An Expedition Through the Last Decade of Heterocycle Construction by Using Palladium, Iron, Copper, or Iodine/tert-Butyl Hydroperoxide

Abstract

Over the past decade, our group has developed a series of synthetic methods for the preparation of heterocycles by using two different approaches: transition-metal-catalyzed cyclization and ­iodine/oxidant-catalyzed oxidative cyclization. Transition-metal salts of palladium or iron and nanoparticulate copper(II) oxide have been used as catalysts for the synthesis of heterocyclic compounds. Palladium-catalyzed Wacker-type oxidative heterocyclic cyclization, iron-catalyzed benzylation and tandem dehydration annulation, and nanoparticulate copper(II) oxide-catalyzed heterogeneous oxidative cyclizations have been developed in our laboratory. For iodine-catalyzed reactions, we have developed an oxidative tandem cyclization, an oxidative decarboxylative coupling cyclization, a direct Mannich-like reaction, and an oxidative amination catalyzed by diiodine and tert-butyl hydroperoxide under mild condition. These methods have enriched the range of synthetic strategies available for the construction of heterocyclic skeletons and they have potential applications in the fields of medicinal chemistry and materials science. 1 Introduction 2 Transition Metal-Catalyzed Heterocyclic Cyclization 2.1 Palladium-Catalyzed Wacker-Type Oxidative Heterocyclic Cyclization 2.1.1 Synthesis of 2-Methyl-2H-chromen-3(4H)-ones 2.1.2 Synthesis of 2-Methylquinolines 2.1.3 Synthesis of Pyrroles from Amino Acids 2.2 Lewis acid Iron(III) Chloride Catalyzed Intermolecular Cyclization Through Benzylation 2.2.1 Preparation of Functionalized 4H-Chromenes 2.2.2 Preparation of 3-Quinolinecarboxylic Acid Esters 2.2.3 Preparation of Highly Functionalized 2,3-Dihydro-1H-pyrroles 2.3 Syntheses of Quinazolines and 2-Aryldihydrobenzofurans Catalyzed by Nanoparticulate Copper(II) Oxide or Copper(I) Chloride 2.3.1 Synthesis of Quinazolines in the Presence of Copper(II) Oxide Nanoparticles 2.3.2 One-Pot Synthesis of 2-Aryl-2,3-dihydro-1-benzofurans Catalyzed by Copper(I) Chloride 3 Diiodine/tert-Butyl Hydroperoxide-Catalyzed Heterocyclic Cyclization 3.2 Synthesis of Highly Functionalized Oxazoles 3.3 Synthesis of 2-Phenylquinazoline by sp3 C–H Functionalization with Diiodine/tert-Butyl Hydroperoxide 3.4 Synthesis of Quinazolines Through Amination of Primary a-Amino Acids or sp3 C–H Bonds Adjacent to Nitrogen or Oxygen Atoms 3.5 Synthesis of Benzofurans and Naphthofurans 4 Conclusion