硫黄原子の酸化的・還元的活性化を経る有機合成反応の開発 Development of Organic Reactions by Means of Oxidative or Reductive Activation of Sulfur Atom

Organosulfur compounds play an important role in organic synthesis owing to their unique reactivities. We have been focusing on development of transformation and synthesis of organosulfur compounds. In this account, we describe our recent advances on the transformations and syntheses of organosulfur compounds via oxidative or reductive activation of sulfur atom. Oxidative activation of sulfur atom on organosulfur compounds promotes substitution reaction involving elimination of sulfur moieties (desulfurization) efficiently, particularly intramolecular cyclization. Indeed, iodine-mediated oxidative desulfurization promoted cyclization of N-2-pyridylmethyl thioamides leading to imidazo [1,5-a]pyridines proceeds rapidly under mild conditions. Although the reaction requires higher temperature, a similar oxidative desulfurization-cyclization of thioamides is achieved using oxygen gas as an oxidant in the presence of copper catalysts. Also, oxidative activation of sulfur atom can be applied to direct sulfidation of aromatic compounds using elemental sulfur via electrophilic substitution fashion. Furthermore, hydrochlorosilane-mediated reductive activation of elemental sulfur promotes direct thionations of carbonyl compounds. The reaction can be applied to a wide variety of carbonyl compounds.