An Efficient Synthesis of Stable Phosphorus Ylides Derived from Pyrazole and Indazole

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of strong NH-acids, such as pyrazole, indazole and 5-nitro Indazole. 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.

Keywords:

• Acetylenic ester
• NH-acid
• stable phosphorus ylides
• triphenylphosphine