The synthesis and Diels-Alder reactions of cyclopropenyl ketones are described. Cyclopropenyl ketones are highly reactive dienophiles that can engage a range of cyclic dienes and 2,3-dimethylbutadiene. The strategy of using cyclopropenyl ketones to facilitate Diels-Alder reactions is not limited to products that contain three-membered rings, as reductive opening by SmI2 can be used to produce a product that lacks a cyclopropane but retains a quaternary stereogenic center.

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 Et 2 O or THF. Upon further study, it was found that there were reproducibility issues for those reactions that were carried out in Et 2 O. 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.

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