Crocetin dimethyl ester

There have been many applications of the Wittig reaction in multistep syntheses. The reaction can be used to prepare extended conjugated systems, such as crocetin dimethyl ester, which has seven conjugated double bonds. In this case, two cycles of Wittig reactions using stabilized ylides provided the seven double bonds. Note the use of a conjugated stabilized ylide in the second step.250... 

Crocetin dimethyl ester (143) was prepared from each of the isomeric dibromo esters (140-142) with DBU in different solvents at ambient temperature (77CB3582). 

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