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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. |
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