Practical stereoselective synthetic routes to the antihistaminic drug olopatadine and its E- isomer have been developed, the key steps being a trans stereoselective Wittig olefination using a nonstabilized phosphorus ylide and a stereoselective Heck cyclization. The stereoselectivity of the Wittig reaction depends on both the phosphonium salt anion and the cation present in the base used to generate the ylide.
![[3-(dimethylamino)propyl]triphenylphosphonium chloride hydrochloride结构式](https://image.chemsrc.com/caspic/018/1160596-81-5.png)
