Dienylation of Unfunctionalized Arenes with 1,6-Diynes via Rhodium-Catalyzed Directing-Group-Free C-H Bond Activation

Article abstract of DOI:10.1055/a-1328-6436

It has been established that the dienylation of unfunctionalized arenes with 1,6-diynes, possessing aryl groups at the diyne termini, proceeds to give the corresponding dienylated arenes in the presence of a catalytic amount of an electron-deficient cyclopentadienyl rhodium(III) complex, [Cp ^ERhCl ₂] ₂, and a stoichiometric amount of silver carbonate. Experimental and theoretical mechanistic studies revealed that a Cp ^ERh(I) complex generated in situ might catalyze the present dienylation- reaction.

Full text of DOI:10.1055/a-1328-6436

SYNTHESIS
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2021, 53, A–J
special topic
A
Bond Activation – in Honor of Prof. Shinji
H. Takahashi et al.
Special Topic
Synthesis
Dienylation of Unfunctionalized Arenes with 1,6-Diynes via Rhodium-
Catalyzed Directing-Group-Free C–H Bond Activation
Hiroto Takahashi
Yusaku Honjo
Yu Shibata
Yuki Nagashima
Ken Tanaka*
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Department of Chemical Science and Engineering,
Tokyo Institute of Technology, O-okayama, Meguro-ku,
Tokyo 152-8550, Japan
ktanaka@apc.titech.ac.jp
Published as part of the Special Topic
Bond Activation – in Honor of Prof. Shinji Murai
Corresponding Author
Received: 13.11.2020
Accepted after revision: 03.12.2020
Published online: 03.12.2020
two alkynes by using a commercially available electron-de-
ficient cyclopentadienyl rhodium(III) complex [CpERhCl2]2
(1) as a catalyst7 and diaryl-substituted 1,6-diynes as the
two alkyne components (Scheme 1c).
DOI: 10.1055/a-1328-6436; Art ID: ss-2020-f0585-st
Abstract It has been established that the dienylation of unfunctional-
ized arenes with 1,6-diynes, possessing aryl groups at the diyne termini,
proceeds to give the corresponding dienylated arenes in the presence
of a catalytic amount of an electron-deficient cyclopentadienyl rhodi-
um(III) complex, [CpERhCl2]2, and a stoichiometric amount of silver car-
bonate. Experimental and theoretical mechanistic studies revealed that
a CpERh(I) complex generated in situ might catalyze the present
dienylation reaction.
a) Tanaka (2007)
R2
5 mol%
H
[Rh(cod)2]BF4/
R2
Z
biaryl bisphosphone
+
H
Z
R2
CH2Cl2, rt
R2
R1
O
R1
O
up to 98% yield
b) Vollhardt (2007)
Key words alkynes, dienylation, directing group-free C–H bond acti-
vation, rhodium, unfunctionalized arenes
R2
1) 100 mol%
[CpCo(C2H4)2]
THF, rt
H
R3
R2
R3
O
N
H
+
O
N
The alkenylation reactions of arenes with alkynes via
transition-metal-catalyzed sp2 C–H bond cleavage is a use-
ful transformation in organic synthesis.1 This transforma-
tion has been reported in great numbers of examples.1 In
contrast, reports on the dienylation reactions of arenes
with two alkynes via transition-metal-catalyzed sp2 C–H
bond cleavage have been quite limited.2–4 Our research
group2 and the Shibata research group3 independently re-
ported the carbonyl-directed dienylation reactions of aryl
ketones with internal 1,6-diynes by using cationic rhodi-
um(I)/biaryl bisphosphine complexes as catalysts (Scheme
1a). The Vollhardt research group reported the directing-
group-free dienylation reactions of 2-pyridones with pen-
dant and external alkynes by using a cyclopentadienyl (Cp)
cobalt(I) complex (Scheme 1b).5 However, this reaction re-
quired a stoichiometric amount of the cobalt(I) complex,
and available substrates were limited to 2-pyridones. Thus,
the dienylation reaction of unfunctionalized arenes with
two alkynes via transition-metal-catalyzed directing-free
sp2 C–H bond activation6 has not been reported to date. In
this paper, we disclose the first example of the directing-
free dienylation reactions of unfunctionalized arenes with
2) Fe(NO3)3·9H2O
MeCN–H2O, 0 °C
n
n
n = 1, 2
up to 84% yield
c) This work
Ar
H
5–10 mol% 1
100 mol% Ag2CO3
Ar
Ar
X
X
X
+
R
Z
Z
R
80–100 °C
under Ar
X
H
Ar
up to 40% yield
Me
EtO2C
Me
CO2Et
Me
Rh
Cl
Cl
2
[CpERhCl2]2 (1)
Scheme 1 Transition-metal-mediated dienylation of arenes with two
alkynes (cod = 1,5-cyclooctadiene)
Our research group reported the convenient synthesis
of [CpERhCl2]2 (1) by reductive complexation of a substitut-
ed silylfulvene with RhCl3 in ethanol.7 This complex showed
high catalytic activity in [3+2],7,8a [4+2],8b,c [2+2+2],8d–f and
[2+1+2+1]8g annulation reactions through cleavage of sp2 C–H
bonds.9 In the course of our recent study on the oxidative
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Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
H. Takahashi et al.
Special Topic
Synthesis
and decarboxylative [2+1+2+1] annulation reaction of ben-
zoic acid with a diphenyl-substituted 1,6-diyne,8g we unex-
pectedly found that the dienylation of toluene, which is
used as a solvent, with the 1,6-diyne, proceeds as a side re-
action to give the corresponding dienylation products as an
inseparable mixture of diastereomers and regioisomers
(Scheme 2).10
5aa and [2+2+2] cycloaddition products 6a/7a (Table 1, en-
try 1). Cu(OAc)2 may not be necessary due to the redox-
neutral nature of the formation of 4aa, and thus the reac-
tion in the absence of Cu(OAc)2 also afforded 4aa in 20%
yield and significantly increased the yield of 6a/7a (entry
2). The use of Ag2CO3 instead of AgOAc increased the selec-
tivity of 4aa, although the conversion of 3a decreased to
57% (entry 3). Pleasingly, the use of a stoichiometric
amount of Ag2CO3 gave 4aa in higher yield than under the
conditions detailed in entry 1 (entry 4). The use of Cs2CO3
(entry 5) and lowering the reaction temperature to 60 °C
(entry 6) decreased the yield of 4aa. Finally, prolonged reac-
tion time (40 h) afforded 4aa in the highest yield of 30%
(entry 7). Even when using a catalytic amount (10 mol%) of
Ag2CO3, further prolonged reaction time (72 h) afforded 4aa
in an improved yield of 29% (entry 8). Under the optimized
a) Reaction scope
5 mol% 1
100 mol% Ag2CO3
Ar
Ar
X
X
+
R
Z
80–100 °C, 20–72 h
under Ar
2
3
Ar
Ar
Ar
(2.0 mL)
(0.10 mmol)
X
X
X
X
+
R
Z
R
Z
Ar
4
5
Ph
Ph
Ph
Ph
reaction
conditions,
moderately
electron-deficient
11
[CpRhI2]n and electron-rich [Cp*RhCl2]2 were ineffective
for the formation of 4aa (entries 9 and 10). Diene 4aa was
not obtained at all by using [Cp*IrCl2]2 (entry 11) or in the
absence of the Rh or Ir complex (entry 12).
NTs
O
Ph
Ph
4aa/5aa 26% (96:4)
(80 °C, 40 h)
4ab/5ab 12% (91:9)
(80 °C, 72 h)
4ac/5ac 24% (94:6)
(80 °C, 72 h)
Me
Me
a) Possible reaction mechanisms for formation of 4, 5, and 6
p-tol
Ph
Me
R
CO2R
CO2R
Z
NTs
NTs
Z
R
Me
R
p-tol
3, –D
Ph
R
CpE
RhIII
R
R
6
4ad/5ad (R = Me) 31% (90:10)
(80 °C, 72 h, 10 mol% 1)
4ae/5ae (R = Bn) 20% (80:20)
(80 °C, 72 h, 10 mol% 1)
4af/5af 40%
Z
(92:8, 4af: E/Z = 20:80)
Me
Me
R
R
(80 °C, 40 h)
4bg/5bg 8% (87:13)
2a
R
3
(100 °C, 20 h)
CpE
RhI
CpE
RhIII
H
Z
E
Z
b) One-pot dienylation–aromatization
A
D
RhIII
CpE
R
1) 5 mol% 1
100 mol% Ag2CO3
80 °C, 40 h, under Ar
CpE
RhIII
Ph
3
F
Ph
Ph
X
X
X
Z
X
+
2a, –H+
H
G
Z
–D
2a
2) blue LED, rt, 1.5–6 h
under air
CpE
Ph
2a
(2.0 mL)
3
5
R
R
R
(0.10 mmol)
RhIII
3
H+
–A
CpE
RhIII
Z
Ph
Ph
Ph
Z
4
B
NTs
R
C
[O]
–A
Ph
Ph
Ph
R
5aa 24%
(LED 6 h)
5ah 38%
(10 mol% 1, LED 1.5 h)
5ai 30%
(10 mol% 1, no LED)
Z
Scheme 2 Substrate scope for dienylation of arenes 2 with 1,6-diynes
3. Complex 1 (0.0050–0.010 mmol), Ag2CO3 (0.10 mmol), 2 (2.0 mL),
and 3 (0.10 mmol) were used. Cited yields are of the isolated products.
5
R
b) Cp*RhIII-catalyzed oxidative cyclization of 3f with phenylboronic acid (ref 12)
Ph
4 mol% [Cp*RhCl2]2
Ph
Ph
AgF ( 2 equiv)
PhB(OH)2
(2 equiv)
+
DMF, rt
To avoid the formation of diastereomers and regioiso-
mers, the reaction of benzene (2a) with diphenyl-substitut-
ed 1,6-diyne 3a was conducted under the same conditions
as in Scheme 2 except for argon atmosphere because the di-
enylation is a redox-neutral process. This reaction afforded
the corresponding dienylation product 4aa as a single dia-
stereomer along with a trace amount of aromatized product
Ph
5af, 57%
Ph
FCp*RhIII
3f
C’
Ph
Scheme 3 Mechanistic considerations
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, A–J

C
H. Takahashi et al.
Special Topic
Synthesis
Table 1 Optimization of Reaction Conditions for Dienylation of Benzene (2a) with 1,6-Diyne 3aa
Rh or Ir complex
(10 mol% Rh or Ir)
10–200 mol% additive
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
N
Ts
N
+
+
+
TsN
NTs
NTs
NTs
Ts
NTs
+
TsN
Ph
under Ar
Ph
Ph Ph
Ph
Ph
Ph
Ph
2a
(2.0 mL)
3a
(0.10 mmol)
4aa
5aa
6a
7a
Entry
Rh or Ir complex Additive (mol%)
Conditions
Conv. of 3a (%)b Yield (%) 4aa + 5aa (4aa/5aa)b Yield (%) 6a + 7a (6a/7a)b
1
2
1
[Cu(OAc)2·H2O] (20), AgOAc (20) 80 °C, 20 h
98
>99
57
24 (94:6)
20 (95:5)
15 (100:0)
28 (100:0)
6 (100:0)
8 (100:0)
30 (100:0)
29 (100:0)
0
27 (88:12)
50 (78:22)
19 (60:40)
37 (72:28)
32 (85:15)
11 (68:32)
42 (64:36)
38 (62:38)
23 (100:0)
59 (92:8)
4 (100:0)
0
1
AgOAc (20)
80 °C, 20 h
80 °C, 20 h
80 °C, 20 h
80 °C, 20 h
60 °C, 20 h
80 °C, 40 h
80 °C, 72 h
80 °C, 40 h
80 °C, 40 h
80 °C, 40 h
80 °C, 20 h
3
1
Ag2CO3 (10)
Ag2CO3 (100)
Cs2CO3 (100)
Ag2CO3 (100)
Ag2CO3 (100)
Ag2CO3 (10)
Ag2CO3 (100)
Ag2CO3 (100)
Ag2CO3 (100)
Ag2CO3 (100)
4
1
94
5
1
54
6
1
39
7
1
>99
96
8
1
9
[CpRhI2]n
[Cp*RhCl2]2
[Cp*IrCl2]2
none
54
10
11
12
76
<1
29
0
<5
0
a Reaction conditions: Rh or Ir complex (0.010 mmol of Rh or Ir), additive (0.010–0.10 mmol), 2a (2.0 mL), and 3a (0.10 mmol) were used.
b Determined by 1H NMR analysis using dimethyl terephthalate as internal standard.
With the optimized reaction conditions in hand, we ex-
plored the scope of these dienylation reactions, as shown in
Scheme 2a. Concerning 1,6-diynes, not only tosylamide (3a)
but also oxygen and methylene-linked 1,6-diynes 3b and 3c
could be employed for this transformation, although the
product yields decreased. The use of malonate-linked 1,6-
diynes 3d and 3e also afforded the corresponding dienylat-
ed products 4ad and 4ae, although high catalyst loadings
were required. Although the reactions using dimethyl-sub-
stituted internal 1,6-diynes and terminal 1,6-diynes were
also tested, dienylation products were not obtained due to
the formation of homo-[2+2+2] cycloaddition products.
Concerning unfunctionalized arenes, not only benzene (2a)
but also sterically demanding m-xylene (2b) reacted with
di-m-xylyl-substituted 1,6-diyne 3g to give diene 4bg, al-
though the yield was low. In these reactions, aromatized
products 5 were not observed in the crude reaction mix-
tures, but 5 was observed upon isolation under air and
light. Thus, upon completion of the dienylation reaction,
the reaction mixture was stirred at room temperature un-
der air and blue LED irradiation to give the corresponding
aromatized product 5aa (Scheme 2b). Highly rigid naphtha-
lene-linked 1,6-diynes 3h and 3i were also suitable sub-
strates for this process, and dienylation products (diphenyl-
fluoranthene) 4ah and 4ai were generated as the sole cou-
pling product. However, isolation by preparative thin-layer
chromatography (PTLC) gave a 1:1 mixture of 4ah and aro-
matized product 5ah. Pleasingly, 5ah could be isolated in a
pure form after blue LED irradiation; on the other hand,
ethylene-bridged electron-rich diene 4ai was aromatized to
diphenylfluoranthene 5ai on the PTLC without blue LED ir-
radiation. The reactions using a biphenyl-linked 1,7-
diyne[2,2′-bis(phenylethynyl)-1,1′-biphenyl] was also test-
ed, but no reaction was observed.
Possible mechanisms for the formation of 4, 5, and 6 are
shown in Scheme 3a. The C–H bond cleavage of 2a with the
CpERh(III) complex A would generate phenylrhodium B,
which reacts with diyne 3 giving dienylrhodium C. Protode-
metalation affords diene 4 and regenerates Rh(III) complex
A. However, in the Cp*Rh(III) complex-catalyzed oxidative
cyclization of naphthalene-linked 1,6-diyne 3f with phen-
ylboronic acid, the same dienylrhodium C′ activates the ad-
jacent arene sp2 C–H bond to give exclusively aromatized
product 5af (Scheme 3b).12 Thus, this mechanism is unlike-
ly due to the selective formation of diene 4. In situ genera-
tion of CpERh(I) complex D from CpERh(III) complex A well
explains the formation of both diene 4 and [2+2+2] cyc-
loaddition product 6, although the reduction mechanism is
not clear at the present stage.13 Complex D reacts with 3 to
give rhodacycle E. Electrophilic aromatic substitution with
rhodium(III) complex E would afford phenylrhodium(III)
complex F.14 Reductive elimination affords diene 4 and re-
generates the catalytically active CpERh(I) complex D. This
mechanism well explains the selective formation of diene 4
without the formation of naphthalene 5 and competitive
formation of [2+2+2] cycloaddition product 6, which can be
generated from common rhodacycle intermediate E. Alter-
natively, the C–H bond cleavage of 2a with CpERh(I)
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, A–J

D
H. Takahashi et al.
Special Topic
Synthesis
complex D giving rhodium(III) hydride G followed by hy-
drorhodation of diyne 3 would also afford the same phenyl-
rhodium(III) complex F. Oxidative aromatization of 4
during isolation under air and light affords aromatized
product 5.
products, but the use of a catalytic amount of 1 gave
[2+2+2] cycloaddition products 6a and 7a (Scheme 4b).16
No reaction was observed in the absence of 3a, and the oxi-
dative coupling of o-xylene giving biphenyl was not ob-
served. These results might suggest the reduction of the
CpERh(III) complex in situ into the CpERh(I) complex with
diyne 3a. The reaction of 2a with monoyne 8 did not afford
monoene 9 at all, which supports the formation of diene 4
via not rhodium hydride G but rhodacycle E (Scheme 4c).
We anticipated that the electron-deficient nature of the
CpERh(III) complex might be important to activate the C–H
bond of electron-rich arenes in the present dienylation re-
action. Thus, the reactions of a highly electron-rich arene
[anisole (2c)] and 3a using the CpERh(III) and Cp*Rh(III)
complexes were examined, as shown in Scheme 4d. As ex-
pected, the CpERh(III) complex catalyzed the dienylation re-
action to give diene 4ca as a mixture of diastereomers and
regioisomers; in contrast, the Cp*Rh(III) complex failed to
catalyze the dienylation reaction. Additionally, both the
CpERh(III) and Cp*Rh(III) complexes failed to catalyze the
dienylation reaction of electron-deficient arenes (chloro-
benzene and fluorobenzene) with 3a.
To confirm the participation of the CpERh(I) complex in
this catalysis even in the presence of a stoichiometric
amount of an oxidant (Ag2CO3),15 several rhodium(I) com-
plexes were tested in the reaction of 2a and 3a, as shown in
Scheme 4a.
A
cationic rhodium(I)-cod complex
[Rh(cod)2]BF4 could indeed catalyze this dienylation, al-
though the product yield was low (9%). The addition of
Ag2CO3 and the use of [Rh(cod)Cl]2 instead of [Rh(cod)2]BF4
decreased the yield of 4aa/5aa (6% and 2%, respectively),
but slightly increased the yield of 6a/7a. Importantly, the
use of a cationic rhodium(I)/rac-binap complex, which was
an effective catalyst for the dienylation reaction shown in
Scheme 1a, catalyzed only the [2+2+2] cycloaddition of 3a.
Thus, a -donor ligand is ineffective for the present C–H ac-
tivation. In the absence of 2a, 3a reacted with stoichiomet-
ric amounts of 1 and Ag2CO3 to give a complex mixture of
To gain more mechanistic insights, we conducted a
computational study concerning each C–H activation path-
way. The pathway for generating phenylrhodium B (IM2)
from CpERh(III) complex A (RT1) requires a high activation
energy (28.9 kcal mol–1) due to the difficulty in approach-
ing A to 2a giving IM1 (ΔG = 19.4 kcal mol–1) without chela-
tion assistance (Scheme 5a). Furthermore, considering that
cationic CpERh(III) complex generated in situ by the addi-
tion of AgSbF6 failed to catalyze the present dienylation, the
direct C–H bond cleavage through electrophilic aromatic
substitution pathway can be excluded. In sharp contrast, η2
coordination of 2a to the CpERh(I) complex greatly stabiliz-
es IM3 (ΔG = –14.2 kcal mol–1), but high activation energy
(20.7 kcal mol–1) is required for the generation of rhodi-
um(III) hydride G (IM4) from IM3 via the non-directed C–H
bond activation (Scheme 5b). The lowest activation energy
(7.5 kcal mol–1) is calculated for the generation of phenyl-
rhodium CpE-F (IM6) from rhodacycle CpE-E (RT3) with the
formation of IM5 (ΔG = 8.2 kcal mol–1) (Scheme 5c). In IM1
and IM3, benzene is coordinated to rhodium, but in IM5,
benzene is not coordinated to rhodium due to steric hin-
drance of the rhodacycle. Thus, the theoretically most fa-
vorable pathway is E to F. Furthermore, computational
studies revealed that this pathway is not available for the
Cp*Rh complex. The C–H bond activation from Cp*-E (RT3)
not only requires the higher activation energy (16.1 kcal
mol–1) but is thermodynamically unfavorable (ΔG = 3.1 kcal
mol–1).
a) Reactions using rhodium(I) complexes
Rh(I) complex (10 mol % Rh)
additive
2a
+
3a
4aa + 5aa + 6a + 7a
(2.0 mL)
(0.10 mmol)
80 °C, 20 h, under Ar
Yield (%)
Rh(I) complex, Additive
6a+7a (6a/7a)
4aa+5aa
[Rh(cod)2]BF4
9
6
2
0
50 (89:11)
57 (86:14)
57 (94:6)
[Rh(cod)2]BF4, Ag2CO3 (100 mol %)
[Rh(cod)Cl]2, Ag2CO3 (100 mol %)
[Rh(cod)2]BF4, rac-binap (10 mol %)
87 (84:16)
b) Reaction of 3a
X mol % 1
100 mol % Ag2CO3
X = 50, 40 °C, 20 h / complex mixture
(100% conv of 3a)
X = 10, 80 °C, 20 h / 6a 33% + 7a 18%
(81% conv of 3a)
Ph
NTs
(CH2Cl)2, under Ar
Ph
3a
c) Reaction of 2a and monoyne 8
10 mol % 1
100 mol % Ag2CO3
Ph
N(Me)Ts
NTs
+
80 °C, 72 h, under Ar
(75% conv of 8)
Me
Ph
9, 0%
2a
8
(2.0 mL)
(0.10 mmol)
d) Recations of electron-rich arene 2c
Ph
5 mol % [CpXRhCl2]2
100 mol % Ag2CO3
MeO
Ph
+
NTs
NTs
MeO
100 °C, 20 h, under Ar
Ph
Ph
+
4ca
2c
(2.0 mL)
3a
(0.10 mmol)
6a/7a
Yield [%]
CpX
6a+7a (6a/7a)
4ca
CpE
Cp*
22%[a]
0%
70% (76:24)
76% (75:25)
Finally, a deuterium kinetic isotope effect (DKIE) of die-
nylation of 2a with 3a was measured. The intermolecular
competition reactions between 2a and 2a-d6 in the pres-
ence of 3a revealed a DKIE value of 1.2 (Scheme 6a). A DKIE
value, measured by comparing the initial rates obtained
a Mixture of isomers and aromatized products (5ca).
Scheme 4 Experimental mechanistic studies
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, A–J

E
H. Takahashi et al.
Special Topic
Synthesis
a) Energy profile for C–H activation pathway A to B
CpE
CpE
CpE
CpE
Model ligand
RhIII
+19.4
O
+9.5
O
–19.7
O
RhIII
Rh
RhIII
AcO
OAc
CpE
+
O
O
O
H
Me
O
O
O
H
MeO2C
CO2Me
Me
O
O
O
Me
A (RT1)
IM1
TS1
B (IM2)
Cp*
b) Energy profile for C–H activation pathway D to G
Me
Me
Me
Me
CpE
CpE
CpE
RhIII
CpE
RhI
Me
RhI
+
–14.2
+20.7
–1.8
Rh
H
H
D (RT2)
IM3
TS2
G (IM4)
c) Energy profile for C–H activation pathway E to F
CpX
CpX
CpX
RhIII
CpX
RhIII
Ph
Ph
CpE: +8.2
Cp*: +3.8
CpE: +7.5
Cp*: +16.1
CpE: –11.6
Cp*: –13.0
RhIII
Rh
H
O
+
H
O
O
O
E (RT3)
IM5
TS3
F (IM6)
Scheme 5 Theoretical mechanistic studies [∆G (kcal mol–1) values are absolute for the step depicted]
from two individual reactions of 2a and 2a-d6 with 3a, was
1.1 (Scheme 6b). These results indicate that the C–H bond
cleavage is not the rate-limiting step in the present dienyla-
tion reactions, which is consistent with the low activation
energy for the C–H bond activation, but high temperature is
required for the present dienylation reaction.
In conclusion, we have established that unfunctional-
ized arenes can be dienylated with 1,6-diynes, possessing
aryl groups at the diyne termini, in the presence of a cata-
lytic amount of an electron-deficient cyclopentadienyl rho-
dium(III) complex, [CpERhCl2]2 (1), and a stoichiometric
amount of silver carbonate to give the corresponding die-
nylated arenes, although the product yields were low. Ex-
perimental and theoretical mechanistic studies suggested
that a CpERh(I) complex generated in situ might catalyze
the present dienylation reaction. A low activation energy
(15.7 kcal mol–1) was calculated for the C–H bond activation
of benzene with a rhodacyclopentadiene intermediate, de-
rived from the CpERh(I) complex and the 1,6-diyne.
a) Intermolecular competition reaction
D
5 mol% 1
100 mol% Ag2CO3
D
D
D
D
Ph
Ph
NTs
+
+
80 °C, 4 h, under Ar
D
2a
2a-d6
3a
(0.10 mmol)
(1.0 mL)
(1.0 mL)
Ph
Ph
D
NTs
NTs
+
D5
Ph
Ph
4aa
4aa-d6
4aa+4aa-d6 5%
4aa/4aa-d6 = 54:46
KIE = 1.2
b) Two individual reactions
Ph
5 mol% 1
100 mol% Ag2CO3
Ph
(CH2Cl)2 (No. 28,450-5), benzene (No. 401765), o-xylene (No.
294780), m-xylene (No. 296325) and anisole (No. 296295) were
obtained from Aldrich and used as received. Benzene-d6 (05080-96)
was obtained from Kanto and used as received. Solvents for the syn-
thesis of substrates were dried over molecular sieves 4Å (Wako) be-
fore use. [CpERhCl2]2 was prepared from RhCl3·nH2O (ca. 39 wt% Rh)
according to the literature.7 Diynes 3a,17 3b,17 3c,17 3d,17 3e,18 3f,19
3g,20 3h,12 3i21 and monoynes 822 were already reported. All other re-
agents were obtained from commercial sources and used as received.
All reactions were carried out under nitrogen or argon in oven-dried
glassware with magnetic stirring unless otherwise noted. 1H and 13C
NMR data were collected with a Bruker Avance III HD 400 (400 MHz)
NTs
NTs
NTs
+
80 °C, 4 h, under Ar
Ph
Ph
2a
(2.0 mL)
3a
(0.10 mmol)
4aa / 5.1%
D
Ph
D
5 mol% 1
100 mol% Ag2CO3
D
D
D
D
Ph
Ph
NTs
+
80 °C, 4 h, under Ar
D5
D
Ph
2a-d6
(2.0 mL)
3a
4aa-d6 / 4.6%
(0.10 mmol)
KIE = 1.1
Scheme 6 DKIE experiments
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, A–J

F
H. Takahashi et al.
Special Topic
Synthesis
at ambient temperature. HRMS data were obtained with a Bruker mi-
crOTOF Focus II.
13C NMR (CDCl3, 100 MHz):  = 143.6, 141.9, 141.5, 139.1, 138.4,
137.6, 136.0, 134.6, 134.3, 133.7, 131.3, 129.8, 129.7, 129.0, 128.6,
128.1, 127.7, 127.6, 127.5, 126.9, 126.7, 126.5, 54.2, 54.1, 49.9, 21.5,
21.2.
Directing Group-Free Dienylation of Arenes with 1,6-Diynes; Typi-
cal Procedure (Scheme 2a)
HRMS (ESI): m/z [M + Na]+ calcd for C75H63N3NaO6S3: 1220.3771;
found: 1220.3778.
To a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol), 1 (4.3 mg,
0.0050 mmol), 3a (40.0 mg, 0.100 mmol), and 2a (2.0 mL) in this or-
der. The mixture was stirred at 80 °C under Ar for 40 h. The resulting
mixture was diluted with hexane, filtered through a silica gel pad, and
washed with diethyl ether. The solvent was removed under reduced
pressure, and the residue was purified by preparative thin-layer chro-
matography (PTLC, toluene/EtOAc = 30:1) to give a mixture of 4aa and
5aa23 (12.4 mg, 0.0259 mmol, 26% yield, 4aa/5aa = 96:4) as a pale-
yellow solid, 6a (8.6 mg, 0.0215 mmol, 22% yield) as a yellow solid,
and 7a (5.0 mg, 0.0125 mmol, 13% yield) as an orange solid.
(4Z)-3-(Diphenylmethylidene)-4-(phenylmethylidene)oxolane
(4ab)24
The title compounds were isolated as a mixture of 4ab and 5ab.
Yield: 4.0 mg (0.0120 mmol, 12%); 4ab/5ab = 91:9; yellow oil.
1H NMR (CDCl3, 400 MHz):  (4ab) = 7.56–7.22 (m, 10 H), 7.17 (d, J =
7.4 Hz, 1 H), 7.12 (dd, J = 8.4, 1.6 Hz, 2 H), 6.88 (d, J = 7.4 Hz, 2 H), 6.02
(t, J = 2.4 Hz, 1 H), 4.81 (d, J = 2.4 Hz, 2 H), 4.57 (s, 2 H); methylene
protons of 5ab:  = 5.08 (s, 4 H).
(4Z)-3-(Diphenylmethylidene)-1-(4-methylbenzenesulfonyl)-4-
(phenylmethylidene)pyrrolidine (4aa)
13C NMR (CDCl3, 100 MHz):  = 142.7, 141.5, 138.3, 137.7, 137.2,
136.3, 136.1, 135.9, 132.4, 132.1, 129.8, 129.6, 128.9, 128.8, 128.7,
128.5, 128.4, 128.1, 127.7, 127.5, 127.4, 127.0, 125.9, 125.7, 125.6,
77.3, 77.2, 77.0, 76.7, 73.5, 72.3, 71.7.
HRMS (APCI): m/z [M + H]+ calcd for C24H21O: 325.1587; found:
325.1574.
Mp 165.0–193.6 °C (dec.)
1H NMR (CDCl3, 400 MHz):  (4aa) = 7.64 (d, J = 8.2 Hz, 2 H), 7.35–7.18
(m, 11 H), 7.04 (dd, J = 8.2, 1.6 Hz, 2 H), 6.96 (dd, J = 8.2, 1.6 Hz, 2 H),
6.89 (d, J = 7.4 Hz, 2 H), 5.96 (t, J = 2.4 Hz, 1 H), 4.34 (d, J = 2.4 Hz, 2 H),
4.11 (s, 2 H), 2.44 (s, 3 H); methylene and methyl protons of 5aa:  =
4.54 (s, 4 H), 2.38 (s, 3 H).
{[(1E)-2-(Diphenylmethylidene)cyclopentylidene]methyl}ben-
zene (4ac)
13C NMR (CDCl3, 100 MHz):  = 143.8, 143.6, 142.3, 141.3, 138.0,
137.7, 136.5, 134.2, 133.8, 133.7, 133.6, 132.9, 132.3, 129.9, 129.8,
129.6, 129.5, 129.4, 128.9, 128.8, 128.7, 128.53, 128.51, 128.3, 128.1,
127.9, 127.8, 127.6, 127.4, 125.91, 125.86, 53.6, 52.9, 52.0, 21.54,
21.51.
The title compounds were isolated as a mixture of 4ac and 5ac.25
Yield: 7.9 mg (0.0244 mmol, 24%); 4ac/5ac = 94:6; pale-yellow solid;
mp 108.5–121.8 °C (dec.).
1H NMR (CDCl3, 400 MHz):  (4ac) = 7.36–7.12 (m, 12 H), 7.11 (t, J =
7.4 Hz, 1 H), 7.04 (d, J = 7.4 Hz, 2 H), 6.04 (t, J = 2.0 Hz, 1 H), 2.74 (td,
J = 7.2, 2.0 Hz, 2 H), 2.55 (t, J = 7.2 Hz, 2 H), 1.78 (tt, J = 7.2, 7.2 Hz, 2
H); methylene protons of 5ac:  = 2.88 (t, J = 8.0 Hz, 4 H), 2.00 (quin,
J = 8.0 Hz, 2 H).
HRMS (ESI): m/z [M + Na]+ calcd for 4aa C31H27NNaO2S: 500.1655;
found: 500.1636; m/z [M
+
Na]+ calcd for 5aa C31H27NNaO2S:
498.1498; found: 498.1493.
4-Methyl-N-{[2-(4-methylbenzenesulfonyl)-4,6,7-triphenyl-2,3-
dihydro-1H-isoindol-5-yl]methyl}-N-(3-phenylprop-2-yn-1-
yl)benzene-1-sulfonamide (6a)
13C NMR (CDCl3, 100 MHz):  = 144.2, 143.4, 142.0, 141.7, 141.1,
139.7, 138.5, 135.8, 134.2, 131.9, 131.6, 130.2, 130.1, 129.6, 128.63,
128.56, 128.3, 128.1, 127.8, 127.3, 127.0, 126.6, 126.5, 126.2, 125.9,
124.7, 34.5, 33.0, 32.1, 25.7, 24.4.
Mp 188.3–189.7 °C
1H NMR (CDCl3, 400 MHz):  = 7.65 (d, J = 8.2 Hz, 2 H), 7.50–7.38 (m, 3
H), 7.36–7.28 (m, 4 H), 7.20 (tt, J = 7.4, 1.6 Hz, 1 H), 7.17–7.08 (m, 8 H),
7.08–7.00 (m, 4 H), 6.93–6.84 (m, 4 H), 6.69 (dd, J = 8.4, 1.4 Hz, 2 H),
4.40 (s, 4 H), 4.23 (s, 2 H), 3.15 (s, 2 H), 2.43 (s, 3 H), 2.12 (s, 3 H).
HRMS (APCI): m/z [M] calcd for C25H22: 322.1722; found: 322.1738.
1,1-Dimethyl (4E)-3-(diphenylmethylidene)-4-(phenyl-
methylidene)cyclopentane-1,1-dicarboxylate (4ad)
13C NMR (CDCl3, 100 MHz):  = 143.6, 143.0, 142.3, 138.8, 138.5,
138.4, 137.6, 136.6, 135.2, 135.0, 133.8, 132.9, 131.3, 131.1, 129.8,
129.23, 129.18, 129.0, 128.8, 128.0, 127.8, 127.7, 127.63, 127.56,
126.8, 126.6, 122.3, 85.0, 82.2, 54.3, 54.2, 47.1, 38.3, 21.5, 21.2.
HRMS (ESI): m/z [M + Na]+ calcd for C50H42N2NaO4S2: 821.2478;
found: 821.2479.
The title compounds were isolated as a mixture of 4ad and 5ad.
Yield: 13.4 mg (0.0307 mmol, 31%); 4ad/5ad = 90:10; yellow oil.
1H NMR (CDCl3, 400 MHz):  (4ad) = 7.35–7.11 (m, 13 H), 7.03 (d, J =
7.4 Hz, 2 H), 6.06 (t, J = 2.4 Hz, 1 H), 3.70 (s, 6 H), 3.35 (d, J = 2.4 Hz, 2
H), 3.12 (s, 2 H); methylene protons of 5ad:  = 3.67 (s, 6 H), 3.55 (s, 4
H).
13C NMR (CDCl3, 100 MHz):  = 171.9, 171.8, 143.4, 142.6, 138.8,
137.9, 137.6, 137.4, 137.1, 136.7, 134.6, 132.3, 131.7, 130.02, 129.96,
129.8, 129.5, 129.0, 128.7, 128.60, 128.56, 128.4, 128.34, 128.28,
128.2, 128.0, 127.9, 127.6, 127.4, 127.3, 127.01, 126.99, 126.7, 125.93,
125.86, 125.2, 60.2, 58.1, 53.1, 52.9, 52.8, 41.1, 40.5, 39.1.
HRMS (ESI): m/z [M + Na]+ calcd for 4ad C29H26NaO4: 461.1723;
found: 461.1723; m/z [M + Na]+ calcd for 5ad C29H24NaO4: 459.1567;
found: 459.1583.
4-Methyl-N,N-bis({[2-(4-methylbenzenesulfonyl)-4,6,7-triphenyl-
2,3-dihydro-1H-isoindol-5-yl]methyl})benzene-1-sulfonamide
(7a)
Mp 170.1–172.5 °C.
1H NMR (CDCl3, 400 MHz):  = 7.59 (d, J = 8.2 Hz, 4 H), 7.43 (br, 6 H),
7.27 (d, J = 6.8 Hz, 6 H), 7.22–6.51 (br, 6 H), 7.14 (t, J = 7.2 Hz, 3 H),
7.05 (br, 9 H), 6.66 (br, 2 H), 6.61 (d, J = 8.0 Hz, 4 H), 6.03 (d, J = 8.2 Hz,
2 H), 4.46–3.86 (br, 12 H), 2.38 (s, 6 H), 2.29 (s, 3 H).
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, A–J

G
H. Takahashi et al.
Special Topic
Synthesis
1,1-Dibenzyl (4E)-3-(diphenylmethylidene)-4-(phenyl-
methylidene)cyclopentane-1,1-dicarboxylate (4ae)
HRMS (APCI): m/z [M + H]+ calcd for 4bg C37H40NO2S: 562.2774;
found: 562.2805; m/z [M + H]+ calcd for 5bg C37H38NO2S: 560.2618;
found: 560.2669.
The title compounds were isolated as a mixture of 4ae and 5ae.
Yield: 11.5 mg (0.0195 mmol, 20%); 4ae/5ae = 80:20; yellow oil.
One-Pot Dienylation and Aromatization; Typical Procedure
(Scheme 2b)
1H NMR (CDCl3, 400 MHz):  (4ae) = 7.35–7.08 (m, 23 H), 7.01 (d, J =
7.4 Hz, 2 H), 6.04 (t, J = 2.4 Hz, 1 H), 5.12 (d, J = 12.4 Hz, 2 H), 5.06 (d,
J = 12.4 Hz, 2 H), 3.38 (d, J = 2.4 Hz, 2 H), 3.18 (s, 2 H); methylene,
protons of 5ae:  = 5.06 (s, 4 H), 3.55 (s, 4 H).
13C NMR (CDCl3, 100 MHz):  = 171.0, 143.3, 142.6, 138.7, 137.9,
137.6, 137.4, 136.9, 136.7, 135.4, 135.3, 134.7, 132.3, 130.0, 129.9,
129.5, 128.7, 128.6, 128.52, 128.49, 128.47, 128.2, 128.02, 127.92,
127.32, 126.97, 126.96, 126.7, 125.9, 125.2, 67.32, 67.28, 60.7, 58.4,
41.1, 40.4, 39.2.
To a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol), 1 (4.3 mg,
0.0050 mmol), 3a (40.0 mg, 0.10 mmol), and 2a (2.0 mL) in this order.
The mixture was stirred at 80 °C under Ar for 40 h. The mixture was
then irradiated with blue LED light at r.t. under air for 6 h. Then, the
mixture was diluted with hexane, filtered through a silica gel pad, and
washed with diethyl ether. The solvent was removed under reduced
pressure, and the residue was purified by PTLC (toluene/EtOAc = 30:1)
to give 5aa (10.9 mg, 0.0229 mmol, 23% yield) as a colorless solid.
HRMS (ESI): m/z [M + Na]+ calcd for 4ae C41H34NaO4: 613.2349;
found: 613.2381; m/z [M + Na]+ calcd for 5ae C41H32NaO4: 611.2193;
found: 611.2231.
2-(4-Methylbenzenesulfonyl)-4,9-diphenyl-1H,2H,3H-benzo[f]iso-
indole (5aa)22
Mp 232.8–234.6 °C (dec.).
1H NMR (CDCl3, 400 MHz):  = 7.69 (d, J = 8.4 Hz, 2 H), 7.63–7.59 (m, 2
H), 7.56–7.46 (m, 6 H), 7.37–7.27 (m, 8 H), 4.54 (s, 4 H), 2.39 (s, 3 H).
13C NMR (CDCl3, 100 MHz):  = 143.7, 137.7, 133.8, 133.6, 132.9,
132.3, 129.8, 129.5, 128.8, 127.9, 127.6, 125.91, 125.87.
HRMS (ESI): m/z [M + Na]+ calcd for C31H25NNaO2S: 498.1498; found:
498.1499.
(4Z)-1-(4-Methylbenzenesulfonyl)-3-[(4-methylphenyl)(phe-
nyl)methylidene]-4-[(4-methylphenyl)methylidene]pyrrolidine
(4af)
The title compounds were isolated as a mixture of 4af and 5af.
Yield: 20.4 mg (0.0404 mmol, 40%); 4af/5af = 92:8, 4af: E/Z = 20:80;
pale-yellow solid; mp 153.8–160.9 °C.
1H NMR (CDCl3, 400 MHz):  (Z)-4af = 7.63 (d, J = 7.6 Hz, 2 H), 7.35–
7.18 (m, 6 H), 7.12 (d, J = 8.0 Hz, 2 H), 7.10–7.01 (m, 2 H), 6.94–6.90
(m, 2 H), 6.82 (t, J = 7.6 Hz, 1 H), 6.78 (d, J = 7.6 Hz, 2 H), 5.91 (t, J = 2.4
Hz, 1 H), 4.33 (br, 2 H), 4.12 (s, 2 H), 2.43 (s, 3 H), 2.37 (s, 3 H), 2.30 (s,
3 H); a part of aromatic protons and vinyl, methylene, and methyl
protons of (E)-4af:  = 7.63 (d, J = 7.6 Hz, 2 H), 6.01 (t, J = 2.4 Hz, 1 H),
4.33 (br, 2 H), 4.08 (s, 2 H), 2.43 (s, 3 H), 2.31 (s, 3 H), 2.29 (s, 3 H);
methylene and methyl protons of 5af:  = 4.54 (s, 4 H), 2.48 (s, 6 H),
2.38 (s, 3 H).
7,12-Diphenylbenzo[k]fluoranthene (5ah)21
Yield: 15.5 mg (0.0384 mmol, 38%); yellow solid.
1H NMR (CDCl3, 400 MHz):  = 7.71–7.55 (m, 14 H), 7.39 (dd, J = 6.4,
3.3 Hz, 2 H), 7.32 (t, J = 7.6 Hz, 2 H), 6.61 (d, J = 7.1 Hz, 2 H).
13C NMR (CDCl3, 100 MHz):  = 138.9, 136.6, 135.6, 134.9, 134.8,
132.9, 130.1, 130.0, 129.2, 128.0, 127.8, 126.8, 125.9, 125.8, 122.2.
13C NMR (CDCl3, 100 MHz):  = 143.7, 143.6, 142.6, 141.5, 139.5,
138.3, 137.7, 137.6, 137.4, 137.0, 134.7, 133.79, 133.76, 133.7, 133.6,
133.4, 133.3, 132.9, 132.7, 132.51, 132.46, 129.81, 129.75, 129.7,
129.52, 129.48, 129.33, 129.25, 129.0, 128.93, 128.88, 128.8, 128.6,
128.48, 128.46, 128.3, 127.84, 127.81, 127.7, 127.6, 127.3, 125.9,
125.7, 53.7, 53.0, 52.9, 52.0, 21.53, 21.49, 21.3, 21.24, 21.2, 21.18.
HRMS (APCI): m/z [M + H]+ calcd for 4af C33H32NO2S: 506.2148;
found: 506.2196; m/z [M + H]+ calcd for 5af C33H30NO2S: 504.1992;
found: 504.2041.
5,10-Diphenyl-1,2-dihydrobenzo[k]cyclopenta[cd]fluoranthene
(5ai)21
Yield: 13.0 mg (0.0302 mmol, 30%); yellow solid.
1H NMR (CDCl3, 400 MHz):  = 7.71–7.58 (m, 12 H), 7.39 (dd, J = 6.4,
3.3 Hz, 2 H), 7.14 (t, J = 7.1 Hz, 2 H), 6.65 (d, J = 7.1 Hz, 2 H), 3.42 (s, 4
H).
13C NMR (CDCl3, 100 MHz):  = 145.1, 139.3, 136.7, 136.2, 134.8,
134.2, 132.4, 132.3, 130.2, 129.1, 127.8, 126.7, 125.5, 123.8, 120.9,
32.1.
(4Z)-3-[Bis(3,5-dimethylphenyl)methylidene]-4-[(3,5-dimethyl-
phenyl)methylidene]-1-(4-methylbenzenesulfonyl)pyrrolidine
(4bg)
Experimental Mechanistic Studies (Scheme 4)
Procedure for [Rh(cod)2]BF4 (Scheme 4a)
The title compounds were isolated as a mixture of 4bg and 5bg.
To
a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol),
Yield: 4.7 mg (0.0084 mmol, 8%); 4bg/5bg = 87:13; yellow oil.
[Rh(cod)2]BF4 (4.1 mg, 0.0101 mmol), 3a (40.0 mg, 0.100 mmol), and
2a (2.0 mL) in this order. The mixture was stirred at 80 °C under Ar for
20 h. The resulting mixture was diluted with hexane, filtered through
a silica gel pad, and washed with diethyl ether. The solvent was re-
moved under reduced pressure to give 4aa (6% yield) and 6a (49%
yield). The yields were determined by 1H NMR analysis using dimeth-
yl terephthalate as an internal standard.
1H NMR (CDCl3, 400 MHz):  4bg = 7.61 (d, J = 8.4 Hz, 2 H), 7.29 (d, J =
8.4 Hz, 2 H), 6.92 (s, 1 H), 6.84 (s, 1 H), 6.83 (s, 1 H), 6.63 (s, 2 H), 6.49
(br, 4 H), 5.88 (t, J = 2.4 Hz, 1 H), 4.33 (d, J = 2.4 Hz, 2 H), 4.08 (s, 2 H),
2.45 (s, 3 H), 2.30 (s, 6 H), 2.27 (s, 3 H), 2.20 (s, 3 H); a part of aromatic
protons and methylene and methyl protons of 5bg:  = 7.64 (d, J = 8.4
Hz, 2 H), 4.46 (s, 2 H), 4.37 (s, 2 H), 2.40 (s, 9 H), 2.36 (s, 6 H), 2.29 (s, 3
H).
13C NMR (CDCl3, 100 MHz):  = 143.5, 142.5, 141.1, 138.3, 138.1,
137.9, 137.6, 136.8, 134.7, 134.22, 134.05, 132.2, 131.9, 129.8, 129.7,
129.4, 129.2, 129.03, 128.96, 128.9, 127.9, 127.8, 127.6, 127.1, 127.0,
126.8, 126.5, 126.2, 54.3, 53.2, 52.2, 21.6, 21.44, 21.37, 21.3.
Procedure for [Rh(cod)Cl]2 (Scheme 4a)
To
a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol),
[Rh(cod)Cl]2 (2.5 mg, 0.00507 mmol), 3a (40.0 mg, 0.100 mmol), and
2a (2.0 mL) in this order. The mixture was stirred at 80 °C under Ar for
© 2020. Thieme. All rights reserved. Synthesis 2021, 53, A–J

H
H. Takahashi et al.
Special Topic
Synthesis
20 h. The resulting mixture was diluted with hexane, filtered through
a silica gel pad, and washed with diethyl ether. The solvent was re-
moved under reduced pressure to give 4aa (2% yield) and 6a (53%
yield). The yields were determined by 1H NMR analysis using dimeth-
yl terephthalate as an internal standard.
the same level. All stationary points were optimized without any
symmetry assumptions, and characterized by normal coordinate
analysis at the same level of theory (number of imaginary frequen-
cies, NIMAG, 0 for minima and 1 for TSs). The intrinsic reaction coor-
dinate (IRC) method was used to track minimum energy paths from
transition structures to the corresponding local minima.28
Procedure for [Rh(cod)2]BF4/rac-binap System (Scheme 4a)
DKIE Measurements (Scheme 6)
rac-Binap (6.2 mg, 0.0100 mmol) and [Rh(cod)2]BF4 (4.1 mg, 0.0101
mmol) were dissolved in CH2Cl2 (2 mL), and the mixture was stirred
at r.t. for 10 minutes. H2 was introduced to the resulting solution in a
Schlenk tube. After stirring at r.t. for 30 minutes, the resulting mix-
ture was concentrated to dryness. To the residue was added 3a (40.0
mg, 0.100 mmol), and 2a (2.0 mL) in this order. The mixture was
stirred at 80 °C under Ar for 20 h. The resulting mixture was diluted
with hexane, filtered through a silica gel pad, and washed with dieth-
yl ether. The solvent was removed under reduced pressure to give 6a
(73% yield) and 7a (14% yield). The yields were determined by 1H NMR
analysis using dimethyl terephthalate as an internal standard.
Intermolecular Competition Reaction (Scheme 6a)
To a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol), 1 (4.3 mg,
0.0050 mmol), 3a (40.0 mg, 0.10 mmol), 2a (1.0 mL), and 2a-d6 (1.0
mL) in this order. The mixture was stirred at 80 °C under Ar for 4 h.
The resulting mixture was diluted with hexane, filtered through a sil-
ica gel pad, and washed with diethyl ether. The solvent was removed
under reduced pressure and the residue was purified by PTLC (tolu-
ene/EtOAc/dichloromethane = 30:1:1) to give 4aa and 4aa-d6 (2.3 mg,
0.0049 mmol, 5% yield, 4aa/4aa-d6 = 54:46).
Procedure for Scheme 4b
Two Individual Reactions (Scheme 6b)
To a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol), 1 (8.5 mg,
0.0100 mmol), 3a (40.0 mg, 0.100 mmol), and (CH2Cl)2 (2.0 mL) in this
order. The mixture was stirred at 80 °C under Ar for 20 h. The result-
ing mixture was diluted with hexane, filtered through a silica gel pad,
and washed with diethyl ether. The solvent was removed under re-
duced pressure, and the residue was purified by a preparative TLC
(toluene/EtOAc = 30:1) to give 6a (13.0 mg, 0.0325 mmol, 33% yield)
and 7a (7.3 mg, 0.0184 mmol, 18% yield).
To a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol), 1 (4.3 mg,
0.0050 mmol), 3a (40.0 mg, 0.10 mmol), and 2a (2.0 mL) in this order.
The mixture was stirred at 80 °C under Ar for 4 h. The resulting mix-
ture was diluted with hexane, filtered through a silica gel pad, and
washed with diethyl ether. The solvent was removed under reduced
pressure. To another Schlenk tube was added Ag2CO3 (27.6 mg, 0.10
mmol), 1 (4.3 mg, 0.0050 mmol), 3a (40.0 mg, 0.10 mmol), and 2a-d6
(2.0 mL) in this order. The mixture was stirred at 80 °C under Ar for 4
h. The resulting mixture was diluted with hexane, filtered through a
silica gel pad, and washed with diethyl ether. The solvent was re-
moved under reduced pressure. Then, the two residues were mixed
and purified by PTLC (toluene/EtOAc/dichloromethane = 30:1:1) to
3-[(Methoxyphenyl)(phenyl)methylidene]-1-(4-methylbenzene-
sulfonyl)-4-(phenylmethylidene)pyrrolidine (4ca, Scheme 4d)
The title compounds were isolated as a mixture of 4ca and 5ca. The
regio- and stereochemistries of 4ca could not be determined.
give 4aa and 4aa-d6 (4.7 mg, 0.0097 mmol, 9.7% yield, 4aa/4aa-d6
=
53:47).
Yield: 11.1 mg (0.0219 mmol, 22%); 4ca/5ca = 92:8, 4ca/isomer ratio
= 75:25; yellow oil.
(3Z)-1-(4-Methylbenzenesulfonyl)-3-[phenyl(2H)methylidene]-4-
{phenyl[(2,3,4,5,6-2H5)phenyl]methylidene}pyrrolidine (4aa-d6)
1H NMR (CDCl3, 400 MHz):  4ca = 7.63 (d, J = 8.0 Hz, 2 H), 7.36–7.24
(m, 8 H), 7.02 (dd, J = 8.4, 2.0 Hz, 2 H), 6.94 (d, J = 7.6 Hz, 2 H), 6.88 (d,
J = 8.4 Hz, 2 H), 6.77 (d, J = 8.8 Hz, 2 H), 6.11 (t, J = 2.4 Hz, 1 H), 4.34 (d,
J = 2.4 Hz, 2 H), 4.08 (s, 2 H), 3.77 (s, 3 H), 2.43 (s, 3 H); a part of aro-
matic, vinyl, methylene, and methyl protons of another isomer of 4ca:
 = 7.63 (d, J = 8.0 Hz, 2 H), 7.05 (dd, J = 8.4, 2.0 Hz, 2 H), 6.03 (t, J = 2.4
Hz, 1 H), 4.33 (d, J = 2.4 Hz, 2 H), 4.10 (s, 2 H), 3.70 (s, 3 H), 2.44 (s, 3
H); methylene and methyl protons of 5ca:  = 4.51 (s, 2 H), 4.49 (s, 2
H), 3.68 (s, 3 H), 2.39 (s, 3 H).
13C NMR (CDCl3, 100 MHz):  = 160.0, 158.9, 143.8, 143.7, 142.7,
142.6, 142.1, 137.7, 136.6, 136.5, 134.5, 134.1, 133.7, 133.6, 133.5,
132.8, 132.4, 130.9, 129.9, 129.83, 129.75, 129.4, 129.0, 128.8, 128.53,
128.52, 128.34, 128.29, 128.2, 127.8, 127.7, 127.6, 127.42, 127.35,
121.9, 115.2, 114.0, 112.8, 55.24, 55.21, 52.94, 52.86, 51.9, 23.8, 21.6.
To a Schlenk tube was added Ag2CO3 (27.6 mg, 0.10 mmol), 1 (4.3 mg,
0.0050 mmol), 3a (40.0 mg, 0.10 mmol), and 2a-d6 (2.0 mL) in this or-
der. The mixture stirred at 80 °C under Ar for 40 h. The resulting mix-
ture was diluted with hexane, filtered through a silica gel pad, and
washed with diethyl ether. The solvent was concentrated under re-
duced pressure and the residue was purified by preparative TLC (tolu-
ene/EtOAc/dichloromethane = 30:1:1) to give 4aa-d6 and 5aa-d6 (14.3
mg, 0.0296 mmol, 30% yield, 4aa-d6/5aa-d6 = 92:8, 4aa-d6, E/Z =
81:29) as a pale-yellow solid.
1H NMR (CDCl3, 400 MHz):  (E)-4aa-d6 = 7.64 (d, J = 8.0 Hz, 2 H),
7.36–7.16 (m, 8 H), 7.04 (dd, J = 8.0, 1.6 Hz, 2 H), 6.89 (d, J = 7.6 Hz, 2
H), 4.34 (s, 1 H), 4.11 (s, 2 H), 2.43 (s, 3 H); (Z)-4aa-d6:  = 7.64 (d, J =
8.0 Hz, 2 H), 7.36–7.16 (m, 8 H), 6.96 (dd, J = 8.0, 1.6 Hz, 2 H), 6.89 (d,
J = 7.6 Hz, 2 H), 4.34 (s, 2 H), 4.11 (s, 2 H), 2.43 (s, 3 H); methylene and
methyl protons of 5aa-d6:  = 4.54 (s, 4 H), 2.38 (s, 3 H).
HRMS (ESI): m/z [M + Na]+ calcd for 4ca, C32H29NNaO3S: 530.1760;
found: 530.1709.
Theoretical Mechanistic Studies (Scheme 5)
All calculations were carried with the Gaussian 16 program pack-
age.26 The hybrid density functional method based on M0627 with a
standard 6-31g* basis set (LANL2DZ basis set for Rh) was used for ge-
ometry optimizations and calculation of the single-point energies.
Geometry optimization and vibrational analysis were performed at
Funding Information
This work was supported partly by a Grant-in-Aid for Scientific Re-
search (No. JP19H00893 to K.T. and No. JP20K22521 to Y.N.) from the
Japan Society for the Promotion of Science (JSPS, Japan).JapanSocietyforth
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cience(JP
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© 2020. Thieme. All rights reserved. Synthesis 2021, 53, A–J

I
H. Takahashi et al.
Special Topic
Synthesis
Acknowledgment
(9) For applications of 1 in C–H bond functionalizations other than
annulation reactions, see: (a) Morimoto, K.; Itoh, M.; Hirano, K.;
Satoh, T.; Shibata, Y.; Tanaka, K.; Miura, M. Angew. Chem. Int. Ed.
2012, 51, 5359. (b) Itoh, M.; Hirano, K.; Satoh, T.; Shibata, Y.;
Tanaka, K.; Miura, M. J. Org. Chem. 2013, 78, 1365. (c) Baars, H.;
Unoh, Y.; Okada, T.; Hirano, K.; Satoh, T.; Tanaka, K.; Bolm, C.;
Miura, M. Chem. Lett. 2014, 43, 1782. (d) Takahama, Y.; Shibata,
Y.; Tanaka, K. Chem. Eur. J. 2015, 21, 9053. (e) Shibata, Y.; Kudo,
E.; Sugiyama, E.; Uekusa, H.; Tanaka, K. Organometallics 2016,
35, 1547. (f) Takahama, Y.; Shibata, Y.; Tanaka, K. Org. Lett. 2016,
18, 2934. (g) Takahama, Y.; Shibata, Y.; Tanaka, K. Chem. Lett.
2016, 45, 1177. (h) Yoshimura, R.; Shibata, Y.; Tanaka, K. J. Org.
Chem. 2019, 84, 13164.
(10) Unfortunately, analytically pure dienylation products could not
be isolated in this reaction.
(11) For examples of the CpRh(III) complex-catalyzed C–H bond
functionalization, see: (a) Lin, W.; Li, W.; Lu, D.; Su, F.; Wen, T.-
B.; Zhang, H.-J. ACS Catal. 2018, 8, 8070. (b) Yoshimura, R.;
Tanaka, K. Chem. Eur. J. 2020, 26, 4969.
We thank Umicore for generous support in supplying RhCl3·nH2O. A
generous allotment of computational resources from TSUBAME
(Tokyo Institute of Technology) is gratefully acknowledged.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/a-1328-6436. Su
p
p
ortingInformatio
n
Su
p
p
ortingInformatio
n
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