Pyrimidine derivatives and related compounds. Part 42. Isolation of the intermediates in the ring transformation of 1,3-oxazine-2,4-diones into pyrimidines and pyrazoles, and their structure determination by 15N nuclear magnetic resonance analysis

Abstract

Reaction of the 6-methyl-1,3-oxazine-2,4-diones (1) and (2) with hydrazine hydrate at room temperature gave the 6-hydroxy-5,6-dihydrouracils (7a) and (8a). The structures of the products were determined by ¹⁵N n.m.r. analysis. The mechanism of the ring transformation of 1,3-oxazines into pyrimidines and pyrazoles is discussed.