A PHOTOCHEMICAL STUDY OF CRYSTALLINE DIBENZOBARRELENE DIESTERS THE DI -»r-METHANE PHOTOREARRANGEMENT IN THE SOLID STATE. By Miguel Angel Garcia Garibay B.Sc, Universidad Michoacana, Mexico, 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY' OF GRADUATE STUDIES (DEPARTMENT OF CHEMISTRY) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October 1988 © Miguel Angel Garcia Garibay, 1988 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of r^BUlSTHJ The University of British Columbia Vancouver, Canada Date bee~L MM DE-6 (2/88) ABSTRACT The di-7r-methane photorearrangement has been investigated for the first time in the solid state. A series of symmetric (-CO2R1 = -CO2R2) and mixed (-CC^Ri * -CO2R2) 11,12-dibenzobarrelene diesters, used as the model substrates, reacted in the solid state with efficiencies that are similar to those observed in solution. Photolysis of symmetric diesters in solution and in the solid state gave a single dibenzosemibullvalene photoproduct. Two diesters (R^ = R2 = Et and R^ = R2 = iPr) turned out to be dimorphic with one of their crystal modifications having the chiral space group P2^2^2^. Photolysis of the chiral crystals resulted in absolute asymmetric syntheses with quantitative (iPr) and near quantitative (80%, Et) enantiomeric yields. The absolute configuration of the starting material and photoproduct was obtained in the case of the isopropyl compounds by X-ray anomalous dispersion analysis. The stereochemical correlation and the X-ray crystallographic results indicated an extremely high stereoselectivity where only one of the four degenerate solution pathways seems to be followed in the solid state. Mixed diesters gave upon photolysis two regioisomeric photoproducts that formed in nearly equal amounts in solution media. The solid state regioselectivity varied from moderate to high with no apparent correlation between the nature of the ester substituent and the photochemical results. X-ray structural information was used to analyze the effect of the ene-dioate conformation on the solid state regioselectivity. The radical delocalizing ability of the carbonyl groups, which is expected to depend on the degree of conjugation with the central vinyl bond, does not seem to play an important role in determining the solid state results. An excellent correlation was found between solid state steric factors and the photochemical results. In general, the reaction occurred at the least tightly packed vinyl carbon. Chiral dibenzobarrelene diesters containing sec-butyl groups were studied in optically active and racemic forms. Crystals of the sec- butyl/isopropyl compound were found to form a solid solution of the enantiomers that is isomorphous with the chiral crystals of the diisopro- pyl compound. A third example of absolute asymmetric synthesis in the solid state was discovered when photolysis of the racemate generated optically active products with very high enantiomeric yields. Photochemi• cal and spectroscopic results from the methyl/sec-butyl compound indicated a second example of solid solution of the enantiomers, but this time with ) a racemic space group. Lack of diastereoslectivity in the solid state reaction of the latter compound was rationalized in terms of efficient steric control in the solid state reaction but inefficient steric control during the crystallization process. An unusual solid state luminescence of the 11,12-diesters was noted and analyzed in terms of the biradical intermediates postulated along the di-w-methane rearrangement pathway. Finally, the solution and solid state photochemical results from dibenzobarrelenes bearing an ester group at the bridgehead position are analyzed. -iv- TABLE OF CONTENTS page ABSTRACT ii LIST OF TABLES . ix LIST OF FIGURES xi ACKNOWLEDGMENTS xix INTRODUCTION 1 The Topochemical Postulate 2 Solid State Chemical Reactivity 5 1. Number of Components 6 2. Thermodynamic Factors 11 3. Kinetic Requirements 13 Photochemical Reactions in Molecular Crystals ... 20 Excited State Partitioning 22 The Di-7r-Methane Rearrangement 26 The Regioselectivity of the Di-7r-Methane Rearrangement 32 Objectives of Present Research and Outline of the Thesis 34 RESULTS AND DISCUSSION 41 Preparation of Substrates 42 11,12-Dibenzobarrelene Diesters 42 10,11- and 9,11-Dibenzobarrelene Diesters .... 46 -V- PART I. THE DI-TT-METHANE REARRANGEMENT IN THE SOLID STATE 49 On the True Solid State Nature of the Rearrangement 52 The Limiting Conversion on the Solid State Reaction of Diester Me/Me-18 55 Perturbations of the Excited State Decay Channels of Crystalline 18 by Accumulation of Photoproduct 56 a) Luminescence Measurements 60 b) Conversion Dependence of the Relative Quantum Yields of Reaction of 18 64 Mechanical Effects and Limiting Conversion ... 67 The Crystal and Molecular Structure of Diester 18 . 70 PART II. STUDIES ON SYMMETRIC DIBENZOBARRELENE DIESTERS 72 Photochemistry in Solution 74 Photochemistry in the Solid State 75 The Solid State Molecular Structures of the Diethyl Diester 21 75 The Solid State Molecular Structure of the Di-n-Propyl Diester 22 79 The Solid State Molecular Structure of the Diisopropyl Diester 23 80 Conformational Polymorphism 83 Spectral Differences Between the Dimorphs of Diesters Et/Et-21 and iPr/iPr-23 85 Diethyl Diester 21 1) Solid State FTIR Spectra 85 2) Solid State CPMAS 13C NMR Spectra 89 Diisopropyl Diester 23 -vi- 1) Solid State FTIR Spectra 91 2) Solid State CPMAS 13C NMR Spectra ..... 93 Differences in Reactivity between Dimorphs ... 95 Molecular and Crystal Chirality 101 Absolute Asymmetric Synthesis 103 Asymmetric Synthesis by Reaction of Diethyl Ester 21 108 Asymmetric Synthesis by Reaction of Diester 23 . Ill Mechanistic Implications of the Solid State Asymmetric Synthesis 115 Correlation of the Absolute Stereochemistry of the Crystalline Diisopropyl Diester pro-(-)-23 (P212121 Form) and its Optically Pure Photoproduct (-)-Dibenzosemibullvalene 57 116 Studies on the Spontaneous Resolution of Diester 23 120 1) Enantiomorphism of Chiral Crystals of Diester 23 from Ethanol Solution 121 2) Enantiomorphism of Chiral Crystals of Diester 23 Grown from the Melt in Open Containers 123 3) Enantiomorphism in Crystals of Diester 23 Grown from the Melt in a Sealed Container . 124 4) Enantiomorphism in Crystals of Diester 23 Grown from the Melt in a Sealed Container (B) . 125 PART III. THE REGIOSELECTIVITY OF THE DI-TT-METHANE REARRANGEMENT IN THE SOLID STATE 129 Compounds Studied and Identification of Photoproduct Stereochemistry 129 Photolysis of Mixed Diesters in Solution and in the Solid State 140 Analysis of the Solution Regioselectivity .... 142 -vii- A Primary Steric Effect? 142 A Secondary Steric Effect? 147 The Regioselectivity in the Solid State 157 Stereoelectronic Factors in the Solid State .... 158 Solid State Primary Steric Effects. Steric Compression 164 Regioselectivity in Chiral Crystals of Diester iPr/iPr-23 172 The Solid State Results at Large 173 PART IV. STUDIES ON CHIRAL MIXED DIESTERS 176 Photochemistry in Solution 178 Studies in the Solid State 186 Crystallization of Chiral Compounds 186 The Solid State Properties and Photochemistry of Diester 42 195 Photochemistry of the Optically Pure Crystalline Material 201 Photochemistry of the Racemate of Compound 42 . 205 Asymmetric Synthesis by Solid State Reaction of the Racemate of 42 206 Extent of Asymmetric Induction in Chiral Crystals of the Racemate 209 On the Reaction Diastereoselectivity 211 The Solid State Properties and Photochemistry of Diesters Me/sBu-31 217 The Solid State Properties and Photochemistry of Diester 39 229 Concluding Remarks 229 -viii- PART V. LUMINESCENCE STUDIES ON THE DIMETHYL DIESTER 18 232 General Observations 234 Observations at Different Temperatures 237 Excitation Spectrum of the Red-Emitting Species 238 Observations at Different Wavelengths 241 What is the Precursor of the Red-Emitting Species? 242 Is the RE Produced by an Impurity? 243 What is the RE Species? 248 The Identity of Species X and Y 256 PART VI STUDIES ON 9 - SUBSTITUTED DIBENZOBARRELENES 265 Photolysis of Diester 10-iPr/ll-Me-44 267 Photolysis of Diester 9-iPr/ll-Me-45 279 EXPERIMENTAL 283 REFERENCES 348 - ix- LIST OF TABLES Table Caption Page I Dibenzobarrelene Diesters Prepared by Stepwise Esterification of Diacid 19 45 II Analytical Photolysis of 18 in Solution and in the Solid State 54 III Symmetrically Substituted Dibenzobarrelene Diesters . 73 IV Relative Reaction Efficiencies of Crystalline Dibenzobarrelene Diesters 96 V Solid State Induced Optical Activity in Crystals of 21 109 VI Solid State Induced Optical Activity in Single Crystals of 23 112 VII Photolysis of Single Crystals of 23 from Batch 3 122 VIII Photolysis of Chiral Crystals of 23 from Batch Melt I 123 IX Photolysis of Chiral Crystals of 23 from Batch Melt II 124 X Photolysis of Chiral Crystals of 23 from Batch Melt III 126 XI Glc and 1H NMR Results from Solution Photolysis of Mixed Dibenzobarrelene Diesters 132 XII High Mass Fragmentation of the Dibenzosemibullvalene Diesters 139 XIII Glc Analysis of the Photoproducts of Diesters Me/sBu-31, Et/sBu-39 and iPr/sBu-42 179 XIV Selected Fragment-Ions from Photoproducts of Diester 42 181 XV The 1H NMR Resonances of H(8d) and H(4b) from Products of Diester iPr/sBu-42 as a Function of Four Different Solvents 183 -x- XVI Relative Yields Of Photoproducts from Diester iPr/sBu-42 184 XVII Lattice Parameters of P2^2^2^ Crystals of Compounds 23, (S)-(+)-42 and (R,S)-42 ............ 198 XVIII Conformation of the Ene-Dioate System in Diesters 23, (S)-(+)-42 and (R,S)-42 199 XIX Melting Points of Mixed Crystals of Diester 42 .