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Oct. 7, Hydrogen-Transfer Annulations Forming Heterocycles by John Hydrogen-Transfer Annulations Forming Heterocycles Samuel John Thompson Dong Group – UT Austin Wednesday – October 7th, 2015 Literature Review This review brought to you by Angewandte. 560 ACCOUNT Minireviews A. Nandakumar,E.Balaraman et al. Cp*Ir Complex-Catalyzed Hydrogen Transfer Reactions Directed toward International Edition:DOI:10.1002/anie.201503247 Synthetic Methods German Edition:DOI:10.1002/ange.201503247 Environmentally Benign Organic Synthesis Cp*IrKen-ichi Complex-Catalyzed Hydrogen Transfer Reactions Fujita, Ryohei Yamaguchi* Transition-Metal-Catalyzed Hydrogen-Transfer Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan Fax +81(75)7536634; E-mail: [email protected]; E-mail: [email protected] Annulations:Access to Heterocyclic Scaffolds Received 1 October 2004 Avanashiappan Nandakumar,* Siba Prasad Midya, Vinod Gokulkrishna Landge, and Ekambaram Balaraman* The stability of organoiridium complexes was advanta- Abstract: Catalytic activity of Cp*Ir complexes toward hydrogen geous for the studies on stoichiometric reactions in detail; annulations ·heterocycles ·hydrogen transfer · transfer reactions are discussed. Three different types of reactions thus the oxidative addition reaction, which is one of the synthetic methods ·transition metal catalysis have been developed. The first is Oppenauer-type oxidation of alco- hols. This reaction proceeds under quite mild conditions (room tem- most fundamental and important process in organo- perature in acetone) catalyzed by [Cp*IrCl2]2/K2CO3, and both metallic chemistry, has been studied using Vaska’s com- primary and secondary alcohols can be used as substrates. Introduc- 2 he ability of hydrogen-transfer transition-metal catalysts,whichen- plex IrCl(CO)(PPh3)2. T tion of a N-heterocyclic carbene ligand to the catalyst considerably able increasingly rapid access to important structural scaffolds from enhances the catalytic activity, and a very high turnover number of The catalytic chemistry of iridium started with the discov- simple starting materials,has led to aplethora of researchefforts on the 950 has been obtained in the oxidation of 1-phenylethanol. The ery of a highly efficient catalyst, [Ir(cod)(PCy3)(py)]PF6, 3 construction of heterocyclic scaffolds.Transition-metal-catalyzed second is the N-alkylation of amines with alcohols. A new effective for hydrogenation of olefin by Crabtree et al. in 1977. catalytic system consisting of [Cp*IrCl2]2/K2CO3 for the N-alkyla- Thereafter, a number of iridium-catalyzed hydrogenation hydrogen-transfer annulations are environmentally benign and highly tion of primary amines with alcohols has been developed. Synthesis systems including enantioselective reactions have been atom-economical as they release of water and hydrogen as by-product of indoles and 1,2,3,4-tetrahydroquinolines via intramolecular N- disclosed.4 In recent years, iridium complexes were found alkylation of amino alcohols and synthesis of nitrogen heterocycles and utilize renewable feedstock alcohols as starting materials.Recent to be effective as catalysts for hydrosilylation,5 carbon- via intermolecular N-alkylation of primary amines with diols cata- 6,7 8,9 advances in this field with respect to the annulations of alcohols with lyzed by a Cp*Ir complex have been also achieved. The third is the carbon and carbon-heteroatom bond formation, hy- transfer strategy involves utilization of drogen transfer reaction,10 functionalization of C-H various nucleophilic partners,thus leading to the formation of hetero- regio- and chemoselective transfer hydrogenation of quinolines. An the initially extracted hydrogen gas for efficient method for the transfer hydrogenation of quinolines cata- bonds,11–13 and the catalytic chemistry of iridium has been cyclic scaffolds,are highlighted herein. the hydrogenation of an intermediate lyzed by [Cp*IrCl2]2/HClO4 using 2-propanol as a hydrogen source attracting quite a lot of interest. Most of these interesting (derived from the reaction of the has been realized. A variety of 1,2,3,4-tetrahydroquinoline deriva- reactions were achieved using low-valent iridium com- tives can be synthesized by this method. These results show that dehydrogenated precursor with nucle- plexes coordinated with olefin, CO, halogen, or phospho- Cp*Ir complexes can be useful catalysts for hydrogen transfer 1. Introduction ophilic partners) in the final step of the reactions from the viewpoint of developing environmentally benign rous ligands (e.g. [IrCl(cod)]2) as a catalyst precursor. reaction, thus leading to the net release of water as the only organic synthesis. On the other hand, a trivalent iridium complex bearing [2g] 1.1. Scope and Organization of Review by-product. Despite reports on several transition-metal- 5 1Introduction an h -pentamethylcyclopentadienyl (Cp*) ligand, catalyzed (Cu, Ni, Zn, Pd, etc.)hydrogen-transfer reactions,[3] 2Hydrogen Transfer Oxidation of Primary and Secondary [Cp*IrCl2]2 (Figure 1), is another well-known stable com- Heterocycles constitute the largest and most diverse Ru-, Ir-, and rare examples of Fe-based catalytic systems have Alcohols (Oppenauer-Type Oxidation) plex of iridium. The first synthesis of [Cp*IrCl2]2 was re- family of organic compounds and have been mostly identified shown excellent activity and selectivity in hydrogen-transfer 3N-Alkylation of Amines with Alcohols 14 ported by Maitlis et al. in 1969. At first, [Cp*IrCl2]2 was by their profound application in synthetic biology and annulations to deliver heterocyclic compounds.In2010, 4Synthesis of N-Heterocyclic Compounds prepared by the reaction of IrCl ·xH O with hexamethyl [1] 3 2 materials science. Theextent to which they can be utilized Yamaguchi et al. reported areview article focusing on the 4.1 Intramolecular N-Heterocyclization of Amino Alcohols 14a,c 4.2 Intermolecular N-Heterocyclization of Primary Amines Dewar benzene, however, a convenient preparation by in these endeavors depends on the selective and efficient construction of nitrogen-based heterocycles by transition- the reaction of IrCl ·xH O with pentamethylcyclopentadi- [4] with Diols 3 2 synthetic methods for their synthesis from simple,and metal-catalyzed hydrogen-transfer annulations. In recent 5Transfer Hydrogenation of Quinolines ene was reported later.15 Now we can purchase it from the abundant starting materials.Hence,the development of an years,this field has evolved in terms of catalyst and ligand 6Conclusion reagent market. The chemistry of Cp*Ir complex has been efficient strategy for the construction of heterocycles is akey design, and reaction conditions,thus taking the place of Key words: iridium, catalysis, hydrogen transfer, alcohols, amines mainly focused on the stoichiometric reactions, and their motivation in contemporary science. conventional synthetic processes and receiving an over- ability toward C-H bond activation of hydrocarbon mole- In the past few decades,the transition-metal-catalyzed whelming amount of attention. In this respect, there is need cules was revealed by Bergman et al. and others.16,17 How- hydrogen-transfer strategy has attracted much interest from for areview article focused on the potential of catalytic ever, catalytic utilizations of Cp*Ir complexes have been [2] the synthetic and organometallic community. Transfer of H2 hydrogen-transfer annulation strategies for the formation of 1 Introduction relatively unexplored. Only a few examples of Cp*Ir plays acrucial role in activating the substrate for further heterocyclic scaffolds.Herein we highlight recent advance- complex-catalyzed reactions for organic synthesis other transformation through C X(C, N, and O) bond-forming ments in hydrogen-transfer annulations of alcohols with In the field of homogeneous catalytic organic synthesis, ˇ than simple hydrogenation reactions had been reported annulations with the liberation of H2Oand H2.The hydrogen- various nucleophilic partners,thus leading to the formation relatively little attention have been paid to the utilization 11a,18 when we started our investigation in 1999. Downloaded by: IP-Proxy University of Texas at Austin, Austin Libraries. Copyrighted material. of heterocyclic scaffolds.This review material is organized of iridium as catalyst for a long time, while its family [*] Dr.A.Nandakumar,S.P.Midya, V. G. Landge,Dr. E. Balaraman into four different categories:a)N-alkylation of amines by member, rhodium and cobalt, have seen extensive use as Catalysis Division alcohols,b)dehydrogenative amide formation from amines 1 catalysts including industrial processes. This difference Cl Cl CSIR-National Chemical Laboratory (CSIR-NCL) and alcohols,c)oxidative cyclization of alcohols,and d) an- would be probably due to the scarcity of iridium as well as Ir Dr.Homi Bhabha Road, Pune, 411008 (India) nulation of unsaturated systems. the preconceived idea that organoiridium complexes are Ir E-mail:[email protected] too stable to be used as catalysts for organic synthesis. Cl Cl [email protected] Dr.A.Nandakumar 1.2. N-Alkylation of Amines by Alcohols SYNLETT 2005, No. 4, pp 0560–0571 04.03.2005 Organic Chemistry Division Figure 1 Advanced online publication: 22.02.2005 Central Leather Research Institute (CSIR-CLRI) DOI: 10.1055/s-2005-862381; Art ID: A36504ST Adyar,Chennai, 600 020 (India) Catalytic N-alkylation of amines is apromising atom- © Georg Thieme Verlag Stuttgart · New York E-mail:[email protected] economical and eco-benign approach for the selective con-
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