Benzo [b] [1,4] diazepin * 2,4-dione compound of preparation

The present invention provides benzo beneficial industrially prepared simply and effectively as a therapeutic agent for arrhythmia [b] [1,4] diazepine key intermediate 2,4-dione compounds. The method of preparation of the present invention is a method of preparing compounds of formula (1), wherein the general formula (2) compound represented by the protective group (R5) deprotecting, [wherein, R1, R2, R3, and same or different and R4, represents a hydrogen atom or a lower alkyl group. ] [Wherein, R1, R2, R3 and R4 are as defined above. R5 represents a hydroxy-protecting group. ].