Synthese von optisch aktiven, natürlichen Carotinoiden und strukturell verwandten Naturprodukten. V. Synthese von (3R, 3′R)‐, (3S, 3′S)‐ und (3R,3′S; meso)‐Zeaxanthin durch asymmetrische Hydroborierung. Ein neuer Zugang zu Optisch aktiven Carotinoidbausteinen. Vorläufige Mitteilung

Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. V. Synthesis of (3R, 3′R)‐, (3S, 3′S)‐ and (3R,3′S; meso)‐zeaxanthin by Asymmetric Hydroboration. A New Approach to Optically Active Carotenoid Building Units The synthesis of (3R, 3′R)‐, (3S, 3′S)‐ and (3R,3′S; meso)‐zeaxanthin (1), (19) and (21) is reported utilizing asymmetric hydroboration as the key reaction. Thus, safranol isopropenylmethylether (4) is hydroborated with (+)‐ and (−)‐(IPC)2BH to give the optically pure key intermediates 5 and 7 resp., which are transformed into the above‐mentioned C40‐compounds.