Theoretical study and synthesis of the reaction between triphenylphosphine, dialkyl acetylenedicarboxylates and 2-aminobenzimidazole, 2-hydroxy-3-nitropyridine or 1,2,3,4-tetrahydrocarbazole

Triphenylphosphine reacts with dialkyl acetylenedicarboxylates in the presence of heterocyclic compounds, such as 2-aminobenzimidazole, 2-hydroxy-3-nitropyridine or 1,2,3,4-tetrahydrocarbazole to generate stable phosphorus ylides. Some ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partical double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group, whereas others occur as a single isomer only. For this reason, the assignments of more stable Z- or E-isomers as the major or minor forms were investigated using theoretical calculations.