Aryliminopropadienone-C-amidoketenimine-amidinoketene-2-aminoquinolone cascades and the ynamine-isocyanate reaction

Imidoylketenes 11 and oxoketenimines 12 are generated by flash vacuum therm olysis of Meldrum's acid derivatives 9, pyrrolediones 17 and 18, and triazo le 19 and are observed by IR spectroscopy. Ketenimine-3-carboxylic acid est ers 12a are isolable at room temperature. Ketenes 11 and ketenimines 12 und ergo rapid interconversion in the gas phase, and the ketenes cyclize to 4-q uinolones 13. When using an amine leaving group in Meldrum's acid derivativ es 9c, the major reaction products are aryliminopropadienones, ArN=C=C=C=O (15). The latter react with 1 equiv of nucleophile to produce ketenimines 1 2 and with 2 equiv to afford maIonic acid imide derivatives 16. N-Arylketen imine-C-carboxamides 12c cyclize to quinolones 13c via the transient amidin oketenes 11c at temperatures of 25-40 degrees C. This implies rapid interco nversion of ketenes and ketenimines by a 1,3-shift of the dimethylamino gro up, even at room temperature. This interconversion explains previously poor ly understood outcomes of the ynamine-isocyanate reaction. The solvent depe ndence of the tautomerism of 4-quinolones/4-quinolinols is discussed. Rotat ional barriers of NMe2 groups in amidoketenimines 12c and malonioc amides a nd amidines 16 (24) are reported.