Synthesis of herbicidal 3-substituted-4(3H)-pyrimidinones under high pressure

The reaction of an N-monosubstituted amidine with a beta -ketoester to affo rd a pyrimidinone is sluggish at best under normal conditions. We now repor t that this reaction can be effected in moderate yield under high pressure. Thus, 2,6-dichloro-4-pyridyl-(N-prop-2-ynyl)ca (4b) was reacted with three alpha -substituted-beta -ketoesters (2b-d) at 10-16 kbar to afford herbici dal 2-(2,6-dichloro-4-pyridyl)-3-(prop-2-ynyl)-4(3H)-pyrimidinones 5b and 5 c in 15-43% yield. This result expands the scope of reactions promoted by a pplication of high pressure.