Technical Procedures for the Syntheses of Carotenoids and Related Compounds from 6‐Oxo‐isophorone: Syntheses of (3<i>R</i>,3′<i>R</i>)‐Zeaxanthin. Part II

Abstract

Abstract Starting from the readily available, optically active (4 R )‐hydroxy‐2,2,6‐trimethylcyclohexanone ( 2 ), a new technical synthesis of (3 R ,3′ R )‐zeaxanthin is described. According to a completely new C 9 +C 2 +C 4 = C 15 scheme, the ketone 2 was protected, ethynylated with Li‐acetylide, and the C 11 ‐intermediate 6 was acetylated, followed by dehydration. The product 10 was protected, deprotonated, and subsequently reacted with methyl vinyl ketone to provide the C 15 ‐propargylate 13 . Reduction in situ of 13 with Vitride yielded the olefinic C 15 ‐alcohol 11 which was transformed into the known C 15 ‐ Wittig salt 3 . A double Wittig reaction of this salt with the C 10 ‐dialdehyde 4 afforded nature‐identical zeaxanthin ( 1 ).