A Convenient and Stereoselective Synthesis of 11Z-3,4-Didehydroretinal by Horner–Emmons Reaction Using Diphenyl Phosphonate

Abstract

A convenient synthesis of 3,4-didehydroretinal was developed. The Horner–Emmons reaction between 3,4-didehydro-β-ionone and diphenyl phosphonate in the presence of crown ether gave the retinonitrile as an isomeric mixture, in which the newly produced double bond was predominantly 11Z-form. After separation of the 11Z-form retinonitrile, it was converted into the corresponding retinal in good yield without isomerization of the double bonds.