Nitro-1, 2-dihydro-1-oxoisoquinoline-3-carboxylate compounds (5a, b and 9a, b) were synthesized by the reaction of methyl isocyanoacetate with nitrophthalic anhydrides in the presence of 1, 8-diazabicyclo [5. 4. 0] undec-7-ene (DBU), followed by esterification with diazomethane and hydrolysis with HCl. In these reactions, the methylidenephthalide compound (10) was also obtained by hydrolysis of the oxazole-4-carboxylate compound (8b) due to the presence of the bulky ortho nitro group. Moreover, 1, 2-dihydro-4-hydroxy-1-oxoisoquinoline-3-carboxylic acid (16) was prepared via the oxazole dicarboxylic acid compound (15) in good yield.