Iron-catalyzed [1+1+1] cyclopropanation by sequential coupling of an ester to two carbenes

Traditional precious metal catalysis benefits from well-characterized inner-sphere elementary steps in which a single complex binds and unites substrates at the metal center. By contrast, base metal catalysts have recently demonstrated competence in cross-coupling transformations through iterative outer-sphere reactions in which product bond formation occurs by serial additions to the ligand, not the metal. Despite the emerging diversity of two-component outer-sphere reactions, comparable multicomponent outer-sphere couplings remain rare. In this study, we describe an iron-catalyzed [1+1+1] synthesis of cyclopropanols through iterative outer-sphere reactions between two carbenes and an ester. This reaction initially generates silyl enol ethers stereo-, regio-, and chemoselectively through a traceless, directed olefination that can be further exploited to enable transformations unavailable to prior methods.