Gold(I)-catalyzed enantioselective intermolecular hydroarylation of allenes with indoles and reaction mechanism by density functional theory calculations

Article abstract of DOI:10.1002/asia.201000651

Chiral binuclear gold(I) phosphine complexes catalyze enantioselective intermolecular hydroarylation of allenes with indoles in high product yields (up to 90 %) and with moderate enantioselectivities (up to 63%ee). Among the gold(I) complexes examined, be

Full text of DOI:10.1002/asia.201000651

FULL PAPERS
DOI: 10.1002/asia.201000651
Gold(I)-Catalyzed Enantioselective Intermolecular Hydroarylation of
Allenes with Indoles and Reaction Mechanism by Density Functional Theory
Calculations
Ming-Zhong Wang,[a] Cong-Ying Zhou,[a] Zhen Guo,[a] Ella Lai-Ming Wong,[a]
Man-Kin Wong,[a, b] and Chi-Ming Che*[a]
812
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Chem. Asian J. 2011, 6, 812 – 824

Abstract: Chiral binuclear gold(I)
phosphine complexes catalyze enantio-
selective intermolecular hydroarylation
of allenes with indoles in high product
yields (up to 90%) and with moderate
enantioselectivities (up to 63% ee).
Among the gold(I) complexes exam-
ined, better ee values were obtained
tioselectivity of the reaction. Electron-
withdrawing groups on the indole sub-
strates decrease the enantioselectivity
of the reaction. The relative reaction
rates of the hydroarylation of 4-X-sub-
stituted 1,3-diarylallenes with N-meth-
ylindole in the presence of catalyst 4c
vealing both the build-up of positive
charge at the allene and electrophilic
nature of the reactive AuI species. Two
plausible reaction pathways were inves-
tigated by density functional theory
calculations, one pathway involving in-
termolecular nucleophilic addition of
free indole to aurated allene intermedi-
ate and another pathway involving in-
tramolecular nucleophilic addition of
aurated indole to allene via diaurated
intermediate E2. Calculated results re-
vealed that the reaction likely proceeds
via the first pathway with a lower acti-
[(AuCl)2(L3)]/AgOTf
[L3=(S)-(À)-
with binuclear gold(I) complexes,
MeO-biphep], determined through
competition experiments, correlate
(r2 =0.996) with the substituent con-
stants s. The slope value is À2.30, re-
I
À
which displayed intramolecular Au
AuI interactions. The binuclear gold(I)
complex 4c [(AuCl)2(L3)] with chiral
biaryl phosphine ligand (S)-(À)-MeO-
biphep (L3) is the most efficient cata-
lyst and gives the best ee value of up to
63%. Substituents on the allene reac-
tants have a slight effect on the enan-
Keywords: allenes
·
enantioselec-
I
I
À
vation energy. The role of Au Au in-
teractions in affecting the enantioselec-
tivity is discussed.
tivity
·
gold
·
hydroarylation
·
indoles
Introduction
tionalization or isomerization of allenes catalyzed by chiral
binuclear gold(I) phosphine complexes [(AuX)2A(P-P)] (P-
CTHUNGTRENNUNG
À
À
Stereoselective addition of indolyl C H bonds across C C
multiple bonds is an efficient and atom-economical strategy
for the synthesis of enantiopure indole compounds which
are prevalent in bioactive natural products and drug leads.[1]
It has been reported that chiral Lewis acids and Brønsted
acids can catalyze asymmetric Friedel–Crafts alkylation of
indole with an alkene conjugated to an electron-withdrawing
group (ketone or nitro group) in high enantioselectivity.[2]
This strategy involves the interaction of a chiral Lewis acid
or Brønsted acid with an electron-withdrawing substituent
on the alkene. However, the catalytic enantioselective hy-
P=chiral bisphosphine) with high enantioselectivity.[6] In
early 2007, the groups of Toste and Widenhoefer independ-
ently reported the gold(I)-catalyzed enantioselective intra-
molecular hydroalkoxylation[6a] and hydroamination[6b] reac-
tions of allenes with up to 99% enantioselectivity. Shortly
after, Widenhoefer and co-workers extended this protocol
to enantioselective intramolecular hydroarylation of 2-(alle-
nyl)indoles (72–92% ee).[3d] With a similar catalytic system,
Toste and co-workers developed a highly enantioselective
intramolecular [2+2] cycloaddition of g-eneallenes (54–
97% ee).[6c] In the same year, Gagnꢁ and co-workers report-
ed a gold(I)-catalyzed enantioselective hydrovinylation of
allenes to form substituted vinylcyclohexenes (45–
72% ee).[6d] More recently, Lꢂpez and co-workers reported
an enantioselective [4+2] intramolecular cycloaddition of al-
lenedienes catalyzed by chiral gold(I) phosphoramidite com-
plexes (52–97% ee).[6h] Despite these advances, to our
knowledge, there has been no report on gold-catalyzed
enantioselective intermolecular hydroarylation of allenes
À
droarylation of unactivated C C multiple bonds with in-
doles through direct coordination and activation of p bonds
by transition-metal ions remains a formidable challenge.[3]
In recent years, AuI and AuIII complexes have emerged to
À
become useful catalysts for electrophilic activation of C C
multiple bonds toward nucleophilic attack.[4] Although AuI
complexes can efficiently and selectively catalyze a number
of organic transformations under mild conditions, only a
handful of examples of AuI-catalyzed enantioselective or-
ganic transformations have been reported.[5,6] Among them,
a notable example is enantioselective intramolecular func-
with arenes.[7] As part of our program to develop gold-cata-
[8]
À
lyzed functionalization of C C multiple bonds, herein is
described an efficient enantioselective intermolecular hydro-
arylation of racemic allenes with indoles catalyzed by chiral
binuclear gold(I) phosphine complexes. Our DFT calcula-
tions revealed that the reaction mechanism involves inter-
molecular nucleophilic addition of free indole to an aurated
[a] M.-Z. Wang, Dr. C.-Y. Zhou, Dr. Z. Guo, Dr. E. L.-M. Wong,
Dr. M.-K. Wong, Prof. C.-M. Che
Department of Chemistry, State Key Laboratory of Synthetic
Chemistry, and Open Laboratory of Chemical Biology of the Institute
of Molecular Technology for Drug Discovery and Synthesis
The University of Hong Kong
Pokfulam Road, Hong Kong (P. R. China)
Fax : (+852)2857-1586
I
I
À
allene intermediate, and the intramolecular Au Au interac-
tion plays a key role in affecting the enantioselectivity of
the reaction.
E-mail: cmche@hku.hk
[b] Dr. M.-K. Wong
Results and Discussion
Department of Applied Biology and Chemical Technology
The Hong Kong Polytechnic University
Hung Hom, Kowloon, Hong Kong (P. R. China)
We recently reported a gold- and a silver-mediated highly
enantioselective synthesis of axially chiral allenes.[9] At the
outset, we investigated the enantioselective hydroarylation
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201000651.
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C.-M. Che et al.
FULL PAPERS
Table 2. Screening of ligands and reaction conditions for enantioselective
of chiral allenes with indoles. The reaction of chiral allene
2a (98% ee) with N-methyl indole 1a in the presence of
5 mol% AuCl/AgOTf at room temperature for 6 h led to 3-
alkylated indole 3a in 95% yield of isolated product without
any enantioselectivity being observed (Table 1, entry 1). A
intermolecular hydroarylation of racemic allene 2b with indole 1a.[a]
Table 1. Gold-catalyzed intermolecular hydroarylation of axially chiral
allene 2a with indole 1a.[a]
Entry Catalyst
Solvent
t
Yield
ee
[h] [%][b]
[%][c]
1
2
3
4
5
6
7
8
N
toluene 12
toluene 12
toluene 16
toluene 36
toluene 16
toluene 16
toluene 16
toluene 16
toluene 16
toluene 16
91
85
90
52
90
82
89
57
trace
trace
82
65
32
18
18
60
17
50
6.5
25
49
–
Entry Catalyst
Solvent
t
Yield
ee
[h] [%][b]
[%][c]
1
2
3
4
AuCl/AgOTf
(PPh3)AuCl/AgOTf
(PPh3)AuCl/AgOTf
[P(tBu)2(o-biphenyl)]AuCl/
THF
toluene
THF
6
6
6
6
95
90
92
60
0
5
0
0
9[d]
10[d]
11
12
13
14
G
–
ACHTUNGTRENNUNG
THF
16
43
48
53
39
N
toluene
CH3CN 16
AgOTf
5
[P(4-MeOC6H4)3]AuCl/
AgOTf
toluene 12 85
0
toluene 16
toluene 16
93
6
7
8
9
G
toluene 12 83
toluene 12 trace
0
–
–
–
15
87
58
toluene
6
trace
[a] Reactions were conducted with 1.5 mmol of 1a, 0.3 mmol of 2b, and
2.5 mol% (AuCl)2(L) /5 mol% AgOTf in 1 mL of toluene at 258C for
16–36 h. [b] Yield of isolated product. [c] ee values were determined by
chiral column; see the Supporting Information. [d] Reaction was conduct-
ed at 608C for 16 h.
toluene 12 trace
[a] Reactions were conducted with 0.6 mmol of 1a, 0.3 mmol of 2a, and
5 mol% catalyst at room temperature. [b] Yield of isolated product.
[c] ee values were determined by chiral column.
number of gold(I) catalysts having different phosphine li-
gands were screened. Although (PPh3)AuCl/AgOTf, [P-
efficiently catalyze enantioselective transformation of al-
lenes, displayed a low catalytic activity towards intermolecu-
lar hydroarylation of 2a with 1a, furnishing product in 52%
isolated yield with 17% ee and with a long reaction time of
36 h (Table 2, entry 4). Complex 4e with an electron-donat-
ing substituent on the phosphine ligand catalyzed the reac-
tion with a better enantioselectivity than complex 4 f with a
phosphine ligand having an electron-withdrawing substitu-
ent (Table 2, entries 5 and 6). The PtII complexes 4i and 4j
with ligand (S)-(À)-MeO-biphep (L3) and (S)-3,5-tBu2-4-
MeO-biphep (L4), respectively, which have been reported
to be effective catalyst for enantioselective intramolecular
hydroarylation of alkenes with indoles,[3c] failed to catalyze
this reaction even at a temperature of up to 608C (Table 2,
entries 9 and 10). With 4c as catalyst, the effect of solvent
was examined. Both THF and acetonitrile were found to
give the desired products in lower product yields and de-
creased enantioselectivity (Table 2, entries 11 and 12). De-
creasing the temperature to 08C led to a low substrate con-
version of 2b. We also examined the effect of catalyst load-
ing on the enantioselective hydroarylation of 2b with 1a
(Table 2, entries 13–15). A mixture of complex 4c (1 mol%)
and AgOTf (2 mol%) as catalyst led to hydroarylation
product in 32% yield with 53% ee (Table 2, entry 13). In-
creasing the catalyst loading to 5 mol% of 4c and 10 mol%
of AgOTf resulted in a reduced enantioselectivity to 39%
A
[P(4-MeOC6H4)3]AuCl/
AgOTf and (PEt3)AuCl/AgOTf all catalyzed the reaction in
high product yields, racemic product was found for each of
the cases examined without chirality transfer (Table 1, en-
tries 2–5). This result is consistent with the works reported
by Toste, Widenhoefer, and Krause et al. showing that axial-
ly chiral allenes could be racemized by gold complexes.[10]
The other metal salts AuCl3, AuCl3/AgOTf, and AgOTf
failed to catalyze this reaction.
As AuI complexes with chiral biaryl phosphine ligands
have been demonstrated to be excellent catalysts for enan-
tioselective intramolecular functionalization of allenes, we
investigated the reaction of racemic allenes with indoles cat-
alyzed by this class of binuclear gold(I) complexes.[6] In pre-
liminary experiments, treatment of racemic allene 2b and
N-methyl indole 1a with a mixture of chiral gold(I) catalyst
4a (2.5 mol%) and AgOTf (5 mol%) in toluene at room
temperature for 12 h led to 3-alkylated indole 3b in 91%
isolated yield with 18% ee (Table 2, entry 1). Under the
same conditions, a series of chiral binuclear gold(I) phos-
phine complexes were examined (Figure 1). Complex 4c
with (S)-(À)-MeO-biphep ligand was found to give the best
result for intermolecular hydroarylation of 2b with 1a, af-
fording product in 90% isolated yield with 60% ee (Table 2,
entry 3). Interestingly, complex 4d, previously reported to
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Chem. Asian J. 2011, 6, 812 – 824

Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles
reactions of racemic allenes
with various substituted indoles
have been examined. Electron-
withdrawing groups were found
to decrease the reaction enan-
tioselectivity. For example, hy-
droarylation of 2b with 5-
chloro-N-methyl indole 1b led
to the corresponding 3-alkylat-
ed indole 3g in 40% ee
(Table 3, entry 7); the reaction
of 2b with 6-carboxyl-N-methyl
indole 1c gave the product 3h
in 37% ee (Table 3, entry 8).
The reaction of indole 1d
having a methyl group at the C-
2 position with allene 2b gave
lower product yield and enan-
tioselectivity than that of the
reaction with 1a (41% ee,
Table 3, entry 9). N-Benzyl
indole also led to lower enan-
tioselectivity than 1a (35% ee,
Table 3, entry 10). Using allene
2e (4-F) as a substrate, its reac-
tions with various indole com-
pounds gave the corresponding
hydroarylation
products
in
moderate enantioselectivities
(43–51% ee, Table 3, en-
tries 11–14). The 4c-catalyzed
hydroarylations of alkyl-substi-
Figure 1. Chiral dimetal phosphine catalysts.
tuted allenes with indoles were
also examined. When cyclohex-
(Table 2, entry 14). The use of excess AgOTf had a slight
effect on both the product yield and enantioselectivity
(Table 2, entry 15). After optimization, the protocol with 4c
(2.5 mol%) and AgOTf (5 mol%) at room temperature was
found to give the best result.
alallene was used, the substrate conversion was low (<5%)
under the same reaction conditions.
Competitive Hydroarylation of Allenes with N-
Methylindole
With the optimized conditions, we examined the scope of
AuI-catalyzed enantioselective intermolecular hydroaryla-
tion of racemic allenes with indoles (Table 3). Most of the
1,3-diaryl allenes and indoles underwent hydroarylation re-
action to give the corresponding 3-alkylated indoles in good
isolated yields with moderate enantioselectivities. A para
substituent on the aryl moiety of allenes has a slight effect
on both the product yield and enantioselectivity. For exam-
ple, the reactions of N-methyl indole 1a with racemic al-
lenes 2b (4-Me), 2c (4-tBu), and 2d (4-OMe) gave the cor-
responding products in high yields (81–90%) with similar
enantioselectivities (53–60% ee, Table 3, entries 2–4). Hy-
droarylation of racemic allene 2e (4-F) having an electron-
withdrawing substituent led to the corresponding product in
a slightly higher enantioselectivity of 63% ee and in 72%
isolated yield (Table 3, entry 5). However, the ortho 2-Me
substituent in racemic allene 2 f resulted in low product
yield and enantioselectivity (7% ee, Table 3, entry 6). The
To get an insight into the reaction mechanism, the relative
reaction rates of p-X-C6H4CH=C=CHACTHNUTRGNE(UGN p-X-C6H4) [X=H
(2a), Me (2b), OMe (2d), and F (2e)] with N-methylindole
1
1a using 4c as catalyst were examined by H NMR analysis
of the corresponding hydroarylation products. The results
are depicted in Figure 2. The rate data display a good Ham-
mett linear free-energy relationship (r2 =0.996). The slope
value 1 was determined to be À2.30, similar to the value
(À2.40) obtained for the reaction of 4-substituted styrene
À
derivatives with [(IPr)Au
N
diisopropylphenyl) imidazol-2-ylidene],[11] revealing the
build-up of positive charge at the allene and electrophilic
character of the active AuI-allene reaction intermediate.
This is consistent with the findings that allene 2d with an
electron-donating p-methoxy substituent is more reactive
than both allenes 2a and 2e with H and F substituents, re-
spectively.
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C.-M. Che et al.
FULL PAPERS
Table 3. Gold(I)-catalyzed enantioselective intermolecular hydroarylation of allenes with indoles.[a]
Deuterium-Labelling
Experiment
A
deuterium-labelling experi-
ment
was
performed
(Scheme 1). The reaction of 2b
with 1a in D2O/toluene led to
3o with 68% deuterium incor-
poration (Scheme 1a). Treat-
ment of 3-deuterium-N-methyl
indole with 2b gave 3o with
42% deuterium incorporation
(Scheme 1b). The moderate
deuterium incorporation can be
rationalized by the presence of
trace water in the reaction mix-
ture. All of these data reveal
that the catalysis involves a cru-
cial intermolecular hydrogen
atom transfer step.
Entry
1
Indole
Allene
Product
Yield [%][b]
85
ee [%][c]
2a: R2 =H
3a: R2 =H
41
2
3
4
5
6
1a
1a
1a
1a
1a
2b: R2 =4-Me
2c: R2 =4-tBu
2d: R2 =4-OMe
2e: R2 =4-F
3b: R2 =4-Me
3c: R2 =4-tBu
3d: R2 =4-OMe
3e: R2 =4-F
90
85
81
72
38
60
56
53
63
7
2 f: R2 =2-Me
3 f: R2 =2-Me
7
8
9
2b
2b
2b
75
73
85
40
37
41
31P NMR Study
A
mixture
of
Ph3PAuCl
(1 equiv) and AgOTf (1 equiv)
in CDCl3 was analyzed by
31P NMR, showing a peak at
d=30.8 ppm
Ph3PAuOTf. To this reaction
mixture was added 1a
assigned
to
(1.1 equiv) and the mixture was
stirred for 180min at room tem-
perature. A new peak at d=
45.10 ppm was observed in the
31P NMR spectrum depicted in
Figure 3. This chemical shift is
similar to related values of
known vinyl-AuI and aryl-AuI
10
11
2b
2e
85
67
35
51
phosphine
complexes
(at
around 44 ppm),[12] suggesting a
À
C Au bond formation between
the indole and gold(I) complex.
Similarly, the 31P NMR spec-
trum of a solution mixture con-
taining complex 4c (1 equiv),
AgOTf (2 equiv), and indole 1a
(1 equiv) for a reaction time of
180min in CDCl3 also gave a
signal peak at d=43.8 ppm
(Figure 4), which is characteris-
tics of aryl-AuI phosphine com-
plexes.
12
2e
83
45
13
14
2e
2e
75
85
43
47
X-ray Crystal Structures
[a] Reactions were conducted with 1.5 mmol of indole 1, 0.3 mmol of racemic allene 2, and 2.5 mol% 4c/
5 mol% AgOTf in 1 mL toluene for 12–20 h. [b] Yield of isolated product. [c] ee values were determined by
chiral column; see the Supporting Information.
The structures of the complexes
4c
[(AuCl)2(L3)],
4 f
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Chem. Asian J. 2011, 6, 812 – 824

Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles
Figure 4. 31P NMR spectrum of the reaction mixture by reacting 4c/
AgOTf (1:2) with N-methylindole 1a in CDCl3 for 180 min.
Figure 2. Hammett plot derived for the hydroarylation of allenes with
indole 1a catalyzed by 4c (2.5 mol%) and AgOTf (5 mol%).
Figure 5. X-ray crystal structure of complex 4c (thermal ellipsoids proba-
bility: 30%); for clarity, hydrogen atoms and solvent molecules are not
shown. Selected bond lengths [ꢃ] and angles [8]: Au(1)-Au(1*) 3.1473(5),
Au(1)-P(1) 2.2415(14), Au(1)-Cl(1) 2.2932(15); P(1)-Au(1)-Cl(1)
173.69(5), P(1)-Au(1)-Au(1*) 187.32(4), Cl(1)-Au(1)-Au(1*) 198.33(4).
Scheme 1. Deuterium-labelling experiment.
Figure 6. X-ray crystal structure of complex 4 f (thermal ellipsoids proba-
bility: 30%); for clarity, hydrogen atoms and solvent molecules are not
shown. Selected bond lengths [ꢃ] and angles [8]: Au(1)-Au(1A) 3.786,
Au(1)-P(1) 2.231(3), Au(1)-Cl(1) 2.289(4); P(1)-Au(1)-Cl(1) 176.41(14),
P(1A)-Au(1A)-Cl(1A) 176.41(14), C(8)-P(1)-Au(1) 111.6(5).
Figure 3. 31P NMR spectrum of the reaction mixture by reacting
(PPh3)AuCl/AgOTf (1:1) with N-methylindole 1a in CDCl3 for 180 min.
[(AuCl)2(L6)], 4d [(AuCl)2(L4)],[13,18] and 4h [(AuCl)2(L8)]
were determined by X-ray crystallography and are shown in
Figures 5–7.[13] The crystals were grown by slow diffusion of
hexane into dichloromethane solutions. As shown in Fig-
À
tramolecular Au Au interaction was observed in 4 f
(3.786 ꢃ, Figure 6).
À
ures 5 and 7, the intramolecular Au Au distances are
3.1473(5) ꢃ for 4c and 2.9347(3) ꢃ for 4h, respectively, indi-
DFT Calculations
À
cating the presence of intramolecular Au Au interaction.
This interaction can render the catalyst less flexible. No in-
Recently, gold(I)-catalyzed functionalization and isomeriza-
À
tion of unsaturated C C bonds have been attracting a surge
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817

C.-M. Che et al.
FULL PAPERS
Scheme 2. Proposed reaction intermediates.
phenyl groups of the digold(I) phosphine complex,
[(L3)Au2]2+ (L3=MeO-biphep)], were replaced by methyl
groups. This leads to the model complex [(L)Au2]2+ (L=
MeO-bimep)] employed in our calculation. The calculated
free energies are depicted in Figure 8 and Figure 9. The op-
timized stationary structures (minima, saddle points) on the
potential energy surface of reactions, energies, and selected
key geometry parameters are depicted in the Supporting In-
formation.
Figure 7. X-ray crystal structure of complex 4h (thermal ellipsoids proba-
bility: 30%); for clarity, hydrogen atoms and solvent molecules are not
shown. Selected bond lengths [ꢃ] and angles [8]: Au(1)-Au(2) 2.9347(3),
Au(1)-P(1) 2.2444(12), Au(1)-Cl(1) 2.2842(15); P(1)-Au(1)-Cl(1)
172.09(6), P(1)-Au(1)-Au(2), 85.60 (3), Cl(1)-Au(1)-Au(2), 100.59 (5).
of interest. In many cases, the catalysis involves a reactive
monoaurated intermediate such as a gold–p complex, vinyl–
gold complex, or gold–carbene species. In 2008, Toste and
co-workers postulated the involvement of a diaurated inter-
mediate in the gold-catalyzed cycloisomerization of 1,5-alle-
nynes on the basis of density functional theory (DFT) calcu-
lations. The diaurated intermediate was proposed to be a
gem-diauraalkene complex in a three-center two-electron
mode.[14] Subsequently Gagnꢁ et al. provided experimental
support for a diaurated reaction intermediate involved in
AuI-catalyzed intramolecular hydroarylation of allenes,[15]
the structure of which is similar to the intermediate pro-
posed by Toste. More recently, Bandini and co-workers re-
ported an enantioselective intramolecular binuclear gold(I)
complex catalyzed allylic alkylation of indole with allylic al-
cohol, presumably via a diaurated reaction intermediate
with dual activation of the C=C bond and hydroxy group.[3g]
In this work, the formation of an aryl-AuI phosphine com-
plex was observed by analysis of the 31P NMR spectrum of
the reaction mixture obtained by reacting complex 4c/
AgOTf and indole 1a in CDCl3 for 180min. To get insight
into the reaction mechanism, two plausible reaction path-
ways were investigated by density functional theory calcula-
tions: 1) the pathway involving intermolecular nucleophilic
addition of free indole to aurated allene intermediate E1
(Scheme 2); 2) the pathway involving intramolecular nucleo-
philic addition of aurated indole to allene via diaurated in-
termediate E2 in which two gold(I) atoms simultaneously
bind to allene and indole.
Figure 8. Calculated free energies for intermolecular reaction of allene
with indole via monoaurated intermediate using DFT approach (B3LYP/
6-31G*, Lanl2dz for Au).
With the optimized geommetry as depicted in Figure 8,
the first reaction pathway starts with intermediate A com-
posed of indole and a gold(I)-allene complex in which one
gold(I) center coordinates to allene and the other binds to
triflate. The coordination of the gold(I) complex to allene is
supported by the Hammett plot experiment with a 1 value
of À2.30, revealing the build-up of positive charge at the
allene. The calculation showed that the nucleophillic addi-
tion of indole to gold(I)-activated allene is relatively facile,
requiring an activation free energy of 14.1 kcalmolÀ1 via
transition state TSA-B. Formation of complex B is endergonic
A
computational study using DFT (B3LYP/6–31G*,
Lanl2dz for Au) was undertaken to model the digold(I)
phosphine complex catalyzed hydroarylation of allene with
indole. In order to reduce the computational time, the
818
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Chem. Asian J. 2011, 6, 812 – 824

Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles
Figure 9. Calculated free energies for the hydroarylation reaction via intermediate E by DFT calculation (B3LYP/6-31G*, Lanl2dz for Au).
Proposed Reaction Mechanism
À1
À
by 2.5 kcalmol . This step leads to C C bond formation be-
tween allene and indole. The subsequent step is rearomati-
zation from intermediate C to D through a deprotonation
process assisted by triflate anion. The transition state TSC-D
for this step needs a low activation energy of 2.4 kcalmolÀ1.
Finally, intermediate D undergoes demetalation to yield hy-
droarylation product and regen-
According to the above experimental results and computa-
tional study, a plausible reaction mechanism is depicted in
Scheme 3. The cationic gold(I) coordinates to the allene to
give intermediate I and the coordination facilitates nucleo-
philic attack of the allene by free indole to generate inter-
erate the gold(I) catalyst. The
relative low reaction barrier
from intermediate A to D re-
veals that the commonly ac-
cepted mechanism involving a
monoaurated intermediate is
operative in this dinuclear
gold(I) phosphine complex cat-
alyzed hydroarylation of allene
with indole.
The potential free energy sur-
face for the second pathway is
shown in Figure 9. With triflate-
assisted deprotonation,[16] the
binuclear gold(I) phosphine
complex
(OTf)]+ interacts with the
indole to generate the digold(I)
species [(Au2(L)(allene)-
[(Au2(L)ACTHNGUTRENNU(G allene)-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
(indoleÀH)]+ E via transition
state TSA-E. The transition state
TSA-E has an activation energy
barrier of 20.8 kcalmolÀ1 in the
gas phase. The intermediate E
Scheme 3. Proposed reaction pathway.
formed via TSA-E is more unstable than A by 17.3 kcalmolÀ1.
mediate II. Subsequent protonolysis of intermediate II af-
fords the desired product and regenerates the catalyst.
À
However, the second step of C C bond formation between
gold-activated allene and aurated indole via TSE-F requires
another activation energy of 26.9 kcalmolÀ1 from E to F.
Thus, the total reaction barrier from intermediate A to F is
44.2 kcalmolÀ1 in the gas phase, revealing that the hydroary-
lation via diaurated species E is unfavorable. As a result,
the reaction more likely proceeds via the first pathway
owing to a relatively low reaction barrier.
Stereoselectivity
As depicted in Scheme 4a,b, the coordination of gold com-
plex to racemic allene gives four isomeric gold-allene inter-
mediates I in which (Si,S)-I and (Re,S)-I are derived from
(S)-2 (Scheme 4a), while (Si,R)-I and (Re,R)-I are derived
from (R)-2 (Scheme 4b). The structure used to model inter-
mediates I was built by ChemBio 3D Ultra 11.0 software
Chem. Asian J. 2011, 6, 812 – 824
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819

C.-M. Che et al.
FULL PAPERS
lished mechanism that gold-catalyzed hydrofunctionalization
of allene involves outer-sphere attack of the nucleophile on
a gold-allene complex from the opposite side of the gold
catalyst; subsequent protonolysis of the resulting vinyl gold
complex (complex (S,Z)-II, (R,E)-II in Scheme 4a; complex
(R,Z)-II, (S,E)-II in Scheme 4b) could give the hydrofunc-
tionalization product with retention of configuration of the
alkene group.[3d,6f] However, only the E isomer was observed
in our experiments. The lack of observation of the Z isomer
can be rationalized by the unfavorable steric interaction be-
tween the indole and aryl groups of allene upon approach of
indole to allene from the same side of aryl group. In this
work, most of the enantiorich E isomers were obtained in
greater than 80% product yields with greater than 30%
enantioselectivities from racemic allenes. This result reveals
that the catalysis involves a dynamic kinetic asymmetric
transformation[6f,17] in which the chiral allenes (S)-2 and (R)-
2 equilibrate rapidly, presumably via a zwitterionic spe-
cies[10b] or a gold s-allyl cation[10d] (Figure 10). As a conse-
quence of the diastereomeric environment of intermediates
Figure 10. The zwitterionic species and gold s-allyl cation.
(Si,S)-I and (Re,R)-I, one of them reacts with the indole
faster than the other and is continually replenished via rapid
interconversion between (S)-2 and (R)-2, leading to the
enantiorich product. According to the model of intermedi-
ates (Si,S)-I and (Re,R)-I, we speculate that the formation
of (S, E)-III is unfavorable owing to close interaction of the
ligand of the catalyst with the approaching indole unit,
thereby giving the enantiorich (R,E)-III.
À
Effect of Intramolecular Au Au Interaction on
Enantioselectivity
[6d]
The Au Au separations of complexes 4b, 4c, 4d,[13,18] 4 f,
À
and 4h are depicted in Table 4. As shown in Table 4, the
complexes 4c (Au-Au=3.1473(5) ꢃ) and 4h (Au-Au=
2.9347(3) ꢃ) were found to give better enantioselectivity in
À
Table 4. The effect of intramolecular Au Au interaction on gold(I)-cata-
lyzed enantioselective intermolecular hydroarylation of allenes with indo-
les.[a]
[a]
À
À
Complex
d
(Au Au) [ꢃ]
Au Au interaction
ee [%]
4b
4c
4d
4 f
4h
5.490
3.147
5.298
3.786
2.934
À
+
À
À
+
18
60
17
6.5
49
Scheme 4. Origin of the enantioselectivity.
based on the X-ray crystal structure of 4c. As shown in
Scheme 4a, the hydroarylation of (S)-2 with indole would
lead to products (S,E)-III and (R,Z)-III based on the estab-
[a] “+” represents the presence of intramolecular aurophilic interaction;
“À” indicates that no Au Au interaction is observed.
À
820
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Chem. Asian J. 2011, 6, 812 – 824

Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles
1
coupling constants are given in Hz. Data for H NMR spectra are record-
the hydroarylation reaction than the other digold(I) com-
ed as follows: chemical shift (ppm), multiplicity (s, singlet; d, doublet; t,
triplet; m, multiplet), coupling constant (Hz), integration. Data for
13C NMR are reported in terms of chemical shift (d, ppm). Lower-resolu-
tion mass spectra or high-resolution mass spectra (HRMS) were obtained
on a Finnigan GC-MS 4021 or a Finnigan MAT-8430 instrument using
the electron impact ionization technique (70 eV).
À
plexes having no Au Au interaction. Presumably, this is at-
tributed to the less flexible conformation of the gold(I) cata-
[18]
À
lyst constrained by the intramolecular Au Au interaction.
A further comparison of the crystal structure of 4c with that
of its analogues [(AuCl)2(Tol-binap)][5f] and [(AuCl)2(3,5-
Xylyl-binap)] 4b[6d] reveals that [(AuCl)2(Tol-binap)] and
[(AuCl)2(3,5-Xylyl-binap)] display intramolecular p–p stack-
ing interactions between the two aryl groups on the phos-
phine ligands and this is not observed in 4c. This p–p stack-
ing interaction renders the structure of the binuclear gold(I)
phosphine complex to be less flexible and is presumed to
affect the intramolecular enantioselective hydrovinylation of
General procedure for the synthesis of (AuCl)2(L) complexes: Chiral
gold complexes were synthesized according to the procedures reported in
the literature.[5g] KAuCl4 (0.5 mmol) was dissolved in water (5 mL), and
the orange solution was placed in an ice bath. To this solution was added
dropwise (ca. 35 min) tetrahydrothiophene (1.5 mmol). After stirring for
0.5 h, the pale-white solid was filtrated off, washed with water and diethyl
ether, and dried under vacuum. The resulting chloro(tetrahydrothiophe-
ne)gold(I) complex was used for the next step without further purifica-
tion. Then, to
a
solution of chloro(tetrahydrothiophene)gold(I)
allenes.[6d] In our experiments, [(AuCl)
2ACTHNUGRTENUNG(binap)] 4a and
[(AuCl)2(3,5-Xylyl-binap)] 4b were found to lead to a lower
enantioselectivity than 4c, revealing that Au Au interaction
is probably more beneficial for the enantioinduction in our
reaction than intramolecular p–p stacking interactions.
Complex 4 f, an analogue of 4c, with an intramolecular Au
Au separation of 3.786 ꢃ, which is slightly longer than that
of 4c, led to much lower enantioselectivity than 4c. This
(1.0 mmol) in CH2Cl2 (5 mL) was added dropwise a solution of the phos-
phine ligand L (0.5 mmol) in CH2Cl2 (3 mL) for 10 min with stirring.
After stirring overnight, the solvent was removed to give the (AuCl)2(L)
complex as a white solid in over 90% yield. The spectral data of the
known compounds 4a–f obtained in this work matched those data report-
ed in the literature.[3c,5e–g,6a]
À
À
(1R,1’R,2S,2’S)-duanphosACHTGNUTERN(NUGN AuCl)2 AHCTUNGTERG(NNUN 4g): Obtained as a white solid.
1H NMR (400 MHz, CDCl3): d=0.91 (s, 9H), 0.96 (s, 9H), 3.24–3.31 (m,
2H), 4.25 (d, J=20.8 Hz, 2H), 4.25 (d, J=18.8 Hz, 2H), 7.31–7.43 ppm
(m, 8H); 13C NMR (75 MHz, CDCl3): d=26.49, 30.68, 30.92, 31.15, 47.92,
48.15, 48.39, 126.18, 127.74, 128.18, 129.38, 139.55, 139.95 ppm; 31P NMR
(160 MHz, CDCl3): d=47.78 ppm; HRMS (EI) for [C24H32Au2ClP2]+
([MÀCl]+), calcd 811.0999, found 811.0986.
À
result further manifests that Au Au interaction may have
an instrumental effect on the enantioselective intermolecu-
lar hydroarylation. Interestingly, for 4d, which was previous-
ly reported to efficiently catalyze intramolecular enantiose-
(+)-1,2-Bis
G
G
ACHTUNGTRENNUNG(4h):
À
lective transformation of allenes, neither Au Au contact nor
Obtained as a white solid. 1H NMR (400 MHz, CDCl3): d=0.45 (d, J=
6.6 Hz, 6H), 0.78 (d, J=6.6 Hz, 6H), 0.97 (d, J=6.6 Hz, 6H), 1.11 (d, J=
6.6 Hz, 6H), 1.55–1.61 (m, 2H), 1.78–1.82 (m, 2H), 2.20–2.29 (m, 8H),
2.55–2.59 (m, 2H), 3.39–3.45 (m, 2H), 7.57–7.59 (m, 2H), 7.84–7.90 ppm
(m, 2H); 13C NMR (75 MHz, CDCl3): d=18.43, 21.84, 21.93, 22.01, 23.77,
23.84, 23.92, 24.26, 25.16, 27.95, 30.05, 30.16, 30.33, 34.83, 48.84, 49.07,
49.28, 50.60, 50.81, 51.03, 130.88, 136.09, 136.18, 136.27 ppm; 31P NMR
(160 MHz, CDCl3): d=37.47 ppm; HRMS (EI) for [C26H44Au2ClP2]+
([MÀCl]+), calcd 847.1938, found 847.1926.
p–p stacking interaction has been observed.[13,18] The flexi-
À
bility owing to the lack of Au Au contact and p–p stacking
interaction may be the reason accounting for the low enan-
tioselectivity found for our reaction catalyzed by 4d. As
shown in the model of intermediates (Si,S)-I and (Re,R)-I,
À
the intramolecular Au Au interaction may pull the aryl
groups on the phosphine ligands close to the reaction
center, thereby facilitating enantiodiscrimination. This may
account for the better enantioselectivity achieved for the re-
action catalyzed by complex 4c.
General procedure for the synthesis of racemic allenes 2:[9] A mixture of
KAuCl4 (0.02 mmol), aldehyde (2.0 mmol), piperidine (2.2 mmol), and
alkyne (3.0 mmol) in water (1 mL) was stirred at 408C for 24 h in the ab-
sence of light under N2 atmosphere. After the reaction, the mixture was
diluted with diethyl ether or CH2Cl2 (10 mL) and washed successively
with water (2ꢄ5 mL) and brine (5 mL), and then dried over anhydrous
sodium sulfate. Filtration of the organic phase through a short pad of
celite, evaporation of the solvent, and purification of the residue by flash
column chromatography on silica gel using ethyl acetate/hexane as eluent
afforded the corresponding racemic propargylamine. A mixture of the
racemic propargylamine (0.2 mmol) and KAuCl4 (0.02 mmol) in CH3CN
(5 mL) was stirred at 408C for 24 h. The solvent was removed under re-
duced pressure. The product was purified by flash column chromatogra-
phy on silica gel using ethyl acetate/hexane as eluent.
Conclusion
In summary, we have developed an enantioselective inter-
molecular hydroarylation of racemic allenes with indoles
using a 1:2 mixture of (S)-(À)-MeO-biphep
ACHTUNGTERNUN(NG AuCl)2 4c and
AgOTf as catalyst. The reaction took place under mild con-
ditions and gave high product yields with moderate enantio-
selectivities. DFT calculations revealed that the reaction
mechanism involving intermolecular nucleophilic addition of
free indole to gold-activated allene is more likely than intra-
molecular cyclization via a diaurated intermediate with dual
activation of allene and indole.
1,3-Bis(4-tert-butylphenyl)propa-1,2-diene (2c): Yellow solid, yield of
52% for two steps. 1H NMR (400 MHz, CDCl3): d=1.29 (s, 18H), 6.55
(s, 2H), 7.26–7.33 ppm (m, 8H); 13C NMR (100 MHz, CDCl3): d=31.79,
35.06, 98.42, 110.16, 126.15, 127.17, 131.32, 150.86 ppm; IR (KBr, neat):
n˜ =2926, 1936, 1706 cmÀ1; EIMS m/z 304 (M+); HRMS (EI) for C23H28,
calcd 304.2191, found 304.2195.
1,3-Bis(4-fluorophenyl)propa-1,2-diene (2e): Yellow oil, yield of 45% for
two steps. 1H NMR (300 MHz, CDCl3): d=6.58 (s, 2H), 6.99–7.05 (m,
4H), 7.29–7.34 ppm (m, 4H); 13C NMR (75 MHz, CDCl3): d=97.69,
115.47, 115.89, 128.41, 129.46, 163.85 ppm; IR (KBr, neat): n˜ =2925, 1938,
Experimental Section
1710 cmÀ1
;
EIMS m/z 228 (M+); HRMS (EI) for C15H10F2, calcd
228.0751, found 228.0756.
General: All manipulations with air-sensitive reagents were carried out
under a dry nitrogen atmosphere. NMR spectra were recorded on a
Bruker AMX 300/400 MHz spectrometer for 1H NMR and 75/100 MHz
for 13C NMR in CDCl3. The chemical shifts are expressed in ppm and
General procedure for gold(I)-catalyzed enantioselective intermolecular
hydroarylation of allenes with indoles (Tables 2 and 3): A mixture of (S)-
(À)-MeO-biphep
ACHTUNGTERNUN(NG AuCl)2 4c (2.5 mol%) and AgOTf (5%mol) in toluene
Chem. Asian J. 2011, 6, 812 – 824
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821

C.-M. Che et al.
FULL PAPERS
(2 mL) was stirred at room temperature for 15 min. Allene (0.3 mmol)
and indole (1.5 mmol) were added successively and the mixture was
stirred for 12 h to 20 h until completion of the reaction. The reaction mix-
ture was concentrated and loaded directly onto a silica column; elution
with ethyl acetate/hexane afforded the product.
1-Methyl-3-((E)-1,3-di-o-tolylallyl)-1H-indole (3 f): Yellow solid, analyti-
cal TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51; 1H NMR
(300 MHz, CDCl3): d=2.30 (s, 3H), 2.41 (s, 3H), 3.72 (s, 3H), 5.29 (d,
J=7.2 Hz, 1H), 6.47–6.61 (m, 2H), 6.65 (s, 1H), 7.00 (t, J=7.2 Hz, 1H),
7.11–7.21 (m, 6H), 7.23–7.32 (m, 3H), 7.41 (d, J=8.2 Hz, 1H), 7.48–
7.60 ppm (m, 1H); 13C NMR (100 MHz, CDCl3): d=20.09, 20.25, 42.87,
109.62, 117.32, 119.28, 120.36, 122.07, 126.23, 126.46, 126.50, 126.76,
127.50, 127.89, 128.12, 128.66, 129.06, 130.61, 130.87, 134.06, 135.76,
136.60, 137.35, 137.91, 142.10 ppm; IR (KBr, neat): n˜ =3058, 3025, 2930,
1602, 1459, 1360, 1266, 1186, 967, 741, 701 cmÀ1; EIMS m/z 351 (M+);
HRMS (EI) for C26H25N, calcd 351.1987, found 351.1989; 7% ee deter-
mined by HPLC (Chiral OD column, 2-propanol/hexane=0.6:99.4,
0.45 mLminÀ1, major isomer 22.17 min, minor isomer 15.07 min).
1-Methyl-3-((E)-1,3-diphenylallyl)-1H-indole (3a): Yellow solid, analyti-
cal TLC (silica gel 60, 2% EtOAc in hexane), Rf =0.25; 1H NMR
(300 MHz, CDCl3): d=3.69 (s, 3H), 5.09 (d, J=7.3 Hz, 1H), 6.41 (d, J=
15.8 Hz, 1H), 6.68–6.75 (m, 2H), 6.99 (t, J=7.1 Hz, 1H), 7.17–7.42 ppm
(m, 13H); 13C NMR (75 MHz, CDCl3): d=32.69, 46.16, 109.16, 118.15,
118.86, 119.94, 121.62, 126.30, 126.33, 127.12, 127.36, 128.39, 128.47,
130.42, 132.71, 137.53, 143.54 ppm; IR (KBr, neat): n˜ =3058, 3024, 2932,
1599, 1489, 1472, 1372, 1329, 1156, 968, 741, 700 cmÀ1; EIMS m/z 323
(M+); HRMS (EI) for C24H2N, calcd 323.1674, found 323.1675; 41% ee
determined by HPLC (Chiral OD column, 2-propanol/hexane=1:99,
0.7 mLminÀ1, major isomer 12.47 min, minor isomer 13.86 min).
5-Chloro-1-methyl-3-((E)-1,3-di-p-tolylallyl)-1H-indole (3g): Yellow
solid, analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51;
1H NMR (300 MHz, CDCl3): d=2.31 (s, 3H), 2.34 (s, 3H), 3.71 (s, 3H),
4.98 (d, J=7.2 Hz, 1H), 6.34 (d, J=15.8 Hz, 1H), 6.56 (dd, J1 =7.2 Hz,
J2 =15.8 Hz, 1H), 6.76 (s, 1H), 7.07–7.12 (m, 5H), 7.17–7.20 (m, 3H),
7.24–7.25 (m, 2H), 7.49 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=
21.03, 21.13, 32.86, 45.46, 110.18, 117.18, 119.27, 121.89, 124.68, 126.19,
128.23, 128.59, 129.16, 130.29, 131.44, 134.63, 135.80, 135.94, 136.93,
140.19 ppm; IR (KBr, neat): n˜ =3057, 3025, 2932, 1697, 1597, 1504, 1227,
1158, 972, 833, 741 cmÀ1; EIMS m/z 312 (M+); HRMS (EI) for C22H20N2,
calcd 312.1626, found 312.1621; 40% ee determined by HPLC (Chiral
OD column, 2-propanol/hexane=0.6:99.4, 0.45 mLminÀ1, major isomer
21.41 min, minor isomer 20.47 min).
1-Methyl-3-((E)-1,3-di-p-tolylallyl)-1H-indole (3b): Yellow solid, analyti-
cal TLC (silica gel 60, 2% EtOAc in hexane), Rf =0.25; 1H NMR
(300 MHz, CDCl3): d=2.32 (s, 3H), 2.33 (s, 3H), 3.67 (s, 3H), 5.05 (d,
J=7.2 Hz, 1H), 6.41 (d, J=15.8 Hz, 1H), 6.61 (dd, J1 =7.3 Hz, J2 =
15.8 Hz, 1H), 6.74 (s, 1H), 6.98 (t, J=7.4 Hz, 1H), 7.07–7.12 (m, 4H),
7.16–7.30 (m, 6H), 7.42 ppm (d, J=7.9 Hz, 1H); 13C NMR (75 MHz,
CDCl3): d=21.03, 21.11, 32.65, 45.73, 109.10, 117.38, 118.78, 119.99,
121.53, 126.18, 127.29, 128.32, 129.05, 129.11, 130.03, 131.91, 134.78,
135.72, 136.76, 137.15, 140.65 ppm; IR (KBr, neat): n˜ =3057, 3025, 2930,
1600, 1459, 1360, 1266, 1185, 969, 741, 701 cmÀ1; EIMS m/z 351 (M+);
HRMS (EI) for C26H25N, calcd 351.1987, found 351.1988; 60% ee deter-
mined by HPLC (Chiral OD column, 2-propanol/hexane=1:99,
0.7 mLminÀ1, major isomer 14.76 min, minor isomer 17.56 min).
Methyl 1-methyl-3-((E)-1,3-di-p-tolylallyl)-1H-indole-6-carboxylate (3h):
Yellow solid, analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =
0.51; 1H NMR (300 MHz, CDCl3): d=2.31 (s, 3H), 2.33 (s, 3H), 3.79 (s,
3H), 3.94 (s, 3H), 5.04 (d, J=6.1 Hz, 1H), 6.35 (d, J=15.8 Hz, 1H), 6.58
(dd, J1 =7.2 Hz, J2 =15.8 Hz, 1H), 6.89 (s, 1H), 7.07–7.13 (m, 4H), 7.18–
7.26 (m, 4H), 7.40 (d, J=8.4 Hz, 1H), 7.67 (dd, J1 =1.1 Hz, J2 =8.4 Hz,
1H), 8.10 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=21.04, 21.13,
32.88, 45.56, 51.90, 111.69, 117.95, 119.57, 119.89, 123.19, 126.19, 127.84,
128.26, 128.65, 129.17, 130.38, 130.66, 130.70, 131.39, 134.59, 135.97,
136.79, 136.98, 140.24, 168.25 ppm; IR (KBr, neat): n˜ =3057, 3026, 2926,
1742, 1600, 1458, 1362, 1265, 1152, 968, 741, 701 cmÀ1; EIMS m/z 409
(M+); HRMS (EI) for C28H27NO2, calcd 409.2042, found 409.2040;
37% ee determined by HPLC (Chiral OD column, 2-propanol/hexane=
5:95, 0.7 mLminÀ1, major isomer 33.35 min, minor isomer 25.20 min).
3-((E)-1,3-Bis(4-tert-butylphenyl)allyl)-1-methyl-1H-indole (3c): Yellow
solid, analytical TLC (silica gel 60, 2% EtOAc in hexane), Rf =0.30;
1H NMR (300 MHz, CDCl3): d=1.30 (s, 9H), 1.34 (s, 9H), 3.68 (s, 3H),
5.06 (d, J=7.2 Hz, 1H), 6.40 (d, J=15.8 Hz, 1H), 6.63–6.72 (m, 2H), 6.99
(t, J=7.3 Hz, 1H), 7.17–7.33 (m, 10H), 7.46 ppm (d, J=7.9 Hz, 1H);
13C NMR (75 MHz, CDCl3): d=26.69, 31.29, 31.41, 32.67, 45.63, 109.09,
117.25, 118.75, 120.06, 121.51, 124.85, 125.22, 125.34, 125.98, 127.32,
128.00, 129.85, 132.16, 134.84, 137.35, 140.58, 158.12, 159.23 ppm; IR
(KBr, neat): n˜ =3058, 3026, 2935, 1602, 1458, 1362, 1265, 1183, 965, 741,
702 cmÀ1; EIMS m/z 435 (M+); HRMS (EI) for C32H37N, calcd 435.2926,
found 435.2928; 56% ee determined by HPLC (Chiral OD column, 2-
propanol/hexane=0.6:99.4, 0.4 mLminÀ1, major isomer 26.12 min, minor
isomer 24.84 min).
1,2-Dimethyl-3-((E)-1,3-di-p-tolylallyl)-1H-indole (3i): Yellow solid, ana-
lytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51; 1H NMR
(300 MHz, CDCl3): d=2.30 (s, 6H), 2.62 (s, 3H), 3.66 (s, 3H), 5.09 (d,
J=7.1 Hz, 1H), 6.33 (d, J=15.8 Hz, 1H), 6.75 (dd, J1 =7.2 Hz, J2 =
15.8 Hz, 1H), 6.93 (t, J=7.3 Hz, 1H), 7.07–7.19 (m, 5H), 7.22–7.30 (m,
6H), 7.49 ppm (d, J=7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3): d=
11.28, 24.49, 21.63, 30.04, 45.45, 109.07, 112.93, 119.23, 119.99, 120.86,
126.64, 127.48, 128.61, 129.12, 129.37, 129.63, 129.75, 130.62, 132.10,
133.83, 135.35, 135.90, 137.28, 141.21 ppm; IR (KBr, neat): n˜ =3058, 3021,
2928, 1599, 1457, 1361, 1265, 1182, 972, 741, 702 cmÀ1; EIMS m/z 365
(M+); HRMS (EI) for C27H27N, calcd 365.2143, found 365.2142; 41% ee
determined by HPLC (Chiral OD column, 2-propanol/hexane=1:99,
0.7 mLminÀ1, major isomer 10.76 min, minor isomer 16.21 min).
3-((E)-1,3-Bis(4-methoxyphenyl)allyl)-1-methyl-1H-indole (3d): Yellow
solid, analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.45;
1H NMR (300 MHz, CDCl3): d=3.72 (s, 3H), 3.78 (s, 3H), 5.02 (d, J=
7.2 Hz, 1H), 6.32 (d, J=15.8 Hz, 1H), 6.47 (dd, J1 =7.2 Hz, J2 =15.8 Hz,
1H), 6.73 (s, 1H), 6.80–6.86 (m, 4H), 7.00 (t, J=7.1 Hz, 1H), 7.16–7.31
(m, 6H), 7.39 ppm (d, J=7.9 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=
32.67, 45.29, 55.25, 55.29, 109.13, 113.75, 113.88, 117.62, 118.16, 118.80,
120.03, 121.56, 127.29, 127.39, 129.39, 129.52, 130.42, 130.92, 135.92,
158.08, 158.85 ppm; IR (KBr, neat): n˜ =3058, 3022, 2932, 1598, 1456,
1360, 1262, 1180, 962, 741, 701 cmÀ1; EIMS m/z 383 (M+); HRMS (EI)
for C26H25NO2, calcd 383.1885, found 383.1882; 53% ee determined by
HPLC (Chiral OD column, 2-propanol/hexane=3:97, 1 mLminÀ1, major
isomer 10.90 min, minor isomer 12.05 min).
1-Benzyl-3-((E)-1,3-di-p-tolylallyl)-1H-indole (3j): Yellow solid, analyti-
cal TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51; 1H NMR
(400 MHz, CDCl3): d=2.31 (s, 3H), 2.32 (s, 3H), 5.06 (d, J=7.4 Hz, 1H),
5.28 (s, 2H), 6.38 (d, J=15.8 Hz, 1H), 6.70 (dd, J1 =7.4 Hz, J2 =15.8 Hz,
1H), 6.86 (s, 1H), 6.98 (t, J=7.4 Hz, 1H), 7.07–7.14 (m, 7H), 7.21–7.30
(m, 8H), 7.42 ppm (d, J=7.9 Hz, 1H); 13C NMR (100 MHz, CDCl3): d=
21.03, 21.11, 45.83, 50.00, 109.68, 119.07, 120.14, 121.77, 126.21, 126.58,
126.77, 127.46, 127.58, 128.34, 128.71, 129.08, 129.13, 130.15, 131.88,
134.79, 135.74, 136.82, 137.09, 137.78, 140.57 ppm; IR (KBr, neat): n˜ =
3-((E)-1,3-Bis(4-fluorophenyl)allyl)-1-methyl-1H-indole (3e): Yellow
solid, analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51;
1H NMR (400 MHz, CDCl3): d=3.74 (s, 3H), 5.06 (d, J=7.3 Hz, 1H),
6.32 (d, J=15.8 Hz, 1H), 6.55 (dd, J1 =7.3 Hz, J2 =15.8 Hz, 1H), 6.73 (s,
1H), 6.93–7.02 (m, 5H), 7.17 (t, J=7.2 Hz, 1H), 7.24–7.32 (m, 5H),
7.35 ppm (d, J=7.9 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=32.71,
45.31, 109.27, 115.03, 115.21, 115.31, 115.50, 116.79, 118.98, 119.79, 121.76,
126.99, 127.27, 127.69, 127.79, 129.78, 129.88, 130.20, 133.47, 137.44,
139.09, 163.15, 163.75 ppm; IR (KBr, neat): n˜ =3056, 3025, 2931, 1595,
1452, 1365, 1265, 1182, 961, 741, 700 cmÀ1; EIMS m/z 359 (M+); HRMS
(EI) for C24H19F2N, calcd 359.1486, found 359.1485; 63% ee determined
3058, 3020, 2931, 1697, 1612, 1450, 1358, 1265, 1180, 972, 741, 702 cmÀ1
;
EIMS m/z 427 (M+); HRMS (EI) for C33H29N, calcd 427.2300, found
427.2301; 35% ee determined by HPLC (Chiral OD column, 2-propanol/
hexane=1:99, 0.7 mLminÀ1
,
major isomer 26.13 min, minor isomer
20.37 min).
by HPLC (Chiral OD-H column, 2-propanol/hexane=1:99, 0.5 mLminÀ1
,
major isomer 31.62 min, minor isomer 29.41 min).
822
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Chem. Asian J. 2011, 6, 812 – 824

Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles
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Yellow solid, analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =
0.51; 1H NMR (400 MHz, CDCl3): d=3.72 (s, 3H), 5.02 (d, J=7.2 Hz,
1H), 6.29 (d, J=15.8 Hz, 1H), 6.50 (dd, J1 =7.3 Hz, J2 =15.8 Hz, 1H),
6.74 (s, 1H), 6.94–7.01 (m, 4H), 7.12–7.14 (m, 1H), 7.18–7.25 (m, 3H),
7.28–7.32 ppm (m, 3H); 13C NMR (75 MHz, CDCl3): d=32.90, 45.04,
110.34, 115.16, 115.25, 115.44, 115.54, 116.32, 119.09, 122.12, 126.15,
127.83, 128.56, 129.69, 129.80, 131.77, 138.64, 139.22, 163.12, 163.58 ppm;
IR (KBr, neat): n˜ =3057, 3026, 2933, 1695, 1599, 1501, 1223, 1157, 970,
831, 741 cmÀ1; EIMS m/z 393 (M+); HRMS (EI) for C24H18ClF2N, calcd
393.1096, found 393.1095; 51% ee determined by HPLC (Chiral OD-H
column, 2-propanol/hexane=1:99, 0.5 mLminÀ1, major isomer 31.23 min,
minor isomer 23.46 min).
3-((E)-1,3-Bis(4-fluorophenyl)allyl)-1,2-dimethyl-1H-indole (3l): Yellow
solid, analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51;
1H NMR (400 MHz, CDCl3): d=2.35 (s, 3H), 3.67 (s, 3H), 5.08 (d, J=
7.2 Hz, 1H), 6.32 (d, J=15.8 Hz, 1H), 6.66 (dd, J1 =7.1 Hz, J2 =15.8 Hz,
1H), 6.91–6.96 (m, 5H), 7.10 (t, J=7.7 Hz, 1H), 7.24–7.32 ppm (m, 6H);
13C NMR (75 MHz, CDCl3): d=11.22, 30.08, 45.11, 109.24, 112.38, 115.32,
115.53, 115.72, 115.94, 119.42, 119.72, 121.09, 127.19, 128.15, 128.23,
129.91, 130.06, 130.14, 132.43, 133.92, 134.02, 137.33, 139.64, 163.08,
163.78 ppm; IR (KBr, neat): n˜ =3052, 3018, 2925, 1596, 1452, 1360, 1261,
1175, 969, 741 cmÀ1; EIMS m/z 373 (M+); HRMS (EI) for C25H21F2N,
calcd 373.1642, found 373.1642; 45% ee determined by HPLC (Chiral
OD-H column, 2-propanol/hexane=0.8:99.2, 0.5 mLminÀ1, major isomer
38.47 min, minor isomer 36.99 min).
3-((E)-1,3-Bis(4-fluorophenyl)allyl)-1-phenyl-1H-indole (3m): Yellow
solid, analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51;
1H NMR (400 MHz, CDCl3): d=5.13 (d, J=7.2 Hz, 1H), 6.39 (d, J=
15.8 Hz, 1H), 6.62 (dd, J1 =7.2 Hz, J2 =15.8 Hz, 1H), 6.95–7.10 (m, 6H),
7.21 (t, J=7.9 Hz, 1H), 7.31–7.35 (m, 5H), 7.41 (t, J=7.9 Hz, 1H) 7.48–
7.49 (m, 4H), 7.55 ppm (d, J=8.3 Hz, 1H); 13C NMR (75 MHz, CDCl3):
d=39.71, 105.02, 109.56, 109.65, 109.77, 109.87, 113.76, 114.43, 114.47,
117.00, 118.59, 120.70, 120.71, 122.13, 122.21, 123.96, 124.11, 124.23,
124.30, 126.17, 133.35, 135.58, 163.05, 163.62 ppm; IR (KBr, neat): n˜ =
3055, 3019, 2960, 1599, 1498, 1457, 1371, 1226, 1086, 1003, 833, 741 cmÀ1
;
EIMS m/z 421 (M+); HRMS (EI) for C29H21F2N, calcd 421.1642, found
421.1639; 43% ee determined by HPLC (Chiral OD-H column, 2-propa-
nol/hexane=1:99, 0.5 mLminÀ1, major isomer 18.78 min, minor isomer
15.34 min).
3-((E)-1,3-Bis(4-fluorophenyl)allyl)-1-butyl-1H-indole (3n): Yellow solid,
analytical TLC (silica gel 60, 5% EtOAc in hexane), Rf =0.51; 1H NMR
(300 MHz, CDCl3): d=0.90 (t, J=7.3 Hz, 3H), 1.27–1.42 (m, 2H), 1.75–
1.84 (m, 2H), 4.06 (t, J=7.3 Hz, 2H), 5.06 (d, J=7.1 Hz, 1H), 6.32 (d,
J=15.8 Hz, 1H), 6.56 (dd, J1 =7.2 Hz, J2 =15.8 Hz, 1H), 6.78 (s, 1H),
6.94–7.01 (m, 5H), 7.18 (t, J=7.2 Hz, 1H), 7.29–7.36 ppm (m, 6H);
13C NMR (75 MHz, CDCl3): d=13.70, 20.23, 32.37, 45.36, 46.10, 109.47,
115.00, 115.20, 115.28, 115.49, 116.63, 118.84, 119.85, 121.56, 126.21,
127.07, 127.69, 127.80, 129.37, 129.88, 132.33, 136.75, 139.14, 163.13,
163.74 ppm; IR (KBr, neat): n˜ =3056, 3022, 2930, 1610, 1458, 1361, 1227,
1180, 966, 741 cmÀ1; EIMS m/z 401 (M+); HRMS (EI) for C27H25F2N,
calcd 401.1955, found 401.1956; 47% ee determined by HPLC (Chiral
OD-H column, 2-propanol/hexane=1:99, 0.5 mLminÀ1
, major isomer
22.80 min, minor isomer 17.89 min).
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Acknowledgements
We are thankful for the financial support of The University of Hong
Kong (University Development Fund), Hong Kong Research Grant
Council (PolyU 5027/09P), the Areas of Excellence Scheme established
under the University Grants Committee of the Hong Kong Special Ad-
ministrative Region, China (AoE/P-10/01), RGC Collaborative Research
Fund (HKU1/CRF/08), and RGC grant (HKU 7007/08P). We thank Dr.
Stephen Sin-Yin Chui and Dr. Nianyong Zhu for solving the X-ray crys-
tal structures.
Chem. Asian J. 2011, 6, 812 – 824
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
823

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Received: September 7, 2010
Published online: December 14, 2010
824
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 812 – 824