The invention relates to a process for recycling L-cis-
lactam as a
diltiazem intermediate by-product. The process comprises the following steps of: reacting by using L-cis-
lactam as a
raw material, IBX as an
oxidizing agent, and DMSO with the
water content of 5-15% as a
solvent, performing TLC detection and stopping reaction until the
raw material disappears, dissolving in water, stirring for an hour and then performing
filtration, collecting filter cakes, washing the filter cakes using
ethyl acetate,
drying a
mother liquor, reducing pressure and concentrating to obtain 2-(4-methoxyphenyl)-1,5-benzothiazepin-3,4(2H,5H)-
diketone,
drying and recycling the filter cakes, and then obtaining IBA. According to the invention, IBX with
high selectivity is used as an
oxidizing agent, the reaction condition is moderate, the condition of absolute no water and
oxygen is not required, the reaction time is shorter, the post-
processing is simple, environmental
pollution does not exist, and the reduction product IBA of the IBX can be oxidized as IBX again for recycling use, so that the cost is reduced. Therefore, the method has the characteristics of convenience, high efficiency and economy; the yield of target products can reach more than 90%.