au coupling reactions - university of pittsburgh
TRANSCRIPT
Gold-Catalyzed Homogeneous Oxidative Cross-Coupling Reactions
Guozhu Zhang, Yu Peng, Li Cui, and Liming Zhang*
Angew. Chem. Int. Ed., 2009, 48, 3112-3115DOI: 10.1002/anie.200900585
Adam HoyeWipf Group
Current LiteratureApril 11th, 2009
R
OAc
R'
R'
O
R
R
R'
O
R'
O
Ph
R
AuI
AuIII
self-couplingor
PhB(OR)2
Adam Hoye @ Wipf Group Page 1 of 13 5/2/2009
Gold reactionsRearrangements
Oxidations/reductions
Cross-couplings?
CyclizationsPh3PAuCl,AgBF4
RR
Me OPiv
n
OPivMe
n
5 mol% Ph3PAuCl,5 mol% AgBF4
DCM, 5 min
Toste, JACS, 2004, 126, 10858
Toste, JACS, 2009, 131, 2056
HO
R
O R
nn
Ar3PAuCl (0.5-5 mol%),AgSbF5 (0.5-5 mol%)
Toste, JACS, 2005, 127, 9708
Nolan, ACIE, 2006, 45, 3647Zhang, Adv. Synth. Catal., 2007, 349, 871
Toste, JACS, 2004, 126, 15978
O
Pr
NTs AuCl3, MeCN
48%
NTs
O
Pr
Hashmi, OL, 2001, 3, 3769
R
OAc
R'
R · OAc
R'
R
[Au]
OAc
R'
[Au]+
[3,3]
R' ! H
[1,2]
R' = H
ROAc
[Au]H
OHO
H
N NArAr
AuCl (5 mol%),Ligand (6 mol%),
O2
Shi, JACS, 2005, 127, 18004
Ph
O
nBu
OTIPS
Ph ·
nBu
OH
OTIPS
H[Ph3PAuOBF4]
(1 mol%)
>20 : 1 d.r.
Adam Hoye @ Wipf Group Page 2 of 13 5/2/2009
Gold in cross-coupling reactionsAu(I), Cu(I) and Pd(0) possess the same d10 electron structure
Corma, J. Catal., 2006, 238, 497
Au/CeO2 (5 mol%)
(nanocrystalline CeO2)
Au0, AuI, AuIII present on nanoparticle
I PhNa2CO3 (2 equiv)
DMF, 150 °C, 24 h
Ph
89% 11%(1 equiv)(2 equiv)
I R' Ph
catalyst (20 mol%),K3PO4 (2 equiv.)
o-xylene, 130 °C, 24 h
(1 equiv)(1.5 equiv)
R R
Corma, ACIE, 2007, 46, 1536Presumably a Au(I)/Au(III) catalytic cycle
Copper-free Sonogashira reaction:
Au(I) Au(III)
oxidative addition
reductive elimination
Adam Hoye @ Wipf Group Page 3 of 13 5/2/2009
Me
Me Me
Me
+ PhI(OAc)2
2 mol% HAuCl4
HOAc, 55 °C, 17 h
R2 R3
R1
MeO
I I
OMeMeO2C
Me
Me
CO2Me
78%
79%
O2N
OMe
MeO
NO2
38%
81%
S SMe Me31%
Cross-coupling reactions with goldSuzuki Coupling:
PhI(OAc)2 as oxidant in biaryl couplings:
Palladium-Catalyzed Carboauration and Palladium/Gold Cross-Coupling:
CO2Me
R
Pd(PPh3)Cl25 mol%
PPh3Au-R'
CO2MePh3PAu
R' R
Br
I
CO2Me
R' R
R' R
CO2Me
Pd cat.
Pd cat.
87 % (2 steps)
94% (2 steps)
Tse, Chem. Commun., 2008, 386
Blum, Organometallics, 2009, 28, 1275
IB(OH)2
RR R
R
cross-coupling homo-coupling
30% catalyst
AuCl3
Au(I)-Salen* 100 (80% yield) 0
0 100
Corma, J. Catal., 2006, 238, 497
Adam Hoye @ Wipf Group Page 4 of 13 5/2/2009
Goal of title paperCombine Au(I)/Au(III) catalytic cycle
in a cross-coupling process
Challenges: Previously substrate as oxidant- oxidative insertion Au(I)-> Au(III)or harsh oxidants (PhI(OAc)2, t-BuOOH, etc.) used.
-Need to find proper (mild, selective) oxidant for the catalytic cycle!
R
R'· R2
R1
R4
R3
LAu(I)+
or
Au(I)
Au(III)
GoldenOpportunity
With contemporary gold chemistryusing alkyne/allene substrates
Adam Hoye @ Wipf Group Page 5 of 13 5/2/2009
Selectfluor observation- Serendipity!
Me
OAc
nBu
nBu
O
Me
Me
nBu
O
nBu
O
H
Me
[Ph3PAu]NTf2 (5 mol %)Selectfluor (1 equiv)
acetone, 80 °C, 36 min75% conversion
19% yield 11% yield
α-Iodo enones from propargylic acetates:
OAc
R3
R2 R3
O
I
Au(PPh3)NTf2 (2 mol%), NIS (1.2 equiv)
Acetone/H2O, 0 °C, 2 h
R1R2
R1
75-99%R1, R2 = alkyl, aryl, HR3 = alkyl, aryl
Zhang, OL, 2007, 9, 2147
R2
Au(I)L
O
R3
R1
nBu
O
F
Me
not observed
Adam Hoye @ Wipf Group Page 6 of 13 5/2/2009
Proposed mechanism
LAu(I) F LAu(I)
F -
Au(I)L
Me
nBu
OAc
Me
OAc
nBuMe · O
nBu
O
LAu(I)
Me
O
nBu
O
LAu(I)
AuI
Me
nBu
OLAu
III
Me
nBu
OL
F
N N
Cl
F
2 BF4-
N N
Cl
H
2 BF4-
AuI
Me
nBu
OL
AuIII
nBu
O
Me
Me
O
nBu
L F
nBu
OMe
MeO
nBu
L = PPh3
oxidation
reductiveelimination
LAu(I) F
(RO)2B-Ar
nBu
O
Ar
Me
nBu
O
AuIII
Me
L
F
Ar
H2O
HOAc + H3O+
A
BCB
D
E
Adam Hoye @ Wipf Group Page 7 of 13 5/2/2009
Suzuki reaction optimization
Me
OAc
nBu
nBu
O
Ph
Me
Ph BXn
CH3CN, 80 °C
Selectfluor(2.0 equiv)
15 min(4.0 equiv)
nBu
O
Me
Me
nBu
O
nBu
O
H
Me
5 2 3
Adam Hoye @ Wipf Group Page 8 of 13 5/2/2009
Suzuki reaction substrate scope
R
OAc
R'
R'
O
Ar
R
Ph3PAuCl (5 mol %)ArB(OH)2 (4 equiv), Selectfluor (2 equiv)
MeCN/H2O = 20:1, 80 °C, 15-30 min
Adam Hoye @ Wipf Group Page 9 of 13 5/2/2009
Oxidative C-O bond formation (3-20-09)
O
O
Ph
R
R
O
O Ph
O
PPh3AuNTf2 (5 mol%)Selectfluor (1.5 equiv)
MeCN/H2O, 80 °C
51 - 83%
O
O
Ph
R
O
Ph
O
RAu
I PPh3
O
Ph
O
RAu
III
PPh3
F
O
RAu
III
PPh3
F
O
O
Ph
R
O
O Ph
O
O
Ph
O
RAu
III
PPh3
F
[3,3]
PPh3Au+
Selectfluor
H2O
reductive
elimination
Ph3PAuF
F -
Proposed Mechanism:
If ‘JACS mechanism’ is correct, why not C-O bond formation in ACIE publication???
Adam Hoye @ Wipf Group Page 10 of 13 5/2/2009
Proposed mechanism
LAu(I) F LAu(I)
F -
Au(I)L
Me
nBu
OAc
Me
OAc
nBuMe · O
nBu
O
LAu(I)
Me
O
nBu
O
LAu(I)
AuI
Me
nBu
OLAu
III
Me
nBu
OL
F
N N
Cl
F
2 BF4-
N N
Cl
H
2 BF4-
AuI
Me
nBu
OL
AuIII
nBu
O
Me
Me
O
nBu
L F
nBu
OMe
MeO
nBu
L = PPh3
oxidation
reductiveelimination
LAu(I) F
(RO)2B-Ar
nBu
O
Ar
Me
nBu
O
AuIII
Me
L
F
Ar
H2O
HOAc + H3O+
A
BCB
D
E
Adam Hoye @ Wipf Group Page 11 of 13 5/2/2009
Compare two mechanistic proposals…
‘JACS mechanism’ appears to be more consistent withexperimental results
square planar
nBu
O
AuIII
Me
O L
F
nBu
O
AuIII
Me
L
F
O
nBu
O
AuIII
Me
L
F nBu
O
Ar
Me
Ar-B(OH)2
nBu
O
O
Me
Me
O
1. [3,3]
2. SelectfluorMe
OAc
nBu
H2O
H2O
red. elim.
‘ACIE sm’
Adam Hoye @ Wipf Group Page 12 of 13 5/2/2009
Outlook/future directions
Merges contemporary Au catalysis with transition metal-catalyzed cross-coupling reactions
-Limitation of Selectfluor compatibility-Mechanistic hypothesis needs investigation
-Strongly suggests the feasibility of Au(I)/Au(III) catalytic cycle
-New opportunities for Au-catalyzed processes.
Drawbacks:
Au R
R'· R2
R1
R4
R3
LAu(I)+
or
Au(I)
Au(III)
Adam Hoye @ Wipf Group Page 13 of 13 5/2/2009