Abstract

Protonation of the highly reactive 1:1 intermediates produced in the reaction between tributylphosphine and dialkyl acetylenedicarboxylates by 2-hydroxy-3-methyl-2-cyclopenten-1-one leads to vinyltributylphosphonium salts, which undergo an addition-elimination reaction in CH   2Cl2 at room temperature to produce dialkyl 2-[(2-methyl-5-oxo-1-E and Z isomers) cyclopentenyl)-oxy]-2-butenedioates (1:1 mixtures of in fairly high yields