Bu_2SnlH-Promoted Proximal Bond Cleavage of Methylenecyclopropanes and Successive Radical Cyclization and/or Pd-Catalyzed Coupling Reaction

摘要

Methylenecyclopropanes (MCPs, 1) are useful building blocks in organic synthesis due to their high level of reactivity derived from ring-strain, and easy availablity. MCPs can be transformed into various organometallic species depend on the reaction positions by metal reagents (such as Sn-H,~(2a) Si-H,~(2b-d) B-B,~(2e) Si-B~(2f,g)). Although some reports have attributed the cleavage of proximal bonds, almost the reported examples are limited to the cleavage of less-substituted bond to give a vinylic metal 3 (eq 1). From this point of view, the selective cleavage at the hindered proximal bond is significant to generate alternate vinylic metals 2. Preparation of a wide range of vinylic metals is strongly required as a valuable coupling partner in the formation of a π-conjugated system. We report here on the selective formation of vinyltins 2 from MCPs 1 by using di-n-butyliodotin hydride (Bu_2SnIH). Furthermore, applications to intramolecular cyclization and one-pot Pd-catalyzed coupling between the resulting vinyltins and aryl iodide are presented.