AIM analysis for the ylide rotamers from the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of 2-pyrrolecarbaldehyde

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reactions between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of NH-acid, such as 2-pyrrolecarbaldehyde. 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. In the recent work, the stability of the Z and E isomers was undertaken for the two rotamers of a phosphorus ylide by means of atoms in molecules (AIM) analysis.