Patent ID: 8865896

Claim:
A method for preparing a compound represented by the following formula (1): wherein m and n are independently an integer of 2 to 5, R 1 is chosen from C 1-6 alkyl groups, R 2 and R 3 are the same or different, and are chosen from a hydrogen atom and C 1-6 alkyl groups, or R 2 and R 3 are combined with an adjacent nitrogen atom to form pyrrolidine, morpholine, thiomorpholine, piperidine, homopiperidine, piperazine or homopiperazine and the nitrogen atom of position 4 of said piperazine or homopiperazine may be substituted by a group chosen from C 1-4 alkyl groups, and R 4 is chosen from C 1-3 alkyl groups, or its pharmaceutically acceptable salt which is characterized by performing the following steps in the order listed below: (i) adding a boron-containing reducing agent to (A) a compound represented by the following formula (2): wherein m, n, R 1 , R 2 and R 3 are the same as defined above, or (B) a mixture of a salt of the compound represented by the formula (2) and a base; and after at least ten minutes. (ii) adding a compound represented by the following formula (3): wherein R 4 is the same as defined above.