Synthesis method of Ramosetron

The invention discloses a synthesis method of Ramosetron. According to the method, 3,4-diaminobenzoic acid is used as a starting raw material for finally preparing the Ramosetron through the synthesis of benzimidazole-5-carboxylic acid, benzimidazole-5-methyl carbonate sulfate, 4,5,6,7-tetrahydro benzimidazole-5-methyl carbonate sulfate, 4,5,6,7-tetrahydro benzimidazole-5-triazolylformate sulfate, N-[(4,5,6,7-tetrahydro benzimidazole-5-yl)] pyrrole hydrochloride and 5-[(1-methylindol -3-yl) carbonyl]-4,5,6,7-tetrahydro benzimidazole. Compared with the prior art, the method provided by the invention has the advantages that the reaction conditions are optimized; after the optimization, the reaction is really feasible; the yield of the 4,5,6,7-tetrahydro benzimidazole-5-methyl carbonate sulfate, the 4,5,6,7-tetrahydro benzimidazole-5-triazolylformate sulfate, the N-[(4,5,6,7-tetrahydro benzimidazole-5-yl)] pyrrole hydrochloride and the like is improved; the reaction total yield reaches more than 30 percent; higher economic benefits are realized.