Copper-Catalyzed Alkynylation/Cyclization/Isomerization Cascade for Synthesis of 1,2-Dihydrobenzofuro[3,2- b]pyridines and Benzofuro[3,2- b]pyridines

Article abstract of DOI:10.1021/acs.joc.9b02512

An efficient copper-catalyzed cascade alkynylation/cyclization/isomerization reaction of aurone-derived azadienes with terminal alkynes has been developed, giving a series of 1,2-dihydrobenzofuro[3,2-b]pyridines with excellent yields. The obtained 1,2-dih

Full text of DOI:10.1021/acs.joc.9b02512

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Article
Copper-Catalyzed Alkynylation/Cyclization/Isomerization
Cascade for Synthesis of 1,2-Dihydrobenzofuro[3,2-
b]pyridines and Benzofuro[3,2-b]pyridines
Huan-Ping Xie, Lei Sun, Bo Wu, and Yong-Gui Zhou
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b02512 • Publication Date (Web): 08 Nov 2019
Downloaded from pubs.acs.org on November 10, 2019
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Copper-Catalyzed Alkynylation/Cyclization/Isomerization Cas-
cade for Synthesis of 1,2-Dihydrobenzofuro[3,2-b]pyridines and
Benzofuro[3,2-b]pyridines
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†‡
Huan-Ping Xie, Lei Sun, Bo Wu, and Yong-Gui Zhou
†
†
*†§
†
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese
Academy of Sciences, Dalian 116023, P. R. China,
‡
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
§
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 200032, P. R. China
*
E-mail: ygzhou@dicp.ac.cn.
ABSTRACT
An efficient copper-catalyzed cascade alkynylation/cyclization/isomerization reactions of aurone-derived
azadienes with terminal alkynes has been developed, giving a series of 1,2-dihydrobenzofuro[3,2-b]pyridines
with excellent yields. The obtained 1,2-dihydrobenzofuro[3,2-b]pyridines can be conveniently transformed
to the corresponding benzofuro[3,2-b]pyridines under basic condition. Additionally, benzofuro[3,2-
b]pyridines can also be prepared from azadienes and terminal alkynes in one-pot reaction. The synthetic
utility was demonstrated by the synthesis of three bioactive molecules with potent topoisomerase inhibition
in high yields. This strategy provides a facile approach to 1,2-dihydrobenzofuro[3,2-b]pyridines and
benzofuro[3,2-b]pyridines.
INTRODUCTION
The direct and rapid construction of complicated and diversified molecules from easily available starting
1
materials has great importance in synthetic chemistry and industrial processes. In this regard, cascade
reactions enable multiple transformations in a single step and provide diverse scaffolds with undoubted
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benefits involving atom economy, efficiency and sustainability of resources. Consequently, the
development of cascade reactions has attracted considerable attention and been a powerful strategy for the
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,3
synthesis of various scaffolds and complex natural products. Dihydropyridines (DHPs) are ubiquitous
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structural fragments in a myriad of biologically active molecules, natural products, and synthetic drugs. In
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particular, 1,2-dihydropyridines are prominent synthetic intermediates to prepare a wide range of organic
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molecules, such as piperidines, indolizidines, quinolizidines, and isoquinuclidines. Due to the prevalence
and significance of 1,2-dihydropyridines, various strategies for their construction have been developed,
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including condensation reactions of amines and carbonyl compounds, partial reduction or nucleophilic
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addition to pyridines and pyridinium salts, and pericyclic reactions. Although considerable progress has
been achieved, there are still some disadvantages, such as harsh conditions, noble metal catalysts, etc.,
inhibiting their wide application. Hence, the development of straightforward and convenient synthesis of 1,2-
dihydropyridines is highly desirable.
Scheme 1. Copper-Catalyzed Cascade Reactions for the Synthesis of 1,2-Dihydrobenzofuro[3,2-b]pyridines
Aurone-derived azadienes have been recognized as a crucial class of highly reactive intermediates in
9
organic synthesis due to the driving force of aromatization. In the past few years, numerous annulations of
9a-h,k-o,s-t
aurone-derived azadienes to construct benzofuran-fused heterocyclic compounds have been reported.
As our contiguous interests in the utilization of azadienes, we previously disclosed the systematic work of
9h-j,9r
asymmetric nucleophilic addition and annulation.
Considering that copper-catalyzed alkynylation with
terminal alkynes is a straightforward and general access to substituted alkynes, we envisioned copper-
catalyzed cascade reactions of azadienes and terminal alkynes to give 1,2-dihydrobenzofuro[3,2-b]pyridines.
The mechanism might be hypothesized as following. Firstly, copper-catalyzed alkynylation of azadiene
produced substituted alkyne A. Subsequently, intermediate A underwent an intramolecular 6-endo-dig
cyclization through the activation of the triple bond with a π-philic metal, delivering 1,4-dihydropyridine B.
Finally, the isomerization of intermediate B afforded 1,2-dihydrobenzofuro[3,2-b]pyridines. Herein, we
described copper-catalyzed cascade alkynyltion/cyclization/isomerization reactions of azadienes with
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terminal alkynes for the synthesis of 1,2-dihydrobenzofuro[3,2-b]pyridines (Scheme 1). The obtained 1,2-
dihydrobenzofuro[3,2-b]pyridines can be conveniently transformed to the corresponding benzofuro[3,2-
b]pyridines under basic conditions.
RESULTS AND DISCUSSION
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To initiate our investigation, azadiene 1a and phenylacetylene 2a were chosen as model substrates for
o
condition optimization. Under the catalysis of Cu(CH
3
CN)
4
BF
4
/BINAP in tetrahydrofuran at 60 C, the
cascade reaction occurred with moderate 48% yield in 48 h (Table 1, entry 1). The structure of the product
was determined to be 1,2-dihydropyridine derivative 3aa by X-ray single crystal diffraction analysis (see SI).
2
Alteration of copper precursors to Cu(OTf) and CuI resulted in a significant decrease in reactivity (Table 1,
entries 2 and 3). A series of commercially available ligands were evaluated, and it was found that ligand had
an obvious influence. Monophosphorus ligands such as triphenylphosphine L4 and tricyclohexylphosphine
L5 exhibited low reactivity. Bipyridine ligand L6 shut down the reaction. Diphosphine ligand XantPhos L3
was the most efficient ligand, providing the product in 86% yield (Table 1, entries 4-9). The effect of base
was explored. Good yield was obtained with N,N-diisopropylethylamine and moderate yield was achieved
with potassium carbonate (Table 1, entries 10 and 11). Subsequently, the effect of solvents was evaluated.
1,4-Dioxane proved to be the most favorable solvent in 96% yield (Table 1, entries 12-14). Notably, the
reactivity could be maintained when the catalyst loading was reduced to 5 mol% (Table 1, entry 15).
Therefore, the optimal condition was established: using Cu(CH CN) BF /XantPhos as catalyst, triethylamine
3
4
4
o
as base and 1,4-dioxane as solvent to perform the reaction at 60 C.
Table 1. Optimization of Reaction Conditions
a
b
Entry
[Cu]
Cu(CH CN)
L
solvent
THF
yield (%)
1
2
3
3
4
BF
4
L1
L1
L1
48
12
17
Cu(OTf)
CuI
2
THF
THF
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Cu(CH
3
CN)
4
BF
4
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L2
L3
L4
L5
L6
--
THF
THF
THF
THF
THF
THF
THF
THF
toluene
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86
12
37
--
Cu(CH CN) BF
3
3
3
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3
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4
Cu(CH
Cu(CH
Cu(CH
Cu(CH
CN)
CN)
CN)
CN)
BF
BF
BF
BF
--
c
1
0
Cu(CH CN) BF
L3
L3
L3
84
32
94
96
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Cu(CH
Cu(CH
Cu(CH
Cu(CH
CN)
CN)
CN)
CN)
BF
BF
BF
BF
1
2
1
3
4
L3 1,4-dioxane
L3
acetonitrile
L3 1,4-dioxane
1
e
1
5
Cu(CH CN) BF
97
3
4
a
Conditions: 1a (0.10 mmol), 2a (0.30 mmol), [Cu] (10 mol%), L
10 mol%), while L4 and L5 were used in 20 mol%, solvent (1.5
mL), Et N (0.10 mmol), 60 C, 48 h. Isolated yields. DIPEA
0.10 mmol) was used.
loading was reduced to 5 mol%.
(
o
b
c
3
d
e
(
2 3
K CO (0.10 mmol) was used. Catalyst
With the aforementioned optimal reaction conditions, we turned our attention to the scope of this cascade
reaction between azadienes 1 and alkynes 2. The results were summarized in Scheme 2. In general, the
transformation proceeded smoothly, delivering the desired benzofuran-fused 1,2-dihydropyridines 3 in
excellent yields. Various aurone-derived azadienes were suitable for the cascade reaction. The steric and
electronic properties of the substituents on the aromatic ring had only marginal effect on yields. For instance,
the reaction afforded the target products 3ba and 3ga in 93% and 96% yield, respectively. For azadienes
with methyl substituent at the 5- or 6-position of benzofuryl ring, products 3ka and 3la in 96% and 98%
yield, respectively. Sulfonylimines 1m-1n were transformed successfully with moderate to good yields.
Additionally, azadiene containing trifluoromethyl substituent performed the cascade reaction smoothly,
offering the target product 3oa in 57% yield. Furthermore, a series of terminal alkynes were evaluated.
Excellent yields were observed for substituted phenylacetylenes as well as terminal alkyne bearing thienyl
functionality. When strong electron-withdrawing group such as trifluoromethyl was introduced to terminal
alkyne, only moderate yield was obtained. The yield decreased dramatically for terminal alkynes bearing
alkyl substituents. Only 11% yield was achieved with tert-butylacetylene and the reaction shut down with
cyclohexylacetylene.
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a
Scheme 2. Substrate Scope
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Conditions: 1 (0.20 mmol), 2 (0.60 mmol), Cu(CH CN) BF (5 mol%), XantPhos (5 mol%), Et N (0.20 mmol),
o
1
,4-dioxane (3.0 mL), 60 C, 48 h.
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To extend the synthetic utility of this cascade reaction, we made further efforts to the transformation of
1,2-dihydrobenzofuro[3,2-b]pyridines. Benzofuro[3,2-b]pyridine moieties have been found with various
pharmaceutical and biological activities, such as antiallergic, anti-inflammatory, antimicrobial, and analgesic
1
0
activity, cyclin-dependent kinase inhibitors, and topoisomerase inhibitors. 1,2-Dihydrobenzofuro[3,2-
b]pyridines were easily deprotected and aromatized to the corresponding benzofuro[3,2-b]pyridines under
basic conditions through E1cb mechanism (Scheme 3).
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Scheme 3. Synthesis of Benzofuro[3,2-b]pyridines
a
Conditions: 3 (0.15 mmol), NaOH (0.75 mmol), EtOH (2.0 mL), reflux, 0.5 h.
A series of 1,2-dihydrobenzofuro[3,2-b]pyridines bearing both electron-donating and electron-
withdrawing groups on the aromatic rings of substrates underwent the deprotection and aromatization
successfully, generating the desired benzofuro[3,2-b]pyridine products 4a-4k in excellent yields. It is worthy
to note that the benzofuro[3,2-b]pyridine bearing thienyl functionality 4l could also be obtained in 96% yield.
This method provides a practical and alternative route to a series of benzofuro[3,2-b]pyridines.
Encouraged by the results above, we decided to apply this new methodology to the one-pot synthesis of
benzofuro[3,2-b]pyridines. As shown in Scheme 4, the corresponding benzofuro[3,2-b]pyridines 4 could be
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prepared from azadienes 1 and terminal alkynes 2 in 86-91% yields via copper-catalyzed cascade reaction
followed by basic deprotection and aromatization.
a
Scheme 4. One-Pot Synthesis of Benzofuro[3,2-b]pyridines
1
1
1
1
1
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a
Conditions: 1 (0.20 mmol), 2 (0.60 mmol), Cu(CH
3
CN)
4
BF
4
3
(5 mol%), XantPhos (5 mol%), Et N (0.20 mmol),
o
o
1
,4-dioxane (3.0 mL), 60 C, 48 h. Then, NaOH (1.0 mmol), 80 C, 2 h.
To evaluate the synthetic potential of this cascade reaction, a gram scale experiment of azadiene 1a and
phenylacetylene 2a was conducted in the presence of Cu(CH CN) BF /XantPhos catalyst (5 mol%).
3
4
4
Gratifyingly, the transformation proceeded smoothly to afford 1,2-dihydropyridine derivative 3aa in 89%
yield without noticeable loss of yield (Scheme 5).
Scheme 5. Gram Scale Experiment and Synthesis of Three Bioactive Molecules
To further demonstrating the synthetic utility, three bioactive molecules with potent topoisomerase (topo)
inhibition were synthesized in high yields (Scheme 5). 2-Chlorophenyl-substituted benzofuro[3,2-b]pyridine
10e
5
exhibits potent topo II inhibition and antiproliferative activity, which could be conveniently obtained in
9
0% yield using the one-pot synthesis. Additionally, the compound 6 which showed endogenous topo I and
1
0d
II inhibitory activity could be achieved in 89% yield with the same method. 3-(4-Phenylbenzofuro[3,2-
1
0d
b]pyridin-2-yl)phenol 7 has been determined be a noninter-calative topo I and II dual catalytic inhibitor,
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and could be also synthesized with 87% yield through deprotection of methyl with tribromoboron.
CONCLUSIONS
In conclusion, an efficient copper-catalyzed alkynylation/cyclization/isomerization cascade has been
developed, giving a variety of 1,2-dihydrobenzofuro[3,2-b]pyridines with high yields. The obtained 1,2-
dihydrobenzofuro[3,2-b]pyridines can be conveniently transformed to the corresponding aromatic
benzofuro[3,2-b]pyridines in high yields under the basic condition. Additionally, the one-pot synthesis of
benzofuro[3,2-b]pyridines can also be realized from azadienes and terminal alkynes via copper-catalyzed
cascade reactions and basic deprotection and aromatization. The synthetic utility of this methodology was
demonstrated by the synthesis of three bioactive molecules with potent topoisomerase inhibition in high
yields. This protocol not only provides a facile approach to 1,2-dihydrobenzofuro[3,2-b]pyridines, but also
affords a new access to aromatic benzofuro[3,2-b]pyridines.
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EXPERIMENTAL SECTION
All reactions were carried out under an atmosphere of nitrogen using the standard Schlenk techniques,
unless otherwise noted. Commercially available reagents were used without further purification. Solvents
1
13
were treated prior to use according to the standard methods. H NMR, C NMR spectra were recorded at
1
9
4
00 MHz and 100 MHz with the Brucker spectrometer. F NMR spectra was recorded at 376 MHz with
Brucker spectrometer. Chemical shifts are reported in ppm using tetramethylsilane as internal standard when
1
using CDCl
3
as solvent for H NMR spectra. The following abbreviations were used to symbolize the
multiplicities: s = singlet, d = doublet, t = triplet, m = multiplet, brs = broad singlet. Flash column
chromatography was performed on silica gel (200-300 mesh). All reactions were monitored by TLC analysis.
High-resolution mass spectrometry (HRMS(ESI-TOF) M/Z ) was measured on an electrospray ionization
(
ESI) apparatus using time-of-flight (TOF) mass spectrometry. The heat source in reaction procedures was
oil bath.
Procedures for Synthesis of Azadienes: azadienes 1 could be synthesized from enones and sulfonamides
[
9,11,12]
[9a]
[9i]
[9a]
[9r]
according to the known literature procedures.
Among them, azadienes 1a-1d, 1e, 1f-1j, 1k,
[9j]
[9c]
[9i]
[12]
1
l, 1m
and 1n
are the known compound. Starting materials benzofuran-3(2H)-ones
are the known compounds.
and
[
9j,11]
intermediate enones
Under nitrogen, aluminium oxide (65 g, activated, basic) was added to a solution of ketones (20 mmol)
and aldehydes (40 mmol) in dichloromethane (80 mL). The mixture was stirred at room temperature under
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nitrogen and exclusion of light. The reaction progress was monitored by TLC. The suspension was filtered
off, the residue washed with dichloromethane, and the filtrate was combined with the filtrate. The solvent
was evaporated in vacuo. The residue was purified by flash chromatography and recrystallized from ethyl
acetate/hexanes to give the intermediate enones for the next step.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
To a solution of the above enones (5 mmol) and sulfonamides (5 mmol) in toluene (50 mL), triethylamine
o
(
1.39 mL, 10 mmol) and titanium tetrachloride (0.55 mL, 5 mmol) were successively added at 0 C in ice
bath. The reaction mixture was heated in oil bath for reflux overnight. The solution was cooled, quenched
with water and extracted with dichloromethane. The combined organic phase was dried over ahydrous
sodium sulfate and concentrated. The residue was purified by silical gel flash chromatography using ethyl
acetate/hexanes as eluent, and further recrystallized from ethyl acetate/ hexanes to give the pure azadienes 1.
4
-Methyl-N-((Z)-2-((Z)-4-(trifluoromethyl)benzylidene)benzofuran-3(2H)-ylidene)benzenesulfon-
o
amide (1o): 0.401 g, 18% yield, yellow solid, m.p. = 145-146 C, new compound, R
f
= 0.50 (hexanes/ethyl
1
acetate = 40/1). H NMR (400 MHz, CDCl ) δ 8.78 (d, J = 7.6 Hz, 1H), 8.19-7.88 (m, 4H), 7.79-7.59 (m,
3
1
3
1
3
1
1
3
H), 7.53-7.28 (m, 4H), 7.04 (s, 1H), 2.48 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 164.9, 164.8, 150.9,
43.8, 138.7, 138.1, 135.7, 131.6, 131.5, 131.1 (q, JC-F = 32.0 Hz), 129.6, 127.2, 125.8 (q, JC-F = 4.0 Hz),
19
24.2, 123.9 (q, JC-F = 271.0 Hz), 118.0, 112.8, 112.5, 21.7; F{1H} NMR (376 MHz, CDCl
3
) δ -62.8.
+
HRMS (ESI-TOF) m/z Calculated for C23
17
H F
3
NO
3
S [M+H] 444.0876, found 444.0879.
General Procedure for Synthesis of Dihydrobenzofuro[3,2-b]pyridines
Under nitrogen, the solution of Cu(MeCN) BF (3.1 mg, 0.01 mmol) and ligand XantPhos (5.8 mg, 0.01
4
4
mmol) in 1,4-dioxane (0.5 mL) was stirred at room temperture for 1.5 h, azadienes 1 (0.20 mmol), 1,4-
dioxane (2.5 mL), triethylamine (20.2 mg, 0.2 mmol), terminal alkynes 2 (0.6 mmol) was added in sequence.
o
The reaction was stirred at 60 C in oil bath for 2 days, which was monitored by thin-layer chromatography.
The solvent was evaporated under the reduced pressure and the crude product was directly purified by silica
gel column chromatography (eluent: hexanes/ethyl acetate = 50:1 to 30:1) to give the desired products 3.
2
,4-Diphenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3aa): 91 mg, 95% yield, pale yellow solid,
o
1
m.p. = 178-179 C, new compound, R
f
= 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ
8
7
1
.11-7.89 (m, 1H), 7.54-7.41 (m, 4H), 7.41-7.33 (m, 4H), 7.34-7.27 (m, 3H), 7.26-7.18 (m, 4H), 7.07 (d, J =
13
1
.9 Hz, 2H), 6.12 (d, J = 5.7 Hz, 1H), 5.88-5.61 (m, 1H), 2.25 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ
3
54.0, 147.4, 144.2, 138.1, 134.6, 134.1, 131.1, 129.3, 128.7, 128.7, 128.5, 128.3, 127.6, 127.6, 127.4, 125.3,
3
124.6, 123.8, 121.9, 121.7, 117.5, 111.7, 59.4, 21.5. HRMS (ESI-TOF) m/z Calculated For C30H24NO S
+
[
M+H] 478.1471, found: 478.1473.
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8
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
-Phenyl-4-(o-tolyl)-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ba): 91 mg, 93% yield, pale
o
1
yellow solid, m.p. = 174-175 C, new compound, R
MHz, CDCl ) δ 8.18-8.01 (m, 1H), 7.62-7.49 (m, 4H), 7.37-7.26 (m, 6H), 7.26-7.23 (m, 1H), 7.22-7.11 (m,
H), 6.86 (d, J = 7.4 Hz, 1H), 6.20 (d, J = 5.9 Hz, 1H), 5.72 (d, J = 5.9 Hz, 1H), 2.38 (s, 3H), 1.77 (s, 3H);
f
= 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400
3
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
13
1
3
C{ H} NMR (100 MHz, CDCl ) δ 154.0, 147.4, 144.2, 138.8, 136.6, 135.6, 134.3, 131.6, 130.3, 129.7,
1
29.6, 128.9, 128.8, 128.4, 127.8, 127.3, 126.0, 125.1, 124.6, 123.7, 123.1, 122.1, 116.1, 111.7, 59.6, 21.6,
+
19.7. HRMS (ESI-TOF) m/z Calculated For C31
H26NO
3
S [M+H] 492.1628, found: 492.1635.
2-Phenyl-4-(m-tolyl)-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ca): 92 mg, 94% yield, pale
o
1
yellow solid, m.p. = 163-164 C, new compound, R
MHz, CDCl ) δ 8.15-7.86 (m, 1H), 7.50-7.43 (m, 4H), 7.42-7.36 (m, 1H), 7.33-7.26 (m, 4H), 7.26-7.20 (m,
H), 7.18 (d, J = 7.7 Hz, 1H), 7.08 (d, J = 8.0 Hz, 2H), 7.04-6.97 (m, 2H), 6.11 (d, J = 6.1 Hz, 1H), 5.73 (d,
f
= 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400
3
2
1
3
1
J = 6.0 Hz, 1H), 2.38 (s, 3H), 2.27 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 154.0, 147.5, 144.2, 138.2,
3
134.6, 134.2, 131.3, 129.5, 129.3, 128.7, 128.4, 128.3, 127.7, 127.4, 125.2, 124.8, 124.7, 123.8, 121.9, 121.7,
+
1
4
17.4, 111.7, 59.4, 21.6, 21.5. HRMS (ESI-TOF) m/z Calculated For C H NO S [M+H] 492.1628, found:
31 26
3
92.1618.
-Phenyl-4-(p-tolyl)-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3da): 94 mg, 96% yield, white solid,
2
o
1
f 3
m.p. = 175-176 C, new compound, R = 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ
8.01-7.97 (m, 1H), 7.49-7.42 (m, 4H), 7.40-7.35 (m, 1H), 7.33-7.26 (m, 3H), 7.25-7.20 (m, 2H), 7.19-7.14
(m, 2H), 7.14-7.08 (m, 2H), 7.07 (d, J = 8.0 Hz, 2H), 6.10 (d, J = 6.1 Hz, 1H), 5.72 (d, J = 6.1 Hz, 1H), 2.38
1
3
1
(
s, 3H), 2.26 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 153.9, 147.5, 144.2, 138.6, 138.2, 134.6, 131.2,
3
1
2
31.0, 129.2, 129.2, 128.6, 128.3, 127.6, 127.5, 127.4, 125.2, 124.7, 123.8, 121.8, 121.1, 117.3, 111.6, 59.4,
+
1.5, 21.4. HRMS (ESI-TOF) m/z Calculated For C31
H26NO
3
S [M+H] 492.1628, found: 492.1615.
4
-(4-Isopropylphenyl)-2-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ea): 103 mg, 99%
o
1
f
yield, pale yellow solid, m.p. = 95-96 C, new compound, R = 0.40 (hexanes/ethyl acetate = 30:1). H NMR
(
(
(
400 MHz, CDCl ) δ 8.05-7.97 (m, 1H), 7.51-7.43 (m, 4H), 7.42-7.38 (m, 1H), 7.33-7.27 (m, 3H), 7.26-7.22
3
m, 4H), 7.21-7.16 (m, 2H), 7.08 (d, J = 8.0 Hz, 2H), 6.11 (d, J = 6.1 Hz, 1H), 5.74 (d, J = 6.1 Hz, 1H), 2.95
1
3
1
hept, J = 6.9 Hz, 1H), 2.25 (s, 3H), 1.30 (s, 3H), 1.28 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 154.0,
3
1
1
49.6, 147.6, 144.2, 138.3, 134.6, 131.6, 130.9, 129.3, 128.6, 128.3, 127.6, 127.6, 127.4, 126.6, 125.2, 124.7,
23.8, 121.9, 121.2, 117.4, 111.7, 59.4, 34.1, 24.1, 24.0, 21.5. HRMS (ESI-TOF) m/z Calculated For
+
C
33
H
30NO
3
S [M+H] 520.1941, found: 520.1931.
4
-(4-Methoxyphenyl)-2-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3fa): 94 mg, 93% yield,
o
1
f
pale yellow solid, m.p. = 169-170 C, new compound, R = 0.50 (hexanes/ethyl acetate = 10:1). H NMR
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(
400 MHz, CDCl
3
) δ 8.08-7.91 (m, 1H), 7.48-7.42 (m, 4H), 7.41-7.36 (m, 1H), 7.33-7.26 (m, 3H), 7.25-7.16
(m, 4H), 7.07 (d, J = 8.0 Hz, 2H), 6.92-6.86 (m, 2H), 6.10 (d, J = 6.1 Hz, 1H), 5.69 (d, J = 6.1 Hz, 1H), 3.84
1
3
1
(
s, 3H), 2.26 (s, 3H); C{ H} NMR (100 MHz, CDCl
3
) δ 160.0, 153.9, 147.6, 144.2, 138.3, 134.6, 130.5,
1
5
29.2, 128.9, 128.6, 128.7, 127.6, 127.4, 126.5, 125.2, 124.7, 123.8, 121.8, 120.4, 117.4, 113.9, 111.6, 59.4,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
5.5, 21.6. HRMS (ESI-TOF) m/z Calculated For C H NO S [M+H] 508.1577, found: 508.1572.
3
1
26
4
4
-(4-Chlorophenyl)-2-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ga): 98 mg, 96% yield,
o
1
pale yellow solid, m.p. = 177-178 C, new compound, R
(400 MHz, CDCl ) δ 8.30-7.70 (m, 1H), 7.46 (d, J = 8.2 Hz, 4H), 7.43-7.38 (m, 1H), 7.38-7.29 (m, 5H),
.28-7.23 (m, 2H), 7.22-7.15 (m, 2H), 7.09 (d, J = 8.0 Hz, 2H), 6.14 (d, J = 6.1 Hz, 1H), 5.77 (d, J = 6.1 Hz,
f
= 0.55 (hexanes/ethyl acetate = 10:1). H NMR
3
7
1
1
1
3
1
3
H), 2.29 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 154.0, 146.9, 144.3, 137.9, 134.7, 134.6, 132.5, 130.0,
29.3, 128.9, 128.7, 128.7, 128.4, 127.7, 127.3, 125.5, 124.5, 124.0, 122.0, 117.8, 111.7, 59.4, 21.5. HRMS
+
(
ESI-TOF) m/z Calculated For C H ClNO S [M+H] 512.1082, found: 512.1100.
3
0
23
3
4-(3-Chlorophenyl)-2-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ha): 99 mg, 97% yield,
o
1
pale yellow solid, m.p. = 70-72 C, new compound, R = 0.45 (hexanes/ethyl acetate = 30:1). H NMR (400
f
MHz, CDCl3) δ 8.08-7.98 (m, 1H), 7.51-7.40 (m, 5H), 7.39-7.30 (m, 5H), 7.29-7.23 (m, 2H), 7.22-7.16 (m,
13
1
1
H), 7.16-7.07 (m, 3H), 6.14 (d, J = 6.1 Hz, 1H), 5.77 (d, J = 6.1 Hz, 1H), 2.31 (s, 3H); C{ H} NMR (100
MHz, CDCl ) δ 154.0, 146.8, 144.5, 137.8, 135.9, 134.5, 134.4, 130.0, 129.8, 129.3, 128.7, 128.4, 127.7,
3
127.3, 125.8, 125.5, 124.5, 124.0, 122.6, 122 .0, 117.8, 111.8, 59.4, 21.5. HRMS (ESI-TOF) m/z Calculated
+
For C30
H
23ClNO
3
S [M+H] 512.1082, found: 512. 1075.
4
-(3-Bromophenyl)-2-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ia): 109 mg, 99% yield,
o
1
pale yellow solid, m.p. = 75-76 C, new compound, R = 0.45 (hexanes/ethyl acetate = 30:1). H NMR (400
f
MHz, CDCl
H), 7.09 (d, J = 8.1 Hz, 2H), 6.11 (d, J = 6.1 Hz, 1H), 5.73 (d, J = 6.1 Hz, 1H), 2.30 (s, 3H); C{ H} NMR
(100 MHz, CDCl ) δ 154.0, 146.8, 144.5, 137.8, 136.2, 134.5, 131.6, 130.6, 130.1, 129.9, 129.3, 128.7,
28.5, 127.7, 127.3, 126.3, 125.5, 124.5, 124.0, 122.7, 122.5, 122.0, 117.8, 111.8, 59.4, 21.6. HRMS (ESI-
3
) δ 8.13-7.91 (m, 1H), 7.53-7.46 (m, 1H), 7.46-7.38 (m, 5H), 7.34-7.26 (m, 4H), 7.25-7.18 (m,
1
3
1
4
3
1
+
TOF) m/z Calculated For C30
3
H23BrNO S [M+H] 556.0577, found: 556.0568.
4
-(Naphthalen-1-yl)-2-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ja): 103 mg, 98% yield,
o
1
pale yellow solid, m.p. = 185-187 C, new compound, R = 0.35 (hexanes/ethyl acetate = 30:1). H NMR
f
(400 MHz, CDCl
3
) δ 8.06 (d, J = 7.9 Hz, 1H), 7.81 (t, J = 8.1 Hz, 2H), 7.56 (t, J = 7.2 Hz, 4H), 7.40 (t, J =
7.5 Hz, 2H), 7.33-7.21 (m, 4H), 7.20-7.03 (m, 6H), 6.71 (brs, 1H), 6.25 (d, J = 5.8 Hz, 1H), 5.89 (d, J = 5.8
1
3
1
Hz, 1H), 2.27 (s, 3H); C{ H} NMR (100 MHz, CDCl
3
) δ 154.1, 147.8, 144.3, 138.8, 135.6, 133.6, 132.6,
1
31.4, 130.7, 129.8, 129.4, 128.8, 128.4, 128.4, 127.9, 127.3, 126.1, 126.1, 125.5, 125.5, 125.2, 124.5, 124.2,
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1
1
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1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
+
1
3
23.7, 122.1, 111.8, 59.6, 21.8. HRMS (ESI-TOF) m/z Calculated For C34H26NO S [M+H] 528.1628, found:
528.1638.
-Methyl-2,4-diphenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ka): 94 mg, 96% yield, pale
8
o
1
yellow solid, m.p. = 160-162 C, new compound, R
f
= 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
MHz, CDCl ) δ 7.79 (s, 1H), 7.54-7.43 (m, 4H), 7.42-7.32 (m, 3H), 7.30-7.18 (m, 6H), 7.14-6.97 (m, 3H),
3
13
1
6
.11 (d, J = 6.1 Hz, 1H), 5.73 (d, J = 6.1 Hz, 1H), 2.46 (s, 3H), 2.24 (s, 3H); C{ H} NMR (100 MHz,
CDCl ) δ 152.5, 147.6, 144.2, 138.2, 134.6, 134.2, 133.4, 131.2, 129.2, 128.6, 128.5, 128.3, 127.7, 127.6,
3
127.4, 126.7, 124.7, 121.5, 121.5, 117.2, 111.2, 59.4, 21.6, 21.5. HRMS (ESI-TOF) m/z Calculated For
+
C
31
H26NO
3
S [M+H] 492.1628, found: 492.1623.
7
-Methyl-2,4-diphenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3la): 96 mg, 98% yield, pale
o
1
yellow solid, m.p. = 139-141 C, new compound, R
MHz, CDCl ) δ 7.89 (d, J = 8.1 Hz, 1H), 7.54-7.43 (m, 4H), 7.40-7.33 (m, 3H), 7.30-7.20 (m, 6H), 7.16-7.11
(m, 1H), 7.07 (d, J = 8.0 Hz, 2H), 6.11 (d, J = 6.1 Hz, 1H), 5.72 (d, J = 6.1 Hz, 1H), 2.46 (s, 3H), 2.25 (s,
f
= 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400
3
1
3
1
3
1
H); C{ H} NMR (100 MHz, CDCl ) δ 154.4, 146.8, 144.1, 138.3, 135.8, 134.6, 134.3, 131.1, 129.2,
3
28.6, 128.5, 128.3, 127.6, 127.6, 127.4, 125.3, 122.2, 121.3, 120.9, 117.5, 111.9, 59.4, 21.9, 21.5. HRMS
+
(
ESI-TOF) m/z Calculated For C31
H26NO
3
S [M+H] 492.1628, found: 492.1603.
1
-(Methylsulfonyl)-2,4-diphenyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ma): 71 mg, 89% yield, pale
o
1
yellow solid, m.p. = 154-155 C, new compound, R
MHz, CDCl ) δ 8.03-7.88 (m, 1H), 7.87-7.74 (m, 2H), 7.60-7.42 (m, 6H), 7.36-7.22 (m, 5H), 6.34 (d, J = 6.1
Hz, 1H), 6.12 (d, J = 6.1 Hz, 1H), 2.94 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 154.2, 146.4, 138.1,
f
= 0.15 (hexanes/ethyl acetate = 30:1). H NMR (400
3
1
3
1
3
1
3
33.9, 131.8, 129.3, 129.0, 128.7, 128.5, 127.7, 127.2, 125.6, 124.2, 123.9, 121.8, 121.2, 117.9, 111.8, 59.2,
+
7.1. HRMS (ESI-TOF) m/z Calculated For C24
H20NO
3
S [M+H] 402.1158, found: 402.1148.
7
-Methyl-1-((4-nitrophenyl)sulfonyl)-2,4-diphenyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3na): 62
o
f
mg, 61% yield, pale yellow solid, m.p. = 192-193 C, new compound, R = 0.20 (hexanes/ethyl acetate =
1
3
7
0:1). H NMR (400 MHz, CDCl ) δ 8.11 (d, J = 8.7 Hz, 2H), 8.04-7.89 (m, 1H), 7.77 (d, J = 8.7 Hz, 2H),
3
.58-7.40 (m, 3H), 7.40-7.27 (m, 7H), 7.25-7.19 (m, 2H), 6.16 (d, J = 6.0 Hz, 1H), 5.84 (d, J = 6.0 Hz, 1H);
1
3
1
C{ H} NMR (100 MHz, CDCl
3
) δ 154.1, 150.3, 147.5, 143.0, 137.2, 133.3, 131.5, 129.2, 128.9, 128.8,
1
28.7, 127.3, 127.2, 125.8, 124.2, 124.0, 123.8, 121.6, 121.3, 116.9, 112.0, 59.8. HRMS (ESI-TOF) m/z
+
Calculated For C32
H
17
N
2
O
5
[M+H] 509.1132, found: 509.1150.
2-Phenyl-1-tosyl-4-(4-(trifluoromethyl)phenyl)-1,2-dihydrobenzofuro[3,2-b]pyridine (3oa): 62 mg,
o
1
5
f
7% yield, white solid, m.p. = 158-159 C, new compound, R = 0.35 (hexanes/ethyl acetate = 30:1). H
NMR (400 MHz, CDCl ) δ 8.13-7.96 (m, 1H), 7.66 (d, J = 8.3 Hz, 2H), 7.49 (d, J = 8.2 Hz, 4H), 7.46-7.41
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(
m, 1H), 7.41-7.29 (m, 6H), 7.29-7.24 (m, 1H), 7.11 (d, J = 8.0 Hz, 2H), 6.19 (d, J = 6.1 Hz, 1H), 5.86 (d, J
1
3
1
= 6.1 Hz, 1H), 2.28 (s, 3H). C{ H} NMR (100 MHz, CDCl
3
) δ 154.0, 146.6, 144.3, 137.7, 137.6, 134.5,
1
1
30.7 (q, JC-F = 32.0 Hz), 129.9, 129.3, 128.8, 128.5, 127.9, 127.7, 127.3, 125.6, 125.5 (q, JC-F = 4.0 Hz),
1
9
1
24.5, 124.1 (q, JC-F = 271.0 Hz), 124.0, 123.1, 122.0, 118.0, 111.7, 59.4, 21.5. F{ H} NMR (376 MHz,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
CDCl ) δ -62.6. HRMS (ESI-TOF) m/z Calculated For C H F NO S [M+H] 546.1345, found: 546.1336.
3
31 23
3
3
4
-Phenyl-2-(p-tolyl)-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ab): 90 mg, 92% yield, pale
o
1
yellow solid, m.p. = 199-201 C, new compound, R
MHz, CDCl ) δ 8.11-7.95 (m, 1H), 7.50-7.44 (m, 2H), 7.43-7.33 (m, 6H), 7.33-7.27 (m, 2H), 7.26-7.22 (m,
H), 7.17-6.98 (m, 4H), 6.11 (d, J = 6.0 Hz, 1H), 5.76 (d, J = 6.0 Hz, 1H), 2.28 (s, 3H), 2.26 (s, 3H); C{ H}
NMR (100 MHz, CDCl ) δ 154.0, 147.4, 144.2, 138.2, 135.0, 134.6, 134.2, 131.0, 129.4, 129.3, 128.6, 128.5,
27.7, 127.6, 127.4, 125.2, 124.7, 123.8, 122.0, 121.9, 117.4, 111.7, 59.3, 21.5, 21.2. HRMS (ESI-TOF) m/z
f
= 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400
3
1
3
1
2
3
1
+
Calculated For C H NO S [M+H] 492.1628, found: 492.1620.
3
1
26
3
4-Phenyl-2-(m-tolyl)-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ac): 88 mg, 90% yield, white solid,
o
1
m.p. = 151-152 C, new compound, R = 0.30 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ
f
3
8
.15-7.95 (m, 1H), 7.52 (d, J = 8.2 Hz, 2H), 7.48-7.40 (m, 4H), 7.40-7.31 (m, 5H), 7.31-7.27 (m, 1H), 7.20 (t,
J = 7.6 Hz, 1H), 7.14-7.06 (m, 3H), 6.17 (d, J = 6.1 Hz, 1H), 5.82 (d, J = 6.1 Hz, 1H), 2.35 (s, 3H), 2.29 (s,
13
1
3
3
H); C{ H} NMR (100 MHz, CDCl ) δ 153.9, 147.4, 144.2, 138.3, 138.0, 134.5, 134.1, 130.9, 129.2,
129.1, 128.6, 128.5, 128.4, 128.1, 127.6, 127.6, 125.2, 124.7, 124.4, 123.7, 121.9, 121.8, 117.4, 111.6, 59.4,
+
21.5, 21.4. HRMS (ESI-TOF) m/z Calculated For C31
H26NO
3
S [M+H] 492.1628, found: 492.1627.
2
-(4-Methoxyphenyl)-4-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ad): 93 mg, 92% yield,
o
1
white solid, m.p. = 201-202 C, new compound, R = 0.20 (hexanes/ethyl acetate = 30:1). H NMR (400
f
MHz, CDCl
3
) δ 8.10-7.84 (m, 1H), 7.45 (d, J = 8.3 Hz, 2H), 7.42-7.33 (m, 6H), 7.33-7.27 (m, 2H), 7.25-7.19
(
m, 2H), 7.07 (d, J = 8.0 Hz, 2H), 6.83-6.75 (m, 2H), 6.07 (d, J = 6.0 Hz, 1H), 5.71 (d, J = 6.0 Hz, 1H), 3.73
1
3
1
(s, 3H), 2.24 (s, 3H); C{ H} NMR (100 MHz, CDCl
3
) δ 159.7, 154.0, 147.4, 144.1, 134.6, 134.2, 130.9,
1
2
29.8, 129.2, 128.8, 128.6, 128.5, 127.6, 125.2, 124.7, 123.8, 122.0, 121.9, 117.3, 114.1, 111.6, 59.1, 55.3,
+
1.5. HRMS (ESI-TOF) m/z Calculated For C31
4
H26NO S [M+H] 508.1577, found: 508.1575.
2
-(4-Fluorophenyl)-4-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ae): 94 mg, 95% yield,
o
1
white solid, m.p. = 193-194 C, new compound, R = 0.35 (hexanes/ethyl acetate = 30:1). H NMR (400
f
MHz, CDCl
6.93 (t, J = 8.7 Hz, 2H), 6.06 (d, J = 6.0 Hz, 1H), 5.70 (d, J = 6.0 Hz, 1H), 2.23 (s, 3H); C{ H} NMR (100
MHz, CDCl ) δ 162.8 (d, JC-F = 247.1 Hz), 154.0, 147.3, 144.3, 134.5, 134.0, 133.8 (d, JC-F = 2.9 Hz), 131.3,
29.3, 129.2 (d, JC-F = 8.4 Hz), 128.8, 128.5, 127.6, 127.6, 125.4, 124.5, 123.9, 121.9, 121.3, 117.4, 115.6 (d,
3
) δ 8.04-7.89 (m, 1H), 7.49-7.33 (m, 8H), 7.30 (m, 2H), 7.21 (m, 2H), 7.06 (d, J = 8.0 Hz, 2H),
1
3
1
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1
1
1
1
1
1
1
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
9
1
J
3
C-F = 21.7 Hz), 111.7, 58.8, 21.5; F{ H} NMR (376 MHz, CDCl ) δ -113.8. HRMS (ESI-TOF) m/z
+
Calculated For C30
H23FNO
3
S [M+H] 496.1377, found: 496.1370.
2
-(4-Bromophenyl)-4-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3af): 101 mg, 91% yield,
o
1
yellow solid, m.p. = 214-216 C, new compound, R
f
= 0.35 (hexanes/ethyl acetate = 30:1). H NMR (400
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
MHz, CDCl ) δ 8.09-7.89 (m, 1H), 7.47-7.41 (m, 2H), 7.41-7.27 (m, 10H), 7.25-7.18 (m, 2H), 7.07 (d, J =
3
13
1
8
.0 Hz, 2H), 6.05 (d, J = 6.1 Hz, 1H), 5.71 (d, J = 6.1 Hz, 1H), 2.24 (s, 3H); C{ H} NMR (100 MHz,
CDCl ) δ 154.0, 147.2, 144.4, 137.3, 134.4, 133.9, 131.8, 131.5, 129.3, 129.1, 128.8, 128.5, 127.6, 127.6,
3
125.5, 124.4, 124.0, 122.4, 121.8, 120.8, 117.5, 111.8, 58.8, 21.5. HRMS (ESI-TOF) m/z Calculated For
+
C
30
H
23BrNO
3
S [M+H] 556.0577, found: 556.0574.
4
-Phenyl-1-tosyl-2-(4-(trifluoromethyl)phenyl)-1,2-dihydrobenzofuro[3,2-b]pyridine (3ag): 69 mg,
o
1
6
3% yield, white solid, m.p. = 170-171 C, R
f
= 0.35 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz,
CDCl
3
) δ 8.07-7.92 (m, 1H), 7.71-7.48 (m, 4H), 7.48-7.43 (m, 2H), 7.42-7.35 (m, 4H), 7.35-7.28 (m, 2H),
7.25-7.19 (m, 2H), 7.08 (d, J = 8.0 Hz, 2H), 6.15 (d, J = 6.1 Hz, 1H), 5.76 (d, J = 6.1 Hz, 1H), 2.25 (s, 3H).
1
3
1
C{ H} NMR (100 MHz, CDCl
3
) δ 154.0, 147.2, 144.5, 142.4, 134.3, 133.8, 131.7, 130.5 (q, JC-F = 32.0
Hz), 129.4, 128.9, 128.6, 127.6, 127.6, 126.0, 125.6 (q, JC-F = 4.0 Hz), 125.6, 124.3, 124.1 (q, JC-F = 271.0
1
9
1
3
Hz), 124.0, 121.8, 120.5, 117.6, 111.8. 58.8, 21.5. F{ H} NMR (376 MHz, CDCl ) δ -62.6. HRMS (ESI-
+
TOF) m/z Calculated For C31
H
23
F
3
NO
3
S [M+H] 546.1345, found: 546.1345.
4
-Phenyl-2-(thiophen-3-yl)-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ah): 84 mg, 87% yield,
o
1
white solid, m.p. = 90-91 C, new compound, R
CDCl ) δ 8.07-7.95 (m, 1H), 7.45 (d, J = 8.3 Hz, 2H), 7.43-7.34 (m, 4H), 7.34-7.28 (m, 2H), 7.25-7.18 (m,
4H), 7.17-7.12 (m, 1H), 7.07 (d, J = 8.1 Hz, 2H), 6.15 (d, J = 5.9 Hz, 1H), 5.76 (d, J = 5.9 Hz, 1H), 2.25 (s,
f
= 0.20 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz,
3
1
3
1
3
1
H); C{ H} NMR (100 MHz, CDCl ) δ 154.0, 147.2, 144.2, 139.2, 134.6, 134.1, 130.7, 129.3, 128.7,
3
28.5, 127.6, 126.8, 126.4, 125.3, 124.6, 123.9, 123.3, 121.8, 121.8, 117.5, 111.7, 56.4, 21.5. HRMS (ESI-
+
TOF) m/z Calculated For C H NO S [M+H] 484.1036, found: 484.1041.
2
8
22
3 2
2
-(tert-Butyl)-4-phenyl-1-tosyl-1,2-dihydrobenzofuro[3,2-b]pyridine (3ai): 10 mg, 11% yield, yellow
1
oil, R
f
= 0.45 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ 8.11-8.02 (m, 1H), 7.43-7.35 (m,
4H), 7.34-7.28 (m, 4H), 7.17-7.09 (m, 2H), 7.02 (d, J = 8.1 Hz, 2H), 5.52 (d, J = 5.9 Hz, 1H), 4.63 (d, J =
1
3
1
5
1
2
3
.9 Hz, 1H), 2.22 (s, 3H), 0.93 (s, 9H); C{ H} NMR (100 MHz, CDCl ) δ 153.9, 147.8, 143.9, 134.5,
34.2, 130.9, 129.0, 128.5, 128.4, 127.7, 127.5, 125.1, 124.7, 123.9, 122.6, 121.7, 119.0, 111.7, 66.2, 37.6,
+
5.9, 21.5. HRMS (ESI-TOF) m/z Calculated For C H NO S [M+H] 458.1784, found: 458.178.
2
8
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General Procedure for Synthesis of Benzofuro[3,2-b]pyridines. The aromatization of 1,2-
dihydrobenzofuro[3,2-b]pyridines 3 were conveniently conducted in ethanol through deprotection of tosyl
[
13]
group in presence of sodium hydroxide according to the known literature procedure.
To the solution of the cyclization products 3 (0.15 mmol) in anhydrous ethanol (2.0 mL), powder sodium
hydroxide (30 mg, 0.75 mmol) was added, the reaction mixture was refluxed in oil bath for 30 min. The
solvent was evaporated under the reduced pressure, the crude product was purified by silica gel column
chromatography using hexanes/ethyl acetate as eluent to give the desirable aromatization products 4.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
[
14]
2,4-Diphenylbenzofuro[3,2-b]pyridine (4a): 43 mg, 89% yield, white solid, the known compound,
R
f
1
=
0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ 8.37 (d, J = 7.7 Hz, 1H), 8.17 (d, J =
1
3
1
8
.1 Hz, 2H), 8.11-8.03 (m, 2H), 7.96 (s, 1H), 7.67-7.50 (m, 7H), 7.50-7.43 (m, 2H); C{ H} NMR (100
MHz, CDCl ) δ 158.0, 154.5, 146.6, 145.1, 139.9, 134.3, 132.7, 129.5, 129.2, 129.1, 128.9, 128.9, 128.7,
3
1
27.4, 123.8, 123.7, 121.7, 117.8, 112.4.
o
2-Phenyl-4-(o-tolyl)benzofuro[3,2-b]pyridine (4b): 45 mg, 90% yield, white solid, m.p. = 54-56 C, new
1
compound, R
f
= 0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ 8.37 (d, J = 7.7 Hz, 1H),
13
1
8
.15 (d, J = 7.4 Hz, 2H), 7.75 (s, 1H), 7.63-7.50 (m, 4H), 7.51-7.32 (m, 6H), 2.34 (s, 3H); C{ H} NMR
(
100 MHz, CDCl ) δ 158.0, 154.0, 147.0, 144.4, 139.8, 136.7, 134.5, 133.9, 130.7, 130.0, 129.3, 129.2,
3
1
29.0, 128.8, 127.4, 126.2, 124.0, 123.7, 121.7, 120.2, 112.4, 20.4. HRMS (ESI-TOF) m/z Calculated For
+
C
24
H
18NO [M+H] 336.1383, found: 336.1386.
o
2-Phenyl-4-(m-tolyl)benzofuro[3,2-b]pyridine (4c): 48 mg, 95% yield, white solid, m.p. = 139-140 C,
1
new compound, R = 0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.42-8.33 (m, 1H),
f
3
8
.24-7.10 (m, 2H), 7.95 (s, 1H), 7.90-7.78 (m, 2H), 7.66 (d, J = 8.3 Hz, 1H), 7.62-7.52 (m, 3H), 7.53-7.44
13
1
(
m, 3H), 7.35 (d, J = 7.6 Hz, 1H), 2.53 (s, 3H); C{ H} NMR (100 MHz, CDCl
3
) δ 158.0, 154.4, 146.7,
1
45.0, 140.0, 138.8, 134.2, 132.9, 130.3, 129.4, 129.2, 129.0, 128.9, 128.7, 127.4, 126.1, 123.8, 123.6, 121.7,
+
117.9, 112.4, 21.8. HRMS (ESI-TOF) m/z Calculated For C24H18NO [M+H] 336.1383, found: 336.1382.
o
2
-Phenyl-4-(p-tolyl)benzofuro[3,2-b]pyridine (4d): 46 mg, 91% yield, white solid, m.p. = 120-122 C,
1
f 3
new compound, R = 0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.35 (d, J = 7.6 Hz,
1
2
1
H), 8.19-8.09 (m, 2H), 8.04-7.87 (m 3H), 7.65 (d, J = 8.3 Hz, 1H), 7.61-7.51 (m, 3H), 7.51-7.36 (m, 4H),
13
1
.48 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 157.9, 154.4, 146.6, 144.9, 140.0, 139.6, 132.6, 131.3,
3
29.8, 129.1, 128.9, 128.7, 128.7, 127.4, 123.8, 123.6, 121.6, 117.5, 112.3, 21.5. HRMS (ESI-TOF) m/z
+
Calculated For C24
H
18NO [M+H] 336.1383, found: 336.1383.
4
-(4-Methoxyphenyl)-2-phenylbenzofuro[3,2-b]pyridine (4e): 47 mg, 89% yield, white solid, m.p. =
o
1
1
41-142 C, new compound, R
f
= 0.70 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ 8.45-
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1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
8
.28 (m, 1H), 8.21-8.11 (m, 2H), 8.04 (d, J = 8.7 Hz, 2H), 7.92 (s, 1H), 7.67-7.51 (m, 4H), 7.45 (t, J = 7.3
1
3
1
Hz, 2H), 7.11 (d, J = 8.7 Hz, 2H), 3.91 (s, 3H); C{ H} NMR (100 MHz, CDCl
3
) δ 160.7, 157.9, 154.4,
1
5
46.5, 144.9, 140.1, 132.3, 130.2, 129.1, 128.9, 128.7, 127.4, 126.5, 123.9, 123.6, 121.7, 117.2, 114.6, 112.3,
+
5.5. HRMS (ESI-TOF) m/z Calculated For C24
2
H18NO [M+H] 352.1332, found: 352.1330.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4
-(4-Chlorophenyl)-2-phenylbenzofuro[3,2-b]pyridine (4f): 47 mg, 93% yield, white solid, m.p. = 164-
o
1
1
66 C, new compound, R = 0.80 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.46-8.25
f
3
1
3
1
(m, 1H), 8.19-8.09 (m, 2H), 8.03-7.95 (m, 2H), 7.89 (s, 1H), 7.66-7.51 (m, 6H), 7.50-7.43 (m, 2H); C{ H}
NMR (100 MHz, CDCl
3
) δ 157.9, 154.5, 146.3, 145.2, 139.8, 135.6, 132.7, 131.3, 130.2, 129.4, 129.0, 128.8,
+
1
3
27.4, 123.8, 123.7, 121.8, 117.3, 112.3. HRMS (ESI-TOF) m/z Calculated For C23
56.0837, found: 356.0837.
H
15ClNO [M+H]
o
8
-Methyl-2,4-diphenylbenzofuro[3,2-b]pyridine (4g): 46 mg, 91% yield, white solid, m.p. = 153-154 C,
1
new compound, R
f
= 0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ 8.24-8.12 (m, 3H),
8.10-8.01 (m, 2H), 7.94 (s, 1H), 7.63-7.49 (m, 6H), 7.49-7.43 (m, 1H), 7.40-7.34 (m, 1H), 2.56 (s, 3H);
1
3
1
3
C{ H} NMR (100 MHz, CDCl ) δ 156.4, 154.2, 146.9, 145.1, 140.0, 134.4, 133.3, 132.5, 130.4, 129.4,
1
29.1, 128.9, 128.7, 127.4, 123.7, 121.5, 117.5, 111.8, 21.5. HRMS (ESI-TOF) m/z Calculated For
+
C
24
H
18NO [M+H] 336.1383, found: 336.1371.
o
7
-Methyl-2,4-diphenylbenzofuro[3,2-b]pyridine (4h): 47 mg, 93% yield, white solid, m.p. = 150-151 C,
1
new compound, R
f
= 0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ 8.22 (d, J = 7.9 Hz,
1H), 8.19-8.12 (m, 2H), 8.10-8.02 (m, 2H), 7.92 (s, 1H), 7.64-7.49 (m, 5H), 7.48-7.40 (m, 2H), 7.32-7.27 (m,
1
3
1
1
1
H), 2.57 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 158.5, 154.3, 146.5, 145.3, 140.2, 140.1, 134.4, 132.4,
3
29.4, 129.1, 128.9, 128.7, 127.4, 125.1, 121.2, 121.2, 117.3, 112.6, 22.3. HRMS (ESI-TOF) m/z Calculated
+
For C24
H
18NO [M+H] 336.1383, found: 336.1376.
o
4
-Phenyl-2-(p-tolyl)benzofuro[3,2-b]pyridine (4i): 46 mg, 92% yield, white solid, m.p. = 186-187 C,
1
new compound, R
f
= 0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl
3
) δ 8.45-8.29 (m, 1H),
8
2
1
.15-8.01 (m, 4H), 7.94 (d, J = 4.4 Hz, 1H), 7.73-7.57 (m, 4H), 7.57-7.43 (m, 2H), 7.35 (d, J = 7.9 Hz, 2H),
1
3
1
3
.46 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 157.9, 154.5, 146.5, 144.9, 138.6, 137.1, 134.4, 132.6,
29.6, 129.4, 129.1, 129.1, 128.9, 127.2, 123.9, 123.6, 121.7, 117.4, 112.3, 21.4; HRMS (ESI-TOF) m/z
+
Calculated For C H NO [M+H] 336.1383, found: 336.1378.
2
4
18
2
-(4-Methoxyphenyl)-4-phenylbenzofuro[3,2-b]pyridine (4j): 49 mg, 93% yield, white solid, m.p. =
o
1
162-164 C, new compound, R
f 3
= 0.70 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.34 (d,
J = 7.6 Hz, 1H), 8.17-8.09 (m, 2H), 8.09-8.00 (m, 2H), 7.90 (s, 1H), 7.70-7.49 (m, 5H), 7.49-7.42 (m, 1H),
1
3
1
7
3
.06 (d, J = 8.8 Hz, 2H), 3.90 (s, 3H); C{ H} NMR (100 MHz, CDCl ) δ 160.4, 157.9, 154.2, 146.3, 144.9,
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34.4, 132.7, 132.6, 129.4, 129.1, 128.9, 128.6, 123.9, 123.6, 121.7, 117.1, 114.3, 112.4, 55.5. HRMS (ESI-
+
TOF) m/z Calculated For C24
H18NO
2
[M+H] 352.1332, found: 352.1325.
2
-(4-Bromophenyl)-4-phenylbenzofuro[3,2-b]pyridine (4k): 54 mg, 90% yield, white solid, m.p. = 213-
o
1
2
7
7
15 C, new compound, R
f 3
= 0.85 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.32 (d, J =
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
.7 Hz, 1H), 8.04 (d, J = 8.5 Hz, 4H), 7.91 (s, 1H), 7.69-7.63 (m, 3H), 7.63-7.56 (m, 3H), 7.56-7.51 (m, 1H),
13
1
.50-7.42 (m, 1H); C{ H} NMR (100 MHz, CDCl ) δ 158.1, 153.1, 146.7, 145.2, 138.8, 134.1, 132.8,
3
132.0, 129.6, 129.4, 129.2, 128.9, 123.8, 123.7, 123.2, 121.7, 117.4, 112.4. HRMS (ESI-TOF) m/z
+
Calculated For C23
H
15BrNO [M+H] 400.0332, found: 400.0328.
4
-Phenyl-2-(thiophen-3-yl)benzofuro[3,2-b]pyridine (4l): 47 mg, 96% yield, white solid, m.p. = 148-
o
1
1
7
49 C, new compound, R
f 3
= 0.65 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.32 (d, J =
13
1
.6 Hz, 1H), 8.12-7.98 (m, 3H), 7.87 (s, 1H), 7.83 (m, 1H), 7.68-7.51 (m, 5H), 7.50-7.42 (m, 2H); C{ H}
NMR (100 MHz, CDCl
3
) δ 157.9, 150.5, 146.3, 144.9, 142.5, 134.2, 132.7, 129.5, 129.2, 129.1, 128.9, 126.8,
+
126.4, 123.7, 123.6, 123.2, 121.7, 117.4, 112.3. HRMS (ESI-TOF) m/z Calculated For C H NOS [M+H]
2
1
14
3
28.0791, found: 328.0791.
One Pot Synthesis of Benzofuro[3,2-b]pyridines. Under nitrogen, the solution of Cu(MeCN)
4
4
BF (3.1
mg, 0.01 mmol) and ligand XantPhos (5.8 mg, 0.01 mmol) in 1,4-dioxane (0.5 mL) was stirred at room
temperture for 1.5 h, azadienes 1 (0.20 mmol), 1,4-dioxane (2.5 mL), triethylamine (20.2 mg, 0.2 mmol),
o
terminal alkynes 2 (0.6 mmol) was added in sequence. The reaction was stirred at 60 C in oil bath for 2 days,
which was monitored by thin-layer chromatography, then powder sodium hydroxide (40 mg, 1.0 mmol) was
o
added, the reaction was stirred at 80 C in oil bath for 2 h. The volatiles were evaporated under the reduced
pressure, the residue was purified by silica gel column chromatography using hexanes/ethyl acetate as eluent
to give the desired products 4.
2
,4-Diphenylbenzofuro[3,2-b]pyridine (4a): 56 mg, 87% yield; 4-(4-Chlorophenyl)-2-phenyl-
benzofuro[3,2-b]pyridine (4f): 65 mg, 91% yield; 7-Methyl-2,4-diphenylbenzofuro[3,2-b]pyridine (4h):
6
1 mg, 86% yield.
4 4
Experiment at Gram Scale. Under nitrogen, the solution of Cu(MeCN) BF (39.3 mg, 0.125 mmol) and
ligand XantPhos (72.3 mg, 0.125 mmol) in 1,4-dioxane (6.0 mL) was stirred at room temperture for 2 h,
azadiene 1a (0.939 g, 2.5 mmol), 1,4-dioxane (31.5 mL), triethylamine (253 mg, 2.5 mmol), terminal alkyne
o
2
a (0.768 g, 7.5 mmol) was added in sequence. The reaction was stirred at 60 C in oil bath for 55 h, which
was monitored by thin-layer chromatography. The volatiles were evaporated under the reduced pressure, the
residue was purified by silica gel column chromatography using hexanes/ethyl acetate as eluent to give the
desired product 3aa, 1.060 g, 89% yield.
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Synthesis of Three Bioactive Molecules.
The Synthesis of Bioactive Molecules 5 and 6
Under nitrogen, the solution of Cu(MeCN) BF (7.8 mg, 0.025 mmol) and ligand XantPhos (14.5 mg,
4
4
0
1
.025 mmol) in 1,4-dioxane (2.0 mL) was stirred at room temperture for 1.5 h, azadienes 1a (0.50 mmol),
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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4
5
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7
8
9
0
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1
2
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6
7
8
9
0
,4-dioxane (5.5 mL), triethylamine (50.6 mg, 0.50 mmol), terminal alkynes (1.50 mmol) was added in
o
sequence. The reaction was stirred at 60 C in oil bath for 2 days, which was monitored by thin-layer
chromatography, then powder sodium hydroxide (100 mg, 2.5 mmol) was added, the reaction was stirred at
o
80 C in oil bath for 2 h. The volatiles were evaporated under the reduced pressure, the residue was purified
by silica gel column chromatography using hexanes/ethyl acetate = 80:1 as eluent to give the bioactive
compounds 5 and 6.
2
-(4-Chlorophenyl)-4-phenylbenzofuro[3,2-b]pyridine (5): 160 mg, 90% yield, white solid, the known
[
10e]
1
compound,
f 3
R = 0.65 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.35 (d, J = 7.7 Hz,
1H), 8.12 (d, J = 8.5 Hz, 2H), 8.06 (d, J = 7.4 Hz, 2H), 7.93 (s, 1H), 7.71-7.59 (m, 4H), 7.59-7.45 (m, 4H);
1
3
1
C{ H} NMR (100 MHz, CDCl
29.2, 129.1, 128.9, 128.6, 123.8, 123.6, 121.7, 117.4, 112.4.
-(3-Methoxyphenyl)-4-phenylbenzofuro[3,2-b]pyridine (6): 157 mg, 89% yield, colorless oil, the
3
) δ 158.0, 153.1, 146.7, 145.2, 138.3, 134.9, 134.1, 132.8, 129.6, 129.4,
1
2
[10d]
1
known compound,
f 3
R = 0.60 (hexanes/ethyl acetate = 30:1). H NMR (400 MHz, CDCl ) δ 8.43-8.32 (m,
1H), 8.12-8.01 (m, 2H), 7.96 (s, 1H), 7.79-7.73 (m, 1H), 7.74-7.40 (m, 8H), 7.11-6.88 (m, 1H), 3.95 (s, 3H).
1
3
1
3
C{ H} NMR (100 MHz, CDCl ) δ 160.3, 158.0, 154.3, 146.7, 145.0, 141.4, 134.3, 132.7, 129.9, 129.5,
1
29.3, 129.2, 128.9, 123.8, 123.7, 121.8, 119.9, 118.0, 114.6, 112.9, 112.4, 55.6
The Synthesis of Bioactive Molecule 7
Under nitrogen, to the solution of 6 (0.157 g, 0.45 mmol) in dichloromethane (2.0 mL) was added BBr3
o
(
0.338 g, 1.35 mmol) in dichloromethane (3.0 mL) at -78 C and stirred for 10 min, then the reaction was
[
15]
moved to room temperature and stirred for overnight. The reaction was quenched by 20 mL water and
extracted with dichloromethane, dried over anhydrous sodium sulfate and concentrated. The crude products
were purified by silica gel column chromatography using hexanes/ethyl acetate = 10:1 as eluent to give the
bioactive compounds 7.
3
-(4-Phenylbenzofuro[3,2-b]pyridin-2-yl)phenol (7): 132 mg, 87% yield, shallow yellow solid, the
[
10d]
1
known compound,
f 3
R = 0.40 (hexanes/ethyl acetate = 5:1). H NMR (400 MHz, CDCl ) δ 8.46-8.25 (m,
1H), 8.14-7.97 (m, 2H), 7.92 (s, 1H), 7.89-7.82 (m, 1H), 7.66-7.49 (m, 6H), 7.43-7.32 (m, 2H), 7.05-6.80 (m,
1
3
1
1
1
3
H); C{ H} NMR (100 MHz, CDCl ) δ 158.0, 157.0, 154.6, 146.8, 144.8, 141.1, 134.0, 133.3, 130.2,
29.7, 129.5, 129.2, 129.0, 123.9, 123.2, 122.0, 119.5, 118.5, 116.4, 115.1, 112.4.
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Determination of the Structure of Compound 3aa
To determine the structure of cascade product, the compound 3aa was obtained as a colorless crystal after
the recrystallization from dichloromethane/hexanes. Based on single crystal X-ray diffraction analysis, the
structure of compound 3aa was determined as 2,4-diphenyl-1-tosyl-1,2-dihydronzofuro[3,2-b]pyridine (see
Supporting Information). The CCDC number is 1911582. These details can be obtained free of charge via
www.ccdc.com.ac.uk /data_request/cif from the Cambridge Crystallographic Data Centre.
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ASSOCIATED CONTENT
Supporting information
NMR spectra of products, This material is available free of charge via the internet at http://pubs.acs.org.
1
13
1
19
1
Copies of H, C{ H}and F{ H} spectra of all new compounds (PDF)
X-ray crystallography data 3aa (CCDC 1911582) (CIF)
AUTHOR INFORMATION
Corresponding author
*
E-mail: ygzhou@dicp.ac.cn.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Financial support from the National Natural Science Foundation of China (21532006, 21690074) and
Chinese Academy of Sciences (XDB17020300, QYZDJ-SSW-SLH035) is acknowledged.
REFERENCES
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