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 C15-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 C25-hexaene yield (derived from 19 and 28) with C15-acetylenic aldehyde (12a) led to all-trans 1 and 2, which were identical with natural specimens.
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Ike et al. (1974) studied this question.
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