Visible-Light-Induced Cascade Reaction of Isocyanides and N-Arylacrylamides with Diphenylphosphine Oxide via Radical C-P and C-C Bond Formation

Article abstract of DOI:10.1021/acs.orglett.6b02413

An effective photoredox-mediated tandem phosphorylation/cyclization reaction of diphenylphosphine oxide with three types of radical acceptors leads to P(O)Ph₂-containing phenanthridines, isoquinolines, and indolin-2-ones by formation of both C-

Full text of DOI:10.1021/acs.orglett.6b02413

Letter
pubs.acs.org/OrgLett
Visible-Light-Induced Cascade Reaction of Isocyanides and
N‑Arylacrylamides with Diphenylphosphine Oxide via Radical C−P
and C−C Bond Formation
Chun-Xiao Li, De-Shuang Tu, Rui Yao, Hong Yan,* and Chang-Sheng Lu*
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing,
Jiangsu 210023, China
S
* Supporting Information
ABSTRACT: An effective photoredox-mediated tandem
phosphorylation/cyclization reaction of diphenylphosphine
oxide with three types of radical acceptors leads to P(O)Ph2-
containing phenanthridines, isoquinolines, and indolin-2-ones
by formation of both C−P and C−C bonds. [Ir-
(ppy)2(dtbpy)]PF6 (1 mol %) was used as the catalyst, CsF
or Cs2CO3 as the base, and K2S2O8 as the oxidant. A series of
functional groups can be tolerated at room temperature.
Moderate to good yields were generated.
rganophosphorous compounds have wide applications in
phosphorylation reactions through C−H activation (Scheme
Oorganic synthesis, as phosphorus ligands, in medicinal 1b-II),5 and other chemists have discovered direct oxidative
dehydrogenative coupling reactions (Scheme 1b-III).6 Fortu-
chemistry, as π-conjugated materials, as well as in inorganic
chemistry.1,2 Traditionally, C−P bond construction relies on
nately, the P−H bond of phosphine oxides prefers homolytic
cleavage with the mediation of Ag(I), Mn(III), or peroxides to
generate P-centered radicals.7 Inspired by this elegant reactivity,
researchers have already disclosed a series of methods to
incorporate a phosphoryl group to radical acceptors (Scheme
1c).7 Despite the present progress in our transition-metal-
mediated P-centered radical ring-closure approach, excess
amounts of silver or manganese salts and higher temperature
were applied, thereby resulting in a waste of transition metals
and energy.
Over the past few years, visible-light-induced photoredox
catalysis has grown at a dramatic pace due to the inherent green
character of light, high reactivity, and good functional group
tolerance.8 Although great efforts have been devoted to
preparative methods for synthesis of a variety of molecules
via a photoinduced single-electron transfer (SET) pathway, the
assembly of organophosphorus compounds from readily
available starting materials under a mild visible-light-mediated
process still remains scarce.9,10 Several recent studies have
shown that the P-centered radical could be generated by a
reductive quenching cycle of the excited state of photocatalyst
with diarylphosphine oxide.10 This might shed some light on a
new pathway for visible-light-induced organophosphorous
compound synthesis.
orthodox nucleophilic substitutions of poisonous R2P(O)Cl
with highly reactive organometallic reagents, which lead to
harsh conditions and a lack of functionality tolerance (Scheme
1a).1a This problem was not overcome until Hirao and co-
workers first realized phosphonation of aryl iodides or
bromides under catalysis of Pd(0).3 It appears that the
transition-metal-catalyzed coupling reaction of ArX (X = I,
OTs, COOZ, etc.) with R2P(O)H has been a powerful
platform for C(sp2)−P bond formation (Scheme 1b-I).4 Yu and
related groups have explored N-directed Pd(II)-catalyzed ortho-
Scheme 1. Construction of C−P Framework
2-Arylphenylisonitrile, which can be used to construct diverse
6-substituted phenanthridines, is a good candidate for radical
acceptors.7a,11 In 2014, Studer and co-workers first revealed an
efficient protocol on preparation of 6-phosphorylated phenan-
Received: August 12, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b02413
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Organic Letters
Letter
thridines by radical phosphorylation of isonitriles.7a Never-
theless, the above transformation required an excess amount of
AgOAc and high temperature. Therefore, it is promising to
exploit an effective, ecofriendly, and mild phosphorylation
strategy. With our continuous interest in exploitation of novel
phosphorescence iridium complexes12 and our endeavors
devoted to synthesis of N-containing organic compounds,13
we herein report on visible-light-induced phosphorylation/
cyclization cascade reactions of diarylphosphine oxide with
isocyanides and N-arylacrylamides.
a
Scheme 2. Scope of Biphenyl Isocyanides
We commenced our evaluation of the reaction parameters
employing 1a and 2a as model substrates (Table S1). The
combination of 1 mol % of Ir-I [Ir(ppy)2(dtbpy)PF6] and 2
equiv of K2CO3 with irradiation by a 23 W white lightbulb in
DMF under air or oxygen atmosphere for 12 h did not yield the
expected compound 3aa (entries 1 and 2). Very recently,
MacMillan and Jin took advantage of photogenerated sulfate
radical anion to activate the inert C(sp3)−H bond with strong
bond dissociation energy (BDE) through a hydrogen-atom-
transfer (HAT) pathway.14 We presumed that the desired P-
centered radical might be formed following this strategy. To
test this hypothesis, 3 equiv of K2S2O8 was added, and as
expected, the cross-coupling product 3aa was observed in a
yield of 56%. A base was found to have important influence on
this cascade reaction. The higher yield (82%) was obtained
when Cs2CO3 was used (entries 3 and 4). CsF was found to be
best, leading to a yield of 89% (entry 16). In addition, a series
of photocatalysts, including Ir(ppy)3, FIrpic, and Ru(bpy)3Cl2,
were examined, and Ir-I was found to be the best choice
(entries 4−7). Several other persulfates were screened as well,
and K2S2O8 was found to be the best choice (entries 4, 8, and
9). A survey of solvents demonstrated that DMF was the best
choice and that moisture can decrease the yield (entries 4 and
10−15). No desired product was detected if photocatalyst or
light irradiation was not applied, indicating that the photoredox
system is essential (entries 23 and 24).
a
Reaction conditions: 1a−q (0.3 mmol), 2a−e (0.9 mmol), K2S2O8
(0.9 mmol), CsF (0.6 mmol), Ir-I (0.003 mmol, 1 mol %), DMF (3
b
mL), 23 W CFL, under Ar for 12 h at rt. Gram-scale preparation of
3aa in an isolated yield of 81% (see the Supporting Information).
With the optimized conditions in hand, we investigated the
scope of biaryl isocyanides. As shown in Scheme 2, substrates
with substituents at the para position of the phenyl ring, such as
Me, H, OMe, F, Cl, t-Bu, and CF3, reacted efficiently to afford
the corresponding products in yields ranging from 60 to 85%
(3aa−ga). The examined ortho-substituted substrates led to
slightly lower yields (3ha, 3ia), probably due to steric reasons.
The pyridyl unit was also compatible as an electron-deficient
heteroarene, and 3ja was produced in a satisfactory yield of
67%. Although the substituent changes were made at the same
aryl ring as the isonitrile group in the substrates, good yields
were still obtained (3la−na). Interestingly, the reaction does
not occur if a strong electron-withdrawing group is located at
the para position (3oa,pa). However, if F substitution takes
place at the meta position, the transformation goes well (3qa).
Different phosphoryl sources were tested as well. Ideal yields
were afforded if di-p-tolylphosphine oxide (2b) and tert-
butyl(phenyl)phosphine oxide (2c) were employed, whereas
the yield was reduced sharply if ethyl pheylphosphinate (2d)
was used. No desired product was generated in the case of
diethyl phosphonate (2e).
(Scheme 3) were obtained after Cs2CO3 and an elongated
reaction time were utilized in comparison with the optimized
conditions in Scheme 2.
N-Arylacrylamide is another type of good radical receptor
that has been used to synthesize bioactive oxindoles through a
radical cyclization pathway.17 Next, we carried out preparation
of diverse oxindoles by our practical strategy. As shown in
Scheme 4, different substrates were screened. All substrates
with substituents at the para position of the arylacrylamides
reacted well (7aa−fa). Electron-withdrawing groups tend to
promote the reaction (7ea,fa). The substrate containing an N-
benzyl group also gave rise to good yield (7ia). However, N-
free arylacrylamide did not work (7ha). Steric hindrance at the
ortho-position led to reduced yields (7ga, 7ja, and 7ka).
Control reactions were executed to gain more insight into
this reaction. First, 2 equiv of TEMPO was enough to quench
the reaction of 2a and 6a (Scheme 5, eq 1), indicating that the
reaction proceeds in a radical pathway. Second, the
intermolecular kinetic isotopic effect was observed to be 1.0,
suggesting that the C−H bond cleavage is not the rate-
determine step (Scheme 5, eq 2).
Inspired by the successful application of this strategy in
preparing 6-phosphorylated phenanthridines, we decided to
apply this protocol to other systems. Recent studies indicate
that vinyl isocyanides are good radical acceptors as well.15
Hence, we set out to prepare less known 1-diphenylphosphoryl
isoquinoline derivatives.16 To our delight, 48−70% yields
On the basis of the mechanistic studies and literature, a
tentative mechanism is proposed in Scheme 6. The photo-
catalyst Ir-I(III) is activated by visible light to the excited-state
Ir-I(III)*, which then reduces persulfate anion to produce Ir-
I(IV), sulfate dianion, and sulfate radical anion. Thereafter, the
key intermediate P-centered radical would be generated
B
DOI: 10.1021/acs.orglett.6b02413
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Organic Letters
Letter
a
Scheme 3. Scope of Vinyl Isocyanides
Scheme 6. Plausible Mechanism
I(IV) to regenerate Ir-I(III) and produce the cation
intermediate III. Finally, in the presence of base, III undergoes
deprotonation to yield the desired product 3ia.
In summary, by using visible-light photocatalysis, we have
demonstrated a diphenylphosphinoyl radical cascade phosphor-
ylation and cyclization reaction. The reaction can be conducted
under mild conditions (room temperature, 23 W household
bulb irradiation), and the photocatalyst loading is as low as 1
mol %. Our process allows convenient and direct access to
three types of phosphorylated N-heterocycles in moderate to
excellent yields. In particular, a novel series of highly substituted
1-diphenylphosphoryl isoquinolines are afforded. The further
development of visible-light-promoted phosphorylation reac-
tions is ongoing in this laboratory.
a
Reaction conditions: 4a−f (0.3 mmol), 2a (0.9 mmol), K2S2O8 (0.9
mmol), Cs2CO3 (0.6 mmol), Ir-I (0.003 mmol, 1 mol %), DMF (3
mL), 23 W CFL, under Ar for 20 h at room temperature.
a
Scheme 4. Scope of N-Arylacrylamides
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.6b02413.
Crystallographic data for compound 3na (CIF)
Procedures and spectroscopic data (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
* E-mail: hyan1965@nju.edu.cn.
* E-mail: luchsh@nju.edu.cn.
Notes
a
Reaction conditions: 6a−k (0.3 mmol), 2a (0.9 mmol), K2S2O8 (0.9
mmol), Cs2CO3 (0.6 mmol), Ir-I (0.003 mmol, 1 mol %), DMF (3
mL), 23 W CFL, under Ar for 20 h at room temperature.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Scheme 5. Control Experiments for Mechanism
■
This work was supported by the National Natural Science
Foundation of China (21271102, 21472086, and 21531004)
and the National Basic Research Program of China
(2013CB922101).
REFERENCES
■
(1) For books and reviews, see: (a) Redmore, D. Chem. Rev. 1971,
71, 315. (b) Quin, L. D. A Guide to Organophosphorus Chemistry; Wiley
Interscience: New York, 2000. (c) Mucha, A.; Kafarski, P.; Berlicki, L.
J. Med. Chem. 2011, 54, 5955. (d) Baumgartner, T.; Rea
Rev. 2006, 106, 4681. (e) Ren, Y.; Baumgartner, T. Dalton Trans.
2012, 41, 7792. (f) Queffelec, C.; Petit, M.; Janvier, P.; Knight, D. A.;
Bujoli, B. Chem. Rev. 2012, 112, 3777. (g) Montchamp, J.-L. Acc.
Chem. Res. 2014, 47, 77. (h) Van der Jeught, S.; Stevens, C. V. Chem.
Rev. 2009, 109, 2672. (i) Tang, W.; Zhang, X. Chem. Rev. 2003, 103,
3029.
́
u, R. Chem.
through a HAT process between highly active sulfate radical
anion and 2a and then undergo intermolecular addition with
radical acceptor 1i to form radical intermediate I. Intra-
molecular cyclization of radical I subsequently produces a
cyclohexadienyl-type radical II, which can be oxidized by Ir-
́
C
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Organic Letters
Letter
(2) For selected research articles, see: (a) Wang, C.; Fukazawa, A.;
Taki, M.; Sato, Y.; Higashiyama, T.; Yamaguchi, S. Angew. Chem., Int.
(9) (a) Rueping, M.; Zhu, S.; Koenigs, R. M. Chem. Commun. 2011,
47, 8679. (b) Yoo, W. J.; Kobayashi, S. Green Chem. 2014, 16, 2438.
(10) (a) Yoo, W. J.; Kobayashi, S. Green Chem. 2013, 15, 1844.
(b) Xuan, J.; Zeng, T. T.; Chen, J. R.; Lu, L. Q.; Xiao, W. J. Chem. -
Eur. J. 2015, 21, 4962. (c) Luo, K.; Chen, Y.-Z.; Yang, W.-C.; Zhu, J.;
Wu, L. Org. Lett. 2016, 18, 452. (d) Quint, V.; Morlet-Savary, F.;
Ed. 2015, 54, 15213. (b) Nem
́
eth, G.; Greff, Z.; Sipos, A.; Varga, Z.;
i, S.; Nemes, Z.; Pirat, J. L.;
Szekely, R.; Sebestyen, M.; Jaszay, Z.; Ben
́
́
́
́
́
́
́
Volle, J. N.; Virieux, D.; Gyuris, A.; Kelemenics, K.; Ay, E.; Minarovits,
̋
J.; Szathmary, S.; Ker
́
i, G.; Orfi, L. J. Med. Chem. 2014, 57, 3939.
Lohier, J.-F.; Lalevee
2016, 138, 7436.
́
, J.; Gaumont, A.-C.; Lakhdar, S. J. Am. Chem. Soc.
(c) Cao, Y.; Nagle, J. K.; Wolf, M. O.; Patrick, B. O. J. Am. Chem. Soc.
2015, 137, 4888. (d) Yamaguchi, E.; Wang, C.; Fukazawa; Taki, A. M.;
Sato, Y.; Sasaki, T.; Ueda, M.; Sasaki, N.; Higashiyama, T.; Yamaguchi,
S. Angew. Chem., Int. Ed. 2015, 54, 4539. (e) Romero-Nieto, C.;
Lopez-Andarias, A.; Egler-Lucas, C.; Gebert, F.; Neus, J.-P.; Pilgram,
́
O. Angew. Chem., Int. Ed. 2015, 54, 15872.
(11) (a) Zhang, B.; Muck-Lichtenfeld, C.; Daniliuc, C. G.; Studer, A.
̈
Angew. Chem., Int. Ed. 2013, 52, 10792. (b) Tobisu, M.; Koh, K.;
Furukawa, T.; Chatani, N. Angew. Chem., Int. Ed. 2012, 51, 11363.
(c) Sun, X.; Yu, S. Org. Lett. 2014, 16, 2938. (d) Liu, J.; Fan, C.; Yin,
H.; Qin, C.; Zhang, G.; Zhang, X.; Yi, H.; Lei, A. Chem. Commun.
2014, 50, 2145. (e) Wang, L.; Zhu, H.; Guo, S.; Cheng, J.; Yu, J.-T.
Chem. Commun. 2014, 50, 10864. (f) Wang, L.; Sha, W.; Dai, Q.; Feng,
X.; Wu, W.; Peng, H.; Chen, B.; Cheng, J. Org. Lett. 2014, 16, 2088.
(12) (a) Shi, C.; Sun, H.; Jiang, Q.; Zhao, Q.; Wang, J.; Huang, W.;
Yan, H. Chem. Commun. 2013, 49, 4746. (b) Shi, C.; Sun, H.; Tang,
X.; Lv, W.; Yan, H.; Zhao, Q.; Wang, J.; Huang, W. Angew. Chem., Int.
Ed. 2013, 52, 13434. (c) Zhu, L.; Tang, X.; Yu, Q.; Lv, W.; Yan, H.;
Zhao, Q.; Huang, W. Chem. - Eur. J. 2015, 21, 4721.
(3) Hirao, T.; Masunaga, T.; Yamada, N. Bull. Chem. Soc. Jpn. 1982,
55, 909.
(4) For transition-metal-catalyzed C−P bond formation from ArX
and H-phosphonates, see: (a) Yang, J.; Chen, T.; Han, L. B. J. Am.
Chem. Soc. 2015, 137, 1782. (b) Zhang, J. S.; Chen, T.; Yang, J.; Han,
L. B. Chem. Commun. 2015, 51, 7540. (c) Zhao, Y. L.; Wu, G. J.; Han,
F. S. Chem. Commun. 2012, 48, 5868. (d) Petrakis, K. S.;
Nagabhushan, T. L. J. Am. Chem. Soc. 1987, 109, 2831. (e) Fu, W.
C.; So, C. M.; Kwong, F. Y. Org. Lett. 2015, 17, 5906. (f) Hu, G.;
Chen, W.; Fu, T.; Peng, Z.; Qiao, H.; Gao, Y.; Zhao, Y. Org. Lett. 2013,
15, 5362. (g) Shen, C.; Yang, G.; Zhang, W. Org. Biomol. Chem. 2012,
10, 3500. (h) Fu, T.; Qiao, H.; Peng, Z.; Hu, G.; Wu, X.; Gao, Y.;
Zhao, Y. Org. Biomol. Chem. 2014, 12, 2895.
(5) For N-directed, Pd(II)-catalyzed phosphorylation reactions, see:
(a) Feng, C. G.; Ye, M.; Xiao, K. J.; Li, S.; Yu, J. Q. J. Am. Chem. Soc.
2013, 135, 9322. (b) Li, C.; Yano, T.; Ishida, N.; Murakami, M. Angew.
Chem., Int. Ed. 2013, 52, 9801. (c) Hong, G.; Mao, D.; Wu, S.; Wang,
L. J. Org. Chem. 2014, 79, 10629.
(6) For direct oxidative dehydrogenative coupling reactions, see:
(a) Ke, J.; Tang, Y.; Yi, H.; Li, Y.; Cheng, Y.; Liu, C.; Lei, A. Angew.
Chem., Int. Ed. 2015, 54, 6604. (b) Zhu, Y.; Chen, T.; Li, S.; Shimada,
S.; Han, L.-B. J. Am. Chem. Soc. 2016, 138, 5825. (c) Wang, T.; Chen,
S.; Shao, A.; Gao, M.; Huang, Y.; Lei, A. Org. Lett. 2015, 17, 118.
(d) Zhou, A. X.; Mao, L. L.; Wang, G. W.; Yang, S. D. Chem. Commun.
2014, 50, 8529. (e) Yang, J.; Chen, T.; Zhou, Y.; Yin, S.; Han, L. B.
Chem. Commun. 2015, 51, 3549. (f) Zhang, H. J.; Lin, W.; Wu, Z.;
Ruan, W.; Wen, T. B. Chem. Commun. 2015, 51, 3450. (g) Huo, C.;
Wang, C.; Wu, M.; Jia, X.; Wang, X.; Yuan, Y.; Xie, H. Org. Biomol.
(13) (a) Jiang, Q.; Duan-Mu, D.; Zhong, W.; Chen, H.; Yan, H.
Chem. - Eur. J. 2013, 19, 1903. (b) Ji, Y. F.; Yan, H.; Jiang, Q. B. Eur. J.
Org. Chem. 2015, 2015, 2051. (c) Dai, H.; Yu, C.; Lu, C.; Yan, H. Eur.
J. Org. Chem. 2016, 2016, 1255. (d) Dai, H.; Yu, C.; Wang, Z.; Yan, H.;
Lu, C. Org. Lett. 2016, 18, 3410.
(14) Jin, J.; MacMillan, D. W. C. Angew. Chem., Int. Ed. 2015, 54,
1565.
(15) (a) Jiang, H.; Cheng, Y.; Wang, R.; Zhang, Y.; Yu, S. Chem.
Commun. 2014, 50, 6164. (b) Wang, H.; Yu, Y.; Hong, X.; Xu, B.
Chem. Commun. 2014, 50, 13485. (c) Zhang, B.; Studer, A. Org.
Biomol. Chem. 2014, 12, 9895.
(16) Wang, X.; Wang, Z. Tetrahedron 2014, 70, 5720.
(17) (a) Wei, W. T.; Zhou, M. B.; Fan, J. H.; Liu, W.; Song, R. J.; Liu,
Y.; Hu, M.; Xie, P.; Li, J. H. Angew. Chem., Int. Ed. 2013, 52, 3638.
(b) Xie, J.; Xu, P.; Li, H.; Xue, Q.; Jin, H.; Cheng, Y.; Zhu, C. Chem.
Commun. 2013, 49, 5672. (c) Xu, P.; Xie, J.; Xue, Q.; Pan, C.; Cheng,
Y.; Zhu, C. Chem. - Eur. J. 2013, 19, 14039. (d) Dai, Q.; Yu, J.; Jiang,
Y.; Guo, S.; Cheng, J. Chem. Commun. 2014, 50, 3865. (e) Song, R.-J.;
Liu, Y.; Xie, Y.-X.; Li, J.-H. Synthesis 2015, 47, 1195. (f) Mai, W.;
Wang, J.; Yang, L.; Yuan, J.; Mao, P.; Xiao, Y.; Qu, L. Youji Huaxue
2014, 34, 1958. (g) Chen, J.-R.; Yu, X.-Y.; Xiao, W.-J. Synthesis 2015,
47, 604.
́
Chem. 2014, 12, 3123. (h) Basle, O.; Li, C.-J. Chem. Commun. 2009,
45, 4124. (i) Kuninobu, Y.; Yoshida, T.; Takai, K. J. Org. Chem. 2011,
76, 7370. (j) Kagayama, T.; Nakano, A.; Sakaguchi, S.; Ishii, Y. Org.
Lett. 2006, 8, 407. (l) Gao, M.; Li, Y.; Xie, F.; Chauvin, R.; Cui, X.
Chem. Commun. 2016, 52, 2846. (m) Hou, C.; Ren, Y.; Lang, R.; Hu,
X.; Xia, C.; Li, F. Chem. Commun. 2012, 48, 5181.
(7) For recent reported phosphorylation/cyclization reactions, see:
(a) Zhang, B.; Daniliuc, C. G.; Studer, A. Org. Lett. 2014, 16, 250.
(b) Furukawa, S.; Haga, S.; Kobayashi, J.; Kawashima, T. Org. Lett.
2014, 16, 3228. (c) Zhou, Z. Z.; Jin, D. P.; Li, L. H.; He, Y. T.; Zhou,
P. X.; Yan, X. B.; Liu, X. Y.; Liang, Y. M. Org. Lett. 2014, 16, 5616.
(d) Mi, X.; Wang, C.; Huang, M.; Zhang, J.; Wu, Y.; Wu, Y. Org. Lett.
2014, 16, 3356. (e) Gao, Y.; Li, X.; Xu, J.; Wu, Y.; Chen, W.; Tang, G.;
Zhao, Y. Chem. Commun. 2015, 51, 1605. (f) Li, D. P.; Pan, X. Q.; An,
L. T.; Zou, J. P.; Zhang, W. J. Org. Chem. 2014, 79, 1850. (g) Li, Y. M.;
Sun, M.; Wang, H. L.; Tian, Q. P.; Yang, S. D. Angew. Chem., Int. Ed.
2013, 52, 3972. (h) Kong, W.; Merino, E.; Nevado, C. Angew. Chem.,
Int. Ed. 2014, 53, 5078. (i) Chen, Y. R.; Duan, W. L. J. Am. Chem. Soc.
2013, 135, 16754. (j) Unoh, Y.; Hirano, K.; Satoh, T.; Miura, M.
Angew. Chem., Int. Ed. 2013, 52, 12975.
(8) For selected reviews of visible-light photoredox catalysis, see:
(a) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev. 2013,
113, 5322. (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) Xuan, J.; Xiao, W. J. Angew. Chem., Int. Ed. 2012, 51,
6828. (e) Romero, N. A.; Nicewicz, D. A. Chem. Rev. 2016, 116,
10075. (f) Xuan, J.; Zhang, Z.-G.; Xiao, W.-J. Angew. Chem., Int. Ed.
2015, 54, 15632. (g) Chen, J.-R.; Hu, X.-Q.; Lu, L.-Q.; Xiao, W.-J.
Chem. Soc. Rev. 2016, 45, 2044.
D
DOI: 10.1021/acs.orglett.6b02413
Org. Lett. XXXX, XXX, XXX−XXX