9-CF3 and 13-CF3-beta-carotene, canthaxanthin and related carotenoids. Synthesis, characterization and electrochemical data

The preparation and characterization of the following trifluoromethylated c arotenoids are reported: 9-CF3-, 13-CF3-, 9,9'-bis-CF3-, 13, 13'-bis-CF3-be ta-carotene, 9-CF3- and 13-CF3-canthaxanthin, 13'-CF3- and, 9'-CF3-4-oxo-be ta-carotene, 13'-CF3-adonirubin and 3-dehydro-13'-CF3-canthaxanthin. The CF 3 group exhibits a strong cis-directing effect leading primarily to the cis isomer (near the CF3 group, i.e., all-E) in the synthetic mixtures. The mi nor all-trans isomer could be enriched by sensitized irradiation; however, they were found to be only marginally stable at room temperature. The CF3 g roup also exhibits a stabilizing effect towards oxidation reactions. Spectr al data and oxidation potentials of these fluorinated carotenoids are repor ted. (C) 1999 Elsevier Science S.A. All rights reserved.