Alkylidenephosphoranes, stabilized

A method for the preparation of symmetrical alkenes by oxidation of resonance-stabilized alkylidenephosphoranes with hydroperoxides has been extended to the preparation of symmetrical carotenoids. Thus treatment of the triphenylphosphonium bromide (60) with hydrogen peroxide and sodium carbonate in aqueous propan-2-ol gave the C24 ester (61) in 33% yield. /S-Carotene. 

Olefins with electrophilic substituents, but not those with electron-donating substituents, add tertiary phosphines 61 the phosphonium betaines first formed stabilize themselves under some circumstanes by forming their tautomers, the alkylidenephosphoranes. Thus, for example, the ylide (5) is obtained in more... 

Hydroxyisoindole-, isoindoline- and indane-l,3-diones have been reacted with both stabilized alkylidenephosphoranes (e.g., acyl-methylenetriphenylphosphoranes) and also active ylides such as phosphacumulenes. ... 

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