Visible-Light Photocatalytic Synthesis of Amines from Imines via Transfer Hydrogenation Using Quantum Dots as Catalysts

Article abstract of DOI:10.1021/acs.joc.8b01651

CdSe/CdS core/shell quantum dots (QDs) can be used as stable and highly active photoredox catalysts for efficient transfer hydrogenation of imines to amines with thiophenol as a hydrogen atom donor. This reaction proceeds via a proton-coupled electron transfer (PCET) from the QDs conduction band to the protonated imine followed by hydrogen atom transfer from the thiophenol to the α-aminoalkyl radical. This precious metal free transformation is easy to scale up and can be carried out by a one-pot protocol directly from aldehyde, amine, and thiophenol. Additional advantageous features of this protocol include a wide substrate scope, high yield of the amine products, extremely low catalyst loading (0.001 mol %), high turnover number (10⁵), and the mild reaction conditions of using visible light or sun light at room temperature in neutral media.

Full text of DOI:10.1021/acs.joc.8b01651

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Article
Visible-light photocatalytic synthesis of amines from imines
via transfer hydrogenation using quantum dots as catalysts
Zi-Wei Xi, Lei Yang, Dan-Yan Wang, Chaodan Pu, Yong-Miao Shen, Chuan-De Wu, and Xiaogang Peng
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b01651 • Publication Date (Web): 31 Aug 2018
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Visible-light photocatalytic synthesis of amines from imines via
transfer hydrogenation using quantum dots as catalysts
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Zi-Wei Xi†,‡, Lei Yang†,†, Dan-Yan Wang, Chao-Dan Pu*,†, Yong-Miao Shen*,†, ‡,, Chuan-De
Wu†, Xiao-Gang Peng†
†Center for Chemistry of Novel & High-Performance Materials, Department of Chemistry, Zhejiang Uni-
versity, Hangzhou, 310027, P. R. China
‡Department of Chemistry and Chemical Engineering, Shaoxing University, Shaoxing, 312000, P. R. China
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, P. R. China
Table of Contents Graphic:
ABSTRACT: CdSe/CdS core/shell quantum dots (QDs) can be used as stable and highly active photo-
redox catalysts for efficient transfer hydrogenation of imines to amines with thiophenol as a hydrogen
atom donor. This reaction proceeds via a proton coupled electron transfer (PCET) from the QDs con-
duction band to the protonated imine followed by hydrogen atom transfer from the thiophenol to the
α-aminoalkyl radical. This precious metal free transformation is easy to scale up and can be carried
out by a one-pot protocol directly from aldehyde, amine and thiophenol. Besides, other advantageous
features of this protocol include a wide substrate scope, high yield of the amine products, extremely
low catalyst loading (0.001 mol %), high turnover number (105) and the mild reaction conditions of
using visible light or sun light at room temperature in neutral media.
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Introduction
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Aliphatic amines are ubiquitous building blocks in organic synthesis and exist as core structures in a
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variety of natural products, pharmaceuticals, and agrichemicals. The overwhelming importance of
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amines demands development of effective and diversity-oriented synthetic methods. Among present
approaches, hydrogenation and transfer hydrogenation of imines constitute one of the most efficient
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and straightforward synthetic routes, which can be realized by transition metal catalysis, organoca-
talysis, 3 and metal-organo cooperative catalysis. 4 However, these reactions suffer from several short-
comings and limitations that often hamper their practical applications, such as the high cost of the pre-
cious metal catalysts, relatively low catalyst activity and turnover number caused by coordination or
reaction of the amine products with the catalysts, limited diversity of organocatalysts, harsh reaction
conditions and narrow substrate scope. It is therefore desirable to develop new, efficient, and versatile
imine reductive hydrogenation methods not relying on precious metal complexes as catalysts.
By application of a series of visible-light responsive photocatalysts, including ruthenium and iridi-
5
5b,6
um coordination compounds, as well as organic dyes,
visible-light photoredox catalysis has re-
cently been actively investigated and established as a powerful technique to induce a myriad of radical
based reactions. In this regard, imine has been reported to take part in photoredox catalyzed alkylation,
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allylation, aminoalkylation, arylation, dimerization, and inverse hydroboration. Most re-
cently, three reports on photoredox transfer hydrogenation of diarylketoimines have appeared, all us-
＋
ing iridium complex—[Ir(ppy)2(dtbbpy)] (PF6 ) or a sulfonated Ir fac-Ir(ppy)3—as photocatalyst.13 In
addition, photocatalyzed synthesis of aliphatic amines has been reported by using iridium complex
Ir[dF(CF3)ppy][bpy]PF6 and ruthenium complex Ru(bpy)3Cl2 as photocatalyst respectively through
aldehyde and ketone reductive amination reactions.14
–
Colloidal semiconductor nanocrystals with their sizes in quantum-confinement regime (quantum
dots, QDs) have recently emerged as a class of potential photocatalysts owing to their excellent elec-
tronic and structure properties, i.e. wide and strong absorption for light harvesting, size dependent
band gap for tunable and selective driving force of redox reaction, large surface-to-volume ratio for
15
charge extraction and rich reaction sites, and potentially good photochemical stability. Studies in
this area have so far focused on hydrogen production via water splitting, and the photodegradation of
organic molecules. 16 Recently, a few reports have studied application of QDs in photocatalytic organ-
ic reactions of synthetic interest, such as reduction of aromatic nitro compounds and azides to amines,
debromination and C−H arylation reactions of aryl bromides,18 and other C−C bond forming reac-
17
tions.19 Kisch and Shiraishi had reported that semiconductors can catalyze imine reductive reactions.
But most of these reactions were performed under UV irradiation with high catalyst loadings.20 It
should be noted that, in most of these studies, plain core QDs have been applied as photocatalysts be-
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cause extraction of photo-generated carriers from core/shell QDs with type-I band offsets is believed
to be difficult. 21 However, photo-stability and chemical-stability (such as aggregation and etching) of
plain QDs have frequently been problematic during photocatalytic reactions, while better stability and
control of carrier dynamics of core/shell QDs render them advantages as catalysts for photocatalytic
reaction. 22
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In this work, nearly defect-free CdSe/CdS core/shell QDs were explored as photocatalysts for trans-
fer hydrogenation reaction of imines with thiophenol as hydrogen source for a wide scope of amines.
In comparison with the plain core CdSe QDs, CdSe/CdS core/shell QDs were stable yet efficient as
photocatalysts in the series of reactions studied. Comparing to the iridium complex catalyzed hydro-
genation of imines, our protocol is a precious-metal free reaction with a wider substrate scope, appli-
cable not only to diaryl and aryl-alkyl ketoimines, but also to a diversity of aldimines.
Results and Discussion
All QDs used in this work were prepared according to our previously published method. 23 The size
of plain CdSe and CdSe core in core/shell QDs was about 3 nm in diameter, with first absorption at
550 nm. CdS was chosen as shell materials because of the superior optical properties and well estab-
lished synthetic methods of CdSe/CdS core/shell QDs. We started our optimization studies by reduc-
tion of 4-fluoro-N-(4-fluorobenzylidene)aniline 1k in the presence of 2a in toluene. Reaction condi-
tions were screened by use of various hydrogen donors in varying amounts. We found that for
CdSe/CdS core/shell QDs with 3 monolayers of CdS shell, 7 eq. of 4-fluorothiophenol with 8 h visible
light irradiation could give satisfactory result (Table 1, entry 8). The catalyst could be applied at ex-
tremely low loading (0.001 mol %) to lead to effective reactions, indicating a turnover number of
about 105. It should be noted that this is not the maximum turnover number since our QDs were still
stable after reaction (see below).
When CdSe/CdS core/shell QDs with 5 monolayers of CdS shells were chosen as the photocatalyst,
the yield decreased slightly (Table 1, entry 10). The yield decreased noticeably when we used the
same amount of plain core CdSe QDs as the catalyst (Table 1, entry 11). We also checked reactions
catalyzed by CdS QDs under the standard reaction conditions, which gave about 60% yield. Moreover,
plain CdSe core precipitated during the reaction. Overall, both photocatalytic efficiency and stability
of core/shell QDs were much better than those of the plain core QDs, indicating that charge extraction
was not the determinant factor for practical photocatalytic use of these QDs as the catalysts. When we
using mercaptan as a hole scavenger, the yield was decreased significantly (Table 1, entry 15, 16, 17).
The reaction could not proceed by using triethanolamine or triethylamine as a hole scavenger, because
of its low ability to extract hole from QDs (Table 1, entry 18, 19). Control experiments confirmed that
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presence of QDs and thiophenol was essential for the reactions to occur (Table 1, entry 13). Also, the
reaction could not proceed in the dark (Table 1, entry 14).
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Table 1. Selected Optimization Experimentsa
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entry
catalyst
mol %)
(×10-3 hole acceptor (equiv)
reaction time yield (%)
(h)
1
2
2a (5)
2a(7)
2a (9)
2a (7)
2a (7)
2b (7)
2a (7)
2a (7)
2a (7)
2a (7)
2a (7)
2a (7)
0
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0
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1d
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0
2a(7)
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0
1
(4-chlorophenyl)methanethiol (7)
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10.7e
3.8e
20.7e
0
1
1-hexylthiol
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1
1,3-dimercaptopropane
Triethanolamine (7)
Triethylamine (7)
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1
8
1
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0
aReactions performed with imine 1k (0.4 mmol, 86.8 mg), QDs with 3 monolayers of CdS (2×10-5
mol/L), 2, toluene 8 mL, purging with Argon gas for 10 minutes before illumination with 3 W Green
b
c
d
LED. The QDs with 5 monolayers of CdS as the photocatalyst. CdSe Core as the photocatalyst.
CdS QDs as the photocatalyst. e Determined by GC-MS.
With the optimal reaction conditions established, we first explored the reaction scope for aldimines
(Table 2). We found that for all aldimines tested, full conversion could be reached by 6 to 10 hours
irradiation. The substituent effects on both the N-aryl and C-aryl were examined. Most of the reactions
proceeded with more than 80% yield whether the substituent was electron-rich (entry 1, 2, 6, 7, 16, 25)
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or electron-deficient (entry 4, 4, 11-15, 20, 24) on either of the phenyl rings. The position and the
number of the substituents on the phenyl rings showed no significant effect on yield (entry 13, 14).
The stability of the imine in the reaction solution was the most important factor affecting the reduction
yield. For example, 4-acetyl substituent on the aniline moiety gave 79% yield of the amine with a 6%
decomposition of the starting imine according to GC-MS measurements. The relatively low yield
(40%) for 3t was also a result of the gradual decomposition of the imine during the reaction course.
We then extended the reaction to the N,N'-dibenzylidene-1,4-phenylenediamine and this diamine was
smoothly reduced to the diamine 4 in 72 % yield (Scheme 1).
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Table 2. Scope of Aldiminesa
entry
1
R1
R2
Yield/%
88
83
84
82
90
93
88
82
86
94
86
92
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86
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68
40
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1
3
H
H
1a
1b
1c
1d
1e
1f
3a
3b
3c
3d
3e
3f
2
H
4-OH
4-OMe
4-F
3
H
4
H
5
H
4-Cl
6
4-Me
4-Me
4-Me
4-Me
4-F
4-OMe
4-Me
4-F
7
1g
1h
1i
3g
3h
3i
8
9
4-Cl
10
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23
4-OMe
4-F
1j
3j
4-F
1k
1l
3k
3l
4-F
4-Cl
4-Cl
4-F
1m
1n
1o
1p
1q
1r
1s
1t
3m
3n
3o
3p
3q
3r
3s
3t
2-Cl
4-F
4-Cl
4-Cl
4-OMe
4-OMe
4-OMe
4-OMe
4-CN
4-PhCH2O
4-F
4-Me
4-F
4-Cl
4-COMe
4-CN
4-F
1u
1v
1w
3u
3v
3w
3,4-diMe
4-CN
4-(n-C6H13O)-
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4-CF3
4-F
82
87
1x
1y
3x
3y
4-OMe
4-OMe
aReactions performed with imine 1 (0.4 mmol, 86.8 mg), QDs with 3 monolayers of CdS (4 ×10-9 mol,
2×10-5 mol/L, 1×10-3 mol %) and 4-fluorophenyl thiophenol (2.8 mmol, 0.359 g, 7 eqiv) in toluene (8
mL), purging with argon gas for 10 minutes before illumination by 3 W green LED.
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We further found that, not only N-aryl aldimines, but also N-alkyl aldimines were suitable substrates
(Scheme 1), affording the corresponding amine products in moderate to high yield (5 and 6). We then
tested the reactions of several diaryl and aryl alkyl ketimines and it turned out that these ketimines
behaved equally well and were reduced in good yields (7, 8, 9).
Scheme 1. Scope of Imines
The reaction is easy to scale up. When we carried out a gram scale reduction of benzylidene-4-
fuoroaniline under the standard reaction conditions using a 20 W green LED as light source, the prod-
uct 3d was isolated in 83 % yield (Scheme 2a). Moreover, direct one-pot reaction between an benzal-
dehyde, an aniline and 4-fuorothiophenol proceeded smoothly to give excellent yields of products 3a
(76 %), 3d (87 %), 3g (93%) although the reaction took 16 h to be completed, twice that using the
imine directly (Scheme 2b). The one-pot reactions can also proceed with aliphatic amines as the start-
ing material, and also give satisfactory yields (products 5 and 6).
As an example to show the potentiality of this reaction for the synthesis of biologically active
amines, we successfully accomplished the synthesis of the antimycotic agent butenafine by using a
direct one-pot reaction between 1-naphthalene aldehyde, 4-t-butylbenzylamine and 4-fuorothiophenol.
This gave the reduction product in 86% yield. Subsequent direct methylation under non-optimized
conditions gave the butenafine 10. The overall yield of 10 covering the photoreduction and methyla-
tion is 65%.
Scheme 2. Practical Applications of the Reaction a) a gram scale reaction. b) one-pot reaction. c)
butenafine synthesis.
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Use of sun light as a light source was tested. It was found that the reaction proceeded swiftly under
solar irradiation and it took only 3 hours in a clear day to reach a completion to give the product 3d in
84% yield (For additional experimental details, see Supplementary Information).
The QDs are very stable in the reaction system, i.e., remaining colloidal stability and no detectable
decrease in activity even after 24 hours illumination (Figure 3s). TEM images show that the shape and
size of the QDs showed no obvious change after reactions (Figure 1). Compared to imine, the amount
of the QD used is only 0.001 mol %. It is therefore quite hard to collect and to recycle the catalyst.
However, QDs still have the ability to photocatalyze the reaction when the starting materials were
added to the solution again.
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Figure 1. TEM images of CdSe/3CdS before (a) and after (b) the reaction.
Several experiments were carried out to clarify the reaction mechanism. Deuterium labeling exper-
iments were carried out to confirm the hydrogen source. When the reaction was conducted under
standard conditions with deuterated thiophenol, almost no deuterium was detected in final products. In
this case, it is obvious that deuterium exchange between the deuterated thiophenol and the ligands in
QD catalyst results in a diminished deuterium incorporation into the imine reduction products. How-
ever, when QDs were pre-deuterium labeled with deuterated isopropanol, almost 70% deuterium in-
corporation was observed at the methylene and amino position (Scheme 3b). It should be noted that
the amount of deuterium in the prepared deuterated thiophenol was also about 70%. No deuterium
incorporation was observed with toluene-d8 as the reaction solvent (see Figure 7s, 8s in supporting
information). All these results demonstrated that thiphenol was the hydrogen source.
Scheme 3. Deuterium Incorporation Studies
When a stoichiometric amount of radical scavenger 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO)
was added to the reaction, no desired product was detected. The TEMPO-thiophenol adduct was
formed in 28% yield judged from the amount of TEMPO (Scheme 4, determined by GC-MS). Mean-
while, the imine remained unchanged during the reaction.
Scheme 4. Trapping of the Radical
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Fluorescence quenching experiments were conducted with the imine 1k and thiophenol 2a as the
QDs quencher, respectively (Figure 2). Thiophenol behaved as strong quencher of QDs (5.68×109
L/mol•s) while the imine quenched the fluorescence weakly (1.95 ×108 L/mol•s). However, thiolate
should be a stronger quencher than thiophenol. The ligand of our core/shell QDs were mostly oleyla-
mine. Considering the relatively strong acidity of the thiophenol (pKa 10.3 in DMSO, as comparing
with the18.0 and 15.4 for the less acidic phenol and aliphatic thiol, respectively)24 proton transfer may
take place between the oleyl amine ligand in QD and the absorbed thiophenol. Indeed, we found that,
thiolate anions were formed when thiophenol was mixed with oleylamine in solution (See Figure 9s in
the Supplementary Information). We therefore believe that thiolate plays an important, if not domi-
nant role as hole trap in the quenching process. This conclusion is also supported by the well correlat-
ed conversion yields with the acidity of the thiophenols shown in Table 1 where using the more acidic
4-fluorothiophenol gave a much higher yield of product (84%) than using the less acidic 4-
methylthiophenol (37%), while the aliphatic thiols which are least acidic and have higher oxidation
potential (1.12 V, SCE)25 fail to afford any product.
Figure 2 Fluorescence quenching data of 4-fluorothiophenol and imine(1K).
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The role of hole trapping in the reaction may also be the reason for the insensitivity of this photo-
catalytic system to imine substrates and the better photocatalysis efficiency for CdSe/CdS core/shell
QDs than plain core. The CdSe/CdS core/shell QDs has quasi-type II structure with hole localized in
the CdSe core and electron delocalized in the whole QDs. As a result, when hole was efficiently ex-
tracted by thiol/thiolate, the subsequent electron transfer would be easy. Considering the moderate
photocatalysis efficiency of CdS QDs, we carried out the reaction by irradiation with yellow light, we
still obtain high conversion yield using core/shell QDs, while the yield of using CdS QD was almost
zero. This means that the higher catalytic efficiency is a result of core/shell structure. CdS shell could
protect photo-induced charge from being trapped by surface defects, which would improve the photo-
catalysis efficiency of core/shell QDs and eliminate undesirable surface reactions, such as degradation
of surface ligands.
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Based on these results, a plausible mechanism for the photo catalytic transfer hydrogenation of
imines to amines is suggested in Scheme 5. The first step should be absorption of visible light by
CdSe/CdS core/shell QDs to generate an electron-hole pair. 26 Holes were transferred from the valence
band to thiolate (route 1 in Scheme 5) and thiophenol (route 2 in Scheme 5) to generate the thiyl radi-
cal either directly or by the deprotonation of the thiophenol cation radical. This was not only support-
ed by the fluorescence-quenching studies but also backed up by the match of the QDs reduction poten-
tial (～0.9 V) (see the supporting information for additional details) 27 and oxidation potentials of the
thiolate (-0.85 V) and thiophenol (0.95 V 25). Meanwhile, reduction of the weak electron acceptor
imine (typical reduction potential of aldimins is about -2 V 28) by electrons in QDs’ conduction band
(～-1.2V)25 should be thermodynamically unfavorable. Proton transfers from the protonated oleyla-
mine and thiophenol to the imine coupled with electron transfer from the conduction bond of QDs to
the protonated imine gives the radical intermediate A. Hydrogen atom transfer (HAT) from a second
thiophenol molecule affords the terminal product and another thiyl radical. The thiyl radical dimeriza-
tion leads to the disulfide.
Scheme 5. Mechanistic Hypothesis for Photoredox-Transfer Hydrogenation Reaction
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Conclusions
In summary, CdSe/CdS core/shell QDs are proven to be stable and highly active photocatalyst in
place of precious metal complexes and organic dyes for visible light induced transfer hydrogenation
reactions of imines to amines. We show here that the strong and much wider absorption of QDs in the
whole visible light region may enable them more efficient and practical for use in catalyzing organic
transformations than transition metal complex. Also, band structure and wavefunction engineering
may render them more versatile photocatalytic activity. The improved stability of core/shell QDs than
plain QDs also makes the former advantageous as photocatalysts for a wide range of reactions. Be-
sides illustrating the potential of core-shell QDs as photoredox catalyst for organic transformations,
practical synthetic value of this precious metal free protocol is manifested by the fact that it has a wide
imine substrate scope, including both aldimine and ketimines of diversified structures to give satisfac-
tory yield of the amines under mild reaction conditions by using visible light or sun light at room tem-
perature in neutral media.
EXPERIMENTAL SECTION
All reagents were commercially available and used without further purification. All solvents were dried according to
standard procedures, and further dried by 4 Å molecular sieves. Melting points were measured on a microscopic melt-
ing point apparatus and are uncorrected. 1H and 13C NMR spectra were recorded at 400 and 100 MHz, respectively,
using CDCl3 or DMSO-d6 as solvent. IR spectra were taken with a FT-IR spectrometer. HRMS was determined by a
AB Triple TOF 5600 plus System. The exact mass calibration was performed automatically before each analysis em-
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ploying the Automated Calibration Delivery System. UV–vis absorption spectra were measured on a UV–vis spec-
trometer. Fluorescence spectra and time-dependent single photon count spectra were measured on a FL900 Instrument.
General procedures for photoredox transfer hydrogenation
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A mixture of imine 1 (0.4 mmol, 1.0 equiv) and 4-fluorothiophenol (0.358 g, 2.8 mmol, 7.0 equiv) in toluene (8 mL)
was added QDs (200 μL) as photocatalyst. The vial was sealed and the reaction mixture sparged with argon for 10
minutes and then irradiated with 3 W green LEDs. After 8 h, the mixture was concentrated by rotary evaporation and
the crude mixture was directly charged on silica gel and purified by column chromatography with petroleum ether/ethyl
acetate as eluents (gradient elution) to afford the target product.
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General procedures for the synthesis of QDs 23a, 23b, 30, 31
Synthesis of 3.0 nm CdSe QDs (first exciton absorption peak at 550 nm) was achieved by a modified literature proce-
dure1. Cadmium acetate (0.0533 g, 0.2 mmol) and stearic acid (0.1707 g, 0.6 mmol) were loaded into a 25 mL three-
neck flask with 4 mL of ODE. After stirring and argon bubbling for 10 min, the mixture was heated to 270 °C by a
digital-controlled heating mantle to remove excess HAC and form a colorless solution. The temperature was reduced to
250 °C, and 1 mL of the Se-Sus was injected quickly into the hot solution. The reaction temperature was kept at 250 °C
for further growth of the QD. After growth for ∼7 min, 0.05 mL of Se-Sus was injected into the reaction solution. Mul-
tiple injections were repeated every 2−3 min until the size of the QDs reached 3.3 nm. Needle-tip aliquots were taken
and dissolved in toluene for UV−vis and fluorescence spectra measurements to monitor the reaction.
Synthesis of CdSe/3CdS core/shell QDs were carried out according to previously published single-precursor approach
23b, 30. Briefly, dodecane (1.5 mL), oleylamine (3.8 mL), and purified CdSe core (containing about 6 × 10−8 mol of
nanocrystals) were added to a three-neck flask under argon flow and then heated to 80 °C. Cd(DDTC)2 was used as the
single precursor for CdS shell growth. For each monolayer, addition of the precursor solutions was at 80 °C and growth
was at 160 °C for 20 min. The amount of the Cd(DDTC)2-amine solution (0.15 M) for each injection was estimated by
extinction coefficients and calibrated by the TEM measurements. For a reaction with 6 × 10−8 mol of 3.0 nm CdSe core,
the amount for three consecutive injections of the precursor solution was calibrated as 0.08, 0.12, and 0.17 mL, respec-
tively. After the targeted shell thickness was achieved, the reaction was stopped and the solution was allowed to be
cooled to room temperature.
Synthesis of 5 nm CdS QDs23e were carried out by injecting S-ODE (0.05 mmol S in 0.5 mL ODE) to the mixture con-
taining ODE (3 mL), cadmium oxide (0.2 mmol) and oleic acid (0.6 mol) at 230 oC. Reaction temperature was then set
at 250 oC and maintained for 20 min. Then S-ODE (0.005 mmol S in 0.05 mL ODE) was injected at interval of 2.5 min
until the first absorption peak reached 455 nm.
Purification of the Core/Shell QDs 23a, 31
:
In order to retain the PL properties, a recently developed purification procedure was applied n precipitation of the
core/shell QDs from the reaction solution. Briefly, the crude reaction solution was mixed with acetonitrile (1:1 volume
ratio). Chloroform was added dropwise in appropriate amount to completely precipitate the QDs. The vial was rapidly
placed in a centrifugation apparatus and centrifuged at 4000 rpm for ∼2 min.
Determination of the Concentration of QDs :
The Concentration of CdSe core QDs was calculated using the extinction coefficient reported by Peng and coworkers 32
Core/shell QDs was synthesized through Single-Precursor Approach 23b, 30, and it was assumed that the concentration of
the core/shell QDs should remain the same as the core QDs. The concentration of the raw CdSe/3CdS QDs solution is
1×10-5 M. The concentration of the purified CdSe/3CdS QDs solution is 2×10-5 M.
.
General procedures for imine synthesis
Synthesis of aldimines 33
:
To a solution of substituted benzaldehyde (5mmol) in dichloromethane (5mL) were slowly added aniline (6mmol).
After 30 min, anhydrous magnesium sulfate (0.75 g) is added in one portion. The reaction mixture is stirred at room
temperature for 2h. The resulting mixture was filtered to remove the magnesium sulfate, and the filtrate is concentrated
at reduced pressure by rotary evaporation at room temperature to afford product.
Synthesis of ketimine 34
:
Benzophenone (0.91 g, 5.0 mmol) and activated molecular sieves 4A (2.0 g) were placed in a 25 mL reaction flask. A
solution of aniline (0.56 g, 6 mmol) in toluene (10.0 mL) were added under argon atmosphere, and the mixture was
heated under reflux overnight. After being cooled, the resulting mixture was filtered to remove the molecular sieves.
The filtrate was evaporated, and the resulting pale yellow solid was recrystallized from ethanol.
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N-benzylaniline (3a). yellow liquid [colorless oil]14,35, 88% (64.5 mg). 1H NMR (400 MHz, CDCl3) δ7.37 – 7.32 (m,
4H), 7.30 – 7.27 (m, 1H), 7.20 – 7.16 (m, 2H), 6.74 (t, 1H, J = 7.2 Hz), 6.67 (d, 2H, J = 8.4 Hz), 4.34 (s, 2H). 13C{1H}
NMR (100 MHz, CDCl3) δ 148.2, 139.4, 129.3, 128.7, 127.6, 127.3, 117.6, 112.9, 48.4.
4-(benzylamino)phenol (3b). brown solid, m.p. 88-90 ℃[88-90℃]36, 83% (66.2 mg). 1H NMR (400 MHz, CDCl3) δ
7.38 – 7.32 (m, 4H), 7.28 (d, 1H, J = 6.8 Hz), 6.70 (d, 2H, J = 8.8Hz), 6.56 (d, 2H, J = 8.8 Hz), 4.28 (s, 2H). 13C{1H}
NMR (100 MHz, CDCl3) δ 147.8, 142.3, 139.5, 128.6, 127.6, 127.2, 116.2, 114.4, 49.3.
N-benzyl-4-methoxyaniline (3c). brown solid, m.p. 49-51℃[48-50℃]36, 84% (71.8 mg). 1H NMR (400 MHz, CDCl3)
δ 7.39 – 7.32 (m, 4H), 7.28 (d, 1H, J = 6.8 Hz), 6.80 – 6.76 (m, 2H), 6.64 (d, 2H, J = 8.8 Hz), 4.29 (s, 2H), 3.74 (s, 3H).
13C{1H} NMR (100 MHz, CDCl3) δ 152.5, 141.7, 139.2, 128.6, 127.7, 127.3, 114.8, 114.6, 55.8, 49.5.
N-benzyl-4-fluoroaniline (3d). brown solid, m.p. 33-34 ℃ [33-35℃]37, 82% (65.8 mg). 1H NMR (400 MHz, CDCl3)
δ 7.38 –7.29 (m, 5H), 6.92 – 6.86 (m, 2H), 6.59 – 6.56 (m, 2H), 4.30 (s, 2H), 3.90 (s, 1H). 13C{1H} NMR (100 MHz,
CDCl3) δ 155.9 (d, J = 234.0 Hz), 144.4, 139.2, 128.7, 127.5, 127.4, 115.7 (d, J = 22.0 Hz), 113.7 (d, J = 8.0 Hz), 48.9.
N-benzyl-4-chloroaniline (3e). brown solid, m.p. 45-46 ℃ [46-47℃]35, 90% (78.5 mg). 1H NMR (400 MHz, CDCl3)
δ 7.34(d, 4H, J = 4.4 Hz), 7.31 – 7.26 (m, 1H), 7.10 (dt, 2H, J = 8.8, 2.7 Hz), 6.55 (dt, 2H, J = 8.8, 2.6 Hz), 4.30 (s, 2H).
13C{1H} NMR (100 MHz, CDCl3) δ 146.5, 138.8, 129.1, 128.7, 127.5, 127.4, 122.2, 114.0, 48.4.
4-methoxy-N-(4-methylbenzyl)aniline (3f).38 brown solid, m.p. 98-99 ℃, 93% (85 mg). 1H NMR (400 MHz, CDCl3)
δ 7.26 (d, 2H, J = 8.0 Hz), 7.14 (d, 2H, J = 8.0 Hz), 6.77 (d, 2H, J = 8.8 Hz), 6.61 (dt, 2H, J = 8.8, 2.9 Hz), 4.23 (s, 2H),
3.74 (s, 3H), 2.34 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 152.2, 142.3, 136.9, 136.5, 129.3, 127.6, 116.4, 114.8,
114.2, 55.8, 49.0, 21.2.
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4-methyl-N-(4-methylbenzyl)aniline (3g). yellow solid, m.p. 55-56 ℃ [55-56℃]39, 88% (74.2 mg). 1H NMR (400
MHz, CDCl3) δ 7.26 (d, 2H, J = 7.6 Hz), 7.14 (d, 2H, J = 7.6 Hz), 6.98 (d, 2H, J = 8.0 Hz), 6.57 – 6.55 (m, 2H), 4.26 (s,
2H), 3.91 (s, 1H), 2.34 (s, 3H), 2.23 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 146.0, 136.8, 136.5, 129.8, 129.3,
127.5, 126.7, 113.0, 48.4, 21.2, 20.5.
4-fluoro-N-(4-methylbenzyl)aniline (3h). 40 yellow solid, m.p. 68-70 ℃, 82% (70.5 mg). 1H NMR (400 MHz, CDCl3)
δ 7.25 (d, 2H, J = 6.8 Hz), 7.15 (d, 2H, J = 7.6 Hz), 6.90 – 6.85 (m, 2H), 6.58 – 6.55 (m, 2H), 4.24 (s, 2H), 2.34 (s, 3H).
13C{1H} NMR (100 MHz, CDCl3) δ 155.9 (d, J = 234.0 Hz), 144.4, 137.0, 136.1, 129.4, 127.5, 115.7 (d, J = 22.0 Hz),
113.7 (d, J = 7.0 Hz), 48.7, 21.2.
4-chloro-N-(4-methylbenzyl)aniline (3i). 40 yellow solid, m.p. 65-67 ℃, 86% (79.3 mg). 1H NMR (400 MHz, CDCl3)
δ 7.23 (d, 2H, J = 8.0 Hz), 7.15 – 7.10 (m, 4H), 6.60 – 6.58 (m, 2H), 4.26 (s, 2H), 2.34 (s, 3H). 13C{1H} NMR (100
MHz, CDCl3) δ 146.7, 137.1, 135.8, 129.4, 129.1, 127.4, 122.0, 113.9, 48.1, 21.2.
N-(4-fluorobenzyl)-4-methoxyaniline (3j).41 brown liquid, 94% (86.6 mg). 1H NMR (400 MHz, CDCl3) δ 7.34 – 7.31
(m, 2H), 7.01 (t, 2H, J = 8.6 Hz), 6.79 – 6.75 (m, 2H), 6.60 – 6.56 (m, 2H), 4.24 (s, 2H), 3.73 (s, 3H). 13C{1H} NMR
(100 MHz, CDCl3) δ 162.0 (d, J = 243.0 Hz), 152.3, 142.1, 135.3, 129.1 (d, J = 8.0 Hz), 115.4 (d, J = 21.0 Hz), 114.9,
114.2, 55. 8, 48.6.
4-fluoro-N-(4-fluorobenzyl)aniline (3k).42 yellow solid, m.p. 49-50 ℃, 86% (75.4 mg). 1H NMR (400 MHz, CDCl3)
δ 7.31 (t, 2H, J = 6.8 Hz), 7.02 (t, 2H, J = 8.6 Hz), 6.90 – 6.85 (m, 2H), 6.56 – 6.52 (m, 2H), 4.24 (s, 2H), 4.01 (s, 1H).
13C{1H} NMR (100 MHz, CDCl3) δ 162.1 (d, J = 244.0 Hz), 156.0 (d, J = 234.0 Hz), 144.2, 134.8, 129.1 (d, J = 8.0
Hz), 115.8, 115.5 (d, J = 21.0 Hz), 113.8 (d, J = 8.0 Hz), 48.3.
4-chloro-N-(4-fluorobenzyl)aniline (3l).43 yellow solid, m.p. 50-52 ℃, 92% (86.7 mg). 1H NMR (400 MHz, CDCl3)
δ 7.31 – 7.29 (m, 2H),7.11 (dt, 2H,J = 8.8, 2.6 Hz), 7.05 – 7.00 (m, 2H), 6.56 – 6.53 (m, 2H), 4.27 (s, 2H). 13C{1H}
NMR (100 MHz, CDCl3) δ 162.1 (d, J = 244.0 Hz), 146.4, 134.6 (d, J = 4.0 Hz), 129.1, 129.0 (d, J = 8.0 Hz), 122.2,
115.6 (d, J = 21.0 Hz), 114.0, 47.6 .
N-(4-chlorobenzyl)-4-fluoroaniline (3m). yellow solid, m.p.123-124℃ [123.1-124.6℃]44, 81% (76.5 mg). 1H NMR
(400 MHz, CDCl3) δ 7.32 – 7.28 (m, 4H), 6.90 – 6.86 (m, 2H), 6.56 – 6.52 (m, 2H), 4.27 (s, 2H). 13C{1H} NMR (100
MHz, CDCl3) δ 156.0 (d, J = 234.0 Hz), 144.2, 137.8, 133.0, 128.8, 128.7, 115.8 (d, J = 23.0 Hz), 113.7 (d, J = 7.0 Hz),
48.2.
N-(2-chlorobenzyl)-4-fluoroaniline (3n). yellow liquid, 88% (82.8 mg). 1H NMR (400 MHz, CDCl3) δ 7.41-7.37 (m,
2H), 7.26 – 7.20 (m, 2H), 6.90 – 6.86 (m, 2H), 6.58 – 6.55 (m, 2H), 4.40 (s, 2H). 13C{1H} NMR (100 MHz, CDCl3) δ
156.0 (d, J = 234.0 Hz), 143.8, 136.2, 133.3, 129. 6, 129.1, 128.6, 127.0, 115.7 (d, J = 23.0 Hz), 114.0 (d, J = 8.0 Hz),
46.6.
4-chloro-N-(4-chlorobenzyl)aniline (3o). yellow solid, m.p.65-66 ℃ [68-70℃]39, 82% (82 mg). 1H NMR (400 MHz,
CDCl3) δ 7.32 – 7.26 (m, 4H), 7.11(dt, 2H, J = 8.8, 2.7 Hz), 6.53 – 6.51(m, 2H), 4.29 (s, 2H). 13C{1H} NMR (100 MHz,
CDCl3) δ 146.2, 137.4, 133.1, 129.1, 128.8, 128.6, 122.5, 114.0, 47.7.
N-(4-methoxybenzyl)-4-methylaniline (3p).43 yellow solid, m.p. 62-64 ℃, 86% (77.7 mg). 1H NMR (400 MHz,
CDCl3) δ 7.28 (d, 2H, J = 8.8 Hz), 6.99 (d, 2H, J = 8.0 Hz), 6.87 (d, 2H, J = 8.8 Hz), 6.59 (d, 2H, J = 8.4 Hz), 4.23 (s,
2H), 3.80 (s, 3H), 2.24 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 158.8, 146.0, 131.6, 129.8, 128.8, 126.7, 114.0,
113.0, 55.3, 48.1, 20.4.
4-fluoro-N-(4-methoxybenzyl)aniline (3q). yellow solid, m.p. 70-71 ℃[70-71℃]45, 93% (85.8 mg). 1H NMR (400
MHz, CDCl3) δ 7.28 (d, 2H, J = 8.8 Hz), 6.90 – 6.86 (m, 4H), 6.58 – 6.55 (m, 2H), 4.21 (s, 2H), 3.80 (s, 3H). 13C{1H}
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NMR (100 MHz, CDCl3) δ 158.8, 157.0, 144.4, 131.1, 128.8, 115.6 (d, J = 22.0 Hz), 114.0, 113.6 (d, J = 7.0 Hz), 55.3,
48.4.
4-chloro-N-(4-methoxybenzyl)aniline (3r). yellow solid, m.p. 72-73 ℃[78-81℃]46, 82% (81.3 mg). 1H NMR (400
MHz, CDCl3) δ 7.27(d, 2H, J = 7.2 Hz), 7.11(d, 2H, J = 8.0 Hz), 6.88(d, 2H, J = 7.6 Hz), 6.56(d, 2H, J = 8.0 Hz), 4.22
(s, 2H), 3.80 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 159.0, 146.5, 130.8, 129.0, 128.8, 122.2, 114.1, 114.0, 55.3,
47.9.
1-(4-((4-methoxybenzyl)amino)phenyl)ethan-1-one (3s). yellow solid, m.p. 124-125 ℃[116-117]47, 68% (69.4 mg).
1H NMR (400 MHz, CDCl3) δ 7.84 – 7.82 (m, 2H), 7.27 (d, 2H, J = 6.8 Hz), 6.90 – 6.88 (m, 2H), 6.64 (d, 2H, J = 8.4
Hz), 4.33 (s, 2H), 3.80 (s, 3H), 2.50 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 196.5, 159.0, 152.0, 130.8, 130.1,
128.8, 126.8, 114.2, 111.6, 55.3, 47.1, 26.1.
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4-((4-cyanobenzyl)amino)benzonitrile (3t). yellow solid, m.p. 148-150 ℃, 40% (37.4 mg). 1H NMR (400 MHz,
CDCl3) δ 7.66 – 7.64 (m, 2H), 7.45 – 7.41 (m, 4H), 6.57 – 6.55 (m, 2H), 4.49 (s, 2H). 13C{1H} NMR (100 MHz, CDCl3)
δ 150.5, 143.5, 133.9, 132.7, 127.6, 120.1, 118.6, 112.6, 111.5, 100.0, 47.0.
N-(4-(benzyloxy)benzyl)-4-fluoroaniline (3u). yellow solid, m.p. 82-83 ℃, 85% (105 mg). 1H NMR (400 MHz,
CDCl3) δ 7.44 – 7.35 (m, 4H), 7.34 – 7.31 (m, 1H), 7.28 (d, 2H, J = 8.4 Hz), 6.95 (d, 2H, J = 8.4 Hz), 6.91 – 6.87 (m,
2H), 6.60 – 6.59 (m, 2H), 5.06 (s, 2H), 4.21 (s, 2H). 13C{1H} NMR (100 MHz, CDCl3) δ 158.1, 155.9 (d, J = 234.0 Hz),
144.3, 136.9, 131.3, 128.9, 128.6, 128.0, 127.5, 115.7 (d, J = 22.0 Hz), 115.0, 113.8 (d, J = 7.0 Hz), 70.0, 48.5.
N-(4-fluorobenzyl)-3,4-dimethylaniline (3v). brown liquid, 90% (82.9 mg). 1H NMR (400 MHz, CDCl3) δ 7.34 –
7.31 (m, 2H), 7.03 – 6.99 (m, 2H), 6.93 (d, 1H, J = 8.0 Hz), 6.47 (d, 1H, J = 2.4 Hz), 6.39 (dd, 1H, J = 8.0, 2.4 Hz),
4.27 (s, 2H), 2.18 (s, 3H), 2.15 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 162.0 (d, J = 243.0 Hz), 146.1, 137.4,
135.4, 130.3, 129.0 (d, J = 8.0 Hz), 125.8, 115.4 (d, J = 22.0 Hz), 114.8, 110.3, 48.0, 20.1, 18.7.
4-((4-(hexyloxy)benzyl)amino)benzonitrile (3w). white solid, m.p. 63-65 ℃, 85% (104.7 mg). IR (KBr) ν 3354, 3039,
2213, 1888, 1761, 1603,1516,1469, 1246, 826 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.42 (d, 2H, J = 8.8 Hz), 7.23 (d,
2H, J = 8.4 Hz), 6.88 (d, 2H, J = 8.4 Hz), 6.61 (d, 2H, J = 8.0 Hz), 4.28 (s, 2H), 3.94 (t, 2H, J = 6.4 Hz), 1.81 – 1.74 (m,
2H), 1.47 – 1.43 (m, 2H), 1.35 – 1.32 (m, 4H), 0.92 – 0.89 (m, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 158.8, 133.7,
128.8, 114.8, 68.1, 31.6, 29.2, 25.7, 22.6, 14.0. HRMS (ESI-TOF)m/z: [M+H]+ Calcd for C20H24N2O 309.1967; found
309.1954.
4-fluoro-N-(4-(trifluoromethyl)benzyl)aniline (3x). yellow solid, m.p. 90-91 ℃, 82% (88.3 mg). 1H NMR (400 MHz,
CDCl3) δ 7.60 (d, 2H, J = 8.4 Hz), 7.48 (d, 2H, J = 8.0 Hz), 6.90 – 6.86 (m, 2H), 6.56 – 6.52(m, 2H), 4.38 (s, 2H).
13C{1H} NMR (100 MHz, CDCl3) δ 156.2 (d, J = 235.0 Hz), 143.6, 143.2, 129.6 (d, J = 32.0 Hz), 127.8, 127.7, 127.6,
125.6 (q, J = 3.7Hz), 115.9, 115.7, 114.1, 114.0, 48.6.
4-methoxy-N-(4-methoxybenzyl)aniline (3y). yellow solid, m.p. 94-96 ℃ [92-94℃]36, 87% (84.7 mg). 1H NMR (400
MHz, CDCl3) δ 7.29 (d, 2H, J = 8.8 Hz), 6.86 (d, 2H, J = 8.4 Hz), 6.78 (d, 2H, J = 8.8 Hz), 6.68(d, 2H, J = 8.4 Hz),
4.21 (s, 2H), 3.80 (s, 3H), 3.75 (s, 3H). 13C{1H} NMR (100MHz, CDCl3) δ 158.8, 152.2, 142.3, 131.5, 128.9, 114.9,
114.3, 114.0, 55.8, 55.3, 48.8.
N1,N4-bis(4-fluorobenzyl)benzene-1,4-diamine (4). brown black solid, m.p. 115-116 ℃ [115-116℃]48, 72% (93 mg).
1H NMR (400 MHz, CDCl3) δ 7.32 (dd, 4H, J = 8.4, 5.6 Hz), 7.00 (t, 4H, J = 8.5 Hz), 6.57 (s, 4H), 4.23 (s, 4H).
13C{1H} NMR (100 MHz, CDCl3) δ 162.0 (d, J = 243.0 Hz), 140.6, 135.6 (d, J = 3.0 Hz), 129.1 (d, J = 7.0 Hz), 115.3
(d, J = 21.0 Hz), 114.7, 48.8.
(4-Fluoro-benzyl)-octyl-amine (5). yellow liquid, 85% (80.7 mg). 1H NMR (400 MHz, CDCl3) δ 7.31 – 7.27 (m, 2H),
7.03 – 6.98 (m, 2H), 3.76 (s, 2H), 2.61 (t, 2H, J = 7.2 Hz), 1.54 – 1.47 (m, 2H), 1.27 (d, 10H, J = 4.4 Hz), 0.88 (t, 3H, J
= 7.0 Hz). 13C{1H} NMR (100 MHz, CDCl3) δ 161.9 (d, J = 243.0 Hz), 136.1 (d, J = 3.0 Hz), 129.6 (d, J = 8.0 Hz),
115.1 (d, J = 21.0 Hz), 53.3, 49.4, 31.8, 30.0, 29.5, 29.2, 27.3, 22.6, 14.1.
Benzyl-cyclohexyl-amine (6). yellow liquid[yellow oil]44, 56% (42.8 mg). 1H NMR (400 MHz, CDCl3) δ 7.30 (d, 4H,
J = 12.8 Hz), 7.25 – 7.23 (m, 1H), 3.80 (s, 2H), 2.52 – 2.45 (m, 1H), 1.92 – 1.90 (m, 2H), 1.75 – 1.72 (m, 2H), 1.62 –
1.61 (m, 1H), 1.30 – 1.26 (m, 2H), 1.23 – 1.17 (m, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 140.9, 128.4, 128.1, 126.8,
56.2, 51.0, 33.5, 26.2, 25.0.
4-fluoro-N-(1-(p-tolyl)ethyl)aniline (7a). yellow liquid, 91% (83.7 mg). 1H NMR (400 MHz, CDCl3) δ 7.22 (d, 2H, J
= 8.4 Hz), 7.12 (d, 2H, J = 8.0 Hz), 6.80 – 6.76 (m, 2H), 6.45 – 6.41(m, 2H), 4.38 (q, 1H, J = 6.8 Hz), 2.31 (s, 3H),
1.48 (d, 3H, J = 6.4 Hz). 13C{1H} NMR (100 MHz, CDCl3) δ 155.7 (d, J = 234.0 Hz), 143.5, 141.9, 136.6, 129.4, 125.8,
115.5 (d, J = 22.0 Hz), 114.2 (d, J = 7.0 Hz), 53.9, 25.1, 21.1.
4-fluoro-N-(1-(4-fluorophenyl)ethyl)aniline (7b). yellow liquid, 83% (86.8 mg). 1H NMR (400 MHz, CDCl3) δ 7.32
– 7.29 (m, 2H), 7.02 – 6.98 (m, 2H), 6.82 – 6.77 (m, 2H), 6.43 – 6.40 (m, 2H), 4.39 (q, 1H, J = 6.8 Hz), 1.49 (d, 3H, J
= 6.8 Hz). 13C{1H} NMR (100MHz, CDCl3) δ 161.8 (d, J = 243.0 Hz), 155.8 (d, J = 233.0 Hz), 143.2, 140.5, 127.4,
127.3, 115.7, 115.6, 115.4, 115.4, 114.4, 114.3, 53.7, 25.1.
N-(1-(4-chlorophenyl)ethyl)-4-fluoroaniline (7c). yellow liquid, 94% (94.3 mg). 1H NMR (400 MHz, CDCl3) δ 7.28
(s, 4H), 6.82 – 6.76 (m, 2H), 6.42 – 6.37 (m, 2H), 4.37 (q, 1H, J = 6.6 Hz), 1.47 (d, 3H, J = 6.8 Hz). 13C{1H} NMR
(100 MHz, CDCl3) δ 155.8 (d, J = 234.0 Hz), 143.6, 143.2, 132.5, 129.8, 128.8, 127.2, 115.7, 115.5, 114.2, 114.1, 53.6,
25.1.
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N-(4-fluorobenzyl)-1-phenylethan-1-amine (8).49 yellow liquid, 63% (57.8 mg). 1H NMR (400 MHz, CDCl3) δ 7.35
– 7.33 (m, 4H), 7.28 – 7.26 (m, 1H), 7.25 – 7.22 (m, 2H), 7.01 – 6.96 (m, 2H), 3.79 (q, 1H, J = 6.6 Hz), 3.59 (q, 2H, J
= 13.1 Hz), 1.37 (d, 3H, J = 6.4 Hz). 13C{1H} NMR (100 MHz, CDCl3) δ 161.9 (d, J = 243.0 Hz), 145.2, 136.0, 129.8,
129.7, 128.5, 127.1, 126.7, 115.2, 115.0, 57.5, 50.8, 24.4.
Benzhydryl-phenyl-amine (9). yellow oil [yellow oil]13, 67% (69.8 mg). 1H NMR (400 MHz, CDCl3) δ 7.34 – 7.30
(m, 8H), 7.27 – 7.24 (m, 3H), 6.84 – 6.79 (m, 2H), 6.48 – 6.46 (m, 2H), 5.42 (s, 1H). 13C{1H} NMR (100 MHz, CDCl3)
δ 142.8, 128.8, 127.4, 127.4, 115.6, 115.4, 114.3,114.3, 63.6.Butenafine (10). yellow liquid [200-202℃]50, 65%
(82.5mg). 1H NMR (400 MHz, CDCl3) δ 8.22 – 8.21 (m, 1H), 7.84 – 7.82 (m, 1H), 7.76 (d, 1H, J = 8.0 Hz), 7.50 – 7.44
(m, 3H), 7.41 – 7.38 (m, 1H), 7.35 – 7.29 (m, 2H), 7.28 (d, 2H, J = 8.4 Hz), 3.93 (s, 2H), 3.58 (s, 2H), 2.20 (s, 3H),
1.31 (s, 9H). 13C{1H} NMR (100 MHz, CDCl3) δ 149.9, 136.2, 135.0, 133.9, 132.5, 128.8, 128.4, 127.9, 127.4, 125.7,
125.6, 125.1, 124.9, 62.0, 60.4, 42.4, 34.5, 31.4.
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ASSOCIATED CONTENT
AUTHOR INFORMATION
Corresponding Author
*E-mail:shenym@zstu.edu.cn (Y.-M. Shen).
*E-mail: puchaodan@zju.edu.cn (C.-D. Pu).
ORCID
Yong-Miao Shen: 0000-0002-9382-9744
Author Contributions
†Zi-Wei Xi and Lei Yang contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of China (NSFC 21202101), Zhejiang Provincial
Natural Science Foundation of China (LY16B020006) and China Postdoctoral Science Foundation (2015M581919 and
2016M601930).
SUPPORTING INFORMATION
Additional experimental details and NMR spectra for obtained compounds (PDF)
The Supporting Information is available free of charge on the ACS Publications website.
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