Interaction of condensed tetrahydropyrido[4,3-d]pyrimidin-4-ones with dehydrobenzene – synthesis of 6-vinylpyrimidinones fused with five-membered heterocycle containing two or three heteroatoms

[Figure not available: see fulltext.] The reaction between dehydrobenzene and tetrahydropyrido[4,3-d]pyrimidin-4-ones condensed with isoxazole, thiazole, thiadiazole, or triazole rings resulted in Hofmann cleavage of the tetrahydropyridine moiety with the formation of 6-vinyl-substituted pyrimidones fused with the corresponding azole rings.