The total synthesis of two natural acetylenic aromatic carotenoids, 7, 8- didehydroisorenieratene (1) and 7, 8-didehydrorenieratene (2), was carried out. Although the condensations involving C 15-acetylenic ylids (derived from the phosphonium salts 7, and 8) as the intermediates gave only 9-cis isomers of 1 and 2, low-temperature condensations of C 25-hexaene yield (derived from 19 and 28) with C 15-acetylenic ...