STRUCfURE AND REACfIVITY OF THE. 1,3-DlOXOLAN-2-YLIUM ION SYSTEM. JOHN PAUL BELLAVIA, B. Sc. A Thesis. Submitted to the School of Graduate Studies

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1 STRUCfURE AND REACfIVITY OF THE 1,3-DlOXOLAN-2-YLIUM ION SYSTEM By JOHN PAUL BELLAVIA, B. Sc. A Thesis Submitted to the School of Graduate Studies in Partial Fulfilment of the Requirements for the Degree Doctor of Philosophy McMaster University (c) Copyright by John Paul Bellavia, September 1994.

2 STRUCTURE AND REACTIVITY OF THE I.3-DIOXOLAN-2-YLIUM ION SYSTEM

3 DOCTOR OF PHILOSOPHY (1994) (Chemistry) McMASTER UNIVERSITY Hamilton, Ontario TITLE: AUTHOR: SUPERVISOR: NUMBER OF PAGES: Structore and Reactivity of the 1,3-Dioxolan-2-ylium Ion System John Paul Bellavia, B. Sc. (McMaster University) Dr. R.F. Childs xiv, 209 ii

4 Abstract The 1,3-dioxolan-2-ylium ion is an important intermediate occurring in many carbohydrate transformations. The system has been widely studied, yet conflicting views on the effect of substituents on the ground state structure of 1,3-dioxolan-2-ylium ions have been presented. This thesis embodies the results of a series of investigations, utilizing a number ofcomplementary techniques, to examine the effect ofsubstitution on th~ structure and reactivity of a homologous series of 1,3-dioxolan-2-ylium ions. The possible use of the 1,3-dioxolan-2-ylium system as a model for the transition state structures of nucleophilic displacement reactions has been explored. The intramolecular nucleophilic attack ofan acetate group on a 1,3-dioxolan-2-ylium ion has been investigated for a series ofc(4)-aryl substituted cations. A Hammett study revealed that this isomerization reaction proceeds via a step-wise mechanism involving a carbenium ion intermediate. In contrast, when the C(4) substituent is hydrogen or methyl, a concerted isomerization mechanism is operative, as revealed by semi-empirical calculations. It is suggested that when the C(4) substituent is sufficiently electron donating, the system may adopt a trigonal bipyramidal geometry and hence may serve as a model for the S..2 transition state. Dual substituent parameter (DSP) correlations were used to establish the dependence of the "c chemical shifts of the 1,3-dioxolan-2-ylium ion system on the iii

5 electro.i donating power of the C(4)-aryl substituent. These correlations support the inclusion ofan ionic resonance contributor to the ground state description of the system. The weight given to the ionic resonance contributor increases with better electron donating C(4)-substituents. X-ray crystallography has been used to determine the solid state structures oftwo 1,3-dioxolan-2-ylium ion salts with different C(4) substituents. The changes in bond lengths observed in going from a hydrogen to a phenyl substituent at C(4) are partly attributedto the increased importance ofthe ionic resonance structure in the aryl system. Semi-empirical calculations at the AM 1 level revealed the effects of differential C(4)-substitution. Better electron donating substituents lowered the isomerization barrier and increased the relative importance of the ionic resonance contributor in the ground state, in accord with the experimentally determined results. The ability of a CF, substituent at C(2) to achieve similar changes in structure and reactivity was also established. iv

6 Acknowledgements I wish to thank my re;;earch supervisor, Dr. R. F. Childs, for his guidance, support and patience throughl1ut the course of this work. I would also like to thank the members of my supervisory committee, Dr. P. Harrison and Dr. J. Warkentin for their helpful comments and suggestions. I am grateful for the technical assistance provided by: Dr. D. Hughes, Mr. B. Sayer, Mr. I. Thompson and Dr. A. Bain of the NMR facility; Dr. R. Smith and Mr. F. Ramelan of the mass spectroscopy facility; Dr. J. Britten, Dr. C. Frampton, and Dr. T. Wark of the x-ray crystallography facility. For providing an enjoyable atmosphere in which to work, I wish to thank my lab mates in ABB 359, past and present. Special thanks goes to Brad, George and Teresa for their friendship inside and outside ofthe lab. I would also to thank Fred, Dave, and Tex for their valued insights into the human condition. Finally, I wish to thank my family for their constant support and encouragement. v

7 Table of Contents Page Descriptive Note Abstract Acknowledgements List of Tables List of Figures ii iii v ix xii Chapter I: Introduction I 1.1 Oxonium Ion Stability 1.2 Preparation of 1,3-dioxolan-2-ylium Ions 1.3 Role of the Anion 1.4 Reaction with Nucleophiles 1.5 Dioxolanylium Ions as Intermediates in Carbohydrate Rearrangements 1.6 Synthetic Utility 1.7 X-ray Crystal10graphic Studies 1.8 "c NMR Investigations 1.9 Semi-Empirical Calculations I.l0 Objectives Chapter 2: Part A: NMR Study Synthesis Routes Toward Dioxolanylium Ion Precursors 2.2 Generation of the Dioxolanylium Ion Part B: Dynamic NMR Studies 2.3 IH NMR of Dioxolanylium Ions 44 vi

8 Table of Contents (cont.) Page 2.4 Measurement of Isomerization Rate Constants 50 by Total Bandsilape Analysis 2.5 Mechanism of Isomerization for Aryl Dioxolanylium Ions Isomerization of Non-aryl Dioxolanylium Salts Lewis Acid Adducts 70 Part C I3C NMR Correlation Analysis C NMR of Aryl Dioxolanylium Salts NMR Correlation Analysis Summary 86 Chapter 3: Crystallographic Study of DioxoIanylium Ion Structure X-ray Structure Determinations Conformation of the Dioxolanylium Cation C-O Bond Lengths in 36 and Summary 106 Chapter 4: Semi-Empirical Investigation of Dioxoianylium Ion 107 Structure and Reactivity 4.1 Structure of the Aryl Substituted Dioxolanylium Ions Charge Distribution Modelling the Isomerization Reaction of the Aryl System Modelling the Isomerization Reaction of the Non-aryl System Effect of the Trifluoroacetate Group Comparison of X-ray Crystal Structures with AMI optimized 147 Geometries 4.7 Summary 147 General Summary 148b Chapter 5: Experimental Materials 5.2 Instrumentation 5.3 Syntheses 5.4 AMI Calculations vii

9 Table of Contents (cont.) Appendix References Page viii

10 List of Tables I.I Stabilization energies of substituted methyl cations 3 in the gas phase. 1.2 Gas phase heats of formation of selected cations. 3 I.3 Relative heats of protonation in FSO,H at 25 C Leaving groups and acceptors for the preparation of 9 1,3-dioxolan-2-ylium ions via Route C-O bond lengths in ethers and esters Selected bond lengths for 1,3-dioxolan-2-ylium salts Mean O-C(alkyl) bond iengths C chemical shift differences in 1,3-dioxolan-2-ylium ions 33 and 1,3-dioxolanes ii. CH,CN. 1.9 Charge densities calculated from 13C chemical shifts NMR data for 36 and 37 in CD,N 'H chemical shifts of 38-4:' Rates of isomerization of in CD,No, C chemical shifts of NMR data for Lewis acid complexes 43 and Rate of isomerization of in CD,N Activation parameters for the isomerization of Page ix

11 List of Tables (cont.) Page 2.7 Rate of isomerization of 36 and 37 in CD,NO, Rate of isomerization of 43 in CD,Cl, Evaluation of the single (SSP) and dual (DSP) substituent 80 parameter correlation models Dual substituent parameter correlations Selected bond lengths for Selected bond angles for Selected bond lengths for Selected bond angles for Selected least-squares plane data for 36 and Selected AMI optimized bond lengths for and Selected AMI optimized bond angles for and 45. no 4.3 Selected AMI optimized bond lengths for 5Ia-f Selected AMI calculated charge densities for and Selected AMI optimized bond lengths and bond angles for 52a-f calculated charge densities for 52a-f calculated isomerization barriers Selected AMI optimized bond angles for 53 and Selected AMI optimized bond lengths for and Selected AMI optimized bond lengths for and x

12 List of Tables (cont.) Page 4.11 Selected AM I optimized bond angles for 59 and Structure determination summary for Structure determination summary for AI Atomic co-ordinates (x 10') and equivalent isotropic displacement 169 parameters (A' x 10') for 36. A2 Anisotropic displacement parameters (A' x 10') for A3 Hydrogen atom co-ordinates (x 10') and isotropic displacement 171 parameters (A' x 10') for 36. A4 Atomic co-ordinates (x 10') and equivalent isotropic displacement 172 parameters (A' x 10') for 39. A5 Anisotropic displacement parameters (A' x 10') for A6 Hydrogen atom co-ordinates (x 10') and isotropic displacement 174 parameters (A' x 10') for 39. A7 Observed and calculated structure factors for A8 Observed and calculated structure factors for xi

13 List of Figures Page 1.1 Reaction of ambident cations with nucleophiles. 1.2 Effect of cation stability on nucleophilic addition. 2.1 Variable temperature 'H NMR spectra of 42 in CD,NO,: coalescence of acetate and acetoxonium methyl resonances. 2.2 Hammett plot for C(4)-aryl substituted dioxolanylium ion isomerization Isomerization mechanisms Plot of isomerization barrier vs u' for aryl dioxolanylium ions Selective inversion experiment: response of C(2) resonance for Selective inversion experiment: response of C(9) resonance for Conformation of Unit cell packing in 36 (viewed along z-axis) Stereoscopic view of unit cell contents for 36 (viewed along 94 z-axis). 3.4 Conformation of Unit cell packing in 39 (viewed along x-axis) Unit cell packing in 39 (viewed along z-axis) Stereoscopic view of unit cell contents for 39 (viewed along 98 z-axis). 3.8 Intermolecular interaction in AMI optimized conformation of xii

14 List of Figures (cont.) Page 4.2 Plot of C(2)-O(3) bond lengths in and 45 vs u' Plot of C(4)-O(3) bond lengths in and 45 vs u' Dihedral angle q, in aryl dioxolanylium ions Plot of O(3)-C(4)-C(1 ')-C(2') dihedral angles in and 45 vs u t 4.6 Plot of calculated charge density vs. C(4) chemical shift 124 for aryl dioxolanylium ions. 4.7 Reaction co-ordinate diagram for step-wise isomerization AMI optimized conformation of 52b Plot of calculated vs. experimental reaction barriers 133 for aryl dioxolanylium ion isomerization 4.10 Reaction co-ordinate diagram for concerted isomerization AMI optimized conformation of AMI optimized conformation of xiii

15 "Nature is a language - can't you read?" Morrissey xiv

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STUDIES OF SOMEd-l,3,4-0XADIAZOLINES -OXADIAZOLINONES

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