Flash vacuum pyrolysis of 5 (aminomethylidene)-2, 2dimethyl-l, 3-~ o~ e-4,~ dion~(Meldrum's acid derivativea) 12 gives 4hydroxyquinolines/4quinolonea 16 or 3- enaminoacroleins 22 in good to excellent yields. Intermediate (aminomethy1ene) ketenes and imidoylketenes are directly observed and their transformation into product 22 monitored by low-temperature IR spectroscopy. Imidoylketenes are also formed and observed upon ...