Synthese von optisch aktiven, natürlichen Carotinoiden und strukturell verwandten Naturprodukten. VIII. Synthese von (3S,3′S)‐7,8,7′,8′‐Tetradehydroastaxanthin und (3S,3′S)‐7,8‐Didehydroastaxanthin (Asterinsäure)

Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. VIII. Synthesis of (3S,3′S)‐7,8,7′,8′‐Tetradehydroastaxanthin and (3S,3′S)‐7,8‐Didehydroastaxanthin (Asterinic Acid) The synthesis of all‐trans‐(3S,3′S)‐3,3′‐dihydroxy‐7,8, 7′,8′‐tetradehydro‐β, β‐carotene‐4,4′‐dione (1), of all‐trans‐(3S,3′S)‐3,3′‐dihydroxy‐7, 8‐didehydro‐β,β‐carotene‐4,4′‐dione (2) (asterinic acid = mixture of 1 and 2), and of their 9,9′‐di‐cis‐ and 9‐cis‐isomers is reported starting from (4′S)(2E)‐5‐(4′‐hydroxy‐2′, 6′,6′‐trimethyl‐3′‐oxo‐l′‐cyclohexenyl)‐3‐methyl‐2‐penten‐4‐ynal (8). The absolute configuration (3S,3′S) for both components 1 and 2 of asterinic acid ex Asterias rubens is confirmed on the basis of spectroscopic and direct comparison.