Patent ID: 8871953

Claim:
A process for the preparation of olopatadine comprising the preparation of the intermediate of formula (V) wherein R is methyl, ethyl, propyl, or butyl, comprising the steps of: a) transforming isoxepac of formula into an ester of formula (IVa) b) transforming the isoxepac ester (IVa) obtained from step a) into the compound of formula (V) by means of a Wittig reaction; and c) hydrolysing the compound of formula (V) to give olopatadine free-base, wherein in step b) the isoxepac ester of formula (IVa) is made to react with an appropriate solution comprising phosphorus ylide in an appropriate solvent, in the presence of sodium hydride, to give the compound of formula (V), wherein R is as previously defined, and the solution comprising the phosphorus ylide in the appropriate solvent is added to the solution comprising the isoxepac ester of formula (IVa).