Table Of ContentTopics in Current Chemistry 357
LeGrande M. Slaughter Editor
Homogeneous
Gold Catalysis
357
Topics in Current Chemistry
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LeGrande M. Slaughter
Editor
Homogeneous Gold Catalysis
With contributions by
A. Aponick (cid:1) O.N. Faza (cid:1) M.R. Gagne´ (cid:1) G.B. Hammond (cid:1)
(cid:1) (cid:1) (cid:1) (cid:1) (cid:1)
A.C. Jones C.S. Lopez D. Malhotra V. Michelet
(cid:1) (cid:1) (cid:1)
P.H.S. Paioti S. Shin D. Weber B. Xu
Editor
LeGrandeM.Slaughter
DepartmentofChemistry
UniversityofNorthTexas
Denton,Texas
USA
ISSN0340-1022 ISSN1436-5049 (electronic)
TopicsinCurrentChemistry
ISBN978-3-319-13721-6 ISBN978-3-319-13722-3 (eBook)
DOI10.1007/978-3-319-13722-3
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Preface
Theriseofhomogeneousgoldcatalysisisthestoryofalong-neglectedmetalboldly
defyingexpectations.Alongwithageneralreputationforinertness,goldpossesses
two common oxidation states which have historically been overlooked as too
uninteresting(AuI)ortoounstable(AuIII)towarrantseriousstudybymostorgan-
ometallic chemists. Despite significant activity in the area of heterogeneous gold
catalystsfromthe1970sonward,andatrickleofseminalreportsofhomogeneous
goldcatalysisbyIto,Hayashi,andUtimotointhe1980sand1990s,thelatterarea
didnotbegintoblossomuntiltheworkofTelesandHashmiin1998–2000unveiled
thepotentialofthefield.Itisnowwellrecognizedthatgold(inparticularAuI)isa
potent,“soft”carbophilicLewisacid,withanabilitytoactivatecarbon–carbonπ-
bonds toward nucleophilic attack which parallels the reactivity of other late tran-
sition metals such as platinum, palladium, and mercury. It is also clear that gold
often outshines its metallic neighbors by activating π-bonds under exceptionally
mild conditions and by channeling these transformations into unique modes of
reactivity which are particularly suited for the synthesis of complex organic
molecules.
Such is the pace of progress in this field that the many excellent reviews
available in the literature are in frequent need of updates. The purpose of this
volumeistohighlightsomekeysubareasofhomogeneousgoldcatalysisthathave
spurredsignificantadvancesinthefieldinthepast3–5years.Thetopicshavebeen
chosen in recognition of two equally powerful forces that have driven the recent
evolution of gold catalysis: an increasing need for synthetic methods that deliver
complex organic structures, and the renaissance of fundamental organometallic
gold chemistry. The authors are active researchers who have made substantial
contributionstotheareasreviewedintheirrespectivechapters.
The volume begins with a chapter by Malhotra, Hammond, and Xu, which
highlights the interplay of ligand effects, substrate structure and mechanism in
goldcatalysis,usingspecificexamplesofliganddesignandreactionsmediatedby
gold–oxonium intermediates. Shin reviews reactions in which alkynes serve as
synthons for reactive gold carbene intermediates, an approach that has yielded
v
vi Preface
numerous routes to complex organic molecules without the need for problematic
diazo reagents as carbene precursors. Paiote and Aponick provide an account of
gold-catalyzedtransformationsofunsaturatedalcohols,animportantreactionclass
in which π-activation leads to formal substitution processes via loss of H O.
2
A chapter by Michelet surveys the rich area of gold-catalyzed domino processes,
in which gold-mediated reactions trigger multistep transformations which can
generate significant molecular complexity. On the organometallic side, Jones
criticallyreviewsrecentstudiesofthestructureandreactivityofgoldπ-complexes
whicharemodelintermediatesforgold-catalyzedprocesses,andWeberandGagne´
summarizethecurrentstateofknowledgeoftheeffectsofaurophilicattractionon
gold catalysis. A chapter by Faza and L(cid:1)opez on computational approaches to the
studyofhomogeneousgoldcatalysiscompletesthevolume.Thelatterissuretobe
a valuable resource for chemists working in the gold catalysis arena, given the
increasinglyindispensableroleofcomputationalchemistryindecipheringcatalytic
reactionmechanismsandthedifficultyofchoosingtheproperapproachamongthe
growingarsenalofavailablemethods.
It is hoped that this volume will serve as a valuable and timely resource for
chemistsactivelypursuingresearchinbothsyntheticapplicationsofhomogeneous
goldcatalysisandfundamentalorganogoldchemistry,aswellasforthosewhoare
simplyinterestedinfollowingtherichandgrowingliteratureofthisfield.
Denton,TX,USA LeGrandeM.Slaughter
September2014
Contents
LigandDesigninGoldCatalysisandChemistryofGold–Oxonium
Intermediates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
DeepikaMalhotra,GeraldB.Hammond,andBoXu
Gold-CatalyzedCarbeneTransferReactions. . . . . . . . . . . . . . . . . . . . . 25
SeunghoonShin
Gold-CatalyzedTransformationofUnsaturatedAlcohols. . . . . . . . . . . 63
PauloH.S.PaiotiandAaronAponick
Gold-CatalyzedDominoReactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Ve´roniqueMichelet
Goldπ-ComplexesasModelIntermediatesinGoldCatalysis. . . . . . . . 133
AmandaC.Jones
AurophilicityinGold(I)Catalysis:ForBetterorWorse?. . . . . . . . . . . 167
DieterWeberandMichelR.Gagne´
ComputationalApproachestoHomogeneousGoldCatalysis. . . . . . . . . 213
OlallaNietoFazaandCarlosSilvaL(cid:1)opez
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
vii
TopCurrChem(2015)357:1–24
DOI:10.1007/128_2014_592
#SpringerInternationalPublishingSwitzerland2014
Publishedonline:24February2015
Ligand Design in Gold Catalysis
and Chemistry of Gold–Oxonium
Intermediates
DeepikaMalhotra,GeraldB.Hammond,andBoXu
Abstract Goldcatalysisisconsideredoneofthemostimportantbreakthroughsin
organicsynthesisduringthelastdecade.Manygold-catalyzedreactionssufferfrom
high catalyst loading, which is a serious limitation on the application of gold
catalysisinlargerscale synthesis.Becauseligandsplay amajor roleinthetuning
of reactivity of transition metal catalysts, there has been an increased effort on
rationallyunderstandingligandeffectsingoldcatalysisandusingarationalligand
design to achieve higher efficiency. In the first part of this chapter, selected
examples of ligand design in gold catalysis are discussed. In the second part, the
chemistryofgold–oxoniumintermediateisexamined.Anoxoniumintermediateis
generatedwhenaoxygennucleophile(ketone,aldehyde,orether)attacksacationic
gold-activatedmultiplebond.Thisoxoniumintermediate,beingahighlyenergetic
species, has the potential to undergo further transformations such as electron
transfer/rearrangement/protodeaurationtoformdiverseproducts.
Keywords Benzannulations(cid:129)Cationicgold catalysis (cid:129)Ligand design(cid:129)Oxonium
intermediates
Contents
1 LigandDesigninCationicGoldCatalysis.................................................. 2
1.1 Introduction............................................................................. 2
1.2 LigandEffectsinGoldCatalysis...................................................... 2
1.3 SelectedExamplesofLigandDesigninGoldCatalysis.............................. 4
2 ChemistryofGold–OxoniumIntermediates................................................. 11
2.1 Introduction............................................................................. 11
2.2 ChemistryofGold–OxoniumIntermediatesDerivedfromCarbonylCompounds.. 11
2.3 ChemistryofaGold–OxoniumIntermediateDerivedfromEthers/Epoxides....... 16
References........................................................................................ 22
D.Malhotra,G.B.Hammond(*),andB.Xu(*)
DepartmentofChemistry,UniversityofLouisville,Louisville,KY40292,USA
e-mail:[email protected];[email protected]
2 D.Malhotraetal.
1 Ligand Design in Cationic Gold Catalysis
1.1 Introduction
Therehasbeenanexponentialincreaseinthenumberofstudiesonhomogeneous
goldcatalysisduringthepastdecade[1–12].Cationicgoldspeciesareregardedas
the most powerful catalysts for the electrophilic activation of alkynes toward a
variety of nucleophiles [2, 4–10, 13, 14]. The reason for this success can be
attributedtothelowerLUMOandpoorback-donationofthecationicgoldspecies
[15–18].Ontheotherhand,thelowturnovernumbersobservedingold-catalyzed
reactionshavelimitedtheapplicabilityofgoldcatalystsinfieldssuchasmedicinal
chemistry and material synthesis. Gold being a precious metal, it is difficult to
recycleaftereachreaction;thecommonpracticeistouse5%loading,whichmakes
its use often impractical in larger scale synthesis. In contrast, in many palladium-
catalyzedcouplingreactions, suchastheSuzukireaction, thecatalystloadinghas
beenreducedtoppmlevels[19].
Ligandsplayamajorroleinthetuningofreactivityoftransitionmetalcatalysts
[20–22].Initially,becauseofthecomplexityofgold-catalyzedreactions,arational
understandingofligandeffectslaggedbehindthedevelopmentofalargenumberof
gold-catalyzedtransformations,andthedevelopmentofnewcatalystsandreactions
mostly relied upon trial and error [5]. However, in the last few years, more effort
wasmadetoachievearationalunderstandingofligandeffectsingoldcatalysisand
the use of a rational ligand design to achieve higher efficiency (TON). There has
alsobeenprogressinthedesignofchiralligandsforenantioselectivegoldcatalysis,
but,becauseofpagelimitations,thedevelopmentofchiralligandsisnotcoveredin
thischapter[23].
1.2 Ligand Effects in Gold Catalysis
1.2.1 LigandEffectsinEachStageoftheGoldCatalyticCycle
Hammond and Xu conducted a relatively comprehensive investigation of ligand
effects in gold catalysis in 2012 [24]. It is generally accepted that most gold-
catalyzed reactions go through three major stages (Scheme 1). In stage 1, a
nucleophileattacksan[L–Au]+-activatedalkyne(oralkene)toformatrans-alkenyl
goldcomplexintermediateB(oranalkylgoldcomplexinthecaseofalkenes).In
stage 2, the resulting vinyl complex B reacts with an electrophile (E+), usually a
proton, to yield the final product via protodeauration, which also regenerates the
cationic gold species (Scheme 1). Additionally, in almost all gold-catalyzed reac-
tions,decayordeactivationofthegoldcatalysttakesplace(stage3)[25].Insome
gold-catalyzed reactions, the formation of off-cycle gold species such as bis-Au-
vinyl species D was observed [26]. As in the decay of cationic gold catalysts,
off-cyclegoldspeciesalsoreducetheturnoverofproductformation.
