Synthesis and dynamic 1H NMR study around the carbon-carbon double bond in the new stable phosphorus ylides derived from the reaction between hexamethyl phosphorous triamide and dimethyl acetylenedicarboxylate in the presence of NH-heterocyclic compounds

New and stable phosphorous ylides are obtained from a simple and efficient one-pot three-component reaction between hexamethyl phosphorous triamide and dimethyl acetylenedicarboxylate in the presence of NH-heterocyclic compounds in excellent yields at an ambient temperature. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of the restricted rotation around the carboncarbon partial double bond resulting from the conjugation of the ylide moiety with the adjacent carbonyl group. Dynamic effects are observed in the 1H NMR spectra that are attributed to the restricted rotation around the carboncarbon double bond. The experimental rotational energy barrier (G) and other activation parameters on the basis of the 1H NMR study for the rotational interchangeable process of major and minor isomers in ylides 4ad are reported. (C) 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:131137, 2012; View this article online at . DOI 10.1002/hc.20761