JOURNAL OF CHEMICAL RESEARCH 2012 585
Table 1 The results of catalytic asymmetric epoxidation of
styrene by D-glucosamine Schiff base dioxomolybdenum (VI)
complexes
(d, 1H, J1,2=8.37 Hz, sugar H-1), 5.63 (t, 1H, J = 9.25 Hz, sugar H-3),
5.00 (t, 1H, J = 9.6 Hz, sugar H-4), 4.31–4.20 (m, 2H, sugar H-6),
4.05 (d, 1H, J1,2 = 10.28 Hz, sugar H-5), 3.60 (t, 1H, sugar H-2), 2.04
(s, 9H, acetyl-1,3,4), 1.85 (s, 3H, acetyl-6). IR (KBr matrix, in cm−1)
1749 (C=O), 1629 (CH=N).
Catalyst
Temperature/°C
Time/h
Yield/%
ee/%
4a
30
0
30
0
50
30
0
50
30
0
4
6
4
6
3
4
6
3
4
6
41.2
27.3
58.7
42.6
74.9
53.3
36.8
92.2
79.5
54.0
22.0
23.8
28.7
32.1
37.2
62.0
62.3
47.6
66.5
67.2
Synthesis of D-glucosamine Schiff base dioxomolybdenum (VI)
complexes
4b
4c
4a–d were prepared according to the following procedure. One of
the Schiff base ligands 3a–d (5 mmol) was dissolved in methanol
(80 mL). After complete dissolution, MoO2(acac)2 (1.64 g, 5 mmol)
was added to the yellow solution. The mixture was allowed to react
for 4 h at room temperature, and then the volume was reduced to
ca 10 mL and diethyl ether (20 mL) was added to precipitate the com-
pound as a yellow solid. The solid was washed twice with diethyl
ether and dried in vacuo.
4d
4a. Yield, 82.7%. Anal. Calcd for C14H18MoN2O11: C, 34.6; H, 3.7;
N, 5.8. Found: C, 34.5; H, 3.5; N, 6.3%. 1H NMR (DMSO-d6) δ (ppm):
8.77 (s, 1H, HC=N), 8.67–7.07 (m, 3H, ArH), 5.65 (d, 1H, J = 3.52
Hz, sugar H-1), 5.62–3.58 (m, 6H, sugar ring H), 1.11 (m, 3H, metha-
nol). IR (KBr matrix, in cm−1) 3373 (–OH), 1637 (CH=N), 946
(Mo=O), 918 (Mo=O).
4b.Yield, 80.5%. Anal. Calcd for C18H21MoNO9: C, 44.0; H, 4.3; N,
2.9. Found: C, 44.6; H, 3.9; N, 3.8%. 1H NMR (DMSO-d6) δ (ppm):
9.46 (s, 1H, HC=N), 8.34–7.13 (m, 8H, ArH), 5.61 (d, 1H, J = 3.67
Hz, sugar H-1), 4.28–2.72 (m, 6H, sugar ring H), 1.11 (m, 3H, metha-
nol). IR (KBr matrix, in cm−1) 3385 (–OH), 1626 (CH=N), 930
(Mo=O), 905 (Mo=O).
dissociation of the complexes in solutions. After partial
dissociation, the enol-imine–keto-amine and the anomeric
equilibria of ligands 3a and 3b could decrease the asymmetric
induction, but there were no such side effects for 3c and 3d
because these equilibria did not exist in the acetyl protected
D-glucosamine ligands. In addition, in all the test reactions, ee
values gradually increased and yields gradually decreased with
decrease of reaction temperature.
Experimental
D-Glucosamine hydrochloride, 5-nitrosalicylaldehyde, and 2-hydroxy-
1-napthaldehyde were purchased from Alfa Aesar. Other reagents
were analytic grade and used as received. MoO2(acac)2 was synthe-
sised according to the literature.22
C, H and N elemental analysis were carried out on a Perkin-Elmer
2400 elemental instrument. IR spectra were recorded on Spectrum
GX using polystyrene as a standard (KBr pellets). FT-Raman spectra
were undertaken with a Bruker RFS100/S apparatus using a laser
source of Nd/YAG λ=1064 nm of 200 mW and a Ge detector at 77 K.
1H NMR spectra were recorded using a Bruker AV-300 spectrometer.
GC analysis was obtained with an HP 6890 gas chromatograph
equipped with a capillary column (50.0 m × 320 µm × 1.05 µm
nominal) and a FID detector.
4c. Yield, 76.6%. Anal. Calcd for C20H24MoN2O14: C, 39.2; H, 4.0;
N, 4.6. Found: C, 39.5; H, 3.5; N, 4.3%. 1H NMR (DMSO-d6) δ (ppm):
8.55 (s, 1H, CH=N), 8.34–7.05 (m, 3H, ArH), 6.18 (m, 1H, sugar H-
1), 5.77 (d, 1H, J = 8.44 Hz, sugar H-3), 4.93 (m, 1H, sugar H-4), 4.21
(m, 2H, sugar H-6), 4.00 (m, 1H, sugar H-5), 3.68 (m, 1H, sugar H-2),
2.21 (s, 6H, acetyl-3,4), 1.88 (s, 3H, acetyl-6), 1.08 (m, 3H, metha-
nol). IR (KBr matrix, in cm−1) 3468 (–OH), 1753 (C=O), 1630
(CH=N), 944 (Mo=O), 908 (Mo=O).
4d. Yield, 79.8%. Anal. Calcd for C24H27MoNO12: C, 46.7; H, 4.4;
N, 2.3. Found: C, 46.8; H, 4.6; N, 2.4%. 1H NMR (DMSO-d6) δ (ppm):
8.77 (s, 1H, CH=N), 8.26–6.98 (m, 8H, ArH), 6.16 (d, 1H, J1,2 = 3.61
Hz, sugar H-1), 5.59 (m, 1H, sugar H-3), 4.90 (t, 1H, sugar H-4),
4.30–4.19 (m, 2H, sugar H-6), 3.98 (d, 1H, sugar H-5), 3.65 (t, 1H,
sugar H-2), 2.12 (s, 6H, acetyl-3,4), 1.89 (s, 3H, acetyl-6), 1.11 (m,
3H, methanol). IR (KBr matrix, in cm−1) 3447 (–OH), 1748 (C=O),
1631 (CH=N), 942 (Mo=O), 909 (Mo=O).
Synthesis of Schiff bases
The compound 1b was obtained from 1a according to the literature
method.23
To an aqueous solution of 1a (or 1b) (0.1 mol) in NaOH (100 mL,
1.0 mol mL−1) or Na2CO3 (100 mL, 0.5 mol mL−1) was added slowly
the aromatic aldehyde 2a (or 2b) (0.1 mol) in methanol (50 mL) at
ice-water bath temperature, and the mixture was then stirred at room
temperature overnight. The bright yellow precipitate was filtered and
washed with methanol and diethyl ether respectively, recrystallised in
methanol and dried in vacuo.
3a. Yield, 82.3%. Anal. Calcd for C13H16N2O8: C, 47.6; H, 4.9; N,
8.5. Found: C, 47.7; H, 5.0; N, 8.7%. 1H NMR (DMSO-d6) δ (ppm):
8.71 (s, HC=N), 8.55 (d, HC=N), 8.15–7.10 (m, 3H, ArH), 6.82 (s,
C=CHN), 6.79 (s, C=CHN), 5.47 (d, H-1´α), 5.22 (d, H-1´α), 4.86 (d,
H-1´β), 4.67 (s, H-1´β), 3.75–2.74 (m, sugar ring). IR (KBr matrix, in
cm−1) 3521, 3352 (–OH), 1654 (CH=N).
3b. Yield, 80.7%. Anal. Calcd for C17H19NO6: C, 61.2; H, 5.8; N,
4.2. Found: C, 61.5; H, 5.6; N, 4.4%. 1H NMR (DMSO-d6) δ (ppm):
9.06 (s, HC=N), 8.96 (d, HC=N), 8.12–7.17 (m, 8H, ArH), 7.01 (s,
C=CHN), 6.83 (d, C=CHN), 5.37 (s, H-1´α), 5.19 (d, H-1´α), 4.77 (d,
H-1´β), 3.75–2.73 (m, sugar ring). IR (KBr matrix, in cm−1) 3477,
3231 (–OH), 1636 (CH=N).
Catalytic asymmetric epoxidations with Mo-complexes 4a–d
Epoxidations of styrene by D-glucosamine Schiff base dioxomolyb-
denum(VI) complexes with cumene hydroperoxide (CHP) as oxidant
were carried out according to the following general procedure: a
mixture of catalyst (0.003 mmol), styrene (0.08 mol) and 1,2-dichlo-
roethane (5 mL) was placed in a three-necked round-bottomed flask
equipped with a condenser and a magnetic stirrer. The mixture was
stirred for 5 min at room temperature and then with the addition of
CHP (2 mL, ca 0.02 mol), the reaction was started. The course of the
reactions was monitored by quantitative GC analysis at certain time
intervals.
This work was supported by Natural Science Foundation of
Jiangxi Province (20114BAB203027 and 20114BAB203028)
and Department of Education of Jiangxi Province (JXJG-11-
15-6).
Received 10 June 2012; accepted 18 July 2012
Paper 1201366 doi: 10.3184/174751912X13457309578443
Published online: 28 September 2012
3c. Yield, 88.6%. Anal. Calcd for C21H24N2O12: C, 50.8; H, 4.9; N,
5.6. Found: C, 50.9; H, 5.0; N, 5.8%. 1H NMR (DMSO-d6) δ (ppm):
8.78 (s, 1H, CH=N), 8.56–7.05 (m, 3H, ArH), 6.23 (d, 1H, J1,2
=
9.17 Hz, sugar H-1), 5.66 (t, 1H, J = 9.63 Hz, sugar H-3), 5.01 (t, 1H,
J = 9.6 Hz, sugar H-4), 4.30–4.20 (m, 2H, sugar H-6), 4.04 (d, 1H, J1,2
= 11.36 Hz, sugar H-5), 3.65 (t, 1H, sugar H-2), 2.03 (s, 9H, acetyl-1,
3, 4), 1.89 (s, 3H, acetyl-6). IR (KBr matrix, in cm−1) 1755 (C=O),
1635 (vs).
3d. Yield, 76.9%. Anal. Calcd for C25H27NO10: C, 59.9; H, 5.4; N,
2.8. Found: C, 59.7; H, 5.6; N, 2.9%. 1H NMR (DMSO-d6) δ (ppm):
12.40 (s, 1H, OH), 8.95 (s, 1H, CH=N), 8.12–7.06 (m, 8H, ArH), 6.20
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