Nickel-Catalyzed Esterification of Amides Under Mild Conditions

Article abstract of DOI:10.1007/s10562-019-02966-6

Abstract: The use of ligands to adjust the catalytic activity of the catalyst for esterification of amides is challenge in organic chemistry. In this paper, Nickel(II)-NHC-catalyzed the esterification reaction between N,N-di-Boc amide and alcohols at room temperature have been demonstrated. The imidazolium salt bearing a hydroxyl functionalized side arm showed high effective catalytic activity in the activation of the amide N–C bond in air atmosphere. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02966-6

Catalysis Letters
https://doi.org/10.1007/s10562-019-02966-6
Nickel‑Catalyzed Esterifcation of Amides Under Mild Conditions
Jun‑Fei Li1,2 · Yao‑Fang Wang1,2 · Yuan‑Yuan Wu1,2 · Wen‑Jing Liu1,2 · Jun‑Wen Wang1,2
Received: 27 July 2019 / Accepted: 20 September 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The use of ligands to adjust the catalytic activity of the catalyst for esterifcation of amides is challenge in organic chemistry.
In this paper, Nickel(II)-NHC-catalyzed the esterifcation reaction between N,N-di-Boc amide and alcohols at room tem-
perature have been demonstrated. The imidazolium salt bearing a hydroxyl functionalized side arm showed high efective
catalytic activity in the activation of the amide N–C bond in air atmosphere.
Graphic Abstract
ligand (5 mol%)
Ni(AcO)2 (3 mol%)
O
O
R1
R1
Boc
+
R
OH
OR
N
K2CO3 / Et3N (1:1, 4 equiv)
rt, 2h
Boc
HO
-
PF6
Ts
N
N
N
Keywords N-heterocyclic carbene · Nickel · Catalysis · Amides
1 Introduction
undergoes activation by the principle of amide bond reso-
nance destabilization, some examples of N-acyl-glutarimides,
N-Boc-amides and N–Ts-amides have been documented the
activation of C-bonds of amides. This approach allows for the
breakdown of amides, and renders amides useful synthetic
building blocks [5–7]. In 2015, Garg and co-workers frst
reported the esterifcation of amides using Ni-catalyzed acti-
vation of the amide bond, and used density functional theory
(DFT) calculations to proved thermodynamically favoured
(Fig. 1a) [8–11]. The catalytic system reported is the use of
Ni(0) precatalyst (Ni(cod)2, SIPr, PhMe, 60–110 °C). How-
ever, Ni(cod)2 is not air-stable and requires handling in an
inert atmosphere, which limits its widespread use in chemical
synthesis. Later, Danoun provided the amide to ester inter-
conversion using Co-catalyzed activation of the amide bond
(Fig. 1b). This methodology presents a very practical process
that does not require an inert atmosphere under mild reaction
conditions (CoBr2, Mn, bipyridine, DMF/pyridine, 60 °C)
[12]. Soon afterwards, Takashi Ohshima and co-workers
developed the direct catalytic alcoholysis of 8-aminoquinoline
amides in presence of Ni(II) diketonate catalysts (Ni(tmhd)2,
Amides are a ubiquitous functional group in organic molecule,
which are the important building blocks of proteins and were
widely found in natural and synthetic compounds [1–4]. It’s
more difcult to break the C–N bond of amide in synthetic
chemistry. Direct catalytic esterifcation of amides is one of
the challenges in organic chemistry. The C–N bond of amide
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02966-6) contains
supplementary material, which is available to authorized users.
Jun-Fei Li and Yao-Fang Wang have contributed equally to this
work.
* Jun-Wen Wang
wangjunwen2013@126.com
1
Key Laboratory of Magnetic Molecules & Magnetic
Information Materials Ministry of Education, Shanxi Normal
University, Linfen 041004, China
2
The School of Chemical and Material Science, Shanxi
Normal University, No. 1, Gongyuan Street, Linfen 041004,
China
Vol.:(0123456789)
1 3

J.-F. Li et al.
Fig. 1 a Conversion of amides
to esters by the nickel-catalysed
activation of amide C–N bonds.
b Cobalt-catalyzed Esterifca-
tion of Amides. c Transition-
metal-free Esterifcation of
Amides at rt (previous works).
d Esterifcation of amides under
the room temperature (this
study)
A Previous work: Conversion of amides to esters by the nickel-catalysed activation of
amide C-N bonds
O
O
Ni(cod)2
R2
+
R OH
R1
N
X
R1
OR
SIPr, 80°C
MePh
X = Boc, Ts
B Previous work : Cobalt-Catalyzed Esterification of Amides
O
CoBr2 (20mol%), Bipy (40 mol%)
Mn0 (3 equiv.)
O
O
Ph
+
OH
N
DMF / Py, 3h, 60°C
Boc
C Previous work : Transition-metal-free Esterification of Amides at rt
O
O
R2
R OH
THF, rt
R1
N
X
R1
OR
X = Boc, Ts
D This work: Esterification of amides under the room temperature
O
O
Ni(AcO)2
Cat., RT
Boc
+
R OH
R1
N
R1
OR
Boc
nickel(II) bis(2,2,6,6-tetramethyl-3,5-heptanedionate) at 80 °C
for 12 h [13]. In 2018, Michal Szostak report a simple method
for transition-metal-free esterifcation of amides under mild
room temperature conditions (Fig. 1c) [14].
2 Experimental Section
2.1 General Procedures
To our knowledge, N-heterocyclic carbene have been
widely used to catalyze organic reactions, and various types
of carbene catalysts with diferent structures have been synthe-
sized [15–22]. Although the system of Ni(0) precatalyst and
N-heterocyclic carbene (Ni(cod)2, SIPr) has been successfully
used in the esterifcation of amides, the esterifcation of amides
reported in the literature was carried out at a high temperature
(60–110 °C). It is necessary to explore a kind of catalyst that
can catalyze the esterifcation of amides under mild conditions.
Here in, we have prepared a novel the imidazolium salt precat-
alyst bearing a hydroxyl functionalized side arm, and designed
a method for esterifcation of amide by using Ni(AcO)2/NHC
catalyst under mild conditions (Fig. 1c). It is worth nothing
that this methodology is particularly efective for esterifcation
of amide in air atmosphere relative to the Ni(0) precatalyst in
an inert atmosphere.
The compounds N,N-di-Boc amides were prepared accord-
ing to literature methods. All reagents were obtained
from commercial sources and used without further puri-
fication. The compound (B) were prepared according
to the literature procedures [23–26], and 3-Bromo-2,2-
bis(bromomethyl)propan-1-ol is commercially available
which using as a flame retardant. NMR spectra were
obtained on a Bruker Avance III HD 600 MHz spectrom-
eter. The chemical shifts are expressed in ppm and are
internally referenced. All products were characterized by
their 1H NMR and 13C NMR that were identical to those in
the literature. Melting point determination were measured
by an WRS-2 melting point apparatus.
1 3

Nickel-Catalyzed Esterifcation of Amides Under Mild Conditions
2.2 Synthesis of Imidazolium Salt Ligand (C)
3 Results and Discussion
3-(Bromomethyl)-1-(p-toluenesulfonyl) azetidin-3-yl)
methanol (B) (2 g, 5.99 mmol) and 1-(naphthalen-1-yl-
methyl) imidazole (1.25 g, 6.0 mmol) was dissolved in
the solvent of THF and the solution was stirred for 5
days at 60 °C. A white powder was obtained. The raw
imidazolium salt was purified by recrystallization with
DMF and water. NH4PF6 (1.23 g, 7.55 mmol) was added
to a CH3OH (30 mL) solution of the obtained imidazo-
lium salt, and a white precipitate formed immediately.
The pure imidazolium salt was obtained by recrystal-
lization with CH3CN and ethyl ether. Yield: 86%, M.P.
186.0–187.3 °C; 1H NMR (d6-DMSO, 600 MHz): δ=9.37
(s, 1H), 8.13 (d, J = 7.9 Hz, 1H), 8.03 (t, J = 6.3 Hz, 2H),
7.76 (d, J = 6.3 Hz, 2H), 7.56–7.65 (m, 5H), 7.50 (d,
J = 6.9 Hz, 1H), 7.45 (d, J = 7.9 Hz, 2H), 5.94 (s, 2H),
5.17 (t, J = 5.0 Hz, 1H), 4.32 (s, 2H), 3.61 (d, J = 8.8 Hz,
2H), 3.45 (d, J = 8.8 Hz, 2H), 3.11 (d, J = 5.0 Hz,2H),
2.44 (s, 3H) ppm. 13C NMR (d6-DMSO, 125 MHz):
δ = 144.571, 137.862, 133.875, 131.233, 130.813,
130.548, 130.418, 130.072, 129.372, 128.596, 127.888,
127.662, 126.926, 126.163, 124.111, 123.336, 123.176,
63.195, 54.956, 51.403, 50.464, 38.910, 21.588 ppm.
Anal. calcd for C26H28F6N3O3PS: C 51.40, H 4.65; found:
C 51.43, H 4.67.
In this work, we prepared a NHC-precatalyst (C) fol-
lowing the synthetic methods shown in Scheme 1. The
6-(p-toluenesulfonyl)-2-oxa-6-azaspiro [3.3] heptane (A)
was synthesized from tribromopentaerythritol and p-tol-
uenesulfonamide by refuxing 96 h in ethanol with KOH
as base. Subsequently, the oxetane opening in a solution of
hydrobromic acid gave a (3-(Bromomethyl)-1-(p-toluene-
sulfonyl) azetidin-3-yl) methanol (B) [23–26]. The imida-
zole hexafuorophosphate ligand (C) was readily prepared
by refuxing the 3-(Bromomethyl)-1-(p-toluenesulfonyl)
azetidin-3-yl) methanol (B) and 1-(naphthalen-1-ylmethyl)
imidazole in THF, followed by ion-exchange with PF6− in
methanol.
Our initial attempt was to optimize reaction conditions
using N,N-di-Boc activated amide and methanol with
diferent bases at room temperature (Table 1). Initially,
among the diferent types of bases examined in the esterif-
cation reaction, yields of 2a vary by 10–90%. We observed
about 10–20% yield of products using strong bases KOtBu
and KOH in the esterifcation of amide at room tempera-
ture for 2 h (Table 1, entries 3 and 4). To our delight, and
then we tried to use some weak bases, such as K2CO3,
Et3N, K3PO4, KOAc and Na3PO4, and the yields went up.
The product 2a was obtained in 62% and 70% yields using
K2CO3 and Et3N as bases in the esterifcation of amides
under mild condition, respectively (Table 1, entries 1 and
2). Interestingly, when the mixed bases K2CO3 and Et3N
(1:1, 4 equiv) were accidentally used as bases, the yield
(90%) was dramatically improved in methanol at 25 °C
(Table 1, entry 6). Recently, Michal Szostak report the
general, mild, and highly chemoselective method for
transamidation of unactivated tertiary amides by a direct
acyl N–C bond cleavage with non-nucleophilic amines
[27–29]. So we tried to reduce the amount of nickel ace-
tate, and found that nickel acetate facilitated the reaction
under optimal conditions (entry 13 and 14). These show
that the nickel plays a vital role in the metal-catalysed
activation of C–N bonds of amides under mild condition
with alcohols as reactants and solvents.
2.3 Typical Procedure for the Esterifcation
of the Amides
In a typical run, a mixture of Ni(AcO)2 (3 mol%),
admides (0.195 mmol), base (4 equiv, 0.78 mmol), ligand
(5 mol%), alcohol (2 mL) was stirred at room tempera-
ture for 2 h. After the reaction time, the contents were
quenched with 10 mL water and extracted with dichlo-
romethane. The combined organic extract was washed
with brine (15 mL) and dried over anhydrous MgSO4, fil-
tered, and concentrated under vacuum. The crude product
was purified by column chromatography to afford ester
compounds.
HO
Br
Br
Br
Scheme 1 Synthesis of the
ligand (C)
TsNH2
KOH, EtOH
(A)
Ts
N
O
HBr CH2Cl2
HO
-
PF6
HO
N
1. THF / refluxe
2. NH4PF6 / CH3OH
Ts
N
N
N
+
N
N
Ts
Br
(B)
(C)
1 3

J.-F. Li et al.
Table 1 Optimization of reaction conditions
Entry
Base
Ligand
Time
Yield (%)a
1
2
3
4
5
6
7
8
K2CO3
C
2
2
2
2
2
2
2
2
2
2
2
2
2
2
62
70
21
12
35
90
78
81
31
41
37
36
58b
38c
Et3N
C
KOtBu
C
KOH
K3PO4
K2CO3 +Et3N
K2CO3 +Et3N
K2CO3 +Et3N
Na2CO3
KOAc
Na3PO4
K2CO3 +Et3N
K2CO3 +Et3N
K2CO3 +Et3N
C
C
C
IPrHCl
IMesHCl
9
C
10
11
12
13
14
C
C
No
C
C
aIsolated yield based on an N,N-Boc2-amide. Reaction condition: 0.195 mmol of admides, 0.78 mmol base, 5 mol% of ligand, 3 mol% of
Ni(AcO)2, rt, 2 h
b1.0 mol% of Ni(AcO)2
cWithout Ni(OAc)2
After extensive optimization, we were delighted to
fnd that the reaction of N,N-di-Boc activated amide and
methanol achieved a yield of 90% at room temperature
using K2CO3 and Et3N (1:1, 4 equiv) as mixed base and
Ni(OAc)2/ligand (C) as catalyst (Table 1, entry 6). We
then focused on testing the catalytic efciency of difer-
ent catalysts. On comparing the results with those cat-
alysts, a considerably higher activity of ligand (C) can
be observed than the analogous IPrHCl and IMesHCl in
methanol under optimized condition of the esterifcation
reaction (entries 6–8). We further evaluated the ligands in
the reaction of N,N-di-Boc activated amides and methanol
at room temperature, and found that the reaction could be
complete within 2 h using the system of Ni(OAc)2/ligand
(C) as catalyst, while other catalysts took 5 h. We identi-
fed the ligand (C) as a promising Ni(II)-NHC precatalyst
for the esterifcation of amides.
The good catalytic activity of ligand (C) may be attrib-
uted to hydroxyl functional groups in ligand molecules
structure. In recent years, some N-heterocyclic carbene
containing functional groups (N, O) has been reported
successively [30]. With the assistance of these functional
arms, the N-heterocyclic carbene complexes formed are
more stable and have better catalytic activity. For example,
in 2014, Hameury studied the infuence of hydroxyl func-
tional group in the arm of the N-heterocyclic carbene Pd
(II) and Ni (II) complexes, the results show that hydroxyl
side arm raised the Ni (II) complex catalytic activity in
1 3

Nickel-Catalyzed Esterifcation of Amides Under Mild Conditions
Scheme 2 Substrate Scope for
the esterifcation of amides.
Isolated yield based on an N,N-
Boc2-amide. Reaction condi-
tion: 0.195 mmol of admides,
0.78 mmol of K2CO3 and Et3N
(1:1, 4 equiv), 5 mol% of ligand
C, 3 mol% of Ni(AcO)2, rt, 2 h
O
O
Boc
Ni(AcO)2
R1
N
+
Me OH
R1
OMe
OMe
C
ligand , 25°C
Boc
1
2
O
O
F
O
OMe
OMe
F
O2N
2a
: 90% yield
O
2b
: 95% yield
2c
: 93% yield
O
H3CO
O
OMe
OMe
OMe
F
H3CO
H3CO
2e
: 89% yield
2f
: 87% yield
2d
: 91% yield
a Isolated yield based on an N,N-Boc2-amide. Reaction condition: 0.195 mmol of
admides, 0.78 mmol of K2CO3 and Et3N (1:1, 4 equiv), 5 mol% of ligand C, 3 mol% of
Ni(AcO)2, rt, 2 h.
ethylene oligomerization [31]. In 2016, Ohmiya also
reported that the chiral N-heterocyclic carbene ligand
modifed by naphthol hydroxyl was used as the precata-
lyst to catalyze allylic alkylation of azoles, and the selec-
tivity of this reaction was as high as 93% [32]. Accord-
ing to the methods reported in the literature, the value
of the one-bond CH J-coupling constant of ligand C is
223.2 Hz, which is slightly smaller than that in the litera-
The scope of alcohols is focus on the alkyl alcohols
(3a–r), and tolerates a range of primary alcohols (3a–f,
3m–r), secondary alcohols (3g–l), and tertiary alcohols
(3s,t). Notable, the reaction can be carried out under mild
conditions with alcohols as reactants and solvents, and aford
the desired products in modest to good yields (Scheme 3).
Importantly, the sterically hindered alcohols such as tertiary
alcohols (3s,t) react relatively slowly under the optimized
conditions. Tertiary alcohols can be smoothly transformed,
afording the desired products (3s,t) in 12 h.
1
ture (1JCH(IPr) = 223.7 and JCH IMes = 225.2 Hz) [33].
This suggests that salt c has a slightly stronger σ-donor
ability than IPr and IMes as a nucleophilic carbene.
Under the optimized conditions, we evaluated the pre-
parative substrate scope of the reaction of the esterifcation
of N,N-di-Boc amides and methanol at room temperature
(Scheme 2). We were pleased to fnd that the formation of
methyl ester (2a–f) occurred in 87–95% of yields for the
substituted aromatic amides, which tolerates electron-rich
(2e,f) and electron-withdraw (2b–d) substituents on the aro-
matic rings. The electron-withdrawing groups substituted
on the benzene ring (2b–d) were lightly favored for the
reaction, and the reaction could be fnished in 2 h at room
temperature. Meanwhile, the position of the substituents
such as ortho-position (2c), meta-position (2f), and para-
position (2b, 2d,e) have little efect under the optimized
reaction conditions. 2,6-difuoro-substituted N,N-di-Boc
amide aforded 2c in 93% yield, 3,5-dimethoxyl-substituted
amide also gave the corresponding ester (2f) in 87% isolated
yields, respectively.
The hypothesis of the reaction mechanism has been
described in reference (Scheme 4) [8, 10, 11]. The catalytic
mechanism of the nickel-catalyzed esterifcation of amides is
thought to proceed via oxidative addition, ligand exchange,
and reductive elimination.
4 Conclusion
In conclusion, a convenient and direct esterifcations of
N,N-di-Boc amides using the Ni-NHC catalyst has been
developed at room temperature. The imidazolium salt with
a hydroxyl functionalized side arm showed high efective
catalytic activity in the esterifcation of N,N-di-Boc amide.
The reactions could be successfully carried out by using
Ni(AcO)2/NHC catalyst in the alkyl alcohols solvents with
the mixed bases of K2CO3 and Et3N (1:1) as base at room
temperature. Notable, this methodology is particularly efec-
tive for esterifcation of amide in air atmosphere relative to
the Ni(0) precatalyst in an inert atmosphere.
1 3

J.-F. Li et al.
C
ligand
(5 mol%)
O
1
O
3
Ni(AcO)2 (3 mol%)
K2CO3 / Et3N (1:1, 4 equiv)
rt, 2h
Boc
+
R OH
O
R1
N
R1
OR
F
Boc
O
F
O
O
OEt
OEt
OEt
OEt
H3CO
O2N
3d
3a
: 91% yield
: 89% yield
O
3b
3c
: 87% yield
: 93% yield
O
H3CO
O
O
O
OEt
O
OEt
F
O2N
3h
H3CO
3g
: 86% yield
O
3e
: 90% yield
: 89% yield
3f
: 86% yield
O
O
F
H3CO
O
O
O
O
O
H3CO
3k
F
F
H3CO
3i
3j
: 88% yield
O
: 85% yield
O
3l
: 87% yield
: 86% yield
O
O
O
O
O
O
O2N
F
H3CO
3p
: 89% yield
O
3o
: 90% yield
3m
3n
: 92% yield
: 87% yield
O
H3CO
O
F
O
O
O
O
O
O2N
H3CO
F
H3CO
3t
3s
: 83% yield
3r
: 85% yield
: 90% yield
3q
: 85% yield
a Isolated yield based on an N,N-Boc2-amide. Reaction condition: 0.195 mmol of
admides, 0.78 mmol of K2CO3 and Et3N (1:1, 4 equiv), 5 mol% of ligand C, 3 mol% of
Ni(AcO)2, rt, 2 h.
Scheme 3 Nickel-NHC-Catalyzed Esterifcation of N,N-di-Boc Amides. Isolated yield based on an N,N-Boc2-amide. Reaction condition:
0.195 mmol of admides, 0.78 mmol of K2CO3 and Et3N (1:1, 4 equiv), 5 mol% of ligand C, 3 mol% of Ni(AcO)2, rt, 2 h
O
R2
N
O
O
O
Ni(OAc)2
R2
R OH
OR
R1
N
X
X
R1
Ni
R1
Ni
NHC
NHC
K2CO3
R1
OR
NHC
X = Boc, Ts
ligand
exchange
oxidative
addition
reductive
elimination
Scheme 4 Proposed mechanism of the reaction nickel-catalyzed esterifcation of amides
1 3

Nickel-Catalyzed Esterifcation of Amides Under Mild Conditions
17. Guo C, Janssen-Müller D, Fleige M, Lerchen A, Daniliuc CG,
Glorius F (2017) J Am Chem Soc 139:4443
5 Supplementary Material
18. Pucino M, Inoue M, Gordon CP, Schowner R, Stöhr L, Sen S,
Hegedüs C, Robé E, Tóth F, Buchmeiser MR, Copéret C (2018)
Angew Chem Int Ed 57:14566
Supplementary data associated with this article can be found
in the online version.
1H and 13C NMR Spectra of Products.
19. Halima TB, Zhang W, Yalaoui I, Hong X, Yang Y-F, Houk KN,
Newman SG (2017) J Am Chem Soc 139:1311
20. Wang D, Astruc D (2017) Chem Soc Rev 46:816
21. Begum T, Mondal M, Borpuzari MP, Kar R, Kalita G, Gogoi PK,
Bora U (2017) Dalton Trans 46:539
Acknowledgements This work is supported by the Shanxi Natural
Science Foundation of China for the Project (No. 2011011006-4), and
1331 Project of Shanxi Province.
22. Ohtsuki A, Yanagisawa K, Furukawa T, Tobisuand M, Chatani N
(2016) J Org Chem 81:9409
23. Burkhard JA, Wagner B, Fischer H, Schuler F, Müller K, Carreira
EM (2010) Angew Chem Int Ed 49:3524
References
24. Burkhard JA, Guérot C, Knust H, Rogers-Evans M, Carreira EM
(2010) Org Lett 12:1944
1. Pattabiraman VR, Bode JW (2011) Nature 480:471
2. Tani K, Stoltz BM (2006) Nature 441:731
25. Burkhard J, Carreira EM (2008) Org Lett 10:3525
26. Wuitschik G, Rogers-Evans M, Buckl A, Bernasconi M, Märki M,
Godel T, Schneider J, Alker A, Schweizer WB, Müller K, Carreira
EM (2008) Angew Chem Int Ed 47:4512
3. Takise R, Muto K, Yamaguchi J (2017) Chem Soc Rev 46:5864
4. Walsh CT, O’Brien RV, Khosla C (2013) Angew Chem Int Ed
52:7098
27. Meng G, Szostak I (2018) ACS Catal 7:7251
28. Meng G, Shi S, Lalancette R, Szostak R, Szostak M (2018) J Am
Chem Soc 140:727
5. Shi S, Nolan SP, Szostak M (2018) Acc Chem Res 51:2589–2599
6. Buchspies J, Szostak M (2019) Catalysts 9:53
7. Meng G, Szostak M (2018) Eur J Org Chem 20–21:2352
8. Hie L, Nathel NF, Shah T, Baker EL, Hong X, Yang Y-F, Liu P,
Houk KN, Garg NK (2015) Nature 524:79
29. Meng G, Shi S, Szostak M (2016) ACS Catal 6:7335
30. Zhang D, Zi G (2015) Chem Soc Rev 44:1898
31. Hameury S, de Frémont P, Breuil PAR, Olivier-Bourbigou H,
Braunstein P (2014) Inorg Chem 53:5189
9. Dander JE, Weires NA, Garg NK (2016) Org Lett 18:3934
10. Dander JE, Garg NK (2017) ACS Catal 7:1413
11. Weires NA, Caspi DD, Garg NK (2017) ACS Catal 7:4381
12. Bourne-Branchu Y, Gosmini C, Danoun G (2017) Chem Eur J
23:10043
32. Ohmiya H, Zhang H, Shibata S, Harada A, Sawamura M (2016)
Angew Chem Int Ed 55:4777
33. Meng G, Kakalis L, Nolan SP, Szostak M (2019) Tetrahedron Lett
60:378
13. Deguchi T, Xin H-L, Morimoto H, Ohshima T (2017) ACS Catal
7:3157
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
14. Li G, Lei P, Szostak M (2018) Org Lett 20:5622
15. She Z, Wang Y, Wang D, Zhao Y, Wang T, Zheng X, Yu Z-X, Gao
G, You J (2018) J Am Chem Soc 140:12566
16. Cheng J, Sun J, Yan J, Yang S, Zheng P, Jin Z, Chi YR (2017) J
Org Chem 82:13342
1 3