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Organometallic Routes to Cross–Conjugated Hydrocarbons

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Organometallic Routes to Cross–Conjugated Hydrocarbons Organometallic Routes to Cross–Conjugated Hydrocarbons a thesis submitted for the degree of Doctor of Philosophy of the australian national university Henry Toombs-Ruane research school of chemistry the australian national university january 2013 I Declaration Except where speci!c acknowledgements of others are made, the author carried out the work described in this thesis during the period of March 2009 to January 2013 in the Research School of Chemistry of the Australian National University, under the supervision of Professor Mick Sherburn. The material presented has not been submitted for any other degree and is less than 100,000 words in length. Henry Toombs-Ruane january 2013 III Acknowledgements My !rst t"anks must go to my super#isor, Mick S"erburn. T"anks for t"e ad#ice, t"e support, t"e guidance, and t"e banter. I "a#en’t e#en !nis"ed and I’m already looking for$ard to our future collaborations. And my t"anks again to Mick for collecting toget"er suc" a great group of guys and gals in t"e form of t"e S"erburn Group. It "as been a pleasure to study %and not& $it" you all, and I "ope t"at it can continue for a long time, eit"er "ere, or from afar. I am extremely grateful to Tony Herlt, T"omas Fallon, and Maxime Riou for t"eir assistance in t"e laboratory. During my researc" I "a#e also been fortunate enoug" to collaborate $it" Tony Willis and Mic"ael Paddon-Ro$. If I "ad not "ad access to t"eir #ast kno$ledge, resources, and tec"nical experience t"en I $ould ne#er "a#e been able to competently carry out researc", let alone complete t"is t"esis. Studying at t"e Australian National Uni#ersity "as gi#en me t"e opportunity to intersect $it" many resident and #isiting academics, in particular I am indebted to Ian Fairlamb, Bill Lording, T"omas Rauc"fuss, Henning Hopf, Claude Spino, Martin Bennett, Scott Ste$art, Da#id Lupton, and Tony Hill for lending me t"eir time and insig"ts. W"ile my !eld "as strayed signi!cantly from my !rst forays into c"emistry, it $as Vladimir Golo#ko and Andy Pratt $"o—in my Honours year—s"o$ed me t"at c"emistry is a !eld t"at can be bot" c"allenging and re$arding. And so I suppose I’ll "a#e to t"ank Vlad & Andy in e#ery ackno$ledgement section I $rite. I t"ink t"ere’s an old adage about any gi#en man not being an island. Per"aps it’s somet"ing about independence and reliance coexisting; about t"e s"ared nature of t"e Human Experience. Or maybe it’s about t"e buoyancy of 'es", and dying at sea. All t"is is a $ay of saying, t"ank you Julia. You’#e "elped me more t"an I can possibly gi#e t"anks for; but more important t"an any "elp, you made any sacri!ce $ort" it. Finally, t"anks mum, you really are t"e best! And Lea", "urry up $it" your no#el. T"ank you all. V Publications Some of the work in this thesis has been previously published: Toombs-Ruane, H.; Osinski, N.; Fallon, T.; Wills, C.; Willis, A. C.; Paddon-Row, M. N.; Sherburn, M. S. Synthesis and Applications of Tricarbonyliron Complexes of Dendralenes. Chem. Asian J. !"##, (, "#$"–"#%&. This research is reported in Chapters # & ". Toombs-Ruane, H.; Pearson, E. L.; Paddon-Row, M. N.; Sherburn, M. S. On the Diels-Alder dimerisation of cross-conjugated trienes. Chem. Commun. !"#!, )*, ''"(–''$). This research is reported in Chapter ". VII Abbreviations * percentage yield equiv. +molar, equivalent+s, heat Et ethyl °C degree/s Celsius EWG electron withdrawing group Ac acetyl eV electron Volts aq. aqueous ESI electrospray ionisation Ar aryl or argon FMO frontier molecular orbital ASE aromatic stabilisation energy Ft tricarbonyliron BDA benzylideneacetone GC gas chromatography BHT #,'-di-tert-butyl-$-methylphenol h hour/s or Planck constant bp boiling point HMBC heteronuclear multiple bond br broad coherence brsm based on recovered starting LDA lithium diisopropylamide material LRMS low resolution mass Bu butyl spectrometry ca. circa +approximately, h light/photochemistry calc calculated HMPA hexamethylphosphoramide CAN ceric ammonium nitrate HSQC heteronuclear single quantum cm-) wave number coherence COSY correlated spectroscopy HOMO highest occupied molecular CSI chlorosulfonylisocyanate orbital chemical shift HPLC high pressure liquid d day/s or doublet/s chromatography DA Diels–Alder HRMS high resolution mass dba dibenzylideneacetone spectrometry DBU ),--diazabicyclo-.%.$.&/undec-0- HWE Horner-Wadsworth-Emmons ene Hz Hertz DFT density functional theory IMDA intramolecular Diels–Alder DMAP $-dimethylaminopyridine i-Pr isopropyl DME dimethoxyethane IR infrared DMF dimethylformamide J coupling constant DIBAL diisobutylaluminium hydride KHMDS potassium hexamethyldisilazide DMSO dimethylsulfoxide lit. literature dppf ),)'-bis+diphenylphosphino,- LUMO lowest unoccupied molecular ferrocene orbital EDG electron donating group M molar +molL–), EI electron impact M1 molecular ion VIII ABBREVIATIONS Me methyl v.i. vide infra +see below, min minute v.s. vide supra +see above, MHz megahertz vol. volume mm Hg millimetres of mercury wt * weight percent mol mole ZCE Z-cyclooctene mol. molar mp melting point MS mass spectroscopy MVK methyl vinyl ketone m/z mass to charge ratio absorption maxima +IR, n-BuLi n-butyl lithium NLO nonlinear optical NMR nuclear magnetic resonance nOe nuclear Overhauser e2ect NOESY nuclear Overhauser and exchange spectroscopy Ph phenyl pin pinacol PMP para-methoxyphenyl PNP para-nitrophenyl ppm parts per million Pr propyl q quartet RCM ring-closing metathesis rt room temperature sat. saturated SM starting material SOI secondary orbital interaction t time t-Bu tert-butyl TBS tert-butyldimethylsilyl temp temperature Tf tri3uoromethanesulfonyl THF tetrahydrofuran TLC thin layer chromatography TM target material TMM trimethylenemethane TS transition state Ts para-toluenesulfonyl p-TsOH para-toluenesulfonic acid v/v volume concentration IX Abstract Molecules with a high degree of unsaturation often have associated with them a concomitant level of instability. In fact, their instability is what hinders the preparation and synthetic utility of large swaths of polyunsaturated frameworks. One form of modulating and controlling that reactivity is the tricarbonyliron group; a functionality that coordinates to a portion of an unsaturated skeleton, often allowing the easy isolation and observation of the unstable compound. This thesis explores the chemistry of cross-conjugated polyenes, and especially their relationship to the tricarbonyliron group, in one review, and three experimental chapters. Chapter ) reviews the known chemistry of highly reactive polyenes, and their stabilisation through coordination to the tricarbonyliron group. Chapter # describes the preparation of tricarbonyliron complexes of the dendralenes. Chapter " investigates the curious reactivity of cross-conjugated trienes. Chapter $ describes a new synthetic strategy towards preparing polyenes that are protected as organometallic complexes. While the ability for the tricarbonyliron group to stabilise reactive polyenes has long been known, their applications in this respect have not been rigorously documented by review. In Chapter ) we comprehensively review the literature on the tricarbonyliron complexes of unstable molecules, and uncover promising areas for future research. In particular, there remain several hydrocarbons of fundamental interest that have never been synthesised, whose preparation could be realised by using tricarbonyliron protection. The dendralenes are a fundamental family of cross-conjugated oligoalkenes that only recently been accessed on a useful scale. The family of molecules has the power to rapidly form compounds with natural-product like complexity through a cascade of bond-forming reactions, but their synthetic utility is hampered by their instability and lack of selectivity. In Chapter # we describe the !rst targeted preparation of the tricarbonyliron complexes of the ."/-.'/dendralenes. We !nd that tricarbonyliron complexation not only protects the dendralenes from decomposition, but also selectively activates them to a broad range of reactions. X ABSTRACT In Chapter " we report the !rst general synthesis of ."/dendralene molecules substituted at the )-position. These compounds were prepared via cross- metathesis on the tricarbonyliron complex of ."/dendralene. With the elusive series of substituted dendralenes in hand, we report the surprising observation that the )E-sub-class undergoes Diels-Alder dimerisation up to #&& times faster than the parent ."/dendralene. This stands in stark contrast to the behaviour of the )Z-, #- , & "'-substituted ."/dendralenes, which are invariably more stable than the unsubstituted case. We explore the mechanistic rationale for this behaviour. Finally, in Chapter $ we use the knowledge gained in the synthetic e2orts described in Chapters # & " to rationally develop a new, general method for the synthesis of polyene complexes via cross-coupling reactions. To verify our approach we use #- & #,"- substituted halobutadiene complexes to directly prepare the tricarbonyliron complexes of the dendralenes, as well as some new cross- conjugated frameworks. XI Table of Contents Declaration i Acknowledgements iii Publications v Abbreviations vii Abstract ix Table of Contents xi Stabilisation of Hyper-Reactive Molecules By Tricarbonyliron 1 1.1 By Way Of An Introduction 1 1.1.1 Preamble 1 1.1.2 Target: Fundamental Molecules 2 1.2 Polyene Protection 3 1.2.1 Alternative to Diene Protection 3 1.2.2 Tricarbonyliron Complexes of Dienes 4 1.2.3 The Preparation of Tricarbonyliron Complexes of Unstable Polyenes 5 1.2.4 Reagents
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