Use of the Wittig Reaction in Carotenoid Synthesis

The Wittig reaction has therefore proved to be useful in carotenoid synthesis, particularly by the synthesis strategies illustrated in Fig. 1. 

Carotenoids of symmetrical structure are synthesized by double Wittig condensations that use as central building blocks either crocetindialdehyde (536) as a C2o-component (bond formation between C(7)/C(8) and C(7 )/C(8 )) or with the Cio-dialdehyde 2,7-dimethylocta-2,4,6-trienediaI (34) (bond formation between C(11)/C(12) and C(1 l )/C(12 )). 

In some cases, a reverse procedure is selected a Cio-biphosphonium salt or Cio-biphosphonate is used as the central unit and this is condensed with the corresponding terminal aldehydes (synthesis strategy 4). 

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