Visible Light as a Sole Requirement for Intramolecular C(sp3)-H Imination

Article abstract of DOI:10.1021/acs.orglett.7b00533

A novel, simple, and practical visible-light-mediated intramolecular α-C(sp³)-H imination of tertiary aliphatic amines containing β-O-aryl oximes leading to N-heterocycles has been developed. The reaction was performed well at rt with tolerance of some functional groups. Importantly, the selective C-H functionalization did not require added catalyst, oxidant, additive, acid, and base; visible light was the sole requirement.

Full text of DOI:10.1021/acs.orglett.7b00533

Letter
pubs.acs.org/OrgLett
Visible Light as a Sole Requirement for Intramolecular C(sp3)−H
Imination
Jingjing Li, Pengxiang Zhang, Min Jiang, Haijun Yang, Yufen Zhao, and Hua Fu*
Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry,
Tsinghua University, Beijing 100084, China
S
* Supporting Information
ABSTRACT: A novel, simple, and practical visible-light-mediated intramolecular α-
C(sp3)−H imination of tertiary aliphatic amines containing β-O-aryl oximes leading to N-
heterocycles has been developed. The reaction was performed well at rt with tolerance of
some functional groups. Importantly, the selective C−H functionalization did not require
added catalyst, oxidant, additive, acid, and base; visible light was the sole requirement.
irect and selective formation of carbon−carbon and
carbon−heteroatom bonds via carbon−hydrogen (C−
Scheme 1. Proposed Mechanism for Intramolecular α-
C(sp3)−H Imination of Tertiary Aliphatic Amines Containing
β-O-Aryl Oximes (1)
D
H) activation has attracted much attention in organic synthesis,
and this strategy can decrease the number of steps to the target
products and reduce cost and waste.1 However, achieving
regioselective C−H activation is a great challenge because C−H
bonds are ubiquitous in organic molecules. The formation of C−
N bonds is a very important transformation because many
bioactive and medicinal molecules are nitrogen-containing
compounds.2 In the past 10 years, there has been great progress
in the formation of C−N bonds via the C−H activation strategy.3
However, transition-metal catalysts, oxidants, additives, acids,
bases, and/or heating conditions are often necessary, which are
unfavorable for the construction of diverse functional molecules.
Recently, photopromoted methods with visible light as a
renewable energy source have become a powerful strategy in
organic synthetic chemistry.4 In previous visible-light photo-
redox research, the chemistry of C-centered radicals has been
widely investigated. However, the generation and synthetic
utility of N-centered radicals is an exciting and emerging field of
research with many novel transformations remaining unex-
plored.5 The N-radical species are classically generated under the
assistance of stoichiometric radical initiators, thermolysis, or UV
photolysis.6 Yet, the harsh conditions greatly hinder broad
applications of N-radical species in organic synthesis. Recently,
several novel and interesting C(sp2)−H functionalizations via
the formation of N-radical intermediates have been developed.7
In particular, Leonori et al. have represented a divergent strategy
for the hydroimination and iminohydroxylation/cyclization of
unactivated olefins containing O-aryl oximes.8
and amine radical cation, freeing anion D. Intramolecular
migration of a hydrogen radical from the α-C(sp3)−H of the
amine radical cation in C provides cation E, and intramolecular
nucleophilic attack in E in the presence of D provides the desired
target product (2), leaving 2,4-dinitrophenol (F). As part of our
continuing investigation on the visible light photoredox
reactions,10 we here report the novel, simple, and practical
visible-light-mediated intramolecular α-C(sp3)−H imination of
tertiary aliphatic amines containing β-O-aryl oximes at rt.
Initially, visible light photoredox intramolecular α-C(sp3)−H
imination of 1-phenyl-2-(piperidin-1-yl)ethanone O-(2,4-
dinitrophenyl)oxime (1a) was applied as the model reaction to
optimize conditions, including solvents, atmosphere, and time.
As shown in Table 1, five solvents were tested under irradiation
of visible light with a 23 W CFL bulb and an argon atmosphere at
room temperature for 5 h (entries 1−5), and dimethyl sulfoxide
(DMSO) provided the highest yield (entry 5). Surprisingly, the
resulting product under the present conditions was the oxidation
Obviously, the more difficult C(sp3)−H functionalization is a
great challenge via N-radical intermediates. Inspired by Leonori’s
research,8 we designed a novel, intramolecular α-C(sp3)−H
imination of tertiary aliphatic amines containing β-O-aryl oximes.
A detailed mechanism is shown in Scheme 1. Reversible binding
of both O-2,4-dinitrophenyl and tertiary amine in 1 makes 1
become a photosensitizer,8 and irradiation of 1 with visible light
gives the excited state (A). A single electron transfer (SET) from
N of the tertiary amine9 to the aromatic ring can form B, and
cleavage of the N−O bond in B produces C with an iminyl radical
1
product (3a) of 2a, whose structure was confirmed by H, 13C
NMR and mass spectrometry. Meanwhile, 2,4-dinitrophenol and
2-amino-4-nitrophenol were isolated in 33% and 22% yields
(Scheme 2), respectively, which showed that 2,4-dinitrophenol
Received: February 21, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b00533
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 1. Optimization of Conditions for Visible Light
Photoredox Intramolecular α-C(sp3)−H Imination of 1-
Phenyl-2-(piperidin-1-yl)ethanone O-(2,4-
Table 2. Substrate Scope of Visible-Light Photoredox
Intramolecular α-C(sp3)−H Imination of Tertiary Aliphatic
a
Amines Containing β-O-Aryl Oximes (1)
a
Dinitrophenyl)oxime (1a)
b
entry
solvent
atmos.
time (h)
yield (%)
1
MeCN
CH2Cl2
THF
Ar
Ar
Ar
Ar
Ar
Ar
Ar
air
O2
Ar
Ar
5
5
5
5
5
3
12
5
5
5
5
53
14
22
39
75
48
73
NR
NR
2
3
4
DMF
5
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
6
7
8
9
c
10
11
NR
d
73
a
Reaction conditions: irradiation of visible light with 23 W CFL and
argon atmosphere, 1-phenyl-2-(piperidin-1-yl)ethanone O-(2,4-
dinitrophenyl)oxime (1a) (0.2 mmol), solvent (2.0 mL), temperature
b
(rt, ∼25 °C), time (3−12 h) in a sealed Schlenk tube. Isolated yield.
c
d
The reaction was carried out in the dark. Addition of acetic acid (0.2
mmol). NR = no reaction. CFL = compact fluorescent light.
Scheme 2. Visible-Light-Mediated Reaction of 1a Leading to
3a and Byproducts
here acted as an oxidant during oxidation of 2a to 3a. Reaction
times shorter than 5 h were deleterious to yield (entry 6), and
extension to 12 h did not improve the yield (entry 7). The
reaction did not proceed under an air (entry 8) or oxygen
atmosphere (entry 9). No reaction occurred without irradiation
of visible light (entry 10). Addition of a stoichiometric acetic acid
did not affect this reaction (entry 11).
With these optimized photoredox conditions in hand, we
investigated the substrate scope for visible-light-mediated
intramolecular α-C(sp3)−H imination of tertiary aliphatic
amines containing β-O-aryl oximes. As shown in Table 2, we
first attempted different substituted aromatic units (Ar parts) in 1
(see 1a−s), and they provided the imidazoles in moderate to
good yields (see 3a−s), but the substrates containing nitro (see
1o) and ortho-site fluoro (see 1g) gave lower yields. When
tertiary aliphatic amine parts in 1 were changed (see 1t−aa), we
found that yields displayed more significant differences. In
general, the substrates containing six-membered cycles provided
higher yields than the seven-membered ring (see 1u) and acyclic
substrates (see 1x−aa). 2-(3,4-Dihydro-1H-isoquinolin-2-yl)-1-
phenyl-ethanone O-(2,4-dinitro-phenyl)-oxime (1t) with
a
Reaction conditions: irradiation of visible light with 23 W CFL and
argon atmosphere, oxime (1) (0.2 mmol), DMSO (2.0 mL),
temperature (rt, ∼25 °C), time (5 or 7 h) in a sealed Schlenk tube.
b
c
Isolated yield. Addition of triethylamine (NEt3) (0.4 mmol).
1,2,3,4-tetrahydroisoquinoline produced 3t in 85% yield. Intra-
molecular imination of 1w provided two products 3w (major)
and 3w′ (minor). For acyclic substrates in the tertiary aliphatic
B
DOI: 10.1021/acs.orglett.7b00533
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
amine parts, those containing N-benzyl (see 1y and 1aa)
exhibited higher reactivity than the others because of the higher
activity of benzyl C−H bonds. In addition, addition of 2 equiv of
triethylamine promoted the reactivity of several substrates (see
1u, 1x−z). The visible-light-mediated intramolecular α-C(sp3)−
H imination of tertiary aliphatic amines containing β-O-aryl
oximes displayed tolerance of various functional groups,
including ethers (see 3c and 3d), C−F bonds (see 3e−3g),
C−Cl bonds (see 3h and 3i), C−Br bond (see 3j), CF3 (see 3l
and 3m), cyano (see 3n), nitro (see 3o), ester (see 3p), and O- or
S-heterocycles (see 3r and 3s). It is well-known to all that the
imidazole derivatives exhibit diverse functions such as acting as
the enzyme inhibitors,11 drugs,12 dyes,13 and polymers.14
Therefore, the present method via visible-light-mediated C−H
activation provides a novel, simple, and practical strategy for
construction of N-heterocycles.
To explore the mechanism of visible-light-mediated intra-
molecular α-C(sp3)−H imination of tertiary aliphatic amines
containing β-O-aryl oximes, we investigated the types of the
radicals produced under different conditions by electron spin
resonance (ESR) using 5,5-dimethyl-1-pyrroline N-oxide
(DMPO) as the spin trapping agent. A mixture of triethylamine
(100 mM), Ir(ppy)3 (2 mM), and DMPO (150 mM) in DMSO
(30 μL) was bubbled with Ar for 10 min, and then a small amount
of the mixture was transferred to a capillary under Ar. After the
capillary was irradiated with visible light for 5 min, ESR
determination was performed. A signal of a nitrogen-centered
DMPO radical adduct appeared (Figure 1a), which indicated that
the nitrogen-centered radical of trialkylamine occurred during
the process. Next, to investigate formation of the iminyl radical, a
mixture of 1-phenyl-ethanone O-(2,4-dinitro-phenyl)-oxime (4)
(100 mM), Ir(ppy)3 (2 mM), and DMPO (150 mM) in DMSO
(30 μL) was monitored by ESR. Fortunately, a clear quartet peak
signal indicative of a nitrogen-centered DMPO radical adduct
was observed (Figure 1b), which demonstrated the formation of
iminyl radical C-4. Subsequently, a mixture of 2-(3,4-dihydro-
1H-isoquinolin-2-yl)-1-phenyl-ethanone O-(2,4-dinitro-phe-
nyl)-oxime (1t) (100 mM) and DMPO (200 mM) in DMSO
(30 μL) was bubbled with Ar for 10 min, then a small amount of
the mixture was transferred to a capillary under Ar, and ESR
determination was carried out. No signal was observed in the
dark (Figure 1c). After the capillary was irradiated with visible
light for 2 min, the ESR superhyperfine spectrum exhibited
signals of two nitrogen-centered DMPO radical adducts (Figure
1d), which indicated the formation of imine and tertary amine
radicals C-1t. The hyperfine and spectral splitting constants of
two nitrogen-centered DMPO radical adducts were obtained
Figure 1. Investigations of mechanism for the visible light photoredox
intramolecular α-C(sp3)−H imination by ESR. ESR spectra of the
mixtures under different conditions: (a) ESR spectrum for a mixture of
triethylamine (100 mM), Ir(ppy)3 (2 mM), and DMPO (150 mM) in
DMSO after irradiation of visible light with 23 W CFL for 5 min. (b)
ESR spectrum for a mixture of 1-phenyl-ethanone O-(2,4-dinitro-
phenyl)-oxime (4) (100 mM), Ir(ppy)3 (2 mM), and DMPO (150 mM)
in DMSO after irradiation of visible light with 23 W CFL for 1 min. (c)
ESR spectrum for a mixture of 1t (100 mM) and DMPO (150 mM) in
DMSO without irradiation of light. (d) ESR spectrum and super-
hyperfine spectrum for a mixture of 1t (100 mM) and DMPO (200
mM) in DMSO after irradiation of visible light with 23 W CFL for 2 min.
Scheme 3. Visible-Light-Mediated Intramolecular α-C(sp3)−
H Imination of Substituted 1-Phenyl-2-(pyrrolidin-1-
yl)ethanone O-(2,4-dinitrophenyl)oximes (1ab−1af) under
the Standard Conditions
according to Figure 1d (AN = 1.060 mT, AH = 1.274 mT, AN′
=
0.132 mT, g = 2.006 for nitrogen-centered DMPO radical adduct
from imine; AN = 1.060 mT, AH = 1.252 mT, AN′ = 0.117 mT, g =
2.006 for nitrogen-centered DMPO radical adducts from tertary
amine). The results above indicate that the process for visible-
light-mediated, intramolecular α-C(sp3)−H imination in
Scheme 1 is reasonable. Subsequently, oxidation of 2 by 2,4-
dinitrophenol gives 3, leaving 2-amino-4-nitrophenol.
We extended the substrate scope to substituted 1-phenyl-2-
(pyrrolidin-1-yl)ethanone O-(2,4-dinitrophenyl)oximes (1ab−
1af). Unexpectedly, products 2ab−2af were obtained in good
yields, but their oxidation products were not found (Scheme 3).
The results showed that the products (2) containing pyrrolidinyl
were more stable than those containing six-membered cycles and
acyclic tertiary amines under the standard conditions.
In summary, we have developed a novel, simple, and practical
visible light-mediated intramolecular α-C(sp3)−H imination of
C
DOI: 10.1021/acs.orglett.7b00533
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Yu, W.-Y.; Che, C.-M. Angew. Chem., Int. Ed. 2002, 41, 3465. (e) Adam,
W.; Krebs, O. Chem. Rev. 2003, 103, 4131. (f) Cui, Y.; He, C. Angew.
Chem., Int. Ed. 2004, 43, 4210. (g) Espino, C. G.; Fiori, K. W.; Kim, M.;
Du Bois, J. J. Am. Chem. Soc. 2004, 126, 15378. (h) Leung, S. K.-Y.; Tsui,
W.-M.; Huang, J.-S.; Che, C.-M.; Liang, J.-L.; Zhu, N. J. Am. Chem. Soc.
2005, 127, 16629. (i) Davies, H. M. L.; Long, M. S. Angew. Chem., Int. Ed.
2005, 44, 3518. (j) Lebel, H.; Huard, K.; Lectard, S. J. Am. Chem. Soc.
2005, 127, 14198. (k) Fructos, M. R.; Trofimenko, S.; Díaz-Requejo, M.
tertiary aliphatic amines containing β-O-aryl oximes. The
reaction only required irradiation with visible light, and no
added catalyst, oxidant, additive, acid, and base were required.
This is a very easy visible light photoredox process, and the
simple C−H activation strategy makes this method very practical.
In addition, the obtained products are imidazole derivatives that
are key building blocks and useful molecules in natural products,
medicinal chemistry, and materials science. We believe that the
present method with good tolerance of functional groups will
find wide applications in synthesis of N-heterocyclic compounds.
́
M.; Perez, P. J. J. Am. Chem. Soc. 2006, 128, 11784. (l) Thu, H.-Y.; Yu,
W.-Y.; Che, C.-M. J. Am. Chem. Soc. 2006, 128, 9048. (m) Zhang, Y.; Fu,
H.; Jiang, Y.; Zhao, Y. Org. Lett. 2007, 9, 3813. (n) Liu, X.; Zhang, Y.;
Wang, L.; Fu, H.; Jiang, Y.; Zhao, Y. J. Org. Chem. 2008, 73, 6207.
(o) Wang, Z.; Zhang, Y.; Fu, H.; Jiang, Y.; Zhao, Y. Org. Lett. 2008, 10,
1863. (p) Wang, L.; Fu, H.; Jiang, Y.; Zhao, Y. Chem. - Eur. J. 2008, 14,
10722. (q) Lu, J.; Jin, Y.; Liu, H.; Jiang, Y.; Fu, H. Org. Lett. 2011, 13,
3694. (r) Xu, W.; Jin, Y.; Liu, H.; Jiang, Y.; Fu, H. Org. Lett. 2011, 13,
1274. (s) Xu, W.; Fu, H. J. Org. Chem. 2011, 76, 3846. (t) Xu, H.; Fu, H.
Chem. - Eur. J. 2012, 18, 1180. (u) Wang, X.; Jin, Y.; Zhao, Y.; Zhu, L.;
Fu, H. Org. Lett. 2012, 14, 452. (v) Yu, J.; Jin, Y.; Zhang, H.; Fu, H. Chem.
- Eur. J. 2013, 19, 16804. (w) Wang, M.; Jin, Y.; Yang, H.; Fu, H.; Hu, L.
RSC Adv. 2013, 3, 8211. (x) Tian, H.; Qiao, H.; Zhu, C.; Fu, H. RSC Adv.
2014, 4, 2694. (y) Yu, J.; Fu, H. Rep. Org. Chem. 2015, 5, 1.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.7b00533.
Experimental details, NMR data (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: fuhua@mail.tsinghua.edu.cn.
ORCID
(4) For selected reviews on visible-light photoredox catalysis, see:
(a) Zeitler, K. Angew. Chem., Int. Ed. 2009, 48, 9785. (b) Yoon, T. P.;
Ischay, M. A.; Du, J. Nat. Chem. 2010, 2, 527. (c) Narayanam, J. M. R.;
Stephenson, C. R. J. Chem. Soc. Rev. 2011, 40, 102. (d) Shi, L.; Xia, W.
Chem. Soc. Rev. 2012, 41, 7687. (e) Tucker, J. W.; Stephenson, C. R. J. J.
Org. Chem. 2012, 77, 1617. (f) Xuan, J.; Xiao, W.-J. Angew. Chem., Int. Ed.
Hua Fu: 0000-0001-7250-0053
Notes
2012, 51, 6828. (g) Hari, D. P.; Konig, B. Angew. Chem., Int. Ed. 2013,
̈
The authors declare no competing financial interest.
52, 4734. (h) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev.
2013, 113, 5322. (i) Xi, Y.; Yi, H.; Lei, A. Org. Biomol. Chem. 2013, 11,
2387. (j) Xuan, J.; Zhang, Z.-G.; Xiao, W.-J. Angew. Chem., Int. Ed. 2015,
54, 15632. (k) Jin, Y.; Fu, H. Asian J. Org. Chem. DOI: 10.1002/
ajoc.201600513.
(5) Chen, J.-R.; Hu, X.-Q.; Lu, L.-Q.; Xiao, W.-J. Chem. Soc. Rev. 2016,
45, 2044.
(6) Zard, S. Z. Chem. Soc. Rev. 2008, 37, 1603.
ACKNOWLEDGMENTS
■
The authors would like to thank Dr. Haifang Li in this
department for her great help in analysis of high resolution
mass spectrometry and the National Natural Science Foundation
of China (Grant No. 21372139) for financial support.
(7) (a) Allen, L. J.; Cabrera, P. J.; Lee, M.; Sanford, M. S. J. Am. Chem.
Soc. 2014, 136, 5607. (b) Kim, H.; Kim, T.; Lee, D. G.; Roh, S. W.; Lee,
C. Chem. Commun. 2014, 50, 9273. (c) Qin, Q.; Yu, S. Org. Lett. 2014,
16, 3504. (d) Song, L.; Zhang, L.; Luo, S.; Cheng, J.-P. Chem. - Eur. J.
2014, 20, 14231. (e) Maity, S.; Zheng, N. Angew. Chem., Int. Ed. 2012,
51, 9562. (f) Jiang, H.; An, X.; Tong, K.; Zheng, T.; Zhang, Y.; Yu, S.
Angew. Chem., Int. Ed. 2015, 54, 4055.
(8) Davies, J.; Booth, S. G.; Essafi, S.; Dryfe, R. A. W.; Leonori, D.
Angew. Chem., Int. Ed. 2015, 54, 14017.
(9) (a) Nakajima, K.; Miyake, Y.; Nishibayashi, Y. Acc. Chem. Res. 2016,
49, 1946. (b) Xie, J.; Shi, S.; Zhang, T.; Mehrkens, N.; Rudolph, M.;
Hashmi, A. S. K. Angew. Chem., Int. Ed. 2015, 54, 6046.
(10) (a) Jiang, M.; Jin, Y.; Yang, H.; Fu, H. Sci. Rep. 2016, 6, 26161.
(b) Jin, Y.; Jiang, M.; Wang, H.; Fu, H. Sci. Rep. 2016, 6, 20068. (c) Gao,
C.; Li, J.; Yu, J.; Yang, H.; Fu, H. Chem. Commun. 2016, 52, 7292. (d) Li,
J.; Tian, H.; Jiang, M.; Yang, H.; Zhao, Y.; Fu, H. Chem. Commun. 2016,
52, 8862. (e) Jin, Y.; Yang, H.; Fu, H. Chem. Commun. 2016, 52, 12909.
(f) Jiang, M.; Yang, H.; Fu, H. Org. Lett. 2016, 18, 1968. (g) Jiang, M.;
Yang, H.; Fu, H. Org. Lett. 2016, 18, 5248. (h) Jin, Y.; Yang, H.; Fu, H.
Org. Lett. 2016, 18, 6400. (i) Zhang, H.; Zhang, P.; Jiang, M.; Yang, H.;
Fu, H. Org. Lett. 2017, 19, 1016. (j) Jiang, M.; Li, H.; Yang, H.; Fu, H.
Angew. Chem., Int. Ed. 2017, 56, 874.
(11) (a) White, A. W.; Almassy, R.; Calvert, A. H.; Curtin, N. J.; Griffin,
R. J.; Hostomsky, Z.; Maegley, K.; Newell, D. R.; Srinivasan, S.; Golding,
B. T. J. Med. Chem. 2000, 43, 4084. (b) Hauel, N. H.; Nar, H.; Priepke,
H.; Ries, U.; Stassen, J.; Wienen, W. J. Med. Chem. 2002, 45, 1757.
(12) VelIk, J.; Baliharova, V.; Fink-Gremmels, J.; Bull, S.; Lamka, J.;
Skalova, L. Res. Vet. Sci. 2004, 76, 95 and reference cited therein.
(13) Sahin, C.; Ulusoy, M.; Zafer, C.; Ozsoy, C.; Varlikli, C.; Dittrich,
T.; Cetinkaya, B.; Icli, S. Dyes Pigm. 2010, 84, 88.
REFERENCES
■
(1) For recent selected reviews on C−H activation, see: (a) Seregin, I.
V.; Gevorgyan, V. Chem. Soc. Rev. 2007, 36, 1173. (b) Alberico, D.; Scott,
M. E.; Lautens, M. Chem. Rev. 2007, 107, 174. (c) McGlacken, G. P.;
Bateman, L. M. Chem. Soc. Rev. 2009, 38, 2447. (d) Chen, X.; Engle, K.
M.; Wang, D.-H.; Yu, J.-Q. Angew. Chem., Int. Ed. 2009, 48, 5094.
(e) Daugulis, O.; Do, H.-Q.; Shabashov, D. Acc. Chem. Res. 2009, 42,
1074. (f) Ackermann, L.; Vicente, R.; Kapdi, A. R. Angew. Chem., Int. Ed.
2009, 48, 9792. (g) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem.
Rev. 2010, 110, 624. (h) Wencel-Delord, J.; Droge, T.; Liu, F.; Glorius,
̈
F. Chem. Soc. Rev. 2011, 40, 4740. (i) Ackermann, L. Chem. Rev. 2011,
111, 1315. (j) Baudoin, O. Chem. Soc. Rev. 2011, 40, 4902.
(k) McMurray, L.; O’Hara, F.; Gaunt, M. J. Chem. Soc. Rev. 2011, 40,
1885. (l) Rousseau, G.; Breit, B. Angew. Chem., Int. Ed. 2011, 50, 2450.
(m) Yamaguchi, J.; Yamaguchi, A. D.; Itami, K. Angew. Chem., Int. Ed.
2012, 51, 8960. (n) Kuhl, N.; Hopkinson, M. N.; Wencel-Delord, J.;
Glorius, F. Angew. Chem., Int. Ed. 2012, 51, 10236. (o) Song, G.; Wang,
F.; Li, X. Chem. Soc. Rev. 2012, 41, 3651. (p) Arockiam, P. B.; Bruneau,
C.; Dixneuf, P. H. Chem. Rev. 2012, 112, 5879. (q) Hartwig, J. Acc. Chem.
Res. 2012, 45, 864. (r) Li, B.-J.; Shi, Z.-J. Chem. Soc. Rev. 2012, 41, 5588.
(s) Neufeldt, S. R.; Sanford, M. S. Acc. Chem. Res. 2012, 45, 936.
(t) Kozhushkov, S. I.; Ackermann, L. Chem. Sci. 2013, 4, 886.
(u) Mousseau, J.; Charette, A. B. Acc. Chem. Res. 2013, 46, 412.
(2) (a) Espino, C. G.; Du Bois, J. In Modern Rhodium-Catalyzed
Organic Reactions; Evans, P. A., Ed.; Wiley-VCH: Weinheim, 2005; pp
379−416. (b) Dick, A. R.; Sanford, M. S. Tetrahedron 2006, 62, 2439.
(c) Du Bois, J. Chemtracts 2005, 18, 1. (d) Halfen, J. A. Curr. Org. Chem.
2005, 9, 657.
(3) For selected papers, see: (a) Johannsen, M.; Jørgensen, K. A. Chem.
Rev. 1998, 98, 1689. (b) Espino, C. G.; Wehn, P. M.; Chow, J.; Du Bois,
J. J. Am. Chem. Soc. 2001, 123, 6935. (c) Espino, C. G.; Du Bois, J. Angew.
Chem., Int. Ed. 2001, 40, 598. (d) Liang, J.-L.; Yuan, S.-X.; Huang, J.-S.;
(14) Tsang, S. W.; Tao, Y.; Lu, Z. H. J. Appl. Phys. 2011, 109, 023711.
D
DOI: 10.1021/acs.orglett.7b00533
Org. Lett. XXXX, XXX, XXX−XXX