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Synthesis of Proazaphosphatranes and Their Applications in Organic Synthesis Philip Barnaba Kisanga Iowa State University

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Synthesis of Proazaphosphatranes and Their Applications in Organic Synthesis Philip Barnaba Kisanga Iowa State University Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1999 Synthesis of proazaphosphatranes and their applications in organic synthesis Philip Barnaba Kisanga Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Inorganic Chemistry Commons, and the Organic Chemistry Commons Recommended Citation Kisanga, Philip Barnaba, "Synthesis of proazaphosphatranes and their applications in organic synthesis " (1999). Retrospective Theses and Dissertations. 12392. https://lib.dr.iastate.edu/rtd/12392 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct prirrt, cokxed or poor quality illustratkxis and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a riote will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6' x 9' t>lack arxj white photographic prints are available for any photographs or illustrations appearing in this copy for an additk)nal charge. Contact UMI directly to order. Bell & Howell lnformatk>n and Learning 300 North 2!eeb Road, Ann Arfaor, Ml 48106-1346 USA 800-521-0600 Synthesis of proazaphosphatranes and their applications in organic synthesis by Philip Bamaba Kisanga A dissertation presented to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Organic Chemistry Major Professor: Dr. John G. Verkade Iowa State University Ames, Iowa 1999 UMI Number: 9992455 UMI ® UMI Microform 9992455 Copyright 2001 by Bell & Howell Information and Leaming Company. AJI rights reserved. This microform edition is protected against unauthorized copying under Title 17. United States Code. Bell & Howell Information and Leaming Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 ii Graduate College Iowa State University This is to certify that the Doctoral dissertation of Philip Bamaba Kisanga has met the dissertation requirements of Iowa State University Signature was redacted for privacy. Major Professor Signature was redacted for privacy. For Major Program Signature was redacted for privacy. For th te College iii DEDICATION To my beloved wife Grace Kabang Mikaya, children, family and friends who stood firmly behind me throughout this endeavor. iv TABLE OF CONTENTS CHAPTER 1. GENERAL INTRODUCTION 1 CHAPTER 2. SYNTHESIS OF NEW PROAZAPHOSPHATRANES AND THEIR APPLICATION IN ORGANIC SYNTHESIS 8 CHAPTER 3. MODIFIED SYNTHESIS OF INTERMEDIATES LEADING TO P(/-PrNCH3CH,)3N 44 CHAPTER 4. P(RNCH2CH2)3N-CATALYZED a,P-DIMEIUZATION OF UNSATURATED MTRILES: FORMATION OF 2-ALKYLIDINE-3-ALKYLGLUTARONITRILES 49 CHAPTER 5. P(RNCHXH,)3N-CATALYZED SYNTHESIS OF (3-HYDROXY NITRILES 70 CHAPTER 6. P(RNCH2CH2)3N: AN EFFICIENT PROMOTER FOR THE NITROALDOL (HENRY) REACTION 96 CHAPTER 7. P(RNCH,CH,)3N: AN EFHCIENT PROMOTER FOR THE DIRECT SYNTESIS OF £-a,P-UNS ATURATED ESTERS AND THE SYNTHESIS OF 3-SUBSTITUTED COUMARINS 145 CHAPTERS. PCRNCHoCH.jsN: EFHCIENT 1,4-ADDITION CATALYSTS 196 CHAPTER 9. P(RNCH2CH2)3N-CATALYZED DIASTEREOSELECTIVE SYNTHESIS OF OXAZOLIDINES 220 CHAPTER 10. GENERAL CONCLUSIONS 236 ACKNOWLEDGEMENTS 1 CHAPTER 1 GENERAL INTRODUCTION Dissertation Organization This dissertation is made up of ten chapters. The first chapter deals with general introduction and a statement of the purpose of the project. The second chapter is dedicated to the synthesis of three new proazaphosphatranes, while the third chapter describes a modified synthesis of intermediates leading to the proazaphosphatrane P(/-PrNCH2CH2)3N. Subsequent chapters focus on applications of proazaphosphatranes in organic synthesis, namely in the synthesis of glutaronitriles, P-hydroxy nitriles, P-nitroalkanols, E-ajP-unsaturated esters and oxazolidines, as well as Michael addition reactions of alcohols, nitroalkanes and imines derived from a-amino esters. The last chapter contains general conclusions and a prospective outlook for the chemistry of proazaphosphatranes. Each of the chapters that describe research, are either papers published or papers still in progress, except for Chapter 3 which discloses a discovery to be submitted as a Record of Invention to Iowa State University Research Foundation (ISURF). 2 Introduction and Statement of the Project Proazaphosphatranes (1) constitute a class of compounds that is emerging as useful bases for important organic transformations. The strong basicity of these compounds has been attributed to their ability to form a transannular bond leading to the highly stable five-membered azaphosphatrane ring systems 2. The first proazaphosphatrane P(MeNCH2CH2)3N (la) was synthesized in our group by Lensink et al. in 1989.^ Following its synthesis, this compound was found to be a very strong base with a pK^ of about 26.8 in THF based on competitive deprotonation." However, the pK^ value extrapolated for acetonitrile (41.6) appears to be questionable and will be revisited in Chapter 2 of this dissertation. The proazaphosphatrane la was also found to be a very efficient catalyst for the trimerization of isocyanates.^ Results of experiments carried out so far suggest that la has a pK^ value higher than that of proton sponge (4) and consequently a much stronger base than either DBU (5) or TMG (6), which are conmionly used nonionic organic bases. The ability of la to equilibrate with P4-r-Bu (7) was taken as an indication that this base has a pK^ value close to that of P4- r-Bu/ However, the current study (Chapter 2) concludes that this observation was erroneous. NHo NHo NH N X (Me2N)3R=N-^N=P(NMe2)3 N-V MeaN NMea n P(NMe2)3 6 7 Several new proazaphosphatranes have been prepared over the last decade. Hence, Lensink et al} prepared the benzylic derivative 8 while Tang prepared the imidate 9.^ Wroblewski^ and D'Sa^ were able to place 8 9 isopropyl groups on the equatorial nitrogens to form proazaphosphatranes lb and 3, respectively, which were also found to be strong bases. With the preparation of these new bases by our group, the list of reactions catalyzed/promoted by proazaphosphatranes grew. D'Sa found that these compounds could fiinction as superior catalysts for the silylation® and 4 acylation^ of alcohols. An elegant use of proazaphosphatranes discovered by D'Sa et al. was the direct synthesis of a,P-unsaturated nitriles.'® With these results, the proazaphosphatranes caught the attention of other researchers," '" including Yamamoto, who was able to prepare the first Cj symmetric derivative (10) of these compounds.'^ Yamamoto's effort was 10 11 12 followed by those Liu et al. who successfully prepared a second Cj symmteric analogue (11) that has been found to be an efficient reagent for the determination of enantiomeric excesses of chiral azides.'"* Ilankumaran has found that the proazaphosphatranes can be used as efficient catalysts for transesterification reactions.'^ Studies by Arumugam and McLeod revealed that proazaphosphatranes can be used for dehydrohalogenations that afforded alkenes in excellent yields.'^ In a recent study, D'Sa observed that these bases promote the most efficient synthesis of benzofurans reported to date.'^ He also found that these compounds are capable of isomerizing methylene-intemipted double bonds.'® 5 Work by Wang has resulted in the preparation of a novel ylide'^ 12 from the proazaphosphatrane la in addition to using the same proazaphosphatrane as a base for Wittig reactions of aldehydes."® Furthermore, Wang et al. have been able to prepare homoallylic alcohols from aldehydes and CH^iCHCH^SiMej in a reaction catalyzed by P(i-PrNCH2CH2)3N.^' In other studies, Wang was able to prepare a- cyanohydrins^^ and to induce the reduction of carbonyl compounds with PHMS in the presence of P(MeNCH2CH2)3N.-^ These results show that proazaphosphatranes do offer advantageous alternatives to conventional methodologies. The current study was initiated in an attempt to develop further uses for proazaphosphatranes as reagents and catalysts in organic synthesis. The focus of this study was to identify reactions in which these bases offer improved methodologies. Since the commercially available base P(MeNCH2CH2)3N synthesized by our group is expensive ($238.00/g), we also decided to seek a preparation of analogous bases that could be made more easily at a lower price. 6 References 1. Lensink, C.; Xi, S. —K.; Daniels, L. M.; Verkade, J. G. J. Am. Chem. Soc. 1989, 111, 3478. 2. Laramay, M. A.; Verkade, J. G. J. Am. Chem. Soc. 1990, 112, 9421. 3. Tang, J. -S.; Verkade, J. G. Angew. Chem., Int. Ed. Engl. 1993, 32, 896. 4. (a) For a review see: Verkade, J. G. Coord. Chem. Rev. 1994, 137, 233. For basicity related studies on these bases see: (b) Milbrath, D. S.; Verkade, J. G. J. Am. Chem. Soc. 1977, 77, 6607. (c) Leffek, K. T.; Pruszynski, P.; Thanapaalasingham, K. Can. J. Chem. 1989, 67, 590; and references cited therein, (d) Laramay, M. A.; Verkade, J. G. Z. Anorg. Allg. Chem. 1991, 605, 163. 5. Tang, J. -S.; Dopke, J.; Verkade, J. G. J. Am. Chem.
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