Selective C-acylation of CH-active dicarbonyl compounds with ketenylidenetriphenylphosphorane: syntheses and structures of 3-phosphoranylideneacyltetronic acids, 3-phosphoranylideneacyl-4-oxocoumarins, and 4-phosphoranylideneacylpyrazol-5-ones

Selective C- over O-/N-acylation of acyclic, carbocyclic and heterocyclic c arbonyl compounds bearing active alpha-CH groups is described. beta-Ketoest ers give the corresponding alpha-acylylidic derivatives in good yields. Lik ewise, tetronic acids and 4-hydroxycoumarins furnish the respective 3-acyly lidic derivatives, and pyrazol-5-ones exclusively yield the corresponding 4 -acylylidic compounds despite the possibility of tautomerism. X-Ray single crystal structure and NMR analyses of the product tricarbonyl ylides are pr esented and structure-reactivity interdependencies are discussed. As a rule , compounds with wide-spread conjugation of the pi-system like 9/13 do not readily undergo Wittig olefination. Acylylides 11 with separated beta-keto moieties react normally.