Dual Photoredox and Gold Catalysis: Intermolecular Multicomponent Oxyarylation of Alkenes

Article abstract of DOI:10.1002/adsc.201400580

Intermolecular three-component oxyarylation reactions of simple alkenes have been developed using a dual gold and photoredox catalytic system. Inexpensive organic dyes could be employed as the photocatalyst using aryldiazonium salts, while the combination of gold and iridium catalysts allowed for diaryliodonium compounds to be employed as the source of the arene coupling partner. In both cases, α-arylated ether products were generated under remarkably mild conditions using readily accessible visible light sources.

Full text of DOI:10.1002/adsc.201400580

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DOI: 10.1002/adsc.201400580
Dual Photoredox and Gold Catalysis: Intermolecular
Multicomponent Oxyarylation of Alkenes
Matthew N. Hopkinson,a Basudev Sahoo,a,b and Frank Gloriusa,*
a
Organisch-Chemisches Institut, Westfꢀlische Wilhelms-Universitꢀt Mꢁnster, Corrensstrasse 40, 48149 Mꢁnster, Germany
Fax : (+49)-251-83-33202; phone: (+49)-251-83-33248; e-mail: glorius@uni-muenster.de
NRW Graduate School of Chemistry, Westfꢀlische Wilhelms-Universitꢀt Mꢁnster, Wilhelm-Klemm-Strasse 10, 48149
b
Mꢁnster, Germany
Received: June 15, 2014; Published online: September 11, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400580.
Abstract: Intermolecular three-component oxyary-
lation reactions of simple alkenes have been devel-
oped using a dual gold and photoredox catalytic
system. Inexpensive organic dyes could be em-
ployed as the photocatalyst using aryldiazonium
salts, while the combination of gold and iridium cat-
alysts allowed for diaryliodonium compounds to be
employed as the source of the arene coupling part-
ner. In both cases, a-arylated ether products were
generated under remarkably mild conditions using
readily accessible visible light sources.
of Au-catalyzed oxyarylations reported to date have
been oxidative processes, requiring super-stoichiomet-
ric amounts of a strong external oxidant.[3–5] An alter-
native approach to oxyarylation involves Meerwein-
type addition of highly reactive aryl radicals, generat-
ed in situ from a suitable precursor.[6] The scope of
these transformations, however, is generally limited to
activated alkene substrates capable of stabilizing the
alkyl radical generated upon addition.
Recently, we reported a novel dual catalytic system
capable of mediating intramolecular oxy- and amino-
arylation reactions of alkenyl alcohols and amines by
combining gold catalysis with visible light photoredox
activation.[7–9] In this process, ruthenium-catalyzed
photoactivation of aryldiazonium salts is thought to
lead to aryl radicals susceptible to gold-catalyzed
cross-coupling.[10] Herein we report the successful ap-
plication of dual gold/visible light photoredox cataly-
Keywords: alkenes; cross-coupling; dual catalysis;
gold; photocatalysis
As fundamental building blocks of organic chemistry, sis to the selective intermolecular three-component
methodologies that enable the selective functionaliza- oxyarylation of alkenes with simple alcohols. This
tion of alkenes are important weapons in the chem- redox neutral process benefits from mild reaction
istꢂs armory. The intermolecular arylation of alkenes conditions and can be applied to a wide range of non-
is most commonly achieved via the venerable palladi- activated terminal alkene substrates. Moreover, judi-
um-catalyzed Mizoroki–Heck reaction between al- cious selection of the photoredox catalyst and light
kenes and aryl halides to afford styrene derivatives. source allows for readily accessible diaryliodonium
An increasing amount of research attention, however, salts to be employed as the source of the arene cou-
has been devoted to related transformations which, pling partner (Scheme 1).
instead of maintaining the alkene functionality, result
In an initial test reaction, the simple alkyl-substitut-
in the overall addition of two groups across the ed alkene 1-octene (1a) was reacted with benzenedia-
double bond. Intermolecular oxyarylation, whereby zonium tetrafluoroborate (2a, 4 equiv.) in the pres-
one aryl group and one oxygen substituent add across ence of the gold(I) catalyst [Ph3PAu]NTf2 (10 mol%)
an alkene in a multicomponent coupling process, is and the photosensitizer [RuACHTNUTRGENNG(U bpy)3]ACHTUNTGRNE(NUGN PF6)2 (2.5 mol%)
one such transformation.[1] With palladium catalysts, in methanol. We were delighted to find that, upon ir-
a major challenge in these reactions is the suppression radiation with visible light from a simple household
of the b-hydride elimination step, which results in un- compact fluorescent light bulb (23 W CFL), a single
desired Mizoroki–Heck-type products. One promising regioisomer of product 3aa, resulting from selective
solution to this problem has been the use of gold cata- addition of one phenyl and one methoxy group across
lysts, which do not generally react via b-hydride elimi- the alkene, was generated as the only detectable
nation.[2] However, gold does not readily undergo oxi- product in 90% NMR yield (84% isolated yield).
dative addition with aryl halides and all the examples Control reactions conducted in the absence of either
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Dual Photoredox and Gold Catalysis
Scheme 1. Intermolecular oxyarylation of alkenes.
the photoredox catalyst or in the dark resulted in
a dramatic drop in the reaction efficiency (<8%
NMR yield) while no product was observed in the ab-
sence of gold.[11] With the feasibility of the dual cata-
lyzed intermolecular oxyarylation reaction validated,
our attention turned to improving the attractiveness
of the process by employing an organic dye as photo-
sensitizer. In comparison to transition metal-based
Scheme 2. Gold and organic dye dual-catalyzed intermolecu-
lar oxyarylation of alkenes with aryldiazonium salts. Reac-
tion conditions: 1a (0.1 mmol), (2a, 0.4 mmol), [Ph3PAu]NTf2
(10 mol%), photocatalyst in degassed MeOH (0.1M) react-
ed under visible light irradiation (23 W CFL) for 16 h at
room temperature. NMR yields using diethyl phthalate as
internal standard, isolated yields in parentheses.
photocatalysts such as [RuACHTUNTRGENNUG(bpy)3]ACHTUNGTREN(NUNG PF6)2, organic dyes addition, non-activated alkyl alkenes could be suc-
are considerably less expensive and benefit from cessfully employed and there was no requirement for
lower toxicity and improved environmental character- radical-stabilizing substituents. A range of functional
istics.[12,13] The results of a short screen of some com- groups either on the alkene substrates or the aryldia-
mercially available organic dyes are shown in zonium salts was tolerated including a bromoaryl
Scheme 2.
(5 mol%) was found to be an effective substitute for further functionalization via cross-coupling methodol-
[Ru(bpy)3](PF6)2, selectively delivering the oxyarylat- ogies. ortho-, meta- and para-substitution patterns on
Pleasingly,
inexpensive
fluorescein moiety (3da, 3ae), which could serve as a handle for
A
ACHTUNGTRENNUNG
ed product 3aa in 88% NMR yield (86% isolated the aryl coupling partner were all tolerated while in
yield). Changing the light source or gold catalyst no case were products resulting either from Mizoro-
failed to lead to an improvement of the reaction out- ki–Heck-type arylation or hydroetherification detect-
come while reducing the loadings of either catalyst or ed in the reaction mixture.
equivalents of the diazonium salt resulted in a dimin-
Having established a dual gold and photoredox cat-
alytic system capable of mediating three-component
ished yield of the oxyarylated product.[11]
The dual gold and organic dye co-catalyzed inter- oxyarylation reactions with aryldiazonium salts, we
molecular oxyarylation reaction was found to be gen- next sought to identify alternative sources of the
eral for a selection of different terminal alkenes and arene coupling partner. In this regard, we were in-
aryldiazonium salts, selectively delivering arylated spired by previous reports demonstrating that diaryl-
ether products 3 in good yields (Scheme 3). In con-
ACHTUNGTRENiNGNU odonium salts can serve as precursors for aryl radi-
trast to oxyarylation processes proceeding via radical cals upon photoredox activation with visible light.[6h,14]
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Matthew N. Hopkinson et al.
In contrast to aryldiazonium salts, diaryliodonium
compounds may be stored for extended periods with
many derivatives being commercially available. Sub-
stituting the aryldiazonium salt 2a with diphenyliodo-
nium trifluoromethanesulfonate in the intermolecular
oxyarylation reaction of 1-octene (1a), however, led
to very low yields of 3aa using either the organic dye
fluorescein or [RuACHTNUTRGENNG(U bpy)3]ACHTUGNTRENN(UNG PF6)2 as the photocatalyst
(3% and 7% NMR yields, respectively, Table 1, en-
tries 1 and 2). Envisaging that photoredox catalysts
with more reducing excited states might be beneficial
for these less oxidizing arene sources, the iridium
ACHTUNGTRENNUNG(III)
complex [Ir(ppy)2A(dtbbpy)]PF6 (ppy=2-phenylpyri-
A
CHTUNGTRENNUNG
dine, dtbbpy=4,4’-di-tert-butyl-2,2’-bipyridine) was
tested. Using this photocatalyst, which exhibits an ex-
cited state reduction potential of E0 (IrIV/IrIII*)=
À0.96 V
{cf.
E0
(RuIII/RuII*)=À0.81 V
for
[RuACTHGUNTRNENUG
(bpy)3]2+},[9h] a small but notable improvement in
the reaction efficiency was observed with 3aa being
delivered in 16% NMR yield after 20 h (Table 1,
entry 3). A much more significant effect was ob-
served, however, upon changing the source of visible
light. Switching to a more powerful 32 W compact flu-
orescent light bulb (CFL) led to an increase in the
oxyarylation yield to 29% (NMR) while 3aa was pro-
duced in a respectable 62% NMR yield upon irradia-
tion with blue LEDs (5 W, Table 1, entries 4 and 5).
This figure could be further increased to 91% (NMR
yield, 82% isolated yield) upon increasing the photo-
redox catalyst loading to 5 mol% and switching the
iodonium salt anion to tetrafluoroborate (4a, Table 1,
entries 6 and 7). An extensive survey of alternative
gold catalysts, photocatalysts and light sources did not
Scheme 3. Scope and limitations of the gold and fluorescein
dual-catalyzed intermolecular oxyarylation of alkenes with
aryldiazonium salts. Reaction conditions: 1 (0.2 mmol), (2,
0.8 mmol), [Ph3PAu]NTf2 (10 mol%), fluorescein (5 mol%)
in degassed MeOH (0.1M) reacted under visible light irradi-
ation (23 W CFL) for 16 h at room temperature. Isolated
yields given.
Table 1. Optimization of the oxyarylation reaction with diaryliodonium salts.
Entry[a]
Gold Catalyst (mol%)/Photocatalyst (mol%)
[Ph3PAu]NTf2 (10)/[Ru(bpy)3](PF6)2 (2.5)
Light Source
XÀ
Yield[b]
1
2
3
4
5
6
7
8
G
G
E
23 W CFL
23 W CFL
23 W CFL
32 W CFL
blue LEDs
blue LEDs
blue LEDs
blue LEDs
blue LEDs
blue LEDs
blue LEDs
–
OTf
OTf
OTf
OTf
OTf
OTf
BF4
BF4
BF4
BF4
BF4
BF4
7%
3%
N
A
E
N
16%
29%
62%
85%
91% (82%)
36%
52%
9%
A
R
CHTUNGTRENNUNG
A
R
CHTUNGTRENNUNG
A
R
CHTUNGTRENNUNG
A
R
CHTUNGTRENNUNG
A
CHTUNGTRENNUNG
9
A
CHTUNGTRENNUNG
10
11
12
A
CHTUNGTRENNUNG
G
<5%
<5%
A
CHTUNGTRENNUNG
[a]
Reaction conditions: 1a (0.1 mmol), (4a, 0.4 mmol), [Ph3PAu]NTf2 (10 mol%), photocatalyst in degassed MeOH (0.1M)
reacted under visible light irradiation for 20 h at room temperature.
NMR yield using diethyl phthalate as internal standard, isolated yield in parentheses.
[b]
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Dual Photoredox and Gold Catalysis
As for the process with aryldiazonium compounds,
a range of non-activated terminal alkenes could be
successfully employed, delivering homobenzyl-substi-
tuted ethers 3 in generally good yields up to 82%. In
most cases where the same products were obtained
using both sets of conditions, the yields were largely
comparable. Significant variations were observed,
however, for the para- and ortho-methyl-substituted
derivatives 3ab and 3ad. The more sterically congest-
ed ortho-substituted substrate was seemingly better
tolerated as the iodonium salt, delivering 3ad in 75%
yield compared to 28% with diazonium salt 2d. The
opposite trend was observed for the para-methyl sub-
stituted aryl group with 3ab being delivered in only
26% using diaryliodonium salt 4b (cf. 62% yield with
2b). The para-halogen-substituted diaryliodonium
salts 4e and 4g reacted smoothly, however, affording
3ae, which bears a bromoaryl group amenable to fur-
ther functionalization, and 3ag in 65% and 82%
yields, respectively. A broad range of functional
groups was also tolerated under these conditions al-
though 3fa, which bears an electron-rich and poten-
tially photoredox active methoxyphenyl ether motif,
was formed in a comparatively low yield of 26%. A
selection of different alcohols was successfully cou-
pled with 1-octene (1a) and diphenyliodonium salt 4a
when employed as the solvent in place of methanol.
Acetic acid was also a suitable oxygen nucleophile,
furnishing the corresponding acetoxylated product 7,
albeit in a modest yield of 26%. Diaryliodonium salts
were also shown to be suitable sources of the aryl
coupling partner in intramolecular oxy- and aminoar-
ylation reactions. Reacting alkenyl alcohol 1h and
amine 1i with diphenyliodonium salt 4a under the op-
timized conditions with [Ph3PAu]NTf2 and [Ir
ACHTUNGTRENNUNG(ppy)2
AHCTUNGTRENNUNG
the corresponding heterocyclic products 8 and 9 in
68% and 79% yields, respectively. The oxyarylation
process was also found to be readily scalable with 3aa
being obtained in 91% isolated yield when the reac-
tion was run on a 2.0 mmol scale. Finally the degree
of selectivity afforded by the process using an unsym-
metrical diaryliodonium salt was tested using (phe-
nyl)(para-bromophenyl)iodonium tetrafluoroborate
(4j). Reacting this substrate with 1-octene (1a) under
the optimized conditions in methanol afforded a mix-
ture of 3aa and 3ae in a ratio of 1:1.3, indicating
Scheme 4. Scope and limitations of the gold and iridium
dual-catalyzed intermolecular oxyarylation of alkenes with
diaryliodonium salts. Reaction conditions: 1 (0.2 mmol), (4,
0.8 mmol), [Ph3PAu]NTf2 (10 mol%), [Ir
ACHUTNGTNERNUG(ppy)2CAHTUNGTRENN(GUN dtbbpy)]PF6
(5 mol%) in degassed MeOH (0.1M) reacted under visible
light irradiation (blue LEDs) for 20 h at room temperature. a slight preference for the more electron-deficient
Isolated yields given.
bromo-substituted aryl group (90% combined NMR
yield, see the Supporting Information for more de-
tails).
reveal superior reaction conditions while control reac-
A mechanistic hypothesis for the dual-catalyzed
tions again confirmed the necessity for both catalysts process is shown in Scheme 5. In accordance with pre-
and visible light (Table 1, entries 8–12).[11]
vious reports on the activation of alkenes with sources
The scope and limitations of the dual gold and iridi- of cationic gold(I),[15] we envisage that initial coordi-
um-catalyzed three-component oxyarylation reaction nation of the gold to the double bond followed by nu-
with diaryliodonium salts are displayed in Scheme 4. cleophilic attack of the methanol solvent would lead
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Experimental Section
General Procedure for Oxyarylation with
Aryldiazonium Salts
Fluorescein (3.3 mg, 10.0 mmol, 5 mol%), [Ph3PAu]NTf2
(14.8 mg, 20.0 mmol, 10 mol%), the aryldiazonium salt 2
(0.80 mmol, 4.0 equiv.) and the alkene substrate
1 (0.20 mmol, 1.0 equiv.) were added to a flame-dried
Schlenk flask containing a stirring bar. In the absence of
light, anhydrous methanol (2.0 mL, 0.10M) was added and
the mixture was degassed using three freeze-pump-thaw
cycles. The flask was then flushed with argon, sealed and the
mixture was stirred under irradiation from a desk lamp
fitted with a 23 W fluorescent light bulb (situated ~5 cm
away from the reaction vessel). After evolution of nitrogen
had ceased (16 h), the mixture was stirred for a further
30 min before being filtered through a short pad of silica gel
(eluent=EtOAc) and the solvent was removed under
vacuum. The crude products were purified by column chro-
matography over silica gel.
Scheme 5. Mechanistic hypothesis for the dual catalyzed
oxyarylation process. [PR]=photoredox catalyst {fluorescein
for diazonium salts 2, [Ir
4}.
(dtbbpy)]+ for iodonium salts
ACHUTGTNRNENUG(ppy)2ACHTUNGTRENNUGN
General Procedure for Oxyarylation with
Diaryliodonium Salts
[IrACHTUNGTREN(NGUN ppy)2ACHTUNGTREG(NNNU dtbbpy)]ACHTGUNTREN(NGUN PF6) (9.2 mg, 10.0 mmol, 5 mol%),
to the alkylgold(I) complex A.[16] Concurrently, in the
case of the reaction with aryldiazonium salts 2, excita-
tion of the fluorescein photocatalyst by visible light
followed by single electron transfer (SET) to the di-
azonium compound and subsequent extrusion of ni-
trogen would generate an aryl radical. With diarylio-
donium salts 4, this species would be generated by
SET from the excited state of the iridium catalyst
[Ph3PAu]NTf2 (14.8 mg, 20.0 mmol, 10 mol%), the diarylio-
donium salt 4 (0.80 mmol, 4.0 equiv.) and the alkene sub-
strate 1 (0.20 mmol, 1.0 equiv.) were added to a flame-dried
Schlenk flask containing a stirring bar. In the absence of
light, anhydrous methanol (or other alcohol, 2.0 mL, 0.10M)
was added and the mixture was degassed using three freeze-
pump-thaw cycles. The flask was then flushed with argon,
sealed and the mixture was stirred under irradiation from
blue LEDs (situated ~5 cm away from the reaction vessel in
a custom-made “light box”). After 20 h of irradiation, the
mixture was filtered through a short pad of silica gel
(eluent=EtOAc) and the solvent was removed under
vacuum. The crude products were purified by column chro-
matography over silica gel.
[IrACHTUNGTRENNUNG(ppy)2ACHTUNGTRENNUNG
(dtbbpy)]+ and loss of an aryl iodide mole-
cule. At this stage, oxidation of the gold(I) complex
A by the aryl radical would afford the gold(II) species
B, bearing both the alkyl and aryl coupling part-
ners.[17] SET between this complex and the oxidized
photocatalyst would then deliver the goldACTHNURTGNEU(GN III) species
C and complete the photoredox catalytic cycle. Subse-
quent reductive elimination from C would then result
in product formation and regeneration of the gold(I)
catalyst.
Acknowledgements
In conclusion, we have developed a novel dual cat-
alyzed multicomponent oxyarylation of alkenes com-
bining gold catalysis and visible light photoredox cat-
alysis. Using aryldiazonium salts as sources of the aryl
coupling partner, the inexpensive organic dye fluores-
cein can be used as the photocatalyst while the combi-
The authors thank M. Wꢀnsche and K. Oldiges for experi-
mental assistance. This work was supported by the European
Research Council under the European Communityꢁs Seventh
Framework Program (FP7 2007-2013)/ERC Grant agreement
no. 25936, the NRW Graduate School of Chemistry (B.S.)
and the Alexander von Humboldt Foundation (M.N.H.).
nation of the iridium complex [IrACHTNUGTRNNEUG(ppy)2ACHTUNGTRENN(UGN dtbbpy)]PF6
and visible light from blue LEDs allows for diarylio-
donium salts to be employed. In both cases, the oxyar-
ylation reactions proceed at room temperature under
irradiation from readily accessible visible light sources
and deliver arylated ether products from simple, non-
activated alkenes.
References
[1] Reviews covering transition metal-catalyzed oxyaryla-
tion: a) J. P. Wolfe, Eur. J. Org. Chem. 2007, 571–582;
b) J. P. Wolfe, Synlett 2008, 2913–2937; reviews on relat-
ed aminoarylation processes: c) S. R. Chemler, J. Orga-
nomet. Chem. 2011, 696, 150–158; d) D. M. Schultz, J. P.
Wolfe, Synthesis 2012, 44, 351–361; examples of palladi-
um-catalyzed intermolecular alkene oxyarylation: e) S.
2798
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COMMUNICATIONS
Dual Photoredox and Gold Catalysis
Kirchberg, R. Frçhlich, A. Studer, Angew. Chem. 2010,
122, 7029–7032; Angew. Chem. Int. Ed. 2010, 49, 6877–
6880; f) A. D. Satterfield, A. Kubota, M. S. Sanford,
Org. Lett. 2011, 13, 1076–1079.
A. S. Hosseini, S. R. Chemler, J. Am. Chem. Soc. 2012,
134, 12149–12156.
[7] a) B. Sahoo, M. N. Hopkinson, F. Glorius, J. Am. Chem.
Soc. 2013, 135, 5505–5508; recent report of a gold/pho-
toredox dual catalyzed arylative ring expansion: b) X.-
Z. Shu, M. Zhang, Y. He, H. Frei, F. D. Toste, J. Am.
Chem. Soc. 2014, 136, 5844–5847.
[8] Review on dual catalysis involving visible light photo-
redox catalysis: a) M. N. Hopkinson, B. Sahoo, J.-L. Li,
F. Glorius, Chem. Eur. J. 2014, 20, 3874–3886; general
review on dual catalysis: b) A. E. Allen, D. W. C. Mac-
Millan, Chem. Sci. 2012, 3, 633–658.
[9] Selected recent reviews on visible light photoredox cat-
alysis: a) K. Zeitler, Angew. Chem. 2009, 121, 9969–
9974; Angew. Chem. Int. Ed. 2009, 48, 9785–9789;
b) T. P. Yoon, M. A. Ischay, J. Du, Nature Chem. 2010,
[2] Selected recent reviews on gold catalysis: a) A. Fꢁrst-
ner, Chem. Soc. Rev. 2009, 38, 3208–3221; b) N. Sha-
piro, F. D. Toste, Synlett 2010, 675–691; c) A. S. K.
Hashmi, Angew. Chem. 2010, 122, 5360–5369; Angew.
Chem. Int. Ed. 2010, 49, 5232–5241; d) N. Krause, C.
Winter, Chem. Rev. 2011, 111, 1994–2009; e) M. Ru-
dolph, A. S. K. Hashmi, Chem. Commun. 2011, 47,
6536–6544; f) M. Bandani, Chem. Soc. Rev. 2011, 40,
1358–1367; g) L.-P. Liu, G. B. Hammond, Chem. Soc.
Rev. 2012, 41, 3129–3139; h) M. Rudolph, A. S. K.
Hashmi, Chem. Soc. Rev. 2012, 41, 2448–2462; i) C. Ob-
radors, A. Echavarren, Chem. Commun. 2014, 50, 16–
28.
´
2, 527–532; c) F. Teply, Collect. Czech. Chem. Commun.
[3] Reviews on gold-catalyzed coupling: a) M. N. Hopkin-
son, A. D. Gee, V. Gouverneur, Chem. Eur. J. 2011, 17,
8248–8262; b) H. A. Wegner, M. Auzias, Angew. Chem.
2011, 123, 8386–8397; Angew. Chem. Int. Ed. 2011, 50,
8236–8247.
[4] a) A. D. Melhado, W. E. Brenzovich Jr, A. D. Lackner,
F. D. Toste, J. Am. Chem. Soc. 2010, 132, 8885–8887;
b) L. T. Ball, M. Green, G. C. Lloyd-Jones, C. A. Rus-
sell, Org. Lett. 2010, 12, 4724–4727; c) W. E. Brenzo-
vich Jr, J.-F. Brazeau, F. D. Toste, Org. Lett. 2010, 12,
4728–4731; d) L. T. Ball, G. C. Lloyd-Jones, C. A. Rus-
sell, Chem. Eur. J. 2012, 18, 2931–2937.
[5] Related gold-catalyzed intramolecular oxy- and amino-
arylation reactions: a) G. Zhang, L. Cui, Y. Wang, L.
Zhang, J. Am. Chem. Soc. 2010, 132, 1474–1475;
b) W. E. Brenzovich Jr, D. Benitez, A. D. Lackner,
H. P. Shunatona, E. Tkatchouk, W. A. Goddard III,
F. D. Toste, Angew. Chem. 2010, 122, 5651–5654;
Angew. Chem. Int. Ed. 2010, 49, 5519–5522; c) E.
Tkatchouk, N. P. Mankad, D. Benitez, W. A. Goddar-
d III, F. D. Toste, J. Am. Chem. Soc. 2011, 133, 14293–
14300; d) G. Zhang, Y. Luo, Y. Wang, L. Zhang,
Angew. Chem. 2011, 123, 4542–4546; Angew. Chem.
Int. Ed. 2011, 50, 4450–4454; related gold-catalyzed oxi-
dative difunctionalization reactions of alkenes: e) A.
Iglesias, K. MuÇiz, Chem. Eur. J. 2009, 15, 10563–
10569; f) T. de Haro, C. Nevado, Angew. Chem. 2011,
123, 936–940; Angew. Chem. Int. Ed. 2011, 50, 906–910.
[6] Reviews on addition of aryl radicals derived from aryl-
diazonium salts to alkenes: a) M. R. Heinrich, Chem.
Eur. J. 2009, 15, 820–833; b) D. P. Hari, B. Kçnig,
Angew. Chem. 2013, 125, 4832–4842; Angew. Chem.
Int. Ed. 2013, 52, 4734–4743; selected examples of oxy-
2011, 76, 859–917; d) J. M. R. Narayanam, C. R. J. Ste-
phenson, Chem. Soc. Rev. 2011, 40, 102–113; e) J.
Xuan, W.-J. Xiao, Angew. Chem. 2012, 124, 6934–6944;
Angew. Chem. Int. Ed. 2012, 51, 6828–6838; f) S. Fuku-
zumi, K. Ohkubo, Chem. Sci. 2013, 4, 561–574; g) Y.
Xi, H. Yi, A. Lei, Org. Biomol. Chem. 2013, 11, 2387–
2403; h) C. K. Prier, D. A. Rankic, D. W. C. MacMillan,
Chem. Rev. 2013, 113, 5322–5363; i) J. Xuan, L.-Q. Lu,
J.-R. Chen, W.-J. Xiao, Eur. J. Org. Chem. 2013, 6755–
6770; j) M. Reckenthꢀler, A. G. Griesbeck, Adv. Synth.
Catal. 2013, 355, 2727–2744; k) D. M. Schultz, T. P.
Yoon, Science 2014, 343, DOI: 10.1126/science.1239176.
[10] Applications of aryldiazonium salts in photoredox cat-
alysis, first report: a) H. Cano-Yelo, A. Deronzier, J.
Chem. Soc. Perkin Trans. 2 1984, 1093–1098; selected
recent examples: b) D. Kalyani, K. B. McMurtrey, S. R.
Neufeldt, M. S. Sanford, J. Am. Chem. Soc. 2011, 133,
18566–18569; c) D. P. Hari, P. Schroll, B. Kçnig, J. Am.
Chem. Soc. 2012, 134, 2958–2961; d) P. Schroll, D. P.
Hari, B. Kçnig, ChemistryOpen 2012, 1, 130–133;
e) D. P. Hari, T. Hering, B. Kçnig, Org. Lett. 2012, 14,
5334–5337; f) T. Xiao, X. Dong, Y. Tang, L. Zhou, Adv.
Synth. Catal. 2012, 354, 3195–3199; g) T. Hering, D. P.
Hari, B. Kçnig, J. Org. Chem. 2012, 77, 10347–10352;
h) D. P. Hari, T. Hering, B. Kçnig, Angew. Chem. 2014,
126, 743–747; Angew. Chem. Int. Ed. 2014, 53, 725–728;
i) W. Guo, H.-G. Cheng, L. Y. Chen, J. Xuan, Z.-J.
Feng, J.-R. Chen, L.-Q. Lu, W.-J. Xiao, Adv. Synth.
Catal. 2014, 356, 2787–2793; review on the chemistry of
aryldiazonium salts: j) C. Galli, Chem. Rev. 1988, 88,
765–792.
[11] For further details of the optimization studies and con-
trol reactions, see the Supporting Information.
arylation proceeding via aryl radicals: c) M. R. Hein-
rich, A. Wetzel, M. Kirschstein, Org. Lett. 2007, 9,
3833–3835; d) A. Dickschat, A. Studer, Org. Lett. 2010,
12, 3972–3974; e) T. Taniguchi, H. Zaimoku, H. Ishiba-
shi, Chem. Eur. J. 2011, 17, 4307–4312; f) M. Hartmann,
Y. Li, A. Studer, J. Am. Chem. Soc. 2012, 134, 16516–
16519; g) H. Jasch, S. B. Hçfling, M. R. Heinrich, J.
Org. Chem. 2012, 77, 1520–1532; h) G. Fumagalli, S.
Boyd, M. F. Greaney, Org. Lett. 2013, 15, 4398–4401;
i) S. Kindt, H. Jasch, M. R. Heinrich, Chem. Eur. J.
2014, 20, 6251–6255; recent example of oxyarylation
proceeding via radical cyclization: j) Y. Miller, L. Miao,
[12] The organic dye fluorescein costs E0.24 mmol whereas
[Ru
G
(PF6)2 costs E97.00 mmol (both values taken
from Sigma–Aldrich, June 2014).
[13] Reviews on photoredox catalysis with organic dyes:
a) D. Ravelli, M. Fagnoni, ChemCatChem 2012, 4, 169–
171; b) D. Ravelli, M. Fagnoni, A. Albini, Chem. Soc.
Rev. 2013, 42, 97–113; c) D. A. Nicewicz, T. M. Nguyen,
ACS Catal. 2014, 4, 355–360; d) D. P. Hari, B. Kçnig,
Chem. Commun. 2014, 50, 6688–6699.
[14] a) S. R. Neufeldt, M. S. Sanford, Adv. Synth. Catal.
2012, 354, 3517–3522; b) Y.-X. Liu, D. Xue, J.-D. Wang,
C.-J. Zhao, Q.-Z. Zou, C. Wang, J. Xiao, Synlett 2013,
Adv. Synth. Catal. 2014, 356, 2794 – 2800
ꢃ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2799

COMMUNICATIONS
Matthew N. Hopkinson et al.
24, 507–513; c) M. Tobisu, T. Furukawa, M. Chantani,
Chem. Lett. 2013, 42, 1023–1205.
[15] R. L. LaLonde, W. E. Brenzovich Jr, D. Benitez, E.
Tkatchouk, K. Kelley, W. A. Goddard III, F. D. Toste,
Chem. Sci. 2010, 1, 226–233.
[16] Alternatively, oxidation of gold(I) by an aryl radical
could precede coordination to the alkene and nucleo-
philic attack of the alcohol. This order of events was re-
cently proposed for a related arylative ring expansion
process (see ref.[7b]). The suitability of coordinatively
saturated gold(I) complexes such as Ph3PAuCl and
Cy3PAuCl as catalysts in this process (albeit less effi-
cient ones) is best explained by such a mechanism.
[17] Previous report on the oxidation of gold by aryl radi-
cals: a) C. Aprile, M. Boronat, B. Ferrer, A. Corma, H.
Garcꢄa, J. Am. Chem. Soc. 2006, 128, 8388–8389; re-
cently, Toste et al. also reported the oxidation of gold
by the trifluoromethyl radical: b) M. S. Winston, W. J.
Wolf, F. D. Toste, J. Am. Chem. Soc. 2014, 136, 7777–
7782.
2800
asc.wiley-vch.de
ꢃ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 2794 – 2800