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Carotinoide mit 7-Oxabicyclo[2.2.1]heptyl-Endgruppen. Teil I. Versuch einer Synthese von Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3,6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotin-5,5′-diol)

✍ Scribed by Michael Roman Gmünder; Conrad Hans Eugster

Publisher
John Wiley and Sons
Year
1990
Tongue
German
Weight
896 KB
Volume
73
Category
Article
ISSN
0018-019X

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✦ Synopsis

Starting from our recently described synthon (+)-24, the enantiomerically pure 3,6:4,5:3',6':4,5'-tetraepoxy-4,5,4,5'-tetrahydro-&,~-carotene (34) and its 15,15'-didehydro analogue 32 were synthesized in eleven and nine steps, respectively (Scheme 4 ) . Chiroptical data show, in contrast to the parent &,&-carotene, a very weak interaction between the chiral centers at C(5), C(5'), C( 6), C ( 6) , and the polyene system. Diisobutylaluminium hydride reduction of 32 lead rather than to the expected 15,15'-didehydro analogue 35 of cycloviolaxanthin (8), to the polyenyne 36 (Scheme 5). We explain this reaction by an oxirane rearrangement leading to a cyclopropyl ether followed by a fragmentation to an aldehyd on the one side and an enol ether on the other (Scheme 6). This complex rearrangement includes a shift of the whole polyenyne chain from C(6), C(6') to C(5), C(5') of the original molecule. I ) Aus der Dissertation [I]; gegenwartige Adresse: F. Hofmunn-La Roche AG, 4002 Basel. ' ) *) Die Zuordnung der Signale bei 71,6 und 65,8 beruht auf Abschiiitzung rnit Hilfe der CSEARCH-Datenbank [28]: C(3) 45-85 und C(4) 64-99 ppm, 'bond level' = 1.

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