SYNTHESIS OF ALPHA-PYRIDONE-BASED AZAHETEROAROMATICS BY INTRAMOLECULAR VINYLKETENE CYCLIZATIONS ONTO THE C=N BOND OF NITROGEN HETEROAROMATICS

Substituted quinolizin-4-ones and ring-fused alpha-pyridone derivative s have been synthesized by the construction of disubstituted-4-(2-azah eteroaryl)-2-cyclobutenones followed by thermal rearrangment. 4-(2-Aza heteroaryl)-2-cyclobutenones have been prepared regioselectively by th e addition of 2-lithioazaheteroaromatics to cyclobutenediones and by p alladium catalyzed cross-coupling of 4-chloro-2-cyclobutenones with 2- tri-n-stannylazaheteroaromatics. The thermal transformation is propose d to occur by ring-opening of the cyclobutenone followed by intramolec ular 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.