Synthesis of Vinyl-P-ionol

A portion (5 ml) of a solution of methyl-4-bromo-3-methylbut-2-enoate (5) (19.3 g, 0.1 mol) and P-cyclocitral (6) in dry benzene (85 ml) and Et20 (15 ml) is added dropwise to activated Zn dust (7.0 g, 0.107 mol). With stirring, the mixture is warmed gently until the reaction commences. The remainder of the solution is added, with stirring, at a rate such as to 

As has been shown in previous Chapters the Wittig and the Horner-Emmons reactions are of utmost importance for the coupling of carotenoid end groups with the polyene chain. In the following example, the synthesis of the naturally occurring C25-apocarotenal 507 (12 -apo-P-caroten-12 -al, (3-apo-12 -carotenal) and also ethyl 8 -apo-P-caroten-8 -oate (1) (P-apo-8-carotenoic acid ethyl ester), which is produced industrially by means of these reactions, is described. 

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