Heterocyclensynthesen mit 5-Phenyl-isoxazoliumsalzen, 3. Mitt.: Synthese von Pyrrolo[1,2-a]chinazolin-5-onen

Refluxing of ethanol-acetic acid solutions of N-aroyl-N-methyl-benzoylacetamides3 causes elimination of acetophenone and generation of N(1)-substituted N(3)-methyl-1H,3H-quinazoline-2,4-diones5. In contrast, at room temperature in acetanhydride3 eliminate water yielding 2-benzoylmethylene-quinazolinones4, which at 60 °C cyclize to pyrrolo[1,2-a] quinazolin-5-ones6. The transformation4 →6 may be explained in terms of a “normal”Knorr reaction. A “anomalous”Knorr reaction was observed in the case of the more rigid4 d leading to a mixture of diasteromere7 d cis and7 d trans in kinetically controlled reaction. Favoured by intramolecular hydrogen bonding7 d cis converts to the thermodynamically more stable6 d by warming of the ethanolic solution for 3 hours.