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 C 10 ‐dialdehyde as central component. This C 10 ‐dialdehyde is lengthened at both ends, first with vinyl ether and then with propenyl ether, leading to a C 20 ‐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 C 10 + C 20 + C 10 = C 40 . 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.