Synthesis of α-pyridone-based azaheteroaromatics by intramolecular vinylketene cyclizations onto the C=N bond of nitrogen heteroaromatics

Article abstract of DOI:10.1021/jo00104a033

Substituted quinolizin-4-ones and ring-fused α-pyridone derivatives have been synthesized by the construction of 2,3-disubstituted-4-(2-azaheteroaryl)-2-cyclobutenones followed by thermal rearrangement. 4-(2-Azaheteroaryl)-2-cyclobutenones have been prepared regioselectively by the addition of 2-lithioazaheteroaromatics to cyclobutenediones and by palladium catalyzed cross-coupling of 4-chloro-2-cyclobutenones with 2-tri-n-stannylazaheteroaromatics. The thermal transformation is proposed to occur by ring-opening of the cyclobutenone followed by intramolecular cyclization of the transient vinylketene onto the carbon-nitrogen double bond of the azaheteroaromatic. A variety of quinolizin-4-ones, imidazo[1,2-a]pyridin-5-ones, 1-oxopyrido[2,1-b]benzothiazoles, and thiazolo[3,2-a]pyridin-5-ones were prepared.