The invention discloses a preparing method for a
caproic acid derivative and provides a preparing method for a
caproic acid derivative IV. The method comprises the following steps that in a polar nonprotic
organic solvent, a compound III and an iodization
reagent are subjected to a
nucleophilic substitution reaction under
inert gas shielding, and the
caproic acid derivative IV is obtained.
Brivaracetam can be prepared from the caproic
acid derivative IV only through two steps, the synthetic
route is short, the reaction condition is mild, posttreatment is simple, the reaction yield is high, and the production cost is low.
Racemization does not happen in the reaction process, further purification is conducted through
crystallization instead of a chiral high-pressure
liquid phase preparing column, the chiral purity of the
brivaracetam I can be improved till the de value is larger than 99.80%, meanwhile, the content of other single impurities of the
brivaracetam I is smaller than 0.1%, the API level is reached, and the method is suitable for industrial production. The expression is shown in the description.