Application of diphenyl diselenide as a new catalyst for photochemical stereoisomerization of carotenoids

Abstract

In a comparative study, diphenyl diselenide was shown to be an alternative to iodine as a catalyst for photochemical E/Z isomerization of carotenoids. Suitable conditions for the stereomutation of zeaxanthin, violaxanthin, canlhaxanthin and fucoxanthin are reported. Photochemical allenic isomerization with increased R to S conversion was achieved by employing diphenyl diselenide rather than iodine as the catalyst. Reproducible and expedient artificial light conditions, avoiding insolation (sunlight), are reported. Diphenyl diselenide tolerated the presence of Hünig's base upon stereoisomerization of acid-sensitive carotenoids. Diphenyl ditelluride effected E/Z stereomutation, but no allenic R/S isomerization of fucoxanthin. The presence of base decreased the isomerization rate in the absence of catalyst and may serve to decrease undesirable E/Z stereoisomerization of base-stable carotenoids. © Acta Chemica Scandinavica 1998.