Asymmetric epoxidation of unfunctionalized alkenes catalyzed by sugar moiety-modified chiral salen-Mn(III) complexes

Article abstract of DOI:10.1016/j.carres.2008.10.005

Several chiral Schiff-base ligands with sugar moieties at C-3 (3′) or C-5 (5′) of salicylaldehyde were synthesized from reaction of salicylaldehyde derivatives with diamine. These ligands coordinated with Mn(III) to afford the corresponding chiral salen-M

Full text of DOI:10.1016/j.carres.2008.10.005

Carbohydrate Research 344 (2009) 61–66
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Asymmetric epoxidation of unfunctionalized alkenes catalyzed
by sugar moiety-modified chiral salen–Mn(III) complexes
*
Jiquan Zhao , Yuecheng Zhang, Furong Han, Shanshan Zhao
School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, PR China
a r t i c l e i n f o
a b s t r a c t
0
0
Article history:
Received 24 July 2008
Received in revised form 5 September 2008
Accepted 7 October 2008
Available online 14 October 2008
Several chiral Schiff-base ligands with sugar moieties at C-3 (3 ) or C-5 (5 ) of salicylaldehyde were syn-
thesized from reaction of salicylaldehyde derivatives with diamine. These ligands coordinated with
Mn(III) to afford the corresponding chiral salen–Mn(III) complexes characterized by FT-IR, MS, and ele-
mentary analysis. These complexes were used as catalysts for the asymmetric epoxidation of unfunction-
0
0
alized alkenes. Only weak enantioselectivity is induced by the chiral sugar moieties at C-3 (3 ) or C-5 (5 )
in the case of absence of chirality in the diimine bridge moiety. It was also shown that the sugars at C-5
Keywords:
Salen–Mn(III) complex
0
(5 ) having the same rotation direction of polarized light as the diimine bridge in the catalyst could
enhance the chiral induction in the asymmetric epoxidation, but the sugars with the opposite rotation
direction would reduce the chiral induction.
1
,2:5,6-Di-O-isopropylidene-
glucofuranose
,2:3,4-Di-O-isopropylidene-
galactopyranose
:5,6-Di-O-isopropylidede-
a
a
-
D
D
-
-
Ó 2008 Elsevier Ltd. All rights reserved.
1
-
3
a
-D
-
mannofuranose
Asymmetric epoxidation
1
. Introduction
catalysts for the enantioselective epoxidation of conjugated
5
olefins. All these results show that the chiral centers of the C-3
0
Salen–Mn(III) catalyzed asymmetric epoxidation, known as the
Jacobsen–Katsuki epoxidation, has been extensively investigated
(3 ) groups on the salen structure play an very important role
on chiral induction. The presence and properties of substituents
1
,2
0
since 1990. Much attention has been focused on the design of
the salen ligand and steric and electronic effects of the catalyst
structure on stereoselectivity. The pathway and orientation of
the approaching alkene to the active oxidant (the coordination
atmosphere around the metal center of the catalyst) are crucial
factors in asymmetric epoxidation of unfunctionalized alkenes.
As is known, the attainment of high enantioselectivity relies on
the steric and electronic properties of the substituent in the salen
on the C-5 (5 ) positions of the ligand also have a significant,
although generally less important, influence on epoxidation
9
enantioselectivity.
Carbohydrates are natural products with chiral centers making
them ideal precursors for the introduction of chiral building blocks
into catalysts. Recently, Yan and Klemm reported the first carbo-
hydrated-derived chiral salen–Mn(III) complex by incorporating a
3
,4
1
0
chiral carbohydrate into the diamine moiety. Ruffo and co-work-
ers also reported new chiral salen ligands derived from -glucose
and -mannose by introducing appropriate functional groups at
5
complex, in addition to the presence of chiral diimine moiety.
a-D
The first generation Jacobsen catalysts had the chiral centers lo-
cated at the diimine bridge. Later, Katsuki et al. developed a series
of salen–Mn(III) complexes with four stereogenic centers, two at
a-D
1
1
the C-2 and C-3 of the sugar ring. High enantiomeric excesses for
epoxidation reactions were received with the ligands-based com-
plexes as catalysts. In another work, Ruffo and co-workers pre-
0
the diimne bridge and two at C-8 (8 ). The epoxidation enantio-
selectivity was improved, and the conformation of the chiral sub-
pared a supported salen–Mn(III) catalyst derived from D-glucose,
0
stituents attached to C-8 (8 ) had considerable influence on
and the catalytic results showed that the complex had good reac-
asymmetric induction.6 Tang synthesized two Mn(III)–Schiff-
–8
tivity and enantioselectivity. These efforts have strengthened
12
base complexes assembled with
C-3 (3 ) positions. The catalysts were found to be highly effective
L
-amino acid ethyl esters at the
the prospects of utilizing natural products as templates for asym-
metric epoxidative catalysts. We also reported sugar-based ligands
by incorporating a glucofuranose moiety into the C-5 (5 ) position
0
0
of the salen structure and found that the carbohydrate moiety has
an asymmetric inducing effect in the epoxidation reaction.13 The
interesting results encourage us to synthesize more sugar-based
*
Corresponding author. Tel.: +86 22 60204279; fax: +86 22 26564733.
E-mail address: zhaojq@hebut.edu.cn (J. Zhao).
0
008-6215/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2008.10.005

6
2
J. Zhao et al. / Carbohydrate Research 344 (2009) 61–66
O
O
O
i
ii
OH
ClH C
OH
HO
2
R 0
t
-Bu
t
-Bu
t-Bu
1
2
3
iii
R1
N
R2
R 1
R1
R2
R 1
R2
R2
N
N
N
Mn
Cl
iv
O
O
OH
-Bu
HO
R 0
R 0
R 0
R0
t
-Bu
t
-Bu
t
t
-Bu
5
a - c
4a-c
3'
O
O
O
i
ii
t
-Bu
OH
t
-Bu
OH
t
-Bu
OH
CH Cl
R 0
2
iii
1
'
2'
R1
R2
R 1
N
R1
R2
R2
R2
R 1
N
N
N
Mn
Cl
iv
t
-Bu
O
O
t
-Bu
t
-Bu
OH
R 0
HO
t-Bu
R 0
R 0
R 0
4'a- c
5
' a- c
O
O
O
O
a: (R,R) R =H, R -R = -(CH2)4 -
3G, 4Ga, 4Gb, 5Ga, 5Gb R0=
1
2
2
O
b: (S ,S) R =Ph, R =H
1
2
O
c:
R =R =H
1
2
O
3
M, 4Mc, 5Mc, 3'M, 4'Mc, 5'Mc R0=
O
O
O
O
O
O
O
O
O
3
g, 4ga, 4gc, 5ga, 5gc, 3'g, 4'gc, 5'gc R0=
O
O
Scheme 1. Preparation of salen–Mn(III) complexes with carbohydrate moiety.
salen–Mn(III) complexes to elucidate the asymmetric induction
effects (Scheme 1).
2.2. Synthesis of the chiral Schiff bases and salen–Mn(III)
complexes
2
.2.1. Synthesis of 3-tert-butyl-5-(chloro-methyl)-2-hydroxy
2
2
. Experimental
benzaldehyde (2)
Compound 2 was prepared by the procedure reported in the lit-
.1. Materials and methods
1
4
erature. Light yellow crystalline solid. Yield 87%, mp 61–63 °C.
1
4
1
1H NMR and 13C NMR spectra were recorded with an AC 400
(
7
(
Lit. mp 63–65 °C ). H NMR (DMSO): d 1.39 (s, 9H), 4.81 (s, 2H),
.63 (d, J = 2.2 Hz, 1H), 7.75 (d, J = 2.2 Hz, 1H), 9.98 (s, 1H), 11.91
s, 1H).
1
Bruker spectrometer operating at 400 MHz for H and 100 MHz
1
3
for C measurements. IR spectra were obtained on a Bruker Vec-
tor-22 FT-IR spectrometer. Melting points were determined on a
Perkin XT-4 microscopic analyzer. Electrospray ionization mass
spectra were performed on a Finnigan LCQ Advanced instrument.
Elemental analyses were performed on an Elementar Vario EL
instrument. Optical rotations were measured on a Shanghai
WZZ-2S/2SS digital rotation analyzer, at 20 °C at 589 nm (Na) using
a 10 cm sample tube. The asymmetric epoxidation products were
analyzed on a Shandong Lunan Ruihong Gas Chromatograph,
2
.2.2. Synthesis of 5-tert-butyl-3-(chloro-methyl)-2-hydroxy
0
benzaldehyde (2 )
0
Compound 2 was prepared by the procedure reported in the lit-
1
4
1
erature. Light yellow liquid. Yield 90%. H NMR (CDCl
3
): d 1.34 (s,
9
9
1
H), 4.70 (s, 2H), 7.53 (d, J = 2.7 Hz, 1H), 7.67 (d, J = 2.4 Hz, 1H),
.91 (s, 1H), 11.29 (s, 1H). IR (film)
370, 910, 830, 700.
m: 2986, 2730, 1656, 1460,
SP-6800A, equipped with
30 m ꢀ 250 m i.d.) using an FID detector. 1,2-Dihydronaptha-
lene, -methylstyrene, cis-b-methylstyrene, N-methylmorpholine
N-oxide (NMO), 1,2:5,6-di-O-isopropylidene- -glucofuranose,
,2:3,4-di-O-isopropylidene- -galactopyranose, and 2,3:5,6-di-
O-isopropylidene- -mannofuranose were purchased from Acros.
Other chemicals were obtained from local suppliers or prepared in
our laboratory. All solvents used were purified by standard
procedures.
a
Cyclodex-b capillary column
2
.2.3. Synthesis of 1,2:3,4-di-O-isopropylidene-3-O-methylene-
(
l
[5-(3-tert-butyl-2-hydroxy benzaldehyde)]-a-D-
a
galactopyranose (3G)
a
-D
Compound 3G was prepared by the procedure reported in the
1
a-D
1
5
20
D
literature. Light yellow solid. Yield 60%, mp 31–32 °C. ½ ꢁ
a
a
-D
1
ꢂ32.1 (c 0.80, EtOH). H NMR(CDCl
3
): d 1.39 (s, 9H), 1.42 (s,
2H), 3.62–3.72 (d, J = 46 Hz, 2H), 4.00–4.62 (m, 4H), 4.63 (s, 2H),
.56 (d, J = 4.8 Hz, 1H), 7.41 (s, 1H), 7.49 (s, 1H), 9.86 (s, 1H)
1
5

J. Zhao et al. / Carbohydrate Research 344 (2009) 61–66
63
1
1
7
1.80 (s, 1H). IR (KBr)
m
: 2982, 2959, 2925, 2870, 1653, 1620, 1458,
by chromatography (EtOAc–petroleum ether 1:2) to afford, after
440, 1383, 1374, 1325, 1259, 1212, 1168, 1151, 1071, 1006, 865
removal of the solvent, the Schiff-base 4Ga as yellow foam solid
ꢂ1
20
D
1
73, 757 cm . Anal. Calcd for C24
H
34
O
8
: C, 63.98; H, 7.61. Found:
(1.02 g, yield 86.4%), mp 83–84 °C, ½
NMR (CDCl
.94 (m, 8H), 3.31 (m, 2H), 3.54–3.65 (m, 4H), 4.23–4.47 (m, 8H),
4.56 (d, J = 2.4 Hz 4H), 5.51 (d, J = 3.6 Hz 2H), 6.98 (s, 2H), 7.22 (s,
2H), 8.27 (s, 2H), 13.82 (s, 2H). IR (KBr) : 3444, 2989, 2934,
a
ꢁ
ꢂ443.7 (c 0.20, EtOH).
H
C, 63.71; H, 7.83.
3
): d 1.25 (s, 12H), 1.31 (s, 18H), 1.42 (s, 12H), 1.56–
1
2
[
(
.2.4. Synthesis of 1,2:5,6-di-O-isopropylidene-3-O-methylene-
5-(3-tert-butyl-2-hydroxy benzaldehyde)]- -glucofuranose
3g)
a-
D
m
1630, 1443, 1381, 1373, 1340, 1257, 1212, 1167, 1071, 1005,
ꢂ1
Compound 3g was prepared by the procedure reported in the
865, 802, 775 cm . Anal. Calcd for C54
H
78
O
14
N
2
: C, 66.26; H,
1
5
20
D
literature.
Light yellow solid. Yield 67%, mp 96–98°C. ½
aꢁ
7.98; N, 2.86. Found: C, 66.54; H, 8.00; N, 2.61.
1
ꢂ34.1 (c 0.80, EtOH). H NMR (CDCl
2H), 4.01–4.68 (m, 8H), 5.90 (d, J = 3.9 Hz, 1H), 7.41 (d,
J = 2.4 Hz, 1H), 7.48 (d, J = 1.8 Hz, 1H), 9.87 (s, 1H), 11.80 (s, 1H).
3
): d 1.38 (s, 9H), 1.42 (s,
Compound 4Gb: Ligand 4Gb was synthesized from compound
3G and (1S,2S)-1,2-diphenylethylenediamine as yellow foam solid.
1
2
D
0
1
Yield 97%, mp 86–88 °C, ½
a
ꢁ
ꢂ122 (c 0.1, EtOH). H NMR (CDCl
3
): d
1
3
C NMR (CDCl
20.3, 111.9, 109.1, 105.3, 82.6, 81.6, 81.3, 77.7, 76.7, 72.4, 71.8,
7.5, 34.9, 29.1, 26.9, 26.8, 26.7, 26.2. IR (KBr) : 3423, 2992,
3
): d 197.0, 161.0, 138.6, 133.9, 131.0, 128.3,
1.25 (s, 12H), 1.34 (s, 18H) 1.41 (s, 12H), 3.56–3.58 (m, 4H), 4.22–
4.56 (m, 8H), 4.58 (d, J = 2.4 Hz 4H), 4.72 (s, 2H), 5.51 (d, J = 4.2 Hz,
2H), 7.17 (s, 2H), 7.18–7.22 (m, 10H), 7.24 (s, 2H), 8.32 (s, 2H),
1
6
2
1
m
969, 2936, 2862, 1655, 1617, 1456, 1440, 1384, 1374, 1321,
265, 1226, 1212, 1167, 1152, 1081, 1024, 847, 771, 759 cm
13.77 (s, 2H). IR (KBr)
1263, 1214, 1163, 1076, 1027, 848, 800, 776 cm . Anal. Calcd for
m
: 3443, 2957, 2871, 1628, 1464, 1373,
ꢂ1
ꢂ1
.
Anal. Calcd for C24
H
34
O
8
: C, 63.98; H, 7.61. Found: C, 63.71; H, 7.83.
62 80 14 2
C H O N : C, 69.12; H, 7.48; N, 2.60. Found: C, 69.42; H, 7.67;
N, 2.53.
2
.2.5. Synthesis of 1,2:5,6-di-O-isopropylidene-3-O-methylene-
Compound 4Mc: Ligand 4Mc was synthesized from compound
3M and ethylenediamine as yellow foam solid. Yield 73%, mp
[
(
3-(5-tert-butyl-2-hydroxy benzaldehyde)]-
3 g)
a-
D
-glucofuranose
0
20
D
1
81–83 °C, ½
a
ꢁ
2 2 3
+69 (c 0.32, CH Cl ). H NMR (CDCl ): d 1.35 (s,
0
Compound 3 g was prepared by the procedure reported in the
18H), 1.41 (s, 24H), 4.10 (s, 4H), 4.12–4.86 (m, 18H), 7.11 (d,
1
6
20
D
literature. Light yellow liquid. Yield 45%. ½
aꢁ
ꢂ95.8 (c 1.30,
J = 1.8 Hz, 2H), 7.32 (d, J = 1.8 Hz, 2H), 8.39 (s, 2H), 13.89 (s, 2H).
1
EtOH). H NMR (CDCl
3
): d 1.34 (s, 9H), 1.44 (s, 12H), 3.71 (s, 1H),
.04–4.85 (m, 7H), 5.91 (d, J = 6.0 Hz, 1H), 7.47 (d, J = 2.7 Hz, 1H),
.69 (s, J = 2.4 Hz, 1H), 9.90 (s, 1H), 11.13 (s, 1H). 13C NMR (CDCl
):
IR (KBr)
m
: 3447, 2958, 2871, 1633, 1464, 1372, 1257, 1217,
ꢂ1
4
7
1165, 1076, 1022, 848, 826, 750 cm
.
Anal. Calcd for
3
50 72 14 2
C H O N : C, 64.92; H, 7.84; N, 3.03. Found: C, 64.91; H, 7.88;
d 192.5, 156.5, 134.0, 130.0, 127.0, 123.4, 115.7, 109.3, 104.8, 97.1,
N, 3.12.
0
0
7
2
1
C
5.2, 74.6, 72.1, 68.8, 66.6, 62.3, 30.4, 24.7, 22.5, 21.2, 20.7, 20.6,
Compound 4 Mc: Ligand 4 Mc was synthesized from compound
3M and ethylenediamine as yellow foam solid. Yield 90%, mp 109–
0.0. IR (film)
m
: 2960, 2872, 1655, 1619, 1459, 1381, 1321, 1268,
ꢂ1
20
D
1
216, 1165, 1076, 1022, 847, 746, 729 cm . Anal. Calcd for
110 °C, ½
aꢁ
2 2 3
+178 (c 0.40, CH Cl ). H NMR (CDCl ): d 1.32 (s, 18H),
24
H
34
O
8
: C, 63.98; H, 7.61. Found: C, 63.95; H, 7.82.
1.44 (s, 24H), 3.92 (s, 4H), 4.44–4.90 (m, 18H), 7.15 (s, 2H), 7.46 (d,
J = 2.4 Hz, 2H), 8.37 (s, 2H), 13.33 (s, 2H). IR (KBr) : 3423, 2959,
m
2
.2.6. Synthesis of 2,3:5,6-di-O-isopropylidene-1-O-methylene-
-mannofuranose
2869, 1635, 1466, 1371, 1341, 1271, 1217, 1157, 1070, 1046,
ꢂ1
[
5-(3-tert-butyl-2-hydroxy benzaldehyde)]-
a-
D
859, 846, 750 cm . Anal. Calcd for C50
H
72
O
14
N
2
: C, 64.92; H,
(
3M)
7.84; N, 3.03. Found: C, 64.99; H, 8.06; N, 3.13.
Compound 4ga: Ligand 4ga was synthesized as described in the
literature.
Compound 3M was prepared by the procedure reported in the
1
5
20
D
13
literature. Light yellow liquid. Yield 79%. ½
aꢁ
+112.0 (c 1.10,
1
EtOH). H NMR (CDCl
J = 3.9, 3.6, 3.9 Hz, 1H), 4.10 (d, J = 5.4 Hz, 2H), 4.47–4.89 (m, 6H),
.43 (d, J = 2.1 Hz, 1H), 7.54 (d, J = 2.1 Hz, 1H), 9.87 (s, 1H), 11.81
s, 1H). IR (film) : 3446, 2957, 2872, 1652, 1620, 1457, 1440,
3
): d 1.39 (s, 9H), 1.42 (s, 12H), 3.61 (q,
Compound 4gc: A solution of compound 3g (1.00 g, 2.2 mmol)
and ethylenediamine (0.07 g, 1.1 mmol) in dry EtOH (25 mL) was
refluxed for 2 h under nitrogen atmosphere. Ethanol was removed
under reduced pressure, the residue was purified by chromatogra-
phy (EtOAc–petroleum ether 1:2) to afford, after removal of the
solvent, the Schiff-base 4g as yellow foam solid (0.65 g, yield
7
(
1
7
6
m
372, 1324, 1267, 1212, 1187, 1157, 1118, 1069, 886, 846, 773,
55 cm . Anal. Calcd for C24
3.78; H, 7.55.
ꢂ1
34 8
H O : C, 63.98; H, 7.61. Found: C,
2
D
0
1
60%), mp 81–83 °C, ½
aꢁ
ꢂ56.0 (c 0.20, EtOH). H NMR (CDCl
3
): d
1
.31 (s, 9H), 1.42 (s, 12H), 3.95 (s, 2H), 4.00–4.34 (m, 5H), 4.55–
2
.2.7. Synthesis of 2,3:5,6-di-O-isopropylidene-1-O-methylene-
-mannofuranose
4.58 (m, 3H), 5.87 (d, J = 3.6 Hz, 1H), 7.10 (s, 1H), 7.26 (s, 1H),
8.38 (s, 1H), 13.87 (s, 1H). C NMR (CDCl ): d 202.8, 167.2,
3
160.5, 137.9, 129.8, 129.5, 126.9, 118.4, 112.0, 109.2, 105.5, 83.0,
81.7, 77.6, 76.8, 72.7, 67.6, 60.8, 59.8, 48.9, 35.1, 29.5, 27.1, 26.5,
1
3
[
(
3-(5-tert-butyl-2-hydroxy benzaldehyde)]-
3 M)
a-
D
0
0
Compound 3 M was prepared by the procedure reported in the
1
6
20
D
literature. White solid. Yield 60%, mp 78–80 °C. ½
aꢁ
+85.0 (c
25.7. IR (KBr)
m
: 3442, 2987, 2932, 1633, 1444, 1373, 1341, 1268,
1
ꢂ1
0
.90, EtOH). H NMR (CDCl
3
): d 1.33 (s, 9H), 1.44 (s, 12H), 3.61
1215, 1164, 1077, 1026, 848, 798, 776 cm . Anal. Calcd for
(
q, J = 3.6, 4.2, 3.9 Hz, 1H), 4.06 (d, J = 5.4 Hz, 2H), 4.46–4.90 (m,
50 72 14 2
C H O N : C, 64.92; H, 7.84; N, 3.03. Found: C, 64.89; H, 8.04;
6
1
1
8
6
H), 7.46 (d, J = 2.7 Hz, 1H), 7.79 (d, J = 2.4 Hz, 1H), 9.90 (s, 1H),
1.09 (s, 1H). IR (KBr) : 3423, 2971, 2870, 1666, 1620, 1461,
N, 3.10.
Compound 4 gc: Ligand 4 gc was synthesized from compound
0
0
m
0
20
379, 1275, 1258, 1246, 1215, 1146, 1119, 1070, 1005, 901, 847,
3 g and ethylenediamine as yellow liquid. Yield 68%, ½
a
ꢁ
ꢂ128
D
ꢂ1
1
02 cm . Anal. Calcd for C24
H
34
O
8
: C, 63.98; H, 7.61. Found: C,
(c 0.50, CH
2 2 3
Cl ). H NMR (CDCl ): d 1.28 (s, 9H), 1.44 (s, 12H),
3.77; H, 7.79.
3.95 (s, 2H), 3.95–4.53 (m, 8H), 5.84 (d, J = 3.9 Hz, 1H), 7.17 (s,
1
3
1
3
H), 7.23 (s, 1H), 8.34 (s, 1H), 13.83 (s, 1H). C NMR (CDCl ): d
0
2
4
.2.8. Synthesis of Schiff-base ligands(4Ga, 4Gb, 4Mc, 4 Mc, 4ga,
gc, 4 gc)
166.9, 160.4, 139.7, 137.7, 126.9, 118.4, 112.0, 109.2, 105.5, 82.9,
81.6, 81.5, 80.2, 76.0, 72.7, 72.5, 67.5, 67.3, 35.0, 29.5, 27.1, 26.5,
0
Compound 4Ga: A solution of compound 3G (1.00 g, 2.2 mmol)
25.7; IR (film)
m
: 3446, 2958, 2871, 1631, 1459, 1372, 1268,
ꢂ1
and (R,R)-1,2-cyclohexanediamine (0.125 g, 1.1 mmol) in dry EtOH
25 mL) was refluxed for 2 h under nitrogen atmosphere. Ethanol
was removed under reduced pressure, the residue was purified
1216, 1165, 1126, 1076, 1022, 885, 847 cm . Anal. Calcd for
C H O N : C, 64.92; H, 7.84; N, 3.03. Found: C, 64.85; H, 7.91;
50 72 14 2
N, 3.22.
(

6
4
J. Zhao et al. / Carbohydrate Research 344 (2009) 61–66
0
2
5
.2.9. Synthesis of salen–Mn(III) complexes (5Ga, 5Gb, 5Mc,
Mc, 5ga, 5gc, 5 gc)
Compound 5Ga: A mixture of 4Ga (0.33 g, 0.34 mmol) and
hydroxy benzaldehyde (2 ) were synthesized as described in the
0
0
11
0
literature in high yields. Compounds 2 and 2 reacted, respec-
tively, with 1,2:3,4-di-O-isopropylidene- -galactopyranose,
1,2:5,6-di-O-isopropylidene- -glucofuranose, and 2,3:5,6-di-O-
isopropylidene- -mannofuranose readily to give the correspon-
dent intermediates 3G, 3M, 3g, and 3 M, 3 g in the presence of
NaH and tetrabutylammonium iodide (TBAI) in THF under reflux.
The synthesis of the ligands 4Ga, 4Gb, 4Mc, 4gc, 4 gc, and 4 Mc is
straightforward, which involves the direct reaction of ethylenedia-
mine with the intermediate 3G, 3M, and 3 M in 1:2 molar ratio
with ethanol as solvent. The correspondent complexes were pre-
a-D
Mn(OAc)
under reflux at the atmosphere of nitrogen for 4 h. Solid LiCl
0.04 g, 1.02 mmol) was added and the mixture was further heated
for 3 h while exposed to air. The solvent was removed and the res-
idue was extracted with CH Cl . The extract was washed with
brine, dried over Na SO , and concentrated to obtain dark brown
2
ꢃ4H
2
O (0.17 g, 0.68 mmol) in EtOH (30 mL) was stirred
a-D
a-D
0
0
(
0
0
2
2
2
4
2
D
0
0
powder 5Ga (0.31 g, yield 86%). Mp 139–141 °C ½
a
ꢁ
ꢂ480.5 (c
0
.80, CH
2
Cl
2
). IR (KBr)
m
: 2957, 1614, 1543, 1440, 1382, 1342,
ꢂ1
1
310, 1260, 1210, 1169, 1072, 1072, 865, 820, 566, 512 cm
.
pared by the reaction of ligands with Mn(OAc)
by the treatment of the mixture with LiCl, same as the preparation
2
2
ꢃ4H O, followed
+
ESIMS: m/z 1032 [MꢂCl] Anal. Calcd for C54
0.73; H, 7.12; N, 2.62. Found: C, 60.06; H, 7.67; N, 2.36.
Compound 5Gb: For complex 5Gb, similar procedures were fol-
lowed as above by use of ligand 4Gb. Dark brown powder, yield
H
76
O
14
N
2
MnCl: C,
1
6
of Jacobsen catalyst.
3.2. Characterization of ligands and complexes
2
D
0
9
1
8
C
6
7.5%, ½
aꢁ
ꢂ163 (c 0.08, EtOH). IR (KBr)
m: 2957, 2875, 1614,
435, 1382, 1344, 1309, 1258, 1209, 1169, 1071, 939, 853, 825,
The ligands and complexes were characterized by 1H NMR, IR,
and Elemental analysis. The data are in accordance with the pro-
posed structures. The IR spectra of all complexes, compared with
the spectra of the corresponding ligands, indicate that
at 1628–1635 cm is shifted to lower energy by 14–17 cm , indi-
ꢂ1
+
05, 556, 513 cm . ESIMS: m/z 1130 [MꢂCl] . Anal. Calcd for
MnCl: C, 63.88; H, 6.74; N, 2.40. Found: C, 63.92; H,
62
78 14 2
H O N
.50; N, 2.35.
m
C@N band
ꢂ1
ꢂ1
Compound 5Mc: For complex 5Mc, similar procedures were fol-
0
lowed as above by use of ligands 4Mc and 4 Mc. Dark brown pow-
cating the ligands are coordinated to the metal ion Mn(III) through
the nitrogen atoms of the ligands. The disappearance of the band
2
D
0
der, yield 93%, ½
a
ꢁ
+209.0 (c 0.02, CH
2
Cl
2
). IR (KBr)
m: 2960, 2872,
ꢂ1
1
8
C
7
616, 1440, 1381, 1339, 1302, 1262, 1210, 1165, 1069, 932, 844,
22, 803, 551, 474 cm . ESIMS: m/z 978 [MꢂCl] . Anal. Calcd for
around 3423–3447 cm
of ligands after coordination indicates
ꢂ1
+
the ꢂOH is transferred to –O–, which is coordinated to Mn directly
50
70
H O
14
N
2
MnCl: C, 59.25; H, 6.96; N, 2.76. Found: C, 59.40; H,
(Fig. 1).
.13; N, 2.50.
0
0
Compound 5 Mc: For complex 5 Mc, similar procedures were fol-
3.3. Asymmetric epoxidation catalyzed by complexes
0
lowed as above by use of ligand 4 M. Dark brown powder, yield 63%,
2
D
0
½
a
1
ꢁ
+257 (c 0.02, CH
2
Cl
2
). IR (KBr)
m
: 2955, 2927, 1620, 1553, 1458,
The catalytic activity and enantioselectivity of complexes were
explored for the asymmetric epoxidation of cis-b-methyl-styrene,
1,2-dihydronaphthalene, styrene, and a-methyl-styrene using Na-
ClO/PyNO or m-CPBA/NMO as an oxidant system, respectively.
444, 1380, 1371, 1264, 1217, 1116, 1069, 1047, 888, 845, 540,
ꢂ1
+
4
N
75 cm . ESIMS: m/z 978 [MꢂCl] . Anal. Calcd for C50
H
70
O
14
-
2
MnCl: C, 59.25; H, 6.96; N, 2.76. Found: C, 59.16; H, 6.90; N, 2.57.
13
Compound 5ga: For complex 5ga, see literature.
Compound 5gc: For complex 5gc, see literature.
Compound 5 gc: For complex 5 gc, similar procedures were fol-
The results are summarized in Table 1.
13
It could be seen that the epoxidation of cis-b-methyl-styrene
and 1,2-dihydronaphthalene in the m-CPBA/NMO system was
much faster than that in the NaClO/PyNO biphasic system and
afforded higher ee values (entries 1–27). For example, complex
5Gb gave 82% ee for the epoxidation of 1,2-dihydronaphthalene
in the m-CPBA/NMO system within 0.17 h (10 min) (entry 19),
whereas the same reaction in NaClO/PyNO system was completed
in 5 h with 72% ee (entry 18). Furthermore, some reactions did not
take place in NaClO/PyNO system (entries 7 and 13). All the com-
0
0
0
lowed as above by use of ligand 4 gc. Dark brown powder, yield
2
D
0
8
1
5
C
7
8%, ½
a
ꢁ
ꢂ190.0 (c 0.02, CH
2 2
Cl ). IR (KBr) m: 2957, 2926, 1620,
553, 1444, 1381, 1262, 1217, 1165, 1074, 1022, 847, 833, 803,
37, 469 cm
H O N MnCl: C, 59.25; H, 6.96; N, 2.76. Found: C, 59.45; H,
70 14 2
ꢂ1
+
.
ESIMS: m/z 978 [MꢂCl] . Anal. Calcd for
50
.19; N, 2.86.
2
2
.3. General procedure for asymmetric epoxidation of alkenes
plexes showed low ee values in the epoxidation of a-methylsty-
rene (entries 37–43). The kind of sugar moiety obviously has
influence on the yields and ee values of epoxides. Though 5Ga
and 5ga have the same diimine bridge structure, the 5ga showed
higher ee than 5Ga for the asymmetric epoxidation of the cis-
substituted alkenes (entries 1, 2, 9, 10; 15, 16, 24, 25).
.3.1. For NaClO/PyNO oxidant system
The solution of alkene (1 mmol), PyNO (20 mg, 0.20 mmol), and
salen–Mn(III) complex (0.02 mmol) in CH
to 0 °C. A precooled NaClO aqueous solution (2 mmol, pH 11.3,
°C) was added. The mixture was stirred at 0 °C, and the reaction
was monitored by gas chromatography.
2 2
Cl (5.0 mL) was cooled
0
In general, the complexes with no chiral centers on the diimine
0
0
bridge such as 5Mc, 5 Mc, 5gc, and 5 gc showed low activity and ee
values, which indicated that the chiral induction of chiral salen–
Mn(III) complexes is mainly derived from the chiral diimine, and
only poor induction effect is received from the sugar moieties at
2
.3.2. For m-CPBA/NMO oxidant system
A solution of alkene (0.5 mmol), NMO (0.30 g, 2.5 mmol), and
0
0
salen–Mn(III) complex (0.01 mmol) in CH
to the desired temperature. Solid m-CPBA (0.20 g, 1.0 mmol) was
added in one time. The reaction was monitored by GC.
2
Cl
2
(2.5 mL) was cooled
C-3 (3 ) or C-5 (5 ) positions. In other words the chiral diimine
bridge is necessary in the salen–Mn(III) complexes as asymmetric
epoxidation catalysts.
0
0
Meanwhile, complexes 5 Mc and 5 gc bearing sugar moieties at
0
C-3 (3 ) positions showed very low activity. In extreme circum-
3
3
. Results and discussion
stances no reaction took place (entries 7 and 13). The reason is that
the sugar moieties that are much more hindered than tert-butyl are
more close to the Mn, which blocks the alkene from approaching
.1. Synthesis of complexes
17
the salen–Mn-oxo species according to side-on approach theory.
0
0
For synthesis of the ligands, 3-tert-butyl-5-(chloro-methyl)-2-
Although the chiral effect of sugar moieties at C-3 (3 ) or C-5 (5 )
positions is weak, it is indeed present in the epoxidation reaction
hydroxy benzaldehyde (2) and 5-tert-butyl-3-(chloro-methyl)-2-

J. Zhao et al. / Carbohydrate Research 344 (2009) 61–66
65
Table 1
2
'
Epoxidation of cis-b-methyl-styrene, 1,2-dihydronaphthalene, styrene and
styrene and using catalysts 5Ga,b
a-methyl-
3
'g
Substratea
Catalystb
Oxidantc
Yieldd
(%)
eee
(%)
Entry
T
Time
(h)
(
°C)
1
2
3
4
5
6
7
8
9
A
A
A
A
A
A
A
A
A
A
A
A
A
A
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
C
C
C
C
C
C
C
D
D
D
D
D
D
D
5Ga (2.0)
5Ga (2.0)
5Gb (2.0)
5Gb (2.0)
5Mc (2.0)
5Mc (2.0)
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
NaClO
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
0
12
0.05
4
0.167
5
0.167
5
0.167
10.5
0.833
5
0.25
5
0.333
7
6
0.25
5
0.167
6.5
1
7
0.333
9.5
1.25
5.5
0.5
9.5
0.197
0.25
0.25
2.0
0.167
0.333
0.333
0.5
0.333
0.167
0.167
0.333
0.333
0.25
0.333
64
88
63
69
34
82
—
71
79
83
85
3
5
—
7
82
84
2
2
—
3
'M
ꢂ78
3
G
0
ꢂ78
0
3
g
ꢂ78
0
5 Mc (2.0)
0
0
5 Mc (2.0)
ꢂ78
0
8
3
M
5ga (1.0)
5ga (1.0)
5gc (2.0)
5gc (2.0)
41
74
28
80
—
10
11
12
ꢂ78
0
ꢂ78
0
4
000
3500
3000
2500
2000
1500
1000
500
13
5
0
0
gc (2.0)
-1
14
15
16
17
18
19
20
21
5 gc (4.0)
5Ga (2.0)
5Ga (1.5)
5Ga (2.0)
5Gb (2.0)
5Gb (2.0)
5Mc (2.0)
5Mc (2.0)
ꢂ78
8
5
Wavenumber (cm )
0
49
46
45
65
74
72
54
34
21
66
44
57
40
19
7
93
93
80
>99
9
99
16
94
89
>99
21
93
82
28
64
62
66
72
82
<1
8
0
ꢂ78
0
4
'gc
ꢂ78
0
4
'Mc
Mc
Gb
ꢂ78
0
0
4
22
5 Mc (2.0)
0
2
23
5 Mc (2.0)
ꢂ78
0
15
67
78
4
11
19
7
72
87
70
6
4
24
5ga (1.0)
5ga (1.0)
5gc (2.0)
5gc (2.0)
25
26
27
28
29
30
31
32
33
34
35
ꢂ78
0
4
Ga
ꢂ78
0
0
0
5 gc (2.0)
5 gc (2.0)
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
ꢂ78
4
gc
ga
5Ga (2.0)
5Gb (2.0)
5Gb (1.0)
5Mc (2.0)
4
0
5 Mc (2.0)
9
4
000
3500
3000
2500
2000
1500
1000
500
5ga (1.0)
37
21
49
26
4
-1
Wavenumber (cm )
36
5 gc (4.0)
0
37
38
39
40
41
42
43
5Ga (2.0)
5Gb (2.0)
5Mc (2.0)
5
'gc
0
5 Mc (2.0)
5
5ga (2.0)
5gc (2.0)
51
10
5
5
'Mc
0
5 gc (4.0)
a
5
gc
A: cis-b-methyl-styrene; B: 1,2-dihydronaphthalene; C: styrene; D: a-
methylstyrene.
b
The number in parentheses is the molar percentage of catalyst used as com-
5
Mc
pared to the amount of substrate.
c
2 2
Reactions were carried out in CH Cl . For the m-CPBA oxidative system the
5Gb
5Ga
5ga
substrate/oxidant/NMO molar ratios were 1:2:5. For the NaClO system the sub-
strate/oxidant/PyNO molar ratios were 1:2:0.2.
d
Determined by GC.
Determined by GC with a chiral Cyclodex-b column.
e
4000
3500
3000
2500
2000
1500
1000
500
(
entry 16), worse than that of 72% displayed by Jacobsen’s cata-
-1
Wavenumber (cm )
18
lyst. However, 5Gb showed ee value of 70% in the epoxidation
of styrene (entry 32) better than that of 64% displayed by Jacob-
Figure 1. The FT-IR spectra of the ligands and complexes.
1
9
sen’s catalyst. It can be concluded that the sugars with opposite
rotation direction of polarized light as the diimine bridge in the
complex could reduce the chiral induction of the complex in the
asymmetry epoxidation, but the sugars with the same one would
enhance the chiral induction. A same result was also observed in
the oxidative kinetic resolution of 1-phenylethanol catalyzed by
(
entries 27, 28, 29, and 36). For further elucidating the chiral induc-
tion of sugar moieties of salen–Mn(III) complexes on epoxidation
reaction, the catalysis of complexes 5Ga and 5Gb was studied thor-
oughly. They showed good activity and moderate to good enanti-
oselectivities in m-CPBA/NMO system (entries 2, 4, 17, 19, 30,
2
0
the sugar-based salen–Mn(III) complexes.
and 31) except for the
a-methylstyrene which afforded low to
moderate ee value (entries 36 and 37). The catalytic properties of
4. Conclusion
5
Ga and 5Gb were compared with that of the Jacobsen’s catalyst
1
8,19
in the literatures.
It was found that 5Ga afforded ee value of
Several salen–Mn(III) complexes bearing sugar moieties have
been synthesized. These complexes have been used for the
6
2% in the epoxidation of 1,2-dihydronaphthalene in NaClO system

6
6
J. Zhao et al. / Carbohydrate Research 344 (2009) 61–66
asymmetric epoxidation of unfunctionalized alkenes. Weak
enantioselectivity is induced by the chiral sugar groups at C-3
5. Liu, X. W.; Tang, N.; Chang, Y. H.; Tan, Y. M. Tetrahedron: Asymmetry 2004, 15,
269–1273.
1
6
7
.
.
Irie, R.; Noda, K.; Ito, Y.; Katsuki, T. Tetrahedron Lett. 1991, 32, 1055–1058.
Sasaki, H.; Irie, R.; Hamade, T.; Suzuki, K.; Katsuki, T. Tetrahedron 1994, 50,
11827–11838.
0
0
(
3 ) or C-5 (5 ) in the case of absence of chirality in the diimine
0
bridge moiety. It was also shown that the sugars at C-5 (5 ) having
the same rotation direction of polarized light as the diimine bridge
in the catalyst could enhance the chiral induction in the asymme-
try epoxidation, but the sugars with the opposite one would reduce
the chiral induction.
8
9
.
.
Irie, R.; Noda, K.; Ito, Y.; Matsumoto, N.; Katsuki, T. Tetrahedron: Asymmetry
1991, 2, 481–494.
McGarrigle, E. M.; Gilheany, D. G. Chem. Rev. 2005, 105, 1563–1602.
10. Yan, S.; Klemm, D. Tetrahedron 2002, 58, 10065–10071.
1
1
1. Borriello, C.; Litto, R. D.; Panunzi, A.; Ruffo, F. Tetrahedron: Asymmetry 2004, 15,
81–686.
2. Borriello, C.; Litto, R. D.; Panunzi, A.; Ruffo, F. Inorg. Chem. Commun. 2005, 8,
717–721.
6
Acknowledgment
1
1
3. Zhao, S. S.; Zhao, J. Q.; Zhao, D. M. Carbohydr. Res. 2007, 342, 254–258.
4. Kureshy, R. I.; Khan, N. H.; Abdi, S. H. R.; Patel, S. T.; Iyer, P. K.; Subramanian, P.
S. J. Catal. 2002, 209, 99–104.
This work was supported by NSFC of China (Grant Nos.
2
0376017 and 20776035).
15. Zhao, S. S.; Zhao, J. Q.; Zhao, D. M. Acta Crystallogr., Sect. E 2006, 62, 02537–
2538.
6. Zhao, S. S.; Zhao, J. Q.; Li, J. X.; Wang, Q.; Zhao, D. M. Acta Crystallogr., Sect. E
006, 62, o3372–o3373.
7. Jacobsen, E. N.; Zhang, W.; Muci, A. R.; Ecker, J. R.; Deng, L. J. Am. Chem. Soc.
991, 113, 7063–7064.
0
1
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