Optically Active Model Carotenoids

For comparative H NMR and CD studies with natural bicyclic C50 carotenoids the Car carotenoids (9), (10), ( D and (0 have Nen synthesized frotn the appropriate irones (d, 6. 10). The C CMOt e (  

17 -dmorplectaniaxanthin acetonide (65) were synthesized in connection with studies on the absolute configuration of plectaniaxanthin [(35), R=R =H] (153). 

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In the present chapter recent total syntheses of chiral carotenoids as racemates which have been useful for assigning relative configuration by NMR, will be discussed as well as syntheses of optically active model carotenoids and of optically active natvurally occurring carotenoids or their enantiomers. Also included are recent syntheses related to naturally occurring carotenoids with Z-configuration in the polyene chain. 

In the absence of X-ray crystallographic analyses the total synthesis of chiral model carotenoids which are more acessible and better yet, of the optically active natural carotenoids for confirmation of configurational assignments represents a challenge. 

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