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Chirality Transfer in 5-Exo Cyclizations of Axially Chiral O-Iodoanilides

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Chirality Transfer in 5-Exo Cyclizations of Axially Chiral O-Iodoanilides CHIRALITY TRANSFER IN 5-EXO CYCLIZATIONS OF AXIALLY CHIRAL O-IODOANILIDES by Andre J. B. Lapierre B. Sc., McMaster University, 2000 Submitted to the Graduate Faculty of Arts and Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 2005 UNIVERSITY OF PITTSBURGH FACULTY OF ARTS AND SCIENCES This dissertation was presented by Andre J. B. Lapierre It was defended on December 6th, 2005 and approved by Dr. Kay Brummond Dr. Theodore Cohen Dr. Michael Mokotoff Dr. Dennis Curran Dissertation Director ii To my wife and family, iii CHIRALITY TRANSFER IN 5-EXO CYCLIZATIONS OF AXIALLY CHIRAL O-IODOANILIDES Andre J. B. Lapierre, Ph.D. University of Pittsburgh, 2005 Stereoselective 5-exo radical and Heck cyclizations of axially chiral o-iodoanilides to enantioenriched oxindoles and dihydroindolones are described. Mechanisms for the transfer of chirality from the atropisomeric anilides to the newly formed stereocenters in the cyclic products are proposed and supported with physical data. Additionally, the N-aryl bond rotation barriers for eight o-iodoanilides are reported. A series of axially chiral N-allyl-o-iodoanilides were cyclized under room temperature radical conditions to dihydroindolones with good to excellent chirality transfer (74–97 %). Cyclization rate constant data is presented to rationalize the regioselective preference for N-allyl over N- acryloyl cyclization when an o-methyl group is present. X-ray crystallography was used to assign absolute configurations to a cyclization precursor/product pair. Radical 5-exo cyclizations of axially chiral o-iodoanilides bearing branched, bulky N-substituents are covered. The bulkiness of N-substituents permitted the resolution of a series of novel o-iodoanilides lacking a second ortho substituent. Radical cyclizations of these o-iodoanilides transferred this transient axial chirality into a new stereocenter in the oxindole products with high fidelity (78–92 %). The first Heck cyclizations of axially chiral o-iodoanilides with chirality transfer (84–89 %) are described. X-ray crystallographic data is presented for one anilide cyclization precursor with studies to elucidate the mechanism of chiral transfer. iv TABLE OF CONTENTS PREFACE..............................................................................................................................xvi 1. AXIALLY CHIRAL ANILIDES.......................................................................................1 1.1. Axial Chirality ..............................................................................................................1 1.2. Stereochemical Designations of Axially Chiral Groups .................................................2 1.3. Atropisomerism.............................................................................................................2 1.4. Tertiary Anilide Conformers .........................................................................................3 1.4.1. Restricted N-CO Bond Rotation .............................................................................3 1.4.2. Tertiary Anilides E/Z Preferences...........................................................................4 1.5. Restricted N-Aryl Bond Rotation ..................................................................................5 1.6. Synthetic Approaches to Enantioenriched Axially Chiral Anilides (Stoichiometric) ......6 1.7. Synthetic Approaches to Enantioenriched Axially Chiral Anilides (Catalytic) ...............9 1.8. Chromatographic Access to Enantioenriched Axially Chiral Anilides..........................10 2. MEMORY OF CHIRALITY ..........................................................................................12 2.1. Background................................................................................................................. 12 2.2. Memory of Chirality in Radical Chemistry..................................................................14 2.3. Chirality Transfer in Radical Cyclizations of Axially Chiral Acrylanilides ..................17 3. RADICAL CYCLIZATIONS OF AXIALLY CHIRAL N-ALLYL-O-IODOANILIDES 20 3.1. Introduction.................................................................................................................20 3.2. Precursor and Product Preparation...............................................................................22 3.3. Resolution and Rotation Barriers of Precursors............................................................23 3.4. Chirality Transfer in Radical Cyclizations of N-Allyl-o-Iodoanilides...........................26 3.5. Determination of Absolute Configuration....................................................................28 3.6. Preliminary Model of Chirality Transfer......................................................................30 3.7. Regioselectivity, Competitive Cyclizations..................................................................32 3.8. Cyclization Rate Constant Measurements....................................................................35 3.9. Conclusions................................................................................................................. 37 4. RELAYING ASYMMETRY OF TRANSIENT ATROPISOMERS OF O- IODOANILIDES ....................................................................................................................38 4.1. Background................................................................................................................. 38 4.2. Resolution of Chiral Auxiliary-based Atropisomers.....................................................41 4.3. Enantiomeric Series.....................................................................................................46 4.4. Determination of Absolute Configuration of Cyclization Precursors and Products.......50 4.5. Conclusion .................................................................................................................. 53 5. ASYMMETRIC HECK-MIZOROKI CYCLIZATIONS OF O-IODOANILIDES ATROPISOMERS..................................................................................................................54 5.1. Introduction.................................................................................................................54 5.2. Heck-Mizoroki Reaction .............................................................................................55 v 5.3. Precursor Preparation, Resolution................................................................................58 5.4. Chirality Transfer in Heck Cyclizations.......................................................................61 5.5. Synthesis of Second Generation Precursor...................................................................64 5.6. Racemic Synthesis of Esermethole..............................................................................65 5.7. Resolution and Recrystallization of Second Generation Precursor ...............................66 5.8. Stereochemistry...........................................................................................................70 5.9. Conclusion .................................................................................................................. 71 6. EXPERIMENTAL...........................................................................................................72 6.1. General Information....................................................................................................72 6.2. General Procedures .....................................................................................................74 6.2.1. General procedure for acylation of anilines (I)......................................................74 6.2.2. General procedure for N-allylation of anilides (II) ................................................74 6.2.3. General procedure for thermally initiated radical cyclization of anilides (III)........75 6.2.4. General procedure for Et3B initiated radical cyclization of N-allyl anilides (IV) ...75 6.2.5. General procedure for Et3B initiated radical cyclizations of acrylanilides (V) .......76 6.3. Compound Data for Chapter 3.....................................................................................76 6.3.1. N-(2-Iodo-4,6-dimethylphenyl)benzamide (not shown in text):.............................76 6.3.2. N-(2-Iodo-4,6-dimethylphenyl)-4-bromobenzamide (not shown in text): ..............77 6.3.3. N-(2-Iodo-4,6-dimethylphenyl)-2-phenylacetamide (not shown in text):...............77 6.3.4. N-(2-Iodo-4,6-dimethylphenyl)-3-phenylpropionamide (not shown in text): .........78 6.3.5. rac-N-Allyl-N-(2-iodo-4,6-dimethylphenyl)benzamide (56a):...............................78 6.3.6. rac-N-(2-Iodo-4,6-dimethylphenyl)-N-(3-methylbut-2-enyl)-4-bromobenzamide (56b): 79 6.3.7. rac-N-Allyl-N-(2-iodo-4,6-dimethylphenyl)-2-phenylacetamide (56c): .................80 6.3.8. rac-N-(2-Iodo-4,6-dimethylphenyl)-N-(3-phenylallyl)-2-phenylacetamide (56d): . 81 6.3.9. rac-N-But-2E-enyl-N-(2-iodo-4,6-dimethylphenyl)-2-phenylacetamide (56e):......81 6.3.10. rac-N-(2-Iodo-4,6-dimethylphenyl)-N-(3-methylbut-2-enyl)-2-phenylacetamide (56f): 82 6.3.11. rac-N-Allyl-N-(2-iodo-4,6-dimethylphenyl)-3-phenylpropionamide (56g):.........83 6.3.12. rac-N-Allyl-N-(2-iodo-4,6-dimethylphenyl)-trans-crotonamide (56h): ...............84 6.3.13. Phenyl-(3,5,7-trimethyl-2,3-dihydroindol-1-yl)methanone (57a):........................84 6.3.14. (4-Bromophenyl)-(3-isopropyl-5,7-dimethyl-2,3-dihydroinol-1-yl)methanone
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