The carotene-like polyenes decapreno-β-carotene (C50), C54-β-carotene (C54, first synthesis) and dodecapreno-β-carotene (C60) with 15, 17 and 19 conjugated double bonds, respectively, were synthesized by double Wittig reactions. Introduction of a leaving group in allylic position failed, and cations were obtained by hydride elimination effected by i) triphenylcarbenium tetrafluoroborate-d15, prepared by a new method, or ii) treatment with ...
