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 α‐branched divinyl ketones 22 are available by bis‐Wittig reaction.
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