In a process where an ortho-alkylnitrobenzene derivative and a vinyl compound as starting materials are used to prepare a 1,5-diaminonaphthalene derivative via a 4-(2-nitrobenzene)propane derivative and a 5-nitro-1-tetralone derivative, the ortho-alkylnitrobenzene derivative and a vinyl compound having an electron withdrawing group such as an acrylonitrile derivative and an acrylate may be reacted in the presence of a base to provide an aromatic nitro compound. An aromatic nitro compound such as 4-(2-nitrobenzene)butanonitrile thus obtained may be cyclized to safely, cost-effectively and selectively provide a 5-nitro-1-tetralone derivative without forming any isomer. Furthermore, from the 5-nitro-1-tetralone derivative, a 1,5-diaminonaphthalene derivative may be prepared without forming any isomer.