Organocatalytic Cascade β-Functionalization/Aromatization of Pyrrolidines via Double Hydride Transfer

Article abstract of DOI:10.1021/acs.orglett.9b03918

An unprecedented cascade β-functionalization/aromatization reaction of N-arylpyrrolidines was established. A series of β-substituted arylpyrroles embedded with trifluoromethyl groups are provided directly from N-arylpyrrolidines. The deuterium-labeling experiments indicate that sequential double hydride transfer processes serve as the key steps in this transformation.

Full text of DOI:10.1021/acs.orglett.9b03918

pubs.acs.org/OrgLett
Letter
Organocatalytic Cascade β‑Functionalization/Aromatization of
Pyrrolidines via Double Hydride Transfer
Lan Zhou, Xiao-De An, Shuo Yang, Xian-Jiang Li, Chang-Lun Shao,* Qing Liu, and Jian Xiao*
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sı Supporting Information
ABSTRACT: An unprecedented cascade β-functionalization/aromatization reaction of N-arylpyrrolidines was established. A series
of β-substituted arylpyrroles embedded with trifluoromethyl groups are provided directly from N-arylpyrrolidines. The deuterium-
labeling experiments indicate that sequential double hydride transfer processes serve as the key steps in this transformation.
he pyrroles scaffold exists as an important structural
element in natural products and functional molecules.
Among these prominent chemical scaffolds, arylpyrroles play
synthesizing β-substituted pyrroles usually suffer from multiple
steps as well as a preinstalled occupying group. Quite recently,
the dehydrogenative aromatization and β-sulfonylation of
1
4
T
an increasingly important role, serving as chiral resolving
pyrrolidines via photoredox catalysis was developed, which
2
5
agents, ligands, and catalysts (Figure 1). Therefore, great
relied on an iridium complex. However, the organocatalytic
and redox-neutral synthesis of β-substituted pyrroles from
pyrrolidines, which still remains a great challenge, has never
been reported.
The functionalization of amines initiated by hydride transfer
(
HT) has attracted great interest from organic chemists in
6,7
recent years. This redox-neutral method allows the facile
construction of α-functionalized amines in a step-economic
and atom-economic manner (Scheme 1a). Recently, B(C F )
6
5 3
has been explored as a hydride shuttle for the amine β-
8
−10
functionalization
and dehydrogenation of N-hetero-
11
cycles. In 2018, the Chang group reported a β-silylation of
six-membered N-heterocycles with B(C F ) as a catalyst.
8
6
5 3
Thereafter, the β-functionalization of acyclic tertiary amines
with p-quinone methides was realized by the Ma and Zhao
9
group. In this year, an efficient β-deuteration of alkylamines
10
Figure 1. Representative functional molecules containing arylpyrrole
skeletons.
was presented by the Wasa group. Quite recently, a cascade
intermolecular hydride transfer protocol was discovered by our
12f
group to synthesize β-functionalized tertiary amines. Despite
these advances, the direct synthesis of β-substituted pyrroles
from pyrrolidines via hydride transfer has never been targeted
attention has been focused on the construction of these
skeletons. However, the majority of methods for synthesis of
pyrrole derivatives are limited to the construction of α-
3
functionalized pyrroles and multisubstituted pyrroles. In sharp
Received: November 4, 2019
contrast, the development of methodologies to access β-
substituted pyrroles lags far behind, which might be ascribed to
their intrinsic weaker nucleophilicity compared with the α-
position of pyrroles. For instance, the approaches for
©
XXXX American Chemical Society
https://dx.doi.org/10.1021/acs.orglett.9b03918
A
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a
Scheme 1. Functionalization of Amines via Hydride
Transfer
Table 1. Optimization of the Reaction Conditions.
b
entry
1
2
catalyst
AcOH
(−)-CSA
solvent
yield (%)
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCM
THF
toluene
64
44
36
35
75
53
trace
53
38
49
nr
c
3
4
5
TfOH
TsOH·H O
2
d
PA
6
7
8
9
TFA
MsOH
Sc(OTf)3
Cu(OTf)2
PA
PA
PA
PA
PA
10
11
12
13
14
nr
nr
nr
CH CN
3
DMF
a
The reactions: 1a (0.2 mmol), 2a (0.1 mmol), catalyst (20 mol %),
b
solvent (1.0 mL), 100 °C. Isolated yield after column chromatog-
c
d
raphy. (−)-CSA = (−)-10-camphorsulfonic acid. PA = 1,1′-
and still remains underdeveloped. Inspired by our previous
binaphthyl-2,2′-diyl hydrogen phosphate.
1
2
research efforts on HT reactions, we now report an
unprecedented cascade reaction containing double HT
protocol to synthesize β-substituted pyrroles directly from
pyrrolidines.
As shown in Scheme 1b, under acid catalysis, the first intra-
or intermolecular HT would render the generation of the
intermediate A from amines via the cascade α‑HT/isomer-
ization/nucleophilic addition/isomerization process. After-
ward, it could undergo an acid-catalyzed dehydration to form
intermediate B, which would engage in an intramolecular
After optimization of reaction conditions, a series of o-
aminobenzyl alcohols 1 and keto esters 2 were engaged in the
reaction to check the applicability of this reaction. As displayed
1
2
in Scheme 2, in terms of R and R groups, either electron-rich
or -deficient groups had insignificant influences on this
reaction, leading to the corresponding β-functionalized
pyrroles 3a−j in acceptable yields. Notably, functional groups
containing different halogens (3f, 3i, 3j) were all well tolerated.
Other aromatic rings, such as naphthalene, acenaphthene,
biphenyl, furan, and thiophene, were also compatible with this
transformation, providing the corresponding products 3k−p in
45−78% yields. Moreover, the vinylbenzyl alcohol was
competent substrate to afford (Z)-3q in 74% yield, which
was assisted by the thermodynamic stability of the π−π
conjugation. Satisfyingly, we found that the cyclohexyl benzyl
alcohol was also suitable to provide the β-functionalized
pyrrole 3r in acceptable yield. Apart from the ethyl
trifluoropyruvate, methyl trifluoropyruvate and diethyl 2-
oxomalonate were also competent candidates for this reaction,
giving 3s and 3t in 67% and 35% yields, respectively. It was
worth mentioning that no Friedel−Crafts-type product was
detected.
[
1,3]-HT (amine β-C−H bond) process to afford β-
substituted N-arylpyrroles. It is worth mentioning that the
HT occurring at β-position of heteroatoms and the synthesis of
β-substituted pyrroles via double HT process have never been
realized to date. Herein, we report the organocatalytic β-
functionalization/aromatization of N-arylpyrrolidines, which
enables the direct synthesis of β-substituted pyrroles with
trifluoromethyl and carboxylic ester functionalities in good
yields.
Initially, o-aminobenzyl alcohol 1a and ethyl trifluoropyr-
uvate 2a were chosen to test this reaction (Table 1). The
reaction efficiency was evaluated by using 20 mol % of AcOH
in 1,2-dichloroethane (DCE) at 100 °C. Gratifyingly, the
predictable reaction occurred smoothly, furnishing the β-
functionalized pyrrole 3a in 64% yield (Table 1, entry 1).
Remarkably, due to the interruption of ethyl trifluoropyruvate,
this reaction did not undergo the previous intramolecular
The success of the intramolecular [1,5]-HT initiated cascade
reaction inspired us to explore the possibility of the more
3
challenging intermolecular HT initiated β-C(sp )−H function-
12c
Pictet−Spengler-type reaction. Then, various Brønsted acids
were examined (Table 1, entries 2−7). Eventually, 1,1′-
binaphthyl-2,2′-diyl hydrogen phosphate (PA) exhibited the
best efficiency to produce 3a in 75% yield. The evaluation of
Lewis acids revealed that the yield was not improved in
comparison with Brønsted acids (Table 1, entries 8 and 9).
Next, the solvent effect was investigated, and it was found that
DCE was the best media for this reaction (Table 1, entries 10−
alization/aromatization reaction of N-arylpyrrolidines. In
consideration of the electron-withdrawing property of
fluoroalkyl and ester groups, ethyl trifluoropyruvate 2a was
expected to work as both hydride acceptor and coupling
partner in this methodology.
To our delight, after slight modification of the reaction
conditions, the β-alkylated pyrrole 5a was produced in 64%
yield with 20 mol % of PA as a catalyst, applying toluene as a
solvent (see the Supporting Information). Subsequently, the
substrate scope with respect to N-arylpyrrolidines was also
1
4). As a consequence, the optimal reaction conditions were
designated as shown in entry 5.
B
https://dx.doi.org/10.1021/acs.orglett.9b03918
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Letter
a
Scheme 2. Substrate Scope for Product 3
reaction, providing the desired arylpyrroles 5f and 5g in 77%
and 21% yields, respectively. In addition, multisubstituted
benzene rings could also tolerate this reaction, albeit in
comparatively lower yields (5h−j).
To shed light on the mechanistic way of this transformation,
the deuterium labeling experiments were carried out (Scheme
4
). The starting materials [D]-1a and [D]-4b were subjected
Scheme 4. Deuterium-Labeling Experiments
to the standard conditions, respectively. Not surprisingly, the
intramolecular [1,5]-HT process was fully confirmed by the
a
benzylic deuteration (D ) of [D]-3a (Scheme 4a). The
observation of >99% deuterium adjacent to trifluoromethyl
b
group of [D]-5b implied that the hydride (D ) came from the
pyrrolidine ring of [D]-4b, which indicated the existence of
13
intramolecular [1,3]-HT (Scheme 4b).
On the basis of the above experimental results and previous
reports, a reasonable mechanism was proposed as follows
(
Scheme 5). Initially, the dehydration of o-aminobenzyl
Scheme 5. Proposed Mechanism
a
Reaction conditions: 1 (0.1 mmol), 2 (0.2 mmol), and PA (20 mol
%
) in 1.0 mL of DCE at 100 °C; isolated yield.
examined (Scheme 3). Various functional groups incorporated
in the benzene rings were well tolerable, such as methyl,
methoxy, and halides (e.g., F, Cl, Br), affording the β-
functionalized arylpyrroles 5a−g in 19−77% yields. In
particular, substrates bearing trifluoromethyl and cyano groups,
which widely exist in bioactive molecules, also survived in this
a
Scheme 3. Substrate Scope for Product 5
alcohol 1 gave rise to the carbocation intermediate I, which
initiated the intramolecular [1,5]-HT to form iminium ion II
immediately. After imine/enamine tautomerization, the
nucleophilic addition would occur between enamine inter-
mediate III and keto esters 2a to afford intermediate IV, which
underwent isomerization/dehydration to generate vinylogous
a
Reaction conditions: 4 (0.1 mmol), 2a (0.2 mmol), PA (20 mol %)
in 1.0 mL of toluene at 100 °C; isolated yield.
C
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Letter
iminium intermediate VI. Then, an intramolecular [1,3]-HT
process occurred, furnishing carbocation intermediate VII.
Finally, intermediate VII readily underwent isomerization/
deprotonation to provide the β-substituted pyrroles 3. When
the N-arylpyrrolidine 4 was chosen as a substrate, an
intermolecular HT from amine 4 to ethyl trifluoropyruvate
would happen and initiate the whole process, thus the iminium
ion II′ was generated. This was different from the production
of iminium ion II, which resulted from an intramolecular [1,5]-
HT. Subsequently, after the cascade synthetic processes similar
to the formation of 3, the final product 5 was created.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.9b03918
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to The Taishan Scholars Construction Projects
of Shandong (tsqn201909131), NSFC (21878167,
U1706210), and the Natural Science Foundation of Shandong
Province for Distinguished Young Scholars (JQ201604). The
Key Research and Development Program of Shandong
Province (2017GSF218073) and Qingdao Special Research
Foundation of Science and Technology (19-6-1-38 nsh) as
well as the First Class Fishery Discipline Programme of
Shandong Province are also gratefully acknowledged. We thank
Dr. Feng-Ying Dong (Central Laboratory of Qingdao
Agricultural University) for NMR determination.
In conclusion, we have developed a novel hydride transfer
initiated cascade β-functionalization/aromatization reaction of
pyrrolidines to construct β-substituted pyrroles. A series of β-
substituted N-arylpyrroles embedded with a trifluoromethyl
group were directly produced from N-arylpyrrolidines. This
protocol represented an unprecedented example of organo-
catalytic dehydrogenative aromatization reaction. Moreover,
3
the β-C(sp )−H bond of nitrogen is employed as a hydride
donor for the first time. We are confident that this
methodology will not only provide a powerful tool for the
construction of β-functionalized pyrroles but also push forward
the development of multiple HT strategy in organic synthesis.
REFERENCES
■
(
1
1) (a) Fan, H.; Peng, J.; Hamann, M. T.; Hu, J.-F. Chem. Rev. 2008,
08, 264. (b) Young, I. S.; Thornton, P. D.; Thompson, A. Nat. Prod.
Rep. 2010, 27, 1801. (c) Kaur, M.; Choi, D. H. Chem. Soc. Rev. 2015,
4, 58. (d) Bhardwaj, V.; Gumber, D.; Abbot, V.; Dhiman, S.; Sharma,
P. RSC Adv. 2015, 5, 15233. (e) Gholap, S. S. Eur. J. Med. Chem.
ASSOCIATED CONTENT
sı Supporting Information
4
■
*
2
2
016, 110, 13. (f) Khajuria, R.; Dham, S.; Kapoor, K. K. RSC Adv.
016, 6, 37039. (g) Ding, X.-B.; Brimble, M. A.; Furkert, D. P. Org.
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.9b03918.
Biomol. Chem. 2016, 14, 5390. (h) Kornienko, A.; La Clair, J. J. Nat.
Prod. Rep. 2017, 34, 1051.
Experimental procedures and characterization data for
all products (PDF)
(2) (a) Faigl, F.; Thurner, A.; Ta
r
́
kan
́
yi, G.; Kovar
Tetrahedron: Asymmetry 2002, 13, 59. (b) Faigl, F.; Mat
Holczbauer, T.; Czugler, M.; Madarasz, J. Tetrahedron: Asymmetry
2011, 22, 1879. (c) Deak, S.; Matravolgyi, B.; Feczku, G.; Erdelyi, Z.;
Nyerges, M.; Faigl, F. Tetrahedron: Asymmetry 2015, 26, 593.
d) Faigl, F.; Erdelyi, Z.; Holczbauer, T.; Matravolgyi, B. ARKIVOC
016, 242.
3) For representative examples, see: (a) Rakshit, S.; Patureau, F.
́
i, J.; Mordini, A.
́
ravolgyi, B.;
̈
́
AUTHOR INFORMATION
Corresponding Authors
■
́
́
̈
́
(
́
́
̈
Chang-Lun Shao − Key Laboratory of Marine Drugs, The
Ministry of Education of China, School of Medicine and
Pharmacy, Ocean Univer sity of China, Qingdao 266003,
China; orcid.org/0000-0001-7230-188X;
2
(
W.; Glorius, F. J. Am. Chem. Soc. 2010, 132, 9585. (b) Chen, Z.; Lu,
B.; Ding, Z.; Gao, K.; Yoshikai, N. Org. Lett. 2013, 15, 1966.
Email: shaochanglun@163.com
(c) Zhang, L.; Zhang, J.; Ma, J.; Cheng, D.-J.; Tan, B. J. Am. Chem.
Jian Xiao − Shandong Province Key Laboratory of Applied
Mycology, School of Chemistry and Pharmaceutical Sciences,
School of Marine Science and Engineering, Qingdao Agricultural
University, Qingdao 266109, China; orcid.org/0000-0003-
Soc. 2017, 139, 1714. (d) Zhang, L.; Xiang, S.-H.; Wang, J.-J.; Xiao, J.;
Wang, J.-Q.; Tan, B. Nat. Commun. 2019, 10, 566. (e) Bharathiraja,
G.; Sakthivel, S.; Sengoden, M.; Punniyamurthy, T. Org. Lett. 2013,
15, 4996. (f) Lian, X.-L.; Ren, Z.-H.; Wang, Y.-Y.; Guan, Z.-H. Org.
Lett. 2014, 16, 3360. (g) Huang, W.; Chen, S.; Chen, Z.; Yue, M.; Li,
M.; Gu, Y. J. Org. Chem. 2019, 84, 5655. (h) Wan, S.-H.; Liu, S.-T.
Tetrahedron 2019, 75, 1166. (i) Xu, J.; Green, A. P.; Turner, N. J.
Angew. Chem., Int. Ed. 2018, 57, 16760. (j) Chiu, H.-C.; Tonks, I. A.
Angew. Chem., Int. Ed. 2018, 57, 6090. (k) Xuan, J.; Xia, X.-D.; Zeng,
T.-T.; Feng, Z.-J.; Chen, J.-R.; Lu, L.-Q.; Xiao, W.-J. Angew. Chem., Int.
Ed. 2014, 53, 5653. (l) Davis-Gilbert, Z. W.; Wen, X.; Goodpaster, J.
D.; Tonks, I. A. J. Am. Chem. Soc. 2018, 140, 7267.
4
272-6865; Email: chemjianxiao@163.com
Other Authors
Lan Zhou − Shandong Province Key Laboratory of Applied
Mycology, School of Chemistry and Pharmaceutical Sciences,
School of Marine Science and Engineering, Qingdao Agricultural
University, Qingdao 266109, China
Xiao-De An − Shandong Province Key Laboratory of Applied
Mycology, School of Chemistry and Pharmaceutical Sciences,
School of Marine Science and Engineering, Qingdao Agricultural
University, Qingdao 266109, China
Shuo Yang − Shandong Province Key Laboratory of Applied
Mycology, School of Chemistry and Pharmaceutical Sciences,
School of Marine Science and Engineering, Qingdao Agricultural
University, Qingdao 266109, China
Xian-Jiang Li − Shandong Kangqiao Biotechnology Co., Ltd.,
Binzhou 256500, China
Qing Liu − College of Chemical and Environmental Engineering,
Shandong University of Science and Technology, Qingdao
(
4) (a) Bunrit, A.; Sawadjoon, S.; Tsupova, S.; Sjoberg, P. J. R.;
̌
̈
Samec, J. S. M. J. Org. Chem. 2016, 81, 1450. (b) Nomiyama, S.;
Ogura, T.; Ishida, H.; Aoki, K.; Tsuchimoto, T. J. Org. Chem. 2017,
̌ ̌
ek, J.; Rezankova, M.; Stibor, I.; Rezanka, M. J.
́ ̌ ́
82, 5178. (c) Lukas
Inclusion Phenom. Macrocyclic Chem. 2018, 92, 339.
5) Muralirajan, K.; Kancherla, R.; Rueping, M. Angew. Chem., Int.
Ed. 2018, 57, 14787.
6) For reviews, see: (a) Tobisu, M.; Chatani, N. Angew. Chem., Int.
Ed. 2006, 45, 1683. (b) Peng, B.; Maulide, N. Chem. - Eur. J. 2013, 19,
3274. (c) Wang, L.; Xiao, J. Adv. Synth. Catal. 2014, 356, 1137.
(
(
1
(
(
d) Haibach, M. C.; Seidel, D. Angew. Chem., Int. Ed. 2014, 53, 5010.
e) Wang, L.; Xiao, J. Top. Curr. Chem. 2016, 374, 17. (f) Wang, L.;
Xiao, J. Org. Chem. Front. 2016, 3, 635. (g) Xiao, M.; Zhu, S.; Shen,
Y.-B.; Wang, L.; Xiao, J. Chin. J. Org. Chem. 2018, 38, 328.
2
66590, China; orcid.org/0000-0001-6233-9112
D
https://dx.doi.org/10.1021/acs.orglett.9b03918
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
(
7) For representative examples, see: (a) Zhang, C. C.; De, K.; Mal,
R.; Seidel, D. J. Am. Chem. Soc. 2008, 130, 416. (b) Kang, Y. K.; Kim,
S. M.; Kim, D. Y. J. Am. Chem. Soc. 2010, 132, 11847. (c) Mori, K.;
Ehara, K.; Kurihara, K.; Akiyama, T. J. Am. Chem. Soc. 2011, 133,
6
1
166. (d) Mori, K.; Sueoka, S.; Akiyama, T. J. Am. Chem. Soc. 2011,
33, 2424. (e) Haibach, M. C.; Deb, I.; De, C. K.; Seidel, D. J. Am.
Chem. Soc. 2011, 133, 2100. (f) Jurberg, I. D.; Peng, B.; Wo
Wasserloos, M.; Maulide, N. Angew. Chem., Int. Ed. 2012, 51, 1950.
̈
stefeld, E.;
(
(
g) Suh, C. W.; Kwon, S. J.; Kim, D. Y. Org. Lett. 2017, 19, 1334.
h) Gandamana, D. A.; Wang, B.; Tejo, C.; Bolte, B.; Gagosz, F.;
Chiba, S. Angew. Chem., Int. Ed. 2018, 57, 6181. (i) Mori, K.; Isogai,
R.; Kamei, Y.; Yamanaka, M.; Akiyama, T. J. Am. Chem. Soc. 2018,
1
40, 6203. (j) Idiris, F. I. M.; Majeste,
́
C. E.; Craven, G. B.; Jones, C.
R. Chem. Sci. 2018, 9, 2873. (k) Bauer, A.; Maulide, N. Org. Lett.
2
7
2
018, 20, 1461. (l) Liu, S.; Qu, J.; Wang, B. Chem. Commun. 2018, 54,
928. (m) Liu, S.; Zhang, W.; Qu, J.; Wang, B. Org. Chem. Front.
018, 5, 3008. (n) Liu, S.; Zhao, T.; Qu, J.; Wang, B. Adv. Synth.
Catal. 2018, 360, 4094. (o) Tamura, R.; Kitamura, E.; Tsutsumi, R.;
Yamanaka, M.; Akiyama, T.; Mori, K. Org. Lett. 2019, 21, 2383.
(
2
p) Tian, J. J.; Zeng, N. N.; Liu, N.; Tu, X. S.; Wang, X. C. ACS Catal.
019, 9, 295.
(
(
8) Zhang, J.; Park, S.; Chang, S. J. Am. Chem. Soc. 2018, 140, 13209.
9) Li, R.; Chen, Y.; Jiang, K.; Wang, F.; Lu, C.; Nie, J.; Chen, Z.;
Yang, G.; Chen, Y.-C.; Zhao, Y.; Ma, C. Chem. Commun. 2019, 55,
217.
10) Chang, Y.; Yesilcimen, A.; Cao, M.; Zhang, Y.; Zhang, B.; Chan,
J. Z.; Wasa, M. J. Am. Chem. Soc. 2019, 141, 14570.
11) (a) Maier, A. F. G.; Tussing, S.; Schneider, T.; Flo
Z.-W.; Grimme, S.; Paradies, J. Angew. Chem., Int. Ed. 2016, 55,
1
(
(
̈
rke, U.; Qu,
1
1
2219. (b) Kojima, M.; Kanai, M. Angew. Chem., Int. Ed. 2016, 55,
2224.
(
12) (a) Zhu, S.; Chen, C.; Xiao, M.; Yu, L.; Wang, L.; Xiao, J. Green
Chem. 2017, 19, 5653. (b) Li, S.-S.; Lv, X.; Ren, D.; Shao, C.-L.; Liu,
Q.; Xiao, J. Chem. Sci. 2018, 9, 8253. (c) Li, S.-S.; Zhou, L.; Wang, L.;
Zhao, H.; Yu, L.; Xiao, J. Org. Lett. 2018, 20, 138. (d) Wang, S.; An,
X.-D.; Li, S.-S.; Liu, X.; Liu, Q.; Xiao, J. Chem. Commun. 2018, 54,
1
3833. (e) Li, S.-S.; Zhu, S.; Chen, C.; Duan, K.; Liu, Q.; Xiao, J. Org.
Lett. 2019, 21, 1058. (f) Zhou, L.; Shen, Y.-B.; An, X.-D.; Li, X.-J.; Li,
S.-S.; Liu, Q.; Xiao, J. Org. Lett. 2019, 21, 8543. (g) Wang, S.; Shen,
Y.-B.; Li, L.-F.; Qiu, B.; Yu, L.; Liu, Q.; Xiao, J. Org. Lett. 2019, 21,
8
904. (h) Lv, X.; Hu, F.; Duan, K.; Li, S.-S.; Liu, Q.; Xiao, J. J. Org.
Chem. 2019, 84, 1833. (i) Zhu, S.; Chen, C.; Duan, K.; Sun, Y.-M.; Li,
S.-S.; Liu, Q.; Xiao, J. J. Org. Chem. 2019, 84, 8440. (j) An, X. D.;
Duan, K.; Li, X.-J.; Yang, J.-M.; Lu, Y.-N.; Liu, Q.; Xiao, J. J. Org.
Chem. 2019, 84, 11839. (k) Shen, Y.-B.; Li, L.-F.; Xiao, M.-Y.; Yang,
J.-M.; Liu, Q.; Xiao, J. J. Org. Chem. 2019, 84, 13935. (l) Shen, Y.-B.;
Wang, L.-X.; Sun, Y.-M.; Dong, F.-Y.; Yu, L.; Liu, Q.; Xiao, J. J. Org.
Chem. 2019, DOI: 10.1021/acs.joc.9b02606.
(
13) For examples of [1,3]-hydride transfer, see: (a) Luan, F.;
Degenhardt, A.; Mosandl, A.; Wust, M. J. Agric. Food Chem. 2006, 54,
0245. (b) Pahadi, N. K.; Paley, M.; Jana, R.; Waetzig, S. R.; Tunge, J.
̈
1
A. J. Am. Chem. Soc. 2009, 131, 16626. (c) Wang, Y.; Li, G.; Liu, H.;
Tang, Z.; Cao, Y.; Zhao, G. Chem. Commun. 2017, 53, 10652.
E
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