Synthesen in der Vitamin‐A2‐Reihe. 3. Mitteilung. Anwendung der W ITTIG ‐Reaktion zur Synthese von all‐trans‐ und 13‐cis‐Vitamin A2

Vitamin A2 acid (m. p. 176–178°) has been prepared by the Wittig reaction of (dehydro‐β‐ionylidene‐ethyl)‐triphenylphosphonium bromide and n‐butyl β‐formyl‐crotonate. Reduction of this acid with lithium‐aluminium hydride gave a mixture of all‐trans‐ and 13‐cis‐vitamin A2, which could be separated by chromatography. The same mixture has been obtained from vitamin A acid according to the first vitamin A2 synthesis by FARRAR, HAMLET, HENBEST & JONES.