Anomalous cyclization of ethyl acetoacetate (3,6-dimethyl-4-oxo-3,4-dihydropyrimidin-2-yl)hydrazone.

Structural modification of some (pyrimidin-2-yl)hydrazones derived from ethyl acetoacetate via methylation at the N3 atom promotes anomalous cyclization to give [1,2,4]triazolo[1,5- a]pyrimidine derivatives. The mechanism of this transformation includes specific cleavage of the aliphatic fragment in the substrate with subsequent rearrangement of carbene-like intermediate. [ABSTRACT FROM AUTHOR]