Palladium-catalyzed formal insertion of carbenoids into: N, O -aminals: Direct access to α-alkoxy-β-amino acid esters

Article abstract of DOI:10.1039/c9cc01374a

A new and efficient reaction has been developed to synthesize α-alkoxy-β-amino acid esters via palladium-catalyzed selective formal insertion of carbenoids into N,O-aminals under mild reaction conditions. A broad range of α-diazoesters with different substituents and various N,O-aminals were compatible with this protocol, affording the corresponding α-alkoxy-β-amino acid esters in good to excellent yields.

Full text of DOI:10.1039/c9cc01374a

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc
first methanofullerene derivatives of Sc
3
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3
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View Article Online
DOI: 10.1039/C9CC01374A
COMMUNICATION
Palladium-Catalyzed Formal Insertion of Carbenoids into N,O-
Aminals: Direct Access to α-Alkoxy-β-Amino Acid Esters
a
a,b
Wenhui Wang, and Hanmin Huang*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A new and efficient reaction has been developed to synthesize α- acid esters has stimulated tremendous efforts to the
6
alkoxy-β-amino acid esters via palladium-catalyzed selective formal development of a wide range of methods for their synthesis. In
insertion of carbenoids into N,O-aminals under mild reaction contrast, the straightforward and general methods for the
conditions. A broad range of α-diazoesters with different synthesis of such kind of compounds bearing a quaternary
substituents and various N,O-aminals were compatible with this carbon-center at the α-position have rarely been achieved,7
protocol, affording the corresponding α-alkoxy-β-amino acid esters although their unique structural and diverse biologic properties
in good to excellent yields.
have been noted. Accordingly, the development of more
general and straightforward synthetic methods toward these
compounds is in high demand.
α-Hydroxyl-β-amino acid esters are a class of important
structure motifs. They are not only frequently found in a wide
range of natural products, bioactive compounds and functional
materials, but also are valuable synthetic building blocks that
can be transformed into many other functional groups via
A: Our previous work: formal insertion reaction with aminals
NR2
N2
Pd
NR
R' CO Et
[
]
2
+
R N
2
R'
CO Et
NR2
2
1
2
simple transformation. Representative examples include the
2
3
anticancer agent Taxol, the renin inhibitor KRI-1314, the
+
P
P
NR2
4
aminopeptidase inhibitors Amastatin, and a dipeptide exotoxin
Pd
A
5
Tabtoxin (Figure 1). The importance of α-hydroxyl-β-amino
O
Ph
O
B: This work: formal insertion reaction with N,O-aminals
Ph
N
H
O
OH
HO
BzO
O
O
NR2
N2
Pd
(dppm)Cl /AgBF
H
2
4
OR'
R' CO Et
O
N
N
+
R N
2
N
H
O
o
R'
CO
Et
xylene,
8
0 C
OR'
2
OAc
O
OH
2
N
H
up to 90% yield
AcO
O
O
N
Scheme 1 Palladium-catalyzed formal insertion reaction with
diazoesters
OH
H
KRI-1314
Taxol
NH
O
OH
O
2
H
N
OH
NH
O
O
OH
OH
O
Transition-metal-catalyzed insertion of carbenoids into X-H
bonds is one of the most reliable methods for constructing
carbon-heteroatom bonds and has received considerable
O
H
N
O
N
2
OH
H
O
OH
O
O
Tabtoxin
Amastatin
Figure 1 Biologically active molecules containing α-hydroxyl-β-amino
8
developments. In contrast, the catalytic insertion of carbenoids
acid esters units.
into C-X (X is not H) bond via the same stepwise ylide
9
mechanism remain elusive, the underlying reason might be
due to the difficulty to control the selectivity for the migration
of two distinct carbon moieties attached in heteroatom. In
a.College of Chemical Engineering, Zhejiang University of Technology, Hangzhou
10
3
10024, China.
this context, we recently developed a synthetic methodology
for the efficient construction of α,β-diamino acid esters bearing
a quaternary carbon-center by palladium-catalyzed formal
insertion of carbenoids into aminals (Scheme 1A).11 In this
approach, the C-N bond of aminals was facilely cleaved by
b.
Hefei National Laboratory for Physical Sciences at the Microscale and Department
of Chemistry, Center for Excellence in Molecular Synthesis, University of Science
and Technology of China, Chinese Academy of Sciences, Hefei, 230026, P. R.
China. E-mail: hanmin@ustc.edu.cn.
†
1
Electronic Supplementary Information (ESI) available. See DOI:
0.1039/x0xx00000x
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COMMUNICATION
Journal Name
oxidation of aminal to Pd(0), enabling the desired reaction took choice for keeping high reactivity (Table 1, entries 7-9). With
View Article Online
12
DOI: 10.1039/C9CC01374A
as the palladium-precursor, the effect of
place under mild reaction conditions. Inspired by this result, Pd(dppm)Cl
2
we envisioned that an analogous reaction for the synthesis of α- counterion was investigated and disclosed that the counterion
alkoxy-β-amino acid esters might be realized by formal insertion was crucial for the reactivity (Table 1, entries 10-13). Although
of carbenoids into N,O-aminals, since the C-O bond of N,O- the reaction was virtually stopped when Pd(dppm)Cl
aminal might be more easily cleaved.13 However, the reaction alone, the cationic palladium catalyst generated in-situ by the
would be more challenging due to the lower nucleophilicity of simply mixed Pd(dppm)Cl and the corresponding silver salt
2
used
2
-
-
the cleaved RO than that of R
2
N . We believed that this problem could promote the reaction efficiently. Lower activity was
-
-
would be addressed by turning the reactivity of the catalyst. observed when ClO
Herein, we report a Pd-catalyzed selective formal insertion contrast, excellent yield was observed when BF
4
or CF
3
COO served as the counterion. In
-
4
was utilized
reaction of carbenoids into N,O-aminals, which provides a rapid (Table 1, entry 11). Highest yield up to 90% was observed when
and reliable approach to a wide range of α-methoxyl-β-amino the loading of 1a was decreased from 2.0 equiv to 1.5 equiv
acid esters with a quaternary carbon-center at the α-position (Table 1, entry 15). Other metal catalysts, such as Fe(OTf)
2
,
(
Scheme 1B).14
Cu(OTf) and Sc(OTf) were also investigated, delivering the
2
3
desired product with relative lower yields (see Supporting
Information). Finally, control reactions demonstrated that the
desired product was not produced in the absence of palladium
catalyst (Table 1, entries 17-18).
Table 1 Optimization of reaction conditions a
N
2
NBn2
[Pd]
OMe
Bn N
80 o 12 h
2
Ph
COOEt
xylene,
C,
Ph CO2Et
OMe
2a
1a
3aa
Table 2 Substrate scope of α-diazoesters a
entry
1
[Pd]
[Ag]
-
solvent
yield (%)
48
mol %)
2
Pd(dppm)Cl (5
N2
NBn2
OMe
Pd(Xantphos)(CH3
CN)
2(OTf)2
xylene
xylene
xylene
xylene
xylene
xylene
AgBF4 (10 mol %)
Bn N
2
-
-
-
-
80 oC, 12 h
2
3
4
5
Pd(dppm)(CH CN) (OTf)
83
41
64
70
R
CO
2
Et
R
CO
2
Et
3
2
2
OMe
2a
xylene,
Pd(dppp)(CH CN) (OTf)
1
3
3
2
2
Pd(dppb)(CH3
CN)
2(OTf)2
2(OTf)2
OMe
OMe
OMe
Bn N
Bn N
Bn N
2
Pd(dppf)(CH3
CN)
2
2
CO Et
2
-
CO
2
Et
CO
Et
2
6
7
8
CN)
67
75
70
Pd(PPh3)2(CH3
2(OTf)2
Cl
-
-
CN)
2(OTf)2
2(OTf)2
CH Cl2
2
Pd(dppm)(CH3
Pd(dppm)(CH3
Cl
3ca, 84%
CN)
CN)
anisole
MeOH
X-structure of 3aa
3ba, 57%
3aa, 90%
-
9
Pd(dppm)(CH3
2(OTf)2
17
80
86
OMe
OMe
OMe
OMe
Bn N
Bn N
Bn N
Bn N
2
2
2
2
1
0
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
Pd(dppm)Cl2
Pd(dppm)Cl2
Pd(dppm)Cl2
Pd(dppm)Cl2
Pd(dppm)Cl2
AgOTf
AgBF4
AgTFA
CO Et
CO Et
CO2
Et
CO2
Et
2
2
11
12
13
14
36
41
NR
Cl
Cl
Cl
F
Br
AgClO4
-
3da, 78%
3ea, 80%
3fa, 87%
3ga, 75%
OMe
OMe
OMe
b
OMe
15
16
17
18
AgBF4
AgBF4
90
72
NR
NR
Bn N
Bn N
Bn N
2
Pd(dppm)Cl2
Bn N
2
2
2
c
CO Et
2
CO Et
CO Et
2
2
Pd(dppm)Cl2
-
CO Et
2
OMe
AgBF4
-
-
OMe
3ia, 88%
MeO
a
Reaction conditions: 1a
mmol), 2a
mmol), [Pd]
mmol, 5
h,
3ha, 75%
, 55%
3ka, 89%
(0.6
(0.3
solvent
(0.015
3ja
o
mol
mmol, 10 mol
80
C,
12 isolated
OMe
OMe
OMe
%
), [Ag] (0.03
%),
mmol).
(1.0 mL),
Bn N
Bn N
Bn N
2
2
2
OMe
b
c
1a
mmol). 1a
Bn N
2
yield.
(0.45
(0.36
CO Et
CO Et
CO Et
2
2
2
H
CO Et
2
On the basis of our previous results, we initiated our study by
investigation of the reaction between ethyl 2-diazo-2-
3
la, 88%
3ma, 89%
3na, 63%
3oa, 65%
b
OMe
OMe
OMe Bn N
Bn N
OMe
Bn N
2
2
2
phenylacetate (1a) and N,N-dibenzyl-1-methoxymethanamine
Bn N
2
O
CO Et
CO
2Et
2
o
CO Et
(
2a) in xylene at 80 C with 5 mol % of cationic palladium. As
2
6
O
expected, the desired product 3aa could be obtained in 48%
isolated yield when Pd(Xantphos)(CH CN) (OTf) was utilized as
PhO
44%c
c
3ra, 55%c
3
2
2
3sa, 81%
3pa
,
3qa, 59%
a catalyst. Further optimizing the reaction conditions by
variation of the phosphine ligands disclosed that both the
bidentate and monodentate phosphine ligands could promote
the desired reaction (Table 1, entries 1-6). The bidentate dppm
bearing small bite angle is superior to all other phosphine
ligands tested here to give the desired product 3aa in 83%
a
mmol,
Reaction conditions: 1 (0.45 mmol), 2a (0.3 mmol), Pd(dppm)Cl2 (0.015
o
5 mol %), AgBF4 (0.03 mmol, 10 mol %), xylene (1.0 mL), 80 C, 12 h, isolated
b
c
mmol, 10 mol
isolated
yield.
Toluene
(1.0 mL),
yield. AgSbF
6
(0.03
%),
isolated yield.
With the optimized reaction conditions identified, the
isolated yield (Table 1, entry 2). The structure of 3aa was generality of the Pd-catalyzed insertion of carbenoids into N,O-
unambiguously confirmed by NMR spectroscopy and further aminals was investigated. The scope of the α-diazoesters was
15
validated by a single-crystal bearing X-ray diffraction analysis.
first examined, and the results are summarized in Scheme 2. To
Screening of the solvent demonstrated that xylene is the best our delight, a wide range of α-diazoesters reacted smoothly
with N,N-dibenzyl-1-methoxymethanamine 2a to afford the
2
| J. Name., 2019, 00, 1-3
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COMMUNICATION
corresponding α-methoxy-β-amino acid esters in good to 2-diazo-2-phenylacetate to give the corresponding products
View Article Online
DOI: 10.1039/C9CC01374A
(3ah-3aj) in moderate yields. N,O-aminals 2k-2n derived from
excellent yields. For the aryl diazoesters, both electron-rich and
electron-deficient substituents on the phenyl-ring underwent different alcohols could also give the desired product 3ak
the reaction smoothly with moderate to good yields (55-90% in good yields (65-83%).
yields). Typical functional groups such as chloride, fluoride,
-3an
Scheme 2 Reaction scale-up and functional group transfor-
bromine, methoxyl and alkyl were well tolerated under the
optimized reaction conditions. For instance, the substrates with
electron-deficient halogen group at ortho-, para- or meta-
position proceeded smoothly to give corresponding products in
mation
(5 mol %)
mol %)
n-Bu
BF3 Et O
4
NI
Pd(dppm)Cl
AgBF
(10
xylene (6.0
2
N
2
NBn
2
OMe
Ph CO Et
OH
4
Bn
N
2
2
2
Bn N
mL)
CH
Cl
Ph
7
CO
2
Et
OMe
2
2
2
Ph CO Et
o
o
2
80
C, 12 h
65 C, 12 h
1
a
2a
5.0 mmol
3aa, 1.7 g, 85%
,
50%
4
.5 mmol
good yields (Table 2, 3ba
-3da, 3fa-3ga). Besides, the substrates
bearing electron-rich group regardless of the position on the
phenyl ring were applicable in the present catalytic system
O
HN
i-PrMgBr
OMe
2/C
(20
wt %)
H N
2
Pd(OH)
OMe
THF, rt, 19 h
Ph CO
Et MeOH, H2 (30 atm)
o
2
(3ha
-
3la). Meanwhile, disubstituted aryl diazoesters (1e
,
1m
)
Ph
, 59%
80
C, 24 h
6
5, 84%
could also get good results in this reaction. In addition, 2-
O
O
napthyl-substitued α-diazoesters 1n was compatible with this
BF
n-Bu NI
3
Et
2
O
HO
O
Ph
-
Ph
N
Ph
N
new reaction (3na, 63%). With SbF
6
as counterion, ethyl 2-
4
Ref. 20
O
N
EtO
2
C
CH
65
Cl
2
EtO C
2
2
o
diazoacetate (1o) could be also transformed into the
corresponding product 3oa in 65% yield. Next, we investigated
the scope of aliphatic diazoesters. As expected, aliphatic
diazoesters with a long chain and functional group were also
OMe
12 h
OH
52%
O
C,
N
3
aj
8
7,
We further evaluated the utility of this reaction by
performing a large-scale experiment (Scheme 2). Under the
standard reaction conditions, the desired product 3aa could be
obtained in gram scale (1.7g) with 85% isolated yield. The
scalability and robustness of this transformation indicates its
potential application in the preparation of fine chemicals. The
applicable, affording the corresponding products 3pa-3ra in
moderate yields (44-59% yields). In addition, the reaction of
cyclic diazo compound 1s could furnish 3sa in 81% yield under
the standard reaction conditions.
Table 3 Substrate scope of N,O-aminals a
mol %)
mol %)
80 o 12 h
methyl-group could be removed by treatment of 3aa with
N2
NR1
Pd(dppm)Cl2 (5
AgBF4 (10
OR2
2
R12N
.
BF
3
Et
2
O/n-Bu
4
NI in CH
2
Cl
2
to afford the corresponding α-
Ph
CO Et
Ph
CO2
Et
2
OR2 xylene,
16
C,
hydroxyl-β-amino acid ester
the two benzyl groups contained in 3aa could be also removed
to give ethyl 3-amino-2-methoxy-2-phenylpropanoate in 84%
4
in moderate yield. In addition,
1a
2
3
R1
R2
entry
3
yield (%)
5
1
2
3
4
5
4-BrC H CH
CH3
3ab
3ac
3ad
3ae
3af
58
85
77
54
67
yield through Pd(OH) /C-catalyzed hydrogenolysis reaction in
6
4
2
2
17
2-FC H CH
CH3
6
4
2
the presence of H
gave 3-methoxy-3-phenylazetidin-2-one
is a key building block for the synthesis of β-lactam antibiotics.
The methyl-group of 3aj was also quickly removed to give ethyl
2
.
Cyclization of product
5
with i-PrMgBr
3-ClC H CH
CH3
18
6
4
2
2
6
in 59% yield, which
4-ClC H CH
CH3
6
4
19
4-CH C H CH
2
CH3
3
6
4
6
7
8
9
4-OCH C H CH
2
CH3
3ag
3ah
3ai
63
57
42
55
83
3
6
4
2
-hydroxy-3-morpholino-2-phenylpropanoate
which could be facilely transferred to quinuclidin-3-yl 2-
hydroxy-3-morpholino-2-phenylpropanoate with
7 in 52% yield,
CH3
(CH2)2
CH3
CH CH CH CH
2
CH3
3
2
2
-
-CH CH OCH CH
2
CH3
3aj
8
2
2
2
2
0
10
11
12
13
C H CH
CH CH
2
3ak
antimuscarinic activity according to the reported procedure.
6
5
2
2
2
2
3
Bn Bn
N
Bn N
C H CH
CH CH CH CH
3al
3am
3an
78
75
65
OTf
N
2
OMe
2
6
5
3
2
2
2
xylene
P
+
+
Et
Bn N
+
MeOH
80 o 1 h
2
Pd
(1)
C H CH
C H CH
Ph
CO
2
C,
2
Ph CO Et
6
5
6
5
2
Ph
2
CO Et
P
A
1a
P
3aa
9aa
12% yield
Bn N
C H CH
CH CH=CH
6
5
2
2
：
Xantphos
25% yield
aReaction conditions: 1a
P
mmol),
2
(0.3
mmol, 10 mol
mmol),
(
0.45
%), AgBF4 (0.03
C, 12 h, isolated yield.
Pd(dppm)Cl2
2
mmol, 5 mol
%), xylene (1.0 mL),
80
(
0.015
o
Ph
CO
2
Et
N
2
OMe
NBn2
OMe
9ra
standard condition Bn
2
N
+
+
Ph
CO
2
Et
CO
2
Et
9% yield
(2)
1
r
Ph
2
Bn N
2a
3ra
55%
The substrate scope was further extended to various
yield
Ph
CO
2
Et
substituted N,O-aminals. As shown in Table 3, N,O-aminals
derived from different amines and alcohols afforded the
corresponding products in moderate to good yields. The
reaction of N,O-aminals, derived from benzylamines bearing a
variety of electron-withdrawing (F, Cl and Br) and electron-
10
not detected
Scheme 3 Controlling experiment
To get some insight into the mechanism of the present
reaction, a stoichiometric reaction of cyclopalladated complex-
donating substitutents (CH
aminals, proceeded well to deliver the products in the range of
4-90% yields (3aa 3ag). Moreover, N,O-aminals prepared from
CH OH and simple alkyl amines, such as diisopropylamine,
3 3
and OCH ) on the phenyl ring of the
A
, 2-diazo-2-phenylacetate (1a) and MeOH was conducted. As a
result, the desired product 3aa was obtained in 25% yield,
together with the dehydrogenated product 9aa in 12% yield,
5
-
3
indicating the plausible intermediacy of complex-
A in this
dibutylamine and morpholine, could react smoothly with ethyl
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2019, 00, 1-3 | 3
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Journal Name
1
678; (b) K. Iizuka, T. Kamijo, H. Harada, K.ViAewkaArhticalne eO,nlinTe.
transformation (Scheme 3, eq.1). Moreover, the compound 9ra
was also detected in the reaction of 1r with 2a under the
standard reaction conditions, but the compound 10 eliminated
hydride from alkyl-chain was not detected (Scheme 3, eq.2),
which suggests that the double bond formation is stemmed
from the Pd-catalyzed β-hydride elimination because the
electron-rich hydride is preferred to be removed in the metal-
Kubota, H; Umeyama, T. Ishida and Y. Kiso, J. Med. Chem.,
DOI: 10.1039/C9CC01374A
1
990, 33, 2707.
4
(a) T. Aoyagi, H. Tobe, F. Kojima, F. Hamada, T. Takeuchi and
H. Umezawa, J. Antibiot., 1978, 31, 636; (b) H. Blomgren and
J. Wasserman, Cancer Lett., 1981, 11, 303; (c) R. Roers and G.
V. Verdine, Tetrahedron Lett., 2001, 42, 3563.
5
6
W. W. Stewart, Nature, 1971, 229, 174.
(a) K. Juhl and A. Jorgensen, J. Am. Chem. Soc., 2002, 124
,
21
promoted β-hydride elimination process.
According to the previous reports and above results,11
plausible mechanism is proposed (Fig. 2). The cyclopalladated
complex is generated via oxidative addition of Pd(0) to the
N,O-aminal, which reacts with diazoester to generate Pd-
. Nucleophilic attacks the intermediate
, which undergoes reductive
(pathway ). On the
would be generated via other
2
420; (b) Z. Liu, N. Ma, Y. Jia, M. Bois-choussy, A. Malabarba
a
and J . Zhu, J. Org. Chem., 2005, 70, 2847; (c) F. Gassa, A.
Contini, G. Fontana, S. Pellegrino and M. L. Gelmi, J. Org.
Chem., 2010, 75, 7099; (d) C. G. Goodman, D. T. Do and J. S.
Johnson, Org. Lett., 2013, 15, 2446; (e) S. Mallik, V.
Bhajammanavar, I. Ramakrishna and M. Baidya, Org. Lett.,
A
1
carbene intermediate
B
2
017, 19, 3843.
-
B
by MeO to give intermediate
C
7
8
9
(a) C. Christensen, K. Juhl, R. G. Hazell and A. Jorgensen, J. Org.
Chem., 2002, 67, 4875; (b) J.-L. Jiang, M. Yao and C.-D. Lu, Org.
Lett., 2014, 16, 318; (c) T. Rajasekaran, G. Karthik, B. Sridhar,
elimination to give the desired product
other hand, the intermediate
3
I
D
S. K. Kumar and B. V. S. Reddy, Eur. J. Org. Chem., 2014, 11
221.
,
migratory insertion. Moreover, due to the electron-donated
2
-
effect of R
2
N group, the hydride adjacent to the amine group
For leading reviews, see: (a) M. P. Doyle, R. Duffy, M. Ratnikov,
L. Zhou, Chem. Rev., 2010, 110, 704; (b) S.-F. Zhu, Q.-L. Zhou,
Acc. Chem. Res., 2012, 45, 1365; (c) X. Zhao, Y. Zhang, J. Wang,
Chem. Commun., 2012, 48, 10162; (d) D. Gillingham and N.
Fei, Chem. Soc. Rev., 2013, 42, 4918.
will be selectively eliminated via β-hydride elimination to give
as the byproduct (pathway II).
9
+
R NCH Pd
2
2
A
NR
COOEt
NR2
2
N
2
R1
C
R N
2
+
R1
J. Wang, In Comprehensive Organic Chemistry III; Mingos, D.
M. P.; Crabtree, R. H.; Eds.; Elsevier, Oxford, 2007; pp 151-178.
Pd
B
R1 CO
Et
2
Pd+
R1
EtO
2
CO
pathway II
2
Et
D
HPdX
-
10 For selected examples, see: (a) J. S. Clark, M. D. Middleton,
Org. Lett., 2002, , 765; (b) C.-Y. Zhou, W.-Y. Yu, P. W. H. Chan
and C.-M. Che, J. Org. Chem., 2004, 69, 7072; (c) J. A. Vaneckoc
and F. G. West, Org. Lett., 2005, , 2949.
1 G. Qin, L. Li, J. Li and H. Huang, J. Am. Chem. Soc., 2015, 137
2490.
MeO
4
NR2
NR2
R1
R1 COOEt pathway
I
MeO
Pd
7
CO
2
Et
OMe
3
1
1
,
Pd(0)
C
1
Figure 2 Plausible reaction pathway
2 (a) Y. Xie, J. Hu, Y. Wang, C. Xia and H. Huang, J. Am. Chem.
Soc., 2012, 134, 20613; (b) Y. Xie, J. Hu, P. Xie, B. Qian and H.
Huang, J. Am. Chem. Soc., 2013, 135, 18327; (c) J. Hu, Y. Xie
and H. Huang, Angew. Chem. Int. Ed., 2014, 53, 7272; (d) Y.
Liu, Y. Xie, H. Wang and H. Huang, J. Am. Chem. Soc., 2016,
In summary, we have developed a new and efficient protocol
for the formal insertion of carbenoids into N,O-aminals under
the catalysis of cationic palladium-complex, which provides a
rapid and reliable approach to α-alkoxy-β-amino acid esters
with a quaternary carbon-center at the α-position. Various α-
diazoesters and N,O-aminals are applicable to give a wide range
of α-alkoxy-β-amino acid esters in good to excellent yields.
1
38, 4314; (e) L. Li, P. Liu, Y. Su and H. Huang, Org. Lett., 2016,
18, 5736; (f) L. Li, X. Zhou, B. Yu and H. Huang, Org. Lett., 2017,
19, 4600; (g) C. Qiao, A. Chen, B. Gao, Y. Liu and H. Huang,
Chin. J. Chem., 2018, 36, 929.
1
1
3 (a) J. Xu, X. Chen, M. Wang, P. Zhang, B.-A. Song and Y. Chi,
Angew. Chem. Int. Ed., 2015, 54, 5161. (b) Y.-Y. Huang, C. Cai,
X. Yang and Z.-C. Lv, ACS Catal., 2016, 6, 5747.
4 During our preparation this manuscript, a Pd-catalyzed
enantioselective protocol with diazoesters, alcohol and N,O-
aminal has been described: Z. Kang, Y. Wang, D. Zhang, R. Wu,
X. Xu and W. Hu, J. Am. Chem. Soc., 2019, 141, 1473.
Acknowledgements
This research was supported by the National Natural Science
Foundation of China (21672199, 21790333, and 21702197), CAS
Interdisciplinary Innovation Team, the Fundamental Research
Funds for the Central Universities and the Anhui provincial
Natural Science Foundation (1708085MB28).
1
5 CCDC 1892100
(3aa
)
contains the supplementary
crystallographic data for this paper. This data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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