ケテンおよびその誘導体の研究(第50報)脂肪族イミドエステルとジケテンとの反応

抄録

Reaction of diketene with aliphatic imido esters (Ia-c) affords 2-alkyl-2-ethoxy-6-methyl-3, 4-dihydro-2H-1, 3-oxazin-4-one (IIa-c), which is converted into 5-acetyl-2, 6-dialkyl-4(3H)-pyrimidone (IIIa-c), N-acylacetoacetamide (IVa-c), and 2-alkyl-6-methyl-4(3H)-pyrimidone (Va-c). On the other hand, aliphatic imido ester, which has an electron-attracting moiety such as ethyl cyanoacetimidate (XII) and ethyl 1-ethoxyformimidoyl acetate (VI), does not produce oxazin derivatives but gives 6-ethoxy-4-methyl-2-pyridone-3-carbonitri1e(XIII) and ethyl 2-ethoxy-4-hydroxy-6-methylpyridine-3-carboxylate (VII), which is considered to have an enamine structure. In the presence of a catalytic amount of acetic acid, VI yields 2-ethoxycarbonylmethylene-6-methyl-3, 4-dihydro-2H-1, 3-oxazin-4-one (XVII : R=CO₂Et). XVII is trasnformed to ethyl N-acetoacetylmalonamate (XVIII) and ethyl 2, 6-dihydoxy-4-methylpyridine-3-carboxylate (XIX).