Synthesis of indolizine derivatives triggered by the oxidative addition of aroyl chloride to pd(0) complex

Article abstract of DOI:10.1021/acs.joc.0c00161

An efficient synthesis of indolizine derivatives from propargylic pyridines and aroyl chlorides was developed. The 5-endo-dig cyclization was initiated by the in situ formed acylpalladium species from the facile oxidative addition of aroyl chloride to Pd(

Full text of DOI:10.1021/acs.joc.0c00161

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Article
Synthesis of Indolizine Derivatives Triggered by the
Oxidative Addition of Aroyl Chloride to Pd(0) Complex
Yahui Li, Wei Xiong, Zhifeng Zhang, and Tongyu Xu
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.0c00161 • Publication Date (Web): 29 Apr 2020
Downloaded from pubs.acs.org on April 29, 2020
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Synthesis of Indolizine Derivatives Triggered by the Oxidative Addition of Aroyl
Chloride to Pd(0) Complex
8
9
Yahui Li,§ Wei Xiong,§ Zhifeng Zhang, Tongyu Xu*
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Key Laboratory of Synthetic and Natural Functional Molecule of the Ministry of Education, College of
Chemistry & Materials Science, Northwest University, Xi’an 710127, P.R. China
*E-mail: xutongyu@nwu.edu.cn
TOC
OR1
[ArC
OR1
O
5-endo-dig
cyclization
PdCl]
OR1
R3
O
Pd cat.
base
N
R2
R3
N
+
O
Ar
R3
N
R2
R2
up to 99% yield
Ar
Cl
ABSTRACT: An efficient synthesis of indolizine derivatives from propargylic pyridines and aroyl
chlorides was developed. The 5-endo-dig cyclization was initiated by the in situ formed acylpalladium
species from the facile oxidative addition of aroyl chloride to Pd(0) complex. This transformation
successfully occurred in the presence of an N-nucleophilic moiety and acid chlorides, a good electrophilic
partner, affording highly functionalized indolizines in good-to-excellent yields.
INTRODUCTION
Pd-catalyzed cross-coupling reactions play a key role in current organic synthesis.1,2 Among different
electrophiles, acid chlorides are a useful and versatile coupling partner, easily available from inexpensive
and numerous available carboxylic acids.3 Owing to the facile oxidative addition to metal centers, acid
chlorides have been used in the reactions with various substrates such as alkenes,4 alkynes,5 allenes,6 and
organometallic reagents.7 Diverse transformations have been achieved because the carbonyl and chloro
functionalities in acid chlorides can be involved in the catalytic system. For example, ketones can be
obtained by arylacylation,8 while various types of C−C bonds can be constructed by decarbonylative
cross-coupling reactions.9 Moreover, C-Cl bonds can be formed with or without the loss of CO.10
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Indolizine is one of the most important skeletons among nitrogen-containing heterocycles and has
been found in several natural products and biologically active compounds. Among the strategies to access
indolizine structures, propargylic pyridines have attracted much attention, affording diverse indolizine
derivatives.11-13 Pd-catalyzed carbonylative cyclization of propargylic pyridines has been developed to
efficiently form indolizines, where acylpalladium species is assumed to be the key intermediate in
initiating the cyclization.13a,13b Considering the convenient formation of acylpalladium species from acid
chlorides and Pd(0) complex, we envisioned that the acylpalladium species would induce 5-endo-dig
cyclization to form highly functionalized indolizine derivatives (Scheme 1, Path a). Transition-metal-
catalyzed coupling reactions using acid chlorides as a good electrophilic partner for substrates with an
N-nucleophilic moiety in the molecular structure were rarely studied, where the nitrogen atom might
easily react with acid chlorides to form the corresponding amides (Scheme 1, Path b). Herein, we report
an efficient synthesis of indolizine derivatives by the cyclization of propargylic pyridines with aroyl
chlorides triggered by the oxidative addition of aroyl chloride to Pd(0) complex.
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[ArC
OR1
O
5-endo-dig
cyclization
OR1
PdCl]
O
(a)
OR1
R3
N
Ar
R3
R3
R2
R2
N
N
R2
N
Pd cat.
base
+
OR1
O
(b)
Cl
R3
Ar
Amidation
R2
O
Ar
Cl
Scheme 1. Possible Reactions of Propargylic Pyridines and Aroyl Chlorides
RESULTS AND DISCUSSION
Initially, the reaction between substrate 1a and benzoyl chloride (2a) was evaluated to optimize the
reaction conditions (Table 1). In the presence of 5 mol% Pd(PPh3)4, indolizine 3aa was isolated in 76%
yield when using toluene as the solvent and Et3N as the base at 60 °C (entry 1). The yield of 3aa increased
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Table 1. Screening of the Reaction Conditionsa
7
8
9
OPiv
Ph
OPiv
O
R
O
Pd cat.
+
N
base, solvent
Ph
Cl
N
Ph
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1a
2a
3aa
entry
cat. (mol %)
Pd(PPh3)4/5
Pd(PPh3)4/5
Pd(PPh3)4/5
Pd(PPh3)4/5
Pd(PPh3)4/5
Pd(PPh3)4/5
Pd(PPh3)4/5
Pd(PPh3)4/5
Pd(tBu3P)2/5
Pd(dppf)Cl2/5
Pd(PPh3)2Cl2/5
Pd(OAc)2/5
Pd(PPh3)4/2
Pd(PPh3)4/2
solvent
base
temp (°C)
yieldb (%)
NEt3
1
2
Toluene
THF
MeCN
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
60
60
60
60
60
60
60
60
60
60
60
60
60
20
76
89
59
0
NEt3
NEt3
3
NaHCO3
4
5
AcONa
DABCO
DBU
0
6
82
0
7
8
pyridine
NEt3
0
9
0
NEt3
10
11
12c
13
14
0
NEt3
70
53
87
3
NEt3
NEt3
NEt3
a Conditions: 0.25 mmol of 1a, 0.5 mmol of 2a, 0.75 mmol of base, 2.5 mL of solvent, 20-24 h. b
Isolated yield. c 10 mol % of PPh3 as the ligand.
to 89% when THF was used as the solvent (entry 2), while 58% yield of 3aa was obtained when MeCN
was used as the solvent (entry 3). Bases were evaluated using THF as the solvent. No desired product
was formed when NaHCO3 or AcONa was used as the base (entries 4 and 5). When DABCO was used
as the base, indolizine 3aa was obtained in 82% yield (entry 6). However, 3aa was not formed when
DBU or pyridine was used as the base (entries 7 and 8). The results showed that the choice of base is
important to the transformation. Inorganic bases did not work due to the heterogeneous reactions. When
organic bases were used, Et3N and DABCO could promote the reaction, while pyridine and DBU
prevented the cyclization. The stable salt formed from pyridine or DBU with aroyl chloride might prevent
the formation of ArCOPd(II)Cl intermediate. Then, different Pd catalysts were evaluated using THF as
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the solvent and NEt3 as the base (entries 9-12). Indolizine 3aa was not formed when using a Pd catalyst
with strong electron-donor ligand tBu3P or bidentate ligand dppf. When Pd(II) catalyst Pd(PPh3)2Cl2 was
replaced with Pd(PPh3)4, the yield of 3aa decreased to 70%. When Pd(OAc)2 was used as the precursor
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of Pd catalyst and PPh3 was used as the ligand, 3aa was obtained in 53% yield. When the content of
Pd(PPh3)4 was reduced to 2 mol%, indolizine 3aa was obtained in 87% yield, similar to that of 5 mol%
Pd(PPh3)4 (entry 13). The yield decreased significantly when the reaction was carried out at room
temperature (entry 14).
Table 2. Synthesis of Indolizine Derivatives from 1a with Different Aroyl Chloridesa
OPiv
OPiv
O
O
R
2 mol% Pd(PPh3)4
Et3N, THF, 60 °C
+
N
R
Cl
N
Ph
Ph
2
1a
3
OPiv
OPiv
Ph
OPiv
O
OPiv
Ph
O
O
O
Me
N
N
N
N
Ph
Ph
Me
Ph
b
Me
3ac
, 95%
OPiv
3ab
, 54%
3ad
, 86%
OPiv
3aa
, 87% (83%)
OPiv
OPiv
O
O
O
O
N
N
N
N
Ph
Ph
Ph
Ph
NO2
F
3ag
, 79%
3ah
CO2Me
, 89%
OMe
3af
, 72%
OPiv
3ae
, 72%
OPiv
OPiv
OPiv
O
O
O
O
N
N
N
N
Cl
Ph
Ph
Ph
Cl
Ph
Cl
, 79%
Br
Cl
3al
3ai
3aj
, 66%
, 91%
3ak
, 85%
OPiv
OPiv
Ph
OPiv
O
O
O
N
N
N
O
Ph
3am
N
Ph
c
3an
, 54%
, 60%
3ao
, 69%
a Conditions: 0.25 mmol of 1a, 0.5 mmol of 2, 2 mol% of Pd(PPh3)4, 0.75 mmol of Et3N, 2.5 mL of
THF, 20-24 h, isolated yield. b yield of 2 mmol scale up reaction. c nicotinoyl chloride hydrochloride
(0.5 mmol) and Et3N (1.25 mmol) were used.
The reactions of 1a with different aroyl chlorides were evaluated in the presence of 2 mol% Pd(PPh3)4,
THF as the solvent, and Et3N as the base at 60 °C (Table 2). Aroyl chlorides with electron-donating (Me
and OMe, 3ab-3ae) or electron-withdrawing (CO2Me, NO2 and F, 3af-3ah) substituents successfully
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afforded indolizines in high isolated yields. The reaction of o-toluoyl chloride afforded the corresponding
indolizine 3ab in 54% yield, indicating that the reaction is affected by steric hindrance. Aroyl chlorides
with different halide substituents also smoothly furnished the corresponding indolizines (3ah-3al).
Indolizine 3am was obtained in moderate yield from 1-naphthoyl chloride because of the steric effect.
Besides, heteroaroyl moieties were successfully introduced to the indolizine structures, affording
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products 3an and 3ao in 60% and 69% yields, respectively.
Table 3. Synthesis of Indolizine Derivatives from Propargylic Pyridines with Aroyl Chloridesa
OR1
OR1
O
O
2 mol% Pd(PPh3)4
Et3N, THF, 60 °C
R3
+
R3
R4 Cl
N
R4
N
R2
R2
2
1
3
OAc
Ph
OAc
Ph
OAc
O
O
OAc
O
O
N
N
N
N
Cl
Cl
Ph
Ph
Cl
Br
Cl
3bl
, 75%
3bk
3bj
, 69%
, 85%
3bi
, 87%
O
O
O
O
OBz
Ph
Ph
OBz
Ph
O
O
O
O
O
N
N
N
Cl
N
Ph
Ph
Ph
Ph
Me
3ea
, 54%
3ck
, 93%
3cd
3da
, 77%
, 97%
OPiv
OPiv
OPiv
OTBS
O
O
O
O
N
N
N
N
Ph
nBu
nBu
nBu
Cl
Ph
CH3
b
Cl
3fa
, 51%
3gi
, 75%
3gk
, 89%
OBz
3gd
, 67%
OPiv
OPiv
OPiv
Cl
O
O
O
O
N
N
N
N
Ph
Ph
Ph
Ph
tBu
Ph
Ph
Ph
Me
3ja
c
3ha
, trace
3ka
, 83%
3ia
, 53%
, 99%
a Conditions: 0.25 mmol of 1, 0.5 mmol of 2, 2 mol% of Pd(PPh3)4, 0.75 mmol of Et3N, 2.5 mL of
THF, 20-24 h, isolated yield. b 30 h. c R1 = H, 0.75 mmol of 2a, 1.0 mmol of Et3N.
The reaction conditions were then applied to diverse propargylic pyridines and aroyl chlorides (Table
3). When the pivaloyl group of substrate was replaced with an acetyl group, the corresponding indolizine
products were isolated in good yields (3bi-3bl). The reactions of benzoate and cinnamate afforded the
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indolizine products in good-to-excellent yields. Indolizine 3ea was obtained in 54% yield from the
corresponding furan-2-carboxylate. The reaction of substrate with a TBS group gave 3fa in 51% yield
with a longer reaction time. The indolizine was obtained in 67-89% yields when the substituent on the
alkynyl moiety was changed to butyl group, but a trace amount of product was observed for tert-butyl
(3ha) due to steric hindrance. The presence of a chlorine or methyl substituent on the pyridine ring
resulted in indolizine 3ia and 3ja in 53% and 99% yields, respectively. When the propargylic alcohol 1k
reacted with benzoyl chloride, the corresponding ester 1c was quickly formed as the major product (92%
yield) using one equivalent of benzoyl chloride. The indolizine product 3ka was obtained in 83% yield
using excessive benzoyl chloride.
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To elucidate the mechanism, (PhCO)Pd(PPh3)2Cl was prepared from Pd(PPh3)4 and benzoyl
chloride.14 Then, (PhCO)Pd(PPh3)2Cl was used in the reaction with propargylic pyridine 1a in the
presence of Et3N, affording indolizine 3aa in 55% isolated yield (Equation 1). The results indicate that
ArCOPdX formed from Pd(0) complex and aroyl chloride might be the key intermediate to induce the
5-endo-dig cyclization. On the basis of the above results, a possible mechanism is proposed in Scheme
2. First, the oxidative addition of aroyl chlorides with Pd(0) complex forms ArCOPd(II)Cl
intermediate. Subsequent coordination of ArCOPd(II)Cl to the triple bond initiates 5-endo-dig
cyclization. The indolizine 3 is released after reductive elimination.
OPiv
OPiv
O
Et3N (2 equiv)
THF, 60 °C
+
(PhCO)Pd(PPh3)2Cl
1 equiv
(1)
N
Ph
N
Ph
Ph
1 equiv
3aa
, 55% yield
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OR1
O
Pd(0)
O
Ar
Cl
R3
2
N
Ar
R2
3
7
OR1
8
9
R3
OR1
Pd(II)
Ar
O
ArCOPd(II)Cl
N
A
R2
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D
R3
N
R2
base•HCl
1
ArCOPd(II)Cl
OR1
base
H
OR1
Pd(II)
Ar
R3
R3
N
R2
N
R2
B
O
C
Scheme 2. Proposed Mechanism for the Cyclization
In conclusion, an efficient synthesis of indolizine derivatives was developed by Pd-catalyzed
cyclization of propargylic pyridines with aroyl chlorides. The cyclization was triggered by the in situ
formed ArCOPdX species obtained from the facile oxidative addition of aroyl chloride to Pd(0) complex.
This method provides a convenient route to synthesize indolizines as an alternative of
carbonylation/cyclization.
EXPERIMENTAL SECTION
General Considerations. Unless otherwise noted, all the chemicals were purchased from commercial
suppliers and were used as received. Solvents were dried and distilled by standard procedures prior to
use. All reactions were performed under an inert atmosphere of nitrogen unless otherwise stated. All 1H
and 13C{1H} NMR spectra were recorded on JEOL 400 and JEOL 600 spectrometers. The NMR chemical
shift values refer to CDCl3 (δ (1H), 7.26 ppm; δ (13C), 77.16 ppm). Mass spectra were obtained on a
micrOTOF-Q II mass spectrometer.
General Procedures for the Preparation of Propargylic Pyridines 1: To a solution of alkyne (6.5
mmol, 1.3 equiv) in THF (10 mL) was added ethylmagnesium bromide (2 mL, 3 M in Et2O, 6 mmol, 1.2
equiv) dropwise at 0 °C under N2 atmosphere. The reaction mixture was stirred at 0 °C for 30 min and
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then cooled to -78 °C. A solution of pyridine-2-carboxaldehyde (5 mmol, 1 equiv) in THF (4 mL) was
added dropwise. The reaction mixture was stirred at -78 °C for 1 h and allowed to warm to room
temperature, quenched with saturated NH4Cl solution (10 mL). The aqueous phase was extracted by ethyl
acetate (10 mL) three times. The combined organic solution was washed with brine and dried over
anhydrous Na2SO4, filtered and concentrated to give the crude propargyl alcohol. The crude propargyl
alcohol was dissolved in DCM (20 mL). DMAP (0.5 mmol, 0.1 equiv) and Et3N (12.5 mmol, 2.5 equiv)
was added. Then acyl chloride (7.5 mmol, 1.5 equiv) was added dropwise to the solution at 0 °C. The
reaction was stirred at 0 °C until the alcohol disappeared, quenched with saturated NH4Cl solution (20
mL). The aqueous phase was extracted by DCM (15 mL) three times. The combined organic solution
was washed with brine and dried over anhydrous Na2SO4, filtered and concentrated. The resultant residue
was purified by column chromatography to give the product. New substrates 1c-e, 1i were prepared by
this known method. Substrates 1a-b, 1f-h and 1j are known compounds and were synthesized following
the literature procedure.13a-c Products 3ag-h, 3aj-o, 3bi-l, 3cd, 3ck, 3da, 3ea, 3fa, 3gd, 3gi, 3gk, 3ia, 3ja
and 3ka are new compounds, 3aa-f and 3ai are known compounds13b and were confirmed by 1H NMR
and 13C NMR.
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3-Phenyl-1-(pyridin-2-yl)prop-2-yn-1-yl benzoate (1c): Purified by flash chromatography on silica gel
1
with hexanes/EtOAc (v/v = 5:1), 1.2 g, 76% yield, brown solid, m.p. 96-97 °C. H NMR (400 MHz,
CDCl3) δ 8.61 (d, J = 4.5 Hz, 1H), 8.09 (d, J = 7.9 Hz, 2H), 7.75-7.68 (m, 2H), 7.54-7.21 (m, 9H), 6.94
(s, 1H). 13C{1H} NMR (101 MHz, CDCl3) δ 165.4, 156.4, 149.8, 137.3, 133.4, 132.2, 130.1, 129.7, 129.0,
128.5, 128.3, 123.7, 122.1, 121.9, 87.7, 85.0, 67.8. HRMS (ESI) m/z calcd for C21H15NO2 (M + Na)+
336.0995, found 336.0996.
3-Phenyl-1-(pyridin-2-yl)prop-2-yn-1-yl cinnamate (1d): Purified by flash chromatography on silica
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gel with hexanes/EtOAc (v/v = 5:1), 1.1 g, 62% yield, pale yellow oil. H NMR (400 MHz, CDCl3) δ
8.60 (d, J = 4.8 Hz, 1H), 7.76-7.69 (m, 2H), 7.63 (d, J = 7.8 Hz, 1H), 7.47-7.42 (m, 4H), 7.33-7.31 (m,
3H), 7.26-7.19 (m, 4H), 6.82 (s, 1H), 6.49 (d, J = 16 Hz, 1H). 13C{1H} NMR (101 MHz, CDCl3) δ165.6,
156.3, 149.8, 146.2, 137.3, 134.4, 132.1, 130.6, 129.0, 128.9, 128.3, 128.3, 123.7, 122.1, 122.0, 117.4,
87.6, 85.0, 67.3. HRMS (ESI) m/z calcd for C23H17NO2 (M + Na)+ 362.1151, found 362.1151.
3-Phenyl-1-(pyridin-2-yl)prop-2-yn-1-yl furan-2-carboxylate (1e): Purified by flash chromatography
on silica gel with hexanes/EtOAc (v/v = 5:1), 0.9 g, 60% yield, brown oil. 1H NMR (400 MHz, CDCl3)
δ 8.65 (ddd, J = 4.8, 1.6, 0.9 Hz, 1H), 7.80-7.72 (m, 2H), 7.60 (dd, J = 1.7, 0.8 Hz, 1H), 7.50-7.47 (m,
2H), 7.235-7.27 (m, 5H), 6.96 (s, 1H), 6.51 (dd, J = 3.5, 1.7 Hz, 1H). 13C{1H} NMR (101 MHz, CDCl3)
δ 157.4, 155.9, 149.8, 146.9, 144.1, 137.3, 132.2, 129.0, 128.4, 123.8, 122.0, 119.2, 112.1, 88.0, 84.6,
67.6. HRMS (ESI) m/z calcd for C19H13NO3 (M + Na)+ 326.0788, found 326.0795.
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1-(4-Chloropyridin-2-yl)-3-phenylprop-2-yn-1-yl pivalate (1i): Purified by flash chromatography on
silica gel with hexanes/EtOAc (v/v = 5:1),1.3 g, 79% yield, white solid, m.p. 58-59 °C. 1H NMR (400
MHz, CDCl3) δ 8.45 (d, J = 5.3 Hz, 1H), 7.54 (d, J = 1.8 Hz, 1H), 7.39 (dd, J = 7.4, 1.6 Hz, 2H), 7.25-
7.19 (m, 4H), 6.61 (s, 1H), 1.21 (s, 9H). 13C{1H} NMR (101 MHz, CDCl3) δ 176.9, 158.3, 150.6, 145.2,
132.2, 129.1, 128.4, 123.9, 122.0, 121.9, 87.6, 84.5, 66.5, 39.0, 27.2. HRMS (ESI) m/z calcd for
C19H18ClNO2 (M + Na)+ 350.0918, found 350.0953.
General Procedure for the Synthesis of Indolizine Derivatives by Pd-Catalyzed Cyclization of
Propargylic Pyridines with Aroyl Chlorides: To a 25 mL Schlenk tube were added 1a (73 mg, 0.25
mmol), Pd(PPh3)4 (5.8 mg, 2 mol%) under nitrogen. Then benzoyl chloride 2a (70 mg, 0.5 mmol), THF
(2.5 mL) and Et3N (104 μL, 0.75 mmol) were added sequentially to the reaction. The Schlenk tube was
placed in an oil bath and heated to 60 °C. After stirring at 60 °C for 20 h, the reaction mixture was cooled
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to room temperature and concentrated under vacuum. The residue was purified by flash chromatography
on silica gel with hexanes/EtOAc (v/v = 5:1) as eluent to afford the product 3aa (86 mg, 87% yield).
Procedure for the 2.0 mmol Scale up Reaction: To a 50 mL Schlenk flask were added 1a (587 mg,
2.0 mmol), Pd(PPh3)4 (46.4 mg, 2 mol%) under nitrogen. Then benzoyl chloride 2a (560 mg, 4.0 mmol),
THF (20 mL) and Et3N (830 μL, 6.0 mmol) were added sequentially to the reaction. The flask was placed
in an oil bath and heated to 60 °C. After stirring at 60 °C for 30 h, the reaction mixture was cooled to
room temperature and concentrated under vacuum. The residue was purified by flash chromatography
on silica gel with hexanes/EtOAc (v/v = 5:1) as eluent to afford the product 3aa (660 mg, 83% yield).
2-(4-Nitrobenzoyl)-3-phenylindolizin-1-yl pivalate (3ag): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 87.7 mg, 79% yield, brown solid, m.p. 158-159 °C. 1H NMR (400
MHz, CDCl3) δ 8.02 (d, J = 8.8 Hz, 2H), 7.89 (d, J = 7.3 Hz, 1H), 7.78 (d, J = 8.7 Hz, 2H), 7.30-7.22
(m, 6H), 6.73 (dd, J = 9.1, 6.4 Hz, 1H), 6.52-6.49 (m, 1H), 1.25 (s, 9H). 13C{1H} NMR (101 MHz,
CDCl3) δ 190.2, 176.9, 149.5, 143.8, 130.8, 130.5, 129.3, 128.9, 128.8, 126.2, 124.0, 123.1, 122.1, 118.7,
117.5, 117.1, 113.1, 39.1, 27.1. HRMS (ESI) m/z calcd for C26H22N2O5 (M + Na)+ 465.1421, found
465.1419.
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2-(4-Fluorobenzoyl)-3-phenylindolizin-1-yl pivalate (3ah): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 92 mg, 89% yield, brown solid, m.p. 121-122 °C. 1H NMR (400
MHz, CDCl3) δ 7.86 (d, J = 7.0 Hz, 1H), 7.70-7.67 (m, 2H), 7.29-7.19 (m, 4H), 7.13 (d, J = 8.8 Hz, 1H),
6.86 (t, J = 8.4 Hz, 2H), 6.64 (dd, J = 8.5, 6.8 Hz, 1H), 6.41 (t, J = 6.7 Hz, 1H), 1.11 (s, 9H). 13C NMR
(101 MHz, CDCl3) δ 190.3, 176.8, 166.6, 164.1, 135.2, 135.2, 132.5, 132.4, 130.7, 129.7, 128.9, 128.5,
125.8, 123.5, 122.7, 122.1, 118.3, 117.1, 115.2, 115.0, 112.6, 39.1, 27.1. HRMS (ESI) m/z calcd for
C26H22FNO3 (M + Na)+ 438.1476, found 438.1470.
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2-(4-Bromobenzoyl)-3-phenylindolizin-1-yl pivalate (3aj): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 79 mg, 66% yield, pale yellow solid, m.p. 106-107 °C. 1H NMR
(400 MHz, CDCl3) δ 7.85 (d, J = 7.2 Hz, 1H), 7.52 (d, J = 8.3 Hz, 2H), 7.33 (d, J = 8.3 Hz, 2H), 7.28-
7.18 (m, 7H), 7.12 (d, J = 9.1 Hz, 1H), 6.64 (dd, J = 9.1, 6.3 Hz, 1H), 6.41 (t, J = 6.7 Hz, 1H), 1.11 (s,
9H). 13C{1H} NMR (101 MHz, CDCl3) δ 190.7, 176.7, 137.6, 131.4, 131.3, 130.7, 129.6, 128.9, 128.6,
127.4, 125.9, 123.6, 122.7, 122.1, 118.3, 118.0, 117.1, 112.7, 39.1, 27.1. HRMS (ESI) m/z Calcd. for
C26H22BrNO3 (M + Na)+ 498.0675, found: 498.0681.
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2-(3-Chlorobenzoyl)-3-phenylindolizin-1-yl pivalate (3ak): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 92.6 mg, 85% yield, pale yellow solid, m.p. 136-137 °C. 1H NMR
(400 MHz, CDCl3) δ 7.81 (d, J = 7.3 Hz, 1H), 7.59 (t, J = 1.5 Hz, 1H), 7.52 (d, J = 7.7 Hz, 1H), 7.28-
7.08 (m, 8H), 6.62 (dd, J = 8.9, 6.4 Hz, 1H), 6.41-6.37 (m, 1H), 1.12 (s, 9H). 13C{1H} NMR (101 MHz,
CDCl3) δ 190.3, 176.7, 140.4, 134.2, 132.1, 130.7, 130.0, 129.6, 129.4, 128.8, 128.6, 127.7, 125.9, 123.9,
122.8, 122.1, 118.3, 117.8, 117.1, 112.7, 39.1, 27.1. HRMS (ESI) m/z calcd for C26H22ClNO3 (M + Na)+
454.1180, found 454.1182.
2-(3,5-Dichlorobenzoyl)-3-phenylindolizin-1-yl pivalate (3al): Purified by flash chromatography on
silica gel with hexanes/EtOAc (v/v = 10:1), 92 mg, 79% yield, pale yellow solid, m.p. 131-132 °C. 1H
NMR (400 MHz, CDCl3) δ 7.91 (d, J = 7.3 Hz, 1H), 7.55 (d, J = 2 Hz, 2H), 7.36-7.27 (m, 6H), 7.25 (d,
J = 9.2 Hz, 1H), 6.74 (ddd, J = 9.2, 6.4, 0.6 Hz, 1H), 6.53-6.50 (m, 1H), 1.29 (s, 9H). 13C{1H} NMR
(101 MHz, CDCl3) δ 189.0, 176.9, 141.1, 134.8, 131.7, 130.7, 129.4, 128.9, 128.8, 128.2, 126.1, 124.1,
122.9, 122.1, 118.6, 117.2, 117.1, 113.0, 39.2, 27.1. HRMS (ESI) m/z calcd for C26H21Cl2NO3 (M + Na)+
488.0791, found 488.0788.
2-(1-Naphthoyl)-3-phenylindolizin-1-yl pivalate (3am): Purified by flash chromatography on silica gel
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with hexanes/EtOAc (v/v = 10:1), 60 mg, 54% yield, pale yellow solid, m.p. 70-71 °C.1H NMR (400
MHz, CDCl3) δ 8.38 (d, J = 7.9 Hz, 1H), 7.78-7.72 (m, 3H), 7.61 (d, J = 6.4 Hz, 1H), 7.51-7.42 (m, 2H),
7.26-7.09 (m, 7H), 6.69 (m, 1H), 6.45 (t, J = 7.0 Hz, 1H), 1.12 (s, 9H). 13C{1H} NMR (101 MHz,
CDCl3) δ 193.3, 177.0, 137.6, 133.6, 131.6, 130.9, 130.5, 129.5, 129.2, 128.3, 128.2, 128.0, 127.3,
126.4, 126.1, 125.9, 125.0, 124.3, 122.8, 122.2, 119.9, 118.1, 117.1, 112.7, 39.1, 27.0. HRMS (ESI)
m/z calcd for C30H25NO3 (M + Na)+ 470.1727, found 470.1733.
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2-(Furan-2-carbonyl)-3-phenylindolizin-1-yl pivalate (3an): Purified by flash chromatography on
silica gel with hexanes/EtOAc (v/v = 10:1), 58 mg, 60% yield, pale yellow solid, m.p. 151-152 °C. 1H
NMR (400 MHz, CDCl3) δ 7.95 (d, J = 7.2 Hz, 1H), 7.44-7.36 (m, 5H), 7.31 (t, J = 7.2 Hz, 1H), 7.20 (d,
J = 9.1 Hz, 1H), 6.91 (d, J = 3.3 Hz, 1H), 6.70 (dd, J = 8.7, 6.5 Hz, 1H), 6.47 (t, J = 6.7 Hz, 1H), 6.33
(d, J = 1.8 Hz, 1H), 1.24 (s, 9H). 13C{1H} NMR (101 MHz, CDCl3) δ 178.3, 176.8, 153.0, 146.5, 130.5,
129.9, 128.9, 128.4, 125.7, 123.0, 122.8, 122.1, 119.8, 118.2, 117.9, 117.1, 112.5, 112.1, 39.2, 27.3.
HRMS (ESI) m/z calcd for C24H21NO4 (M + Na)+ 410.1363, found 410.1357.
2-Nicotinoyl-3-phenylindolizin-1-yl pivalate (3ao): Purified by flash chromatography on silica gel
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with hexanes/EtOAc (v/v = 5:1), 68.7 mg, 69% yield, yellow solid, m.p. 157-158 °C. H NMR (600
MHz, CDCl3) δ 8.78 (s, 1H), 8.47 (s, 1H), 7.86 (d, J = 7.8 Hz, 1H), 7.81 (d, J = 7.2 Hz, 1H), 7.27-7.22
(m, 4H), 7.18 (t, J = 6.5 Hz, 1H), 7.15 (d, J = 9.1 Hz, 1H), 7.08 (dd, J = 7.6, 4.9 Hz, 1H), 6.64 (dd, J =
9.1, 6.5 Hz, 1H), 6.41 (t, J = 6.8 Hz, 1H), 1.14 (s, 9H). 13C{1H} NMR (150 MHz, CDCl3) δ 190.1, 176.8,
152.4, 150.9, 136.8, 134.3, 130.9, 129.4, 128.9, 128.7, 126.1, 124.0, 122.9, 122.1, 118.5, 117.7, 117.1,
112.9, 39.1, 27.1. HRMS (ESI) m/z calcd for C25H22N2O3 (M + Na)+ 421.1523, found 421.1519.
2-(4-Chlorobenzoyl)-3-phenylindolizin-1-yl acetate (3bi): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 85 mg, 87% yield, yellow solid, m.p. 160-161 °C. 1H NMR (400
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MHz, CDCl3) δ 7.93 (d, J = 7.0 Hz, 1H), 7.62 (d, J = 8.0 Hz, 2H), 7.33-7.26 9 (m, 6H), 7.20 (d, J = 8.0
Hz, 2H), 6.73 (t, J = 7.7 Hz, 1H), 6.50 (t, J = 6.7 Hz, 1H), 2.14 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3)
δ 190.8, 169.7, 138.6, 137.0, 131.2, 130.7, 129.6, 128.9, 128.6, 128.2, 126.0, 123.7, 123.1, 122.2, 118.5,
117.8, 117.2, 112.8, 20.5. HRMS (ESI) m/z calcd for C23H16ClNO3 (M + Na)+ 412.0711, found 412.0707.
2-(4-Bromobenzoyl)-3-phenylindolizin-1-yl acetate (3bj): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 92 mg, 85% yield, pale yellow solid, m.p. 129-130 °C. 1H NMR
(400 MHz, CDCl3) δ 7.93 (d, J = 7.3 Hz, 1H), 7.54 (d, J = 8.6 Hz, 2H), 7.37 (d, J = 8.6 Hz, 2H), 7.33-
7.28 (m, 6H), 6.73 (ddd, J = 9.2, 6.4, 0.8 Hz, 1H), 6.50 (m, 1H), 2.14 (s, 3H). 13C{1H} NMR (101 MHz,
CDCl3) δ 191.0, 169.7, 137.4, 131.3, 131.2, 130.7, 129.5, 128.9, 128.6, 127.3, 126.0, 123.7, 123.1, 122.1,
118.5, 117.7, 117.1, 112.8, 20.5. HRMS (ESI) m/z calcd for C23H16BrNO3 (M + Na)+ 456.0206, found
456.0206.
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2-(3-chlorobenzoyl)-3-phenylindolizin-1-yl acetate (3bk): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 67 mg, 69% yield, pale yellow solid, m.p. 110-111 °C. 1H NMR
(600 MHz, CDCl3) δ 7.85 (d, J = 7.3 Hz, 1H), 7.55 (s, 1H), 7.49 (d, J = 7.7 Hz, 1H), 7.27-7.18 (m, 7H),
7.09 (t, J = 7.8 Hz, 1H), 6.67 (dd, J =9.1, 6.5 Hz, 1H), 6.43 (t, J = 7.1 Hz, 1H), 2.10 (s, 3H). 13C{1H}
NMR (150 MHz, CDCl3) δ 190.6, 169.7, 140.2, 134.1, 132.0, 130.7, 129.9, 129.6, 129.3, 128.9, 128.7,
127.7, 126.2, 124.0, 123.2, 122.2, 118.6, 117.5, 117.2, 112.9, 20.5. HRMS (ESI) m/z Calcd. for
C23H16ClNO3 (M + Na)+ 412.0711, found: 412.0711.
2-(3,5-Dichlorobenzoyl)-3-phenylindolizin-1-yl acetate (3bl): Purified by flash chromatography on
silica gel with hexanes/EtOAc (v/v = 10:1), 79.3 mg, 75% yield, orange solid, m.p. 130-131 °C. 1H NMR
(400 MHz, CDCl3) δ 7.89 (d, J = 7.3 Hz, 1H), 7.47 (d, J = 1.8 Hz, 2H), 7.34-7.24 (m, 7H), 6.74 (dd, J =
9.1, 6.4 Hz, 1H), 6.50 (m, 1H), 2.24 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ 189.3, 169.8, 140.9,
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134.7, 131.6, 130.7, 129.4, 128.9, 128.0, 126.3, 124.2, 123.3, 122.2, 118.8, 117.2, 116.9, 113.1, 20.6.
HRMS (ESI) m/z calcd for C23H15Cl2NO3 (M + Na)+ 446.0321, found 446.0323.
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silica gel with hexanes/CH2Cl2 (v/v = 5:1), 83 mg, 77% yield, brown solid, m.p. 130-131 °C. 1H NMR
(400 MHz, CDCl3) δ 8.00-7.94 (m, 3H), 7.65 (d, J = 8.1 Hz, 2H), 7.55 (t, J = 7.4 Hz, 1H), 7.45-7.27 (m,
8H), 6.99 (d, J = 8.0 Hz, 2H), 6.73 (dd, J = 8.6, 6.4 Hz, 1H), 6.53- 6.49 (m, 1H), 2.20 (s, 3H). 13C{1H}
NMR (101 MHz, CDCl3) δ 191.7, 165.0, 143.0, 136.2, 133.5, 130.7, 130.2, 129.9, 129.8, 129.1, 128.8,
128.7, 128.4, 128.4, 125.9, 123.5, 123.1, 122.2, 118.5, 118.3, 117.6, 21.6. HRMS (ESI) m/z calcd for
C29H21NO3 (M + H)+ 432.1594, found 432.1584.
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2-(3-Chlorobenzoyl)-3-phenylindolizin-1-yl benzoate (3ck): Purified by flash chromatography on
silica gel with hexanes/CH2Cl2 (v/v = 5:1), 105 mg, 93% yield, brown oil. 1H NMR (400 MHz, CDCl3)
δ 8.05-8.03 (m, 2H), 7.95 (d, J = 7.3 Hz, 1H), 7.67 (t, J = 1.7 Hz, 1H), 7.61-7.56 (m, 2H), 7.45-7.27 (m,
8H), 7.20-7.17 (m, 1H), 7.09 (t, J = 7.8 Hz, 1H), 6.75 (ddd, J = 9.1, 6.4, 0.6 Hz, 1H), 6.55-6.51 (m, 1H).
13C{1H} NMR (101 MHz, CDCl3) δ 190.5, 165.1, 140.4, 134.1, 133.7, 131.9, 130.8, 130.3, 129.9, 129.6,
129.3, 129.0, 128.9, 128.7, 128.5, 127.6, 126.1, 124.1, 123.3, 122.2, 118.6, 117.7, 117.6, 112.9. HRMS
(ESI) m/z calcd for C28H18ClNO3 (M + Na)+ 474.0867, found 474.0863.
2-Benzoyl-3-phenylindolizin-1-yl cinnamate (3da): Purified by flash chromatography on silica gel
with hexanes/CH2Cl2 (v/v = 5:1), 107.5 mg, 97% yield, brown oil. 1H NMR (400 MHz, CDCl3) δ 7.96
(dt, J = 7.3, 1.0 Hz, 1H), 7.74-7.72 (m, 2H), 7.64 (d, J = 16 Hz, 1H), 7.49-7.46 (m, 2H), 7.41-7.37 (m,
5H), 7.34-7.26 (m, 5H), 7.25-7.20 (m, 2H), 6.73 (ddd, J = 9.2, 6.4, 0.9 Hz, 1H), 6.52-6.48 (m, 1H), 6.44
(d, J = 16 Hz, 1H). 13C{1H} NMR (101 MHz, CDCl3) δ 192.1, 165.4, 146.7, 138.7, 134.3, 132.3, 130.8,
130.7, 129.8, 129.8, 129.0, 128.8, 128.5, 128.4, 128.0, 126.0, 123.8, 123.1, 122.2, 118.3, 118.3, 117.5,
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116.6, 112.6. HRMS (ESI) m/z calcd for C30H21NO3 (M + Na)+ 466.1414, found 466.1436.
2-Benzoyl-3-phenylindolizin-1-yl furan-2-carboxylate (3ea): Purified by flash chromatography on
silica gel with hexanes/CH2Cl2 (v/v = 3:1), 53 mg, 54% yield, brown oil. 1H NMR (400 MHz, CDCl3) δ
7.87 (d, J = 7.3 Hz, 1H), 7.63-7.61 (m, 2H), 7.48 (d, J = 0.7 Hz, 1H), 7.31-7.15 (m, 7H), 7.09 (d, J = 7.3
Hz, 2H), 7.03 (d, J = 3.4 Hz, 1H), 6.64 (dd, J = 8.9, 6.3 Hz, 1H), 6.43-6.39 (m, 1H), 6.38 (dd, J = 3.5,
1.7 Hz, 1H). 13C{1H} NMR (101 MHz, CDCl3) δ 191.9, 156.8, 147.2, 143.5, 138.7, 132.1, 130.7, 129.7,
129.6, 128.8, 128.5, 127.9, 125.2, 123.8, 123.2, 122.1, 119.6, 118.2, 117.4, 112.7, 112.1. HRMS (ESI)
m/z calcd for C26H17NO4 (M + Na)+ 430.1050, found 430.1049.
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(1-((tert-Butyldimethylsilyl)oxy)-3-phenylindolizin-2-yl)(phenyl)methanone (3fa): Purified by flash
chromatography on silica gel with hexanes/EtOAc (v/v = 10:1), 54.5 mg, 51% yield, brown oil. 1H NMR
(400 MHz, CDCl3) 1H NMR (400 MHz, CDCl3) δ 7.89-7.86 (m, 3H), 7.47-7.27 (m, 9H), 6.53 (ddd, J =
9.1, 6.3, 0.8 Hz, 1H), 6.39-6.35 (m, 1H), 0.79 (s, 9H), -0.06 (s, 6H). 13C{1H} NMR (101 MHz, CDCl3) δ
192.9, 138.8, 132.6, 131.3, 130.7, 130.5, 130.4, 128.8, 128.1, 128.0, 122.1, 121.7, 121.6, 118.3, 118.2,
115.4, 112.2, 25.6, 18.0, -4.6. HRMS (ESI) m/z calcd for C27H29NO2Si (M + K)+ 466.1605, found
466.1613.
3-Butyl-2-(4-methylbenzoyl)indolizin-1-yl pivalate (3gd): Purified by flash chromatography on silica
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gel with hexanes/EtOAc (v/v = 10:1), 65.6 mg, 67% yield, brown oil. H NMR (400 MHz, CDCl3) δ
7.72-7.69 (m, 3H), 7.22 (d, J = 7.9 Hz, 2H), 7.08 (dt, J = 9.1, 1.3 Hz, 1H), 6.61 (ddd, J = 9.1, 6.4, 0.9
Hz, 1H), 6.54-6.50 (m, 1H), 3.03 (t, J = 7.6 Hz, 2H), 2.39 (s, 3H), 1.65-1.57 (m, 2H), 1.39-1.30 (m, 2H),
0.97 (s, 9H), 0.87 (t, J = 7.3 Hz, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ 192.2, 176.5, 143.1, 137.3,
130.0, 129.0, 125.1, 124.4, 121.7, 121.4, 117.5, 117.4, 116.7, 112.1, 39.0, 30.2, 26.9, 24.1, 22.7, 21.7,
14.0. HRMS (ESI) m/z calcd for C25H29NO3 (M + Na)+ 414.2040, found 414.2040.
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3-Butyl-2-(4-methylbenzoyl)indolizin-1-yl pivalate (3gi): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 77 mg, 75% yield, yellow oil. 1H NMR (400 MHz, CDCl3) δ 7.76-
7.71 (m, 3H), 7.40 (d, J = 8.5 Hz, 2H), 7.08 (dt, J = 9.1, 1.2 Hz, 1H), 6.63 (ddd, J = 9.1, 6.4, 0.7 Hz, 1H),
6.57-6.53 (m, 1H), 3.03 (t, J = 7.6 Hz, 2H), 1.66-1.58 (m, 2H), 1.40-1.31 (m, 2H), 1.00 (s, 9H), 0.89 (t,
J = 7.3 Hz, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ 191.1, 176.5, 138.7, 138.2, 131.2, 128.6, 125.5,
124.3, 121.6, 121.5, 117.3, 116.9, 116.8, 112.3, 39.0, 30.1, 26.8, 24.1, 22.7, 13.9. HRMS (ESI) m/z calcd
for C24H26ClNO3 (M + Na)+ 434.1493, found 434.1493.
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3-Butyl-2-(3-chlorobenzoyl)indolizin-1-yl pivalate (3gk): Purified by flash chromatography on silica
gel with hexanes/EtOAc (v/v = 10:1), 92 mg, 89% yield, pale yellow oil. 1H NMR (400 MHz, CDCl3) δ
7.76 (t, J = 1.7 Hz, 1H), 7.73-7.68 (m, 2H), 7.49 (ddd, J = 8.0, 2.1, 1.1 Hz, 1H), 7.37 (t, J = 7.8 Hz, 1H),
7.10 (dt, J = 9.0, 1.0 Hz, 1H), 6.54 (ddd, J = 9.0, 6.4, 0.8 Hz, 1H), 6.57-6.53 (m, 1H), 3.04 (t, J = 7.7 Hz,
2H), 1.67-1.59 (m, 2H), 1.42-1.33 (m, 2H), 1.01 (s, 9H), 0.90 (t, J = 7.3 Hz, 3H). 13C{1H} NMR (101
MHz, CDCl3) δ 190.8, 176.4, 141.5, 134.5, 132.2, 129.9, 129.7, 127.7, 125.8, 124.4, 121.6, 121.5, 117.4,
116.9, 116.6, 112.4, 39.0, 30.1, 26.9, 24.1, 22.7, 13.9. HRMS (ESI) m/z calcd for C24H26ClNO3 (M +
Na)+ 434.1493, found 434.1495.
2-Benzoyl-7-chloro-3-phenylindolizin-1-yl pivalate (3ia): Purified by flash chromatography on silica
gel with hexanes/CH2Cl2 (v/v = 5:1), 57 mg, 53% yield, brown oil. 1H NMR (600 MHz, CDCl3) δ 7.78
(d, J = 7.6 Hz, 1H) 7.65 (d, J = 7.4 Hz, 2H), 7.34-7.18 (m, 8H), 7.08 (d, J = 1.3, 1H), 6.36 (dd, J = 7.6,
2.0 Hz, 1H), 1.04 (s, 9H). 13C{1H} NMR (150 MHz, CDCl3) δ 191.4, 176.6, 138.6, 132.6, 130.6, 129.9,
129.3, 128.9, 128.8, 128.2, 125.6, 124.3, 124.2, 123.2, 122.3, 119.4, 115.5, 114.0, 39.1, 27.0. HRMS
(ESI) m/z calcd for C26H22ClNO3 (M + Na)+ 454.1180, found 454.1172
2-Benzoyl-5-methyl-3-phenylindolizin-1-yl pivalate (3ja): Purified by flash chromatography on silica
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gel with hexanes/CH2Cl2 (v/v = 5:1), 102 mg, 99% yield, brown solid, m.p. 134-135 °C. 1H NMR (400
MHz, CDCl3) δ 7.66-7.64 (m, 2H), 7.33-7.33 (m, 3 H), 7.26-7.20 (m, 3H), 7.18-7.14 (m, 2H) 7.03 (d, J
= 8.8 Hz, 1H), 6.57 (dd, J = 9.0, 6.6 Hz, 1H), 6.18 (d, J = 6.6 Hz, 1H), 1.92 (s, 3H), 0.97 (s, 9H). 13C{1H}
NMR (101 MHz, CDCl3) δ 191.7, 176.5, 139.2, 135.0, 132.9, 132.7, 132.4, 129.8, 128.5, 128.1, 126.8,
125.0, 124.4, 124.1, 120.4, 117.9, 115.0, 113.9, 39.0, 26.9, 22.8. HRMS (ESI) m/z calcd for C27H25NO3
(M + Na)+ 434.1727, found 434.1731.
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2-Benzoyl-3-phenylindolizin-1-yl benzoate (3ka): Purified by flash chromatography on silica gel with
hexanes/CH2Cl2 (v/v = 5:1), 87 mg, 83% yield, yellow solid, m.p. 145-146 °C. 1H NMR (400 MHz,
CDCl3) δ 7.90-7.87 (m, 3H), 7.65 (d, J = 7.2 Hz, 2H), 7.46 (t, J = 7.4 Hz, 1H), 7.34-7.23 (m, 7H), 7.21-
7.16 (m, 2H), 7.09 (t, J = 7.7 Hz, 2H), 6.64 (dd, J = 8.8, 6.4 Hz, 1H), 6.44-6.41 (m, 1H). 13C{1H} NMR
(101 MHz, CDCl3) δ 192.0, 165.1, 138.8, 133.5, 132.2, 130.7, 130.2, 129.7, 129.7, 129.0, 128.8, 128.5,
128.4, 128.0, 126.0, 123.8, 123.1, 122.2, 118.4, 118.3, 117.6, 112.6. HRMS (ESI) m/z calcd for
C28H19NO3 (M + Na)+ 440.1257, found 440.1258.
Procedure for the quantitative reaction of (PhCO)Pd(PPh3)2Cl with propargylic pyridine 1a: To
a 25 mL Schlenk tube were added 1a (29 mg, 0.1 mmol) and (PhCO)Pd(PPh3)2Cl (77 mg, 0.1 mmol)
under nitrogen atmosphere. Then THF (1.0 mL) and Et3N (30 μL, 0.2 mmol) were added by syringe to
the reaction. The Schlenk tube was placed in an oil bath and heated to 60 °C. After stirring at 60 °C for
20 h, the reaction mixture was cooled to room temperature and concentrated under vacuum. The residue
was purified by flash chromatography on silica gel with hexanes/EtOAc (v/v = 5:1) as eluent to afford
the product 3aa (22 mg, 55% yield).
ASSOCIATED CONTENT
Supporting Information
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The Supporting Information is available free of charge on the ACS Publications website at DOI: .
Spectra of new compounds, including 1H and 13C NMR.
AUTHOR INFORMATION
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Corresponding Author
*E-mail: xutongyu@nwu.edu.cn.
ORCID
Tongyu Xu: 0000-0001-5337-2949
Author Contributions
§ Y. Li and W. Xiong contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We are grateful to the Science and Technology Department of Shaanxi Province (2017JM2005,
2019JLM-17), the Education Department of Shaanxi Province (17JK0793), Wisteria Project of
Northwest University (XM06190378) and Shaanxi Coal and Chemical Industry Group Co., Ltd. for
financial support.
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