Enantioselective epoxidation of olefins with hydrogen peroxide catalyzed by bioinspired aminopyridine manganese complexes derived from L-proline

Article abstract of DOI:10.1016/S1872-2067(18)63116-X

Three chiral aminopyridine ligands derived from L-proline were prepared. Careful evaluation of the corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed a broad substrate scope in the presence of 0.2 mol% manganese complex and 0.5 equiv. 2,2-dimethylbutyric acid, with aqueous hydrogen peroxide as an oxidant. A variety of olefins including styrenes, chromenes, and cinnamamides were transformed successfully into the target epoxides with moderate to excellent enantioselectivity (yield up to 95%, ee up to 99%).

Full text of DOI:10.1016/S1872-2067(18)63116-X

Chinese Journal of Catalysis 39 (2018) 1463–1469
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Enantioselective epoxidation of olefins with hydrogen peroxide
catalyzed by bioinspired aminopyridine manganese complexes
derived from L‐proline
Wenfang Wang a,b, Qiangsheng Sun a, Chungu Xia a, Wei Sun a,*
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000,
Gansu, China
b University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Three chiral aminopyridine ligands derived from L‐proline were prepared. Careful evaluation of the
corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed
a broad substrate scope in the presence of 0.2 mol% manganese complex and 0.5 equiv.
2,2‐dimethylbutyric acid, with aqueous hydrogen peroxide as an oxidant. A variety of olefins in‐
cluding styrenes, chromenes, and cinnamamides were transformed successfully into the target
epoxides with moderate to excellent enantioselectivity (yield up to 95%, ee up to 99%).
© 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 26 March 2018
Accepted 22 May 2018
Published 5 September 2018
Keywords:
Aminopyridine ligand
Manganese
Published by Elsevier B.V. All rights reserved.
Asymmetric epoxidation
Hydrogen peroxide
Olefin
1. Introduction
peroxide as the oxidant; note that acetic acid served as an im‐
portant additive in the iron catalytic system. Earlier in the same
Metalloenzymes can promote a wide range of oxidative
transformations, such as hydroxylation, epoxidation, and
cis‐dihydroxylation. Inspired by the properties of metalloen‐
zymes, researchers have established biomimetic synthetic met‐
al (e.g., Mn, Fe) complexes coordinated with tetradentate ni‐
trogen (N4) ligands as excellent catalysts in oxidation reactions
in the past decades [1–4]. The landmark investigations of
epoxidation of olefins by biomimetic N4 metal complexes were
begun in 2001 by Jacobsen and co‐workers [5]. They reported
that an Fe(II)(mep) complex (mep = N,N′‐dimethyl‐N,N′‐bis
(2‐pyridinylmethyl)ethane‐1,2‐diamine) could rapidly mediate
the epoxidation of aliphatic alkenes with aqueous hydrogen
year, Que and co‐workers [6] first demonstrated enantioselec‐
tive cis‐dihydroxylation of olefins catalyzed by the iron complex
of the aminopyridine N4 ligand. In 2003, Mn‐MCP‐(OTf)2 [MCP
= N,N‐dimethyl‐N,N‐bis(2‐pyridylmethyl) cyclohexane‐trans‐
1,2‐diamine] was used in the epoxidation of olefins with
peracetic acid as an oxidant by Stack and co‐workers; im‐
portantly, an ee of 10% was observed in the epoxidation of
vinyl cyclohexane [7]. The development of novel elegant lig‐
ands is considered the key approach to obtaining highly effi‐
cient catalysts [8,9]. In this context, Costas [10–14], Talsi and
Bryliakov [15–20], Gao [21,22], and our group [23–31] have
developed many chiral N4 ligands, and their manganese and
* Corresponding author. Tel: +86‐931‐4968278; Fax: +86‐931‐4968129; E‐mail: wsun@licp.cas.cn
This work was supported by the National Natural Science Foundation of China (21473226, 21773273), Key Research Program of Frontier Sciences,
CAS (QYZDJ‐SSW‐SLH051), and Natural Science Foundation of Jiangsu Province (BK20170420).
DOI: 10.1016/S1872‐2067(18)63116‐X | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 39, No. 9, September 2018

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Wenfang Wang et al. / Chinese Journal of Catalysis 39 (2018) 1463–1469
iron complexes exhibit good to excellent stereocontrol in the
enantioselective epoxidation of various olefins (Scheme 1).
Among them, the chiral N4 ligands derived from chiral
2,2′‐bipyrrolidine play an important role in iron‐ or manga‐
nese‐catalyzed asymmetric epoxidation of olefins (Scheme 1)
[11,12,14,16–20]. However, these chiral 2,2′‐bipyrrolidine
skeletons are not easily available and are costly. In addition, the
epoxidation catalyzed by manganese or iron complexes coor‐
dinated by these documented ligands requires a large quantity
of acids as a vital additive [16,23]. It has been proposed that
protonation of the hydroperoxide ligand by the coordinated
carboxylic acid in metal‐hydroperoxo intermediates facilitates
O–O bond cleavage, generating high‐valent metal‐oxo species
as reactive epoxidizing intermediates. Recently, Costas and
co‐workers reported that the quantity of carboxylic acid could
be dramatically decreased to catalytic loading by including
dimethylamino groups at the 4‐position of the PDP ligand
2. Experimental
2.1. General
The starting materials were purchased from commercial
suppliers and used without further purification. H NMR and
1
13C NMR spectra were recorded on a Bruker Avance III 400
MHz spectrometer using CDCl3 as the solvent with tetrame‐
thylsilane as an internal reference. Gas chromatography–mass
spectrometry (GC–MS) spectra were recorded on an Agilent
Technologies 7890A GC system with an Agilent 5975 inert
mass‐selective detector (EI) and an HP‐5MS column (0.25 mm
× 30 m, film: 0.25 μm). High‐performance liquid chromatog‐
raphy (HPLC) analysis was performed on a Waters‐Breeze in‐
strument (2487 Dual λ absorbance detector and 1525 binary
HPLC pump). Chiralpak OD‐H, AS‐H, and IC columns were pur‐
chased from Daicel Chemical Industries, Ltd. GC analysis was
[Scheme
1,
NMe2PDP,
PDP
=
2‐({2‐[1‐(pyridin‐
performed on an Agilent 6820 GC instrument with a
2‐ylmethyl)‐pyrrolidin‐2‐yl]pyrrolidin‐1‐yl}methyl) pyridine]
[12,13]. In 2012, we reported a series of facile N4 ligands
(Scheme 1, S‐PMP, S‐PEB) derived from L‐proline, which exhib‐
ited enantioselectivity comparable to those of chiral
2,2′‐bipyrrolidine skeletons [28–32]. More importantly,
L‐proline is abundant in nature and easily transformed and
diversified.
CP‐Chirasil‐Dex CB column. Column chromatography was gen‐
erally performed on silica gel (300–400 mesh), and thin‐layer
chromatography inspections were performed on silica gel GF254
plates.
L‐proline‐based diamines 1 and 2 were synthesized using a
previously reported method [28,29,33].
On the basis of our previous work, we hypothesized that
modification of the substituents on the pyridyl groups and di‐
amine backbone of the N4 ligand from L‐proline would provide
several new and practical N4 ligands. Herein, we report three
structurally new aminopyridine ligands derived from L‐proline
and the catalytic performance of the corresponding manganese
complexes in asymmetric epoxidation of a variety of olefins
using aqueous hydrogen peroxide as an oxidant.
2.2. Synthesis and characterization of ligands L1–L3
For L1, (S)‐N‐methyl‐1‐(pyrrolidin‐2‐yl)methanamine (1)
(2.1 mmol) and 30 mL of dichloromethane (DCM) were added
to a 100‐mL round‐bottom flask. Then K2CO3 (6 eq.) was added.
Next, 2‐(chloromethyl)‐N,N‐dimethylpyridin‐4‐amine (3) (5.0
mmol) was dissolved in 20 mL of DCM by addition through a
constant‐pressure dropping funnel at 0 °C. Then the mixture
Scheme 1. Tetradentate nitrogen (N4) ligands.

Wenfang Wang et al. / Chinese Journal of Catalysis 39 (2018) 1463–1469
1465
was stirred in an ice bath for 1 h and gradually warmed to
room temperature overnight. The mixture was then filtered,
and the filter was washed with DCM. The combined filtrates
were evaporated under reduced pressure. To the resulting
residue, a solution of NaOH (2 mol/L) was added to adjust the
pH to greater than 10, and the mixture was extracted with 3 ×
20 mL of DCM. The combined organic phases were washed
successively with saturated aqueous solutions of NaCl and H2O.
The organic phase was dried over anhydrous Na2SO4, and the
solvent was removed under reduced pressure. The residue was
purified by a silica column to yield the ligand L1 (330 mg,
41%). 1H NMR (400 MHz, CDCl3) δ 8.10–7.94 (m, 2H), 6.60 (d, J
= 8.0 Hz, 2H), 6.31 (dd, J = 8.0, 4.0 Hz, 2H), 4.17 (d, J = 12.0 Hz,
1H), 3.50 (dt, J = 28.0, 16.0 Hz, 3H), 2.89 (dd, J = 12.0, 4.0 Hz,
12H), 2.82 (t, J = 8.0 Hz, 2H), 2.58–2.47 (m, 1H), 2.39–2.25 (m,
2H), 2.21 (s, 3H), 2.02–1.87 (m, 1H), 1.7–1.51 (m, 3H). 13C NMR
(101 MHz, CDCl3) δ 158.2, 157.9, 155.2, 155.1, 147.6, 147.5,
105.8, 105.4, 105.3, 105.2, 64.1, 62.5, 62.2, 60.9, 54.7, 43.2, 39.2,
39.1, 29.8, 23.0. High‐resolution MS (HRMS) [electrospray ion‐
ization (ESI) MS] calcd. for C22H35N6 [M+H]+: 383.2918, found:
383.2924.
under vacuum to yield C1 (yield, >90%). HRMS (ESI‐MS) calcd.
for C23H34F3MnN6O3S [M‐OTf]+: 586.1740, found: 586.1763.
C2 was prepared using a method analogous to that used for
C1 starting with L2 and Mn(CF3SO3)2 to obtain the product as a
solid (yield, >90%). HRMS (ESI‐MS) calcd. for C29H38F3MnN6O3S
[M‐OTf]+: 662.2058, found: 662.2070.
C3 was prepared using a method analogous to that used for
C1 starting with L3 and Mn(CF3SO3)2 to obtain the product as a
solid (yield, >90%). HRMS (ESI‐MS) calcd. for C24H36MnN4O2
[M‐2OTf]2+: 233.6104, found: 233.6096.
2.4. General procedures for asymmetric epoxidation
In a typical reaction, a MeCN (0.5 mL) solution consisting of
the substrate (0.4 mmol), catalyst (0.2 mol%), and acid (0.5 eq.)
was mixed in a 10‐mL ꢀlask at −30 °C. Then a H2O2 solution (1.5
eq., diluted from a 30% aqueous solution in 0.5 mL of MeCN)
was added via a syringe pump over 30 min with stirring at −30
°C. The solution was further stirred at –30 °C for 30 min. At this
point, decane was added to the mixture as an internal refer‐
ence. The reaction was quenched with saturated NaHCO3
aqueous solution and saturated Na2S2O3 aqueous solution and
extracted with DCM; the sample was then investigated using GC
and GC–MS analysis or purified by chromatography on silica gel
to afford the epoxide product.
L2 was prepared using a method analogous to that used for
L1 starting with (S)‐N‐benzyl‐1‐(pyrrolidin‐2‐yl) methanamine
(2)
(2.1
mmol)
and
2‐(chloromethyl)‐N,
N‐dimethylpyridin‐4‐amine (6) (5.0 mmol) to provide a yellow
oil (356 mg, 37%). 1H NMR (400 MHz, CDCl3) δ 7.62 (t, J = 4.0
Hz, 4H), 7.43–7.12 (m, 5H), 6.41 (d, J = 2.0 Hz, 1H), 6.34 (dd, J =
8.0, 4.0 Hz, 1H), 4.33 (d, J = 8.0 Hz, 1H), 4.24–4.01 (m, 2H),
3.66–3.50 (m, 3H), 2.99 (s, 12H), 2.81 (dd, J = 12.0, 4.0 Hz, 2H),
2.67 (dd, J = 12.0, 8.0 Hz, 1H), 2.37 (dd, J = 12.0, 8.0 Hz, 1H),
3. Results and discussion
The structure of a ligand is known to have an important ef‐
fect on the activity of metal complex catalysts. In 2013, Costas
and coworkers [12,34] reported that the electronic properties
of a metal center could be tuned by introducing different sub‐
stituents on the pyridine ring at the 4‐position. In particular, a
metal complex bearing dimethylamino groups on the ligand
framework exhibited excellent activity (Scheme 1, Me2NPDP
ligand). Further, Que and coworkers [35] captured a key ox‐
oiron(V) intermediate with a 50% yield, which was considered
to be the active species in the oxidation reaction and was hard
2.05–1.80 (m, 2H), 1.76–1.60 (m, 3H), 1.61–1.42 (m, 1H). 13
C
NMR (101 MHz, CDCl3) δ 156.1, 155.3, 143.2, 132.1, 130.2,
128.8, 105.2, 104.7, 61.4, 59.1, 54.4, 53.5, 51.7, 51.3, 39.7, 29.1,
23.9. HRMS (ESI‐MS) calcd. for C28H39N6 [M+H]+: 459.3231,
found: 459.3218.
L3 was prepared using a method analogous to that used for
L1 starting with (S)‐N‐methyl‐1‐(pyrrolidin‐2‐yl) methanamine
(1)
(2.1
mmol)
and
2‐(chloromethyl)‐
4‐methoxy‐3,5‐dimethylpyridine (4) (5.0 mmol) to yield the
ligand L3 (398 mg, 46%). 1H NMR (400 MHz, CDCl3) δ 8.07 (s,
2H), 4.04 (d, J = 12.0 Hz, 1H), 3.65 (d, J = 8.0 Hz, 6H), 3.46 (dd, J
= 44.0, 12.0 Hz, 3H), 2.76 (s, 1H), 2.59 (s, 1H), 2.36 (dd, J = 12.0,
4.0 Hz, 2H), 2.23 (s, 3H), 2.19 (s, 4H), 2.14 (s, 5H), 2.11 (s, 3H),
2.03–1.78 (m, 2H), 1.63–1.49 (m, 2H), 1.48–1.37 (m, 1H). 13C
NMR (101 MHz, CDCl3) δ 164.0, 163.8, 157.0, 148.3, 148.2,
126.1, 125.5, 125.0, 124.8, 63.6, 62.6, 59.9, 59.8, 59.7, 54.9, 43.1,
30.2, 22.6, 13.2, 10.9. HRMS (ESI‐MS) calcd. for C24H37N4O2
[M+H]+: 413.2911, found: 413.2905.
to
synthesize
and
characterize,
by
introducing
4‐methoxy‐3,5‐dimethylpyridine
(
dMM‐pyridine) instead of
pyridine donors into the tris(pyridine‐2‐ylmethyl)amine ligand.
Recently, Wang and coworkers [36] also demonstrated, using
density functional theory calculations, that an Fe(IV)‐oxo cation
radical species was generated when dimethylamino groups
were introduced into PDP‐Fe complex catalysts. These results
indicated that using different substituents on ligands did
change the spin state of the metal center and the activity of
these metal complexes. Thus, we tried to synthesize three dif‐
ferent tetradentate nitrogen ligands bearing strong elec‐
tron‐donating substituents (the Me2N or dMM group) and the
corresponding manganese complexes.
2.3. Synthesis and characterization of the manganese
complexes C1–C3
The aminopyridine ligands L1–L3 derived from L‐proline
were readily prepared, as shown in Scheme 2, and the manga‐
nese complexes were synthesized using the modified N4 lig‐
ands L1–L3 with Mn(OTf)2 and stirring in CH3CN at room tem‐
perature for 24 h.
C1: Mn(CF3SO3)2 (0.25 mmol, 1 eq.) was added to a stirred
solution of chiral ligand L1 (0.25 mmol, 1 eq.) in acetonitrile (3
mL) at room temperature. The reaction mixture was stirred for
24 h. After drying under vacuum, the resulting solid was
washed thoroughly with ether three times. It was then dried
The activities of three structurally new catalysts were then

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Wenfang Wang et al. / Chinese Journal of Catalysis 39 (2018) 1463–1469
Scheme 2. Preparation of tetradentate nitrogen ligands derived from L‐proline.
examined in asymmetric epoxidation. We selected
cis‐β‐methylstyrene as model substrate and used
(Table 1, entry 2). In addition, the manganese complex C3, with
fewer electron‐donating dMM groups, exhibited lower yield
and enantioselectivity under the same conditions (Table 1,
entry 3). To improve the conversion in epoxidation, a larger
catalyst loading (0.2 mol%) was tested, and it was found that
the substrate converted completely, and a 92% yield and 88%
ee were obtained (Table 1, entry 4). The reaction proceeded
well even in the presence of 50 mol% DMBA when 0.2 mol%
manganese complex C1 was used (Table 1, entry 5).
a
2,2‐dimethylbutanoic acid (DMBA) as the additive [26]. Epoxi‐
dation was performed in CH3CN at –30 °C using 30% aqueous
H2O2 (1.5 eq.) as the oxidant. It was shown that the catalyst C1
(0.1 mol%) was the most effective, furnishing epoxide in 84%
yield and 82% ee (Table 1, entry 1). Surprisingly, the manga‐
nese catalyst C2, with a larger steric hindrance, exhibited de‐
creased performance despite its richer electronic properties
In addition, the carboxylic acids also played an important
role in the non‐heme‐metal‐complex‐promoted epoxidation by
H2O2 because these reactions were achieved by the proposed
“carboxylic‐acid‐assisted” O–O bond cleavage mechanism
(Scheme 3) [16]. In 2016, Talsi and coworkers [20] studied the
effect of carboxylic acids on the electronic structure of the in‐
termediates in asymmetric epoxidation. They found that these
acids with tertiary α‐carbon atoms displayed a smaller g‐factor
anisotropy, which resulted in higher enantioselectivities [20].
Very recently, we demonstrated that only the carboxylic acid
binding on the manganese center can activate H2O2 to produce
a presumed carboxylic MnV=O (II) as the oxidizing reagent
(Scheme 3). Thus, the carboxylic ligand coordinated on the
manganese center could affect the stereocontrol of the asym‐
metric epoxidation [37]. In this context, we then evaluated the
contribution of different carboxylic acids to this process. The
results showed that DMBA was the best additive, giving a 90%
Table 1
Reaction condition screening.
Entry
Cat.
(x mol%)
Acid
(x eq.)
Conv.
(%)
Yield a
(%)
ee b
(%)
1
2
3
4
1(0.1)
2(0.1)
3(0.1)
1(0.2)
1(0.2)
1(0.2)
1(0.2)
1(0.2)
1(0.2)
1(0.2)
1(0.2)
1(0.2)
DMBA(1.0)
DMBA(1.0)
DMBA(1.0)
DMBA(1.0)
DMBA(0.5)
D‐CPA(0.5)
HOAc(0.5)
4‐MHA(0.5)
PVA(0.5)
92
66
46
100
100
89
88
82
92
93
84
41
27
92
90
85
86
78
93
85
90
34
82
82
71
88
89
80
65
68
80
84
86
80
5
6
7
8
9
10
11
12
EHA(0.5)
DMBA(0.25)
DMBA(0.05)
100
57
Reaction conditions: cis‐β‐methylstyrene (0.4 mmol), manganese com‐
plex (0.1–0.2 mol%), CH3CN as a solvent (0.5 mL), DMBA (1.0 eq.), and
30% H2O2 (1.5 eq.) in 0.5 mL MeCN was added dropwise via a syringe
pump over 30 min with stirring at –30 °C and then further stirring for
30 min.
a The yield was determined by GC with decane as an internal standard.
b Determined by chiral GC.
Scheme 3. Proposed mechanism of catalysis by tetradentate manga‐
nese complexes assisted by carboxylic acid.

Wenfang Wang et al. / Chinese Journal of Catalysis 39 (2018) 1463–1469
1467
yield and 89% ee (Table 1, entry 5). Other acids, such as
D‐camphoric acid (D‐CPA), acetic acid, 4‐methylhexanoic acid
(4‐MHA), pivalic acid (PVA), and 2‐ethylhexanoic acid (EHA),
resulted in lower ee values (Table 1, entries 6–10). Further
lowering the acid loading degraded the performance (Table 1,
entries 11 and 12).
Table 2
Substrate scope of olefins.
After establishing the optimized conditions using the man‐
ganese complex C1, we investigated the generality of the reac‐
tion of different olefins. First, various styrenes were examined
under the optimal conditions. Gratifyingly, styrenes bearing
different substituents were transformed to epoxides success‐
fully, albeit with moderate enantioselectivities (Table 2, entries
1–7). In addition, the epoxidation of stilbene compounds pro‐
vided epoxides in low yield, but the enantioselectivity was
quite good (Table 2, entries 6 and 7). To our delight, chromenes
(Table 2, entries 8 and 9) and cinnamamides (Table 2, entries
10–15) were well‐tolerated, and the target products were as‐
sembled with excellent enantioselectivities (up to 99% ee).
Entry
1
Substrate
Yield a (%) ee b (%)
90
66
89
62
2
3
90
64
4
5
67
66
61
61
4. Conclusions
In conclusion, we developed a series of novel tetradentate
nitrogen ligands derived from L‐proline. The corresponding
manganese complexes were then prepared, and their catalytic
activities and selectivities were evaluated in asymmetric epox‐
idation of olefins. Various olefins were transformed into epox‐
ides successfully with low loading of the manganese catalyst
together with aqueous H2O2 as the oxidant in the presence of a
small amount of carboxylic acid as an additive. Notably, the
enantioselective epoxidation of chromenes and cinnamamides
provided the target products with excellent enantioselectivities
(up to 99% ee). Unlike the substituted PDP ligands, these N4
ligands were prepared from readily available and inexpensive
amino acids, thus making the manganese catalysts more prac‐
tical. Further utilization of these biomimetic manganese com‐
plexes in oxidation reactions is ongoing in our laboratory.
6
7
21
33
86
81
F
8
9
93
95
98
99
O
Bn
10
11
12
13
81
40
91
84
98
98
98
97
N
Bn
Acknowledgments
Technical assistance, material support, and other help or
advice may be acknowledged briefly in this section (excluding
financial support, which should appear in the footnote on the
title page).
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Wenfang Wang et al. / Chinese Journal of Catalysis 39 (2018) 1463–1469
Graphical Abstract
Chin. J. Catal., 2018, 39: 1463–1469 doi: 10.1016/S1872‐2067(18)63116‐X
Enantioselective epoxidation of olefins with hydrogen peroxide
catalyzed by bioinspired aminopyridine manganese complexes
derived from L‐proline
Wenfang Wang, Qiangsheng Sun, Chungu Xia, Wei Sun *
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences
Three tetradentate nitrogen ligands derived from L‐proline were
developed, and the catalytic activities and selectivities of the corre‐
sponding manganese complexes were carefully evaluated in asym‐
metric epoxidation of olefins.
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脯氨酸衍生的胺基吡啶四氮锰配合物催化双氧水参与的烯烃不对称环氧化反应
王文芳a,b, 孙强盛a, 夏春谷a, 孙 伟a,*
a中国科学院兰州化学物理研究所羰基合成与选择氧化国家重点实验室, 甘肃兰州730000
b中国科学院大学, 北京100049
摘要: 自然界中存在许多的金属酶, 它们参与促进各种各样的氧化反应, 例如羟化反应, 环氧化反应等. 金属酶催化的反应
具有催化效率高、反应条件温和、选择性高等优点. 受大自然中的金属酶结构及其性质的启发, 人们提出了仿生催化氧化
的理念, 并开始对金属酶进行模拟, 致力于发展清洁氧化的反应方式. 在过去的几十年中, 科学家们设计合成了一系列仿
生 金 属 配 合 物 催 化 剂 . 例 如 , 利 用 非 手 性 的 乙 二 胺 骨 架 设 计 合 成 出 四 齿 氮 配 体 MEP (N,N'-dimethyl-
N,N'-bis(2-pyridinylmethyl)ethane-1,2-diamine), 将其制备成相应的铁配合物催化剂, 该铁催化剂可以很好的实现脂肪族烯
烃的环氧化, 产率高达90%. 2003年, Stack小组首次报道了利用手性N,N-二甲基环己二胺骨架衍生的四齿氮配体金属配合

Wenfang Wang et al. / Chinese Journal of Catalysis 39 (2018) 1463–1469
1469
物Mn-MCP-(OTf)2 (MCP = N,N-dimethyl-N,N-bis(2-pyridylmethyl)cyclohexane-trans-1,2-diamine)催化的不对称环氧化反应.
该反应的对映选择性仅仅为10%. 因此, 发展新型手性四氮配体金属配合物, 用于高产率、高对映选择性的不对称环氧化反
应, 值得进行深入研究.
近 年 来 发 展 的 一 些 含 手 性 二 胺 骨 架 的 四 齿 氮 配 体 , 例 如 PDP (2-[[2-(1-(pyridin-2-ylmethyl)-pyrrolidin-
2-yl)pyrrolidin-1-yl]methyl]pyridine), 被应用到不对称环氧化反应中, 但是其手性二胺骨架为联吡咯, 价格昂贵, 难以制备.
这在很大程度上限制了其在不对称合成中的实际应用. 因此, 利用一些易于合成的手性二胺骨架, 发展结构新颖、催化性
能优良的四氮金属配合物, 成为实现高效、高选择性不对称环氧化反应的关键.
在之前的工作基础上, 本文以简单易得、价格低廉的天然氨基酸——L-脯氨酸为起始原料, 选取吡啶环和含取代基的
吡啶环作为侧基氮供体, 制备了三种手性四齿氮配体. 随后, 我们利用新发展的手性四齿氮配体, 合成了相应的锰配合物,
并且分别将其运用于烯烃不对称环氧化反应中, 仔细评估了这些锰金属配合物的催化性能. 建立了以0.2 mol%的锰配合物
为催化剂, 0.5当量的2,2-二甲基丁酸为添加剂, 30%双氧水为氧化剂, 反应温度为–30 oC, 乙腈为溶剂的催化不对称环氧化
反应体系. 反应结果显示: 该催化剂催化的不对称环氧化反应底物适用性广泛, 其中苯乙烯、苯并吡喃、烯酰胺等化合物
均可以被成功地转化为相应的环氧化物, 得到中等至优异的对映选择性(产率最高可达95%, 对映选择性最高可达99%).
关键词: 胺基吡啶配体; 锰; 不对称环氧化; 双氧水; 烯烃
收稿日期: 2018-03-26. 接受日期: 2018-05-22. 出版日期: 2018-09-05.
*通讯联系人. 电话: (0931)4968278; 传真: (0931)4968129; 电子信箱: wsun@licp.cas.cn
基金来源: 国家自然科学基金(21473226, 21773273); 中国科学院前沿科学重点研究项目(QYZDJ-SSW-SLH051); 江苏省自然科
学青年基金项目(BK20170420).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).