Mechanistic studies in the chemistry of urea. Part I. Reaction with pentane-2,4-dione (acetylacetone)

Abstract

Urea, methylurea, and NN′-dimethylurea react with pentane-2,4-dione in acidic solution to give hydroxypyrimidines (pyrimidones). Kinetic and spectral evidence suggests that the mechanism of reaction is acid-catalysed attack of urea on the keto–enol form of pentane-2,4-dione followed by cyclisation. This is confirmed by examination of the reactions of 1,1,1-trifluoro- and 1,1,1,5,5,5-hexafluoro-pentane-2,4-dione with methylurea. Absence of an enolizable hydrogen at the 3-position in pentane-2,4-dione completely changes the course of the reaction.