Summary The relative migratory aptitude of two acetylenic substituents in the a-alkynone cyclization, a thermal conversion of a-acetylenic ketones A to 2-cyclopentenones C, was investigated by isotope-labeling experiments. The a-alkynone [p-'3C]-1, specifically labeled with I3C at the P-acetylenic C-atom C (3), was synthesized by an intramolecular Wittig reaction (230-300') of the diacylmethylidenephosphorane ['3C]-7. The latter resulted from ...
