APPLICATION OF DIPHENYL DISELENIDE AS A NEW CATALYST FOR PHOTOCHEMICAL STEREOISOMERIZATION OF CAROTENOIDS

In a comparative study, diphenyl diselenide was shown to be an alterna tive to iodine as a catalyst for photochemical E/Z isomerization of ca rotenoids. Suitable conditions for the stereomutation of zeaxanthin, v iolaxanthin, canthaxanthin and fucoxanthin are reported. Photochemical allenic isomerization with increased R to S conversion was achieved b y employing diphenyl diselenide rather than iodine as the catalyst. Re producible and expedient artificial light conditions, avoiding insolat ion (sunlight), are reported. Diphenyl diselenide tolerated the presen ce of Hunig's base upon stereoisomerization of acid-sensitive caroteno ids. Diphenyl ditelluride effected E/Z stereomutation, but no allenic RIS isomerization of fucoxanthin. The presence of base decreased the i somerization rate in the absence of catalyst and may serve to decrease undesirable E/Z stereoisomerization of base-stable carotenoids.