Wittig reaction Astaxanthin and zeaxanthin

In the target carotenoid, the middle part and the end groups are defined. By using the well established Wittig reaction for the final step, there are two possible strategies  

Since deprotonation of the C o-diphosphonium salt tends to eliminate PPhs instead of forming the diphosphorane, this Wittig reaction with the C 15-aldehyde must be carried out at low temperatures. In contrast, the first approach, using a Ci5-phosphonium salt and the Cio-dialdehyde, gives higher and more reproducible yields even at ambient temperature. 

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