-methyl and C-benzyl derivatives, with ethyl carbamate and with NN-dimethylurea provided various 6-aryl- and 6-alkyl-oxazinediones and 5,6-dialkyloxazinediones. Treatment of the oxazinediones and their N-alkyl derivatives with ammonia and with primary amines gave substituted uracils and with secondary amines, acylated ureas. The 6-methyloxazinedione dimerised when heated with sodium hydroxide to give (6-hydroxy-4-methyl-2-pyridyl)acetic acid.