Science of synthesis : Houben-Weyl methods of molecular transformations. Compounds with All-Carbon Functions. Cumulenes and Allenes

466 Pages·2008·4.91 MB·English

by  Krause N. (ed.)

VII
Volume Editor(cid:2)s Preface
Whereasallenesandhighercumuleneshavebeenregardedaschemicalcuriositiesfora
longtime,theyarenowrecognizednotonlyasvaluablesyntheticprecursorsforcomplex
molecules of biological or industrial interest, but also as intriguing target molecules in
their own right. Thus, it is not surprising that a surge of new synthetic methods for al-
lenesandcumuleneshastakenplaceinrecentyears.Volume44ofScienceofSynthesis
providesawell-organizedoverviewofallthesemethods,togetherwithasectiononthe
applicationsofallenesinorganicsynthesis.
Iamverygratefultotheauthorsfortheiroutstandingcommitmenttothisventure.It
wasapleasuretoplanthevolumewiththeexceptionalexperienceandinsightprovided
by Dr. Daniel Bellus and Dr. Joe Richmond, and to bring it into existence with the im-
mense support of the Thieme editorial team headed by Dr. Fiona Shortt de Hernandez.
In particular, I thank Dr. Caroline J. Taylor, Dr. Marcus White, and Dr. Mark Smith for
theirgreathelpthroughouteditingofthechapters.SpecialmentiongoestoAngelaGil-
denandMichaelaFreyfortheirsmoothhandlingofthe(quitesubstantial)paperwork.
VolumeEditor
NorbertKrause Dortmund,November2007
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Volume 44:
Cumulenes and Allenes
Preface .................................................................. V
VolumeEditor(cid:2)sPreface ................................................. VII
TableofContents ........................................................ XI
Introduction
N.Krause ................................................................ 1
44.1 ProductClass1:Cumulenes
M.Ogasawara ............................................................ 9
44.2 ProductClass2:LinearAllenes
44.2.1 SynthesisbySubstitution
H.OhnoandK.Tomioka .................................................. 71
44.2.2 SynthesisbyElimination
V.GandonandM.Malacria ................................................ 175
44.2.3 SynthesisbyAddition
K.K.Wang ............................................................... 229
44.2.4 SynthesisbyRearrangement
A.S.K.Hashmi ........................................................... 287
44.2.5 SynthesisfromOtherAllenes
H.-U.ReissigandR.Zimmer ............................................... 301
44.2.6 ApplicationsofAllenesinOrganicSynthesis
M.A.Tius ................................................................ 353
44.3 ProductClass3:CyclicAllenes
T.Kawase ................................................................ 395
KeywordIndex ........................................................ 451
AuthorIndex ............................................................ 485
Abbreviations ........................................................... 503
Science of Synthesis Original Edition Volume 44
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Science of Synthesis Original Edition Volume 44
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Table of Contents
Introduction
N.Krause
Introduction .............................................................. 1
44.1 ProductClass1:Cumulenes
M.Ogasawara
44.1 ProductClass1:Cumulenes .............................................. 9
44.1.1 ProductSubclass1:[6]-andHigherCumulenes ........................... 10
44.1.1.1 SynthesisofProductSubclass1 ............................................ 10
44.1.1.1.1 SynthesisbyElimination ................................................... 10
44.1.1.1.1.1 Method1: ReductionofÆ,w-Dihydroxypolyynes ........................ 10
44.1.1.1.1.2 Method2: DoubleEliminationofMethanolfrom1,7-Dimethoxy-
hepta-2,4-diynes ........................................... 11
44.1.2 ProductSubclass2:Hexapentaenes([5]Cumulenes) ...................... 12
44.1.2.1 SynthesisofProductSubclass2 ............................................ 12
44.1.2.1.1 SynthesisbyElimination ................................................... 12
44.1.2.1.1.1 Method1: DehydroxylationofHexa-2,4-diyne-1,6-diols ................. 12
44.1.2.1.1.2 Method2: Debrominationof3,4-Dibromohexa-1,2,4,5-tetraenes ....... 13
44.1.2.1.1.3 Method3: OtherMethodsInvolvingElimination ........................ 14
44.1.2.1.2 SynthesisMediatedbyCarbeneSpecies ..................................... 15
44.1.2.1.2.1 Method1: DimerizationofAllenylideneSpecies ........................ 15
44.1.2.1.2.1.1 Variation1: DimerizationofAllenylideneSpeciesGeneratedfrom
PropargylicPrecursors ...................................... 15
44.1.2.1.2.1.2 Variation2: DimerizationofAllenylideneSpeciesGeneratedfrom
Bromoallenes .............................................. 17
44.1.2.1.2.1.3 Variation3: DimerizationofAllenylidene–ChromiumSpecies ............ 17
44.1.2.1.2.2 Method2: TrappingofHexapentaenylideneSpecies .................... 17
44.1.3 ProductSubclass3:Pentatetraenes([4]Cumulenes) ...................... 18
44.1.3.1 SynthesisofProductSubclass3 ............................................ 18
44.1.3.1.1 SynthesisbySubstitution .................................................. 18
44.1.3.1.1.1 Method1: LithiationandSilylationofHexa-2,4-diynes .................. 18
44.1.3.1.1.2 Method2: S 2¢¢SubstitutiononPenta-2,4-diynylEsters ................. 19
N
44.1.3.1.2 SynthesisbyElimination ................................................... 20
44.1.3.1.2.1 Method1: DoubleDehydrobrominationof2,4-Dibromopenta-1,4-dienes 20
44.1.3.1.2.2 Method2: 1,2-and1,4-Eliminationfrom5-Methoxypent-2-yn-1-ols ..... 20
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44.1.3.1.2.3 Method3: OxidationofHexapentaenesFollowedby
CarbonMonoxideElimination ............................... 21
44.1.3.1.2.4 Method4: Reductive1,4-Dechlorinationofa2,5-Dichloropent-1-en-3-yne 22
44.1.3.1.2.5 Method5: 1,1-DehalogenationandRearrangementof
1,1-Dihalocyclopropanes ................................... 22
44.1.3.1.2.6 Method6: SulfurEliminationfromPenta-1,2,3,4-tetraeneEpisulfides .... 23
44.1.3.1.2.7 Method7: WittigReaction ............................................ 24
44.1.3.1.2.7.1 Variation1: WittigReactionofCarbonSuboxidewith
Alkylidenephosphoranes ................................... 24
44.1.3.1.2.7.2 Variation2: WittigReactionofAlka-2,3-dienoylChlorideswith
Alkylidenephosphoranes ................................... 25
44.1.3.1.2.8 Method8: Retro-Diels–AlderReaction ................................. 25
44.1.4 ProductSubclass4:Butatrienes([3]Cumulenes) .......................... 26
44.1.4.1 SynthesisofProductSubclass4 ............................................ 26
44.1.4.1.1 SynthesisbySubstitution .................................................. 26
44.1.4.1.1.1 Method1: S 2¢¢SubstitutiononPent-4-en-2-ynylDerivativesand
N
RelatedReactions .......................................... 26
44.1.4.1.1.1.1 Variation1: OnPent-4-en-2-ynylMethanesulfinateswith
Alkylsilver(I)Reagents ...................................... 26
44.1.4.1.1.1.2 Variation2: On2-(But-3-en-1-ynyl)oxiraneswithAlkylsilver(I)Reagents ... 27
44.1.4.1.1.1.3 Variation3: ReductionofAlka-4,5-dien-2-ynolsorRelatedAlcoholsby
LithiumAluminumHydride ................................. 27
44.1.4.1.1.2 Method2: S 2¢Substitutionon2-Bromo-1-en-3-ynes ................... 28
N
44.1.4.1.1.2.1 Variation1: WithAlkylcopperReagents ................................. 28
44.1.4.1.1.2.2 Variation2: WithSoftCarbonNucleophilesCatalyzedby
aPalladiumComplex ....................................... 29
44.1.4.1.1.3 Method3: SynthesisofPhosphinobutatrienesfrom
2-Vinyl-1H-phosphirenesandAlkyllithiumReagents .......... 30
44.1.4.1.2 SynthesisbyElimination ................................................... 30
44.1.4.1.2.1 Method1: Dehydrohalogenation ...................................... 30
44.1.4.1.2.1.1 Variation1: SingleDehydrohalogenationofHaloallenes ................. 30
44.1.4.1.2.1.2 Variation2: DoubleDehydrohalogenationof2,3-Dihalobut-2-enes ....... 31
44.1.4.1.2.1.3 Variation3: DoubleDehydrohalogenationof1,4-Dihalobut-2-enes ....... 32
44.1.4.1.2.1.4 Variation4: DoubleDehydrochlorinationandRingOpeningof
1,1-Dichlorocyclopropanes ................................. 33
44.1.4.1.2.2 Method2: Dehydration ............................................... 34
44.1.4.1.2.2.1 Variation1: 1,2-DehydrationofAlka-2,3-dienols ......................... 34
44.1.4.1.2.2.2 Variation2: RearrangementandDehydrationofEpoxyalkynols ........... 34
44.1.4.1.2.3 Method3: EliminationofAlcoholsandRelatedReactions ............... 35
44.1.4.1.2.3.1 Variation1: 1,4-EliminationofAlcohols ................................. 35
44.1.4.1.2.3.2 Variation2: 1,6-EliminationofAlcohols ................................. 37
44.1.4.1.2.4 Method4: PyrolysisofHexakis(trimethylsilyl)but-2-yne ................. 37
44.1.4.1.2.5 Method5: Dehalogenation ............................................ 37
44.1.4.1.2.5.1 Variation1: 1,4-Dehalogenationof1,4-Dihaloalk-2-ynes ................. 37
44.1.4.1.2.5.2 Variation2: 1,2-Dehalogenationof2,3-Dihalo-1,3-dienes ................ 39
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44.1.4.1.2.6 Method6: 1,1-DehalogenationandRearrangementof
2-Alkenylidene-1,1-dihalocyclopropanes ..................... 40
44.1.4.1.2.7 Method7: DehydroxylationofAlk-2-yne-1,4-diols ...................... 41
44.1.4.1.2.8 Method8: 1,4-Eliminationfrom4-Hydroxybut-2-ynylsilanesor-stannanes 42
44.1.4.1.2.8.1 Variation1: From4-Hydroxybut-2-ynylsilanes ........................... 42
44.1.4.1.2.8.2 Variation2: From4-Hydroxybut-2-ynylstannanes ........................ 44
44.1.4.1.2.9 Method9: DesulfurizationofCyclicTrithiocarbonates .................. 44
44.1.4.1.2.10 Method10: SulfurEliminationfromAlkylidenecyclopropanethiones ...... 45
44.1.4.1.2.11 Method11: WittigandRelatedReactions ............................... 46
44.1.4.1.2.11.1 Variation1: WittigReactionofAldehydesorKetoneswith
Allenylidenephosphoranes .................................. 46
44.1.4.1.2.11.2 Variation2: DoubleWittigReactionofaPhosphorusDiylidewith
anAldehyde ............................................... 47
44.1.4.1.2.11.3 Variation3: Horner–Emmons-TypeReactionsofAldehydesorKetones .... 48
44.1.4.1.2.11.4 Variation4: WittigReactionofaKetenewithaVinylidenephosphorane ... 49
44.1.4.1.2.12 Method12: Base-InducedBoraneEliminationfrom
Bis(1-iodoalkenyl)boranes .................................. 49
44.1.4.1.2.13 Method13: Retro-Diels–AlderReactions ................................ 50
44.1.4.1.2.14 Method14: ThermalDecompositionofaDisodiumSaltof
aCyclobutane-1,3-dioneBis(tosylhydrazone) ................ 51
44.1.4.1.3 SynthesisbyAddition ...................................................... 51
44.1.4.1.3.1 Method1: Electrophilic1,4-Additionto1,3-Diynes ..................... 51
44.1.4.1.3.2 Method2: 1,4-Disilylationof1,4-Disilyl-1,3-diynes ...................... 52
44.1.4.1.3.2.1 Variation1: 1,4-Disilylationof1,4-Disilyl-1,3-diynesby
aSilylmanganeseReagent .................................. 52
44.1.4.1.3.2.2 Variation2: Palladium-Catalyzed1,4-Disilylationof1,4-Disilyl-1,3-diynes 53
44.1.4.1.3.3 Method3: Palladium-CatalyzedDoubleArylationof1,4-Diaryl-1,3-diynes 54
44.1.4.1.3.4 Method4: 1,6-AdditionofBromineto1,5-Dien-3-ynes ................. 54
44.1.4.1.4 SynthesisbyRearrangement ............................................... 55
44.1.4.1.4.1 Method1: Base-PromotedRearrangementofaConjugatedBisalleneto
anAlkenylbutatriene ....................................... 55
44.1.4.1.4.2 Method2: PhotorearrangementofVinylidenecyclopropanesto
ButatrieneDerivatives ...................................... 55
44.1.4.1.5 SynthesisMediatedbyCarbeneSpecies ..................................... 56
44.1.4.1.5.1 Method1: DimerizationofVinylideneSpeciesorVinylideneEquivalents 56
44.1.4.1.5.1.1 Variation1: DimerizationofVinylideneSpeciesorVinylideneEquivalents
Generatedfromgem-Dihaloalkenes ......................... 56
44.1.4.1.5.1.2 Variation2: DimerizationofVinylideneSpeciesorVinylideneEquivalents
Generatedfrom1-Halo-1-hydroalkenes ..................... 57
44.1.4.1.5.1.3 Variation3: FormationofaButatrienefrom2-Nitro-1,1-diphenylethene 58
44.1.4.1.5.1.4 Variation4: DimerizationofAlkenylideneSpeciesGeneratedfrom
Dialkenylcuprates .......................................... 59
44.1.4.1.5.1.5 Variation5: Desulfurization–DimerizationofDithioacetalswith
Hexacarbonyltungsten(0) ................................... 59
44.1.4.1.5.1.6 Variation6: DimerizationofVinylidene–TungstenSpecies ............... 59
44.1.4.1.5.2 Method2: ReactionsInvolvingAllenylideneSpecies .................... 60
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44.1.4.1.5.2.1 Variation1: ReactionsofAllenylideneSpecieswithDiazoalkanes ........ 60
44.1.4.1.5.2.2 Variation2: ReactionsofAllenylidene–RhodiumComplexeswith
Diazomethane ............................................ 60
44.1.4.1.5.3 Method3: Reactionsof1,2,3-TrienylideneSpecies ..................... 61
44.1.4.1.5.3.1 Variation1: Reactionsof1,2,3-TrienylideneSpecieswithAlkenes ........ 61
44.1.4.1.5.3.2 Variation2: Reactionsof1,2,3-TrienylideneSpecieswith
Group14Hydrides ........................................ 61
44.1.4.1.6 OtherMethodsfortheSynthesisofButatrienes ............................ 62
44.1.4.1.6.1 Method1: DimerizationofTerminalAlkynesby
Transition-MetalCatalysts ................................. 62
44.1.4.1.6.2 Method2: CouplingReactionsbetween1,1-Dichloroalkenesand
TerminalAlkenes .......................................... 64
44.1.4.1.6.3 Method3: Zirconium-MediatedCouplingReactionsof1,3-Diyneswith
AldehydesorKetones ..................................... 64
44.1.4.1.6.3.1 Variation1: ReactionsofZirconacycleswithAldehydesToForm
ButatrienylMonoalcohols ................................. 64
44.1.4.1.6.3.2 Variation2: ReactionsofZirconacycleswithKetonesToForm
ButatrienylDiols .......................................... 65
44.2 ProductClass2:LinearAllenes
44.2.1 SynthesisbySubstitution
H.OhnoandK.Tomioka
44.2.1 SynthesisbySubstitution ................................................ 71
44.2.1.1 Method1: Organocopper-MediatedReactionsofPropargylicand
RelatedSubstrates ........................................ 71
44.2.1.1.1 Variation1: ReactionsofVariousPropargylicSubstrates ................ 75
44.2.1.1.2 Variation2: ReactionsUsingVariousCopperNucleophiles .............. 81
44.2.1.1.3 Variation3: SynthesisofEnantiomericallyEnrichedAllenes ............. 83
44.2.1.1.4 Variation4: Ring-OpeningReactions ................................... 94
44.2.1.1.5 Variation5: 1,5-SubstitutionReactions ................................. 100
44.2.1.1.6 Variation6: HalogenationofPropargylicSubstrates .................... 101
44.2.1.2 Method2: Aluminum-MediatedReactionsofPropargylicSubstrates .... 102
44.2.1.2.1 Variation1: ReactionsofPropargylicHalides ........................... 102
44.2.1.2.2 Variation2: ReactionsofPropargylicAlcohols .......................... 103
44.2.1.2.3 Variation3: ReactionsofPropargylicSulfonates ........................ 106
44.2.1.2.4 Variation4: ReactionsofPropargylicEthers ............................ 108
44.2.1.2.5 Variation5: ReactionsofPropargylicAmineDerivatives ................. 110
44.2.1.2.6 Variation6: Ring-OpeningReactions ................................... 111
44.2.1.2.7 Variations7: MiscellaneousReactions ................................... 115
44.2.1.3 Method3: Lithium-,Magnesium-,orZinc-MediatedReactionsof
PropargylicandRelatedSubstrates ......................... 115
44.2.1.3.1 Variation1: Lithium-MediatedReactions ............................... 115
44.2.1.3.2 Variation2: Magnesium-MediatedReactions ........................... 117
44.2.1.3.3 Variation3: Zinc-MediatedReactions .................................. 119
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44.2.1.4 Method4: Borane-orGallium-MediatedReactionsof
PropargylicSubstrates ..................................... 120
44.2.1.4.1 Variation1: Borane-MediatedReactions ............................... 120
44.2.1.4.2 Variation2: Gallium-MediatedReactions ............................... 123
44.2.1.5 Method5: Iron-CatalyzedReactionsofPropargylicSubstrates .......... 123
44.2.1.5.1 Variation1: Ring-OpeningReactionsofEpoxides ....................... 125
44.2.1.6 Method6: Palladium-CatalyzedReactionsofPropargylicSubstrates .... 126
44.2.1.6.1 Variation1: ReactionswithGrignardReagents ......................... 127
44.2.1.6.2 Variation2: ReactionswithZincReagents .............................. 127
44.2.1.6.3 Variation3: ReactionswithBoraneReagents ........................... 129
44.2.1.6.4 Variation4: ReactionswithAluminumorTinReagents .................. 131
44.2.1.6.5 Variation5: ReactionswithCopperAcetylides .......................... 132
44.2.1.6.6 Variation6: ReactionswithSamariumReagents ........................ 133
44.2.1.6.7 Variation7: CarbonylationReactions ................................... 134
44.2.1.6.8 Variation8: ReactionswithHydrideReagents .......................... 138
44.2.1.6.9 Variations9: MiscellaneousReactions ................................... 141
44.2.1.7 Methods7: MiscellaneousReactionsofPropargylicSubstrates .......... 145
44.2.1.7.1 Variation1: ReactionswithNitrogenNucleophiles ...................... 145
44.2.1.7.2 Variation2: ReactionswithEnolEthers ................................. 146
44.2.1.7.3 Variation3: Chromium-CatalyzedReactions ............................ 146
44.2.1.7.4 Variation4: Nickel-MediatedReactions ................................ 147
44.2.1.7.5 Variation5: ReactionswithCopperCyanide ............................ 147
44.2.1.7.6 Variation6: Zirconocene-MediatedReactions .......................... 148
44.2.1.7.7 Variation7: Ruthenium-CatalyzedReactions ........................... 148
44.2.1.7.8 Variation8: Samarium-MediatedReactions ............................ 149
44.2.1.8 Method8: SubstitutionofHaloallenes ................................ 150
44.2.1.8.1 Variation1: Copper-MediatedReactions ............................... 150
44.2.1.8.2 Variation2: Palladium-CatalyzedReactions ............................. 155
44.2.1.8.3 Variation3: OtherReactionswithCarbonNucleophiles ................. 161
44.2.1.8.4 Variation4: ReactionswithNitrogenNucleophiles ...................... 163
44.2.1.8.5 Variation5: ReactionswithOxygenNucleophiles ....................... 166
44.2.1.8.6 Variation6: ReactionswithSulfurNucleophiles ......................... 166
44.2.1.9 Method9: Substitutionof2-Halobuta-1,3-dienesand
RelatedCompounds ...................................... 166
44.2.1.9.1 Variation1: Copper-MediatedReactions ............................... 166
44.2.1.9.2 Variation2: Palladium-CatalyzedReactions ............................. 167
44.2.2 SynthesisbyElimination
V.GandonandM.Malacria
44.2.2 SynthesisbyElimination ................................................. 175
44.2.2.1 1,3-EliminationfromSubstitutedVinylicorAllylicDerivatives ............... 176
44.2.2.1.1 Method1: Dehydrohalogenationof2-Halopropenes ................... 176
44.2.2.1.1.1 Variation1: FromNonactivatedSubstrates ............................. 176
44.2.2.1.1.2 Variation2: FromÆ,(cid:2)-UnsaturatedSubstrates .......................... 178
44.2.2.1.2 Method2: DehydrosilylationofSilylEnolEthers ....................... 178
44.2.2.1.3 Method3: DehydrosulfonylationofVinylTrifluoromethanesulfonates 180
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44.2.2.1.4 Method4: DehydrationofAllylicAlcohols ............................. 181
44.2.2.1.5 Method5: EliminationfromVinylSulfoxidesandVinylSulfones ........ 182
44.2.2.1.6 Method6: EliminationfromPhenylVinylSelenoxides .................. 182
44.2.2.1.6.1 Variation1: Oxidationwith3-ChloroperoxybenzoicAcid ................ 182
44.2.2.1.6.2 Variation2: AsymmetricEliminationUsingSharplessOxidation ......... 183
44.2.2.1.6.3 Variation3: AsymmetricEliminationUsingChiralDiferrocenylDiselenides 185
44.2.2.1.7 Method7: EliminationfromEnolPhosphates .......................... 186
44.2.2.1.8 Method8: EliminationfromVinylsilanesandVinylstannanes ........... 188
44.2.2.1.9 Method9: PetersonReaction ......................................... 190
44.2.2.1.10 Method10: EliminationfromVinyl-andAllylmetalIntermediates ........ 192
44.2.2.1.10.1 Variation1: VinylcopperandVinylmagnesiumIntermediatesfrom
PropargylEthersandOrganocopperandOrganomagnesium
Reagents ................................................. 192
44.2.2.1.10.2 Variation2: AllylzincIntermediatesfromAlkynylSulfoxidesand
AlkynylSulfones .......................................... 194
44.2.2.1.10.3 Variation3: VinylpalladiumIntermediatesfromN-Propargylsulfonamides 194
44.2.2.1.10.4 Variation4: VinylzirconiumandVinyltitaniumIntermediatesfrom
PropargylEthersandPropargylBromides ................... 195
44.2.2.1.11 Method11: Dehalogenationof2,3-Dihalopropenesand
Deoxyhalogenationof(cid:2)-HaloallylAlcoholDerivatives ....... 197
44.2.2.1.12 Method12: Debromosulfinylationof1-(Bromomethyl)vinylSulfoxidesand
Sulfimides ................................................ 197
44.2.2.1.12.1 Variation1: UsingTributyltinHydride .................................. 198
44.2.2.1.12.2 Variation2: UsingTris(trimethylsilyl)silane ............................. 199
44.2.2.1.13 Method13: Debromosulfinylationfrom1-(Bromomethyl)vinylSulfides 200
44.2.2.1.14 Method14: Eliminationfrom(cid:2)-SulfinylallylAlcoholDerivativesand
1-(Sulfinylalkyl)vinylTrifluoromethanesulfonates ............ 201
44.2.2.1.14.1 Variation1: Eliminationfrom1-(Sulfinylalkyl)vinylTrifluoromethane-
sulfonates ................................................ 201
44.2.2.1.14.2 Variation2: Eliminationfrom(cid:2)-SulfinylallylAlcoholDerivatives .......... 202
44.2.2.2 WittigAlkenationsandRelatedReactions .................................. 203
44.2.2.2.1 Method1: SynthesisUsingorvia(Hydroxyalkenyl)phosphonateand
(Hydroxyalkenyl)phosphineOxideIntermediates ............ 204
44.2.2.2.1.1 Variation1: Baylis–Hillman-TypeReactionofAlkenylphosphorus
CompoundswithAldehydes ............................... 204
44.2.2.2.1.2 Variation2: Sulfanyl-,Selanyl-,orCarbometalationofAlkynylphosphine
OxidesandReactionwithAldehydes ....................... 205
44.2.2.2.2 Method2: Synthesisvia(cid:2)-HydroxyallylphosphonateDerivatives
PreparedfromKetenesorKeteneEquivalents .............. 207
44.2.2.2.2.1 Variation1: UsingAcidChlorides ...................................... 208
44.2.2.2.2.2 Variation2: UsingArylEsters .......................................... 209
44.2.2.3 Metal–VinylideneRoutestoAllenes ....................................... 211
44.2.2.3.1 Method1: Synthesisfrom1,1-Dimetalloalkenes ....................... 211
44.2.2.3.2 Method2: SynthesisviaAlkenyltitanoceneDerivatives ................. 212
44.2.2.3.3 Method3: DoubleAlkenationUsingTitanium-SubstitutedYlides ....... 214
44.2.2.3.4 Method4: SynthesisviaAlkenylidenemagnesiumIntermediates ....... 215
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