a process for producing a compound represented by formula , wherein each of r 1 , r 2 , r 3 and r 4 , which may be the same or different , represents a hydrogen atom or a lower alkyl group , the process includes deprotecting a protective group of a compound represented by formula , wherein r 1 , r 2 , r 3 and r 4 are as defined above , and r 5 represents a protective group of a hydroxy group . the process is an industrially advantageous , simple , and efficient process for producing a key intermediate of a benzodiazepine - 2 , 4 - dione compound , which is a therapeutic medicine for arrhythmia .