Oxidative annulation of anilides with internal alkynes using an (Electron-Deficient η5-cyclopentadienyl)rhodium(III) catalyst under ambient conditions

Article abstract of DOI:10.1002/adsc.201300884

A dinuclear (electron-deficient η⁵-cyclopentadienyl) rhodium(III) complex was synthesized on a preparative scale via the rhodium-catalyzed cross [2+2+1] cyclotrimerization of silylacetylenes and two alkynyl esters, leading to substituted silylf

Full text of DOI:10.1002/adsc.201300884

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DOI: 10.1002/adsc.201300884
Oxidative Annulation of Anilides with Internal Alkynes Using an
(Electron-Deficient h5-Cyclopentadienyl)Rhodium
(III) Catalyst
G
Under Ambient Conditions
Yuki Hoshino,a Yu Shibata,a and Ken Tanakaa,b,*
a
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology,
Koganei, Tokyo 184-8588, Japan
Fax : (+81)-42-388-7037; e-mail: tanaka-k@cc.tuat.ac.jp
Japan Science and Technology Agency (JST), ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
b
Received: September 10, 2013; Revised: December 18, 2013; Published online: January 31, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300884.
Abstract:
cyclopentadienyl)rhodiumAHCTNUGTRENNNUG
A
dinuclear (electron-deficient h5- precatalyst for the oxidative annulation of anilides
(III) complex was synthe- with internal alkynes under ambient conditions (at
sized on a preparative scale via the rhodium-cata- room temperature under air). A preference for annu-
lyzed cross[2+2+1]cyclotrimerization of silylacety- lation across electron-rich substrates over electron-
lenes and two alkynyl esters, leading to substituted deficient substrates was observed using this electron-
silylfulvenes, followed by reductive complexation deficient rhodium
with rhodium(III) chloride in ethanol. The thus ob-
tained dinuclear (electron-deficient
h5-cyclo- Keywords: alkynes; anilides; annulation; C H bond
pentadienyl)rhodium(III) complex is a highly active functionalization; rhodium
ACHTUNGTREN(NUNG III) complex.
ACHTUNGTRENNUNG
À
N
ACHTUNGTRENNUNG
Introduction
À
The C H bond functionalization reactions catalyzed
by (h5-cyclopentadienyl)rhodium
N
have been widely examined and numerous successful
examples have been reported.[2] The majority of re-
ports employed
a
commercially available (h5-
pentamethylcyclopentadienyl)rhodiumACTHNUGTREN(NUG III) complex
(Cp*RhX2) as the catalyst. In order to improve the
selectivity and reactivity, sterically or electronically
tuned cyclopentadienyl ligands have been investigated
recently in rhodium catalysis (Scheme 1).[3–7] For ex-
amples of sterically tuned cyclopentadienyl ligands,
Satoh, Miura, and co-workers reported that the use of
phenyl-substituted cyclopentadienes as ligands could
improve the catalytic activity and change the reaction
À
pathway in the rhodium-catalyzed oxidative C H
bond functionalization.[5] Rovis and co-workers re-
ported that the use of
a tert-butyl-substituted
cyclopentadienylrhodium
AHCTUNGTRENNUNG
proves the regioselectivity in the oxidative pyridone
synthesis[6] and inverts the regioselectivity in the oxi-
dative pyridine synthesis.[7] However, only a single ex-
ample has been reported for the electronically tuned
cyclopentadienyl ligand. Rovis and co-workers tested
À
Scheme 1. Directed C H bond functionalization catalyzed
cyclopentadienyl- by CpRhACHTGNURTEN(NUGN III)-type complexes.
a
trifluoromethyl-substituted
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complex 4 were synthesized on a preparative scale.
Trimethylsilylacetylene 1 (0.91 g) and ethyl 2-butyn-
ACHUTNGRENNUoG ate 2 (1.12 g) were treated with [RhACHTUNGTREN(NUNG cod)2]BF4
(5 mol%) in dioxane at 808C to give the correspond-
ing silylfulvene 3 (1.55 g) in 76% isolated yield. Sub-
sequent reductive complexation of 3 with RhCl3 in
EtOH at 808C furnished the corresponding rhodium-
AHCTUNGTREG(NNUN III) complex 4 (1.30 g) in 80% isolated yield. These
isolated yields are comparable to the small-scale syn-
thesis [3: 80% isolated yield (98 mg) and 4: 88% iso-
lated yield (75 mg)].[10] Importantly, the use of EtOH
is essential for the reductive complexation step. The
use of MeOH or i-PrOH did not afford complex 4.
A mechanistic proposal for the reductive complexa-
tion of silylfulvene 3 with RhCl3 in EtOH, leading to
(electron-deficient h5-cyclopentadienyl)rhodium
ACHTUNGTRENNUNG(III)
Scheme 2. Preparative scale synthesis of silylfulvene 3 and
rhodium(III) complex 4.
N
complex 4, is shown in Scheme 3.[12] RhCl3·H2O reacts
with EtOH to generate rhodium ethoxide A and
R
ACHTUNGTRENNUNG
(III) complex (CpCF3RhX2) in the oxidative HCl.[13] Elimination of acetaldehyde from A affords
AHCTUNGTRENNUNG
A
ACHTUNGTRENN(UNG III)/Cp*
via the rhodium(I)-catalyzed cross[2+2+1]cyclotri- complex, derived from [Cp*RhCl2]2, is a highly effec-
merization[8] of silylacetylenes and two alkynyl esters, tive catalyst for a number of C H bond functionaliza-
À
leading to substituted silylfulvenes,[9] followed by re- tion reactions.[2] For example, Fagnou and co-workers
ductive complexation with RhCl3 (Scheme 1).[10] reported the oxidative annulation of acetanilides with
Pleasingly, this new electron-deficient rhodiumACTHUNTGRENNUG(III) internal alkynes using the dicationic rhodiumACHTUNGTERN(NUGN III)/Cp*
complex is a highly active and selective precatalyst
for the oxidative annulation of acetanilides with an in-
ternal alkyne.[10] In this full paper, we wish to present
full details of our study on the oxidative annulation of
anilides with alkynes using the (electron-deficient h5-
cyclopentadienyl)rhodium
ACHTUNGTNER(NUNG III) catalyst under ambient
conditions.[11]
Results and Discussion
As shown in Scheme 2, silylfulvene 3 and dinuclear
Scheme 4. Fagnouꢁs oxidative annulation of acetanilide 5a
ACTHNUTRGNEUNG
(electron-deficient h5-cyclopentadienyl)rhodium(III) with diphenylacetylene (6a) using [Cp*RhCl2]2.[14]
Scheme 3. Plausible mechanism for the formation of 4.
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Oxidative Annulation of Anilides with Internal Alkynes
7ma can also be explained by the larger steric
demand of the methyl group than the methoxy group.
Both electronic and steric factors showed smaller
impact on the product yields when using the
CpERh
ACTHNUTRGENNUG(III) catalyst than using the Cp*RhACHTUNTGREN(NUNG III) cata-
lysts.[15a,b] With respect to internal alkynes, a variety of
diaryl (6b, c) and aryl-alkyl (6d–i) acetylenes reacted
with 5a to give the corresponding indoles 7ab–ai in
good to high yields. Trimethylsilyl-substituted alkyne
6j and ethoxycarbonyl-substituted alkyne 6k were
also able to react with 5a, although the product yields
were moderate. The successful use of labile cyclo-
propyl- or trimethylsilyl-substituted alkynes 6g, j and
sterically demanding alkynes 6h, i is worthy of note.
In terms of regioselectivity, the use of monoarylacety-
Scheme 5. Oxidative annulation of acetanilides 5a, b with di-
phenylacetylene (6a) using 4 or [Cp*RhCl2]2 under ambient
conditions.[10]
complex as a catalyst.[15–17] In their initial communica- lenes 6d–k showed good to high regioselectivities and
tion, the reaction of acetanilide 5a with diphenylace- aryl groups are located in 2-position of the product in-
tylene (6a) was conducted at high temperature doles except tert-butyl-substituted internal alkyne 6i.
(1208C, 1 h) using [Cp*RhCl2]2 as a precatalyst and Unfortunately, poor regioselectivities were observed
a stoichiometric amount of CuACTHNUTRGENUN(G OAc)2 as an oxidant using unsymmetrical diarylacetylenes 6b, c, possessing
to give the corresponding indole 7aa in 81% yield electronically or sterically different aryl groups. Im-
(Scheme 4).[15a] In their subsequent article, the same portantly, dialkylacetylenes showed low reactivity in
reaction proceeded under mild conditions (608C, the Cp*Rh
16 h) in improved product yield (90%) by using an on the contrary, dialkylacetylenes 6l, m were highly
isolated dicationic rhodium(III)/Cp* (III) cata-
complex, reactive substrates when using the CpERh
[Cp*Rh(MeCN)3][SbF6]2, as a catalyst and O2/a cata- lyst.
lytic amount of Cu The preparative reaction of 5a with 6a was conduct-
(OAc)2 as oxidants (Scheme 4).[15b]
It was anticipated that an in situ generated elec- ed under low catalyst loading as shown in Scheme 7.
tron-deficient dicationic rhodium(III) complex, de- Pleasingly, indole 7aa was obtained in quantitative
rived from 4, would show higher catalytic activity yield.
ACHTUNGTRENUN(NG III) complex-catalyzed indole synthesis,
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
than dicationic Cp*Rh
philic C H bond activation of acetanilides. Indeed, in the Cp*Rh
G
Boc-protected anilide 5o was ineffective substrate
(III) complex-catalyzed indole synthesis
À
G
the reactions of acetanilides 5a and 5b with diphenyl- presumably due to attenuated Lewis basicity at the
ACHTUNGTRENNUNG
acetylene (6a) proceeded at room temperature under amide oxygen.[15b] Pleasingly, 5o was able to react
air to give the corresponding indoles 7aa and 7ba in with both diaryl- and dialkylacetylenes 6a, l to give
quantitative yields (Scheme 5).[10] Under the same re- the corresponding indoles 7oa and 7ol in high yields,
action conditions, the use of [Cp*RhCl2]2 in place of 4 although high catalyst loadings (5 mol% 4) were re-
significantly decreased the product yields due to low quired (Scheme 8).
substrate conversions (Scheme 5).[10]
Fagnou and co-workers reported that not only ani-
The scope of the rhodium-catalyzed oxidative annu- lides but also enamides are able to react with internal
lation of acetanilides 5 with internal alkynes 6 under alkynes to give the corresponding pyrroles by using
ambient conditions is shown in Scheme 6. With re- the dicationic rhodiumACHTNUGTRNEUNG(III)/Cp* complex, derived
spect to acetanilides, both electron-deficient and elec- from [Cp*RhCl2]2.[15b,18] They reported that enamides
tron-rich acetanilides 5c–i smoothly reacted with 6a to are more reactive than anilides, and so the reaction of
give the corresponding indoles 7ca–ia in high yields. enamide 8 with 6a (Scheme 9) proceeds at room tem-
The reactions of meta-substituted anilides 5g–j provid- perature to give the desired pyrrole 9a in high yield
ed 6-substituted indoles 7ga–ja as the major regioiso- (88%) by using the isolated dicationic rhodium
mer. 6-Methyl- and 6-trifluoromethyl-substituted in- Cp* complex, [Cp*Rh(MeCN)3][SbF6]2, as a catalyst
doles 7ia and 7ja were each obtained as a single re- and O2/a catalytic amount of Cu(OAc)2 as oxi-
ACHTUNGTRENNUNG(III)/
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
gioisomer, while 6-chloro- and 6-methoxy-substituted dants.[14b] The same reaction conditions, employed in
indoles 7ga and 7ha were obtained as an about 2:1 the indole synthesis (Scheme 6), were applied to the
mixture of regioisomers, presumably due to larger oxidative annulation of 8 with 6a, which revealed that
steric demand of the methyl and trifluoromethyl the desired pyrrole 9a was obtained in high yield
groups than the chloro and methoxy groups. Sterically (Scheme 8). Under the identical conditions, the use of
demanding acetanilides 5k–n were also able to react [Cp*RhCl2]2 in place of 4 significantly decreased the
with 6a to give the corresponding indoles 7ka–na in product yield due to low substrate conversion
moderate to high yields. The higher yield of 7la than (Scheme 8). Not only diarylacetylene 6a but also
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Scheme 6. Oxidative annulation of acetanilides 5c–n with internal alkynes 6a–m using 4 under ambient conditions.
Scheme 8. Oxidative annulation of Boc-protected anilide 5o
with internal alkynes 6a, l using 4 under ambient conditions.
Scheme 7. Preparative scale reaction of 5a with 6a under
low catalyst loading.
alkyl
G
A plausible mechanism for the rhodiumACTHNGUTERN(UNG III)-cata-
employed for this pyrrole synthesis, although the lyzed indole and pyrrole synthesis, proposed by
product yields decreased (Scheme 8).
Fagnou and co-workers, is shown in Scheme 10.[14b]
À
Rhodium
N
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Oxidative Annulation of Anilides with Internal Alkynes
Scheme 9. Oxidative annulation of enamide 8 with alkynes
6a, 6d, and 6l using 4 or [Cp*RhCl2]2 under ambient condi-
tions.
age of anilide 5 or enamide 8 producing amide
oxygen-coordinated rhodiumACTHNUGTRNEUNG(III) complex B. Coordi-
nation of internal alkyne 6 forms intermediate C, fol-
lowed by migratory insertion of 6 to afford azarhoda-
À
cyle D. C N bond reductive elimination affords the
desired indole 7 or pyrrole 9 along with rhodium(I)
complex E. This rhodium(I) complex E is then oxi-
dized back to the active rhodiumACTHNUTRGNEUNG(III) complex A with
copper(II) acetate which is then reoxidized by the
combination of molecular oxygen and acetic acid.
Scheme 11. Chemoselectivity between anilide and benza-
mide C H bonds in N-phenylbenzamide (5p).
À
À
We anticipated that highly electrophilic nature of sively afforded indole 7pa through the anilide C H
À
rhodium
G
bond cleavage of electron-rich substrates over elec- conditions, electron-deficient complex 4 showed sig-
tron-deficient substrates. Indeed, the reaction of N- nificantly higher catalytic activity than electron-rich
phenylbenzamide (5p) with 6a under the same condi- [Cp*RhCl2]2. On the contrary, the reaction of 5p with
tions (conditions A), employed in Scheme 6, exclu- 6a in the absence of a silver salt (conditions B), re-
Scheme 10. Plausible mechanism for the formation of 7 and 9.
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Scheme 12. Competition experiments between electron-defi-
cient and electron-rich anilides (5b and 5f).
ported in the oxidative annulation of benzamide with
alkynes,[19] exclusively afforded isoquinolone 10pa
through the benzamide C H bond cleavage
(Scheme 11). Under these reaction conditions, elec-
Scheme 14. Reaction of 5a-d5 and 6a using
[Cp*RhCl2]2 as the precatalyst under ambient conditions.
4
and
À
tron-rich [Cp*RhCl2]2 showed higher catalytic activity The preference for the migratory insertion across
than electron-deficient complex 4. electron-rich alkyne 6l over electron-deficient alkyne
Similarly, the intermolecular competition experi- 6a was observed using electron-deficient complex 4.
ments between electron-deficient and electron-rich On the contrary, the slight preference for the migrato-
anilides 5b and 5f with 6a revealed that the prefer- ry insertion across electron-deficient alkyne 6a over
ence for annulation across electron-rich anilide 5f electron-rich alkyne 6l was observed using electron-
over electron-deficient anilide 5b is more significant rich [Cp*RhCl2]2.[20]
on using electron-deficient complex 4 than electron-
rich [Cp*RhCl2]2 (Scheme 12).
Reversibility of the acetanilide cyclorhodation was
examined under ambient conditions by using 4 and
We anticipated that highly electrophilic nature of and [Cp*RhCl2]2 (Scheme 14). The metalation of acet-
rhodium(III) complex B would also facilitate migrato- anilide was found to be irreversible using both 4 and
ACHTUNGTRENNUNG
ry insertion of electron-rich internal alkynes over and [Cp*RhCl2]2 as the precatalysts, with almost no
electron-deficient internal alkynes. Thus, the intermo- loss in deuterium from both 5a-d5 and 7aa-d4.
lecular competition experiments between electron-de-
ficient diarylacetylene 6a and electron-rich dialkyl- were investigated in the reactions of 5a, 5a-d5, and 6a
ACHTUNGTRENNUNGacetylene 6l with 5a were conducted (Scheme 13).
Thus, deuterium kinetic isotope effects (DKIE)
Scheme 13. Competition experiments between diaryl- and
dialkylacetylenes (6a and 6l).
Scheme 15. Reaction of 5a, 5a-d5, and 6a using 4 and
[Cp*RhCl2]2 as the precatalyst under ambient conditions.
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Oxidative Annulation of Anilides with Internal Alkynes
(1:1:1) using 4 and [Cp*RhCl2]2 as the precatalyst Preparative Scale Synthesis of Rhodium
under ambient conditions (Scheme 15). The study re- Complex 4
vealed that DKIE using 4 is significantly smaller than
ACHTUNGTNER(NUNG III)
To an ethanol (4.0 mL) solution of RhCl3·nH2O (38.16 wt%
Rh, 1.00 g, 3.81 mmol Rh) was added an ethanol (6.0 mL)
solution of 3 (1.55 mg, 3.81 mmol), and the mixture was
stirred at 808C for 16 h. The resulting solution was concen-
trated under reduced pressure. The residue was diluted with
CH2Cl2 (40 mL) and filtered. The filtrate was poured into
hexane (200 mL). The resulting precipitates were collected,
washed with Et2O (20 mL) twice, and dried under vacuum
to give 4 as a red powder; yield: 1.30 g (1.53 mmol, 80%).
that using [Cp*RhCl2]2. Therefore, the electron-defi-
À
cient catalyst 4 would facilitate the C H bond activa-
tion step in the catalytic cycle.
Conclusions
In conclusion, a dinuclear (electron-deficient h5-
cyclopentadienyl)rhodiumACTHNUGRTNEUNG(III) complex was synthe-
Dichloro
pentadienyl]rhodium
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
sized on a preparative scale via the rhodium-catalyzed
cross[2+2+1]cyclotrimerization of silylacetylenes and
two alkynyl esters, leading to substituted silylfulvenes,
followed by reductive complexation with RhCl3 in
EtOH. The thus obtained dinuclear (electron-defi-
500 MHz): d=4.45–4.33 (m, 8H), 2.23 (s, 6H), 1.96 (s,
12H), 1.36 (t, J=6.9 Hz, 12H); 13C NMR (CDCl3,
125 MHz): d=163.9, 110.5 (d, J=7.2 Hz), 102.4 (d, J=
7.2 Hz), 77.2 (d, J=9.6 Hz), 62.6, 14.1, 12.5, 11.2.
cient h5-cyclopentadienyl)rhodium
ACHTUNGTRENNUNG
tion of anilides with internal alkynes under ambient Typical Procedure for Rhodium-Catalyzed Oxidative
conditions (at room temperature under air). Employ- Annulation Under Ambient Conditions (7ca, Scheme
ing air as a terminal oxidant in acetone at room tem- 6)
perature is operationally more convenient than the
To a 13.5-mL screw-cap vial bottle was added AgSbF6
(6.9 mg, 0.020 mmol), Rh(III) complex (4.3 mg,
0.0050 mmol), Cu(OAc)2·H2O (8.0 mg, 0.040 mmol), 4’-
previously reported Fagnou system (employing O2 as
a terminal oxidant in tert-amyl alcohol at 608C). Our
new CpERhX2 precatalyst 4 is more active for the di-
G
4
AHCTUNGTRENNUNG
chloroacetanilide (5c, 33.9 mg, 0.200 mmol), diphenylacety-
lene (6a, 39.2 mg, 0.220 mmol), and acetone (1.0 mL) under
air in this order. The mixture was sealed and stirred at room
temperature under air for 16 h. The resulting mixture was
diluted with ether, filtered through a silica gel pad, and
washed with EtOAc. The solvent was concentrated under
reduced pressure and the residue was purified by a prepara-
tive TLC (hexane/toluene/CH2Cl2 =1:2:1) to give 7ca; yield:
66.3 mg (0.192 mmol, 96%).
À
rected C H bond functionalization of electron-rich
arenes than the conventional Cp*RhX2 precatalyst.
The preference for annulation across electron-rich
substrates over electron-deficient substrates was ob-
served using this electron-deficient rhodiumACTHNUTRGENUG(N III) com-
plex. The study of deuterium kinetic isotope effects
revealed that the electron-deficient catalyst 4 would
À
facilitate the C H bond activation step in the catalyt-
ic cycle.
1-(5-Chloro-2,3-diphenylindol-1-yl)ethanone (7ca): Color-
less solid; mp 204.2–205.08C; IR (KBr): n=3084, 3061,
1
3029, 1702, 1447 cmÀ1; H NMR (CDCl3, 500 MHz): d=8.41
(d, J=8.5 Hz, 1H), 7.54–7.50 (m, 1H), 7.41–7.23 (m, 9H),
7.22–7.16 (m, 2H), 1.99 (s, 3H); 13C NMR (CDCl3,
125 MHz): d=171.5, 136.3, 135.2, 132.6, 132.5, 130.8, 130.7,
130.0, 129.5, 129.0, 128.8, 128.5, 127.3, 125.6, 122.8, 119.2,
117.6, 27.9; HR-MS (ESI): m/z=368.0816, calcd. for
C22H16NONaCl [M+Na]+: 368.0813.
Experimental Section
Preparative Scale Synthesis of Silylfulvene 3
To a 1,4-dioxane (2.0 mL) suspension of [RhACTHUNTRGNE(UNG cod)2]BF4
(0.102 g, 0.250 mmol) was added a 1,4-dioxane (8.0 mL) so-
lution of 1 (0.912 g, 5.00 mmol) and 2 (1.121 g, 10.00 mmol),
and the mixture was stirred at 808C for 24 h. The resulting
solution was concentrated under reduced pressure and puri-
Rhodium-Catalyzed Oxidative Annulation Under
Ambient Conditions on a Preparative Scale (7aa,
Scheme 7)
fied by
a silica gel column chromatography (hexane/
EtOAc=5:1) to give 3 as a red oil; yield: 1.55 g (3.81 mmol,
76%); E/Z=78:22.
To
(27.5 mg, 0.080 mmol), Rh
0.020 mmol), Cu(OAc)2·H2O (31.9 mg, 0.160 mmol), acetani-
lide (5a, 270.3 mg, 2.00 mmol), diphenylacetylene (6a,
392.1 mg, 2.20 mmol), and acetone (10 mL) under air in this
order. The flask was sealed and the mixture stirred at room
temperature under air for 72 h. The resulting mixture was
diluted with ether, filtered through a silica gel pad, and
washed with EtOAc. The solvent was concentrated under
reduced pressure and the residue was purified by a silica gel
a
50-mL round-bottom flask was added AgSbF6
A
4
2,4-Dimethyl-5-[(triisopropylsilanyl)methylene]cyclopen-
ta-1,3-diene-1,3-dicarboxylic acid diethyl ester (3, E/Z=
78:22): 1H NMR (CDCl3, 500 MHz): d=7.86 (s, 1H), 4.32
(q, J=7.2 Hz, 2H), 4.31 (q, J=7.2 Hz, 2H), 2.47 (s, 3H),
2.36 (s, 3H), 1.39–1.28 (m, 3H), 1.37 (t, J=7.2 Hz, 6H), 1.11
(d, J=7.4 Hz, 18H); 13C NMR (CDCl3, 125 MHz): d=165.5,
165.1, 156.9, 151.9, 147.3, 144.8, 133.9, 120.9, 60.3, 59.8, 19.1,
15.2, 14.4, 14.2, 13.6, 13.2.
ACHTUNGTRENNUNG
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column chromatography (hexane/EtOAc=5:1) to give
7aa;[10]yield: 622.8 mg (2.00 mmol, >99%).
[4] As sterically tuned cyclopentadienyl ligands, several
chiral cyclopentadienyl ligands have been prepared for
À
the rhodium-catalyzed asymmetric C H bond function-
alization. For recent examples, see: a) J. M. Zimbron,
T. Heinisch, M. Schmid, D. Hamels, E. S. Nogueira, T.
Schirmer, T. R. Ward, J. Am. Chem. Soc. 2013, 135,
5384; b) B. Ye, N. Cramer, J. Am. Chem. Soc. 2013,
135, 636; c) B. Ye, N. Cramer, Science 2012, 338, 504;
d) T. K. Hyster, L. Knçrr, T. R. Ward, T. Rovis, Science
2012, 338, 500; e) J. Dimroth, J. Keilitz, U. Schedler, R.
Schomꢄcker, Adv. Synth. Catal. 2010, 352, 2497; f) M.
Ito, Y. Endo, N. Tejima, T. Ikariya, Organometallics
2010, 29, 2397.
Acknowledgements
This work was supported partly by Grants-in-Aid for Scien-
tific Research (Nos. 23105512 and 25105714) from the Minis-
try of Education, Culture, Sports, Science and Technology
(MEXT, Japan) and ACT-C from Japan Science and Tech-
nology Agency (JST, Japan). We thank Umicore for generous
support in supplying the rhodium complex.
[5] a) T. Uto, M. Shimizu, K. Ueura, H. Tsurugi, T. Satoh,
M. Miura, J. Org. Chem. 2008, 73, 298; b) M. Shimizu,
H. Tsurugi, T. Satoh, M. Miura, Chem. Asian J. 2008, 3,
881; c) N. Umeda, H. Tsurugi, T. Satoh, M. Miura,
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(5 mol%) and Cu
ACHUTNGTREN(NUG MeCN)3]ACHTUNGTRENNUNG[SbF6]2
AHCTUNGTRENNUNG
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