Gold-catalysed oxyarylation of styrenes and mono- and gem-disubstituted olefins facilitated by an iodine(III) oxidant

Article abstract of DOI:10.1002/chem.201103061

1-Hydroxy-1,2-benziodoxol-3(1H)-one (IBA) is an efficient terminal oxidant for gold-catalysed, three-component oxyarylation reactions. The use of this iodine(III) reagent expands the scope of oxyarylation to include styrenes and gem-disubstituted olefins, substrates that are incompatible with the previously reported Selectfluor-based methodology. Diverse arylsilane coupling partners can be employed, and in benzotrifluoride, homocoupling is substantially reduced. In addition, the IBA-derived co-products can be recovered and recycled. The I's have it: The unprecedented use of an iodine(III) reagent as the terminal oxidant for gold-catalysed oxyarylation allows the substrate scope to be significantly expanded; in addition to monosubstituted olefins, styrenes and gem-disubstituted olefins are well tolerated (see scheme). With benzotrifluoride as solvent, unproductive homodimerisation of the arylsilane coupling partner is effectively suppressed. Copyright

Full text of DOI:10.1002/chem.201103061

FULL PAPER
DOI: 10.1002/chem.201103061
Gold-Catalysed Oxyarylation of Styrenes and Mono- and gem-Disubstituted
Olefins Facilitated by an IodineACTHNUGRTENUNG(III) Oxidant
Liam T. Ball, Guy C. Lloyd-Jones,* and Christopher A. Russell*[a]
Abstract: 1-Hydroxy-1,2-benziodoxol-3(1H)-one (IBA) is an efficient terminal oxi-
dant for gold-catalysed, three-component oxyarylation reactions. The use of this
iodine
(III) reagent expands the scope of oxyarylation to include styrenes and gem-
Keywords: arylation
·
gold
·
·
disubstituted olefins, substrates that are incompatible with the previously reported
Selectfluor-based methodology. Diverse arylsilane coupling partners can be em-
ployed, and in benzotrifluoride, homocoupling is substantially reduced. In addi-
tion, the IBA-derived co-products can be recovered and recycled.
homogeneous
catalysis
hypervalent iodine · styrenes
Introduction
The past decade has seen homogeneous gold catalysis trans-
formed from a chemical curiosity into an intensely active
field of research.[1] The methodology developed to date,
which has found application in several target-oriented syn-
theses,[2] is unified by a mechanistic theme in which the
metal, most commonly cationic AuI, functions as a carbo-
philic Lewis acid, mediating nucleophilic addition to an un-
saturated substrate. Importantly, the metal remains redox
neutral throughout the transformation, which stands in stark
contrast to the facile two-electron redox cycles typically ex-
hibited by other late transition metals.[3]
Recently, however, access to higher oxidation states from
AuI precatalysts during the catalytic cycle has been realised
by addition of a stoichiometric oxidant, thereby increasing
the diversity of gold-promoted transformations.[4] In this
Scheme 1. a) Two-[6] and b) three-component[8–10] heteroarylation of mon-
osubstituted olefins, employing Selectfluor as both terminal oxidant and
fluoride source. c) Envisaged electrophilic fluorination of more-nucleo-
philic substrates.
regard, the Selectfluor[5]-mediated two-component heteroar-
ylation of olefins with arylboronic acids[6] (Scheme 1 a) con-
stitutes a particularly significant development, as it served
to illustrate the feasibility of oxidative CACTHNUGRTNENUG ACHUTNGTRENNUGN
(sp3)–C(sp2) bond
formation in an intermolecular (i.e., cross-coupling) fash-
ion.[7] The concept has subsequently been extended to three-
component oxyarylation (Scheme 1 b),[8] and the suitability
of arylsilanes as the aryl source has been reported both by
ourselves[9] and by Toste.[10] Importantly, replacement of the
arylboronic acid by an arylsilane was found to reduce the
formation of biaryl side products.
reagent combinations were reported to promote the trans-
formation, all were outperformed by Selectfluor in the dual
role of oxidant and nucleophilic activator,[11] further illus-
trating the unique utility of the fluoronium reagent within
gold-mediated oxidative catalysis.[12] However, in addition to
acting as an oxidant in both organic[13] and organometallic[14]
chemistry, Selectfluor is widely employed as a potent elec-
trophilic fluorinating agent.[15] We recognised that direct flu-
orination may be competitive for more-nucleophilic sub-
strates (Scheme 1 c), and therefore envisaged that an alter-
native oxidant needed to be identified before the scope of
gold-catalysed oxyarylation could be extended further.
Indeed, whilst the existing oxyarylation methodology has
been demonstrated to allow transfer of electronically and
sterically diverse aryl moieties, and to tolerate a range of O-
Previous studies[6,8a,9,10] indicated that the choice of oxi-
dant is critical for successful heteroarylation. Whilst several
[a] L. T. Ball, Prof. Dr. G. C. Lloyd-Jones, Dr. C. A. Russell
School of Chemistry, University of Bristol
Cantockꢀs Close, Bristol, BS8 1TS (UK)
Fax : (+44)117-9251295
E-mail: guy.lloyd-jones@bris.ac.uk
chris.russell@bris.ac.uk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201103061.
Chem. Eur. J. 2012, 18, 2931 – 2937
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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nucleophiles, the olefin scope has been entirely restricted to
substrates bearing a single alkyl substituent.[16] Herein, we
report the gold-catalysed, three-component methoxyaryla-
tion of both styrenes and gem-disubstituted olefins in the
successful (entry 1), the addition of two equivalents of p-tol-
uenesulfonic acid monohydrate (p-TSA) afforded the de-
sired product 1 in a promising yield of 20% (entry 2). The
facile nature of ligand exchange at iodine
that the active oxidant was likely based on [hydroxy-
(tosyloxy)iodo]benzene (HTIB, Koserꢀs reagent)[18] rather
AHCTUNGTRENNUNG
(III)[17] suggested
ACHTUNGTRENNUNG
presence of an iodineACTHNUGTRNEUNG(III) oxidant.
than PhIACTHNUTRGENNG(U OAc)2; this supposition was supported by the very
Results and Discussion
similar yields obtained with either freshly prepared[19] or
commercially sourced HTIB (entry 3).[20]
Oxidant development and reaction optimisation: The pres-
ence of basic/nucleophilic additives (e.g., Cs2CO3, TBAF=
tetrabutylammonium fluoride) was shown to have a detri-
mental effect on the Selectfluor-mediated oxyarylation of
monosubstituted olefins.[10] In addition, the combination of
nucleophilic promoters (e.g., TBAF, TBAT=tetrabutylam-
monium triphenyldifluorosilicate) and alternative oxidants
The yield of 1 was doubled by portionwise addition of
HTIB (entry 4), but, despite significant efforts, could not be
improved further. Subsequent investigation of iodineACHTUNGTRENNUNG(III) re-
agents derived from 2-iodobenzoic acid[21] revealed that the
use of the tosyloxy analogue IBA-Ts (entry 6) was prefera-
ble to either the parent benziodoxolone IBA (1-hydroxy-
1,2-benziodoxol-3ACTHNUTRGNEUNG(1H)-one; entry 5) or its acyclic relative
(e.g., PhI
(OAc)2) afforded only traces of the desired oxyary-
HTIB. The yield of 1 was increased to 83% by employing a
combination of IBA and two equivalents of p-TSA (entry 7)
in place of preformed IBA-Ts; this result could not be im-
proved by varying the acid additive (entries 8–10)[23] or the
aryl source (entries 11–13). IBX (2-iodoxybenzoic acid)
proved an unsuitable oxidant (entries 14 and 15), presuma-
bly owing to the competing reaction between the iodine(V)
reagent and the alcohol.[24] Importantly, control reactions[25]
indicated the need for both the acid and the oxidant, as well
as a gold precatalyst; the failure of palladium, and various
other late transition metals, to catalyse the transformation
provided evidence against low-level impurities being respon-
sible for the catalytic activity ascribed to gold.[26]
(Table 1). Thus, whilst employing PhIACTHNUTRGENUG(N OAc)2 in place of Se-
lectfluor (under previously optimised conditions) proved un-
Table 1. Oxidant screen.[a]
Subsequent reaction optimisation[25] revealed that both
AuI and AuIII species—as well-defined complexes, simple
salts or in combination with AgI salts—were able to act as
precatalysts for the IBA/p-TSA-mediated oxyarylation
(Table 2, entries 1–12). As with our previously reported
methodology,[9] the reaction was sensitive to the steric and
electronic environment about the gold centre: [AuClACHTUNGTRENNUNG(PPh3)]
proved a more efficient precatalyst than complexes of bulky
and/or strong donor ligands (entry 1 vs. entries 6–10). Inter-
Entry
Oxidant
Additive
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
PhI
PhI
U
–
<1
20
23
48[c]
0
55
83[d]
65
15
4
p-TSA
–
–
–
–
p-TSA
MsOH
TfOH
TFA
p-TSA
p-TSA
p-TSA
–
estingly, the reactivity of [AuCl
ACHTUNGTRENNUNG
HTIB
HTIB
IBA
IBA-Ts
IBA
IBA
IBA
IBA
IBA
IBA
IBA
IBX
IBX
by the digold complexes [(AuX) CTHNUGTRENNUNG
dppm=bis(diphenylphosphino)methane; X=Cl, Br).[27]
Whilst a significant halide effect was observed for the Se-
lectfluor system at approximately 508C, this was found to di-
minish at higher temperatures,[6b,8a,10] as is reflected in our
own results (compare entry 11, X=Cl with entry 12, X=
Br).
3[e]
0[f]
0[g]
44
37
Notably, upon changing the reaction solvent[25] to benzo-
trifluoride (PhCF3) and diluting from 0.1m (entry 13) to
0.05m (entry 14), the yield of 1 was significantly improved
and the formation of biaryl side products was largely sup-
pressed (<3%).[28] However, no additional benefits resulted
from further dilution. Subsequent investigations indicated
that, whilst the amounts of arylsilane, IBA and p-TSA could
be reduced, two molar equivalents of each reagent were re-
quired for consistently high yields, particularly when em-
ploying more challenging substrates.[29] In addition, the reac-
tion proceeded most efficiently at 708C; hence, optimised
p-TSA
[a] Conditions: [AuClACHTUNGTRENNUNG(PPh3)] (5 mol%), 1-octene (0.1 mmol), PhSiMe3
(0.2 mmol), oxidant (0.2 mmol), additive (0.2 mmol), MeCN/MeOH (9:1,
1 mL), 708C, 15 h. Ms=methanesulfonyl; Tf= trifluoromethanesulfonyl;
TFA=trifluoroacetic acid. [b] Yields are an average of at least 2 repeti-
tions and were determined by GC-FID (FID=flame ionisation detector)
against an internal standard. [c] HTIB was added in six equal portions
over 100 min. [d] 1 was not formed in the absence of [AuCl
[e] PhB(OH)2 was used in place of PhSiMe3. [f] PhSi(OMe)3 was used in
place of PhSiMe3. [g] PhSiMe2OH was used in place of PhSiMe3.
(PPh3)].[25]
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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Gold-Catalysed Oxyarylation
Table 2. Reaction optimisation.[a]
FULL PAPER
Table 3. Oxyarylation of monosubstituted olefins.[a]
Entry
Precatalyst
[AuCl(PPh3)]
[AuCl(PPh3)]/AgBF4
AuCl
HAuCl4·3H2O
[AuCl2A(pyca)]
[AuCl(PCy3)]
[AuCl{P(o-tol)3}Cl]
[AuCl(JohnPhos)]
[AuCl{P(tBu)3}]
[AuCl(IPr)]
[(AuCl)2A(dppm)]
[(AuBr)2A(dppm)]
[AuCl(PPh3)]
[AuCl(PPh3)]
Yield [%][b]
Entry
Product
Yield
[%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
G
N
83
38
59
29
6
33
21
1
R
1
2
1
2
69[c]
E
CHTUNGTRENNUNG
68
N
N
ACHTUNGTRENNUNG
R
3
3
71
N
A
1
0
N
38[c]
40[c]
43[d]
93[e,f]
4
5
6
7
4 R2: H
87
65
62
8[d]
R
G
5 R2: 4-Br
6 R2: 2-Me
7 R2: 4-OMe
N
CHTUNGTRENNUNG
T
A
[a] Conditions: Precatalyst (5 mol%), 1-octene (0.1 mmol), PhSiMe3
(0.2 mmol), IBA (0.2 mmol), p-TSA (0.2 mmol), MeCN/MeOH (9:1,
1 mL), 708C, 15 h. [b] Yields are an average of at least 2 repetitions and
were determined by GC-FID against an internal standard. Pyca=2-pyri-
dinecarboxylato; JohnPhos=2-(di-tert-butylphosphino)biphenyl; IPr=
1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene. [c] Pre-
catalyst (2.5 mol%) was used. [d] Solvent system: PhCF3/MeOH (9:1,
1 mL). [e] Solvent system: PhCF3/MeOH (9:1, 2 mL). [f] 1 was not
8 R3: Et
58[e]
44[e]
49[e]
0[d,e]
2[e]
8
9
10
11
12
9 R3: (CH2)2OMe
10 R3: iPr
11 R3: tBu
12 R3: Ac
13
13
46[e]
formed in the absence of [AuClACTHNURTGNENUG(PPh3)].
[a] Conditions: [AuClACTHNUTRGNE(NUG PPh3)] (5 mol%), olefin (0.5 mmol), arylsilane
(1.0 mmol), IBA (1.0 mmol), p-TSA (1.0 mmol), PhCF3/MeOH (9:1,
10 mL), 708C. PhthN=phthalimido. [b] Isolated yield. [c] Isolated yield
is lower than chemical yield (Table 2, entry 14) owing to difficulties in pu-
conditions were assessed to be those shown in Table 2,
entry 14.
1
rification. [d] Yield determined by H NMR spectroscopy using nitroben-
zene as internal standard. [e] MeCN/R3OH was used in place of PhCF3/
MeOH.
Scope—monosubstituted olefins: The generality of the
newly developed oxyarylation conditions was probed initial-
ly for monosubstituted olefins (Table 3). A range of methyl
ethers was prepared in good yield from the reaction of
PhSiMe3 with both simple and functionalised substrates (en-
tries 1–4). The potentially sensitive functionality of nitroben-
zoate 3 (entry 3) was well tolerated and no transesterifica-
tion side products were observed.[30] In addition, both mod-
erately electron-rich and electron-poor aryl moieties could
be transferred (entries 4–6), including the sterically demand-
ing o-tolyl moiety, which had proved challenging with Se-
lectfluor as the oxidant.[9] For O-nucleophiles other than
MeOH, MeCN was required as the solvent: water and a
range of alcohols could then be employed, giving the expect-
ed products in moderate yields (entries 8–13).[31] Carboxylic
acids performed poorly in the role of O-nucleophile
(entry 12), and, as observed previously, very electron-rich ar-
ylsilanes (entry 7) and tertiary alcohols (entry 11) were un-
suited to the reaction.
Scheme 2. Reaction of olefins bearing a tethered arylsilane (top) and a
tethered nucleophile (bottom) under oxyarylation conditions.
Intramolecular coupling of an olefin and a tethered arylsi-
lane occurred in a 6-endo-trig fashion to give tetrahydro-
naphthalene 14 in a yield similar to that obtained with Se-
lectfluor as the oxidant[10] (Scheme 2, top). By contrast, the
two-component heteroarylation of olefins bearing tethered
O- or N-nucleophiles did not proceed to afford the expected
tetrahydrofurans or pyrrolidines: in the case of 4-penten-1-
ol, a complex mixture of products was obtained, whilst N-(4-
pentenyl)tosylamide furnished a 9:1 mixture of piperidine
15 and pyrrolidine 16 (Scheme 2, bottom). Although the es-
sential role of gold in related aminooxygenations has been
demonstrated under basic conditions,[32] we found that, as
expected under acidic conditions,[33] the formation of 15 and
16 proceeded equally efficiently in the absence of gold.[25]
In all cases, the oxyarylation products were accompanied
by alkyl 2-iodobenzoates, formed in situ from the IBA-de-
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L. T. Ball, G. C. Lloyd-Jones and C. A. Russell
Table 4. Methoxyarylation of styrenes.[a]
rived 2-iodobenzoic acid. Typically isolated in 65–98%
yield, the ester side products could be hydrolysed and subse-
quently oxidised[34] to IBA in near-quantitative yield
(Scheme 3), allowing for the efficient and scalable recycling
of the organoiodine moiety.
Entry
Product
Yield
[%][b]
1
2
3
4
5
6
7
8
17 R2: H
77
54
77
75
69
78
55
48
18 R2: 2-Me
19 R2: 3-Me
20 R2: 4-Me
21 R2: 4-OMs
22 R2: 4-NMeTs
23 R2: 4-F
24 R2: 4-Cl
9
25
26
77
83
Scheme 3. Hydrolysis and subsequent oxidation of recovered methyl
2-iodobenzoate.
10
Having established the scope and limitations of the new
conditions with respect to monosubstituted olefins, we con-
sidered substrate classes incompatible with the existing
methodology: gratifyingly, both styrenes and gem-disubsti-
tuted olefins[35] were found to undergo oxyarylation (see
below).
11
12
13
14
27 R2: H
71
54
35
36
28 R2: 4-F
29 R2: 4-Cl
30 R2: 3-CO2Me
15
16
31 R2: 3-Me
51
29
32 R2: 4-OMs
Scope—styrenes: The high reactivity of styrenes towards
electrophiles, and their propensity to polymerise in the pres-
ence of Brønsted or Lewis acids, including gold,[36] renders
them a particularly challenging class of substrates for oxyar-
ylation. Indeed, attempting to employ styrenes under condi-
tions optimised previously with Selectfluor[9] afforded only a
trace of the desired product, and significant amounts of fluo-
rinated compounds.[25] In contrast, oxyarylation proceeded
smoothly in the presence of IBA and p-TSA (Table 4), al-
though the scope of the O-nucleophile was limited to
MeOH.[31] Whilst the electronic nature of the arylsilane cou-
pling partner was more pronounced than for monosubstitut-
ed olefins, oxyarylation proved less sensitive to the electron-
ic nature of the substrate (entry 18 vs. 20).[37] The expected
bibenzyls were obtained in good to excellent yields for elec-
tron-neutral and moderately electron-rich arylsilanes (en-
tries 1–6, 9–11 and 15–21), including a synthetically useful[38]
aryl mesylate (entry 5). In comparison, coupling with elec-
tron-deficient arylsilanes proved more challenging (entries 7,
8 and 12–14): presumably the slower reaction of the deacti-
vated arylsilanes allowed for consumption of the styrene by
competing side reactions. Additionally, both sterically de-
manding arylsilanes (entry 2) and styrenes (entry 20) were
well tolerated, and even the very congested product 37
(entry 21) was isolated in reasonable yield.
17
18
19
33 R1: 4-Cl
34 R1: 3-NO2
35 R1: 4-Me
72
92
37
20
21
36 R2: H
65
31
37 R2: 2-Me
[a] Conditions: [AuClACTHNUTRGNE(NUG PPh3)] (5 mol%), styrene (0.5 mmol), arylsilane
(1.0 mmol), IBA (1.0 mmol), p-TSA (1.0 mmol), PhCF3/MeOH (9:1,
10 mL), 708C. [b] Isolated yield.
Figure 1. Oxyarylation products from a-methylstyrene (left) and (E)-b-
methylstyrene.
copy[40]). Despite the low yield, this latter result is particular-
ly significant, as it represents the first example of an internal
olefin being successfully subjected to gold-catalysed oxyary-
lation and demonstrates the stereospecific nature of the
transformation.
Subjecting (Z)-b-[D1]-styrene to the standard reaction
conditions (Scheme 4) afforded bibenzyl (ꢀ)-[D1]-27 as a
single diastereoisomer,[41] confirming the stereospecificity
observed for methoxyarylation of (E)-b-methylstyrene. The
net anti-addition across the olefin precludes intermediacy of
a benzylic carbocation or radical, and is consistent with, but
Oxyarylation of a-methylstyrene afforded methyl ether 38
1
(Figure 1) in 8% yield (determined by H NMR spectrosco-
py[39]), whilst reaction of (E)-b-methylstyrene proved more
successful: ether 39 was formed as a single regio- and diaste-
1
reoisomer in 22% yield (determined by H NMR spectros-
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Gold-Catalysed Oxyarylation
FULL PAPER
Scheme 5. Dioxygenation of gem-disubstituted olefins under oxyarylation
conditions.
Conclusion
Scheme 4. Stereospecific oxyarylation of (Z)-b-[D1]-styrene.
In summary, we have demonstrated that the combination of
IBA and p-TSA acts as an efficient oxidant in the gold-cata-
lysed oxyarylation of olefins. The iodineACTHNUTRGNE(NUG III) reagent can be
cannot differentiate between, two possible scenarios: 1)
anti-oxyauration, followed by arylation with retention of
configuration, or 2) syn-oxyauration, followed by arylation
with inversion.[42]
prepared in near-quantitative yield on a multigram scale
from 2-iodobenzoic acid; the requirement for superstoichio-
metric amounts of the oxidant is offset by the recovery and
subsequent recycling of the organoiodine moiety. A diverse
range of arylsilanes are readily transferred, and in PhCF3,
biaryl formation is largely suppressed. Although the scope
in terms of the O-nucleophile is largely restricted to MeOH,
the new conditions allow substrates incompatible with Se-
lectfluor, namely styrenes and gem-disubstituted olefins, to
be employed, thereby significantly expanding the scope of
the existing methodology. Furthermore, successful methox-
yarylation of b-methylstyrene hints that further refinement
will allow internal, tri- and tetrasubstituted olefins to be em-
ployed as substrates. The mechanism of the reaction under
our newly developed conditions is under investigation.
Scope—gem-disubstituted olefins: As for styrenes, attempt-
ed oxyarylation of gem-disubstituted olefins in the presence
of Selectfluor afforded several fluorinated compounds as
part of a complex mixture, of which the desired product was
only a minor component.[25] Using the combination of IBA
and p-TSA, however, allowed for methoxyarylation of 2-
methyl-2-alkyl olefins with various arylsilanes (Table 5).
Table 5. Methoxyarylation of gem-disubstituted olefins.[a]
Experimental Section
General methoxyarylation procedure: Olefin (0.50 mmol), arylsilane
(1.00 mmol) and [AuClACHTNUTRGNE(NUG PPh3)] (12.4 mg, 0.025 mmol, 5 mol%) were
Entry
Product
Yield
[%][b]
added to a 28 mL vial containing a mixture of IBA (264.0 mg, 1.00 mmol)
and p-TSA (190.2 mg, 1.00 mmol) in PhCF3 (9 mL) and MeOH (1 mL).
The vial was sealed and placed in a preheated aluminium heating block.
The reaction was stirred at 708C until the olefin was consumed (as moni-
tored by TLC), allowed to cool to room temperature and then passed
through a silica pad (eluent: CH2Cl2). The filtrate was concentrated in
vacuo and the crude material was purified by column chromatography.
1
2
3
4
5
6
40 R: H
86
24
67
55
58
43
41 R: 2-Me
42 R: 4-Me
43 R: 4-NMeTs
44 R: 4-F
45 R: 4-Br
7
46
62
[a] Conditions: [AuClACHTUNGTRENNUNG(PPh3)] (5 mol%), olefin (0.5 mmol), arylsilane
(1.0 mmol), IBA (1.0 mmol), p-TSA (1.0 mmol), PhCF3/MeOH (9:1,
10 mL), 708C. [b] Isolated yield.
Acknowledgements
We thank Umicore AG & Co. KG for the generous donation of HAuCl4.
L.T.B. thanks the Bristol Chemical Synthesis Doctoral Training Centre,
funded by EPSRC (EP/G036764/1), AstraZeneca, GlaxoSmithKline, No-
vartis, Pfizer, Syngenta and the University of Bristol, for the provision of
Ph.D. studentship. G.C.L.J. is a Royal Society Wolfson Research Merit
Award holder.
Aryl moieties bearing electron-donating substituents (en-
tries 1–4 and 7) were transferred more readily than those
featuring electron-withdrawing substiuents (entries 5 and 6)
or ortho-substitution (entry 2). The modest yields, relative to
monosubstituted olefin and styrene substrates, may be at-
tributed to the difficulty of forming a quaternary centre.
Attempts to extend the methodology to a wider range of
O-nucleophiles[31] in MeCN resulted in vic-dioxygenation of
the substrate: products of type 47 (Scheme 5) were formed
equally efficiently in the absence of gold.[43]
[1] For seminal reports of homogeneous gold catalysis, see: a) A. S. K.
Hashmi, L. Schwarz, J.-H. Choi, T. M. Frost, Angew. Chem. 2000,
112, 2382; Angew. Chem. Int. Ed. 2000, 39, 2285; b) A. S. K.
Hashmi, T. M. Frost, J. W. Bats, J. Am. Chem. Soc. 2000, 122, 11553.
For dedicated review volumes, see: c) Chem. Rev. 2008, 108;
Chem. Eur. J. 2012, 18, 2931 – 2937
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2935

L. T. Ball, G. C. Lloyd-Jones and C. A. Russell
d) Chem. Soc. Rev. 2008, 37; e) J. Organomet. Chem. 2009, 694;
f) Tetrahedron 2009, 65.
[14] a) M. N. Hopkinson, A. D. Gee, V. Gouverneur, Isr. J. Chem. 2010,
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MeOH
was
discounted,
as
the
resulting
[methoxy-
AHCTUNGTREG(NNUN tosyloxy)iodo]benzene is known to be very prone to hydrolysis
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AHCTUNGTRENNUNG
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alysed oxyarylation (see the Supporting Information).
[3] Transition Metals for Organic Synthesis, Vol. 1, 2nd ed. (Eds.: M.
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2
ꢁ
[7] For intermolecular C
(sp ) C
(sp2) bond formation, see: a) G. Zhang,
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both the electrophilicity and solubility of the oxidant.
[24] V. V. Zhdankin, J. Org. Chem. 2011, 76, 1185.
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[26] The possible role of low-level Pd-impurities in gold catalysis has
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[27] Caution must be exercised, when extending the mechanism recently
disclosed (ref. [8c]) for Selectfluor-promoted oxyarylation to our
present conditions; an in-depth investigation of the reaction mecha-
nism is ongoing.
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13C and 29Si NMR spectroscopy), which indicates that the silyl
moiety is ultimately sequestered by MeOH, although it does not ne-
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lane-derived side products; the products of oxidation (i.e., phenols)
or protodesilylation (i.e., arenes) were not detected.
[29] An excess of p-TSA (relative to IBA) gave no observed increase in
the activity of the oxidant (C. W. Bielawski, M. Zhu, B. Olofsson,
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Table S3. Attempts to form hypervalent iodine species in situ from
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were not pursued owing to the high reactivity of peracids towards
olefins.
[30] In a control experiment, treating but-3-enyl 4-nitrobenzoate with p-
TSA (2 equiv) at 708C in PhCF3/MeOH resulted in <7% methanol-
ysis after 2 h, and 47% methanolysis after 14 h.
[31] The poor performance of O-nucleophiles other than MeOH cannot
be explained at present, although oxidation of the alcohol (as a non-
productive pathway for consumption of both IBA and O-nucleo-
phile) was precluded by control experiments; see the Supporting In-
formation.
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2936
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Chem. Eur. J. 2012, 18, 2931 – 2937

Gold-Catalysed Oxyarylation
FULL PAPER
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1
for both diastereoisomers have been reported: J. Woning, A. Oude-
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[43] See the Supporting Information. Similar vic-dioxygenations have
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forded the expected products in a 1.2:1 (27/2) ratio (see the Sup-
porting Information); the small difference between the reaction
rates for the 2 substrate classes further illustrates the low sensitivity
of oxyarylation to the electronic nature of the substrate, although
only traces of product were detected (1H NMR spectroscopy) for
the very electron-rich 4-methoxystyrene.
Received: September 29, 2011
Published online: February 1, 2012
Chem. Eur. J. 2012, 18, 2931 – 2937
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2937