Preparation and ( E / Z )‐Isomerization of the Diastereoisomers of Violaxanthin

Violaxanthin A (=(all‐ E ,3 S ,5 S ,6 R ,3′ S ,5′ S ,6′ R )‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐ β , β ‐carotene‐3,3′‐diol = syn , syn‐ violaxanthin; 5 ) and violaxanthin B (=(all‐ E ,3 S ,5 S ,6 R ,3′ S ,5′ R ,6′ S )‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐ β , β ‐carotene‐3,3′‐diol= syn,anti‐ violaxanthin; 6 ) were prepared by epoxidation of zeaxanthin diacetate ( 1 ) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I 2 ‐catalyzed photoisomerization. The structure of the main products, i.e. , (9 Z )‐ 5 , (13 Z )‐ 5 , (9 Z )‐ 6 , (9′ Z )‐ 6 , (13 Z )‐ 6 , and (13′ Z )‐ 6 , was determined by their UV/VIS, CD, 1 H‐NMR, 13 C‐NMR, and mass spectra.