Palladium‐Catalyzed S‐Allylation of Vinyl Carbinols – Total Syntheses of Carotenoids by Julia‐Kocienski Olefination

Abstract

AbstractPalladium catalyzed S‐allylation of vinyl carbinols from ionones (or conjugated carbonyls) with 2‐mercapto‐1,3‐benzothiazole (BT‐SH) provides versatile C15 dienyl benzothiazolyl (BT) sulfides. This Pd(dppe)Cl2‐catalyzed S‐allylation is highly selective for free allylic alcohols in the presence of allylic acetates, resulting in 3‐ or 4‐acetoxy C15 dienyl BT‐sulfides suitable for xanthophyll synthesis. The corresponding C15 dienyl BT‐sulfones undergo Julia‐Kocienski olefination reactions with C10 2,7‐dimethyl‐2,4,6‐octatrienedial under mild conditions to produce carotenoids natural products. Efficient synthesis is achieved for a range of carotenoids including xanthophylls such as iso‐zeaxanthin, zeaxanthin, and lutein as well as carotenes like β‐carotene, ϵ‐carotene, and 9′‐Z‐phenyl‐carotene.