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70-6667 Mccombs, Douglas Arthur, 1942- SYNTHESIS AND SYNTHESIS AND REARRANGEMENTS OF PENTADIENYL AND HEPTATRIENYL CARBANIONS Item Type text; Dissertation-Reproduction (electronic) Authors McCombs, Douglas Arthur, 1942- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 28/09/2021 17:31:13 Link to Item http://hdl.handle.net/10150/287434 This dissertation has been microfilmed exactly as received 70-6667 McCOMBS, Douglas Arthur, 1942- SYNTHESIS AND REARRANGEMENTS OF PENTADIENYL AND HEPTATRIENYL CARB ANIONS. University of Arizona, Ph.D., 1969 Chemistry, organic University Microfilms, Inc., Ann Arbor, Michigan SYNTHESIS AND REARRANGEMENTS OF PENTADIENYL AND HEPTATRIENYL CARBANIONS by Douglas Arthur McCombs A Dissertation Submitted to the Faculty of the DEPARTMENT OF CHEMISTRY In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 19 6 9 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by Douglas Arthur McCombs entitled SYNTHESIS AND REARRANGEMENTS OF PENTADIENYL AND HEPTATRIENYL CARBANIONS be accepted as fulfilling the dissertation requirement of the degree of DOCTOR OF PHILOSOPHY J-JLV dj Dissertation Director Date After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:" ~K- Cnicy UjW V* fThis approval and acceptance is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination. STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at "The University of Arizona and is deposited in the University Library to be made available to bor­ rowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or re­ production of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the in­ terests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED: ACKNOWLEDGMENTS The author wishes to acknowledge Dr. R. B. Bates for his suggestions and guidance throughout the preparation of this work and Mrs. J, L. Cude for the final typing of the manuscript. iii TABLE OP CONTENTS Page LIST OF ILLUSTRATIONS v ABSTRACT vii INTRODUCTION . 1 Pentadienyl Carbanions ..... 1 Heptatrienyl Carbanions ................... 4 EXPERIMENTAL 6 1,4-Cyclooctadiene 6 Cyclooctadienyllithium (1) 7 Protonation of Cyclooctadienyllithium (1).. 8 cis-Bicyclof3.3.0]oct-2-ene (3) . ....... 8 1.4-Cycloheptadiene 8 Cycloheptadienyllithium (9a) .... 9 Protonation of Cycloheptadienyllithium (9a) 10 Heptatrienyl lithium (8a) 10 n-Heptane From Heptatrienyllithium (8a) 11 1-Methylheptatrienyllithium (8b) 11 2,6-Dimethylheptatrienyllithium (8c) 12 6-Methylcycloheptadienyllithium (9b) ..... 12 1.5-Dimethylcycloheptadienyllithium (9c) 12 1,3,5-Trimethylcycloheptadienyllithium (9d) ......... 13 6-n-Butylcycloheptadienyllithium (9e) .. ..... 13 DISCUSSION 14 Formation of Cyclooctadienyllithium (1).... 14 NMR Studies of Cyclooctadienyllithium (1) . 14 Rearrangement of Cyclooctadienyllithium (1) 17 Cycloheptadienyllithium (9a) 22 NMR Studies of Cycloheptadienyllithium (9a) ......... 24 Heptatrienyl lithiums 27 NMR Studies of Heptatrienyllithiums ............. 28 Cyclization of Heptatrienyl Anions ... 29 APPENDIX: KINETIC DATA 44 LIST OF REFERENCES . 45 iv LIST OF ILLUSTRATIONS Figure Page 1. NMR spectrum of 1,4-cyclooctadiene 15 2. NMR spectrum of anion (1) (35°) ............ 15 3. NMR parameters for anion (l)........ 16 4. NMR parameters for anion (2) 16 5. NMR spectrum of anions (l) and (2) (35°) 18 6. NMR spectrum of (3) 18 7. Graph of the (l) to (2) conversion (35°). Points are experimental and curves are computer dravm 20 8. NMR spectrum of 1,4-cycloheptadiene 23 9. NMR spectrum of anion (9a) (35°) 23 10. NMR parameters for anion (9a) 25 11. Protonation of anions (l), (7), and (9a) 26 12. NMR spectrum of 1,3,6-heptatriene 31 13. NMR spectrum of anions (8a) and (9a) (-30°) ...... 31 14. NMR parameters for anion (8a) 32 15. NMR spectrum of 1,3,6-octatriene ............ 33 16. NMR spectrum of anion (8b) (-30°) ........... 33 17. NMR parameters for anion (8b) 34 18. NMR spectrum of 2,6-dimethyl-1,3,6-heptatriene 35 19. NMR spectrum of anions (8c) and (9c) (-40°) 35 20. NMR parameters for anion (8c) 36 21. NMR spectrum of anions (8a) and (9a) (-30°) ...... 37 v vi LIST OF ILLUSTRATIONS—Continued ige NMR spectrum of(9b)(35°) 37 NMR spectrum of anion (9c) (35°) . 38 NMR parameters for anion (9b) 39 NMR parameters for anion (9c) 39 NMR spectrum of 2,4,6-trimethyl-l,3,6-heptatriene . 40 NMR spectrum of anion (9d) (35°) 40 NMR parameters for anion (9d) 41 NMR spectrum of cycloheptatriene 42 NMR spectrum of anion (9e)(35°) 42 NMR parameters for anion (9e) 43 ABSTRACT The first synthesis of lithium salts of three heptatrienyl carbanions in high concentration (ca 20%) is reported; when 1,3,6- heptatrienes in tetrahydrofuran are treated with n-butyllithium quan­ titative yields of heptatrienyl anions are observed. Nuclear magnetic resonance studies showed that the preferred shape of these anions at low temperatures (-30°) is the fully extended shape rather than the all-cis helical form predicted by Hoffmann and Olofson. Two new electrocyclic carbanion reactions were observed. Several heptatrienyl carbanions were found to rearrange to cyclohepta- dienyl carbanions at -30°, and cyclooctadienyl anion was observed to rearrange to £iis-bicyclo[3.3.0]octenyl anion at 35°. vii INTRODUCTION PentadienyI and heptatrienyl carbanions have been proposed as intermediates in base-catalyzed diene and triene isomerizations and rearrangements (Birch, Shoukry, and Stansfield 1961; Slaugh 1967; Zuech, Crain, and Kleinschmidt 1968). Until recently (Bates, Gosse- link, and Kaczynski 1967a), no convenient method of obtaining such carbanions in high concentrations was available. It was the purpose of this work to prepare in high concentration and to characterize several proposed carbanion intermediates and to study their reactions. Pentadienyl Carbanions Slaugh (1967) observed the high-yield metal hydride-catalyzed rearrangements of 1,3- and 1,5-cyclooctadienes to cjLs-bicyclo[3.3.0]- oct-2-ene (3). He suggested two possible mechanisms for these con­ versions. One involves the formation of the eyelooctadieny1 anion (1) from 1,3-cyclooctadiene and its rearrangement to cis-bicyclof3.3.01- octenyl anion (2). (1) 1 © (1) • CO (2) (2) + a) + CO o (3) Anion (2) would then abstract a proton from 1,3-cyclooctadiene to form the final product (3) and more cyclooctadienyl anion (l). The other mechanism proposed requires a hydride addition-elimination process. First, 1,3-cyclooctadiene was converted to 1,5-cyclooctadiene (the less thermodynamically stable diene) which added potassium hydride. The re­ sulting anion (4) then underwent a transannular ring closure to the bicyclo anion (5) which eliminated potassium hydride to form (3). © K + (5) 3 The suggestion was made that since no rearrangement to a bicyclo derivative was observed in the potassium t-butoxide-catalyzed rearrangement of 1,5-cyclooctadiene to 1,3-cyclooctadiene, the re­ arrangement was facilitated by formation of the anion on the metal hydride surface. Of the three possible planar shapes (U, Sickle, and W) of the pentadienyl carbanions (Bates, Carnighan, and Staples 1963), a bent U-shape (6) is the only possible form for the cyclooctadienyl anion 2 (1). For maximum overlap of the p-orbitals on the five adjacent sp hybridized carbons, the five carbons must be coplanar and their © © // (6) p-orbitals must be perpendicular to this plane. Models indicate, how­ ever, that the five adjacent p-orbitals cannot possibly be perpendicu­ lar to that plane. Thus, the cyclooctadienyl anion (1), if prepared, could only approximate the U-shape. The anion would be expected to be quite unstable with respect to 6,6-dimethylcyclohexadienyl anion (7). CH3 CH3 (7) (9a) 4 It was decided to attempt synthesis of cyclooctadienyl anion (1) in order to study its structure by NMR and to determine which, if either, of Slaugh's (1967) mechanisms was more likely. If (l) were the intermediate in the first mechanism, then it was of interest to deter­ mine if the metal hydride surface were necessary for rearrangement. If (l) were not the intermediate, then its synthesis should give the same result as the potassium t-butoxide equilibrations of 1,3- and 1,5-cyclo- octadienes. In view of the fact that the cycloheptadienyl anion (9a) would have similar geometry to that of the cyclooctadienyl anion (1), it was thought that the cycloheptadienyl anion (9a) might, if the anion re­ arrangement proposed by Slaugh (1967) were correct, rearrange to the cis_-bicyclo[3.2.0]heptenyl anion. This rearrangement would then pro­ vide a convenient
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