Highly Stereoselective Positional Isomerization of Styrenes via Acid-Catalyzed Carbocation Mechanism

Article abstract of DOI:10.1002/cjoc.202100218

The first transition metal-free highly stereoselective positional isomerization of various α-alkyl styrenes through a carbocation mechanism triggered strategy is developed by using Al(OTf)₃ as a hidden Br?nsted acid catalyst, which provides facile access to value-added acyclic tri- and tetra-substituted alkenes in good yields with high stereoselectivity under mild conditions. The practicality of this protocol is further highlighted by the gram-scale synthesis, high stereoselectivity, good functional group tolerance, and simple operation. Mechanistic studies support that Al(OTf)₃ acts as a hidden Br?nsted acid catalyst and a carbocation intermediate is formed.

Full text of DOI:10.1002/cjoc.202100218

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Title: Highly Stereoselective Positional Isomerization of Styrenes via Acid-Catalyzed
Carbocation Mechanism
Authors: Xiao-Si Hu, Jun-Xiong He, Ying Zhang, Jian Zhou,* and Jin-Sheng Yu*
This manuscript has been accepted and appears as an Accepted Article online.
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Cite this paper: Chin. J. Chem. 2021, 39, XXX—XXX. DOI: 10.1002/cjoc.202100XXX
Highly Stereoselective Positional Isomerization of Styrenes via
Acid-Catalyzed Carbocation Mechanism
Xiao-Si Hu,a Jun-Xiong He,a Ying Zhang,a Jian Zhou,*,ab and Jin-Sheng Yu*,a
a Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engi-
neering, East China Normal University, 3663N Zhongshan Road, Shanghai 200062, P. R. China.
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Shanghai 200032, China.
Keywords
Alkene positional isomerization | Stereoselective | Carbocation mechanism | Hidden Brønsted acid catalysis
Main observation and conclusion
The first transition metal-free highly stereoselective positional isomerization of various α-alkyl styrenes through a carbocation mecha-
nism triggered strategy is developed by using Al(OTf)3 as a hidden Brønsted acid catalyst, which provides facile access to value-added
acyclic tri- and tetra-substituted alkenes in good yields with high stereoselectivity under mild conditions. The practicality of this protocol
is further highlighted by the gram-scale synthesis, high stereoselectivity, good functional group tolerance, and simple operation. Mech-
anistic studies support that Al(OTf)3 act as a hidden Brønsted acid catalyst, and the formation of a carbocation intermediate.
Comprehensive Graphic Content
a
The first
stereoselective alkene
isomerization via carbocation mechanism
highly
positional
R
mol%)
R
Al(OTf)3 (3~15
rt
ClCH CH Cl
,
2
2
examples
32
=
(
F
aryl,
alkyl,
)
to
H
E Z
/
94%
100/1
up
-
yield,
H
H
H
R
as a
Deprotonation
Al(OTf)3
hidden
Carbocation Mechanism
acid
Brønsted
Transition-metal-free
Operational simplicity
stereoselectivity
High
Functional
tolerance
group
Gram-scale
Mechanistic studies
synthesis
*E-mail: jzhou@chem.ecnu.edu.cn, jsyu@chem.ecnu.edu.cn
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Supporting Information
Chin. J. Chem. 2021, 39, XXX－XXX©
2021
SIOC,
CAS,
Shanghai,
&
WILEY-VCH
GmbH
This article has been accepted for publication and undergone full peer review but has not been
through the copyediting, typesetting, pagination and proofreading process which may lead to
differences between this version and the Version of Record. Please cite this article as doi:
10.1002/cjoc.202100218
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Hu et al.
Report
Rh catalyzed positional isomerization of functionalized α-alkyl sty-
renes via π-allylmetal intermediate.[15b] Although these protocols
were proven to be suited for the synthesis of certain classes of acy-
clic trisubstituted alkenes, further progress is required to expand
the substrate scope, to improve the stereoselectivity, and to avoid
the use of transition-metal catalysts, a complex ligand that is usually
not easy to obtain, and/or additives (Scheme 1a). In addition,
Brønsted acid mediated alkene isomerization via a carbocation
mechanism[16] has also emerged as an alternative strategy.[17] How-
ever, although the positional isomerization of several cyclic alkenes
has been reported,[17] the acyclic alkene isomerization remains un-
derdeveloped,[17c,e] possibly due to the challenging E/Z selectivity
control and reaction efficiency issues.
Recently, we have developed an unprecedently Markovnikov re-
gioselective hydrodifluoroalkylation of alkenes with difluo-
roenoxysilanes via carbocation intermediate.[18] During the mecha-
nistic studies, we found that the generated in situ carbocation in-
termediate from tertiary alcohol would eliminate a β-proton to de-
liver an E-alkene with high stereoselectivity under the catalysis of
hidden Brønsted acid Mg(ClO4)2⸱6H2O, and the observation of al-
kene isomerization phenomenon in the deuterated experiment.[18]
Motivated by these interesting findings, we wondered whether it
was possible to develop a transition-metal-free highly stereoselec-
tive positional isomerization of acyclic alkenes via a carbocation
mechanism using hidden Brønsted acid catalysis[19] (Scheme 1b).
Herein, we report our successful implementation of this transfor-
mation under mild and operationally simple conditions, which con-
stitutes a facile tactic for alkene positional isomerization
Background and Originality Content
Alkene isomerization is a very useful and atom-economic trans-
formation, which constitutes a powerful strategy for the synthesis
of internal alkenes in a stereoselective manner.[1] The past few dec-
ades have witnessed tremendous progress in this area, and a vari-
ety of efficient catalytic systems based on either noble-metal (eg.
Ru,[2] Rh,[3] Pd,[4] Ir,[5] and Pt[6]) or base-metal (eg. Co,[7] Ni,[8] Fe,[9]
and Mo[10]) complexes have been developed for the positional
isomerization of aliphatic mono-substituted or 1,2-dialkyl alkenes.
Despite these achievements, the stereoselective positional isomer-
ization of α-alkyl-α-aryl alkenes remains underexplored and is still a
challenge. Therefore, the development of efficient catalytic strate-
gies for realizing such isomerization is highly sought after, which
would provide a facile route for accessing value-added acyclic tri- or
tetrasubstituted alkenes that are a kind of structural units widely
distributed in natural products, pharmaceuticals and materials,[11]
and serve as a versatile precursor in modern organic synthesis.[12]
In this context, much effort has been paid to developing this
transformation in the past few years. Consequently, a variety of cat-
alytic systems based on three main mechanisms: (a) metal-hydride
mechanism;[13] (b) hydrogen (H) radical mechanism;[14] (c) π-al-
lylmetal intermediate based 1,3-hydrogen shift mechanism,[15] have
been established by transition-metal catalysis (Scheme 1a). For ex-
ample, in 2009, RajanBabu reported a Pd(II)-catalyzed isomerization
of α-alkyl styrenes via a Pd-H insertion and β-H elimination path-
way.[13a] Recently, the groups of Lu,[13b] Findlater,[13c] and Xia[13d] in-
dependently reported the cobalt(II)-catalyzed highly stereoselec-
tive positional isomerization of α-alkyl styrenes through Co-H
mechanism, which delivered the desired acyclic trisubstituted al-
kenes with excellent stereoselectivity by employing their developed
thiazoline iminopyridine, phosphamide iminopyridine, or phos-
phine-amidooxazoline ligand. Most recently, Huang and Liu re-
ported an iron-catalyzed isomerization of α-alkyl styrenes to trisub-
stituted alkenes with chiral phosphine-pyridine-oxazoline ligand via
Fe-H mechanism.[13f] Through H radical initiated mechanism, Nor-
ton et al. developed an isomerization of α-functionalized alkyl sty-
renes by cobalt catalysis under H2 pressure.[14]
Results and Discussion
At the outset, α-ethylstyrene 1a was chosen as a model sub-
strate for the optimization of reaction conditions, as shown in Table
1. Mg(ClO4)2⸱6H2O, which was previously an effective catalyst for
the alkene hydrodifluoroalkylation,[18] was first examined for the
isomerization of 1a in ClCH2CH2Cl at room temperature, unfortu-
nately, no any desired product 2a was detected after 12 h (entry 1).
Table 1 Optimization of conditionsa
Scheme 1 Strategies for isomerization of α-alkyl styrenes
Cat. mol%)
(5
(E)
α
-alkyl
styrenes
art:
State of the
Known three main mechanism
isomerization
R
for
of
(a)
poitional
solvent,
h
rt,12
Transition-metal catalysis
Pd, Ru, Rh, Co, Fe, etc
2a
R
mmol)
1a
(0.2
Entry
1
Cat.
Solvent
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
CH2Cl2
Yield(%)b
E/Zc
-
2
1
Metal-hydride mechanism
H radical mechanism
2)
shift mechanism
1,3-H
3)
1)
Mg(ClO4)2‧6H2O
Al(ClO4)3‧9H2O
In(ClO4)3‧8H2O
Cd(ClO4)2‧6H2O
Ga(OTf)3
0
14
44
58
60
72
90
50
16
87 (82)d
0
Y
M
H
+
H
H
[M]
[M-H]
R
2
18/1
21/1
6.4/1
6.8/1
6.9/1
8.5/1
5.3/1
27/1
24/1
-
R
X
R
H
3
H
[M]
H
M
4
13a)
R
[Pd]: RajanBabu (ref.
H
5
Lu, Findlater, Xia
13b-d)
[Co]:
[Fe]:
(ref.
15a)
[Ru]: Grotjahn (ref.
Zhao
15b)
Norton
14)
[Co]:
(ref.
Koh, Huang
13e-f)
(ref.
6
In(OTf)3
[Rh]:
(ref.
7
Fe(OTf)3
♣
♣
Transition-metal and/or delicately modified
required
Limitations:
ligand
scope
Stereoselectivity & substrate
confined
8
Bi(OTf)3
work:
This
Carbocation mechanism initiated
isomerization
(b)
positional
H
9
Sc(OTf)3
10
11
12
13
14
15
Al(OTf)3
R
-X
H
R
R
Cu(OTf)2
Acid
(Cat.)
H
-X
H
or
2
3
1
Mg(OTf)2
Al(OTf)3
0
-
Carbocation mechanism
Simple
stereoselectivity
81
0
25/1
-
Transition-metal-free
scope
& Mild condition
operation
Broad substrate
examples)
High
Al(OTf)3
EtOAc
(32
Al(OTf)3
Toluene
0
-
Besides, noble-metal ruthenium (Ru) or rhodium (Rh) based
a The reaction was conducted using alkene 1a (0.2 mmol) and Cat. (5 mol%)
complexes were found to be capable of catalyzing the similar isom-
erization through a concerted 1,3-H shift mechanism. Grotjahn de-
veloped a stereoselective alkene isomerization catalyzed by their bi-
functional Ru complex.[15a] Zhao, Liu and coworkers accomplished a
in solvent (2 mL) at room temperature for 12 h in air. b Determined by H
1
NMR analysis of the crude product using 1,3,5-trimethoxybenzene as inter-
nal standard. c The E/Z ratio was determined by the 1H NMR of crude prod-
uct. d The value in parentheses indicates an isolated yield of 2a.
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Running title
Chin. J. Chem.
Further investigation of other metal perchlorate hydrates such
different substituents on the phenyl ring were all tolerated, and af-
forded the corresponding trisubstituted alkenes 2a-2i in good to
high yields and E/Z ratio, regardless of the position and nature of
the substituents. 2-(But-1-en-2-yl)naphthalene could also deliver
the desired product 2j in 53% yield with 17:1 E/Z ratio. α-Benzyl
styrenes with electron-withdrawing or electron-donating group
proceeded smoothly as well to produce the conjugated trisubsti-
tuted alkenes 2k-2o with good results (up to 93% yield, 14:1 E/Z
selectivity). α-Propyl, α-isobutyl, and α-phenylethyl substituted sty-
renes were viable substrates, providing the desired alkenes 2p-2r
in good to excellent yields and E/Z selectivity. However, α-ethylsty-
renes bearing a strong electron-withdrawing CF3 or CN group led to
almost no reaction, possibly because the corresponding carbo-
cation intermediates are not easy to form. And no target was ob-
served in the case of alkenes bearing a 2-thienyl or 2-benzofuryl
functionality; only olefin dimerization and/or trimerization byprod-
ucts detected by GC-MS analysis. Five-, six-, and seven-membered
exocyclic 1,1-disubstituted olefins were found to be amenable sub-
strates, delivering the corresponding endocyclic trisubstituted al-
kenes 2s-2v with 63-88% yields.
as Al(ClO4)3⸱9H2O, In(ClO4)3⸱8H2O, and Cd(ClO4)2⸱6H2O revealed
that the isomerization indeed proceeded smoothly, and the desired
trisubstituted alkene 2a could be generated in moderate to high E/Z
stereoselectivity, albeit with low to moderate yields (entries 2-4).
Meanwhile, a series of metal triflates, including Ga(OTf)3, In(OTf)3,
Fe(OTf)3, Bi(OTf)3, Sc(OTf)3, Al(OTf)3, Cu(OTf)2, and Mg(OTf)2 were
also investigated (entries 5-12). Although no product 2a was ob-
served in the presence of Cu(OTf)2 and Mg(OTf)2 (entries 11-12), all
other tested catalysts furnished product 2a, and the use of 5 mol%
of Al(OTf)3 turned to be the best choice in terms of reactivity and
selectivity,[20] affording 82% yield of 2a with 24:1 E/Z selectivity (en-
try 10). Next, the solvent effects were examined using Al(OTf)3 as
the catalyst. It was found that CH2Cl2 was also a suitable solvent,
and gave rise to 2a with 25:1 E/Z selectivity but slightly lower yield
(81% NMR yield) (entries 13 vs 10). And the use of ethyl acetate
(EtOAc) and toluene could not afford the product at all (entries 14-
15). For more details of optimization of conditions, see section 2 of
the supporting information (SI).
With the optimized condition in hand, the scope of alkenes was
then explored (Table 2). A wide range of α-ethyl styrenes bearing
Table 2 Scope of alkene isomerizationa
mol%)
R
R
Al(OTf)3 (5
rt, 12 h
ClCH CH Cl
,
2
2
mmol)
or
3
1
2
(0.5
Cl
F
Br
2c
Cl
c
b
d
=
=
=
=
2b
2d
2e
, 78%,
=
E Z 22/1
/
E Z 21/1
/
E/Z 24/1
E/Z 25/1
2a
, 83%,
,
70%,
, 84%,
, 83%,
E
25/1
/Z
OMe
F
Me
MeO
e
c
e
d
=
=
=
=
73%,
/
=
2f
2g
2h
2i
E Z 100/1
E Z 25
E Z 26/1
E Z 11/1
E Z 17/1
/
85%,
84%,
/
/1
/
53%,
80%,
2v
/
, 79%,
,
, 81%,
,
2j,
Ph
Ph
Ph
Ph
Ph
F
Br
MeO
Cl
2m
d
d
d
d
d
=
=
=
E Z 14/1
=
=
2k
, 83%,
2l
2n
2o
,
E Z 14/1
E Z 14/1
E Z 14/1
E Z 6.4/1
/
/
91%,
/
93%,
/
/
,
,
,
R1
1
:
:
=
=
=
2p
R
Et,
iPr,
Bn,
E
5.5/1
23/1
74%, /Z
1
=
2q
R
E
81%, /Z
Ph
O
1
-
:
=
=
2r
R
E Z 20/1
94%,
/
63%d
88%
,
2p 2r
2s
2t
2u
74%
70%
,
,
,
Me
CO2
OMe
CN
I
Cl
Ph
3c
Ph
3d
Ph
3e
Ph
3a
Ph
d
d
d
d
d
=
E Z
/
7.9/1
=
=
=
=
,
83%,
3b
E Z
/
E Z 4.4/1
E Z
/
E Z 17/1
10/1
/
4.8/1
/
,
74%,
, 87%,
,
57%,
,
78%,
OMe
F
Ph
Me
Cl
89%f
87%f
E Z
/
63%e
3j
,
,
d
3f 74%f
3g
3h
3i
=
1/1.2
,
,
, 87%,
a The reaction was conducted using alkenes (0.5 mmol), Al(OTf)3 (5 mol%) and ClCH2CH2Cl (5 mL), in air at room temperature for 12 h. The E/Z ratio was
determined by the 1H NMR analysis of crude product. b Using 10 mol% Al(OTf)3. c Using 15 mol% Al(OTf)3. d Using 15 mol% Al(OTf)3, at 50 oC. e Using 3 mol%
Al(OTf)3. f At 50 oC.
Chin. J. Chem. 2021, 39, XXX－XXX
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Hu et al.
Report
Moreover, functionalized trisubstituted alkenes 3a-3e featuring
thereby ensuring a higher yield and selectivity.
halogen atom, ester, ether, or cyano group at the alkyl chain were
effectively achieved in good to high yields with moderate to excel-
lent E/Z ratio. A salient feature is that halogen atoms on both aro-
matic ring and aliphatic chain were tolerable under the current cat-
alytic system, allowing further transformation. Remarkably,
tetrasubstituted alkenes 3f-3i could be formed in up to 89% yields,
by employing bulky 1,1-disubstituted alkenes that were a kind of
problematic substrates in previous conditions.[13] 2-Fluoro-1-meth-
ylene-2,3-dihydro-1H-indene could be isomerized into tetrasubsti-
tuted monofluoroalkene 3j, which is not easy to synthesize by other
methods,[21] with a yield of 63%.
Second, a deuterium labeling experiment using a deuterated al-
kene 1a-D (95% D) was carried out under standard conditions in a
glove box, giving the deuterated 2a-D with 17% D on the methyl
group and 95% D on the vinyl group (Scheme 2c). The low deuter-
ium abundance at the methyl group illustrated that the step for the
protonation of terminal alkenes 1 was likely reversible. Meanwhile,
the addition of D2O led to the incorporation of 8% D on the vinyl
group of 2a-D suggested that the last step for the removal of β-pro-
ton might be also reversible, and Al(OTf)3, as a hidden Brønsted acid,
would be partially hydrolyzed to HOTf as the real catalytic species.
Third, an intramolecular trapping experiment using an alkenol 4 was
To demonstrate the synthetic utility of this methodology further, carried out under the standard conditions, and found that 52% yield
a gram-scale isomerization of 1a (15 mmol) was conducted. Under
the catalysis of 5 mol% Al(OTf)3 at room temperature, 1.64 g of 2a
was obtained in 83% yield with a slightly lower E/Z ratio (Scheme
2a). Besides, the alkenyl functionality in the products was capable
of undergoing a variety of diversifying reactions.[13b]
of tetrahydrofuran 5 was formed as the product via acid catalyzed
alkene hydroalkoxylation pathway, which further supported that
the reaction proceeds via a carbocation intermediate (Scheme
2d).[24] Additionally, a mixed isomer of product 2a (Z/E = 3.6:1) was
subjected to the standard conditions to explore the origin of stere-
oselectivity, and the E/Z ratio of 2a just increased slightly to 1:2.2
after 12 h (Scheme 2e), which was far less than 24:1 E/Z selectivity
produced from the isomerization of 1a. These reaction outcomes
suggested the stereoselectivity might mainly originate from the po-
sitional isomerization of terminal alkenes 1 to internal alkenes 2,[25]
not from the geometrical isomerization of trisubstituted alkenes
2.[13c] Based on the above mechanistic studies, together with our
previous work,[18] a plausible reaction pathway involved a carbo-
cation intermediate was proposed in Scheme 2f. The active catalytic
species HOTf was gradually generated in the reaction system, which
would react with the alkenes 1 to form a key carbocation interme-
diate I. After undergoing a deprotonation, the desired tri- or
tetrasubstituted alkenes would be produced, accompanied by the
regeneration of HOTf.
To gain insights into the isomerization mechanism, several con-
trol experiments were performed. First, the possibility of Al(OTf)3
function as a hidden Brønsted acid in the reaction was investi-
gated,[22] and found that the addition of 10 or 15 mol% noncoordi-
nating bulky base 2,6-di-tert-butylpyridine (DTBP) terminated the
reaction completely (Scheme 2b). Meanwhile, the use of 0.5 mol%
HOTf was also able to catalyze the isomerization, although no de-
sired product was detected in the presence of 5 mol% HOTf (be-
cause severe olefin dimerization occurred by GC-MS analysis in this
case).[23] These results supported the idea that Al(OTf)3 functioned
as a hidden Brønsted acid catalyst, and the in situ generated trace
amount of HOTf was the real catalytic species. The gradually releas-
ing HOTf from Al(OTf)3 and trace amount of moisture in the reaction
system inhibited the dimerization or other undesired pathway,
Scheme 2 Gram-scale synthesis and mechanistic studies
Gram-scale
Intramolecular
(d)
experiment
trapping
OH
(a)
synthesis
O
mol%)
Al(OTf)3 (5
mol%)
Al(OTf)3 (5
rt, 12 h
ClCH CH Cl
,
2
2
2a
rt, 12 h
ClCH CH Cl
,
2
2
mmol)
4
1a
(15
5
52%
,
=
/
E Z 22/1
1.64 g
, 83%,
rt, 12 h)
study
Steroselectivity
origin
Control
ClCH CH Cl,
(b)
(c)
experiments (in
Conditions
(e)
2
2
=
E/Z 24/1
mol%), 82%,
1) Al(OTf)3 (5
2) Al(OTf)3 (5
mol%)
Al(OTf)3 (5
or
no reaction
mol%), DTBP
15 mol%)
,
(10
1a
2a
HOTf
HOTf
alkene dimerization
rt, 12 h
mol%),
ClCH CH Cl
,
3)
4)
(5
(0.5
2
2
=
E/Z 5.6/1
yield,
mol%),
25% NMR
=
=
2a
2a
, 75%,
Z/E 3.6/1)
Z/E 2.2/1
(
Deuterium labeling
experiment
Al(OTf)3 (10
A
(f) plausible pathway
CH3
D 17% D
),
(
mol%)
H O
D
D
(trace)
2
D
rt, 12 h
ClCH CH Cl
,
(95%)
2
2
+
Al(OTf)3
HOTf
acid
Hidden
Brønsted
x
Al(OTf) (OH)y
in
box
,
glove
=
65%,
/
E Z
1a-D
D)
2a-D
10/1
(95%
H
D O
mol%)
(30
2
CH3
D
5% D
(
),
H
H
mol%)
Al(OTf)3 (5
Ar
Ar
Ar
rt, 12 h
H(D
D
ClCH CH Cl
,
8%
),
2
2
H
I
1a
1
or
2
3
in
box
glove
,
Carbocation intermediate
=
/
E Z 21/1
2a-D
84%,
eration, and easy to the scale-up application, make our method po-
tentially very useful. Mechanistic studies reveal that a carbocation
intermediate initiated reaction pathway should be involved in this
reaction.
Conclusions
In summary, we have disclosed the first transition-metal-free
highly stereoselective positional isomerization of α-alkyl styrenes
through a carbocation mechanism, allowing facile synthesis of var-
ious acyclic tri- and tetra-substituted alkenes with high stereoselec-
tivity by using Al(OTf)3 as a hidden Brønsted acid catalyst. The sali-
ent features, including mild conditions, inexpensive & commercially
available acid catalyst, good functional group tolerance, simple op-
Experimental
General procedure for the alkene isomerization is as follows: To
a 25.0 mL tube were added Al(OTf)3 (11.9 mg, 0.025 mmol, 5.0
mol%, unless otherwise noted) and anhydrous ClCH2CH2Cl (5.0 mL),
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Running title
Chin. J. Chem.
followed by the sequential addition of alkenes (0.5 mmol). After be-
ing stirred at room temperature under air for 12 h, the reaction
mixture was filtrated through a short pad of silica gel, and washed
with dichloromethane. The combined organic phases were concen-
trated under vacuo to give the crude products. To determine the
E/Z selectivity of products, the crude residue was first dissolved in
CDCl3, and took some samples for 1H NMR analysis. Then the sam-
ple for analysis and the rest of crude residue were recombined and
purified by silica gel column chromatography using the indicated
eluent to afford the corresponding products 2 or 3.
Y. Y.; Aϊssa, C. Isomerization of Olefins Triggered by Rhodium-Cata-
lyzed C—H Bond Activation: Control of Endocyclic β-Hydrogen Elimina-
tion. Angew. Chem. Int. Ed. 2015, 54, 6870－6873.
(a) Fan, J.; Wan, C. Wang, Q.; Gao, L.; Zheng, X.; Wang, Z. Palladium
catalyzed isomerization of alkenes: a pronounced influence of an o-
phenol hydroxyl group. Org. Biomol. Chem. 2009, 7, 3168－3172; (b)
Gauthier, D.; Lindhardt, A. T.; Olsen, E. P. K.; Overgaard, J.; Skrydstrup,
T. In Situ Generated Bulky Palladium Hydride Complexes as Catalysts
for the Efficient Isomerization of Olefins. Selective Transformation of
Terminal Alkenes to 2-Alkenes. J. Am. Chem. Soc. 2010, 132, 7998－
8009; (c) Mamone, P.; Grünberg, M. F.; Fromm, A.; Khan, B. A.; Gooßen,
L. J. [Pd(μ-Br)(PtBu3)]2 as a Highly Active Isomerization Catalyst: Syn-
thesis of Enol Esters from Allylic Esters. Org. Lett. 2012, 14, 3716－
3719; (d) Kocen, A. L.; Brookhart, M.; Daugulis, O. Palladium-catalysed
alkene chain-running Isomerization. Chem. Commun. 2017, 53, 10010
－10013; (e) Murai, M.; Nishimura, K.; Takai, K. Palladium-catalyzed
double-bond migration of unsaturated hydrocarbons accelerated by
tantalum chloride. Chem. Commun. 2019, 55, 2769－2772; (f) Ren, W.;
Sun, F.; Chu, J.; Shi, Y. A Pd-Catalyzed Site-Controlled Isomerization of
Terminal Olefins. Org. Lett. 2020, 22, 1868－1873.
(a) Chianese, A. R.; Shaner, S. E.; Tendler, J. A.; Pudalov, D. M.; Shopov,
D. Y.; Kim, D.; Rogers, S. L.; Mo, A. Iridium Complexes of Bulky CCC-
Pincer N-Heterocyclic Carbene Ligands: Steric Control of Coordination
Number and Catalytic Alkene Isomerization. Organometallics 2012, 31,
7359－7361; (b) Li, H.-H.; Mazet, C. Steric Parameters in the Ir-Cata-
lyzed Regio- and Diastereoselective Isomerization of Primary Allylic Al-
cohols. Org. Lett. 2013, 15, 6170－6173; (c) Wang, Y.-L.; Qin, C.; Jia, X.-
Q.; Leng, X.-B.; Huang, Z. An Agostic Iridium Pincer Complex as a Highly
Efficient and Selective Catalyst for Monoisomerization of 1-Alkenes to
trans-2-Alkenes. Angew. Chem. Int. Ed. 2017, 56, 1614－1618.
(a) Clark, H. C.; Kurosawa, H. Chemistry of Metal Hydrides. XIII. Inser-
tion and Isomerization Reactions of Allylic Compounds with Cationic
Platinum(II)-Hydrido Complexes. Inorg. Chem. 1973, 12, 357－362; (b)
Scarso, A.; Colladon, M.; Sgarbossa, P.; Santo, C.; Michelin, R. A.;
Strukul, G. Highly Active and Selective Platinum(II)-Catalyzed Isomeri-
zation of Allylbenzenes: Efficient Access to (E)-Anethole and Other Fra-
grances via Unusual Agostic Intermediates. Organometallics 2010, 29,
1487－1497.
(a) Kobayashi, T.; Yorimitsu, H.; Oshima, K. Cobalt-Catalyzed Isomeri-
zation of 1-Alkenes to (E)-2-Alkenes with Dimethylphenylsilylmethyl-
magnesium Chloride and Its Application to the Stereoselective Synthe-
sis of (E)-Alkenylsilanes. Chem. Asian J. 2009, 4, 1078－1083; (b) Chen,
C.; Dugan, T. R.; Brennessel, W. W.; Weix, D. J.; Holland, P. L. Z-Selec-
tive Alkene Isomerization by High-Spin Cobalt(II) Complexes. J. Am.
Chem. Soc. 2014, 136, 945－955; (c) Crossley, S. W. M.; Barabé, F.;
Shenvi, R. A. Simple, Chemoselective, Catalytic Olefin Isomerization. J.
Am. Chem. Soc. 2014, 136, 16788－16791; (d) Schmidt, A.; Nödling, A.
R.; Hilt, G. An Alternative Mechanism for the Cobalt-Catalyzed Isomer-
ization of Terminal Alkenes to (Z)-2-Alkenes. Angew. Chem. Int. Ed.
2015, 54, 801－804; (e) Liu, X.; Zhang, W.; Wang, Y.; Zhang, Z.-X.; Jiao,
L.; Liu, Q. Cobalt-Catalyzed Regioselective Olefin Isomerization Under
Kinetic Control. J. Am. Chem. Soc. 2018, 140, 6873－6882; (f) Meng,
Q.-Y.; Schirmer, T. E.; Katou, K.; König, B. Controllable Isomerization of
Alkenes by Dual Visible-Light-Cobalt Catalysis. Angew. Chem. Int. Ed.
2019, 58, 5723－5728.
(a) Bricout, H.; Mortreux, A.; Monflier, E. Isomerization of olefins in a
two-phase system by homogeneous water-soluble nickel complexes. J.
Organomet. Chem. 1998, 553, 469－471; (b) Weber, F.; Schmidt, A.;
Röse, P.; Fischer, M.; Burghaus, O.; Hilt, G. Double-Bond Isomerization:
Highly Reactive Nickel Catalyst Applied in the Synthesis of the Phero-
mone (9Z,12Z)-Tetradeca-9,12-dienyl Acetate. Org. Lett. 2015, 17,
2952－2955.
Supporting Information
The supporting information for this article is available on the
WWW under https://doi.org/10.1002/cjoc.2021xxxxx.
Acknowledgement
We gratefully acknowledge the financial support from the Na-
tional Natural Science Foundation of China (Grant Nos. 21901074),
and “Zijiang Scholar Program” of East China Normal University.
References
For reviews, see: (a) Uma, R.; Crévisy, C.; Grée, R. Transposition of Al-
lylic Alcohols into Carbonyl Compounds Mediated by Transition Metal
Complexes. Chem. Rev. 2003, 103, 27 － 52; (b) Donohoe, T. J.;
O’Riordan, T. J. C.; Rosa, C. P. Ruthenium-Catalyzed Isomerization of
Terminal Olefins: Applications to Synthesis. Angew. Chem. Int. Ed.
2009, 48, 1014－1017; (c) Hilt, G. Double Bond Isomerisation and Mi-
gration-New Playgrounds for Transition Metal-Catalysis. Chem-
CatChem 2014, 6, 2484－2485; (d) Larionov, E.; Li, H.; Mazet, C. Well-
Defined Transition Metal Hydrides in Catalytic Isomerizations. Chem.
Commun. 2014, 50, 9816－9826; (e) Hassam, M.; Taher, A.; Arnott, G.
E.; Green, I. R.; van Otterlo, W. A. L. Isomerization of Allylbenzenes.
Chem. Rev. 2015, 115, 5462－5569; (f) Vasseur, A.; Bruffaerts, J.; Ma-
rek, I. Remote Functionalization through Alkene Isomerization. Nat.
Chem. 2016, 8, 209－219; (g) Ai, W.; Zhong, R.; Liu, X.; Liu, Q. Hydride
Transfer Reactions Catalyzed by Cobalt Complexes. Chem. Rev. 2019,
119, 2876－2953; (h) Molloy, J. J.; Morack, T.; Gilmour, R. Positional
and Geometrical Isomerisation of Alkenes: The Pinnacle of Atom Econ-
omy. Angew. Chem. Int. Ed. 2019, 58, 13654－13664; (i) Massad, I.;
Marek I. Alkene Isomerization through Allylmetals as A Strategic Tool
in Stereoselective Synthesis. ACS Catal. 2020, 10, 5793－5804.
(a) Hanessian, S.; Giroux, S.; Larsson, A. Efficient Allyl to Propenyl Isom-
erization in Functionally Diverse Compounds with a Thermally Modi-
fied Grubbs Second-Generation Catalyst. Org. Lett. 2006, 8, 5481－
5484; (b) Grotjahn, D. B.; Larsen, C. R.; Gustafson, J. L.; Nair, R.; Sharma,
A. Extensive Isomerization of Alkenes Using a Bifunctional Catalyst: An
Alkene Zipper. J. Am. Chem. Soc. 2007, 129, 9592 － 9593; (c)
Donohoe,T. J.; O,Riordan, T. J. C.; Rosa, C. P. Ruthenium-Catalyzed
Isomerization of Terminal Olefins: Applications to Synthesis. Angew.
Chem. Int. Ed. 2009, 48, 1014－1017; (d) Clark, J. R.; Griffiths, J. R.;
Diver, S. T. Ruthenium Hydride-Promoted Dienyl Isomerization: Access
to Highly Substituted 1,3-Dienes. J. Am. Chem. Soc. 2013, 135, 3327－
3330; (e) Larsen, C. R.; Erdogan, G.; Grotjahn, D. B. General Catalyst
Control of the Monoisomerization of 1-Alkenes to trans-2-Alkenes. J.
Am. Chem. Soc. 2014, 136, 1226－1229; (f) Trost, B. M.; Cregg, J. J.;
Quach, N. Isomerization of N-Allyl Amides to Form Geometrically De-
fined Di-, Tri-, and Tetrasubstituted Enamides. J. Am. Chem. Soc. 2017,
139, 5133－5139.
(a) Schroeder, M. A.; Wrighton, M. S. Pentacarbonyliron(0) Photocata-
lyzed Hydrogenation and Isomerization of Olefins. J. Am. Chem. Soc.
1976, 98, 551－558; (b) Sawyer, K. R.; Glascoe, E. A.; Cahoon, J. F.;
Schlegel, J. P.; Harris, C. B. Mechanism for Iron-Catalyzed Alkene Isom-
erization in Solution. Organometallics 2008, 27, 4370 － 4379; (c)
(a) Boons, G.-J.; Burton, A.; Isles, S. A new procedure for the isomeri-
sation of substituted and unsubstituted allyl ethers of carbohydrates.
Chem. Commun. 1996, 141－142; (b) Zhuo, L.-G.; Yao, Z.-K.; Yu, Z.-X.
Synthesis of Z-Alkenes from Rh(I)-Catalyzed Olefin Isomerization of
β,γ-Unsaturated Ketones. Org. Lett. 2013, 15, 4634－4637; (c) Yip, S.
Chin. J. Chem. 2021, 39, XXX－XXX
© 2021 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
www.cjc.wiley-vch.de

Hu et al.
Report
Mayer, M.; Welther, A.; Wangelin, A. J. v. Iron-Catalyzed Isomeriza-
Isomerization of Normal Butenes. J. Am. Chem. Soc. 1934, 56, 2696－
2698; (b) Linstead, R. P.; Michaelis, K. O. A.; Thomas, S. L. S. Catalytic
Diqwoprtionation and Dehydrogenation of some Terpenes and Ter-
pene Ketones. J. Chem. Soc. 1940, 1139－1147; (c) Hiromi, K.; Shig-
etaka, S.; Gaku, Y.; Tsutomu, M.; Nobuo, N.; Michinori, O.; Reactivities
of Stable Rotamers. VIII. Difference in Reactivities of 1,2,3,4-Tetra-
chloro-9-(2-halo-1,1-dimethylethyl)triptycene Rotamers in Lewis Acid-
catalyzed Reactions. Bull. Chem. Soc. Jpn. 1982, 55, 1514-1521; (d)
Sugimoto, A.; Yamano, J.; Yasueda, M.; Yoneda, S. Preparation and
Chemical Behaviour of exo-Methylene Compounds: lsoelectronic Com-
pounds of 5-Methylenecyclohexa-I ,3-diene. J. Chem. Soc., Perkin
Trans. 1, 1988, 2579－2584; (e) Blatter, K.; Schlüter, A.-D. A Conven-
ient Synthesis of Some (1-Alkylethenyl)arenes and Bis(1-al-
kylethenyl)arenes. Synthesis, 1989, 356－359; (f) Pflästerer, D.; Schu-
macher, S.; Rudolph, M.; Hashmi, A. S. K. Mechanistic Insights into the
Post-Cyclization Isomerization in Gold-Catalyzed 7-exo-dig-Hydroary-
lations. Chem. -Eur. J. 2015, 21, 11585－11589; (g) Boureghda, C.;
Macé, A.; Berrée, F.; Roisnel, T.; Debache, A.; Carboni, B. Ene reactions
of 2-borylated α-methylstyrenes: a practical route to 4-methylene-
chromanes andderivatives. Org. Biomol. Chem. 2019, 17, 5789－5800.
Hu, X.-S.; He, J.-X.; Dong, S.-Z. Zhao, Q.-H.; Yu, J.-S.; Zhou, J. Regiose-
lective Markovnikov hydrodifluoroalkylation of alkenes using difluo-
roenoxysilanes. Nat. Commun. 2020, 11, 5000.
tions of Olefins. ChemCatChem 2011, 3, 1567－1571; (d) Jennerjahn,R.;
Jackstell, R.; Piras, I.; Franke, R.; Jiao, H.; Bauer, M.; Beller, M. Benign
Catalysis with Iron: Unique Selectivity in Catalytic Isomerization Reac-
tions of Olefins. ChemSusChem 2012, 5, 734－739; (e) Xia, T.; Wei, Z.;
Spiegelberg, B.; Jiao, H.; Hinze, S.; de Vries, J. G. Isomerization of Allylic
Alcohols to Ketones Catalyzed by Well-Defined Iron PNP Pincer Cata-
lysts. Chem. -Eur. J. 2018, 24, 4043－4049.
(a) Castro-Rodrigo, R.; Chakraborty, S.; Munjanja, L.; Brennessel, W. W.
Jones, W. D. Synthesis, Characterization, and Reactivities of Molyb-
denum and Tungsten PONOP Pincer Complexes. Organometallics 2016,
35, 3124－3131; (b) Becica, J.; Glaze, O. D.; Wozniak, D. I.; Dobereiner,
G. E. Selective Isomerization of Terminal Alkenes to (Z)‑2-Alkenes Cat-
alyzed by an Air-Stable Molybdenum(0) Complex. Organometallics
2018, 37, 482－490.
(a) Bhatt, U.; Christmann, M.; Quitschalle, M.; Claus, E.; Kalesse, M.
The First Total Synthesis of (+)-Ratjadone. J. Org. Chem. 2001, 66, 1885
－1893; (b) Williams, D. R.; Ihle, D. C.; Plummer, S. V. Total Synthesis
of (-)-Ratjadone. Org. Lett. 2001, 3, 1383－1386; (c) Itami, K.; Yoshida,
J. Multisubstituted Olefins: Platform Synthesis and Applications to Ma-
terials Science and Pharmaceutical Chemistry. Bull. Chem. Soc. Jpn.
2006, 79, 811－824.
(a) Larock, R. C. Comprehensive Organic Transformations: A Guide to
Functional Group Preparations. ed. 2, VCH, 1999; (b) Ma, S.-M.; Zhang,
J.-L. In Comprehensive Organic Synthesis. Knochel, P.; Molander, G. A.
Eds. Vol. 4, Elsevier, Amsterdam, 2014; (c) Deiters, A.; Martin, S. F. Syn-
thesis of Oxygen- and Nitrogen-Containing Heterocycles by Ring-Clos-
ing Metathesis. Chem. Rev. 2004, 104, 2199－2238; (d) McDonald, R.
I.; Liu, G.; Stahl, S. S. Palladium(II)-Catalyzed Alkene Functionalization
via Nucleopalladation: Stereo-chemical Pathways and Enantioselec-
tive Catalytic Applications. Chem. Rev. 2011, 111, 2981－3019; (e) Zhu,
Y.; Wang, Q.; Cornwall, R. G.; Shi, Y. Organo-catalytic Asymmetric Epox-
idation and Aziridination of Olefins and Their Synthetic Applications.
Chem. Rev. 2014, 114, 8199－8256.
(a) Lim, H. J.; Smith, C. R.; RajanBabu, T. V. Facile Pd(II)- and Ni(II)-Cat-
alyzed Isomerization of Terminal Alkenes into 2-Alkenes. J. Org. Chem.
2009, 74, 4565－4572; (b) Zhao, J.; Cheng, B.; Chen, C.; Lu, Z. Cobalt-
Catalyzed Migrational Isomerization of Styrenes. Org. Lett. 2020, 22,
837－841; (c) Zhang, S.; Bedi, D.; Cheng, L.; Unruh, D. K.; Li, G.;
Findlater, M. Cobalt(II)-Catalyzed Stereoselective Olefin Isomerization:
Facile Access to Acyclic Trisubstituted Alkenes. J. Am. Chem. Soc. 2020,
142, 8910－8917; (d) Liu, H.; Cai, C.; Ding, Y.; Chen, J.; Liu, B.; Xia, Y.
Cobalt-Catalyzed E-Selective Isomerization of Alkenes with a Phos-
phine-Amido-Oxazoline Ligand. ACS Omega 2020, 5, 11655－11670; (e)
Yu, X.; Zhao, H.; Li, P.; Koh, M. J. Iron-Catalyzed Tunable and Site-Se-
lective Olefin Transposition. J. Am. Chem. Soc. 2020, 142, 18223－
18230; (f) Xu, S.; Liu, G.; Huang, Z. Iron Catalyzed Isomerization of α-
Alkyl Styrenes to Access Trisubstituted Alkenes. Chin. J. Chem. 2021,
39, 585－589.
(a) Wabnitz, T. C.; Yu, J.-Q.; Spencer, J. B. Evidence That Protons Can
Be the Active Catalysts in Lewis Acid Mediated Hetero-Michael Addi-
tion Reactions. Chem. - Eur. J. 2004, 10, 484－493; (b) Rosenfeld, D. C.;
Shekhar, S.; Takemiya, A.; Utsunomiya, M.; Hartwig J. F. Hydroamina-
tion and Hydroalkoxylation Catalyzed by Triflic Acid. Parallels to Reac-
tions Initiated with Metal Triflates. Org. Lett. 2006, 8, 4179－4182; (c)
Šolić, I.; Lin, H. Bates, R. W. Testing the veracity of claims of Lewis acid
catalysis. Tetrahedron Lett. 2018, 59, 4434－4436; (d) Sletten, E. T.; Tu,
Y.-J.; Schlegel, H. B.; Nguyen, H. M. Are Brønsted Acids the True Pro-
moter of Metal-Triflate-Catalyzed Glycosylations?
A Mechanistic
Probe into 1,2-cis-Aminoglycoside Formation by Nickel Triflate. ACS
Catal. 2019, 9, 2110－2123.
The difference in the reactivity and selectivity is possibly attributed to
the different effective proton concentrations, because different metal
triflates and perchlorate hydrates hydrolyze in a different rate in the
reaction condition. In addition, the hydrolysis of the metal salts would
produce some metal hydroxides or other metal ion species that might
influence the reaction. However, the exact reason for the origin of ste-
reoselectivity is unclear currently.
(a) Bergeron, M.; Johnson, T.; Paquin, J.-F. The Use of Fluoride as a
Leaving Group: SN2’ Displacement of a C—F Bond on 3,3-Difluoropro-
penes with Organolithium Reagents to Give Direct Access to Mono-
fluoroalkenes. Angew. Chem. Int. Ed. 2011, 50, 11112－11116; For a
review, see: (b) Liao, F.; Yu, J.; Zhou, J. Recent Advances in the Highly
Stereoselective Synthesis of Tri- or Tetrasubstituted Monofluoroal-
kenes. Chin. J. Org. Chem. 2017, 37, 2175－2186.
Li, G.; Kuo, J. L.; Han, A.; Abuyuan, J. M.; Young, L. C.; Norton, J. R.;
Palmer, J. H. Radical Isomerization and Cycloisomerization Initiated by
H• Transfer. J. Am. Chem. Soc. 2016, 138, 7698－7704.
Metal triflate has been found to be a hidden Brønsted acid catalyst in
the alkene hydrofunctionalization: (a) Weïwer, M.; Coulombel, L.;
Dunãch, E. Regioselective indium(III) trifluoromethanesulfonate-cata-
lyzed hydrothiolation of non-activated olefins. Chem. Commun. 2006,
332－334; (b) Dang, T. T.; Boeck, F.; Hintermann, L. Hidden Brønsted
Acid Catalysis: Pathways of Accidental or Deliberate Generation of Tri-
flic Acid from Metal Triflates. J. Org. Chem. 2011, 76, 9353－9361; (c)
Chen, J.; Goforth, S. K.; McKeown, B. A.; Gunnoe, T. B. Brønsted acid-
catalysed intramolecular hydroamination of unactivated alkenes:
metal triflates as an in situ source of triflic acid. Dalton Trans. 2017, 46,
2884－2891. Also see ref. 19.
Other Brønsted acids with different pKa value were also investigated,
and found that the use of 5 mol% of H2SO4 or HClO4 (70%, aq.) in the
model reaction only provided the product 2a in 10% NMR yield with
7.1/1 E/Z ratio, and 13% NMR yield with 7.1/1 E/Z ratio, respectively.
However, only alkene dimerization detected by GC-MS analysis in the
case of Tf2NH (5 mol%), and no reaction occurred in the presence of
CF3CO2H or conc. HCl (5 mol%). These data further reveals that the
(a) Larsen, C. R.; Grotjahn, D. B. Stereoselective Alkene Isomerization
over One Position. J. Am. Chem. Soc. 2012, 134, 10357－10360; (b)
Huang, R.-Z.; Lau, K. K.; Li, Z.; Liu, T.-L.; Zhao, Y. Rhodium-Catalyzed
Enantioconvergent Isomerization of Homoallylic and Bishomoallylic
Secondary Alcohols. J. Am. Chem. Soc. 2018, 140, 14647－14654; (c)
Kapat, A.; Sperger, T.; Guven, S.; Schoenebeck, F. E-Olefins through In-
tramolecular Radical Relocation. Science 2019, 363, 391－396.
(a) Olah, G. A.; Prakash, G. K. S. Carbo-cation Chemistry, Wiley:ꢀHobo-
ken, NJ. 2004; (b) Olah, G. A.; Prakash, G. K. S.; Sommer, J.; Molnar, A.
Superacid Chemistry, ed. 2, Wiley: Hoboken, NJ, 2009; (c) Olah, G. A.
100 Years of Car-bocations and Their Significance in Chemistry. J. Org.
Chem. 2011, 66, 5943－5957; (d) Naredla, R. R.; Klumpp, D. A. Con-
temporary Carbocation Chemistry: Applications in Organic Synthesis.
Chem. Rev. 2013, 113, 6905－6948.
The related early reports, see: (a) Ipatieff, V. N.; Pines, H.; Schaad, R. E.
www.cjc.wiley-vch.de
© 2021 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
Chin. J. Chem. 2021, 39, XXX－XXX

Running title
Chin. J. Chem.
uniqueness and superiority of Al(OTf)3 as a hidden Brønsted acid cata-
the reaction time in the model reaction, and found that the E/Z ratio
of 2a was same (24:1 E/Z) after 2 h, 4 h, 6 h, and 10 h, which suggested
that the selectivity was likely not based on thermodynamic control.
lyst in this reaction. This is possibly due to the gradually release of
Brønsted acid catalyst HOTf via hydrolysis of Al(OTf)3 played a crucial
role, thus maintaining a low concentration of HOTf to suppress side
reactions, while the direct use of Brønsted acids would give a false im-
pression of catalytic inefficiency of the Brønsted acid owing to com-
petitive side reactions, such as dimerization or polymerization of the
substrate or product at high concentrations of acid.
Tsuji, N.; Kennemur, J. L.; Buyck, T.; Lee, S.; Prévost, S.; Kaib, P. S. J.;
Bykov, D.; Farès, C.; List, B. Activation of olefins via asymmetric
Brønsted acid catalysis. Science 2018, 359, 1501－1505.
(The following will be filled in by the editorial staff)
Manuscript received: XXXX, 2021
Manuscript revised: XXXX, 2021
Manuscript accepted: XXXX, 2021
Accepted manuscript online: XXXX, 2021
Version of record online: XXXX, 2021
We also examined whether the E/Z selectivity of product change with
Chin. J. Chem. 2021, 39, XXX－XXX
© 2021 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
www.cjc.wiley-vch.de

Entry for the Table of Contents
Highly Stereoselective Positional Isomerization of Styrenes via Acid-Catalyzed Carbocation Mechanism
Xiao-Si Hu,a Jun-Xiong He,a Ying Zhang,a Jian Zhou,*,ab and Jin-Sheng Yu*,a
Chin. J. Chem. 2021, 39, XXX—XXX. DOI: 10.1002/cjoc.202100XXX
R
mol%)
R
Al(OTf)3 (3~15
rt, 12 h
ClCH CH Cl
,
2
2
=
to
E Z
/
F
aryl,
)
94%
100/1
up
yield,
(
alkyl,
♣
♣
stereoselectivity
Carbocation mechanism
High
The first transition-metal-free highly stereoselective positional isomerization of various α-alkyl styrenes through a carbocation mechanism is developed
by using Al(OTf)3 as a hidden Brønsted acid catalyst.
a Shanghai Engineering Research Center of Molecular Therapeutics c Department, Institution, Address 3
and New Drug Development, School of Chemistry and Molecular E-mail:
Engi-neering, East China Normal University, 3663N Zhongshan
Road, Shanghai 200062, P. R. China
E-mail: jzhou@chem.ecnu.edu.cn, jsyu@chem.ecnu.edu.cn
b State Key Laboratory of Organometallic Chemistry, Shanghai Insti-
tute of Organic Chemistry, Shanghai 200032, China.
Chin. J. Chem. 2018, template© 2018 SIOC, CAS, Shanghai,
&
WILEY-VCH Verlag GmbH
&
Co. KGaA,
Weinheim