Ruthenium(II)-catalyzed C-H bond activation: An efficient route toward indenamines

Article abstract of DOI:10.1002/cctc.201402393

An efficient and atom-economical method for the synthesis of substituted indenamines from N-tosylarylimines and alkynes via ruthenium(II)-catalyzed C-H bond activation and annulation is described. The catalytic reaction proceeds well with a broad substrate scope and in good yields. A possible mechanism is proposed that involves imine nitrogen chelation-assisted ortho-C-H bond activation of the substrate, alkyne insertion, and intramolecular insertion of the C￡ NTs group into the C-Ru bond. Isotope-labeling experiments are performed to understand the underlying mechanism of the reaction. Atomic bean counters succeed! An efficient and atom-economical method for the synthesis of substituted indenamines from N-tosylarylimines and alkynes via ruthenium(II)-catalyzed C-H bond activation and annulation is described.

Full text of DOI:10.1002/cctc.201402393

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DOI: 10.1002/cctc.201402393
Ruthenium(II)-Catalyzed CÀH Bond Activation: An Efficient
Route toward Indenamines
Chen-Hsun Hung, Parthasarathy Gandeepan,* and Chien-Hong Cheng*[a]
An efficient and atom-economical method for the synthesis of
substituted indenamines from N-tosylarylimines and alkynes
via ruthenium(II)-catalyzed CÀH bond activation and annula-
tion is described. The catalytic reaction proceeds well with
a broad substrate scope and in good yields. A possible mecha-
nism is proposed that involves imine nitrogen chelation-assist-
ed ortho-CÀH bond activation of the substrate, alkyne inser-
tion, and intramolecular insertion of the C=NTs group into the
CÀRu bond. Isotope-labeling experiments are performed to un-
derstand the underlying mechanism of the reaction.
Introduction
Transition-metal-catalyzed CÀH bond functionalization has
emerged as a prevailing method for the construction of CÀC
and CÀheteroatom bonds.[1] Various chelating functional
groups have been used to control the site selectivity of CÀH
bond functionalization owing to their ubiquitous nature. The
chelating groups are usually nitrogen- or oxygen-containing
functional groups.[2] The installation and removal of these func-
tional groups often limit the applicability of the CÀH bond ac-
tivation methodology in the synthesis of complex organic mol-
ecules. Therefore, the development of reactions that involve
the transformation of chelating groups into other functional
groups is highly desirable.
type annulation reaction to form substituted indenols via tran-
sition-metal-catalyzed CÀH activation and carbocyclization of
aryl ketones with alkynes. Similarly, the [3+2] annulation of ar-
omatic imines with alkynes via CÀH bond activation was re-
ported to be effective in forming various cyclic amines.[4]
Mostly, rhenium[4a,5a,7] and rhodium[4b,c,5b,6c,d,8] complexes were
found to be efficient catalyst systems for these types of CÀH
activation and [3+2] annulation reactions. The less expensive
ruthenium complexes demonstrated better catalytic activity in
CÀH bond activation reactions,[3f,9] which provides an opportu-
nity to explore the possibility of using them in the [3+2] annu-
lation reaction of aryl imines with alkynes to form indenamine
derivatives.[4d,e] As an extension of our effort in the develop-
ment of new organic transformations through CÀH bond acti-
The transition-metal-catalyzed, directing group-assisted
ortho-CÀH bond activation and annulation reactions with al-
kynes have recently been reported to play an indis-
pensable role in the synthesis of heterocyclic and car-
bocyclic compounds.[3] These reactions involve direct-
ed CÀH bond activation and metallacycle formation,
alkyne insertion into organometallic intermediates,
and reductive elimination to form final products.
However, a similar strategy to perform the nucleo-
philic addition of organometallic intermediates to the
directing functional groups instead of reductive elimi-
nation is less explored (Scheme 1). There are only
a few examples of reactions involving CÀH activation
and [3+2] annulation via nucleophilic addition of or-
Scheme 1. Transition-metal-catalyzed CÀH activation and annulation pathways.
ganometallic intermediates to the directing function-
al groups (e.g., ketone, imine, and amide).[4–8] Our
group[6d] and others[6] previously reported a [3+2]-
TM=transition metal. X=O or NR; Y, R1, and R2 =alkyl or aryl.
vation,[10] herein we report an efficient method for the synthe-
sis of N-tosylindenamines through the ruthenium(II)-catalyzed
CÀH activation reactions.
[a] C.-H. Hung, Dr. P. Gandeepan, Prof. Dr. C.-H. Cheng
Department of Chemistry
National Tsing Hua University
Hsinchu 30013 (Taiwan)
Fax: (+886)3-5724698
E-mail: d9723889@oz.nthu.edu.tw
chcheng@mx.nthu.edu.tw
Results and Discussion
The reaction of N-tosylbenzaldimine 1a with diphenylacetylene
2a in the presence of 2 mol% [RuCl2(p-cymene)]2, 20 mol%
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reaction by replacing DCE with other solvents, and most of
them were less effective or ineffective (Table 1, entries 8–13).
Finally, lowering the amount of AgSbF6 or Cu(OAc)2·H2O sup-
pressed the yield of 3aa (Figure 1).
Table 1. Optimization studies for the annulation of imines with alkynes.[a]
Under the optimized reaction conditions described above,
several substituted N-tosylbenzaldimines 1b–l were tested
with diphenylacetylene 2a to understand the scope of the re-
action (Table 2). The 4-F-, 4-Cl-, and 4-Br-substituted aldimines
1b–d underwent CÀH activation and annulation smoothly
with 2a to give the corresponding indenamine derivatives
3ba–da in 93, 84, and 95% yields, respectively (Table 2, en-
tries 2–4). Similarly, aldimines substituted with 4-Ph and 4-CF3
groups effectively reacted with 2a under standard conditions
to afford 3ea–fa in excellent yields. The 4-Me- and 4-OMe-sub-
stituted substrates 1h and i reacted in a less effective manner
with 2a to give 3ha and ia in 50 and 39% yields, respectively.
In addition, 3-bromobenzaldimine 1j reacted with 2a to give
3ja in 82% yield (Table 2, entry 10). In the reaction, despite the
presence of two possible CÀH bond activation sites at C2 and
C6 of 1j, the CÀH activation occurred only at C6, likely owing
to the steric effect of the bromo group at C3. Similarly, 3-iodo
Entry
Additive
Solvent
Yield[b]
[%]
1
2
3
4
5
6
7
8
–
DCE
DCE
DCE
DCE
DCE
DCE
DCE
–
AgSbF6
AgBF4
AgOAc
Ag2O
93 (90)[c]
57
–
–
8
9
KPF6
NaBF4
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
t-amyl alcohol
1,2-dimethoxyethane
toluene
–
–
9
10
11
12
13
14
15
32
25
26
27
42[d]
54[e]
THF
1,4-dioxane
ethyl acetate
DCE
DCE
[a] Unless otherwise stated, all reactions were performed with 1a
(0.20 mmol), 2a (0.24 mmol), [RuCl2(p-cymene)]2 (0.004 mmol), Cu-
(OAc)2·H2O (0.40 mmol), and an additive (0.04 mmol) in a solvent (1 mL)
at 1008C for 15 h; [b] Yields were determined from 1H NMR analysis with
1,2-dimethoxyethane as the internal standard; [c] Isolated yield;
[d] 10 mol% AgSbF6 was used; [e] 1 equiv. of Cu(OAc)2·H2O was used.
Table 2. Results of the reaction of N-tosylaldimines 1 with diphenylacety-
lene 2a.[a]
AgSbF6, and 2 equiv. of Cu(OAc)2·H2O in 1,2-dichloroethane
(DCE) at 1008C for 15 h gave N-tosylindenamine 3aa in 90%
isolated yield (Table 1, entry 2). The structure of 3aa was con-
1
firmed by its H and 13C NMR and HRMS data. The choice of
the oxidant, silver additive, and solvent is vital to the catalytic
reaction. The reaction did not proceed smoothly in the ab-
sence of Cu(OAc)2·H2O. We tested various other metal additives
in the formation of 3aa, and none of them was found to be
superior to AgSbF6 (Table 1, entries 3–7). We also examined the
Entry
1
Product 3
Yield[b]
[%]
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1 f
1g
1h
1i
3aa; R1 =H
90
93
84
95
70
97
93
50
39
82
42
3ba; R1 =F
3ca; R1 =Cl
3da; R1 =Br
3ea; R1 =Ph
3 fa; R1 =CF3
3ga; R1 =4-C(CH3)3
3ha; R1 =Me
3ia; R1 =OMe
3ja; R1 =Br
9
10
11
1j
1k
3ka; R1 =I
12
1l
3la
48
[a] Unless otherwise stated, all reactions were performed with
1 (0.40 mmol), 2a (0.480 mmol), [RuCl2(p-cymene)]2 (0.008 mmol), Cu-
(OAc)2·H2O (0.80 mmol), and AgSbF6 (0.080 mmol) in DCE (2 mL) at 1008C
for 15 h; [b] Isolated yield.
Figure 1. Effect of Cu(OAc)2·H2O on indenamine formation.
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aldimine 1k gave 3ka in moderate yield. The reaction worked
well for 2-bromo aldimine 1l to form the corresponding prod-
uct 3la in moderate yield (Table 2, entry 12). The substrates 1c,
d, j, and k produced halogen-substituted indenamine deriva-
tives in good to excellent yields, which were set aside for fur-
ther transformations.[11]
pyne (2h), but-1-yn-1-ylbenzene (2i), and hex-1-yn-1-ylbenzene
(2j) reacted efficiently with 1a to give two regioisomeric prod-
ucts in high yields and with high regioselectivity (Table 3, en-
tries 7–9). Similarly, prop-1-yne-1,3-diyldibenzene (2k) reacted
with 1c to give 3ck in good yield and with excellent regiose-
lectivity (95:5). We also tested the reaction of the enyne sub-
strate 2l with 1a, which afforded 3al in 73% yield and with
high regioselectivity (Table 3, entry 11).
In addition to that of 2a, we examined the scope of various
symmetrical and unsymmetrical alkynes in the present reaction
(Table 3). 4-Methyl (2b)- and 3-methyl (2c)-substituted diphe-
nylacetylenes reacted with 1c to give the corresponding prod-
ucts in excellent yields (Table 3, entries 1 and 2). Similarly, 4-F-,
4-Cl-, 4-Br-, and 4-CF3-containing diarylacetylenes 2d–g pro-
duced respective indenamine products in excellent yields at
a slightly higher reaction temperature and longer reaction
time (Table 3, entries 3–6).
In addition to N-tosylaldimines, we investigated other imine
substrates under our reaction conditions (Table 4). Aldimine
(1m) derived from benzenesulfonamide reacted with 2a to
afford 3ma in 76% yield (Table 4, entry 1). Similarly, the reac-
tion of substrates 1n and o with 2a gave the corresponding
products in moderate yields. N-Tosylketimine (1p) also under-
went CÀH activation and [3+2] carbocyclization with 2a to fur-
nish the tertiary carbinamine product 3pa in moderate yield
(Table 4, entry 4). Notably, the reaction did not proceed with N-
aryl or N-H imines of aldehyde or ketone instead of
To probe the regioselectivity of the catalytic reaction, the
unsymmetrical alkynes 2h–j were investigated. 1-Phenyl-1-pro-
N-tosylimines (Table 4, entries 5 and 6).
Table 3. Scope of alkynes in ruthenium(II)-catalyzed CÀH activation and annulation.[a]
To elucidate the mechanism of the present catalyt-
ic reaction, we first performed an intermolecular
competition reaction of imine substrates with differ-
ent substitutions (Scheme 2). In the three sets of re-
actions, the nucleophilicity of the substrate had no
effect on their relative reactivity, which indicates that
the CÀH bond ruthenation unlikely follows an elec-
trophilic aromatic substitution mechanism.
To understand the mechanism of this catalytic re-
action in detail, we treated 1a with 10 equiv. of D2O
under standard reaction conditions at the end of the
reaction; 75% hydrogen–deuterium–exchanged 1a
was recovered in 83% yield. This result indicates re-
versible CÀH bond ruthenation with N-tosylimine
(Scheme 3). To further understand the underlying
nature of the mechanism of the present reaction, we
measured inter- and intramolecular kinetic isotopic
effects (KIEs) of the catalytic reaction of 1a with 2a.
An intermolecular KIE of kH/kD =1.08 was observed
for the competition reaction of 1a and deuterium-la-
beled [D5]-1a with 2a. Similarly, an intramolecular
competition experiment of [D1]-1a with 2a revealed
a KIE of kH/kD =1.27 (Scheme 3). These small KIE
values indicate that the CÀH bond activation step
may not be the rate-limiting step.[10d–f,12]
Entry
1
2
Product 3
3cb; R2, R3 =4-MeC6H4
Yield[b]
[%]
1
2
3
4
5
1c
1c
1c
1c
1c
2b
2c
2d
2e
2 f
90
97
83[c]
89[c]
86[c]
3cc; R2, R3 =3-MeC6H4
3 cd; R2, R3 =4-FC6H4
3ce; R2, R3 =4-ClC6H4
3cf; R2, R3 =4-BrC6H4
6
1a
2g
3ag; R2, R3 =4-CF3C6H4
63[c]
7
8
9
1a
1a
1a
2h
2i
2j
3ah; R2 =Me
3ai; R2 =Et
3aj; R2 =(CH2)3CH3
91 (7:1)[d]
90 (10:1)[d]
58 (7:1)[d]
Based on our experimental results and the known
metal-catalyzed, directing group-assisted CÀH bond
activation and [3+2] annulation reactions,[4–8,10] a pos-
sible mechanism of the present ruthenium(II)-cata-
lyzed CÀH activation and annulation is proposed in
Scheme 4. The catalytic cycle is probably initiated by
the removal of chloride by Ag+ in [RuCl2(p-cymene)]2
to form a coordinatively unsaturated ruthenium mo-
nomer followed by the coordination of imine nitro-
gen to the ruthenium complex and subsequent
ortho-CÀH bond activation to form five-membered
ruthenacycle A. The coordination of alkyne 2a to
ruthenium complex A and the regioselective inser-
10
11
1c
1a
2k
2l
3ck
3al
66 (95:5)[d]
73 (7:1)[d]
[a] Unless otherwise stated, all reactions were performed with 1 (0.40 mmol), 2
(0.48 mmol), [RuCl2(p-cymene)]2 (0.008 mmol), Cu(OAc)2·H2O (0.80 mmol), and AgSbF6
(0.08 mmol) in DCE (2 mL) at 1008C for 15 h; [b] Isolated yield; [c] 1208C, 24 h;
[d] Ratios of regioisomers are given in parentheses and were determined from
1H NMR analysis; major isomers are shown.
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sponding indenones with tetrabutylammonium fluoride
(Scheme 5).[14]
Table 4. Scope of imines in ruthenium(II)-catalyzed CÀH activation and
annulation.[a]
Conclusions
We developed an efficient ruthenium-catalyzed, chelation-as-
sisted ortho-CÀH bond activation of N-tosylbenzaldimines and
[3+2] annulation with alkynes to afford substituted indena-
mine derivatives in good to excellent yields. A possible mecha-
nism is proposed for the catalytic reaction. The kinetic isotope
labeling studies suggest that CÀH activation follows reversible
cyclometalation and that an initial CÀH activation step may
not be the rate-limiting step. Further studies on the intramo-
lecular CÀH activation and related transformations are ongoing
in our laboratory.
Entry
1
Product 3
Yield[b]
[%]
1
2
3
4
5
6
1m
1n
1o
1p
1q
1r
3ma; R=SO2Ph, R4 =H
3na; R=SO24-ClC6H4, R4 =H
3oa; R=SO2Et, R4 =H
3pa; R=Ts, R4 =Ph
3qa; R=Ph, R4 =H
3ra; R=H, R4 =Ph
76
31
35
57
–
–
[a] Unless otherwise stated, all reactions were performed with
(0.40 mmol), 2a (0.48 mmol), [RuCl2(p-cymene)]2 (0.008 mmol), Cu-
(OAc)2·H2O (0.80 mmol), and AgSbF6 (0.08 mmol) in DCE (2 mL) at 1008C
Experimental Section
1
General information
for 15 h; [b] Isolated yield.
Unless otherwise stated, all reactions were performed under a nitro-
gen atmosphere on a dual-manifold Schlenk line and in
oven-dried glassware. All solvents were dried according
to known methods and distilled before use.[15]
General method for the synthesis of N-tosylinden-
amines
A sealed tube containing [RuCl2(p-cymene)]2 (5.0 mg,
0.008 mmol), AgSbF6 (27.0 mg, 0.08 mmol), Cu(OAc)2·H2O
(160.0 mg, 0.80 mmol), N-tosylimines 1 (0.4 mmol), and
alkyne 2 (0.48 mmol) was evacuated and purged thrice
with nitrogen gas. Then, DCE (2.0 mL) was added to the
system with a syringe under a nitrogen atmosphere and
the reaction mixture was stirred at 1008C for 15 h. After
the completion of the reaction, the mixture was cooled
and diluted with CH2Cl2 (10 mL). The mixture was filtered
through a Celite pad (Celite 545, Showa Chemical Indus-
try Co.) , and the Celite pad was washed several times
with CH2Cl2 (50 mL). The combined filtrate was concen-
trated in vacuo, and the residue was purified by column
chromatography using ethyl acetate/n-hexane (1:4) to
afford the desired product 3.
Scheme 2. Intermolecular competition studies.
N-(2,3-Diphenyl-1H-inden-1-yl)-4-methylbenzenesulfona-
mide (3aa)
tion of alkyne into the CÀRu bond gives the seven-membered
ruthenacycle B with the N-tosylimine group p-coordinated to
the ruthenium center.[4,5,6c,d,10g] The subsequent intramolecular
insertion of the C=NTs group into the Ru–alkenyl bond affords
the ruthenium amido intermediate C. Active ruthenium(II) is re-
leased likely through protonation. The reaction does not pro-
ceed without Cu(OAc)2·H2O, and the yield was low with use of
a small amount of copper salt. Therefore, Cu(OAc)2 could be an
acetate source for acetate-assisted cyclometalation.[9c]
White solid; m.p. 181–1838C; 1H NMR (400 MHz, CDCl3): d=7.69
(d, J=8.0 Hz, 2H), 7.55 (d, J=7.2 Hz, 1H), 7.36–7.30 (m, 3H), 7.28–
7.20 (m, 6H), 7.19–7.16 (m, 1H), 7.09 (t, J=7.2 Hz, 1H), 6.97 (t, J=
8.0 Hz, 2H), 6.84 (d, J=7.6 Hz, 2H), 5.50 (d, J=8.8 Hz, 1H), 4.52 (d,
J=8.4 Hz, 1H), 2.47 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=
143.7 (C), 143.4 (C), 143.3 (C), 141.2 (C), 141.0 (C), 138.0 (C), 134.1
(C), 133.1 (C), 129.6 (2 CH), 129.3 (2 CH), 129.1 (2 CH), 128.6 (2 CH),
128.4 (CH), 128.0 (2 CH), 127.8 (CH), 127.4 (2 CH), 127.1 (CH), 126.5
(CH), 124.8 (CH), 120.7 (2 CH), 61.0 (CH), 21.5 ppm (CH3); IR (neat):
n˜ =3301, 1596, 1157 cmÀ1; HRMS (EI+): m/z: calcd for C28H23NO2S:
437.1449; found: 437.1444.
The N-tosylindenamines prepared by using this method can
be readily unprotected by treating them with SmI2.[13] Similarly,
these N-tosylindenamines are easily converted into the corre-
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(2 CH), 127.3 (2 CH), 126.9 (CH), 126.3 (CH), 124.3 (CH),
119.2 (CH), 61.0 (CH), 21.5 (CH3), 11.6 ppm (CH3); ; IR
(neat): n˜ =3062, 2923, 1596, 1326, 1157 cmÀ1; HRMS (EI+
): m/z: calcd for C23H21NO2S: 375.1293; found: 375.1294.
N-(3-Benzyl-5-chloro-2-phenyl-1H-inden-1-yl)-4-
methylbenzenesulfonamide (3ck)
1
White solid; m.p. 144–1468C; H NMR (400 MHz, CDCl3):
d=7.56 (d, J=8.4 Hz, 2H), 7.42 (d, J=8.0 Hz, 1H), 7.26–
7.17 (m, 5H), 7.15–7.08 (m, 6H), 7.01–6.96 (m, 3H), 5.35
(d, J=8.4 Hz, 1H), 4.84 (d, J=8.8 Hz, 1H), 3.89 (s, 2H),
2.44 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=145.3
(C), 144.4 (C), 143.3 (C), 141.7 (C), 137.9 (C), 137.7 (C),
137.7 (C), 134.4 (C), 133.1 (C), 129.5 (2 CH), 128.7 (2 CH),
128.7 (2 CH), 128.4 (2 CH), 128.0 (2 CH), 127.6 (CH), 127.2
(2 CH), 126.4 (CH), 126.1 (CH), 125.4 (CH), 120.7 (CH), 60.8
(CH), 31.8 (CH2), 21.5 ppm (CH3); IR (neat): n˜ =3262, 2923,
1596, 1434, 1326, 1157 cmÀ1; HRMS (EI+): m/z: calcd for
C29H24ClNO2S: 485.1216; found: 485.1219.
N-(2,3-Diphenyl-1H-inden-1-yl)benzenesulfonamide
(3ma)
Scheme 3. Isotope-labeling studies. D=deuterium; H=hydrogen.
1
White solid; m.p. 169–1718C; H NMR (400 MHz, CDCl3):
d=7.81 (d, J=7.6 Hz, 2H), 7.60 (t, J=7.2 Hz, 1H), 7.51–
7.44 (m, 3H), 7.35–7.20 (m, 6H), 7.17 (t, J=6.4 Hz, 2H),
7.08 (t, J=7.6 Hz, 1H), 6.97 (t, J=7.6 Hz, 2H), 6.84 (d, J=7.2 Hz,
2H), 5.51 (d, J=7.6 Hz, 1H), 4.60 ppm (d, J=8.4 Hz, 1H); 13C NMR
(100 MHz, CDCl3): d=143.7 (C), 143.3 (C), 141.2 (C), 141.1 (C), 141.1
(C), 134.1 (C), 133.1 (C), 132.6 (CH), 129.3 (2 CH), 129.1 (2 CH), 129.0
(2 CH), 128.6 (2 CH), 128.5 (CH), 128.0 (2 CH), 127.8 (CH), 127.3 (2
CH), 127.2 (CH), 126.6 (CH), 124.8 (CH), 120.7 (CH), 61.2 ppm (CH);
IR (neat): n˜ =3301, 1596, 1157 cmÀ1; HRMS (EI+): m/z: calcd for
C27H21NO2S: 423.1293; found: 423.1289.
N-(2,3-Diphenyl-1H-inden-1-yl)ethanesulfonamide (3oa)
1
White solid; m.p. 147–1498C; H NMR (400 MHz, CDCl3): d=7.78 (d,
J=6.4 Hz, 1H), 7.37–7.27 (m, 8H), 7.25–7.19 (m, 5H), 5.64 (d, J=
9.2 Hz, 1H), 4.18 (d, J=9.2 Hz, 1H), 2.91 (sxt, J=7.2 Hz, 1H), 2.79
(sxt, J=6.8 Hz, 1H), 1.00 ppm (t, J=7.6 Hz, 3H); 13C NMR (100 MHz,
CDCl3): d=143.7 (C), 143.4 (C), 142.0 (C), 140.6 (C), 134.1 (C), 133.8
(C), 129.5 (2 CH), 129.1 (2 CH), 128.5 (3 CH), 128.2 (2 CH), 127.7
(CH), 127.5 (CH), 126.5 (CH), 124.5 (CH), 120.7 (CH), 61.7 (CH), 49.0
Scheme 4. Proposed reaction mechanism.
(CH2), 8.0 ppm (CH3); IR (neat): n˜ =3278, 3054, 1319, 1141 cmÀ1
;
HRMS (EI+): m/z: calcd for C23H21NO2S: 375.1293; found: 375.1297.
4-Methyl-N-(1,2,3-triphenyl-1H-inden-1-yl)benzenesulfon-
amide (3pa)
Scheme 5. Synthesis of indenamine and indenone. TBAF= tetrabutylammo-
nium fluoride.
1
White solid; m.p. 203–2058C; H NMR (400 MHz, CDCl3): d=7.58 (d,
J=7.2 Hz, 2H), 7.33–7.29 (m, 5H), 7.28–7.26 (m, 1H), 7.19–7.09 (m,
6H), 7.05–7.00 (m, 7H), 6.68 (d, J=7.2 Hz, 2H), 5.36 (s, 1H),
2.39 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=144.5 (C), 144.3
(C), 143.3 (C), 142.8 (C), 141.7 (C), 141.7 (C), 137.6 (C), 134.1 (C),
132.8 (C), 129.6 (2 CH), 129.1 (CH), 129.1 (3 CH), 128.7 (2 CH), 128.5
(2 CH), 128.2 (2 CH), 128.2 (CH), 127.8 (CH), 127.8 (CH), 127.7 (CH),
127.7 (CH), 127.7 (CH), 127.6 (CH), 126.1 (CH), 124.9 (2 CH), 120.5
(CH), 73.8 (C), 21.4 ppm (CH3); IR (neat): n˜ =3054, 1596, 1326,
1157 cmÀ1; HRMS (EI+): m/z: calcd for C34H27NO2S: 513.1762; found:
513.1771.
4-Methyl-N-(2-methyl-3-phenyl-1H-inden-1-yl)benzene-
sulfonamide (3ah)
Brown solid; m.p. 119–1218C; 1H NMR (400 MHz, CDCl3): d=7.61
(d, J=8.4 Hz, 2H), 7.47 (d, J=7.6 Hz, 1H), 7.36–7.30 (m, 2H), 7.24–
7.14 (m, 6H), 7.01 (d, J=6.8 Hz, 2H), 5.31 (d, J=8.8 Hz, 1H), 4.47
(d, J=8.4 Hz, 1H), 2.44 (s, 3H), 2.12 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3): d=144.5 (C), 143.2 (C), 143.2 (C), 140.4 (C), 138.1
(C), 136.7 (C), 133.9 (C), 129.5 (2 CH), 129.0 (2 CH), 128.4 (CH), 128.1
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ChemCatChem 2014, 6, 2692 – 2697 2696

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Acknowledgements
We acknowledge the financial support of the Ministry of Science
and Technology of the Republic of China (NSC-102-2628M-007-
005 and NSC-102-2633M-007-002).
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Keywords: alkynes · annulation · CÀH activation · imine ·
ruthenium
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Received: May 29, 2014
Published online on August 13, 2014
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ChemCatChem 2014, 6, 2692 – 2697 2697