Neue Zugänge zu einigen aromatischen Retinoiden

New Approaches to Some Aromatic Retinoids Starting from 2,3,5‐trimethylphenol ( 2 ), two pathways to ethyl (all‐ E )‐9‐(4‐methoxy‐2,3,6‐trimethylphenyl)‐3,7‐dimethylnona‐2,4,6,8‐tetraenoate ( 1 ) and to some of its ( Z )‐isomers have been developed. The first one is based on a Pd(O)‐catalyzed arylation of ( Z )‐3‐methylpent‐2‐en‐4‐yn‐l‐ol ( 6 ) with 4‐bromo‐2,3,5‐trimethylanisol ( 5 ). The acetylenic C 15 −alcohol 9 was transformed into the corresponding acetylenic phosphonium salt 10 , which was catalytically hydrogenated to the olefinic Wittig salt. Wittig olefination led, then, to the (6 Z , 8 Z )‐ and (4 Z , 6 Z , 8 Z )‐isomers, 7 and 8 , respectively. In a second approach, Friedel ‐ Crafts reaction of 3‐methylpent‐l‐en‐4‐yn‐3‐ol with the 2,3,5‐trimethylanisol gave a C 15 ‐intermediate with a terminal CC bond in the side chain. After deprotonation and reaction with a C 5 aldehyd, the corresponding C 20 ‐intermediate could be isolated in high yield. Finally, further conversion led predominantly to the (all‐ E )‐retinoid, accompanied by its (9 Z )‐ and (13 Z )‐isomers.