Functionalized Tetrahydropyridines by Enantioselective Phosphine-Catalyzed Aza-[4 + 2] Cycloaddition of N-Sulfonyl-1-aza-1,3-dienes with Vinyl Ketones

Article abstract of DOI:10.1021/acs.orglett.7b00489

The development of electron-demand disfavored [4 + 2] cycloaddition of two electron-deficient reacting partners poses a considerable challenge. An enantioselective aza-[4 + 2] cycloaddition of electron-deficient N-sulfonyl-1-aza-1,3-dienes is possible with vinyl ketones via phosphine catalysis, which provides facile access to a wide range of enantioenriched trifluoromethylated tetrahydropyridines in up to 97% yield with 97% ee and >20:1 dr. The mechanistic study indicated that this cycloaddition proceeds via a tandem intermolecular aza-Rauhut-Currier/intramolecular aza-Michael addition reaction.

Full text of DOI:10.1021/acs.orglett.7b00489

Letter
pubs.acs.org/OrgLett
Functionalized Tetrahydropyridines by Enantioselective Phosphine-
Catalyzed Aza-[4 + 2] Cycloaddition of N‑Sulfonyl-1-aza-1,3-dienes
with Vinyl Ketones
Huamin Wang, Wei Zhou, Mengna Tao, Anjing Hu, and Junliang Zhang*
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China
Normal University, 3663 North Zhongshan Road, Shanghai 200062, P. R. China
S
* Supporting Information
ABSTRACT: The development of electron-demand disfavored [4 + 2] cycloaddition of two electron-deficient reacting partners
poses a considerable challenge. An enantioselective aza-[4 + 2] cycloaddition of electron-deficient N-sulfonyl-1-aza-1,3-dienes is
possible with vinyl ketones via phosphine catalysis, which provides facile access to a wide range of enantioenriched
trifluoromethylated tetrahydropyridines in up to 97% yield with 97% ee and >20:1 dr. The mechanistic study indicated that this
cycloaddition proceeds via a tandem intermolecular aza-Rauhut−Currier/intramolecular aza-Michael addition reaction.
etrahydropyridines are an important class of six-
membered nitrogen-containing heterocycles which are
with alkyl vinyl ketones have been reported by Loh and
Zhong,6a Shi,6b,c and Wu6d by utilizing the chiral phosphine
catalysts derived from natural or unnatural amino acids.
However, the development of more efficient new chiral
phosphine catalyst to further expand the range of N-sulfonyl-
1-aza-1,3-butadienes is still desirable.
T
widely found in a variety of natural products and biologically
active compounds (Figure 1).1 Meanwhile, tetrahydropyridines
Meanwhile, the introduction of a CF3 group at a specific site
to a bioactive molecule is considered as a more and more useful
strategy to improve its physicochemical, biological, and
pharmaceutical properties;7 for example, a trifluoromethylated
piperidine was introduced to the janus kinase inhibitors, which
observed a significant enhancement of its pharmaceutical
activity (Figure 1).8 However, the asymmetric synthesis of
trifluoromethylated heterocycles is largely lagging due to the
limited availability of trifluoromethylated substrates and robust
chiral catalysts. Recently, we developed several new phosphine
catalysts, such as Xiao-Phos, Wei-Phos, and Peng-Phos, which
have shown good performance in enantioselective Rauhut−
Currier reactions and allylation reactions.9 With these chiral
phosphine catalysts in hand, we wished to examine their
performance in the enantioselective aza-[4 + 2] cycladdition.
Herein, we wish to report the first phosphine catalyzed
asymmetric aza-[4 + 2] cycloadditions of 1-aza-1,3-butadienes
derived from β-fluoroalkylated-α,β-enones with vinyl ketones,
which provide a facile access to valuable chiral fluoroalkylated
tetrahydropyridines (Scheme 1). Besides β-fluoroalkylated α,β-
enone derived imines, the chalcone-derived imines could also
furnish the desired products with satisfactory diastereo- and
Figure 1. Bioactive molecules having tetrahydropyridine and
piperidine cores.
are important organic synthons which can be readily reduced to
piperidines.2 Therefore, tremendous efforts for the synthesis of
tetrahydropyridines, especially in an asymmetric manner, have
been undertaken, among which an organocatalytic [4 + 2]
cycloaddition reaction3 has been widely recognized as one of
powerful approaches. However, compared to the well-
established Brønsted acids4a−e and proline4f−h-catalyzed
enantioselective aza-[4 + 2] cycloaddition reactions, the
development of other organocatalysts such as chiral phosphine5
has been less explored and unbalanced. To date, only a few
examples of asymmetric phosphine-catalyzed intermolecular
aza-[4 + 2] cycloadditions of N-sulfonyl-1-aza-1,3-butadienes
Received: February 17, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b00489
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Scheme 1. Enantioselective Phosphine-Catalyzed Aza [4 + 2]
Cycloaddition
Table 1. Variation of Aza Diene and Aryl Vinyl Ketone
Components
a
b
entry
1, R1/Rf
Ar
yield (%) ee (%)
enantioselectivity. Furthermore, the mechanistic study indi-
cated that this cycloaddition proceeds via a tandem
intermolecular aza-Rauhut−Currier/intramolecular aza-Michael
addition reaction.
Aza diene 1a and vinyl ketone 2a were selected as model
substrates for screening chiral phosphine catalysts (Figure 2).
1
2
3
4
5
6
7
8
9
1a, Ph/CF3
2a, Ph
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
3aa, 92
3ba, 91
3ca, 84
3da, 94
3ea, 83
3fa, 88
3ga, 90
3ha, 92
3ia, 82
3ja, 88
3ka, 62
3la, 97
3ma, 96
3na, 90
3oa, 92
3pa, 92
3qa, 72
3ra, 93
3sa, 79
3ta, 65
3va, 70
3cb, 84
3cc, 90
3cd, 90
3ce, 75
3cf, 85
3cg, 84
3ch, 60
3ci, 60
3cj, 74
3ck, 95
3cl, 89
95
95
94
95
91
94
96
96
92
91
95
91
85
95
94
97
92
94
94
92
82
92
92
93
91
90
92
90
92
90
90
93
c
1b, 4-MeC6H4/CF3
1c, 4-MeOC6H4/CF3
1d, 4-PhC6H4/CF3
1e, 4-FC6H4/CF3
1f, 4-ClC6H4/CF3
1g, 4-BrC6H4/CF3
1h, 4-IC6H4/CF3
1i, 4-NCC6H4/CF3
1j, 4-MeO2CC6H4/CF3
1k, 4-MeO2SC6H4/CF3
1l, 2-FC6H4/CF3
1m, 2-O2NC6H4/CF3
1n, 3-ClC6H4/CF3
1o, 3-BrC6H4/CF3
1p, 2-naphthyl/CF3
1q, 2-furyl/CF3
1r, Ph/CF3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Figure 2. Phosphine catalysts employed in this study.
d
e
To our delight, chiral sulfinamide phosphines (P1 and P2)
could catalyze the reaction, but low yields and ee values were
obtained (Table S1, entries 1 and 2). Further screening showed
that the amide moiety plays a significant effect on the
enantioselectivity; the acetyl- (P3) and p-toluoyl- derived
(P4) amide phosphines delivered relatively lower ee’s (Table
S1, entries 3 and 4), while phosphine P5 bearing a more acidic
amide moiety derived from 3,5-ditrifluoromethylbenzonic acid
turned out to be a promising catalyst, furnishing the desired [4
+ 2] cycloaddition product in 77% yield with 90% ee (Table S1,
entry 5). The introduction of different aryl groups at the ortho-
position of the phenyl ring, structured as P6 and P7, resulted in
elevated enantioselectivity and diastereoselectivity (Table S1,
entries 6 and 7). With the use of the best catalyst P7 as the
catalyst, various solvents were then screened, and acetone was
found to be the best solvent with regard to activity (Table S1,
entries 8−12). Further increase of the catalyst loading to 7.5
mol % led to a slightly higher yield (Table S1, entry 13). A
slightly higher ee was observed when the reaction was run at 0
°C but led to lower yield (Table S1, entry 14).
1s, Ph/CF3
1t, Ph/C2F5
1v, cyclopropyl/CF3
1c
2b, 4-MeC6H4
2c, 4-MeOC6H4
2d, 4-PhC6H4
2e, 4-FC6H4
1c
1c
1c
1c
2f, 4-ClC6H4
2g, 4-BrC6H4
2h, 4-O2NC6H4
2i, 4-NCC6H4
2j, 4-CF3C6H4
2k, 2-naphthyl
2l, 2-furyl
1c
1c
d
d
1c
1c
1c
1c
a
Yield of isolated trans isomer, dr >20:1; determined by 19F NMR
analysis of the crude reaction mixture. Determined by HPLC analysis.
10 mol % of P7 was used. 10 mol % of P7 was used at 0 °C. 10 mol
% of P7 was used at −20 °C.
b
c
d
e
With the optimal reaction conditions in hand, we then
turned to explore the generality of this cycloaddition process
with a variety of 1-aza-1,3-dienes with ketone 2a (Table 1).
Regardless of their electronic nature and the substitution
pattern of the aryl ring, high yields and ee values were furnished
(Table 1, entries 1−15). The 2-naphthyl group and heterocyclic
ring were also applicable, furnishing the corresponding
products 3pa and 3qa in 72−92% yields with 92−97% ee’s
(Table 1, entries 16 and 17). When the substituent R2 on N-
sulfonylimine 1 was changed, other groups, including p-
methoxyphenyl and phenyl, were all well tolerated in the
reactions (Table 1, entries 18 and 19). Changing the fluoroalkyl
group from a CF3 group to the C2F5 group also worked well to
give the corresponding product 3ta with 92% ee in 65% yield
(Table 1, entry 20). Notably, alkyl-substituted β-trifluoroalkyl
α,β-enone derived imine also worked well giving rise to the
fused heterocyclic 3va in acceptable yield with 82% ee (Table 1,
entry 21). Moreover, we examined the scope of the
cycloaddition reaction of 1c with a series of aryl vinyl ketones
2. Aryl vinyl ketones with electron-donating groups such as 4-
Me (2b), 4-OMe (2c), and 4-Ph (2d) on the phenyl ring
exhibited higher enantioselectivity (Table 1, entries 22−24).
Halogenated substrates 2e−g were also well tolerated, affording
the corresponding products 3ce−cg in 75−85% yields with
90−92% ee (Table 1, entries 25−27). Vinyl ketones 2h−j with
electron-withdrawing aromatic rings also successfully afforded
the corresponding products 3ch−cj with good to excellent
enantioselectivity (Table 1, entries 28−30). 2-Naphthyl- and 2-
furyl-substituted vinyl ketones afforded the desired products in
90% and 93% ee, respectively (Table 1, entries 31 and 32).
Next, we turned our attention to the challenge of
enantioselective [4 + 2] cycloaddition of alkyl vinyl ketones
with β-fluoroalkylated enone derived imines. For the alkyl vinyl
B
DOI: 10.1021/acs.orglett.7b00489
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ketones, catalyst P6 was identified as the best catalyst, and the
substrate scope was then examined (Table S2). In general, the
reaction worked quite well, delivering the corresponding
products with excellent ee values and high dr values. Similar
to the reaction with aryl vinyl ketone, in general, β-
fluoroalkylated enone derived imines with electronically and
sterically different aromatic groups were also examined, and the
reaction could proceed smoothly to afford the desired products
(3bn−fo) with high stereoselectivity (Table S2, entries 1−13).
The absolute configuration of 3dn was established by single-
crystal X-ray diffraction analysis10 (see the SI).
Scheme 2. Gram-Scale Synthesis of 3a and Further Synthetic
Transformations
a
The enantioselective cycloaddition between chalcone-derived
imines (4) and methyl vinyl ketone (2n) poses considerable
challenges due to their relatively lower reactivity.7a,7 Inspired
a
d
Gram-scale reaction and synthetic applications. Reaction conditions:
by above results and with diverse catalysts in hand, we made
our efforts to this cycloaddition. Gratifyingly, as shown in Table
2, the corresponding cycloadducts 5an−fn could be obtained in
(a) P7 (5 mol %), 1a (2.8 mmol), 2a (1.5 equiv), acetone (0.1 M), rt,
88% yield, 94% ee, dr > 20:1; (b) NaBH4, 0 °C, 90% yield, 90% ee, dr
> 20:1; (c) RuCl3, NaIO4, 0 °C, 75% yield, 92% ee, dr > 20:1; (d)
TFA/thioanisole, rt, 70% yield, 93% ee, dr > 20:1; (e) BF3·Et2O,
Et3SiH, 70 °C, 80% yield, 94% ee, dr > 20:1; (f) NaCNBH3, MeOH/
AcOH, rt, 94% ee, dr >20:1.
Table 2. [4 + 2] Cycloaddition of Methyl Vinyl Ketones with
a
Chalcone-Derived Imines
idine 6d was also obtained in good yield by chemoselective
reduction the olefin moiety of 3aa without any reduction of the
carbonyl group.
In summary, we have developed an enantioselective
phosphine-catalyzed aza-[4 + 2] cycloaddition of N-sulfonyl-
1-aza-1,3-dienes with vinyl ketones, which provides a facile
access to various functional trifluoromethylated tetrahydropyr-
idines in moderate to good yields with high diastereo- and
enantioselectivities. Mechanistic study11 indicated that this aza-
[4 + 2] cycloaddition proceeded via a tandem aza-Rauhut−
Currier/intramolecular aza-Michael addition reaction. Further-
more, the phosphonium enolate intermediate12 plays a dual
role, acting as a key intermediate for the first aza-Rauhut−
Currier reaction and a real catalyst for the second aza-Michael
addition step. Further efforts toward the application of these
novel multifunctional phosphine catalysts for other asymmetric
transformations are currently underway in our group and will
be reported in due course.
b
c
entry
R1
dr
yield (%)
ee (%)
1
2
3
4
5
6
7
4a, Ph
13:1
12:1
13:1
10:1
13:1
12:1
>20:1
5an, 70
5bn, 65
5cn, 60
5dn, 60
5en, 63
5fn, 67
5gn, 75
90
90
90
90
92
90
92
4b, 4-MeoC6H4
4c, 4-FC6H4
4d, 4-ClC6H4
4e, 4-BrC6H4
4f, 4-CF3C6H4
4g, perfluorophenyl
a
Unless otherwise stated, reactions were performed by using 0.1 mmol
of 4, 0.3 mmol of 2n, 10 mol % of P2, and 30 mol % of 2-chlorophenol
in 1.0 mL of CHCl3 at 0 °C for 72 h. Yield of isolated cycloadduct.
b
c
Determined by HPLC analysis.
60−70% yields with 90−92% ee’s regardless of the substituent,
from electron-donating group MeO to weak electron-with-
drawing groups such as F, Cl, and Br and even strong electron-
withdrawing group CF3 with the chiral sulfinamide phosphine
P2 as the catalyst, indicating that this type of cycloaddition is
sensitive to the structure of the substrate and an appropriate
catalyst must be correctly chosen. In addition, pentafluoro-
substituted N-tosyl ketimine gave the product 5gn with 75%
yield and 92% ee (Table 2, entry 7).
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.7b00489.
Experimental procedures; spectroscopic data for the
substrates and products (PDF)
In order to display the potential synthetic applications of this
methodology, a gram-scale reaction of 1a and 2a was also
carried out to furnish 1.2 g of the desired product 3aa in 88%
yield and 94% ee with the use of 5 mol % of P7 as the catalyst
(Scheme 2). The selective reduction of carbonyl group
provided effective access to valuable chiral alcohol 6a in 90%
yield as a single diastereomer (>20:1 dr) and 90% ee. The
diastereoselective dihydroxylation of the olefin moiety with
RuCl3/NaIO4 delivered a functionalized piperidine 6b in 75%
yield with 92% ee. The deprotection of tosyl group was realized
by treatment of 3aa with TFA/thioanisole, and the imine
product 6c was obtained as single diastereomer in 70% yield
with 93% ee and trifluoromethylated piperidine 7c was
furnished in 90% yield with 94% ee by subsequent reduction
with sodium cyanoborohydride. The enantioenriched piper-
X-ray data for (−)-3dn (CIF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: jlzhang@chem.ecnu.edu.cn.
ORCID
Junliang Zhang: 0000-0002-4636-2846
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We are grateful to the 973 Program (2015CB856600), the
National Natural Science Foundation of China (21425205,
■
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DOI: 10.1021/acs.orglett.7b00489
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
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(6) (a) Shi, Z.; Yu, P.; Loh, T.-P.; Zhong, G. Angew. Chem., Int. Ed.
2012, 51, 7825. (b) Zhang, X.; Chen, G.; Dong, X.; Wei, Y.; Shi, M.
Adv. Synth. Catal. 2013, 355, 3351. (c) Zhang, X. N.; Dong, X.; Wei,
Y.; Shi, M. Tetrahedron 2014, 70, 2838. (d) Wang, G.; Rexiti, R.; Sha,
F.; Wu, X. Tetrahedron 2015, 71, 4255.
21672067), and the Changjiang Scholars and Innovative
Research Team in University (PCSIRT) for financial support.
REFERENCES
■
(1) (a) Nantermet, P. G.; Barrow, J. C.; Selnick, H. G.; Homnick, C.
F.; Freidinger, R. M.; Chang, R. S. L.; O’Malley, S. S.; Reiss, D. R.;
Broten, T. P.; Ransom, R. W.; Pettibone, D. J.; Olah, T.; Forray, C.
Bioorg. Med. Chem. Lett. 2000, 10, 1625. (b) Michael, J. P. Nat. Prod.
Rep. 2004, 21, 625. (c) Maison, W. Pipecolic Acid Derivatives. In
Highlights in Bioorganic Chemistry; Wiley-VCH: New York, 2004; p 18.
(d) Kawagishi, F.; Toma, T.; Inui, T.; Yokoshima, S.; Fukuyama, T. J.
Am. Chem. Soc. 2013, 135, 13684. (e) Lei, B. L.; Zhang, Q. S.; Yu, W.
H.; Ding, Q. P.; Ding, C. H.; Hou, X. L. Org. Lett. 2014, 16, 1944.
(f) Aridoss, G.; Amirthaganesan, S.; Jeong, Y. T. Bioorg. Med. Chem.
Lett. 2010, 20, 2242.
(7) For leading references, see: (a) Fujita, T.; Iwasa, J.; Hansch, C. J.
Am. Chem. Soc. 1964, 86, 5175. (b) Leo, A.; Hansch, C.; Elkins, D.
Chem. Rev. 1971, 71, 525. (c) Katritzky, A. R.; Lobanov, V. S.;
Karelson, M. Chem. Soc. Rev. 1995, 24, 279. (d) Huang, Y. Y.; Yang, X.;
Chen, Z.; Verpoort, F.; Shibata, N. Chem. - Eur. J. 2015, 21, 8664.
(8) For janus kinase inhibitors, see: (a) Childers, M. L.; Fuller, P.;
Guerin, D.; Katz, J. D.; Pu, Q.; Scott, M. E.; Thompson, C. F.;
Martinez, M.; Falcone, D.; Torres, L.; Deng, Y.; Kuruklasuriya, R.;
Zeng, H.; Bai, Y.; Kong, N.; Liu, Y.; Zheng, Z. WO Patent
2014146491, A1, 2014. (b) Dinsmore, C.; Fuller, P.; Guerin, D.;
Katz, J. D.; Thompson, C. F.; Falcone, D.; Deng, W.; Torres, L.; Zeng,
H.; Bai, Y.; Fu, J.; Kong, N.; Liu, Y.; Zheng, Z. WO Patent
2014146493, A1, 2014.
(9) (a) Su, X.; Zhou, W.; Li, Y.; Zhang, J. Angew. Chem., Int. Ed. 2015,
54, 6874. (b) Zhou, W.; Su, X.; Tao, M.; Zhu, C.; Zhao, Q.; Zhang, J.
Angew. Chem., Int. Ed. 2015, 54, 14853. (c) Zhou, W.; Chen, P.; Tao,
M.; Su, X.; Zhao, Q.; Zhang, J. Chem. Commun. 2016, 52, 7612.
(d) Chen, P.; Yue, Z.; Zhang, J.; Lv, X.; Wang, L.; Zhang, J. Angew.
Chem., Int. Ed. 2016, 55, 13316. (e) Zhou, W.; Gao, L.; Tao, M.; Su,
X.; Zhao, Q.; Zhang, J. Huaxue Xuebao 2016, 74, 800.
(10) The X-ray crystal structure information is available at the
Cambridge Crystallographic Data Centre (CCDC) under deposition
no. CCDC 1500207 ((−)-3dn).
(11) Details of experiments and results are summarized in the
Supporting Information.
(12) Some examples for phosphonium enolate as Brønsted base:
(a) Wang, H.-Y.; Zhang, K.; Zheng, C.-W.; Chai, Z.; Cao, D.-D.;
Zhang, J.-X.; Zhao, G. Angew. Chem., Int. Ed. 2015, 54, 1775. (b) Lou,
Y.-P.; Zheng, C.-W.; Pan, R.-M.; Jin, Q.-W.; Zhao, G.; Li, Z. Org. Lett.
2015, 17, 688. (c) Wang, H.-Y.; Zheng, C.-W.; Chai, Z.; Zhang, J.-X.;
Zhao, G. Nat. Commun. 2016, 7, 12720.
(2) (a) Rubiralta, M.; Giralt, E.; Diez, A. Piperidine: Struture,
Preparation, Reactivity, and Synthetic Applications of Piperidine and Its
Derivatives; Elsevier: New York, 1991. (b) Hwang, Y. C.; Fowler, F. W.
J. Org. Chem. 1985, 50, 2719. (c) Michael, J. P. Nat. Prod. Rep. 2004,
21, 625. (d) Sahn, J. J.; Su, J. Y.; Martin, S. F. Org. Lett. 2011, 13, 2590.
(e) Sahn, J. J.; Martin, S. F. Tetrahedron Lett. 2011, 52, 6855. (f) Jian,
T.; Sun, L.; Ye, S. Chem. Commun. 2012, 48, 10907.
(3) For a review of [4 + 2] cycloadditions, see: (a) Klier, L.; Tur, F.;
Poulsen, P. H.; Jørgensen, K. A. Chem. Soc. Rev. 2017, 46, 1080.
(b) Jeon, B.-S.; Wang, S.-A.; Ruszczycky, M. W.; Liu, H.-W. Chem. Rev.
2016, DOI: 10.1021/acs.chemrev.6b00578. (c) Masson, G.; Lalli, C.;
Benohoud, M.; Dagousset, G. Chem. Soc. Rev. 2013, 42, 902.
(4) For selected examples of chiral Brønsted acids catalyed by aza-[4
+ 2] cycloaddition, see: (a) Dagousset, G.; Retailleau, P.; Masson, G.;
Zhu, J. Chem. - Eur. J. 2012, 18, 5869. (b) Dagousset, G.; Zhu, J.;
Masson, G. J. Am. Chem. Soc. 2011, 133, 14804. (c) Xu, A. H.; Zuend,
S. J.; Woll, M. G.; Tao, Y.; Jacobsen, E. N. Science 2010, 327, 986.
(d) Liu, H.; Dagousset, G.; Masson, G.; Retailleau, P.; Zhu, J. J. Am.
Chem. Soc. 2009, 131, 4598. (e) Akiyama, T.; Morita, H.; Fuchibe, K. J.
Am. Chem. Soc. 2006, 128, 13070. For recent examples of proline-
catalyed aza-[4 + 2] cycloaddition, see: (f) Han, B.; He, Z.-Q.; Li, J.-L.;
Li, R.; Jiang, K.; Liu, T.-Y.; Chen, Y.-C. Angew. Chem., Int. Ed. 2009,
́ ́
48, 5474. (g) Sunden, H.; Ibrahem, I.; Eriksson, L.; Cordova, A. Angew.
Chem., Int. Ed. 2005, 44, 4877. (h) Li, J.-L.; Liu, T.-Y.; Chen, Y.-C. Acc.
Chem. Res. 2012, 45, 1491.
(5) For reviews related to phosphines catalysis, see: (a) Ye, L.-W.;
Zhou, J.; Tang, Y. Chem. Soc. Rev. 2008, 37, 1140. (b) Cowen, B. J.;
Miller, S. J. Chem. Soc. Rev. 2009, 38, 3102. (c) Wei, Y.; Shi, M. Acc.
Chem. Res. 2010, 43, 1005. (d) Wang, S.-X.; Han, X.; Zhong, F.; Wang,
Y.; Lu, Y. Synlett 2011, 2011, 2766. (e) Zhao, Q.-Y.; Lian, Z.; Wei, Y.;
Shi, M. Chem. Commun. 2012, 48, 1724. (f) Wei, Y.; Shi, M. Chem.
Rev. 2013, 113, 6659. (g) Fan, Y.; Kwon, O. Chem. Commun. 2013, 49,
11588. (h) Xie, P.; Huang, Y. Eur. J. Org. Chem. 2013, 2013, 6213.
(i) Wang, Z.; Xu, X.; Kwon, O. Chem. Soc. Rev. 2014, 43, 2927.
(j) Voituriez, A.; Marinetti, A.; Gicquel, M. Synlett 2015, 26, 142.
(k) Xie, P.; Huang, Y. Org. Biomol. Chem. 2015, 13, 8578. (l) Li, W.;
Zhang, J. Chem. Soc. Rev. 2016, 45, 1657. (m) Wang, T.; Han, X.;
Zhong, F.; Yao, W.; Lu, Y. Acc. Chem. Res. 2016, 49, 1369. For
selected examples since 2015 because of space limitations, see: (n) Gu,
Y.; Hu, P.; Ni, C.; Tong, X. J. Am. Chem. Soc. 2015, 137, 6400.
(o) Zhang, L.; Liu, H.; Qiao, G.; Liu, Y.; Xiao, Y.; Guo, H.; Hou, Z. J.
Am. Chem. Soc. 2015, 137, 4316. (p) Lee, S.; Fujiwara, Y.; Nishiguchi,
A.; Kalek, M.; Fu, G. J. Am. Chem. Soc. 2015, 137, 4587. (q) Yao, W.;
Dou, X.; Lu, Y. J. Am. Chem. Soc. 2015, 137, 54. (r) Dong, X.; Liang,
L.; Li, E.; Huang, Y. Angew. Chem., Int. Ed. 2015, 54, 1621. (s) Ziegler,
D.; Fu, G. J. Am. Chem. Soc. 2016, 138, 12069. (t) Wang, T.; Yu, Z.;
Hoon, D.; Phee, C.; Lan, Y.; Lu, Y. J. Am. Chem. Soc. 2016, 138, 265.
(u) Li, E.; Jin, H.; Jia, P.; Dong, X.; Huang, Y. Angew. Chem., Int. Ed.
2016, 55, 11591. (v) Sankar, M. G.; Castro, M. G.; Golz, C.;
Strohmann, C.; Kumar, K. Angew. Chem., Int. Ed. 2016, 55, 9709.
(w) Han, X.; Chan, W.-L.; Yao, W.; Wang, Y.; Lu, Y. Angew. Chem., Int.
Ed. 2016, 55, 6492. (x) Cai, L.; Zhang, K.; Kwon, O. J. Am. Chem. Soc.
2016, 138, 3298. (y) Satpathi, B.; Ramasastry, S. S. V. Angew. Chem.,
Int. Ed. 2016, 55, 1777.
D
DOI: 10.1021/acs.orglett.7b00489
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