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Efficient Carbohydrate Synthesis by Controlled Inversion Strategies

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Efficient Carbohydrate Synthesis by Controlled Inversion Strategies Efficient Carbohydrate Synthesis by Intra- and Supramolecular Control Hai Dong Doctoral Thesis Stockholm 2008 Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm framlägges till offentlig granskning för avläggande av teknologie doktorsexamen i kemi, med inriktning mot organisk kemi, torsdagen den 5 Feb 2009, kl 10.00 i sal F3, KTH, Lindstedtsvägen 26, Stockholm. Avhandlingen försvaras på engelska. Opponent är Ulf Nilsson, Lunds Tekniska Högskola/Lunds Universitet. ISBN 978-91-7415-207-4 ISSN 1654-1081 TRITA-CHE-Report 2009:2 © Hai Dong, 2008 Universitetsservice US AB, Stockholm 献给晓溪, 东东和爱玲. Till Emilia, Dongdong och Ailing. The road ahead is hard and long, but nothing will stop me as I go searching up and down. ………Qu Yuan (B.C. 340 - 278) Translated by Hai Hai Dong, 2008: “Efficient Carbohydrate Synthesis by Intra- and Supramolecular Control” Organic Chemistry, KTH Chemistry, Royal Institute of Technology, S- 10044 Stockholm, Sweden. Abstract The Lattrell-Dax method of nitrite-mediated substitution of carbohydrate triflates is an efficient method to generate structures of inverse configuration. In this study, the effects of the neighboring group on the Lattrell-Dax inversion were explored. A new carbohydrate/anion host-guest system was discovered and the ambident reactivity of the nitrite anion was found to cause a complicated behavior of the reaction. It has been demonstrated that a neighboring equatorial ester group plays a highly important role in this carbohydrate epimerization reaction, restricting the nitrite N-attack, thus resulting in O-attack only and inducing the formation of inversion compounds in good yields. Based on this effect, efficient synthetic routes to a range of carbohydrate structures, notably β-D-mannosides and β-D-talosides, were designed by use of double parallel and double serial inversion. A supramolecularly activated, triggered cascade reaction was also developed. This cascade reaction is triggered by a deprotonation process that is activated by anions. It was found that the anions can activate this reaction following their hydrogen bonding tendencies to the hydroxyl group in aprotic solvents. Keywords: Carbohydrate Chemistry, Carbohydrate Protection, Epimerization, Inversion, Neighboring Group Participation, Supramolecular Control, Anion Activation, Ambident Reactivity, Cascade Reaction, Hydrogen Bonding, Basicity. Abbreviations A Anion Ac Acetyl group AcCl Acetyl chloride Ac2O Acetic anhydride aq aqueous Bn Benzyl group BnBr Benzyl bromide Bz Benzoyl group BzCl Benzoyl chloride Bu Butyl Bu2SnO Dibutyltin oxide Conv Conversion DCM Dichloromethane DMF Dimethylformamide DMSO Dimethylsulfoxide eq./equiv. equivalent Et Ethyl EDA Ethylenediamine Gal Galactoside Glc Glucoside h hour HSAB Hard-Soft Acid-Base theory IM Imidazole Man Mannoside Manp Mannopyranoside Me Methyl NGP Neighboring group participation NMR Nuclear magnetic resonance rt/r.t. room temperature S Solvent T Temperature Tal Taloside TBA Tetrabutylammonium TEA Triethylamine Tf2O Trifluoromethylsulfonic anhydride THF Tetrahydrofuran P/PG Protecting group py. Pyridine PMO Perturbation Molecular Orbital theory List of publications This thesis is based on the following papers, referred to in the text by their Roman numerals. I. Reagent-Dependent Regioselective Control in Multiple Carbohydrate Esterifications Hai Dong, Zhichao Pei, Styrbjörn Byström and Olof Ramström J. Org. Chem. 2007, 72, 1499-1502. II. Stereospecific Ester Activation in Nitrite-Mediated Carbohydrate Epimerization Hai Dong, Zhichao Pei and Olof Ramström J. Org. Chem. 2006, 71, 3306-3309. III. Supramolecular Control in Carbohydrate Epimerization: Discovery of a New Anion Host-Guest System Hai Dong, Martin Rahm, Tore Brinck, and Olof Ramström J. Am. Chem. Soc. 2008, 130, 15270-15271. IV. Control of the Ambident Reactivity of the Nitrite Ion in Carbohydrate Epimerization Hai Dong, Lingquan Deng, and Olof Ramström Preliminary manuscript. V. Efficient Synthesis of β-D-Mannosides and β-D- Talosides by Double Parallel or Double Serial Inversion Hai Dong, Zhichao Pei, Marcus Angelin, Styrbjörn Byström and Olof Ramström J. Org. Chem. 2007, 72, 3694-3701. VI. Synthesis of Positional Thiol Analogs of β-D- Galactopyranose Zhichao Pei, Hai Dong, Rémi Caraballo and Olof Ramström Eur. J. Org. Chem. 2007, 29, 4927-4934. VII. Supramolecular Activation in Triggered Cascade Inversion Hai Dong, Zhichao Pei and Olof Ramström Chem. Commun. 2008, 11, 1359-1361. VIII. Enhanced Basicity by Supramolecular Anion Activation Hai Dong and Olof Ramström Preliminary manuscript. Papers not included in the thesis. IX. Solvent Dependent, Kinetically Controlled Stereoselective Synthesis of Thioglycosides Zhichao Pei, Hai Dong and Olof Ramström J. Org. Chem. 2005, 70, 6952-6955. X. Direct, Mild, and Selective Synthesis of Unprotected Dialdo-Glycosides Marcus Angelin, Magnus Hermansson, Hai Dong and Olof Ramström Eur. J. Org. Chem. 2006, 19, 4323-4326. Table of Contents ABSTRACT ABBREVIATIONS LIST OF PUBLICATIONS 1 Introduction ..............................................................................................1 1.1 Carbohydrates – A General Introduction ............................................1 1.2 Carbohydrates – Challenging Synthetic Targets.................................2 1.3 Regioselective Protection/Deprotection..............................................4 1.4 Epimerization ......................................................................................4 1.5 Neighboring Group Participation........................................................6 1.6 Aim of Study .......................................................................................7 2 Regioselective Carbohydrate Protection................................................9 2.1 Common Protection Strategies............................................................9 2.1.1 Acylation ......................................................................................9 2.1.2 Alkylation.....................................................................................9 2.1.3 Organotin Protection ..................................................................10 2.1.4 Integrated Protection Strategies .................................................10 2.2 Organotin Mutiple Esterification ......................................................11 3 Lattrell-Dax Epimerization ...................................................................15 3.1 Effects of Protecting Groups.............................................................15 3.1.1 Effects of Protection Patterns.....................................................15 3.1.2 Effects of Neighboring Group Configurations...........................17 3.2 Neighboring and Remote Group Participation..................................18 3.2.1 Neighboring Group Participation Effects...................................18 3.2.2 Remote Group Participation.......................................................19 3.3 Supramolecular Control ....................................................................21 3.3.1 Unusual Solvent Effect...............................................................21 3.3.2 Carbohydrate-Anion Complex ...................................................22 3.3.3 Binding Model............................................................................24 3.4 Ambident Reactivity of Nitrite Anions .............................................25 3.4.1 An O/N Selectivity Case in Carbohydrate Epimerization..........26 3.4.2 Carbohydrate Epimerization with Non-Ambident Reagents .....27 3.4.3 Nitration Products ......................................................................27 3.4.4 Solvent Effect.............................................................................29 3.4.5 Neighboring Equatorial Ester Group Activation........................30 3.5 Conclusions .......................................................................................31 4 Applications of the Lattrell-Dax Epimerization..................................33 4.1 Application in Synthesis of β-D-Mannosides and Talosides ...........33 4.1.1 Introduction................................................................................33 4.1.2 Double Parallel Inversion...........................................................33 4.1.3 Double Serial Inversion..............................................................35 4.2 Application in Synthesis of Thio-β-D-Galactosides ........................37 4.2.1 Introduction................................................................................37 4.2.2 Synthesis of Methyl 3-Thio-β-D-Galactoside ...........................37 4.2.3 Synthesis of Methyl 4-Thio-β-D-Galactoside............................38 4.3 Conclusions .......................................................................................39 5 Enhanced Basicity by Supramolecular Anion Activation ..................41 5.1 Supramolecular Activation in Cascade Inversion ............................41 5.1.1 Triggered Cascade Inversion......................................................41 5.1.2 Anion Activation........................................................................42 5.2 Enhanced Basicity by Supramolecular Effects .................................44 5.2.1 Supramolecular Effects of Anions and Solvents........................44 5.2.2 Basicity Controlled Cascade Reaction ......................................46 5.2.3 Enhanced Basicity by Supramolecular effects...........................48 5.3 Conclusions .......................................................................................50
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