Synthesen in der Carotinoid‐Reihe. 6. Mitteilung. Synthese von Crocetindialdehyd und Lycopin

A simple and efficient synthesis of lycopene is described based on stepwise lengthening of a symmetrical C10‐dialdehyde as central component. This C10‐dialdehyde is lengthened at both ends, first with vinyl ether and then with propenyl ether, leading to a C20‐dialdehyde which is transformed into crocetin dialdehyde by partial hydrogenation of the central triple bond. By means of a new reaction devised by Wittig, crocetin dialdehyde is condensed at both ends with geranylidene‐triphenylphosphorane and lycopene is obtained according to the scheme C10 + C20 + C10 = C40. This synthetic pigment is identical with pure natural lycopene isolated from tomato juice. The Wittig reaction also allows a new β‐carotene synthesis using the components cyclogeranylidene‐triphenylphosphorane and 8,8′‐dehydro‐crocetin dialdehyde.