Synthesis method of diltiazem chiral intermediate

The invention relates to a diltiazem chiral intermediate synthesis method, which comprises: uniformly mixing and heating L-epoxy ester, chlorobenzene and a catalyst, adding a ferric trichloride methanol solution, dropwise adding o-aminothiophenol, and carrying out a heating reflux reaction; adding methanesulfonic acid into the reaction system for reaction, and distilling in the reaction process to remove the solvent and carry out methanol at the same time; and after the reaction is finished, cooling, crystallizing, filtering, rinsing a filter cake with icy methanol, and drying to obtain a diltiazem chiral intermediate finished product. According to the technical scheme, the reaction selectivity is high, few or basically no trans-isomer impurities are generated, so that the product yield and purity are greatly improved, the amount of a solvent needed by subsequent product refining is small, and the product refining loss is reduced; and compared with the original process, the yield is improved, the product qual