Studies on the stability of cycloprop-2-ene carboxylate dianions and reactions with electrophiles

Dianions are generated from alkyllithium reagents and cycloprop-2-ene carboxylic acids, and these dianions can be functionalized by electrophiles at the vinylic position. In a previous report, we described that such dianions could be generated and reacted with electrophiles in Et2O or THF. Upon further study, it was found that there were reproducibility issues for those reactions that were carried out in Et2O. Working under the assumption that an impurity may have promoted these reactions, a detailed study was undertaken to determine the effect of variables on the generation, stability, and reactivity of cycloprop-2-ene carboxylate dianions. It has been found that certain additives can have a substantial effect on the chemistry of cycloprop-2-ene carboxylate dianions. In particular, it was determined that amine N-oxide additives have a beneficial effect both on the stability of cycloprop-2-ene carboxylate dianions and on the rates that such dianions undergo alkylation. Conditions for reacting dianions with a broad range of electrophiles are described.