NOVELTY - Toluene and triethylamine are mixed with 2-(7-methoxy-1-naphthyl)ethylamine. Acetic anhydride is slowly dripped and reacted. After reaction completion, water is dripped and residual acetic anhydride is hydrolyzed. The reaction mixture is filtered and the caked is washed with water to a pH of 7. The toluene layer of filtrate is washed with water to a pH of 7. The combined toluene layers are concentrated under reduced pressure to dryness, and the residue is added to toluene, heat-dissolved, cooled, crystallized, filtered, and dried to obtain agomelatine.    USE - Preparation of agomelatine (claimed).    ADVANTAGE - The method enables quick, environmentally-friendly and simple large-scale preparation of agomelatine using economical raw materials, under mild reaction conditions, with high yield and product purity.    DETAILED DESCRIPTION - In a reaction container, ethylene glycol dimethyl ether and sodium hydride are added at 15 plus minus 2 degrees C. (2E)-(7-Methoxy-3,4-dihydronaphthalen-1(2H)-ylidene)acetonitrile is added and dimethyl methylphosphonate is dripped in 3-4 hours at 10 degrees C, stirred for 15 hours, cooled to 5 degrees C or less, and added with water. Remaining sodium hydride is added and 10% hydrochloric acid solution is dripped to adjust the pH to 5-6. Extraction is carried out using methylene chloride and the organic layer is concentrated to dryness under reduced pressure. The residue is added to ethanol, heat-dissolved, cooled, crystallized, and filtered to obtain (2E)-(7-methoxy-3,4-dihydronaphthalen-1(2H)-ylidene)acetonitrile. Tetrachlorobenzoquinone is added to a reactor, and glacial acetic acid and (2E)-(7-methoxy-3,4-dihydronaphthalen-1(2H)-ylidene)acetonitrile are added and mixed. The mixture is heat-refluxed, reacted for 12 hours, cooled to room temperature, and distilled under reduced pressure. The residue is dissolved in toluene and filtered. The filtrate is washed with 5% sodium sulfite solution, dried, washed with water, filtered, and layered. The toluene layer is concentrated under reduced pressure, and the residue is dissolved in ethanol, mixed, cooled, crystallized, and filtered to obtain 1-cyano-7-methoxy-1-naphthyl methyl acetate derivative of formula (I). Raney nickel, ethanol, and ammonia, are added to the obtained compound. Nitrogen is purged at 0.3-0.8 MPa and 40-60 degrees C, and the contents are reacted for 7 hours. The reaction solution is cooled and Raney nickel is recovered by filtration. The filtrate is concentrated under reduced pressure to dryness, toluene is added, and the reaction mixture is washed with water and layered. The toluene layer is further added with saturated brine and layered. The toluene layer is concentrated under reduced pressure to obtain give 2-(7-methoxy-1-naphthyl)ethylamine. Toluene and triethylamine are mixed with the obtained compound. Acetic anhydride is slowly dripped at 30 degrees C or less and reacted at 20-30 degrees C for 5 hours. After reaction completion, water is dripped and residual acetic anhydride is hydrolyzed. The reaction mixture is filtered and the caked is washed with water to a pH of 7. The toluene layer of filtrate is washed with water to a pH of 7. The combined toluene layers are concentrated under reduced pressure to dryness, and the residue is added to toluene, heat-dissolved, cooled to 0-5 degrees C, crystallized, filtered, and dried to obtain agomelatine.    R=methyl, ethyl or propyl.