Aza-Claisen rearrangement in the cyclization reactions of nitrogen-containing enynes via ruthenium vinylidene complexes

Article abstract of DOI:10.1021/om100292d

The cyclization reaction of several diallyl aromatic amine molecules, each containing an ethynyl group at the ortho position of the aromatic ring, is accompanied by an aza-Claisen rearrangement, causing an allyl group migration to give substituted indole

Full text of DOI:10.1021/om100292d

5776 Organometallics 2010, 29, 5776–5782
DOI: 10.1021/om100292d
Aza-Claisen Rearrangement in the Cyclization Reactions
of Nitrogen-Containing Enynes via Ruthenium Vinylidene Complexes
Pei-Yun Chiang, Ying-Chih Lin,* Yu Wang, and Yi-Hong Liu
Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
Received April 12, 2010
The cyclization reaction of several diallyl aromatic amine molecules, each containing an ethynyl
group at the ortho position of the aromatic ring, is accompanied by an aza-Claisen rearrangement,
causing an allyl group migration to give substituted indole compounds. This cyclization is catalyzed
by ruthenium triphenylphosphine and diphenylphosphinoethane (dppe) complexes as well as gold
complexes with silver reagent. The less sterically crowded dppe complex is a more efficient catalyst.
The mechanism involving a vinylidene intermediate is proposed on the basis of isolation of several
intermediates in the ruthenium-catalyzed system. Single crystals of a metal complex with the cyclized
ligand were obtained, and the structure was determined by an X-ray diffraction analysis.
Introduction
derivatives using transition-metal catalysts.6 However, reac-
tions of nitrogen-containing enynes aiming at substituted
indole have been much less explored.
During the past decade, metal-catalyzed reactions of
enynes have become the focus of many explorations, because of
their rich and versatile reactivity.1,2 The chemistry of com-
plexes containing vinylidene ligands, which are considered
important key intermediates, reveals mechanistic insight into
these reactions of enyne. Particularly, readily isolable ruthe-
nium vinylidene complexes have attracted a great deal of
attention in stoichiometric3 as well as catalytic reactions
involving enyne.4 The indole nucleus, an important compo-
nent in today’s pharmaceuticals and bioactive products, is a
widely distributed heterocycle found in nature. New and
straightforward methods to access these substrates are thus
always highly desirable.5 Recently, alkynes become attrac-
tive starting materials for the synthesis of a variety of indole
Various metals, such as zirconium,7a titanium,7b-e and zinc,7f
are known to catalyze the intermolecular hydroamination of
alkynes with arylhydrazines. The synthesis of indoles from
o-haloaniline with alkynes via a heteroannulation process is
an attractive method. The Larock heteroannulation and
other palladium-catalyzed indolizations with alkynes are
also known.8 Cyclizations of o-alkynylaniline derivatives
catalyzed by rhodium, palladium, and gold complexes have
been reported.9 These metal-catalyzed cyclizations proceed
via intermolecular processes to produce functionalized in-
doles and their derivatives through external addition to the
triple bond. However, a more efficient intramolecular cycli-
zation accompanied by a migration of an unsaturated functional
€
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*To whom correspondence should be addressed. E-mail: yclin@ntu.
edu.tw.
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pubs.acs.org/Organometallics
Published on Web 10/21/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 22, 2010 5777
Scheme 1
Scheme 2
group, bonded to the heteroatom, is not known. We report
herein a high-yield synthesis of substituted indoles from
cyclization of enynes containing nitrogen atoms accompa-
nied by an aza-Claisen rearrangement. Mechanistic insight
into the formation of substituted indoles was obtained by the
isolation and characterization of several ruthenium com-
plexes as key intermediates.
Results and Discussion
Synthesis and Catalytic Reactions of 1,7-Enynes. Synthesis
of the N,N-diallyl aromatic amine 3a was achieved first by
the Sonogashira coupling reaction10 of 2-iodoaniline with
(trimethylsilyl)acetylene. This is followed by a high-yield
allylation reaction using allyl iodide in acetone to give 2a.
Deprotection of 2a in the presence of anhydrous K2CO3 gave
3a, with a terminal alkynyl group (Scheme 1). The analogous
compounds 3b,c containing additional methyl groups were
similarly prepared from a mixture of trans- and cis-crotyl
bromide (6:1) via 2b and 1-bromo-3-methyl-2-butene via
2c, respectively. These enynes have been characterized by
1H and 13C NMR spectra, EI mass spectra, and elemental
analysis. In the 1H NMR spectrum of 3a the olefinic terminal
trans hydrogen shows a doublet peak at δ 5.18 with J =
15.5 Hz and the cis hydrogen at δ 5.14 with J = 8.7 Hz. In the
1H NMR spectrum of 3c, two methyl signals appear at δ 1.67
and 1.56. The N,N-dicrotyl aromatic amine 3b presumably
consists of a mixture of trans/trans (tt), trans/cis, (tc), and
and an EI mass spectrum. The single allylic pattern observed
for the original N,N-diallyl groups in the 1H NMR spectrum
of 3a changes to two different allylic patterns, and a new
olefinic ring hydrogen peak appears at δ 6.87 as a singlet for
6a. The singlet signal of the alkynyl hydrogen of 3a at δ 3.36
disappears after transformation, and there is no resonance
characteristic of an sp carbon in the 13C NMR spectrum of
6a. The EI mass spectrum confirms the formation of com-
pound 6a, showing a parent peak at m/z 197.0 and a frag-
mentation peak at m/z 156.1, corresponding to the cleavage
of one allyl group.
1
In order to better understand the mechanism of the
catalytic reaction, we studied the reaction of 3a with 1 equiv
of 1. Interestingly, treatment of 3a with 1 in the presence of
AgPF6 in CH2Cl2 afforded initially the cationic ruthenium
vinylidene complex 4a, which shows a broad singlet signal at
δ 47.03 in the 31P NMR spectrum, in moderate yield and
other side products. Unfortunately, it is difficult to purify 4a.
From the residual solution of this reaction, the organic
product 6a and 1 were also isolated. For further character-
ization of 4a we carried out the deprotonation reaction to
generate the neutral acetylide complex 5a (see Scheme 2).
The singlet 31P NMR resonance of 5a at δ 51.64 is in the
region of an acetylide complex. Singlet 31P NMR signals are
observed for both 4a and 5a. The solution of 4a at room
temperature and protonation of 5a both yielded 6a. How-
ever, no other isolable intermediate was obtained from the
cyclization of 3a in the presence of a stoichiometric amount
of 1.
cis/cis (cc) isomers in a statistical ratio of 36:12:1. The H
NMR spectrum of the mixture of 3b shows two singlet
signals at δ 3.40 and 3.41 assigned to the proton of the
terminal alkyne of tt and tc isomers, and after purification,
the tt:tc ratio is about 4.7:1. The cc isomer, probably present
in only a very small quantity, shows no signal. Multiplet
resonances for the olefinic hydrogens of the tt and tc isomers
are overlapped at δ 5.66-5.49. The doublet signal at δ 3.84 is
assigned to the methylene group of the trans-crotyl group.
The corresponding 1H resonance of the cis-crotyl group
shows a doublet resonance at δ 3.89. No attempt was made
to separate the mixture.
As shown in Scheme 2, transformation of 3a to 6a,
catalyzed by [Ru]Cl (1; [Ru] = Cp(PPh3)2Ru), is observed at
room temperature. This process involves both a cyclization
and an aza-Claisen rearrangement of one allyl group from
nitrogen to the internal carbon of the triple bond. This
cyclization/rearrangement reaction of 3a could also be cat-
alyzed with 5 mol % of AuClPPh3/AgSbF6 in CH2Cl2, also
affording 6a. The cyclization product 6a, purified by chro-
matography, was characterized by 1D and 2D NMR spectra
Cyclization of the isomeric mixture of 1,7-enyne 3b, which
contains a terminal methyl substituent at the allyl group, was
also explored. The reaction of the mixture of tt and tc isomers
of 3b with 1 in a 1:1 ratio in the presence of KPF6 in CH2Cl2
for 1 day at room temperature directly afforded a mixture of
6b in almost quantitative yield. The mixture of 6b consists of
(10) Lavastre, O.; Cabioch, S.; Dixneuf, P. H. Tetrahedron 1997, 53,
7595–7604.

5778 Organometallics, Vol. 29, No. 22, 2010
Chiang et al.
trans and cis isomers in a ratio of 4.5:1. A catalytic reaction
could be achieved with almost quantitative yield by using
7.5 mol % of 1 at room temperature over 12 h. Using a 5 mol %
AuClPPh3/AgSbF6 catalyst system, this cyclization reaction
of 3b in CH2Cl2 also afforded a mixture of 6b in 85%
maximum isolated yield over 7 h at room temperature. The
product 6b was characterized by 1H, 13C, 2D COSY, HSQC,
and HMBC NMR spectra and an EI mass spectrum. In this
transformation, migration of one linear crotyl group of 3b to
the five-membered ring to form a substituted branched but-
3-en-2-yl group, a result of aza-Claisen rearrangement, is
clearly observed by NMR. In the 1H NMR spectrum of 6b,
both trans and cis isomers display identical resonances for
the substituted but-3-en-2-yl group. Resonances at δ 6.10,
5.15, and 5.04 in a ratio of 1:1:1, respectively, are assigned to
three olefinic hydrogens of the terminal vinyl group of the
substituted but-3-en-2-yl group with the last two having
3JHH = 17.2 and 10.2 Hz, respectively. In addition, the
singlet peak at δ 1.49 and the multiplet peak at δ 3.78,
assigned to the methyl and the methyne group, respectively,
on the stereogenic carbon center are identical for both
isomers of 6b. For the two isomers of 6b, the differences on
NMR data mainly appear for the trans- and cis-crotyl group
on the nitrogen. A broad peak at δ 1.71 is assigned to methyl
groups of the trans isomer, and for the cis isomer, the
corresponding methyl doublet peak appears at δ 1.83. The
characteristic broad multiplet resonance at δ 5.65 is consis-
tent with the two olefinic protons in a trans configuration for
the crotyl group. Well-separated olefinic resonances at δ 5.72
and 5.62 are observed for the cis isomer. The EI mass
spectrum showing a parent peak at m/z 225.2 is consistent
with the formula of 6b. Transformation of the linear crotyl
group to the branched species in the product clearly reveals
that the process proceeds via the aza-Claisen rearrangement,
instead of a direct allyl migration. With a stereogenic center
near the but-3-en-2-yl group, identical NMR data for this
group may indicate that only the trans-crotyl group can
undergo the aza-Claisen rearrangement, thus fixing the
stereochemistry of the methyl-substituted sp3 carbon in the
product. In addition, the steric effect should prohibit intra-
molecular approach of the double bond of the cis-crotyl
group. Presumably the trans and cis isomeric products are
obtained from the tt and tc isomers of 3b, respectively. The tt
isomer gives the trans product, and the tc isomer gives the cis
product. The product distribution and the proposed mech-
anism discussed below most likely indicate that only the
trans-crotyl group undergoes the aza-Claisen rearrange-
ment. The selectivity will be discussed later on the basis of
the structure determination of an intermediate.
Figure 1. ORTEP drawing of trans-7b0. Phenyl groups on the
chelating dppe ligand possibly control the stereochemistry of the
substituted indole ring. Thermal ellipsoids are set at the 30%
probability level.
directly gave 7b0 (trans:cis = 4.6:1). Further heating of 7b0 to
50 °C in a chlorinated solvent such as CH2ClCH2Cl, CH2Cl2,
or CHCl3 resulted in formation of 6b and 10 possibly pro-
ceeding via a [Ru0]H species. The lower yield of 7b0 directly
from 3b in chlorinated solvent is thus due to the rapid
replacement of the cyclized ligand on the metal by the chloride
to form 10 and 6b. Use of methanol as a solvent increases the
yield of 7b0 up to 77%.
31
The P NMR spectrum of the crude product of 7b0 in
acetone-d6 shows two sets of two doublet peaks at δ 76.35,
2
2
64.12 with JPP = 59.4 Hz and δ 76.82, 64.52 with JPP
=
53.6 Hz in a ratio of 4.6:1. Two isomers presumably originate
from the tt and tc forms, respectively, of 3b. In order to
separate two products, the mixture containing isomers of 7b0
was dissolved in CH2Cl2 and the solution was passed through
a column packed with acidic Al2O3. From the second yellow
band eluted with ethyl acetate, the major product trans-7b0
13
was obtained. The C NMR spectrum of trans-7b0 was
acquired at 243 K to prevent decomposition. The triplet
13C NMR resonance for CR appears at δ 263.9 with 2JCP
=
14.7 Hz, indicating carbene character. The complex trans-7b0
was also characterized by 2D COSY, HSQC, and HMBC
NMR techniques at 243 K. In the H,1H-COSY spectrum,
1
the multiplet 1H peak at δ 2.98, assigned to the sp3-CH unit,
1
shows correlations with the H resonances at δ 0.35, 4.08,
and 4.43, assigned to CH3, RuCCH, and dCH, respectively.
The HMBC spectrum of trans-7b0 displays long-range cor-
relation between CR and NCH2. The ESI mass spectrum,
showing a parent peak at m/z 790.23 and fragmentation ions
corresponding to dissociation of the whole indole moiety,
confirms the formation of complex 7b0.
Isolation of dppe Indole Complexes. In order to better
understand the mechanism, the reaction of 3b and [Ru0]Cl
(10; [Ru0] = Cp(dppe)Ru) was carried out with a 1:1 ratio of
two reactants, leading to the isolation of intermediates. Treat-
ment of 10 with an isomeric mixture of 3b in the presence of
AgPF6 in CH2Cl2 afforded the vinylidene product 4b0. Un-
fortunately, 4b0 is also unstable and displays broad reso-
nances in its NMR spectrum. Slight heating of 4b0 in CDCl3
at 50 °C yielded a mixture of 6b and trans/cis isomers of the
ruthenium complex 7b0, containing a bicyclic indole ring. It is
therefore reasonable to assume that 4b0, like 4a, is a cationic
ruthenium vinylidene complex (see Scheme 2). Attempted
deprotonation of 4b0 failed to give the desired acetylide
complex. Interestingly, in MeOH, the reaction of 3b with 10
in the presence of KPF6 for 4 days at room temperature
Yellow single crystals of trans-7b0 were grown by slow
diffusion of diethyl ether into a CH2Cl2 solution at -20 °C,
and the solid-state crystal structure was determined by an
X-ray crystallographic study. An ORTEP drawing of the
cationic complex is shown in Figure 1.; selected bond dis-
tances and angles are given in Table 1. The space group is
˚
monoclinic P21/c with unit cell dimensions a = 11.7330(1) A,
˚
˚
b = 20.3209(3) A, c = 20.8087(2) A, and β = 90.761(1)°. The
final residuals of the refinement, R1 and wR2, are 0.0409 and
0.1110, respectively. The three-legged piano-stool geometry
around the ruthenium center was determined by two phosphorus
atoms of the chelating ligand and the bicyclic substituted

Article
Organometallics, Vol. 29, No. 22, 2010 5779
˚
Table 1. Selected Bond Distances (A) and Angles (deg) of
Complex trans-7b0
involves the aza-Claisen rearrangement of the crotyl group
from nitrogen to Cβ of the vinylidene ligand. In the synthesis
of furan derivatives, other types of allyl transfer have been
described.14 In their case, stabilization of the vinyl-metal
intermediate via an enolate species seems necessary, since
only the acetylenic esters and nitriles were reported to under-
go the transfer reaction. Another type resembling allyl
transfer in the presence of PtCl2 or acids was reported,15 in
which the allyl group rearranges from the nitrogen to CR of
the terminal alkyne. However, in our case, the allyl group
transfers to Cβ, instead of CR. In addition, the reaction of 3 to
give 6 is not catalyzed by acid in the presence of silica. Other
benzofuran syntheses were reported by Cacchi and Balme
using Pd(PPh3)3 catalysts.16,17
Bond Distances
Ru1-C1
Ru1-P1
Ru1-P2
2.037(3)
2.2871(7)
2.3167(8)
N1-C1
N1-C7
C1-C2
1.343(4)
1.465(4)
1.526(4)
Bond Angles
P1-Ru1-C1
P2-Ru1-C1
N1-C1-Ru1
95.99(9)
90.04(8)
126.4(2)
N1-C1-C2
C1-N1-C11
C11-N1-C7
105.0(2)
113.7(2)
118.8(3)
Scheme 3
With two stereogenic carbon centers in complex 7b0, the
stereoselectivity for its formation is discussed, even though,
uponformation of6b0, construction of a double bondremoves
one stereogenic center. As shown in Scheme 3, cyclization of
4b0 possibly proceeds via intermediates A and 7b0 sequen-
tially. Presumably, in A, the less crowded sides of the indole
plane, namely that near the Cp ligand, should favor approach
of the crotyl group on the nitrogen toward Cβ; however, free
rotation of the Ru-C bond nullifies the selectivity of the
stereogenic carbon on the five-membered ring. In this aza-
Claisen rearrangement, the steric effect may also inhibit the
cis-crotyl group to approach Cβ. This, along with the transi-
tion state, in either boat or chair form, in the Claisen
rearrangement then determines the stereochemistry on the
but-3-en-2-yl group. Hence, complex tt-4b0 transforms to
trans-7b0 and complex tc-4b0 to cis-7b0. Namely, only the
trans-crotyl group undergoes the aza-Claisen rearrange-
ment. Thus, the minor product of 7b0 would be the cis isomer.
Notably, this cyclization reaction provides a direct approach
to the substituted indole compound under mild conditions
and gives a good selectivity without significant observation
of the other probable isomers.
Steric Effect for the Catalytic Cyclization. As shown in
Scheme 4, reactions of the TMS-protected dimethylsubsti-
tuted allylic amine 2c were also investigated. We first carried
out the reaction of 1 with 2c in the presence of KF and KPF6
in a MeOH/THF mixed solvent at room temperature, giving
directly the acetylide complex 5c, which shows a 31P NMR
singlet resonance at δ 51.30. Protonation of 5c by HBF4 in
Et2O generated the vinylidene complex 4c. The 31P NMR
spectrum of 4c shows a sharp singlet resonance at δ 40.80. In
the 13C NMR spectrum the triplet signal at δ 346.77 with
JCP = 11.0 Hz is assigned to CR. Interestingly, complex 4c,
displaying normal NMR signals, is stable in CDCl3. This
is different from the aforementioned results of analogous
vinylidene complexes 4a and 4b. The reaction of 1 with 3c
also stopped at the stage of the vinylidene complex 4c, not
proceeding further for cyclization and rearrangement or
catalytically giving any indole product in chlorinated sol-
vent. This can be explained by the steric hindrance between
indole ligand around the metal. The Ru(1)-C(1) bond length
˚
is 2.037(3) A, typical for a Ru-C single bond. The N(1)-
˚
C(1) bond distance of 1.343(4) A is well within the range of
values for a conjugated NdC double bond.11 The crotyl
group on the nitrogen is in a trans configuration. The two
atoms C(2) and C(3) are stereogenic carbon atoms.
Proposed Mechanism. A proposed mechanism for the
formation of 7b0 is shown in Scheme 3. First, the reaction
of [Ru0]Cl with the terminal alkyne gives the cationic vinyl-
idene intermediate 4b0, which then undergoes a 5-endodig
cyclization.12 Namely, the intramolecular nucleophilic at-
tack of nitrogen to the electrophilic CR forms the species A.
This is followed by an aza-Claisen rearrangement13 to give
the cationic carbene complex 7b0, in which the cationic
charge could be delocalized either at Ru or at nitrogen.
However, the solid-state structure seems to favor the form
with the M-C single bond, as shown by the structure deter-
mination. This intramolecular cycloisomerization process
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63, 1001–1011.
(17) Monteiro, N.; Balme, G. Synlett 1998, 746–747.

5780 Organometallics, Vol. 29, No. 22, 2010
Chiang et al.
Scheme 4
cyclization is controlled by the steric effect. This could also
imply that, for 3b, only the trans-crotyl group undergoes the
aza-Claisen rearrangement.
Conclusion
In conclusion, cyclopentadienyl ruthenium chloride com-
plexes with phosphine ligands catalyze the transformation of
diallylarylamine with a terminal alkynyl group on the aromatic
ring to give the substituted-indole product. The reaction
proceeds by the formation of the vinylidene intermediate
from the terminal alkyne followed by a cyclization reaction
to give the indole product. Subsequent aza-Claisen rearran-
gement under mild conditions results in migration of the
substituted or nonsubstituted allyl group to the indole ring.
The catalytic reaction is influenced by the steric bulk of the
phosphine ligands. All transformations of 3a-c to 6a-c can
be catalyzed smoothly by the less bulky CpRu(dppe)Cl com-
plex. However, transformation of 3c could not be catalyzed
by CpRu(PPh3)2Cl because of the steric hindrance between
the bulkier phosphine ligand and the substituted allylic
groups. Several intermediates were observed, and one of
them was fully characterized by single-crystal X-ray diffraction
analysis.
PPh3 and the slightly bulkier substituted allylic groups on the
vinylidene ligand of 4c, thus restraining the nitrogen attack.
However, the transformation of 3c to 6c could be cata-
lyzed by 10 in high yield (Scheme 4). Compound 6c has been
characterized by 1D, 2D COSY, HSQC, and HMBC NMR
and EI mass techniques. The 1H NMR spectrum of 6c shows
a new singlet peak at δ 1.58 assigned to two internal methyl
groups. This, along with the terminal vinyl pattern at δ 5.15
and 5.08 with 3JHH = 17.4 and 10.6 Hz, respectively, clearly
indicates the result of an aza-Claisen rearrangement. In the
13C NMR spectra the 3 sp3-carbon and 8 sp2-carbon reso-
nances of 3c change to 5 sp3-carbon and 12 sp2-carbon
resonances of 6c. The reaction of the TMS-protected enyne
2c with 10 was carried out in the presence of KF in methanol/
THF. The fluoride ion induces both desilylation and depro-
tonation to generate the resulting acetylide complex 5c0. The
31P NMR spectrum of 5c0 shows a singlet resonance at δ
92.14. Complex 5c0 is stable in solution. Interestingly, under
basic conditions, the reaction of 3c with 1 equiv of 10 also
afforded 5c0. The ratio of 5c0 to 10 was 2:1, as indicated from
the 31P NMR spectra. This is probably due to the steric bulk
of 3c, such that when it is π-coordinated to the ruthenium,
the steric repulsion causes dissociation of the ligand. Further
protonation of complex 5c0 by excess HBF4 was carried out
in an NMR tube, and the reaction was monitored by 31P
NMR spectra. Transformation of the acetylide complex into
two new products was observed over a few minutes. The two
31P NMR signals at δ 79.91 and 80.47 are in a ratio of 1.5:1.
The former could be presumably attributed to the vinylidene
intermediate,18 and the latter could be due to a cyclization
product from addition of nitrogen to CR. After a few hours,
the peak at δ 79.91 decreased but the peak at δ 80.47
increased and a set of two doublets, assigned to complex
Experimental Section
General Procedures. All manipulations were performed under
an atmosphere of dry nitrogen using vacuum-line, drybox, and
standard Schlenk techniques unless mentioned otherwise. Hex-
anes and CH2Cl2 were distilled from CaH2, diethyl ether and
THF were distilled from sodium benzophenone ketyl, and
methanol was distilled from Mg/I2. All other solvents and
reagents were of reagent grade and were used as received.
NMR spectra were recorded on Bruker AM-300, Avance-400,
and DMX-500 FT-NMR spectrometers at room temperature
unless stated otherwise and were reported in units of δ with
residual protons in the solvent as a standard (CDCl3, δ 7.24;
C6D6, δ 7.16; d6-acetone, δ 2.04). FT-IR spectra were carried out
on a Bruker Tensor 27 spectrometer. Mass spectrometry, ele-
mental analyses, and X-ray diffraction studies were carried out
at the Regional Center of Analytical Instrument located at the
National Taiwan University. All reagents were obtained from
commercial suppliers. The complexes Cp(PPh3)2RuCl19a and
Cp(dppe)RuCl19b were prepared using literature methods.
Synthesis of 2a and 3a. Excess allyl iodide (2.40 mL, 26.15 mmol)
was added to a solution of 2-[(trimethylsilyl)ethynyl]aniline
(1.00 g, 5.28 mmol) and K2CO3 (2.92 g, 21.13 mmol) in 40 mL
of dried acetone. The mixture was stirred at 55 °C overnight. The
resulting solution was filtered through Celite, and the solvent of
the filtrate was evaporated to give the crude product, which was
purified by flash chromatography on silica gel with n-hexane/
CH2Cl2 (8.5/1.5) as eluent to afford a yellow band. The solvent
was removed under vacuum to give the pure liquid 2a (1.27 g,
1
89% yield). Spectroscopic data of 2a are as follows. H NMR
(400 MHz, CDCl3): δ 7.40, 7.16, 6.86, 6.79 (m, 4H, Ph), 5.86 (m,
2H, dCH), 5.20 (d, J = 16.9 Hz, 2H, dCHH trans), 5.14 (d, J =
10.1 Hz, 2H, dCHH cis), 3.91 (d, J = 5.4 Hz, 4H, CH2), 0.22 (s,
9H, TMS). Then K2CO3 (14.11 g, 102.09 mmol) was added to a
solution of 2a (1.27 g, 4.72 mmol) in MeOH/THF (1:1). The
mixture was stirred at room temperature for 5 h. The resulting
solution was filtered through Celite and was dried by rotary
evaporation to give yellow liquid 3a (0.90 g, 97% yield). Spectro-
scopic data of 3a are as follows. 1H NMR (400 MHz, CDCl3): δ
2
7c0, appeared at δ 78.44 and 66.05 with JPP = 22.5 Hz.
Finally, the formation of the indole product 6c was also
observed in the 1H NMR spectrum. The transformation of
3c to 6c, catalyzed by 10, clearly demonstrates that the
(19) (a) Bruce, M. I.; Windsor, N. J. Aust. J. Chem. 1977, 30, 1601–
1604. (b) Ashby, G. S.; Bruce, M. I.; Tomkins, I. B.; Wallis, R. C. Aust. J.
Chem. 1979, 32, 1003–1016.
(18) Chang, C. W.; Lin, Y. C.; Lee, G. H.; Wang, Y. J. Organomet.
Chem. 2002, 660, 127–132.

Article
Organometallics, Vol. 29, No. 22, 2010 5781
7.45-6.84 (m, 4H, Ph), 5.84 (m, 2H, dCH), 5.18 (d, J = 15.5 Hz,
2H, dCHH trans), 5.14 (d, J = 8.7 Hz, 2H, dCHH cis), 3.89 (d,
J = 4.6 Hz, 4H, CH2), 3.36 (s, 1H, tCH). 13C NMR (125 MHz,
CDCl3): δ 153.1 (dCN), 135.1, 135.0, 129.3, 120.6, and 119.6
(Ph), 117.3, 114.9 (CdC), 83.0, 82.2 (CtC), 54.5 (CH2). EI-MS:
m/z 197.00 (Mþ). Anal. Calcd for C14H15N: C, 85.24; H, 7.66; N,
7.10. Found: C, 85.08; H, 7.53; N, 7.01.
(Ph), 135.01, 121.57 (CdC), 83.18, 81.98 (CtC), 48.79 (CH2),
24.91, 18.20 (CH3). EI-MS: m/z 253.20 (Mþ). Anal. Calcd for
C18H23N: C, 85.32; H, 9.15; N, 5.53. Found: C, 85.72; H, 9.04;
N, 5.48.
Synthesis of Complexes 5c and 5c0. To a Schlenk flask contain-
ing [Ru]Cl (1; 100 mg, 0.137 mmol), 2c (70 mg, 0.215 mmol), KF
(24 mg, 0.411 mmol), and KPF6 (50 mg, 0.274 mmol) were
added 20 mL of MeOH and 10 mL of THF. Then the solution
was stirred overnight under nitrogen at room temperature. The
solvent was removed in vacuo, and diethyl ether was used to ex-
tract the crude product. The ether solution was filtered through
the Celite. Removal of the solvent under vacuum gave the desired
product, characterized as 5c (103 mg, 80% yield). Spectroscopic
data of 5c are as follows. 1H NMR (400 MHz, CDCl3): δ
7.60-6.70 (m, 34H, Ph), 5.43 (t, 2H, dCH), 4.40 (s, 5H, Cp),
4.16 (d, 4H, CH2), 1.79 (s, 3H, CH3), 1.71 (s, 3H, CH3). 31P
NMR (162 MHz, CDCl3): δ 51.30. MS (FABþ): m/z 943.30
(M þ 1)þ. Anal. Calcd for C59H57NP2Ru: C, 75.14; H, 6.09; N,
1.49. Found: C, 75.09; H, 6.21; N, 1.32. Complex 5c0 (110 mg,
0.134 mmol, 81% yield) was similarly prepared from the reac-
tion of [Ru’]Cl (10; 100 mg, 0.166 mmol), 2c (69 mg, 0.212 mmol),
KF (25 mg, 0.428 mmol), and KPF6 (48 mg, 0.263 mmol) in
20 mL of methanol and 10 mL of THF. Spectroscopic data of 5c0
are as follows. 1H NMR (400 MHz, acetone-d6): δ 7.92-6.58 (m,
24H, Ph), 5.25 (t, 3JHH = 6.4 Hz, 1H, dCH), 4.68 (s, 5H, Cp),
3.84 (d, 3JHH = 6.4 Hz, 2H, CH2), 2.25 (m, 2H, dppe), 2.09 (m,
2H, dppe), 1.71 (s, 3H, CH3), 1.64 (s, 3H, CH3). MS (FABþ):
m/z 817.20 (M þ 1)þ. 31P NMR (162 MHz, acetone-d6): δ 92.14.
Anal. Calcd for C49H51NP2Ru: C, 72.04; H, 6.29; N, 1.71.
Found: C, 72.22; H, 6.36; N, 1.59.
Synthesis of 2b and 3b. An aliquot of trans- and cis-crotyl
bromide (6:1, 5.50 mL, 52.83 mmol) was added to a suspension
of 2-[(trimethylsilyl)ethynyl]aniline (2.01 g, 10.57 mmol) and
K2CO3 (4.38 g, 31.69 mmol) in 50 mL of dried acetone. The
mixture was stirred at 55 °C overnight. The resulting solution
was filtered through Celite and evaporated to give the crude
product, which was purified by flash chromatography on silica
gel with n-hexane/CH2Cl2 (9:1) as eluent to afford a yellow
band. Solvent was then removed under vacuum to give the liquid
product 2b (2.64 g, 84% yield). The ratio of trans/trans (tt) to
trans/cis (tc) product is 4.7:1. Spectroscopic data of 2b are as
1
follows. H NMR (400 MHz, CDCl3): tt isomer, δ 7.39-6.73
(m, 4H, Ph), 5.61-5.48 (m, 4H, dCH), 3.82 (d, 3JHH = 5.4 Hz,
4H, CH2), 1.67 (d, 3JHH = 5.9 Hz, 6H, CH3), 0.23 (s, 9H, TMS);
tc isomer, δ 7.39-6.73 (m, 4H, Ph), 5.61-5.48 (m, 4H, dCH),
3.89 (d, 3JHH = 5.7 Hz, 4H, CH2), 1.63 (d, 3JHH = 6.8 Hz, 6H,
CH3), 0.22 (s, 9H, TMS). 13C NMR (125 MHz, CDCl3): tt
isomer, δ 153.29 (dCN), 135.06, 129.04, 119.47, and 118.71
(Ph), 128.25, 127.86 (CdC), 104.92, 98.84 (CtC), 52.86 (CH2),
17.77 (CH3), 0.04 (TMS); tc isomer, 153.11 (dCN), 134.94-
118.91 (Ph), 127.98, 126.20 (CdC), 104.76, 98.99 (CtC), 47.32
(CH2), 13.13 (CH3), 0.32 (TMS). Then K2CO3 (0.48 g, 3.47 mmol)
was added to a solution of 2b (2.64 g, 8.88 mmol) in MeOH/THF
(1:1). The mixture was stirred at room temperature for 5 h. The
resulting solution was filtered through Celite, and the filtrate
was dried by rotary evaporation to give yellow liquid product 3b
(1.96 g, 98% yield). The ratio of tt to tc product remained the
same. Spectroscopic data of 3b are as follows. 1H NMR (400 MHz,
CDCl3): tt isomer, δ 7.48-6.82 (m, 4H, Ph), 5.66-5.49 (m, 4H,
dCH), 3.84 (d, 3JHH = 5.9 Hz, 4H, CH2), 3.40 (s, 1H, tCH),
1.69 (d, 3JHH = 5.4 Hz, 6H, CH3); tc isomer, δ 7.48-6.82 (m,
4H, Ph), 5.66-5.49 (m, 4H, dCH), 3.89 (d, 3JHH = 6.1 Hz, 4H,
Synthesis of Complex 4c. A dilute solution of HBF4 Et2O in
3
diethyl ether was added dropwise at 0 °C to a stirred solution of
complex 5c (100 mg, 0.122 mmol) in 20 mL of diethyl ether.
Immediately, an insoluble solid precipitated, but the addition
was continued until no further solid was formed. The solution
was then decanted, and the pink solid was washed with diethyl
ether and dried in vacuo to give 4c (100 mg, 79% yield).
1
Spectroscopic data of 4c are as follows. H NMR (400 MHz,
CDCl3): δ 7.87-6.56 (m, 34H, Ph), 5.95 (s, 1H, Hβ), 5.20 (7H,
Cp and dCH), 4.38 (d, 3JHH = 6.7 Hz, 4H, CH2), 1.53 (s, 3H,
CH3), 1.52 (s, 3H, CH3). 13C NMR (125 MHz, CDCl3): δ 346.77
CH2), 3.41 (s, 1H, tCH), 1.63 (d, 3JHH = 6.1 Hz, 6H, CH3); 13
C
NMR (125 MHz, CDCl3): tt isomer, δ 153.38 (dCN), 134.94,
129.10-114.72 (Ph), 128.19, 127.79 (CdC), 83.18, 81.98 (tC),
53.38 (CH2), 17.72 (CH3); tc isomer, δ 153.47 (dCN), 134.90-
115.17 (Ph), 127.94, 127.79 (CdC), 83.06, 82.08 (CtC), 47.77
(CH2), 13.07 (CH3). EI-MS: m/z 225.00 (Mþ). Anal. Calcd for
C16H19N: C, 85.28; H, 8.50; N, 6.22.
2
(t, JCP = 11.0 Hz, CR), 145.26-111.89 (m, Ph), 134.29 (dC),
129.04 (dCH), 123.07 (Cβ), 95.72 (Cp), 57.76 (CH2), 26.03,
18.21 (CH3). 31P NMR (162 MHz, CDCl3): δ 40.80. MS
(FABþ): m/z 944.29 (M þ 1)þ. Anal. Calcd for C59H58BF4-
NP2Ru: C, 68.74; H, 5.67; N, 1.36. Found: C, 68.79; H, 5.77; N,
1.51.
Synthesis of 2c and 3c. 1-Bromo-3-methyl-2-butene (1.00 mL,
8.52 mmol) was added to a suspension of 2-[(trimethylsilyl)-
ethynyl]aniline (0.51 g, 2.69 mmol) and K2CO3 (1.12 g, 8.07
mmol) in 20 mL of dried acetone. The mixture was stirred at
50 °C overnight. The resulting solution was filtered through
Celite and evaporated to give the crude product, which was
purified by flash chromatography on silica gel with n-hexane/
CH2Cl2 (8:2) as eluent to afford a yellow band. Solvent was then
removed under vacuum to give the yellow liquid 2c (0.76 g, 87%
yield). Spectroscopic data of 2c are as follows. 1HNMR(400MHz,
CDCl3): δ 7.39-6.72 (m, 4H, Ph), 5.26 (t, 3JHH = 6.3 Hz, 2H,
dCH), 3.82 (d, 3JHH = 6.3 Hz, 4H, CH2), 1.69 (s, 6H, CH3), 1.61
(s, 6H, CH3), 0.22 (s, 9H, TMS). 13C NMR (125 MHz, CDCl3): δ
153.62 (CNH2), 133.99-115.23 (Ph), 134.91, 122.46 (CdC),
104.85, 99.05 (Ct), 49.30 (CH2), 25.77, 17.89 (CH3), 0.03
(TMS). Then K2CO3 (0.65 g, 4.68 mmol) was added to a
solution of 2c (0.76 g, 2.34 mmol) in MeOH/THF (1:1). The
mixture was stirred at room temperature for 4.5 h. The proce-
dure for the preparation of 3c (0.57 g, 97% yield) is similar to
that for 3b. Spectroscopic data of yellow liquid 3c are as follows.
1H NMR (400 MHz, CDCl3): δ 7.43-6.82 (m, 4H, Ph), 5.21 (t,
3JHH = 6.4 Hz, 2H, dCH), 3.80 (d, 3JHH = 6.4 Hz, 4H, CH2),
3.37 (s, 1H, tCH), 1.67 (s, 6H, CH3), 1.56 (s, 6H, CH3). 13C
NMR (125 MHz, CDCl3): δ 153.38 (C-NH2), 133.79-114.08
Synthesis of 7b0. To a Schlenk flask containing [Ru’]Cl, (10;
110 mg, 0.183 mmol) and KPF6 (70 mg, 0.38 mmol) was added
methanol (25 mL) under nitrogen. Then to the solution was
added 2.1 equiv of 3b (78 mg, 0.39 mmol) in methanol (5 mL),
and the solution was stirred at room temperature for 4 days. The
solvent was removed in vacuo, and CH2Cl2 was used to extract
the product. After filtration through Celite the solution was
concentrated to ca. 5 mL and was added to a stirred diethyl ether
(50 mL) solution to produce the yellow precipitates. The powder
was collected, washed with diethyl ether, and dried under
vacuum to give the crude product. 31P NMR of the crude
2
product (162 MHz, acetone-d6): δ 76.35, 64.12 (2 d, JPP
=
59.4 Hz); δ 76.82, 64.52 (2 d, 2JPP = 53.6 Hz) in a ratio of 4.6:1.
The mixture was redissolved in EtOAc and chromatographed
over acidic Al2O3 with EtOAc as eluent. A yellow band was
collected and dried to give the major product trans-7b0 (132 mg,
77% yield). Spectroscopic data of t-7b0 are as follows. 1H NMR
(400 MHz, acetone-d6): δ 8.10-6.54 (m, 24H, Ph), 5.63 (m, 1H,
dCH), 5.43 (m, 1H, dCH), 5.23 (s, 5H, Cp), 4.73 (d, JHH =
3
3
17.2 Hz, 1H, trans dCH2), 4.63 (d, JHH = 10.5 Hz, 1H, cis
dCH2), 4.43 (m, 1H, dCH), 4.08 (d, 3JHH = 2.4 Hz, 1H, CH),
3,13-2.38 (m, 4H, dppe), 2.98 (m, 1H, CH), 2.66 (d, 3JHH = 4.3
3
Hz, 2H, CH2), 1.61 (d, JHH = 6.4 Hz, 3H, dCCH3), 0.35 (d,

5782 Organometallics, Vol. 29, No. 22, 2010
Chiang et al.
3JHH = 7.0 Hz, 3H, HCCH3). 13C NMR (125 MHz, acetone-d6):
δ 263.9 (dd, JPC = 14.7 Hz, CR), 147.2-112.5 (Ph), 138.2,
(CH3). EI-MS: m/z 225.2 (Mþ). Anal. Calcd for C16H19N: C,
85.28; H, 8.50; N, 6.22. Found: C, 85.21; H, 8.51; N, 6.17.
Compound 6c (68 mg, 97% yield) was obtained from 3c
(70 mg, 0.276 mmol) by a similar catalytic process using 10.
2
130.2, 124.6, and 116.2 (dC), 85.0 (Cp), 71.8 and 42.5 (CH), 55.0
(CH2), 19.4 and 17.9 (CH3). 31P NMR (162 MHz, acetone-d6): δ
76.35, 64.12 (2 d, 2JPP = 59.4 Hz). MS (ESI): m/z 790.23 (Mþ).
Anal. Calcd for C49H53Cl4F6NP3Ru (with solvent molecule
obtained from recrystallization): C, 53.22; H, 4.83; N, 1.27.
Found: C, 52.98; H, 4.77; N, 1.18. The reaction of [Ru’]Cl, (10;
100 mg, 0.166 mmol) and 3b (66 mg, 0.332 mmol) was also
carried out in CH2Cl2 (4 mL) in the presence of AgPF6 (43 mg,
0.170 mmol) under nitrogen for 5 min. The resulting solution
was filtered through Celite, concentrated to ca. 3 mL, and added
to stirred diethyl ether (40 mL) to produce precipitates. The
powder (79 mg) was collected by filtration, washed with diethyl
ether, and dried under vacuum. Spectroscopic data are as
follows. 1H NMR (400 MHz, CDCl3): δ 5.81 (br, 1H, Hβ),
4.88 (br, 5H, Cp). 31P NMR (162 MHz, CDCl3): δ 80.61 (br).
Thermolysis of this powder considered as the vinylidene inter-
mediate at 50 °C also gave 7b0.
1
Spectroscopic data of 6c are as follows. H NMR (400 MHz,
CDCl3): δ 7.78 (d, 3JHH = 8.1 Hz, 1H, Ph), 7.34 (d, 3JHH = 8.3
Hz, 1H, Ph), 7.21 (t, 1H, Ph), 7.11 (t, 1H, Ph), 6.92 (s, 1H, dCH),
6.20 (dd, 3JHH = 17.4 and 10.6 Hz, 1H, dCH), 5.43 (t, 3JHH
=
6.7 Hz, 1H, dCH), 5.15 (d, 3JHH = 17.4 Hz, 1H, dCH2), 5.08
(d, 3JHH = 10.6 Hz, 1H, dCH2), 4.69 (d, 3JHH = 6.7 Hz, 2H,
CH2), 1.88 (s, 3H, CH3), 1.82 (s, 3H, CH3), 1.58 (s, 6H, CH3).
13C NMR (125 MHz, CDCl3): δ 143.90-109.51 (Ph, dC), 44.01
(CH2), 37.47 (C), 28.11, 25.62, and 17.99 (CH3). EI-MS: m/z
253.18 (Mþ). Anal. Calcd for C18H23N: C, 85.32; H, 9.15; N,
5.53.
Catalytic Synthesis of 6a and 6b by a Gold Complex. Treat-
ment of 3a (330 mg, 1.67 mmol) in CH2Cl2 in the presence of a
catalytic amount of AuClPPh3 (42.0 mg, 0.084 mmol) and
AgSbF6 (28.6 mg, 0.084 mmol) at room temperature for 6 h
afforded the yellow indole product 6a (287 mg, 87% yield).
Treatment of 3b (300 mg, 1.33 mmol) in CH2Cl2 in the presence
of a catalytic amount of AuClPPh3 (33.0 mg, 0.066 mmol) and
AgSbF6 (22.5 mg, 0.066 mmol) at room temperature for 5 h also
afforded the yellow indole product 6b (255 mg, 85% yield, trans:
cis = 4.5:1).
Catalytic Synthesis of 6a-c by Ruthenium Complexes. To a
Schlenk flask containing 1 (100 mg, 0.137 mmol) and AgPF6
(41.6 mg, 0.164 mmol) was added CH2Cl2 (3 mL) under nitro-
gen. Then to the solution was added 2.0 equiv of 3a (54.0 mg,
0.274 mmol) in CH2Cl2 (4 mL), and the mixture was stirred for
5 min. The resulting solution was filtered through Celite, concen-
trated to ca. 3.0 mL, and added to stirred diethyl ether (40 mL)
to produce a yellowish brown precipitate and a yellow solution.
After filtration, the solvent of the filtrate was removed under
vacuum to afford the yellow product 6a (48.6 mg, 90% yield).
Single-Crystal X-ray Diffraction Analysis of trans-7b0. Single
crystals suitable for an X-ray diffraction study were grown via
slow diffusion of diethyl ether into a CH2Cl2 solution of 7b0 at
-20 °C. A single crystal of dimensions 0.20 ꢀ 0.15 ꢀ 0.10 mm3
was glued to a glass fiber and mounted on a Nonius Kappa CCD
diffractometer. The diffraction data were collected using 3 kW
sealed-tube molybdenum KR radiation (T = 100(2) K). The
exposure time was 5 s per frame. Multiscan absorption correc-
tion was applied, and decay was negligible. Data were processed,
and the structure was solved and refined by the SHELXTL
program.20 The structure was solved using direct methods and
confirmed by Patterson methods refined on intensities of all data
(31 671 reflections) to give R1 = 0.0409 and wR2 = 0.1110 for
11 375 unique observed reflections (I > 2σ(I)). Hydrogen atoms
were placed geometrically using the riding model with thermal
parameters set to 1.2 times that for the atoms to which the
hydrogen is attached and 1.5 times that for the methyl hydrogen.
1
Spectroscopic data of 6a are as follows. H NMR (400 MHz,
=
3
3
CDCl3): δ 7.57 (d, JHH = 7.9 Hz, 1H, Ph), 7.27 (d, JHH
8.3 Hz, 1H, Ph), 7.18 (t, 1H, Ph), 7.08 (t, 1H, Ph), 6.87 (s, 1H, dCH),
6.05 (m, 1H, dCH), 5.96 (m, 1H, dCH), 5.18-5.03 (m, 4H,
dCH2), 4.66 (ddd, 3J = 5.4 Hz, 4J = 1.6 Hz, 2H, N-CH2), 3.50
(dd, 3J = 6.5 Hz, 4J = 0.8 Hz, 2H, CH2). 13C NMR (125 MHz,
CDCl3): δ 137.4, 133.7, 125.4 (dCH), 136.6 (dC), 117.1,
115.1 (dCH2), 128.0, 121.6, 119.2, 118.8, 113.4, 109.5 (6C,
Ph), 48.7, 29.8 (CH2). EI-MS: m/z 197.0 (Mþ). Anal. Calcd for
C14H15N: C, 85.24; H, 7.66; N, 7.10. Found: C, 85.21; H, 7.70;
N, 7.03.
Similarly, treatment of 3b (100 mg, 0.444 mmol) in CH2Cl2 in
the presence of a catalyticamountof[Ru]Cl(1; 48.7 mg, 0.067 mmol)
and KPF6 (24.5 mg, 0.13 mmol) at room temperature for 7 h
afforded the yellow indole product 6b (100 mg, 99%, trans:cis
ratio 4.5:1) in almost quantitative isolated yield. Spectroscopic
Crystal data for trans-7b0: C47H48NF6P3Ru 2CHCl3; Mr =
3
1174.59; 0.20 ꢀ 0.15 ꢀ 0.10 mm; monoclinic, space group P21/
˚
˚
˚
c; a = 11.7330(1) A, b = 20.3209(3) A, c = 20.8078(2) A; β =
1
3
90.761(1)°; V = 4960.5(1) A ; Z = 4; Fcalcd = 1.573 g cm-3; μ =
˚
data of 6b are as follows. H NMR (400 MHz, CDCl3): trans
isomer, δ 7.65, 7.31, 7.21, 7.10 (4H, Ph), 6.88 (s, 1H, dCH), 6.10
(m, 3JHH = 17.2, 10.2 Hz, 1H, dCH), 5.65 (m, 2H, HCdCH),
5.15 (d, 3JHH = 17.2 Hz, 1H, dCH2), 5.04 (d, 3JHH = 10.2 Hz,
1H, dCH2), 4.62 (br, 2H, CH2), 3.78 (m, 1H, CH), 1.71 (br, 3H,
CH3), 1.49 (d, 3JHH = 7.0 Hz, 3H, CH3); cis isomer, δ 7.65-7.10
(4H, Ph), 6.89 (s, 1H, dCH), 6.10 (m, 3JHH = 17.2, 10.2 Hz, 1H,
0.795 mm-1; F(000)= 2388; T = 100(2) K; R1 = 0.0409;
wR2 = 0.1110; 11 375 independent reflections.
Acknowledgment. This research was supported by the
National Science Council and National Center of High-
Performance Computing of Taiwan, Republic of China.
dCH), 5.72 (m, 1H, dCH), 5.62 (m, 1H, dCH), 5.15 (d, 3JHH
=
17.2 Hz, 1H, dCH2), 5.04 (d, 3JHH = 10.2 Hz, 1H, dCH2), 4.72
Supporting Information Available: A CIF file giving crystal-
lographic data for trans-7b0. This material is available free of
charge via the Internet at http://pubs.acs.org.
(d, 3JHH = 6.6 Hz, 2H, CH2), 3.78 (m, 1H, CH), 1.83 (d, 3JHH
=
6.9 Hz, 3H, CH3), 1.49 (d, 3JHH = 7.0 Hz, 3H, CH3). 13C NMR
(125 MHz, CDCl3): trans isomer, δ 143.45-109.57 (Ph, dC),
48.08 (CH2), 34.85 (CH), 20.30, 17.06 (CH3); cis isomer, δ
143.45-109.42 (Ph, dC), 42.82 (CH2), 34.85 (CH), 20.30, 13.06
(20) SHELXTL: Structure Analysis Program, version 5.04; Siemens
Industrial Automation Inc., Madison, WI, 1995.