Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus Oxo-isophoron. I. Modifizierung der Kienzle-Mayer-Synthese von (3S,3'S)-Astaxanthin

Article abstract of DOI:10.1002/hlca.19810640749

An efficient synthesis of (3S,3'S)-astaxanthin (1a) in high yield and optical purity starting from (4R,6R)-4-hydroxy-2,2,6-trimethylcyclohexanone (4) is reported.The absolute configuration of 1a, previously derived from ORD. data, has been confirmed by X-ray analysis of 5, a derivate of 6-oxo-isophorone (2).The key features of the improved synthesis are the two-step conversion of 4 to the key intermediate (4S)-2,6,6-trimethyl-4-hydroxy-2-cyclohexen-1-one (14), a new method for the partial reduction of the sterically hindered triple bond of (S)-6-hydroxy-3-(5-hydroxy-3-methyl-3-penten-1-ynyl)-2,4,4-trimethyl-2-cyclohexen-1-one (32), and Wittig olefination of the dialdehyde 1,6-dimethyl-1,3,5-octatrienedial (38) using phosphonium salt 37 with a free hydroxyl group.