Synthesis and flash vacuum pyrolysis of isoxazolo- and isothiazolo[5,4-d]pyrimidines

The multi-step synthesis of isothiazolo[5,4-d]pyrimidines (1c,d) and isoxazolo[5,4-d]pyrimidine (1b) is described. Flash vacuum pyrolysis of lb leads to phenyliminopropadienone, Ph-N=C=C=C=O, which was identified by Ar matrix infrared spectroscopy.