CUMULATED YLIDES .22. REACTIONS OF (TRIPHENYLPHOSPHORANYLIDENE)ETHENONE WITH HALOGEN COMPOUNDS AND THEIR PREPARATIVE APPLICATION

(Triphenylphosphoranylidene)ethenone (6) reacts with halogen compounds 7 to yield four-membered ylide phosphonium salts 9. Ring opening of 9 under different conditions gives rise to the formation of bis-ylides 13, ylide salts 14, or bis-phosphonium salts 15. Compounds 13/14 are hydrolysed to mono-ylides 16, and the Wittig reaction with aldehydes yields unsaturated acylphosphoranes 17, which on thermolysis afford enyne carboxylic esters 18. From the bis-salts 15 alpha-branched divinyl ketones 22 are available by bis-Wittig reaction.