Synthesis and NMR‐Spectroscopic Structure Determination of Novel 7,7′‐Diphenyl‐7,7′‐diapocarotenoids

Wittig reaction of crocetindial (1) and benzylidenetripenylphosphorane (2) gave (7E, 7′Z)‐7,7′‐diphenyl‐7‐7′‐diapocarotene (3), instead of the previously reported (7E, 7′E)‐isomer. Similar reaction of 8,9‐didehydrocrocetindial (4) with 2 yielded the three acetylenic isomers 5a–c which differ in the configuration of the terminal double bonds. Structures were established by 1D‐ and 2D‐NMR studies. Illustrative spectra and their interpretation are presented. Most chemical shifts of corresponding protons in 3 and 5 and nearly identical, but 13C shifts differ considerably.