PROCESS FOR PREPARING 3-PHENYL-7-METHYL-4-OXO-1,4-DIHYDRO-1,8-NAPHTHIRIDINE

摘要

derivs. of formula (I): (where R is 1-6C alkyl, phenyl, 1-6C acyl or 1-6C alkoxycarbonyl), are prepd. by heating a 1-20% soln. of a pyridine deriv. of formula (II) in a high-boiling solvent at a temp. of 240-350 degrees C (when R = alkyl or phenyl), 240-310 degrees C (when R = acyl) or 240-260 degrees C (when R = alkoxycarbonyl), and subjecting the resulting pyrido 1,2-a pyrimidine deriv. (III) to thermal isomerisation without isolating it, as follows: (where R1 is 1-6C alkyl). Cpds. (I) are useful as inters. for nalidixic acid (1-ethyl-7-methyl-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxyli- c acid), which is an antibacterial. The solvent is pref. "diphyl" (an eutectic mixt. of biphenyl and diphenyl ether) or paraffin oil.