Synthese von optisch aktiven, natürlichen Carotinoiden und strukturell verwandten Naturprodukten. V. Synthese von (3 R , 3′ R )‐, (3 S , 3′ S )‐ und (3 R ,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 (3 R , 3′ R )‐, (3 S , 3′ S )‐ and (3 R ,3′ S ; meso )‐zeaxanthin by Asymmetric Hydroboration. A New Approach to Optically Active Carotenoid Building Units The synthesis of (3 R , 3′ R )‐, (3 S , 3′ S )‐ and (3 R ,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) 2 BH to give the optically pure key intermediates 5 and 7 resp., which are transformed into the above‐mentioned C 40 ‐compounds.