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