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Synthese und Chiralität von (5S, 6R)-5,6-Epoxy-5,6-dihydro-β,β-carotin und (5R, 6R)-5,6-Dihydro-β,β-carotin-5,6-diol, einem Carotinoid mit ungewöhnlichen Eigenschaften

✍ Scribed by Walter Eschenmoser; Conrad Hans Eugster

Publisher
John Wiley and Sons
Year
1978
Tongue
German
Weight
555 KB
Volume
61
Category
Article
ISSN
0018-019X

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✦ Synopsis

Synthesis and Chirality of (5__S__,6__R__)‐5,6‐Epoxy‐5,6‐dihydro‐β,β‐carotene and (5__R__,6__R__)‐5,6‐Dihydro‐β,β‐carotene‐5,6‐diol, a Compound with Unexpected Solubility Characteristics

Wittig‐condensation of azafrinal (1e) with the phosphorane derived from 7 leads to a (1:3)‐mixture of (E)‐9′‐ and (Z)‐9′‐β,β‐carotene‐diol 3, from which pure and optically active 3 ((5R,6R)‐5,6‐dihydro‐β,β‐carotene‐5,6‐diol) has been isolated as bright violet leaflets, m.p. 168°. Due to the trans‐configuration of the diol moiety and to severe steric hindrance, hydrogen bonding is reduced to such an extent, that 3 behaves much more as a hydrocarbon than as a diol. There is good evidence that the so‐called ‘β‐oxycarotin’ obtained by Kuhn & Brockmann [15] by chromic acid oxidation of β, β‐carotene is the corresponding racemic cis‐diol. 3 has been converted into (5S, 6R)‐5,6‐epoxy‐5.6‐dihydro‐β,β‐carotene (4), m.p. 156°. This transformation establishes for the first time the chirality of a caroteneepoxide (without other O‐functions).

Full spectral and chiroptical data including a complete assignement of ^13^C‐chemical shifts for azafrin methyl ester and 3 are presented.

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