Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6‐Oxo‐isophoron. II. Ein neues Konzept für die Synthese von (3 RS , 3′ RS )‐Astaxanthin

Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6‐Oxo‐isophorone. II. A Novel Concept for the Synthesis of (3 RS , 3′ RS )‐Astaxanthin Starting from 6‐oxo‐isophorone ( 2 ) a new concept for a seven‐step synthesis of (3 RS , 3′ RS )‐astaxanthin ( 1 ) has been developed. As a key feature of the new approach, the oxidation state of astaxanthin ( 1 ) is adjusted already at an early stage of the synthesis. Thus, manipulation on more complex intermediates later in the synthesis is reduced to a minimum. Acetonide 10 or dimer 13 represent the key intermediates of this concept (Scheme 2) . The whole sequence has been run on a kg scale with an overall yield of 52% (s. Scheme 5 ).