Cobalt-Catalyzed Asymmetric Cyclopropanation of Electron-Deficient Olefins

摘要

Metal-catalyzed cyclopropanation of olefins with diazo reagents has attracted great research interest because of its fundamental and practical importance. The resulting cyclopropyl units are recurrent motifs in biologically important molecules and serve as versatile precursors in organic synthesis. In the past two decades, outstanding asymmetric catalytic processes, notably those based on copper, rhodium, and ruthenium, have been developed to allow for the synthesis of chiral cyclopropane derivatives from olefins with diazoacetates in high yields and high selectivities. While a number of catalytic systems worked exceptionally well with styrene derivatives and some electron-rich olefins, asymmetric cyclopropanation of electron-deficient olefins containing electron-withdrawing groups such as α, β-unsaturated carbonyl compounds and nitriles have proven to be a challenging problem presumably due to the electrophilic nature of the metal—carbene intermediates in the catalytic cycles. This catalytic asymmetric process would be highly desirable as the corresponding electrophilic cyclopropanes containing two or more electron-withdrawing groups have shown to be valuable synthetic intermediates for various applications.