Abstract: This invention relates to a method for producing compounds of the formula (I) or their salts: wherein each of R1 and R2 is hydrogen, unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted alkynyl, unsubstituted or substituted aryl, unsubstituted or substituted heteroaryl, OR3, SR3, COR3, COOR3 or cyano; R1 and R2 may combine together with the adjacent carbon atom of ═CR1R2 to form an unsubstituted or substituted cyclic ring; each of R4 and R5 is hydrogen, unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted alkynyl, unsubstituted or substituted aryl, unsubstituted or substituted heteroaryl, NR6R7, OR8 or SR9; R4 and R5 may combine together with the adjacent skeleton of C/N bond to form a heterocyclic ring; which comprises rearranging compounds of the formula (II) or their salts: wherein R1, R2, R4 and R5 are as defined above.