Free accessResearch articleFirst published online 2006-4
Synthesis and Dynamic 1 H NMR Study of Stable Phosphorus Ylides Derived from Reaction between Heterocyclic NH-Acids and Triphenylphosphine in the Presence of Acetylenic Esters
Stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylate in the presence of a strong NH-acid, such as 2-indolinone, 3-acetylindole and saccharine. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. Dynamic effects are observed in 1H NMR spectra. The calculated free-energy of activation for interconversion of the rotational isomers in 2-indolinone amounts to about 68.2±2 J/mol.
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