Rhodium-catalyzed intramolecular alkynylsilylation of alkynes

Article abstract of DOI:10.1039/c5cc04172d

Rhodium-catalyzed intramolecular alkynylsilylation of alkynes is described. The reaction proceeds through syn-insertion by a cationic rhodium/triarylphosphine catalyst, representing the first alkynylsilylation of alkynes via the cleavage of a C(sp)-Si bond by transition-metal catalysis. A highly enantioselective variant is also described for the creation of a silicon stereogenic center.

Full text of DOI:10.1039/c5cc04172d

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Pleaseꢀd Co hꢀ ne omt ꢀ Ca do jmu smt ꢀmarginsꢀ
View Article Online
DOI: 10.1039/C5CC04172D
ChemCommꢀ
COMMUNICATIONꢀ
ꢀ
Rhodium-CatalyzedꢀIntramolecularꢀAlkynylsilylationꢀofꢀAlkynesꢀꢀ
a
a
a
RyoꢀShintani,* ꢀHirokiꢀKurata ꢀandꢀKyokoꢀNozaki*
Receivedꢀ00thꢀJanuaryꢀ20xx,ꢀ
Acceptedꢀ00thꢀJanuaryꢀ20xxꢀ
DOI:ꢀ10.1039/x0xx00000xꢀ
www.rsc.org/ꢀ
Aꢀrhodium-catalyzedꢀintramolecularꢀalkynylsilylationꢀofꢀalkynesꢀisꢀ alkynylsilylationꢀ productꢀ 3aꢀ inꢀ 20%ꢀ yield.ꢀ Onꢀ theꢀ basisꢀ ofꢀ thisꢀ
described.ꢀ Theꢀ reactionꢀ proceedsꢀ throughꢀ syn-insertionꢀ byꢀ aꢀ unexpectedꢀresult,ꢀweꢀdecidedꢀtoꢀfocusꢀonꢀtheꢀimprovementꢀofꢀthisꢀ
cationicꢀrhodium/triarylphosphineꢀcatalyst,ꢀrepresentingꢀtheꢀfirstꢀ alkynylsilylationꢀreactionꢀunderꢀrhodiumꢀcatalysis.ꢀToꢀourꢀsurprise,ꢀ
alkynylsilylationꢀ ofꢀ alkynesꢀ viaꢀ theꢀ cleavageꢀ ofꢀ aꢀ C(sp)–Siꢀ bondꢀ however,ꢀ simpleꢀ removalꢀ ofꢀ 1,4-dimethoxy-2-butyneꢀ fromꢀ theꢀ
underꢀtransition-metalꢀcatalysis.ꢀAꢀhighlyꢀenantioselectiveꢀvariantꢀ reactionꢀ inꢀ eqnꢀ (1)ꢀ didꢀ notꢀ provideꢀ 3aꢀ atꢀ allꢀ (eqnꢀ (2)).ꢀ Weꢀ
isꢀalsoꢀdescribedꢀforꢀtheꢀcreationꢀofꢀaꢀsiliconꢀstereogenicꢀcenter.ꢀ
hypothesizedꢀthatꢀthisꢀseeminglyꢀinconsistentꢀresultꢀmightꢀindicateꢀ
thatꢀtheꢀcoordinationꢀofꢀ1,4-dimethoxy-2-butyneꢀtoꢀrhodiumꢀhadꢀaꢀ
beneficialꢀeffectꢀonꢀpromotingꢀtheꢀalkynylsilylationꢀofꢀ1a.ꢀWeꢀthenꢀ
triedꢀtoꢀsearchꢀforꢀanꢀinnocentꢀreplacementꢀandꢀfoundꢀthatꢀtheꢀuseꢀ
ofꢀMeCNꢀasꢀanꢀadditiveꢀgaveꢀproductꢀ3aꢀinꢀ51%ꢀyield,ꢀandꢀaꢀhigherꢀ
Stereoselectiveꢀ insertionꢀ ofꢀ alkynesꢀ intoꢀ carbon–siliconꢀ bondsꢀ
representsꢀ aꢀ powerfulꢀ andꢀ efficientꢀ approachꢀ forꢀ theꢀ synthesisꢀ ofꢀ
highlyꢀ substitutedꢀ alkenylsilanes.ꢀ Mostꢀ ofꢀ theꢀ reportedꢀ examplesꢀ
1
employꢀ eitherꢀ strainedꢀ organosiliconꢀ substrates ꢀ orꢀ (Lewis)ꢀ acidꢀ
3
yieldꢀofꢀ82%ꢀwasꢀachievedꢀbyꢀchangingꢀtheꢀratioꢀofꢀRh/PPh ꢀfromꢀ
2
1a–f
1
2
catalysts/additives ꢀ toꢀ promoteꢀ theꢀ reactionꢀ toꢀ achieveꢀ alkyl-,
ꢀ
1
/2ꢀtoꢀ1/1. ꢀ
1g–i,2b–e,3
1g–j,2f–i,4
1b,k,2h,i
allyl-,
ꢀ
alkenyl-,
ꢀ
aryl-,
ꢀ
andꢀ
Me
Si
Me
2
j
5
Ph
propargyl/allenylsilylation ꢀ ofꢀ alkynes.ꢀ Moreꢀ reactiveꢀ acylsilanes ꢀ
6
andꢀ trimethylsilylcyanide ꢀ areꢀ alsoꢀ knownꢀ toꢀ undergoꢀ insertionꢀ ofꢀ
[RhCl(C2H4)2]2
8 mol% Rh)
PPh3 (16 mol%)
(
OMe
OMe
2a: 9% yield
alkynesꢀ toꢀ giveꢀ 2-acyl-ꢀ andꢀ 2-cyanoalkenylsilanes,ꢀ respectively.ꢀ Inꢀ
contrast,ꢀvirtuallyꢀnoꢀprogressꢀhasꢀbeenꢀmadeꢀforꢀalkyneꢀinsertionꢀ
toꢀalkynylsilanes.ꢀInꢀfact,ꢀthereꢀhasꢀbeenꢀonlyꢀoneꢀreportꢀwhereꢀtheyꢀ
describedꢀaꢀformalꢀinsertionꢀreactionꢀthroughꢀaꢀconjugateꢀadditionꢀ
ofꢀ 2-silylynamidesꢀ toꢀ acetylenedicarboxylatesꢀ followedꢀ byꢀ silylꢀ
Me
OMe
Me
Me
Si
Ph
NaBArF4 (16 mol%)
+
(1)
CH2Cl2, 40 °C, 18 h
Me
Me
Si
Me
a (0.10 M)
OMe (ArF = 3,5-(CF ) C H )
3
2 6 3
Ph
1
1.0 equiv
7,8
migration. ꢀInꢀthisꢀcommunication,ꢀweꢀdescribeꢀtheꢀdevelopmentꢀ
ofꢀ aꢀ rhodium-catalyzedꢀ intramolecularꢀ alkynylsilylationꢀ ofꢀ alkynesꢀ
throughꢀ theꢀ cleavageꢀ ofꢀ aꢀ C(sp)–Siꢀ bondꢀ underꢀ mildꢀ conditions,ꢀ
includingꢀaꢀhighlyꢀenantioselectiveꢀvariantꢀforꢀtheꢀconstructionꢀofꢀaꢀ
Me
3
a: 20% yield
ꢀ
[
RhCl(C
PPh3 (L/Rh = x/1)
NaBArF
(16 mol%)
2 4 2 2
H ) ] (8 mol% Rh)
Me Me
Si
Me
Me
Si
Ph
4
Ph
(2)
9
siliconꢀstereogenicꢀcenter. ꢀ
additive (1.0 equiv)
CH Cl , 40 °C, 16 h
Me
a (0.10 M)
2
2
Duringꢀtheꢀcourseꢀofꢀourꢀstudyꢀdirectedꢀtowardꢀtheꢀdevelopmentꢀ
Me
3a
(ArF = 3,5-(CF
)
C
H
)
1
3
2
6
3
ofꢀ syntheticꢀ methodsꢀ forꢀ variousꢀ silicon-bridgedꢀ π-conjugatedꢀ
1
0
x
2
2
1
additive
none
conv (%)
52
yield (%)
compounds, ꢀ weꢀ attemptedꢀ toꢀ synthesizeꢀ benzonaphthosilineꢀ 2aꢀ
fromꢀ silicon-containingꢀ diyneꢀ 1aꢀ andꢀ 1,4-dimethoxy-2-butyneꢀ
0
51
82
11
MeCN
MeCN
66
throughꢀaꢀrhodium-catalyzedꢀ[2ꢀ+ꢀ2ꢀ+ꢀ2]ꢀcycloadditionꢀreaction. ꢀAsꢀ
shownꢀinꢀeqnꢀ(1),ꢀunderꢀtheꢀconditionsꢀusingꢀaꢀcationicꢀRh/2PPh
catalystꢀgeneratedꢀinꢀsitu,ꢀonlyꢀ9%ꢀyieldꢀofꢀdesiredꢀproductꢀ2aꢀwasꢀ
100
3
ꢀ
ꢀ
Underꢀtheseꢀconditions,ꢀseveralꢀdifferentꢀalkynylꢀgroupsꢀonꢀtheꢀ
obtainedꢀ andꢀ theꢀ majorꢀ productꢀ turnedꢀ outꢀ toꢀ beꢀ intramolecularꢀ siliconꢀ atomꢀ ofꢀ 1ꢀ areꢀ toleratedꢀ inꢀ theꢀ presentꢀ intramolecularꢀ
alkynylsilylationꢀ reactionꢀ toꢀ giveꢀ correspondingꢀ 3ꢀ inꢀ highꢀ yields,ꢀ
althoughꢀanꢀelevatedꢀtemperatureꢀisꢀnecessaryꢀforꢀtheꢀreactionꢀofꢀ
1
-propynylꢀ substitutedꢀ substrateꢀ 1dꢀ (Tableꢀ 1,ꢀ entriesꢀ 1–4).ꢀ Theꢀ
structureꢀ ofꢀ 3bꢀ wasꢀ confirmedꢀ byꢀ X-rayꢀ crystallographicꢀ analysis,ꢀ
establishingꢀtheꢀsyn-insertionꢀofꢀanꢀalkyneꢀtoꢀtheꢀalkynylsilaneꢀinꢀtheꢀ
1
3
presentꢀ catalysis. ꢀ Withꢀ respectꢀ toꢀ theꢀ alkynylꢀ substituentꢀ atꢀ 8-
positionꢀofꢀtheꢀnaphthaleneꢀtether,ꢀinꢀadditionꢀtoꢀalkylꢀgroupsꢀsuchꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ1ꢀꢀ
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Pleaseꢀd Co hꢀ ne omt ꢀ Ca do jmu smt ꢀmarginsꢀ
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asꢀ 1aꢀ andꢀ 1e,ꢀ arylꢀ groupsꢀ suchꢀ asꢀ 1fꢀ canꢀ alsoꢀ beꢀ effectivelyꢀ
employedꢀ byꢀ changingꢀ theꢀ ligandꢀ fromꢀ PPh ꢀ toꢀ P(4-MeOC
entriesꢀ1,ꢀ5ꢀandꢀ6).ꢀSubstratesꢀ1g–1iꢀhavingꢀanꢀalkylbis(alkynyl)silylꢀ
[RhCl(C2H4)2]2 (8 mol% Rh)
View Article Online
Me
PPh3 (8 mol%)
DOI: 10.1039/C5CC04172D
3
6
H
4
)
3
ꢀ
Me Me
Si
F
NaBAr 4 (16 mol%)
Si
(
MeCN (1.0 equiv)
CH2Cl2, 40 °C, 16 h
Me Me
groupꢀatꢀ1-positionꢀareꢀalsoꢀsuitableꢀforꢀtheꢀpresentꢀalkynylsilylationꢀ
toꢀ giveꢀ 3g–3iꢀ inꢀ 73–93%ꢀ yieldꢀ (entriesꢀ 7–9).ꢀ Furthermore,ꢀ theꢀ
reactionꢀisꢀapplicableꢀtoꢀsubstratesꢀcontainingꢀsomeꢀotherꢀtethersꢀ
asꢀ well.ꢀ Asꢀ shownꢀ inꢀ eqnsꢀ (3)ꢀ andꢀ (4),ꢀ 1,2-
Me
(
ArF = 3,5-(CF3)2C6H3)
4
(0.05 M)
Me
Me
Si
bis(dimethyl(phenylethynyl)silyl)benzeneꢀ
(1j)ꢀ
andꢀ
1,8-
Si
Me
(5)
Me
Me
bis(dimethyl(phenylethynyl)silyl)naphthaleneꢀ(1k)ꢀsimilarlyꢀundergoꢀ
theꢀ intramolecularꢀ alkynylsilylationꢀ toꢀ giveꢀ productsꢀ 3jꢀ andꢀ 3kꢀ inꢀ
highꢀyields.ꢀTheꢀreactionꢀalsoꢀproceedsꢀsmoothlyꢀwithꢀsubstrateꢀ4ꢀ
havingꢀ twoꢀ alkynylsilaneꢀ moietiesꢀ throughꢀ theꢀ two-foldꢀ
alkynylsilylationꢀprocess,ꢀgivingꢀhighlyꢀconjugatedꢀproductꢀ5ꢀinꢀ78%ꢀ
Me
5: 78% yield
ꢀ
Aꢀ proposedꢀ catalyticꢀ cycleꢀ forꢀ theꢀ reactionꢀ ofꢀ 1aꢀ toꢀ 3aꢀ isꢀ
illustratedꢀinꢀSchemeꢀ1.ꢀCoordinationꢀofꢀ1aꢀtoꢀcationicꢀrhodium(I)ꢀinꢀ
theꢀformꢀofꢀAꢀfacilitatesꢀtheꢀoxidativeꢀadditionꢀofꢀC(sp)–Siꢀbondꢀtoꢀ
giveꢀ intermediateꢀ B.ꢀ Successiveꢀ intramolecularꢀ insertionꢀ ofꢀ alkyneꢀ
toꢀ Si–Rhꢀ bondꢀ providesꢀ alkenyl(alkynyl)rhodium(III)ꢀ C,ꢀ reductiveꢀ
eliminationꢀ ofꢀ whichꢀ leadsꢀ toꢀ theꢀ formationꢀ ofꢀ productꢀ 3aꢀ alongꢀ
withꢀregenerationꢀofꢀtheꢀcationicꢀrhodium(I)ꢀspecies.ꢀAlthoughꢀtheꢀ
roleꢀ ofꢀ MeCNꢀ isꢀ notꢀ yetꢀ completelyꢀ understood,ꢀ itꢀ probablyꢀ
stabilizesꢀcoordinativelyꢀunsaturatedꢀrhodiumꢀintermediatesꢀduringꢀ
theꢀcatalyticꢀcycle.ꢀToꢀgainꢀsomeꢀinsightsꢀintoꢀtheꢀpresentꢀcatalysis,ꢀ
weꢀconductedꢀtheꢀfollowingꢀcontrolꢀexperimentsꢀasꢀshownꢀinꢀeqnsꢀ
(6)ꢀ andꢀ (7).ꢀ Byꢀ changingꢀ theꢀ electronicꢀ propertiesꢀ ofꢀ theꢀ
triarylphosphineꢀligandꢀinꢀtheꢀreactionꢀofꢀ1a,ꢀweꢀdeterminedꢀthatꢀ
theꢀreactionꢀproceedsꢀfasterꢀbyꢀusingꢀmoreꢀelectron-richꢀphosphineꢀ
ligandsꢀ (eqnꢀ (6)).ꢀ Weꢀ alsoꢀ foundꢀ thatꢀ electron-deficientꢀ
alkynylsilanesꢀtendꢀtoꢀreactꢀfasterꢀbyꢀchangingꢀtheꢀpara-substituentꢀ
ofꢀ arylethynylꢀ groupꢀ onꢀ theꢀ siliconꢀ ofꢀ 1ꢀ (eqnꢀ (7)).ꢀ Bothꢀ ofꢀ theseꢀ
resultsꢀ areꢀ consistentꢀ withꢀ theꢀ assumptionꢀ thatꢀ theꢀ oxidativeꢀ
additionꢀisꢀtheꢀturnover-limitingꢀstepꢀinꢀtheꢀcatalyticꢀcycle,ꢀalthoughꢀ
moreꢀevidenceꢀisꢀnecessaryꢀtoꢀfullyꢀestablishꢀtheꢀcatalyticꢀcycle.ꢀ
1
4
yieldꢀ(eqnꢀ(5)). ꢀ
Tableꢀ1ꢀꢀRhodium-catalyzedꢀalkynylsilylation:ꢀscope ꢀ
Entryꢀ Substrateꢀ Productꢀ
a
b
Yieldꢀ(%) ꢀ
Me Me
Si
Me
Me
R1
Si
R1
ꢀ
ꢀ
R2
R2
ꢀ
1
2
1
2
3
4
5
6
ꢀ
1aꢀ(R ꢀ=ꢀPh,ꢀR ꢀ=ꢀMe)ꢀ
3aꢀ
82ꢀ
c
1
2
d
ꢀ
1bꢀ(R ꢀ=ꢀ4-MeOC
6
H
4
2
,ꢀR ꢀ=ꢀMe)ꢀ 3bꢀ
90 ꢀ
e
1
ꢀ
1cꢀ(R ꢀ=ꢀ4-ClC
6
H
4
,ꢀR ꢀ=ꢀMe)ꢀ
3cꢀ
3dꢀ
3eꢀ
3fꢀ
93ꢀ
82ꢀ
84ꢀ
f
1
2
ꢀ
1dꢀ(R ꢀ=ꢀR ꢀ=ꢀMe)ꢀ
g
1
2
ꢀ
1eꢀ(R ꢀ=ꢀPh,ꢀR ꢀ=ꢀn-Pr)ꢀ
c,h
1
2
i
ꢀ
1fꢀ(R ꢀ=ꢀR ꢀ=ꢀPh)ꢀ
82 ꢀ
R1
R1
R
R
Si
R1
ꢀ
Si
R1
Me
ꢀ
Me
ꢀ
ꢀ
g
1
7
8
9
ꢀ
1gꢀ(Rꢀ=ꢀCy,ꢀR ꢀ=ꢀPh)ꢀ
3gꢀ
3hꢀ
3iꢀ
93ꢀ
82ꢀ
73ꢀ
F
3
a
1a
c,e
1
+
ꢀ
ꢀ
1hꢀ(Rꢀ=ꢀCy,ꢀR ꢀ=ꢀMe)ꢀ
reductive
elimination
Rh (I)
c,h
1
coordination
1iꢀ(Rꢀ=ꢀR ꢀ=ꢀMe)ꢀ
ꢀ
a
ꢀ
Conditions:ꢀ[RhCl(C
2
H
4
)
2
]
2
ꢀ(8ꢀmol%ꢀRh),ꢀPPh
3
ꢀ(8ꢀmol%),ꢀNaBAr
4
ꢀ(16ꢀ
Ph
Me Me
Si
Me
Si
b
mol%),ꢀMeCNꢀ(1.0ꢀequiv),ꢀCH
2
Cl ꢀ(0.10ꢀM),ꢀ40ꢀ°C,ꢀ16ꢀh.ꢀꢀ ꢀIsolatedꢀ
2
Me
Ph
c
yieldꢀ(Z-isomerꢀwasꢀobtainedꢀexclusivelyꢀunlessꢀotherwiseꢀnoted).ꢀꢀ ꢀ
+
Rh (III)
d
Me
Theꢀreactionꢀwasꢀconductedꢀatꢀ0.05ꢀMꢀsubstrateꢀconcentration.ꢀꢀ ꢀ
+
Me
Rh (I)
e
f
Z/Eꢀ=ꢀ98/2.ꢀꢀ ꢀTheꢀreactionꢀtimeꢀwasꢀ1ꢀh.ꢀꢀ ꢀTheꢀreactionꢀwasꢀ
C
A
Ph
g
h
conductedꢀatꢀ80ꢀ°Cꢀinꢀtoluene.ꢀꢀ ꢀTheꢀreactionꢀtimeꢀwasꢀ2ꢀh.ꢀꢀ ꢀTheꢀ
Me Me
i
reactionꢀwasꢀconductedꢀwithꢀP(4-MeOC
6
H
4
)
3
ꢀinsteadꢀofꢀPPh
3
.ꢀꢀ ꢀZ/Eꢀ=ꢀ
insertion
+
oxidative
addition
Si Rh (III)
9
4/6.ꢀ
Me
[
RhCl(C2H4)2]2 (8 mol% Rh)
B
Me
Ph
ꢀ
Me
PPh3 (8 mol%)
NaBArF4 (16 mol%)
Me
Me
Si
Si
Ph
Ph
Schemeꢀ 1ꢀ Proposedꢀ catalyticꢀ cycleꢀ forꢀ theꢀ rhodium-catalyzedꢀ
intramolecularꢀalkynylsilylationꢀofꢀ1a.ꢀ
(
3)
MeCN (1.0 equiv)
CH2Cl2, 40 °C, 16 h
Si
Si
Ph
Me
Me
j (0.10 M)
Me Me
3j: 80% yield
[RhCl(C2H4)2]2
(2 mol% Rh)
PAr3 (2 mol%)
NaBArF4 (4 mol%)
(
ArF = 3,5-(CF3)2C6H3)
1
Me Me
Si
Me
ꢀ
Me
[
RhCl(C2H4)2]2 (8 mol% Rh)
PPh3 (8 mol%)
Ph
Ph
Si
Ph
Me Me
Si
(6)
Me
Me
Si
MeCN (25 mol%)
CH2Cl2, 40 °C, 5 min
Ph
Ph
NaBArF4 (16 mol%)
Me
1a (0.10 M)
(
4)
Me
3a
MeCN (1.0 equiv)
CH2Cl2, 40 °C, 2 h
(ArF = 3,5-(CF ) C H )
Si
Si
Ph
3 2 6 3
Me
Me Me
k (0.10 M)
PAr3
conv. of 1a (%) yield of 3a (%)
ArF = 3,5-(CF3)2C6H3)
Me
(
1
3k: 95% yield
ꢀ
P(4-FC6H4)3
PPh3
23
29
63
19
29
61
P(4-MeOC6H4)3
ꢀ
2
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
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Pleaseꢀd Co hꢀ ne omt ꢀ Ca do j mu smt ꢀmarginsꢀ
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ꢀCOMMUNICATIONꢀ
[
RhCl(C2H4)2]2
2 mol% Rh)
View Article Online
(
Me Me
Si
Me
Si
OMe
PPh2
DOI: 10.1039/C5CC04172D
PAr3 (2 mol%)
NaBArF (4 mol%)
Me
Ar
O
O
Ar
4
(7)
Ph2P
N
Ph2P
N
MeCN (25 mol%)
Me
(0.10 M)
CH2Cl2, 40 °C, 5 min
Ph
(S )-Ph-phox
iPr
Me
3
(R )-MeO-mop
(R )-iPr-phox
1
(ArF = 3,5-(CF ) C H )
3
2 6 3
Ar
-MeOC6H4
Ph
-ClC6H4
conv. of 1 (%) yield of 3 (%)
Ph
N
Ph
O
4
15
29
35
10
29
35
O
O
P
P
N
O
4
ꢀ
Ph
Ph
Finally,ꢀweꢀhaveꢀalsoꢀbegunꢀtoꢀdevelopꢀanꢀasymmetricꢀvariantꢀofꢀ
(
S,S,S )-phosphoramidite
(R,S,S )-phosphoramidite
15
ꢀ
thisꢀprocess. ꢀOnꢀtheꢀbasisꢀofꢀtheꢀconditionsꢀforꢀtheꢀnonasymmetricꢀ
reactions,ꢀ weꢀ conductedꢀ aꢀ reactionꢀ ofꢀ prochiralꢀ 1gꢀ byꢀ employingꢀ
Inꢀ summary,ꢀ weꢀ haveꢀ developedꢀ aꢀ rhodium-catalyzedꢀ
intramolecularꢀ alkynylsilylationꢀ ofꢀ alkynesꢀ underꢀ mildꢀ conditions.ꢀ
Theꢀ reactionꢀ proceedsꢀ throughꢀ syn-insertionꢀ inꢀ theꢀ presenceꢀ ofꢀ aꢀ
cationicꢀ rhodium/triarylphosphineꢀ catalystꢀ withꢀ MeCNꢀ asꢀ anꢀ
additive.ꢀAlthoughꢀapplicableꢀsubstratesꢀareꢀcurrentlyꢀstillꢀlimited,ꢀ
thisꢀrepresentsꢀtheꢀfirstꢀalkynylsilylationꢀofꢀalkynesꢀviaꢀtheꢀcleavageꢀ
ofꢀ aꢀ C(sp)–Siꢀ bondꢀ underꢀ transition-metalꢀ catalysis.ꢀ Weꢀ haveꢀ alsoꢀ
describedꢀourꢀpreliminaryꢀinvestigationꢀforꢀitsꢀasymmetricꢀvariant,ꢀ
creatingꢀ aꢀ siliconꢀ stereogenicꢀ centerꢀ withꢀ highꢀ enantioselectivity.ꢀ
Futureꢀstudiesꢀwillꢀbeꢀdirectedꢀtowardꢀtheꢀdevelopmentꢀofꢀaꢀmoreꢀ
generalꢀcatalystꢀsystemꢀtoꢀexpandꢀtheꢀscopeꢀofꢀalkynylsilylationꢀofꢀ
alkynesꢀandꢀrelatedꢀreactions.ꢀ
1
6
(
R)-MeO-mop, ꢀaꢀchiralꢀmonophosphineꢀligand,ꢀinꢀtheꢀpresenceꢀofꢀ
.0ꢀ equivꢀ ofꢀ MeCN.ꢀ Underꢀ theseꢀ conditions,ꢀ 77%ꢀ yieldꢀ ofꢀ 3gꢀ wasꢀ
1
obtained,ꢀbutꢀnoꢀasymmetricꢀinductionꢀwasꢀobservedꢀatꢀtheꢀsiliconꢀ
stereocenterꢀ (Tableꢀ 2,ꢀ entryꢀ 1).ꢀ Inꢀ comparison,ꢀ 83%ꢀ eeꢀ wasꢀ
achievedꢀ withꢀ theꢀ sameꢀ ligandꢀ inꢀ theꢀ absenceꢀ ofꢀ MeCN,ꢀ butꢀ theꢀ
yieldꢀofꢀ3gꢀbecameꢀsignificantlyꢀlowerꢀ(entryꢀ2).ꢀToꢀaccommodateꢀ
theꢀ nitrogenꢀ coordinationꢀ toꢀ theꢀ structureꢀ ofꢀ aꢀ chiralꢀ ligand,ꢀ weꢀ
17
examinedꢀ(S)-Ph-phox, ꢀaꢀP,N-bidentateꢀligand,ꢀandꢀfoundꢀthatꢀ3gꢀ
wasꢀ producedꢀ inꢀ 74%ꢀ yieldꢀ inꢀ theꢀ absenceꢀ ofꢀ MeCNꢀ withꢀ
appreciableꢀ eeꢀ ofꢀ 69%ꢀ (entryꢀ 3).ꢀ Unfortunately,ꢀ however,ꢀ furtherꢀ
improvementꢀwasꢀunsuccessfulꢀbyꢀusingꢀotherꢀphosphinooxazolineꢀ
17
ligandsꢀ suchꢀ asꢀ (R)-iPr-phox ꢀ (entryꢀ 4).ꢀ Asꢀ aꢀ differentꢀ structuralꢀ
ꢀ
motifꢀ forꢀ theꢀ chiralꢀ ligand,ꢀ weꢀ alsoꢀ employedꢀ phosphoramiditeꢀ
Supportꢀ hasꢀ beenꢀ providedꢀ inꢀ partꢀ byꢀ Challengingꢀ Exploratoryꢀ
Research,ꢀ theꢀ Ministryꢀ ofꢀ Education,ꢀ Culture,ꢀ Sports,ꢀ Scienceꢀ andꢀ
Technology,ꢀJapan.ꢀWeꢀthankꢀProf.ꢀTakuzoꢀAidaꢀandꢀDr.ꢀYoshimitsuꢀ
Itohꢀ atꢀ Theꢀ Universityꢀ ofꢀ Tokyoꢀ forꢀ theꢀ measurementꢀ ofꢀ
fluorescenceꢀspectra.ꢀ
1
8
ligands. ꢀForꢀexample,ꢀtheꢀuseꢀofꢀ(S,S,S)-phosphoramiditeꢀhavingꢀaꢀ
1
9
2
,5-diphenylpyrrolidineꢀmoiety ꢀgaveꢀ3gꢀinꢀ60%ꢀyieldꢀwithꢀ36%ꢀeeꢀ
inꢀ theꢀ absenceꢀ ofꢀ MeCNꢀ (entryꢀ 5).ꢀ Weꢀ subsequentlyꢀ foundꢀ thatꢀ
significantlyꢀhigherꢀenantioselectivityꢀ(92%ꢀee)ꢀcouldꢀbeꢀachievedꢀbyꢀ
changingꢀ theꢀ ligandꢀ toꢀ itsꢀ diastereomerꢀ ((R,S,S)-
19a,20
phosphoramidite)
ꢀwithꢀaꢀmoderateꢀyieldꢀofꢀ53%ꢀ(entryꢀ6).ꢀBothꢀ
theꢀyieldꢀandꢀtheꢀeeꢀwereꢀsomewhatꢀfurtherꢀimprovedꢀbyꢀloweringꢀ
theꢀinitialꢀsubstrateꢀconcentrationꢀfromꢀ0.10ꢀMꢀtoꢀ0.03ꢀMꢀtoꢀgiveꢀ
Notesꢀandꢀreferencesꢀ
1
(a)ꢀ H.ꢀ Sakuraiꢀ andꢀ T.ꢀ Imai,ꢀ Chem.ꢀ Lett.,ꢀ 1975,ꢀ 891;ꢀ (b)ꢀ Y.ꢀ
Takeyama,ꢀ K.ꢀ Nozaki,ꢀ K.ꢀ Matsumoto,ꢀ K.ꢀ Oshimaꢀ andꢀ K.ꢀ
Utimoto,ꢀBull.ꢀChem.ꢀSoc.ꢀJpn.,ꢀ1991,ꢀ64,ꢀ1461;ꢀ(c)ꢀZ.ꢀNevárezꢀ
andꢀK.ꢀA.ꢀWoerpel,ꢀOrg.ꢀLett.,ꢀ2007,ꢀ9,ꢀ3773;ꢀ(d)ꢀR.ꢀShintani,ꢀK.ꢀ
MoriyaꢀandꢀT.ꢀHayashi,ꢀJ.ꢀAm.ꢀChem.ꢀSoc.,ꢀ2011,ꢀ133,ꢀ16440;ꢀ
(e)ꢀR.ꢀShintani,ꢀK.ꢀMoriyaꢀandꢀT.ꢀHayashi,ꢀOrg.ꢀLett.,ꢀ2012,ꢀ14,ꢀ
2902;ꢀ(f)ꢀJ.ꢀLiu,ꢀQ.ꢀZhang,ꢀP.ꢀLi,ꢀZ.ꢀQu,ꢀS.ꢀSun,ꢀY.ꢀMa,ꢀD.ꢀSu,ꢀY.ꢀ
Zongꢀ andꢀ J.ꢀ Zhang,ꢀ Eur.ꢀ J.ꢀ Inorg.ꢀ Chem.,ꢀ 2014,ꢀ 3435;ꢀ (g)ꢀ H.ꢀ
SasoꢀandꢀW.ꢀAndo,ꢀChem.ꢀLett.,ꢀ1988,ꢀ1567;ꢀ(h)ꢀH.ꢀSaso,ꢀW.ꢀ
Andoꢀ andꢀ K.ꢀ Ueno,ꢀ Tetrahedron,ꢀ 1989,ꢀ 45,ꢀ 1929;ꢀ (i)ꢀ K.ꢀ M.ꢀ
BuchnerꢀandꢀK.ꢀA.ꢀWoerpel,ꢀOrganometallics,ꢀ2010,ꢀ29,ꢀ1661;ꢀ
(j)ꢀJ.ꢀLiu,ꢀX.ꢀSun,ꢀM.ꢀMiyazaki,ꢀL.ꢀLiu,ꢀC.ꢀWangꢀandꢀZ.ꢀXi,ꢀJ.ꢀOrg.ꢀ
Chem.,ꢀ 2007,ꢀ 72,ꢀ 3137;ꢀ (k)ꢀ N.ꢀ Agenet,ꢀ J.-H.ꢀ Mirebeau,ꢀ M.ꢀ
Petit,ꢀR.ꢀThouvenot,ꢀV.ꢀGandon,ꢀM.ꢀMalacriaꢀandꢀC.ꢀAubert,ꢀ
Organometallics,ꢀ2007,ꢀ26,ꢀ819.ꢀ
6
2%ꢀyieldꢀ(59%ꢀisolatedꢀyield)ꢀofꢀ3gꢀwithꢀ94%ꢀeeꢀ(entryꢀ7).ꢀ
Tableꢀ3ꢀꢀRhodium-catalyzedꢀasymmetricꢀalkynylsilylationꢀ
Ph
2 4 2 2
[RhCl(C H ) ] (10 mol% Rh)
Ph
Cy
Si
ligand (10 mol%)
NaBArF
(20 mol%)
Cy
4
Ph
*
Si
Ph
additive (1.0 equiv)
CH Cl , 40 °C
2
2
Me
g (0.10 M)
Me
3g
1
ꢀ
a
b
Entryꢀ Ligandꢀ
Additiveꢀ Yieldꢀ(%) ꢀ Eeꢀ(%) ꢀ
1
2
3
4
5
6
7
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(R)-MeO-mopꢀ
(R)-MeO-mopꢀ
(S)-Ph-phoxꢀ
(R)-iPr-phoxꢀ
MeCNꢀ
Noneꢀ
Noneꢀ
Noneꢀ
77ꢀ
23ꢀ
74ꢀ
27ꢀ
60ꢀ
53ꢀ
ꢀꢀ0ꢀ
83ꢀ(–)ꢀ
69ꢀ(+)ꢀ
42ꢀ(–)ꢀ
36ꢀ(+)ꢀ
92ꢀ(+)ꢀ
2
Forꢀ aꢀ review:ꢀ (a)ꢀ K.ꢀ Motokuraꢀ andꢀ T.ꢀ Baba,ꢀ Greenꢀ Chem.,ꢀ
2012,ꢀ14,ꢀ565;ꢀForꢀexamples:ꢀ(b)ꢀN.ꢀAsao,ꢀE.ꢀYoshikawaꢀandꢀY.ꢀ
Yamamoto,ꢀJ.ꢀOrg.ꢀChem.ꢀ1996,ꢀ61,ꢀ4874;ꢀ(c)ꢀE.ꢀYoshikawa,ꢀV.ꢀ
Gevorgyan,ꢀ N.ꢀ Asaoꢀ andꢀ Y.ꢀ Yamamoto,ꢀ J.ꢀ Am.ꢀ Chem.ꢀ Soc.ꢀ
(S,S,S)-phosphoramiditeꢀ Noneꢀ
(R,S,S)-phosphoramiditeꢀ Noneꢀ
ꢀ
c
1
997,ꢀ119,ꢀ6781;ꢀ(d)ꢀT.ꢀMatsuda,ꢀS.ꢀKadowaki,ꢀY.ꢀYamaguchiꢀ
d
ꢀ
(R,S,S)-phosphoramiditeꢀ Noneꢀ
62ꢀ(59) ꢀ 94ꢀ(+)ꢀ
ꢀ
andꢀ M.ꢀ Murakami,ꢀ Chem.ꢀ Commun.,ꢀ 2008,ꢀ 2744;ꢀ (e)ꢀ K.ꢀ
Motokura,ꢀS.ꢀMatsunaga,ꢀA.ꢀMiyaji,ꢀT.ꢀYashimaꢀandꢀT.ꢀBaba,ꢀ
TetrahedronꢀLett.ꢀ2011,ꢀ52,ꢀ6687;ꢀ(f)ꢀN.ꢀAsao,ꢀT.ꢀShimadaꢀandꢀ
Y.ꢀYamamoto,ꢀJ.ꢀAm.ꢀChem.ꢀSoc.,ꢀ1999,ꢀ121,ꢀ3797;ꢀ(g)ꢀN.ꢀAsao,ꢀ
K.ꢀNabatameꢀandꢀY.ꢀYamamoto,ꢀChem.ꢀLett.,ꢀ2001,ꢀ982;ꢀ(h)ꢀN.ꢀ
Asao,ꢀT.ꢀShimada,ꢀT.ꢀShimadaꢀandꢀY.ꢀYamamoto,ꢀJ.ꢀAm.ꢀChem.ꢀ
Soc.,ꢀ 2001,ꢀ 123,ꢀ 10899;ꢀ (i)ꢀ T.ꢀ Matsuda,ꢀ Y.ꢀ Yamaguchi,ꢀ M.ꢀ
Shigeno,ꢀS.ꢀSatoꢀandꢀM.ꢀMurakami,ꢀChem.ꢀCommun.,ꢀ2011,ꢀ
a
1
b
ꢀ
Determinedꢀbyꢀ HꢀNMRꢀagainstꢀanꢀinternalꢀstandard.ꢀꢀ ꢀ
DeterminedꢀbyꢀchiralꢀHPLCꢀonꢀaꢀChiralcelꢀOD-Hꢀcolumnꢀwithꢀ
c
hexane/2-propanolꢀ=ꢀ98/2.ꢀꢀ ꢀTheꢀreactionꢀwasꢀconductedꢀatꢀ0.03ꢀMꢀ
d
substrateꢀconcentration.ꢀꢀ ꢀIsolatedꢀyieldꢀinꢀparentheses.ꢀ
47,ꢀ 8697;ꢀ (j)ꢀ E.ꢀ Yoshikawa,ꢀ M.ꢀ Kasahara,ꢀ N.ꢀ Asaoꢀ andꢀ Y.ꢀ
Yamamoto,ꢀTetrahedronꢀLett.,ꢀ2000,ꢀ41,ꢀ4499.ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ3ꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Pleaseꢀd Co hꢀ ne omt ꢀ Ca do jmu smt ꢀmarginsꢀ
Page 4 of 4
COMMUNICATIONꢀ
JournalꢀNameꢀ
3
4
5
Forꢀ aꢀ radicalꢀ process:ꢀ K.ꢀ Miura,ꢀ H.ꢀ Saito,ꢀ T.ꢀ Nakagawa,ꢀ T.ꢀ 16 (a)ꢀT.ꢀHayashi,ꢀAcc.ꢀChem.ꢀRes.ꢀ2000,ꢀ33,ꢀ354;ꢀ(Vbie)wꢀYA.ꢀrtUicolezOunmlinie,ꢀ
Hondo,ꢀJ.ꢀTateiwa,ꢀM.ꢀSonodaꢀandꢀA.ꢀHosomi,ꢀJ.ꢀOrg.ꢀChem.,ꢀ
998,ꢀ63,ꢀ5740.ꢀ
Forꢀ aꢀ ruthenium-catalyzedꢀ intramolecularꢀ process:ꢀ S.ꢀ Liu,ꢀ J.ꢀ 17 (a)ꢀ P.ꢀ vonꢀ Mattꢀ andꢀ A.ꢀ Pfaltz,ꢀ Angew.ꢀ Chem.ꢀ Int.ꢀ Ed.ꢀ Engl.ꢀ
A.ꢀTanahashi,ꢀS.-Y.ꢀLeeꢀandꢀT.ꢀHayashi,ꢀJ.ꢀOrg.ꢀChem.ꢀ1993,ꢀ58,ꢀ
DOI: 10.1039/C5CC04172D
1
1945.ꢀ
Zhao,ꢀL.ꢀKaminsky,ꢀR.ꢀJ.ꢀWilson,ꢀM.ꢀMarinoꢀandꢀD.ꢀA.ꢀClark,ꢀ
Org.ꢀLett.,ꢀ2014,ꢀ16,ꢀ4456.ꢀ
1993,ꢀ32,ꢀ566;ꢀ(b)ꢀG.ꢀJ.ꢀDawson,ꢀC.ꢀG.ꢀFrost,ꢀJ.ꢀM.ꢀWilliamsꢀ
andꢀS.ꢀJ.ꢀCoote,ꢀTetrahedronꢀLett.ꢀ1993,ꢀ34,ꢀ3149.ꢀ
2
(a)ꢀH.-J.ꢀZhang,ꢀP.ꢀBecker,ꢀH.ꢀHuang,ꢀR.ꢀPirwerdjan,ꢀF.-F.ꢀPanꢀ 18 Forꢀ exampleꢀ ofꢀ P–(η -arene)ꢀ chelatingꢀ coordinationꢀ ofꢀ aꢀ
andꢀ C.ꢀ Bolm,ꢀ Adv.ꢀ Synth.ꢀ Catal.,ꢀ 2012,ꢀ 354,ꢀ 2157;ꢀ (b)ꢀ P.ꢀ
Becker,ꢀD.ꢀL.ꢀPriebbenow,ꢀH.-J.ꢀZhang,ꢀR.ꢀPirwerdjanꢀandꢀC.ꢀ
Bolm,ꢀJ.ꢀOrg.ꢀChem.,ꢀ2014,ꢀ79,ꢀ814.ꢀ
phosphoramiditeꢀ ligandꢀ toꢀ rhodium,ꢀ see:ꢀ I.ꢀ S.ꢀ Mikhel,ꢀ H.ꢀ
Rüegger,ꢀP.ꢀButti,ꢀF.ꢀCamponovo,ꢀD.ꢀHuberꢀandꢀA.ꢀMezzetti,ꢀ
Organometallicsꢀ2008,ꢀ27,ꢀ2937.ꢀ
6
N.ꢀChatani,ꢀT.ꢀTakeyasu,ꢀN.ꢀHoriuchiꢀandꢀT.ꢀHanafusa,ꢀJ.ꢀOrg.ꢀ 19 (a)ꢀ Y.ꢀ H.ꢀ Choi,ꢀ J.ꢀ Y.ꢀ Choi,ꢀ H.ꢀ Y.ꢀ Yangꢀ andꢀ Y.ꢀ H.ꢀ Kim,ꢀ
Chem.,ꢀ1988,ꢀ53,ꢀ3539.ꢀ
H.ꢀGerhard,ꢀJ.ꢀChem.ꢀRes.,ꢀSynopses,ꢀ1978,ꢀ104.ꢀ
Forꢀ alkynylsilylationꢀ ofꢀ alkynesꢀ byꢀ aꢀ three-component-
Tetrahedron:ꢀAsymmetryꢀ2002,ꢀ13,ꢀ801;ꢀ(b)ꢀB.ꢀM.ꢀTrost,ꢀJ.ꢀP.ꢀ
Stambuli,ꢀS.ꢀM.ꢀSilvermanꢀandꢀU.ꢀSchwörer,ꢀJ.ꢀAm.ꢀChem.ꢀSoc.ꢀ
2006,ꢀ128,ꢀ13328.ꢀ
7
8
couplingꢀ reaction:ꢀ N.ꢀ Chatani,ꢀ N.ꢀ Amishiroꢀ andꢀ S.ꢀ Murai,ꢀ J.ꢀ 20 M.ꢀ Fañanás-Mastral,ꢀ M.ꢀ Pérez,ꢀ P.ꢀ H.ꢀ Bos,ꢀ A.ꢀ Rudolph,ꢀ S.ꢀ R.ꢀ
Am.ꢀChem.ꢀSoc.,ꢀ1991,ꢀ113,ꢀ7778.ꢀ
HarutyunyanꢀandꢀB.ꢀL.ꢀFeringa,ꢀAngew.ꢀChem.ꢀInt.ꢀEd.ꢀ2012,ꢀ
51,ꢀ1922.ꢀ
9
Forꢀ recentꢀ reviewsꢀ onꢀ theꢀ synthesisꢀ ofꢀ enantio-enrichedꢀ
silicon-stereogenicꢀ organosilanes:ꢀ (a)ꢀ M.ꢀ Oestreich,ꢀ Synlett,ꢀ
ꢀ
2
007,ꢀ 1629;ꢀ (b)ꢀ A.ꢀ Weickgenannt,ꢀ M.ꢀ Mewaldꢀ andꢀ M.ꢀ
Oestreich,ꢀOrg.ꢀBiomol.ꢀChem.,ꢀ2010,ꢀ8,ꢀ1497;ꢀ(c)ꢀL.-W.ꢀXu,ꢀL.ꢀ
Li,ꢀG.-Q.ꢀLaiꢀandꢀJ.-X.ꢀJiang,ꢀChem.ꢀSoc.ꢀRev.,ꢀ2011,ꢀ40,ꢀ1777;ꢀ
(
d)ꢀL.-W.ꢀXu,ꢀAngew.ꢀChem.ꢀInt.ꢀEd.,ꢀ2012,ꢀ51,ꢀ12932;ꢀ(e)ꢀR.ꢀ
Shintani,ꢀ Asianꢀ J.ꢀ Org.ꢀ Chem.,ꢀ 2015,ꢀ 4,ꢀ
DOI:ꢀ10.1002/ajoc.201500066.ꢀ
1
1
0 (a)ꢀR.ꢀShintani,ꢀH.ꢀOtomo,ꢀK.ꢀOtaꢀandꢀT.ꢀHayashi,ꢀJ.ꢀAm.ꢀChem.ꢀ
Soc.ꢀ 2012,ꢀ 134,ꢀ 7305;ꢀ (b)ꢀ R.ꢀ Shintani,ꢀ E.ꢀ E.ꢀ Maciver,ꢀ F.ꢀ
Tamakuniꢀ andꢀ T.ꢀ Hayashi,ꢀ J.ꢀ Am.ꢀ Chem.ꢀ Soc.ꢀ 2012,ꢀ 134,ꢀ
16955;ꢀ (c)ꢀ R.ꢀ Shintani,ꢀ C.ꢀ Takagi,ꢀ T.ꢀ Ito,ꢀ M.ꢀ Naitoꢀ andꢀ K.ꢀ
Nozaki,ꢀAngew.ꢀChem.ꢀInt.ꢀEd.ꢀ2015,ꢀ54,ꢀ1616.ꢀ
1 Forꢀ recentꢀ reviewsꢀ onꢀ theꢀ rhodium-catalyzedꢀ [2ꢀ +ꢀ 2ꢀ +ꢀ 2]ꢀ
cycloadditionꢀ reactions,ꢀ see:ꢀ (a)ꢀ K.ꢀ Tanaka,ꢀ Chem.ꢀ Asianꢀ J.ꢀ
2
2
4
2
009,ꢀ4,ꢀ508;ꢀ(b)ꢀN.ꢀWedingꢀandꢀM.ꢀHapke,ꢀChem.ꢀSoc.ꢀRev.ꢀ
011,ꢀ40,ꢀ4525;ꢀ(c)ꢀY.ꢀShibataꢀandꢀK.ꢀTanaka,ꢀSynthesisꢀ2012,ꢀ
4,ꢀ323;ꢀ(d)ꢀD.ꢀL.ꢀJ.ꢀBroereꢀandꢀE.ꢀRuijter,ꢀSynthesisꢀ2012,ꢀ44,ꢀ
639.ꢀ
F
1
1
2 Theꢀ useꢀ ofꢀ 8ꢀ mol%ꢀ ofꢀ NaBAr
providedꢀ3aꢀwithꢀsimilarꢀefficiency.ꢀ
4
ꢀ insteadꢀ ofꢀ 16ꢀ mol%ꢀ alsoꢀ
3 CCDC-1401151ꢀ containsꢀ theꢀ supplementaryꢀ crystallographicꢀ
dataꢀ forꢀ thisꢀ paper.ꢀ Theseꢀ dataꢀ canꢀ beꢀ obtainedꢀ freeꢀ ofꢀ
chargeꢀfromꢀtheꢀCambridgeꢀCrystallographicꢀDataꢀCentreꢀviaꢀ
www.ccdc.cam.ac.uk/data_request/cif.ꢀ Seeꢀ alsoꢀ theꢀ
ElectronicꢀSupplementaryꢀInformationꢀforꢀdetails.ꢀ
1
1
4 Seeꢀ theꢀ Electronicꢀ Supplementaryꢀ Informationꢀ forꢀ opticalꢀ
propertiesꢀofꢀcompoundꢀ5.ꢀ
5 Forꢀexamplesꢀofꢀcatalyticꢀasymmetricꢀpreparationꢀofꢀsilicon-
stereogenicꢀorganosilanes,ꢀsee:ꢀ(a)ꢀR.ꢀJ.ꢀP.ꢀCorriuꢀandꢀJ.ꢀJ.ꢀE.ꢀ
Moreau,ꢀTetrahedronꢀLett.ꢀ1973,ꢀ14,ꢀ4469;ꢀ(b)ꢀT.ꢀHayashi,ꢀK.ꢀ
YamamotoꢀandꢀM.ꢀKumada,ꢀTetrahedronꢀLett.ꢀ1974,ꢀ15,ꢀ331;ꢀ
(
1
c)ꢀR.ꢀJ.ꢀP.ꢀCorriuꢀandꢀJ.ꢀJ.ꢀE.ꢀMoreau,ꢀJ.ꢀOrganomet.ꢀChem.ꢀ
975,ꢀ 85,ꢀ 19;ꢀ (d)ꢀ R.ꢀ J.ꢀ P.ꢀ Corriuꢀ andꢀ J.ꢀ J.ꢀ E.ꢀ Moreau,ꢀ J.ꢀ
Organomet.ꢀ Chem.ꢀ 1976,ꢀ 120,ꢀ 337;ꢀ (e)ꢀ T.ꢀ Ohta,ꢀ M.ꢀ Ito,ꢀ A.ꢀ
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