Total synthesis of prolycopene, a novel 7,9,7′,9′-tetra-cis(Z) carotenoid and main pigment of the tangerine tomato Lycopersicon esculentum

A total synthesis of the 7,9,7′,9′-tetra-cis(Z) isomer of lycopene, also known as ‘prolycopene’, produced as the major carotenoid pigment in fruits of the tangerine tomato Lycopersicon esculentum (‘Tangella’) is described. The synthesis is based on: (i) a modified Sonogashira coupling reaction between the E-alkenyl bromide 6 and the Z-enynol 7, leading to the 2Z-trienynol 8, followed by (ii) a Wittig reaction between the phosphonium salt 4 and the C₁₀-triene dialdehyde 5 producing the symmetrical 9,9′-Z isomer of the bis-acetylene 3 and (iii) semi-hydrogenation of 3 in the presence of Lindlar's catalyst, and chromatography.