Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6‐Oxo‐isophoron. IV. Neues Konzept für die Synthese von (3 RS , 3′ RS )‐, (3 S , 3′ S )‐ und (3 R , 3′ R )‐9,9′‐di cis ‐7,8,7′,8′‐Tetradehydroastaxanthin

Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6‐Oxo‐isophorone. IV. A Novel Concept for the Synthesis of (3 RS , 3′ RS )‐, (3 S , 3′ S )‐ and (3 R , 3′ R )‐9,9′‐di cis ‐7,8,7′,8′‐Tetradehydroastaxanthin Starting from readily available intermediates of the synthesis of astaxanthin, (3 RS , 3′ RS )‐, (3 R , 3′ R )‐ and (3 S , 3′ S )‐9,9′‐di‐ cis ‐tetradehydroastaxanthin ( 1, 1a and 1b , resp.) were synthesized, 1 and 1b for the first time. Key features of this concept are: a) use of the unprotected, acetylenic phosphonium salts 8–12 , b) a two‐step synthesis with 47% overall yield, and c) good chemical and optical purity of the end products.