Side reactions in the pyroglutamic acid-7-amino-4-methylcoumarin synthesis.

N-Formylpyroglutamic acid-7-amido-4-methylcoumarine and pyroglutamyl-pyroglutamic acid-7-amido-4-methylcoumarin are the major products in the synthesis of pyroglutamic acid-7-amido-4-methylcoumarin by phosphorus pentachloride in dimethylformamide and dicyclohexylcarbodiimide under pyridine activation.