49 - Addition Reactions of Electron Deficient Cyclopropanes Catalyzed by Calcium(II) Complexes
University of Richmond
Calcium(II) complexes are proving to be versatile catalysts for the activation of electron deficient cyclopropanes in addition reactions. The synthesis of ?-sulfanyl malonates was achieved through the homologous conjugate addition of thiols to electron deficient cyclopropanes. These addition reactions were catalyzed by calcium acetylacetonate, Ca(acac)2, and did not require prior activation or exogenous base. Differentially substituted ?-sulfanyl malonates were synthesized in good to excellent yield. In addition, the activation of cyclopropanes by calcium(II) complexes has been expanded to include 1,3-dipolar additions. In the presence of a Ca(II) complex, the reaction of nitrones with electron-deficient cyclopropanes provides the corresponding tetrahydro-1,2-oxazines in good to excellent yield with high diastereoselectivity.