Optisch aktive 4,5-Epoxy-4,5-dihydro-α-ionone und Synthese der stereoisomeren 4,5:4',5'-Diepoxy-4,5,4',5'-tetrahydro-ε,ε-carotine und der sterische Verlauf ihrer Hydrolyse

Article abstract of DOI:10.1002/hlca.19860690409

We prove that epoxidation with peracid of α-ionone, contrary to a recently published statement, predominantly leads to the cis-epoxide.Acid hydrolysis affords a single 4,5-glycol whose structure, established by an X-ray analysis, shows that oxirane opening occured with inversion at the least substituted position (C(4)).Stable cis- and trans-epoxides are prepared by epoxidation of the C15-phosphonates derived from α-ionone.Both the racemic and optically active form are used for the synthesis of the 4,5:4',5'-diepoxy-4,5,4',5'-tetrahydro-ε,ε-carotenes having the following configuration in the end goups: meso-cis/cis, meso-trans/trans, rac-cis/trans, rac- and (6R,6'R)-cis/cis, rac- and (6R,6'R)-trans/trans, rac- and (6R,6'R)-cis/trans, and (6R,6'R)-cis/ε.Acid hydrolysis of the cis/cis-epoxycarotenoids under relatively strong conditions occurs again with inversion at C(4)/C(4') in case of the cis/cis-epoxycarotenoids, but at C(5)/C(5') in case of the trans/trans-epoxycarotenoids.An independent synthesis of this 4,5,4',5'-tetrahydro-ε,ε-carotene-4,5,4',5'-tetrol is presented.The irregular results of the oxirane hydrolysis are explained by assumption of neighbouring effects of the lateral chain. 400-MHz-1H-NMR data are given for each of the stereoisomeric sets.In the visible range of the CD spectra, the (6R,6R')-epoxycarotenoids compared with (6R,6R')-ε,ε-carotene exhibit an inversion of the Cotton effects.