β,β-Carotene, 15,15′-didehydro- → 15-cis-beta-Carotene

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Reaction Steps

Two moles of β-C19 -aldehyde (I) are condensed with acetylenedimagnesium bromide to give the C40 -diol (II). The C40 -diol is converted into 15,15' didehydro-β-carotene (III) by allylic rearrangement with simultaneous dehydration. The product is partially hydrogenated over Lindlar catalyst to give mainly 15-cis-β-carotene (IV) which is isomerized to all-trans-β-carotene by treatment in high boiling petroleum ether. While several methods of obtaining β-carotene from vitamin A have been proposed, the conditions required in these methods are extreme, the reagents are expensive, and, worst of all, the yields are low.

Provenance & Evidence