Stereoselective formation of activated cyclopropanes with pyridinium ylides bearing a (−)-8-phenylmenthyl group as the chiral auxiliary

The reaction of various mono-substituted methylidenemalononitriles with (−)-8-phenylmenthyl α-pyridiniumacetate in the presence of base afforded the corresponding dicyanocyclopropane compounds with exclusive trans-selectivity and good diastereoselectivity (up to 86:14). The stereochemistry of the major products were determined to be of 1R configuration by X-ray structural analysis of the crystalline trans-2,2-dicyano-3-(4-pyridyl)cyclopropanecarboxylate. The geometric and diastereofacial selectivities were rationalized assuming anti-periplanar approach in the open-chain model, followed by epimerization and then cyclization to give the cyclopropane compounds.