The Pennsylvania State University The Graduate School Department of Chemistry ALKYNYLIODONIUM SALTS IN ORGANIC SYNTHESIS. APPLICATION TOWARDS THE SYNTHESIS OF THE CORE OF (±)-HALICHLORNIE. and ATTEMPTS TOWARDS THE SYNTHESIS OF KINAMYCIN F. A Thesis in Chemistry by Angela Lyn Perkins © 2005 Angela Lyn Perkins Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2005 The thesis of Angela Lyn Perkins was reviewed and approved* by the following: Ken S. Feldman Professor of Chemistry Thesis Advisor Chair of Committee Blake R. Peterson Associate Professor of Chemistry Raymond L. Funk Professor of Chemistry Squire J. Booker Assistant Professor of Biochemistry and Molecular Biology Ayusman Sen Professor of Chemistry Head of the Department of Chemistry *Signatures are on file in the Graduate School iii ABSTRACT Alkynyliodonium salts are synthetically useful intermediates that serve as electrophilic acetylene equivalents due to the electron withdrawing nature of the hypervalent iodine. In one example, reaction of an alkynyliodonium salt with soft nucleophiles via conjugate addition, followed by loss of iodobenzene, generates alkylidenecarbenes. Alkylidenecarbenes are divalent, short lived intermediates capable of participating in a various bond-forming processes depending upon the functionality present within the molecule. Due to the wide variety of possible reactions, alkylidenecarbenes are useful reactive intermediates in natural product synthesis. The application of alkynyliodonium salts to generate alkylidenecarbenes is described in the first part of this thesis. Chapter 1 discusses the formation of alkynyliodonium salts and their application towards the generation of alkylidenecarbenes. The total synthesis of radermachol, a natural product target, was examined utilizing an alkylidenecarbene addition to a double bond as a key step. However, preliminary results shifted the focus away from this synthesis. Instead, aryl C-H insertion was examined by the reaction of phenoxide anions of naphthol derivatives with an alkynyliodonium salt. A variety of naphthol derivatives were used to study the preference for C-H insertion in these aromatic systems. Halichlorine is a natural product target to which alkynyliodonium chemistry was applied in chapter 2. Halichlorine is a structurally unique marine alkaloid, which has interesting biological activity, in that it is a selective inhibitor of VCAM- 1. The focus of the synthesis of halichlorine centers on the formation of a key quaternary center of the spirocyclic ring system. This bond can be formed using an alkynyliodonium salt to generate an alkylidenecarbene, which can undergo a 1,5-C-H insertion to generate the quaternary center with retention of stereochemistry. This synthesis highlights the use of alkynyliodonium salt chemistry for increasing molecular complexity in a single operation. iv The final project discussed in this thesis is the progress made towards the total synthesis of kinamycin F. Kinamycin F is a compound in a class of potent antibiotics, whose members have also exhibited interesting cytotoxicity to a variety of tumor cell lines via cleavage of double stranded DNA. The proposed mechanism of action of these kinamycin compounds is thought to be through a bio-reductive process, generating a radical species which interacts with DNA leading to strand scission. Completion of the total synthesis of kinamycin F will permit a more thorough evaluation of the hypothesized biological mechanism of action. v TABLE OF CONTENTS LIST OF FIGURES .........................................................................................viii LIST OF TABLES ...........................................................................................xiv ACKNOWLEDGEMENTS...............................................................................xv Chapter 1 ALKYNYLIODONIUM SALT CHEMISTRY FOR THE GENERATION OF ALKYLIDENECARBENES FOR 1,6-ARYL C-H INSERTIONS ...........................................................................................1 1.1 Overview............................................................................................1 1.2 Alkynyl(aryl)iodonium Salts................................................................2 1.3 The Generation of Alkylidenecarbenes from Alkynyliodonium Salts..5 1.4 Alkylidenecarbenes............................................................................8 1.4.1 Structure and Electronic Properties of an Alkylidenecarbene ...8 1.4.2 Reactive Pathways of Alkylidenecarbenes ...............................11 1.4.2.1 1,2 – Rearrangements.....................................................12 1.4.2.2 Intermolecular H-X Insertions..........................................13 1.4.2.3 Carbon-Hydrogen Insertions ...........................................14 1.4.2.4 Heteroatom-Lone Pair Additions .....................................17 1.4.2.5 Alkene Additions – Cyclopropanations ............................19 1.5 Alkylidenecarbene Aromatic C-H Insertions ......................................21 1.6 Radermachol .....................................................................................25 1.6.1 Isolation and Previous Total Syntheses....................................25 1.6.2 Proposed Total Synthesis.........................................................27 1.7 Naphthol Derivatives..........................................................................28 1.8 Anthroxy-Substituted Alkylidenecarbene ...........................................32 1.9 Conclusions .......................................................................................32 1.10 References.......................................................................................33 Chapter 2 STUDIES DIRECTED TOWARDS THE SYNTHESIS OF THE SPIROCYCLIC CORE OF HALICHLORINE ............................................40 2.1 Overview............................................................................................40 2.2 Isolation and Biological Activity..........................................................41 2.2.1 Isolation of Halichlorine.............................................................41 2.2.2 Biological Activity of Halichlorine ..............................................42 2.3 Previous Studies Directed Towards the Synthesis of Halichlorine.....44 2.3.1 The First Asymmetric Total Synthesis of Halichlorine...............44 2.3.2 Synthesis of the Spirocyclic Core of Halichlorine......................46 2.3.2.1 Uemura’s Asymmetric Synthesis of the Core ..................47 2.3.2.2 Imine Formation to Generate Spirocycle .........................48 2.3.2.3 Radical Cyclization to Generate the Spirocyclic Core .....50 vi 2.3.2.4 Intramolecular [3 + 2] Cycloaddition ................................52 2.3.2.5 Kibayashi’s Generation of the Core via an Ene Reaction................................................................................55 2.4 A New Synthesis of Halichlorine Based upon Alkylidenecarbene Chemistry ..........................................................................................56 2.4.1 Retrosynthetic Analysis of Halichlorine.....................................56 2.4.2 Precedent for the Key Step.......................................................58 2.5 Racemic Synthesis of the Core of Halichlorine..................................59 2.5.1 Synthesis of the Alkynylstannane Precursor.............................59 2.5.2 Alkynyliodonium Salt Chemistry................................................61 2.5.3 Macdonald Chemistry to Generate the C Ring of the Spirocyclic Core ..........................................................................62 2.5.4 Removal of the Tributyltin Moiety..............................................64 2.5.5 Reductive Methylation ..............................................................66 2.5.6 Removal of the Tributyltin Moiety Revisited..............................69 2.5.7 Cleavage of the Amide .............................................................71 2.5.8 Completion of the Core Tricycle................................................74 2.6 Conclusions .......................................................................................75 2.7 References ........................................................................................76 Chapter 3 STUDIES DIRECTED TOWARDS THE SYNTHESIS OF KINAMYCIN F..........................................................................................83 3.1 Overview............................................................................................83 3.2 Isolation .............................................................................................84 3.3 Biology...............................................................................................87 3.3.1 Previous Biological Mechanism of Action .................................88 3.3.1.1 Proposed Oxidation of the Diazo Compound to Induce DNA Cleavage ......................................................................88 3.3.1.2 Nucleophilic Addition to the Electrophilic Diazonium Ion to Induce DNA Cleavage ................................................89 3.3.2 Hypothesized Mechanism of Action..........................................90 3.4 Previous Total Syntheses ..................................................................92 3.4.1 Synthesis of Prekinamycin........................................................92 3.4.2 Gould’s Synthesis of Stealthin C and Kinobscurinone ..............93 3.4.3 Synthesis of