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.

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