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Oxidative Desulfurization of Azole-2-Thiones with Benzoyl Peroxide

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Oxidative Desulfurization of Azole-2-Thiones with Benzoyl Peroxide OXIDATIVE DESULFURIZATION OF AZOLE-2-THIONES WITH BENZOYL PEROXIDE by DEREK MICHAEL WOLFE (Under the Direction of Peter R. Schreiner) ABSTRACT 1-Alkyl-3-methylimidazole-2-thiones were prepared in one pot and subsequently converted to 1-alkyl-3-methylimidazolium benzoates through a sequence consisting of an oxidative desulfurization with benzoyl peroxide and a novel anion exchange. Also reported are the outcomes of exchanges with other anions, acidifications of the imidazolium benzoates to other salts, and the syntheses of both 1,3-diphenylimidazolium and 3-alkylthiazolium salts from the corresponding azole-2-thiones. This oxidative desulfurization was also appropriate for the synthesis of neutral imidazoles from 1-alkylimidazole-2-thiones, which were prepared from amino acids by way of 2-thiohydantoins. Four such sequences are described, one of which constitutes a formal synthesis of three imidazole alkaloids from the sponge Leucetta. The merits of these routes in terms of both adaptability and operational simplicity are emphasized. A chiral imidazolium salt featuring camphor was pursued, but an imidazole-2-thione precursor suited to desulfurization could not be prepared; the desired salt could not be assembled with conventional methods, either. The unsuitability of some imidazolium ionic liquids in an adaptation of the phase transfer catalyzed halogenation is discussed in the context of γ-adamantane amino acids. INDEX WORDS: Anion exchange, Desulfurizations, Heterocycles, Imidazoles, Ionic Liquids, Oxidations, Sulfur OXIDATIVE DESULFURIZATION OF AZOLE-2-THIONES WITH BENZOYL PEROXIDE by DEREK MICHAEL WOLFE B.S., Roanoke College, 1999 A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY ATHENS, GEORGIA 2007 © 2007 Derek M. Wolfe All Rights Reserved OXIDATIVE DESULFURIZATION OF AZOLE-2-THIONES WITH BENZOYL PEROXIDE by DEREK MICHAEL WOLFE Major Professor: Peter R. Schreiner Committee: George F. Majetich Vladimir V. Popik Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2007 DEDICATION For Mom and Dad iv ACKNOWLEDGEMENTS In the late 90s, graduate students in the Department of Chemistry drew the same salary all the rest of their years in the Department as they did in their first. As I understand it, I entered with the first class that received annual cost of living raises. I’m grateful to whatever group of people saved me from subsisting on turn of the century dollars because it kept my name out of the AJC alongside the words “clandestine”, “Airstream”, and “Danielsville”. I am appreciative that Dr. Schreiner gave me a great deal of latitude researchwise and did not breathe down my neck for results at the same time, and that he saw to it that I visited his labs in Giessen in 2003. I didn’t want to go because of the time I thought I would waste in duplicating work here (going) and there (coming back); at the time, I didn’t know how little whatever time was lost was going to figure into the span of my graduate career. Working abroad proved to be incalculably valuable for all the intangible reasons, and I couldn’t / wouldn’t have done it without Schreiner’s insistence. When I went back in 2005, I rediscovered the value of working in labs full of people and having regular group meetings—which feels weird for me to admit, because I had always thought I was so dedicated to the discharge of my own brand of misanthropy. Team Giessen (if they are reading this) know who they are and I hope they are not offended that I do not thank each of them by name for their hospitality during my sojourns in 2003 and 2005. I am, however, compelled to explicitly thank Binh Bui for putting me up in his apartment (on his floor) within walking distance of the Chemistry Building, and Dr. Andrey Fokin for brightening a room just by being in it. Fokin also gave Ellen Downs (now Ellen Beaulieu) and me countless hours of enjoyment as we repeated ad nauseum the phrase (with the best Russian v accents we could muster), “No, Peter! Peter, no!” This utterance came out over lunch one day when Schreiner made the observation that milk is white and opaque because it is an emulsion of fat and water, and that fat free milk gets its natural look from titanium dioxide added to it. Fokin came in on the tail end of Schreiner’s comment, and took him to mean that skim milk is only titanium dioxide in water. A hilarious comedy of errors ensued. Fokin has been eminently quotable for as long as I’ve known him. Speaking in reference to my horror that he had just unsealed a steel canister of commercial methyl magnesium bromide only to go into it with a syringe he found hanging out, chilling under atmospheric conditions, Fokin also gave us the phrase that would be my epitaph were I of Russian extraction: “For Russian, is no big deal.” As I recall, that reaction went in 78% yield; no big deal, indeed. Other combinations of words that are made cooler by Fokin saying them (and which I figure I will hear in my head for the rest of my life) are “boiling hot bromine”, “was cheapest thing” (in reference to benzene–carbon tetrachloride mobile phases in silica gel chromatography), “this is how Russians discipline their children” (in reference to a picture of himself [shirtless] holding his daughter under a Siberian waterfall), and “tonight we will have party with meat, beer, everything.” The unflappable Boryslav Tkachenko and the inimitable Volker Lutz each visited Schreiner’s labs here at Georgia and I appreciated their company immensely. Alexander Wittkopp and I only overlapped for a year or so, but I list him among my contemporaries and I feel as though I learned a great deal from him. None of it is coming to me right now, but I’m sure it’s there. If nothing else, he gets my thanks for letting me sleep on the floor of his apartment in Munich for Oktoberfest 2005 because that’s the rule: I sleep on your floor in Germany, you get acknowledged (vide supra). As I stop to think about it, it occurs to me that Ellen was the only coworker I ever had who was American born and bred, and if you have to vi have coworkers, it’s nice to have ones that get “it” for all the same reasons as you do, and she did. It was also fun to hear her say “Ich bin Auslander!” to Giesseners as they tried to make small talk. I never told her that, for want of an “-in” on “Auslander”, she was saying, “I’m a boy from another country!” It’s the simple pleasures that keep me going. Christopher Rinderspacher was my longest running (nigh constant) coworker. He also got “it”, and got “it” so well and was around so often for so long that I expect to be diagnosed with schizophrenia and discover he was just an imaginary friend—in a Fight Club and not in an A Beautiful Mind kind of way. As the only other member of Team Georgia, and considering that no mortal power could have moved our research projects farther apart, he deserves special credit for feigning interest in what I was doing during what I guess qualify as impromptu group meetings. I was primed for graduate school by the faculty of the Roanoke College Chemistry Department, Drs. Gary Hollis, Ben Huddle, Vern Miller, Ron Oetgen, and Jack and Gail Steehler. They were, and are, committed to getting undergraduates, including me, all the research experience the law allows, and they don’t stop there—they had me back last April to give my first invited lecture. The invitation was extended by Hollis, who taught me Organic Chemistry and supervised my research project in college. The Roanoke College Chemistry Department and Hollis in particular have been instrumental to my development as a chemist. While I’m here, thanks are due Dr. David Gardner for waiving the prerequisites for his classes on immunology and cell physiology, and sparing me lab work in taxonomy and animal behavior. Dr. James Ogier didn’t only teach me German, but he willingly did it privately in addition to his regular teaching load because I had Biochemistry in the same time slot. There will be some very confused authorities in Frankfurt if they ever run upon the real Ogier, because we look nothing alike. I feel he has only himself to blame. vii At Georgia, the people who chaperoned me to this point (aside from Schreiner) were Drs. Geert-Jan Boons, Robert Phillips, and Paul Schleyer, none of whom will be available at the time appointed to defend this dissertation, and I appreciate their service to this point. I thank Schleyer in particular for both his class on the structure and energy of carbon compounds and the voluminous, largely first-hand account that is his lecture notes on structural and physical organic chemistry. It’s a post-Talladega Nights world, and it would be great if Schleyer could be convinced to drop an occasional, “Did that blow your mind? Because that just happened!” in future lectures—especially in reference to anything planar / hypervalent carbon in nature, or pertaining to X-ray crystal structures being wrong. At the 11th hour, Drs. George Majetich and Vladimir Popik have come on board as my advisory committee. I am immensely grateful that they will give up an entire morning in July to, presumably, get me out of here, and that they will do so in exchange for only an offering of baked goods, juice, coffee, and their choice of 2% milk or aqueous titanium dioxide.
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