A sustainable synthesis of 2-aryl-3-carboxylate indolines from N-aryl enamines under visible light irradiation

Article abstract of DOI:10.1039/c7cc04358a

With visible light irradiation of a catalytic amount of Ir(ppy)₃ at room temperature, a number of N-aryl enamines were transformed into their corresponding indoline products in good to excellent yields without requiring any extra additives. This is the first example of the synthesis of indolines via the intramolecular cyclization of enamines under visible light irradiation.

Full text of DOI:10.1039/c7cc04358a

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: L. Wu, C. Wu, W.
Cao, T. Lei, Z. Li, Q. Meng, X. Yang , B. Chen, V. Ramamurthy and C. Tung, Chem. Commun., 2017, DOI:
10.1039/C7CC04358A.
This is an Accepted Manuscript, which has been through the
Volume 52 Number
1 4 January 2016 Pages 1–216
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Accepted Manuscripts are published online shortly after
Chemical Communications
www.rsc.org/chemcomm
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
first methanofullerene derivatives of Sc N@D5h-C80
=
3
rsc.li/chemcomm

Please do not adjust margins
Page 1 of 5
ChemComm
View Article Online
DOI: 10.1039/C7CC04358A
Journal Name
COMMUNICATION
A sustainable synthesis of 2-aryl-3-carboxylate indolines from N-
aryl enamines under visible light irradiation
Received 00th January 20xx,
Accepted 00th January 20xx
Cheng-Juan Wu,a Wen-Xiao Cao,a Tao Lei,a Zhi-Hua Li,a Qing-Yuan Meng,a Xiu-Long Yang,a Bin
Chen,a Vaidhyanathan Ramamurthy,b Chen-Ho Tunga and Li-Zhu Wu*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
With visible light irradiation of catalytic amount of Ir(ppy)3 at numerous organic synthetic transformations.8 In this context,
room temperature, number of N-aryl enamines were we report below a new route to indolines under visible light
a
transformed to their corresponding indoline products in good to irradiation. By utilizing catalytic amounts of Ir(ppy)3 as the
excellent yields without requiring any extra additives. This is the photosensitizer and visible light as the energy source, we have
first example to synthesize indolines via intramolecular cyclization achieved the synthesis of indolines via intramolecular
of enamines under visible light irradiation.
cyclization of enamines at room temperature (Scheme 1e). The
system contained only photosensitizer as the catalyst and
easily synthesizable enamine as the reactant making the
reaction condition very much affordable. Moreover, no other
additives were required to achieve the transformation. By
employing the above strategy, we have transformed a large
number of enamines to their corresponding indolines. To the
best of our knowledge, such a methodology has not been
achieved earlier.
Indolines and their derivatives are important scaffolds that are
found in numerous naturally occurring alkaloids and synthetic
drugs. Their importance has stimulated considerable interest
in developing strategies for their synthesis.1-7 Until now, direct
reduction of indoles is still one of the most important
approach toward this important class of compounds (Scheme
1a).1-2 However, reduction of the highly resonance-stabilized
aromatic nucleus was not an easy task. Usually,
superstoichiometric amounts of hydride reagents1 or high
hydrogen pressure and elevated reaction temperature2 were
required. Transition-metal mediated cyclization3 was another
important strategy to synthesize indolines, which included aryl
amination, olefinic amination and so on to construct C-C or C-N
bonds. For example, Buchwald and co-workers reported the
Pd-catalyzed aryl amination and amidation reactions, which
allow efficient access to a variety of indolines (Scheme 1b).3a In
addition, other methods such as anionic cyclization (Scheme
1c),4 and radical cyclization (Scheme 1d)5 were also found to
work. Despite the progress achieved in the synthesis of
indolines, most of the existing methods require harsh reaction
conditions, and extra additives such as ligand, acid or base.
Development of mild and convenient procedures for the
synthesis of indolines is highly desirable.
rev ous wor :
k
P
i
a
e
uc on o o es
n
ti l
f i d
R
t
d
(
)
rans er
or
ro ena on
r
es: e .
d id f
R 1
[ ]
f
d
h
g
d
ti
y
b
d
h
g
y
g
y
y
ro ena on
ro en as: e .
h
y
ti
b
h
y
R
f
2
g
[
]
R3
R3
-
ac
H / id
R2
R2
or
ac ca a s
id / l t
y
H2
/
t
N
N
R1
R1
rans on-me a me a e
c c
y
za on: e .
a
3
[ ]
b
T
iti
t
l
di
t
d
li ti
R
f
(
)
H
N
R
an
Pd / Li
d
g
ase o uene
b
t
l
100
,
,
℃
N
r
B
R
c
n on c c
c
za on: e .
a
A
i
i
li ti
R
f
4
[
b
,
y
(
)
]
Li
E
r
B
ro
ec e
El t hil
p
-
u
TMEDA
warm
t B Li
n-
C5H12 / Et2O
N
N
N
-
78
℃
R
R
R
a
ca
c c
y
za on: e .
a
5
d
R
di
l
li ti
R
f
(
)
[
]
Owing to its mild, green and selective properties, visible
light is recently being explored as the energy source in
N
R2
n
u
n
H
,
B
3S
AIBN
N
R1
C6H6 80
,
℃
r
B
R2
R1
s wor
Thi
:
k
e
s
e
ca a ze
c c
d
li ti
y
za on o enam nes:
Vi ibl li ht
t
l
y
f
i
g
(
)
a.Key Laboratory of Photochemical Conversion and Optoelectronic Materials,
Technical Institute of Physics and Chemistry & University of Chinese Academy of
Sciences, the Chinese Academy of Sciences, Beijing, 100190, P. R. China.
E-mail: lzwu@mail.ipc.ac.cn
CO2R
r
A
ν
r
I
r
t
h
2
%
ppy
(
)
3
r
A
N
N
H
H
CO2R
b.Department of Chemistry, University of Miami, Miami, FL 33124-0431, USA.
† Electronic Supplementary Information (ESI) available. CCDC 1542178. For ESI and
Scheme 1. Representative synthesis of indolines.
crystallographic
date
in
CIF
or
other
electronic
format
see
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 5
COMMUNICATION
Journal Name
Table 2. Scope of the reactiona
We initially established the feasibility of the proposed
methodology and optimized the conditions with N-aryl
enamine 1a as the starting material, and Ir(ppy)3 as the
photosensitizer. A degassed solution containing 0.2 mmol of
1a and 2 mol% of Ir(ppy)3 in 3 mL DMF was irradiated with
blue LEDs at room temperature. Following 12 h irradiation,
View Article Online
DOI: 10.1039/C7CC04358A
R2
R1
CO2
R1
r
I
%
ppy
(
r
A
2
)
3
r
A
N
H
nm
LED
t 12 h
s
450
N
H
R2
r. .
CO2
1
2
t
CO2Et
CO2E
t
CO2E
F
50% of indoline product 2a was obtained with
a
diastereoisomeric ratio of 2:1 (Table 1, entry 1). Among the
solvents screened, CH3CN was found to be the best which gave
indoline 2a in 76% yield and 4:1 diastereoselectivity (Table 1,
entries 2-4). We also investigated the optimum volume of
solvent, which suggested that 4.0 mL CH3CN was the best to
N
N
N
H
H
H
. : rc
5
7
)
b
:
. :
7 1
r
d
c:
2
. : r
4 1 1 d
a:
2
2b 57 42
% , 3
%
8 % 6 %
7
,
86% 0% 4 0 1 d
,
(
)
(
(
)
t
CO2E
t
CO2E
t
CO2E
N
N
H
N
H
yield indoline product in
a yield of 86%, with the
H
diastereoisomeric ratio of 4:1 (Table 1, entries 4-7). Variation
of the photosensitizer concentration revealed that 2 mol% of
Ir(ppy)3 gave the best yield (Table 1, entries 8-10). Further, of
the four common photosensitizers attempted in this reaction,
only Ir(ppy)3 gave the best result (Table S1, entries 1-3, ESI†).
Control experiments established that both visible light and
Ir(ppy)3 were required for the reaction (Table 1, entries 11-12),
and direct excitation of enamine 1a with UV light (λ > 300 nm)
did not yield 2a in the absence of Ir(ppy)3 (Table S1, entry 4,
ESI†). To summarize, the visible light catalyzed conversion of
enamines to indolines proceeded well under the optimized
condition which included irradiation (450 nm LED; 12 h) of 4.0
mL degassed CH3CN solution of 0.2 mmol 1a and 2 mol%
Ir(ppy)3. The structure of the major product 2a was confirmed
to be trans-indoline by converting 2a to 3a (Scheme S1, ESI†)
and determining its crystal structure (Fig. 1).9
e:
. :
r
:
. :
r
2
5 5 1
:
. : r
3 3 1 d
86% 69%
(
d
2d 7
,
2f
9% 64% 4 2 1 d
91 76
% ,
,
)
%
)
(
(
)
e
OM
t
CO2E
t
CO2E
t
CO2E
e
M
O
N
N
N
e
M O
H
H
H
e
OM
:
g
>
:
r
2
7
(
:
. :
4 0 1 d
r
94% 8% 19 1 d
2h
,
)
84 70
% ,
%
:
. : r
4 0 1 d
2i
7
1
% ,
( )
(
)
88
%
t
CO2E
CO2
Et
t
CO2E
e
OM
F
N
N
N
H
H
H
:
2k
. :
r
:
. :
6% 62% 4 4 1 d
,
r
7
1 d
2l 7
60% 45%
(
3
,
:
2
j
. :
r
86% 2% 4 0 1 d
7
(
,
)
)
(
)
O
O
e
M
e
M
t
CO2E
CO2
O
4
e
F
r
OM
N
N
N
H
H
H
o:
. :
r
d
n
2
:
. :
5 1
63% 8% 3 d
,
( )
44
%
1
m
2
30% 3 6
:
. :
84% 0% 4 0 1 d
r
4
,
)
2
7
(
,
)
(
We have established the generality of the reaction with a
number of N-aryl enamines substituted with electron-
withdrawing, electron-donating and bulky alkyl groups, which
O
O
O
O
O
O
N
N
N
H
H
H
Table 1. Optimization of reaction conditionsa
:
2
p
. :
4 3 1 d
r
:
2
q
. :
3 3 1 d
r
r
2
:
. :
6% 3 %
4
,
)
r
d
5
7
42
% ,
50 40
% % ,
4
5
1
%
9
(
)
(
)
(
a
t
CO2E
CO2
Et
Reaction conditions: 0.2 mmol 1a, 2 mol% Ir(ppy)3 were added in 4 mL
r
I
Ph
ppy
(
)
3
CH3CN, and the solution was strictly deaerated and irradiated under blue
LEDs (λ = 450 nm) for 12 hours at room temperature. b Yield was determined
by 1H NMR analysis of the unpurified reaction mixture using
diphenylacetonitrile as an internal standard; isolated total yields of two
+
Ph
Ph
nm
LED
t 12 h
s
N
H
450
r. .
N
H
rans
N
H
t
CO2E
t
c s
i
a
1
a
2
c
Ir(ppy)3
2%
Solvent
Yieldb
dr (trans/cis)c
2.0:1
2.9:1
5.1:1
4.0:1
4.0:1
4.0:1
4.0:1
4.0:1
4.0:1
4.0:1
--
diastereomers are given in parentheses. Diastereomer ratios (trans/cis)
Entry
1
were determined by 1H NMR analysis of the unpurified reaction mixture.
3 mL DMF
50%
45%
68%
76%
70%
86%
85%
65%
84%
80%
None
None
2%
3 mL CH3OH
3 mL THF
2
are presented in Table 2. Analysis of these results lead to the
following conclusions: (a) N-aryl enamines substituted with
electron-withdrawing and electron-donating groups gave the
indoline products in modest diastereoselectivity. (b)
Substitution with electron-withdrawing fluorine substituent
resulted in poorer yield (2b, 2k, 2n) than the ones substituted
with electron-donating groups (2c-2j, 2l-2m). (c) Of the various
substituents, 3,5-dimethyl and 3,4,5-trimethoxy group
substituted enamines produced indolines in highest yields of
91% (2f) and 94% (2g). The later gave the product in high
diastereoselectivity (>19:1) as well. (d) The ethyl ester of the
enamine could be replaced by n-hexyl, i-propyl, cyclopentyl,
and cyclohexyl esters, which could also proceed smoothly to
afford corresponding indolines (2o-2r). The large gram-scale
reaction was performed to give indolines in 68% yield (Scheme
S2, ESI†).
2%
3
2%
3 mL CH3CN
2 mL CH3CN
4 mL CH3CN
5 mL CH3CN
4 mL CH3CN
4 mL CH3CN
4 mL CH3CN
4 mL CH3CN
4 mL CH3CN
4
2%
5
2%
6
2%
7
1%
8
3%
9
4%
10
11d
12
a
2%
0%
--
Reaction conditions: 0.2 mmol 1a, corresponding Ir(ppy)3 were added in
solvent, and the solution was strictly deaerated with N2 and irradiated under
b
blue LEDs (λ = 450 nm) for 12 hours at room temperature. Yield was
determined by 1H NMR analysis of the unpurified reaction mixture using
c
diphenylacetonitrile as an internal standard. Diastereomer ratios were
determined by 1H NMR analysis of the unpurified reaction mixture. d In dark.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 3 of 5
ChemComm
Journal Name
COMMUNICATION
a
Ph
( )
Ph
ν
h
r
I
ppy
(
)
3
View Article Online
H
a
Et
CO2
DOI: 10.1039/C7CC04358A
N
N
O
H
H
Et
CO2
Hb
a
1
a
E
(
N
Z
( )
1
)
Ph
Ph
Et
O2C
3
*
a
3
Et
CO2
Ph
Et
CO2
b
( )
ener
*
rans er
f
t
gy
Fig. 1. X-ray crystal structure of compound 3a.
N
H
N
Ph
H
a
1
a3
Z/E
1
* Z/E
(
(
)
)
r
I
ppy
(
r
I
ppy
)
3
(
)
3
To probe the mechanism of the reaction, we monitored the
quenching of photosensitizer Ir(ppy)3 by 1a through steady
state and time resolved emission techniques (Fig. 2a-b). Similar
quenching constants obtained by monitoring the emission
intensity (2.6 × 108 M-1 s-1) and the lifeime (1.5 × 108 M-1 s-1)
confirmed that the quenching occurs by a dynamic process and
there is no static component (i.e., there is no aggregation of
the photosensitizer and the enamine substrate 1a in the
ground state). According to our previous study,10 the oxidation
potential of 1a was 0.71 V vs. SCE and the reduction potential
of excited Ir(ppy)3* was 0.26 V vs. SCE, the electron transfer
from 1a to the excited Ir(ppy)3* was excluded to be the cause
for the above emission quenching. Therefore, we speculated
that the quenching of the excited photosensitizer Ir(ppy)3* by
1a is the result of singlet-singlet or triplet-triplet energy
transfer. Because of the non-overlapping absorption spectra of
enamine 1a and emission spectra of photosensitizer Ir(ppy)3*
at room temperature (Fig. 2c), we concluded that singlet-
singlet energy transfer is unlikely. Thus, the emission spectra
c c za on
li ti
ν
y
h
Et
CO2
H
H
H
H
Et
Et
CO2
CO2
s
hift
H
Ph
N
N
H
N
Ph
Ph
H
H
a
2
:
r
c
4 1 d
b
(
)
Scheme 2. (a) Photoinduced geometric isomerization. (b) Proposed
reaction mechanism.
triplet-triplet energy transfer from Ir(ppy)3* to 1a is possible.
The fact that rate constant (~108 M-1 s-1) for energy transfer is
two orders of magnitude lower than diffusion constant (~1010
M-1 s-1) in CH3CN is in line with the slightly higher triplet energy
of enamine 1a (Fig. 2d, 58 kcal/mol) than that of Ir(ppy)3* (Fig.
2d, 57 kcal/mol).
Occurence of triplet-triplet energy transfer was supported
by geometric isomerziation of enamines (Scheme 2a), a
process well known to take place in the excited state.10,12 Prior
to visible light irradiation, the structure of 1a was confirmed by
1H NMR to be in the Z-form. Intramolecular hydrogen bonding,
most likely, favored this isomer in CH3CN (Fig. S2a, ESI†).13
11
of Ir(ppy)3 and 1a at 77 K were recorded to investigate the
feasibility of triplet-triplet energy transfer. The occurence of
overlap between the emission of Ir(ppy)3 and
phosphorescence of 1a at 77 K (Fig. 2d) suggested that the
1
However, H NMR signal of the E-isomer of 1a was detected
when the system containing Ir(ppy)3 and 1a in degassed CD3CN
was irradiated by blue LEDs for 1 minute (Fig. S2b, ESI†).
Clearly, geometric isomerization competes with the cyclization
in the excited state. Thus the final indolines most likely derive
from both E and Z isomers of N-aryl enamines.
Based on the above experimental observations, we
proposed a plausible mechanism outlined in Scheme 2b for the
conversion of N-aryl enamine to indolines. We believe that the
excited photosensitizer Ir(ppy)3* transfers energy to both E
and Z isomers of 1a to generate the excited triplet state of 1a
via triplet-triplet energy transfer process, and the latter
undergoes geometric isomerziation and electrocyclization
yielding the diradical intermediate b 14-15
intermediate relaxes to a zwitterionic intermediate
.
The diradical
, which
b
c
affords a mixture of cis and trans diastereoisomeric indoline
product via multiple 1,2-hydrogen shifts. Feasibility of
cyclization of enamine type of molecules from triplet state has
been established earlier.16 We believe that geometric
isomerization of Z to E competes with the cyclization process
but eventually both isomers are converted to indolines as the
final isolated product.
Fig. 2. (a) Emission spectra of Ir(ppy)3* (1×10-4 M) as a function of
concentration of 1a in degassed CH3CN. The inset shows the plot of I0/I
versus [1a] for the reaction of Ir(ppy)3* with 1a. (b) Lifetime of Ir(ppy)3*
(1×10-4 M) as a function of concentration of 1a in degassed CH3CN. The inset
shows the plot of τ0/τ versus [1a] for the reaction of Ir(ppy)3* with 1a. (c)
UV-vis absorption of 1a (5×10-5 M) and normalized emission spectra of
Ir(ppy)3 (1×10-4 M) in degassed CH3CN at room temperature with excitation
at 350 nm. (d) Normalized emission intensity of Ir(ppy)3 (1×10-4 M) and
enamine 1a (1×10-2 M) in degassed DMF at 77K with excitation at 350 nm.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 5
COMMUNICATION
Journal Name
Glorius, Angew. Chem. Int. Ed., 2009, 48, 6892; (h) T.-S. Mei,
X. Wang, J.-Q. Yu, J. Am. Chem. Soc., 2009, 131, V1ie0w80Ar6tic;le(iO) nGli.ne
In summary, we developed a green methodology to
synthesize indolines under visible light irradiation. By using
catalytic amount of Ir(ppy)3 as the photosensitizer, a number
of N-aryl enamines were transformed to their corresponding
indoline products in good to excellent yields without requiring
any extra additives. This is, to the best of our knowledge, the
first example to synthesize indolines via intramolecular
cyclization of enamines by visible light catalysis. Mechanistic
studies revealed that the reaction was initiated at the triplet
state of the enamines produced by energy transfer from the
excited Ir(ppy)3 sensitizer. The generated triplet enamines
then underwent intramolecular 6π-cyclization to afford
diastereoisomeric indoline products under extremely mild
condition. We believe that such a mild methdology could find
wide applications in organic synthetic transformations.
Financial support for this research from the Ministry of
Science and Technology of China (2013CB834804,
2014CB239402 and 2013CB834505), the National Natural
Science Foundation of China (21390404 and 91027041), the
Strategic Priority Research Program of the Chinese Academy of
Science (XDB17030400), and the Chinese Academy of Sciences
is gratefully acknowledged. V. Ramamurthy acknowledges the
Chinese Academy of Sciences for a fellowship and the US
National Science Foundation (CHE-1411458) for its support.
He, C. Lu, Y. Zhao, W. A. Nack, G. ChenD, OOIr:g1.0L.1e0t3t9.,/C270C1C20,413458A
,
2944; (j) M. K. Manna, A. Hossian, R. Jana, Org. Lett., 2015,
17, 672; (k) S. Z. Tasker, T. F. Jamison, J. Am. Chem. Soc.,
2015, 137, 9531; (l) F. Pan, B. Wu, Z.-J. Shi, Chem. Eur. J.,
2016, 22, 6487.
4
(a) D. Zhang, L. S. Liebeskind, J. Org. Chem., 1996, 61, 2594;
(b) W. F. Bailey, X.-L. Jiang, J. Org. Chem., 1996, 61, 2596; (c)
M. Uchiyama, M. Koike, M. Kameda, Y. Kondo, T. Sakamoto, J.
Am. Chem. Soc., 1996, 118, 8733; (d) W. F. Bailey, M. W.
Carson, Tetrahedron Lett., 1997, 38, 1329; (e) J. Nakao, R.
Inoue, H. Shinokubo, K. Oshima, J. Org. Chem., 1997, 62
,
1910; (f) W. F. Bailey, M. J. Mealy, J. Am. Chem. Soc., 2000,
122, 6787; (g) G. S. Gil, U. M. Groth, J. Am. Chem. Soc., 2000,
122, 6789; (h) W. F. Bailey, M. R. Luderer, M. J. Mealy,
Tetrahedron Lett., 2003, 44, 5303.
5
(a) R. Viswanathan, E. N. Prabhakaran, M. A. Plotkin, J. N.
Johnston, J. Am. Chem. Soc., 2003, 125, 163; (b) C. Leroi, D.
Bertin, P.-E. Dufils, D. Gigmes, S. Marque, P. Tordo, J.-L.
Couturier, O. Guerret, M. A. Ciufolini, Org. Lett., 2003,
4943; (c) J. N. Johnston, M. A. Plotkin, R. Viswanathan, E. N.
Prabhakaran, Org. Lett., 2001, , 1009; (d) F. Brucelle, P.
5,
3
Renaud, J. Org. Chem., 2013, 78, 6245; (e) L. Lv, L. Qi, Q. Guo,
B. Shen, Z. Li, J. Org. Chem., 2015, 80, 12562; (f) H.-Y. Zhang,
L.-L. Mao, B. Yang, S.-D. Yang, Chem. Commun., 2015, 51
4101.
,
6
7
(a) B. Robinson, Chem. Rev., 1969, 69, 785; (b) S. Anas, H. B.
Kagan, Tetrahedron: Asymmetr, 2009, 20, 2193; (c) D. Liu, G.
Zhao, L. Xiang, Eur. J. Org. Chem., 2010, 2010, 3975.
(a) T. Watanabe, S. Oishi, N. Fujii, H. Ohno, Org. Lett., 2008,
10, 1759; (b) R. Miyaji, K. Asano, S. Matsubara, Org. Lett.,
2013, 15, 3658; (c) Y. Yu, G. Li, L. Jiang, L. Zu, Angew. Chem.
Int. Ed., 2015, 54, 12627; (d) K. G. Liu, J. R. Lo, A. J. Robichaud,
Tetrahedro, 2010, 66, 573; (e) M. Rueping, C. Brinkmann, A.
P. Antonchick, I. Atodiresei, Org. Lett., 2010, 12, 4604; (f) D.
Zhao, S. Vásquez-Céspedes, F. Glorius, Angew. Chem. Int. Ed.,
2015, 54, 1657; (g) D. Yadagiri, A. C. S. Reddy, P. Anbarasan,
Notes and references
1
(a) G. W. Gribble, P. D. Lord, J. Skotnicki, S. E. Dietz, J. T.
Eaton, J. Johnson, J. Am. Chem. Soc., 1974, 96, 7812; (b) A. E.
Lanzilotti, R. Littell, W. J. Fanshawe, T. C. McKenzie, F. M.
Lovell, J. Org. Chem., 1979, 44, 4809; (c) D. M. Ketcha, B. A.
Lieurance, Tetrahedron Lett., 1989, 30, 6833; (d) M. Tan, Y.
Zhang, Tetrahedron Lett., 2009, 50, 4912; (e) H. Cho, F. Torok,
B. Torok, Org. Biomol. Chem., 2013, 11, 1209; (f) L. Zhang, R.
Qiu, X. Xue, Y. Pan, C. Xu, H. Li, L. Xu, Adv. Synth. Catal., 2015,
357, 3529.
For examples on heterogeneous catalysts: (a) S. Coulton, T. L.
Gilchrist, G. Keith, Tetrahedron, 1997, 53, 791; (b) A. Kulkarni,
W. Zhou, B. Török, Org. Lett., 2011, 13, 5124; (c) H. Bernas, N.
Kumar, A. Aho, R. Leino, D. Y. Murzin, Catal. Commun., 2014,
56, 41; (d) F. Chen, A.-E. Surkus, L. He, M.-M. Pohl, J. Radnik,
Chem. Sci., 2016, 7, 5934.
8
9
(a) J. M. R. Narayanam, C. R. J. Stephenson, Chem. Soc. Rev.,
2011, 40, 102; (b) C. K. Prier, D. A. Rankic, D. W. Macmillan,
Chem. Rev., 2013, 113, 5322; (c) D. M. Schultz, T. P. Yoon,
Scienc, 2014, 343, 985; (d) G. Zhang, C. Bian, A. Lei, Chin. J.
Catal., 2015, 36, 1428; (e) K. L. Skubi, T. R. Blum, T. P. Yoon,
Chem. Rev., 2016, 116, 10035; (f) N. A. Romero, D. A.
Nicewicz, Chem. Rev., 2016, 116, 10075; (g) J.-R. Chen, X.-Q.
Hu, L.-Q. Lu, W.-J. Xiao, Chem. Soc. Rev., 2016, 45, 2044; (h)
D. Ravelli, S. Protti, M. Fagnoni, Chem. Rev., 2016, 116, 9850.
CCDC 1542178 (3a)†.
2
C. Topf, K. Junge, M. Beller, J. Am. Chem. Soc., 2015, 137
11718; For examples on homogeneous catalysts: (e) R.
,
Kuwano, K. Sato, T. Kurokawa, D. Karube, Y. Ito, J. Am. Chem.
Soc., 2000, 122, 7614; (f) D.-S. Wang, Q.-A. Chen, W. Li, C.-B.
Yu, Y.-G. Zhou, X. Zhang, J. Am. Chem. Soc., 2010, 132, 8909;
(g) D.-S. Wang, J. Tang, Y.-G. Zhou, M.-W. Chen, C.-B. Yu, Y.
10 C.-J. Wu, Q.-Y. Meng, T. Lei, J.-J. Zhong, W.-Q. Liu, L.-M. Zhao,
Z.-J. Li, B. Chen, C.-H. Tung and L.-Z. Wu, ACS Catal., 2016,
4635.
6,
11 T. Hofbeck, H. Yersin, Inorg. Chem., 2010, 49, 9290.
12 J. B. Metternich, R. Gilmour, Synlet, 2016, 27, 2541.
13 Z.-H. Zhang, L. Yin, Y.-M. Wang, Adv. Synth. Catal., 2006, 348
184.
Duan, G.-F. Jiang, Chem. Sci., 2011, 2, 803; (h) Y.-C. Xiao, C.
Wang, Y. Yao, J. Sun, Y.-C. Chen, Angew. Chem. Int. Ed., 2011,
50, 10661; (i) Y. Duan, L. Li, M.-W. Chen, C.-B. Yu, H.-J. Fan,
Y.-G. Zhou, J. Am. Chem. Soc., 2014, 136, 7688; (j) T. Touge, T.
Arai, J. Am. Chem. Soc. 2016, 138, 11299; (k) Z. Yang, F. Chen,
,
14 N. J. Turro, V. Ramamurthy, J. C. Scaiano, Modern Molecular
Photochemistry of Organic Molecules, University Science
Books, Sausalito, CA, 2010, p. 856.
15 (a) O. L. Chapman, G. L. Eian, A. Bloom, J. Clardy, J. Am. Chem.
Soc., 1971, 93, 2918; (b) A. G. Schultz, C.-K. Sha, Tetrahedro,
1980, 36, 1757; (c) J.-C. Gramain, H. P. Husson, Y. Troin, J.
Org. Chem., 1985, 50, 5517; (d) M. Ibrahim-Ouali, M.-È.
Sinibaldi, Y. Troin, D. Guillaume, J.-C. Gramain, Tetrahedro,
1997, 53, 16083.
Y. He, N. Yang, Q.-H. Fan, Angew. Chem. Int. Ed., 2016, 55
13863.
,
3
(a) J. P. Wolfe, R. A. Rennels, S. L. Buchwald, Tetrahedron,
1996, 52, 7525; (b) R. Lira, J. P. Wolfe, J. Am. Chem. Soc.,
2004, 126, 13906; (c) P. Thansandote, M. Raemy, A. Rudolph,
M. Lautens, Org. Lett., 2007, 9, 5255; (d) P. H. Fuller, J.-W.
Kim, S. R. Chemler, J. Am. Chem. Soc., 2008, 130, 17638; (e) C.
E. Houlden, C. D. Bailey, J. G. Ford, M. R. Gagné, G. C. Lloyd-
16 (a) I. Tanaka, H. Shizuka, Y. Takayama, T. Morita, J. Am. Chem.
Soc., 1970, 92, 7270; (b) E. W. Foerster, K. H. Grellmann, H.
Linschitz, J. Am. Chem. Soc., 1973, 95, 3108.
Jones, K. I. Booker-Milburn, J. Am. Chem. Soc., 2008, 130
,
10066; (f) J.-J. Li, T.-S. Mei, J.-Q. Yu, Angew. Chem. Int. Ed.,
2008, 47, 6452; (g) J. J. Neumann, S. Rakshit, T. Dröge, F.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 5
ChemComm
View Article Online
DOI: 10.1039/C7CC04358A
TOC