Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6‐Oxo‐isophoron. IV. Neues Konzept für die Synthese von (3RS, 3′RS)‐, (3S, 3′S)‐ und (3R, 3′R)‐9,9′‐dicis‐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 (3RS, 3′RS)‐, (3S, 3′S)‐ and (3R, 3′R)‐9,9′‐dicis‐7,8,7′,8′‐Tetradehydroastaxanthin Starting from readily available intermediates of the synthesis of astaxanthin, (3RS, 3′RS)‐, (3R, 3′R)‐ and (3S, 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.