Preparation method and intermediate of midazolam

The invention belongs to the field of pharmaceutical chemistry preparation, and discloses a preparation method of midazolam and an intermediate M2 of midazolam. The preparation method provided by the invention comprises the following steps: taking SM1 as a starting material, reacting with SM2 of 1, 3-diamino acetone protected by alkoxycarbonyl or acyl to obtain an intermediate M2, carrying out reductive amination, removing a protecting group under an acidic condition, carrying out in-situ alkalization ring closing reaction, reacting with orthoacetate, and finally oxidizing to obtain midazolam. The preparation method disclosed by the invention has the advantages of short steps, high yield, mild reaction conditions and simple and convenient post-treatment, and avoids dangerous reactions, dangerous reagents, control reagents and genotoxic impurities related to a traditional route, so that the operation and product safety is relatively high, and industrial large-scale production is facilitated. 本发明属于药物化学制备领域，公开了一