9-CF 3 and 13-CF 3–β-carotene, canthaxanthin and related carotenoids. Synthesis, characterization and electrochemical data

Abstract

The preparation and characterization of the following trifluoromethylated carotenoids are reported: 9-CF 3–, 13-CF 3–, 9,9′-bis-CF 3–, 13,13′-bis-CF 3–β-carotene, 9-CF 3– and 13-CF 3–canthaxanthin, 13′-CF 3– and, 9′-CF 3–4-oxo-β-carotene, 13′-CF 3–adonirubin and 3-dehydro-13′-CF 3–canthaxanthin. The CF 3 group exhibits a strong cis-directing effect leading primarily to the cis isomer (near the CF 3 group, i.e., all- E) in the synthetic mixtures. The minor all- trans isomer could be enriched by sensitized irradiation; however, they were found to be only marginally stable at room temperature. The CF 3 group also exhibits a stabilizing effect towards oxidation reactions. Spectral data and oxidation potentials of these fluorinated carotenoids are reported.