Polyketoenols and chelates. An N-methyl-2-pyridone relative of the xanthyrones : 4H-quinolizone and 1,2-dihydro-2-quinolone formation and chemistry

Abstract

Methyl methoxymethylenecyanoacetate and methyl sodioacetoacetate condense to give a substituted 4H-quinolizone (7) which can also be made by sodium methoxide catalysed condensation of 3,5-bismethoxycarbonyl-6-methyl-2-pyridone with methyl methoxymethylenecyanoacetate. Employment of the N-methylated pyridones (14) and (20) in reactions with methyl methoxymethyleneacetoacetate gives substituted 1,2-dihydro-2-quitolinones, and this behaviour is compared with the 2-pyrone series where xanthyrones are isolated.

Methoxide-ion catalysed condensation of 3,5-bismethoxycarbonyl-1,6-dimethyl-2-pyridone (20) with methyl methoxymethylenecyanoacetate gives an acidic N-methylpyridone analogue of the xanthyrone type (28), lacking the enolised terminus and having unsaturation at 2′ rather than 1′. Boiling water converts it into an oxo-pyrano-2-pyridone (31), further degraded by methoxide ion into the pyridone (20). Again, there are significant structural and chemical contrasts with typical xanthyrones : these appear to arise from two sources; the lower reactivity of the pyridone ring, and steric compression between the N-methyl and the 2′-hydrogen of a 1′-unsaturated trans-sidechain.