SYNTHESIS OF PYRIDO[2,3-D]PYRIMIDINONES BY THE REACTION OF AMINOPYRIMIDIN-4-ONES WITH BENZYLIDENE MELDRUMS ACID-DERIVATIVES

A series of pyrido[2,3-d]pyrimidine-4,7-diones 5a-h were prepared from 6-amino-4-pyrimidones 1 and benzylidene Meldrum's acid derivatives 2 by cyclization reactions in boiling nitrobenzene. The structure of 5, determined by nmr measurements, reveals a selective orientation of 1 a nd 2 in the addition step.