Vanadium-catalyzed enantioselective oxidation of allyl sulfides

Article abstract of DOI:10.1016/j.tetasy.2011.04.023

The enantioselective oxidation of allyl sulfides with a vanadyl complex of 3,5-diiodosalicylidene tert-leucinol as a catalyst and aqueous hydrogen peroxide as an oxidant afforded chiral allyl sulfoxides with high enantioselectivities of up to 97.3% ee and moderate yields.

Full text of DOI:10.1016/j.tetasy.2011.04.023

Tetrahedron: Asymmetry 22 (2011) 717–721
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Tetrahedron: Asymmetry
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Vanadium-catalyzed enantioselective oxidation of allyl sulfides
Qingle Zeng a, , Yuxing Gao b, Junyu Dong a, Wen Weng c, Yufen Zhao b
⇑
a College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, China
b Department of Chemistry, Xiamen University, Xiamen 361005, China
c Department of Chemistry and Environmental Science, Zhangzhou Normal University, Zhangzhou 363000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The enantioselective oxidation of allyl sulfides with a vanadyl complex of 3,5-diiodosalicylidene tert-leu-
cinol as a catalyst and aqueous hydrogen peroxide as an oxidant afforded chiral allyl sulfoxides with high
enantioselectivities of up to 97.3% ee and moderate yields.
Received 27 January 2011
Revised 26 April 2011
Accepted 28 April 2011
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Chiral allyl aryl sulfoxides were reported to racemize readily,11
but the extremely high ee values obtained in biotransformations6,7
Chiral sulfoxides have important and diverse applications in the
fields of medicine, catalysis, and organic synthesis.1 Chiral allyl
sulfoxides are an important subclass of chiral sulfoxides. Some chi-
ral allyl sulfoxides show biological activities. For example, alliin
demonstrate that optically active allyl aryl sulfoxides are relatively
stable within a certain time. As part of our continuous studies on
enantioselective sulfoxidations,12 we herein report the vana-
dium-catalyzed enantioselective oxidation of allyl sulfides.
[(+)-(S)-2-propenyl-L-cysteine sulfoxide], which exists in garlic, is
a chiral allyl sulfoxide, and shows strong antioxidant and hydroxyl
radical scavenging properties2 and promotes an obvious increase
in the engulfing capacity of phagocyting cells.3 Some other chiral
allyl sulfoxides have been extensively used as chiral intermediates,
and chiral auxiliaries for organic synthesis, especially in the total
synthesis of natural products.4
2. Results and discussion
2.1. The effects of various factors on vanadium-catalyzed
oxidation of allyl phenyl sulfide 1a
Chiral catalysts are one of the most important factors for a cat-
alytically enantioselective reaction, and the chiral ligand is the key
to high enantioselectivity. Therefore, we mainly investigated the
effect of the vanadyl catalyst on the oxidation of allyl phenyl sul-
fide 1a. The preformed chiral vanadyl complexes 3 were prepared
from vanadyl acetoacetonate and chiral salicylidene amino alco-
hols derived from salicylaldehydes and chiral amino alcohols
according to the literature (Fig. 1).9 When the vanadyl complexes
3a–3d derived from salicylaldehyde and alaninol, isoleucinol,
valinol and tert-leucinol, respectively, were used for the sulfoxida-
tion, an obvious increase in enantioselectivity from 33.5% ee to
65.9% ee was observed, which correlates with the size of the R2
group in the salicylidene amino alcohols from methyl, to isobutyl,
to isopropyl, to tert-butyl (Table 1, entries 1–4). The more bulky
the R2 group, the higher the ee value of allyl phenyl sulfoxide 2a.
When a bulky tert-butyl group was used as the R3 group in van-
adyl complexes 3e–3h of salicylidene amino alcohols, ee values
from 22.0% ee to 55.7% ee corresponding to the size of the R2 group
in complexes 3e–3h were observed, but the enantioselectivities
decreased, (Table 1, entries 5–8).
The methods for the synthesis of chiral allyl sulfoxides mainly
include Andersen’s method, biotransformations, and enantioselec-
tive methods. The Andersen method was first reported in 1962.5
Until now, chiral allyl sulfoxides were mainly synthesized by
Andersen’s method. However, this method is environmentally un-
friendly, not atom-economical, and the separation of alkyl methyl-
sulfinate diastereomers is complicated.4g Biotransformations are
promising processes for the preparation of chiral allyl sulfoxides.
Ohta carried out the microbial oxidation of allyl sulfides with Cory-
nebacterium equi IFO 3730. Allyl phenyl sulfoxide (100% ee) and al-
lyl tolyl sulfoxide (92.4% ee) can be obtained by this method.6
Gonzalo utilized 4-hydroxyacetophenone monooxygenase from
Pseudomonas fluorescens ACB as an oxidative biocatalyst to trans-
form allyl phenyl sulfide into its sulfoxide with up to 98% ee.7
Enantioselective sulfoxidation is a straightforward and atom-eco-
nomical protocol. Chemists have developed enantioselective sul-
fide oxidations catalyzed by Ti,8 V,9 Fe,10 and so on,1 but the
enantioselective oxidation of allyl sulfide has been less studied. Re-
cently Bolm reported the iron-catalyzed oxidation of allyl phenyl
sulfide to give 63% ee.10b
When an iodo group was used as the R3 group in vanadyl com-
plexes 3i–3l, higher enantioselectivities (44.3–72.0%) were ob-
served when compared to vanadyl complexes 3a–3d with R3 = H
and vanadyl complexes 3e–3h with R3 = tert-butyl, (Table 1, entries
⇑
Corresponding author. Tel.: +86 13568999842; fax: +86 28 84079074.
E-mail address: qinglezeng@hotmail.com (Q. Zeng).
0957-4166/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2011.04.023

718
Q. Zeng et al. / Tetrahedron: Asymmetry 22 (2011) 717–721
The reaction temperature was then examined. The reaction at
O
S
Vanadium catalyst
30% H2O2
3
R1
S
R1
room temperature (about 25 °C) gave a lower ee value of 72.8% (Ta-
ble 1, entry 14). When the reaction was kept at a lower tempera-
ture at about ꢀ15 to ꢀ20 °C in an ice-salt bath, the ee value was
nearly the same as that in the ice-water bath, but the yield de-
creased (Table 1, entry 15 vs 13).
Ar
Ar
1
2
a, Ar = Ph,
b, Ar = p-Tol,
c, Ar = p-ClPh, R1 = H
d, Ar = Ph,
R1 = H
R1 = H
R2
R1 = Ph
From the experience of our previous research12a,d and Jackson’s
study,9b we knew that the amount of hydrogen peroxide could
influence the vanadium-catalyzed sulfide oxidation, and excess
oxidant may cause a kinetic resolution during the sulfoxidation.
When less than 1 equiv of H2O2 was used, both the enantioselectiv-
ity and the yield decreased (Table 1, entry 16). When 1.6 equiv of
H2O2 wasere employed, the ee value increased to 90.6% and an
overoxidised product sulfone was seen (13.6% yield) (Table 1, entry
17). When the oxidant was further increased to 2 equiv, the ee va-
lue decreased marginally, but the yield noticeably decreased while
the sulfone yield increased (up to 29.3%) (Table 1, entry 18).
The effects of the amounts of catalyst were investigated with
the aim of improving the ee value of the allyl phenyl sulfoxide.
When the amounts of vanadyl complex 3l increased to 2 and
3 mol %, the enantioselectivities of allyl phenyl sulfoxide increased
up to 92.8% and 97.3%, respectively (Table 1, entries 19 and 20 vs
17). Therefore, the conditions of 3% catalyst and 1.6 equiv of 30%
aqueous H2O2 were used for other allyl sulfides (Table 2).
e, Ar = p-Tol, R1 = Ph
f, Ar = p-ClPh, R1 = Ph
Catalyst 3 is
N
O
O
V
R3
OEt
O
R3
3a, R2 = Me, R3 = H
3b, R2 = i-Bu, R3 = H
3c, R2 = i-Pr, R3 = H
3d, R2 = t-Bu, R3 = H
3i, R2 = Me, R3 = I
3j, R2 = i-Bu, R3 = I
3k, R2 = i-Pr, R3 = I
3l, R2 = t-Bu, R3 = I
3e, R2 = Me, R3 = t-Bu
3f, R2 = i-Bu, R3 = t-Bu
3g, R2 = i-Pr, R3 = t-Bu
3h, R2 = t-Bu, R3 = t-Bu
Figure 1. Oxidation of allyl sulfides 1 catalyzed by chiral vanadium complexes 3
derived from salicylidene amino alcohols.
Table 1
Effects of various factors on the sulfide oxidationa
Entry
Catalyst
H2O2 (equiv)
Yieldb (%)
eec (%)
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3l
3l
3l
3l
3l
3l
3l
3l
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
0.8
1.6
2.0
1.6
1.6
61.3
70.1
67.3
73.2
49.2
68.2
58.0
64.3
63.2
69.1
71.5
75.4
78.0
75.2
70.6
57.0
33.5
51.2
56.0
65.9
22.0
46.2
51.0
55.7
46.3
55.4
65.9
72.0
84.6
73.8
84.4
51.1
90.6
88.2
92.8
97.3
Table 2
Vanadium-catalyzed oxidation of allyl and cinnamyl aryl sulfides with the catalyst 3la
Yieldb (%)
eec (%)
9
Entry
Substrate
Sulfoxide
10
11
12
13d
14d,e
15d,f
16d
17d
18d
19d,g
20d,h
1
2
3
4
5
6
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
57 (15.5)
50 (20.7)
56 (17.2)
51 (28.0)
43 (32.8)
47 (27.5)
97.3
89.6
92.7
81.5
72.0
73.8
62.1 (13.6)
49.0 (27.3)
58.2 (16.2)
57.0 (15.5)
a
Reaction conditions: purified vanadyl complexes 3l (0.015 mmol), sulfide
(0.5 mmol) and aqueous H2O2 (30%, 0.8 mmol), at 0 °C, 16 h.
b
Isolated yield based on sulfide. Data in parentheses are the yields of the
sulfones.
c
a
Determined by HPLC on a Daicel Chiralcel OD-H column. The absolute config-
Reaction conditions: vanadium–Schiff base complex 3, allyl phenyl sulfide 1
(1.0 mmol) and 30% aqueous H2O2 in 2 ml CH2Cl2 in an ice-water bath (about 0 °C)
urations were assigned by comparing specific rotations.6,7,9b All of the sulfoxides
configurations were (S).
for 16 h, unless otherwise mentioned.
b
Isolated yield after column chromatography. Data in parentheses are the yields
of allyl phenyl sulfone.
c
The ee values were determined by HPLC analysis on a Chiralcel OD-H column.
The absolute configurations were assigned by comparing specific rotations.6,7,9b All
The absolute configuration of the product allyl phenyl sulfoxide
2a was assigned as (S) by comparison of its specific rotation
of the sulfoxide configurations were (S).
d
Vanadium–Schiff base complexes purified by silica column chromatography
(½a 2D2
ꢁ
¼ ꢀ160:2) with the literature data (½a D25
¼ 164:8 for 98% ee
ꢁ
were used in the sulfide oxidation.
(S)-form7 and +176 for 100% ee (R)-form6). All of the configurations
of allyl phenyl sulfoxide 2a were (S) for the (S)-form catalysts 3
(Table 1, entries 1–20). The configurations of product 2 were deter-
mined by the configuration of the amino alcohol moieties in vana-
dyl complexes 3.
e
Reaction temperature was room temperature (about 25 °C).
f
Reaction was kept in ice-salt bath (about ꢀ15 to ꢀ20 °C).
g
2 mol % vanadium–Schiff base complexes was used.
h
3 mol % vanadium–Schiff base complexes was used.
9–12 vs 1–4 and 5–8). Perhaps the bulky tert-butyl group influ-
ences the effective coordination of the sulfide to vanadium.12b
2.2. Vanadium-catalyzed oxidation of allyl and cinnamyl aryl
sulfides with the ligand 3l
Canadyl complexes 3l derived from L-tert-leucinol and 3,5-dii-
odosalicylaldehyde gave the highest ee value of 72.0% (Table 1, en-
try 12), but this was still not high enough for practical purposes.
While trying to improve the enantioselectivity of allyl phenyl
sulfoxide, we noticed that the thin-layer chromatography of vana-
dyl complex 3l showed more than one spot on the silica gel plate,
and means that the vanadyl complex was not pure. Hence, vanadyl
complex 3l was purified on a silica gel chromatography column
and the purified complex 3l was used to evaluate the oxidation
of allyl phenyl sulfide again. The ee value was improved to 84.6%
with the purified complex 3l, and the yield was good (Table 1, en-
try 13).
Once the optimal reaction conditions were determined, various
allyl aryl sulfides 1a–1c and cinnamyl aryl sulfides 1d–1f were
investigated. Under the optimal reaction conditions, allyl p-tolyl
sulfide and allyl p-chlorophenyl sulfide were oxidized into the cor-
responding sulfoxides with 92% and 93% ee, respectively (Table 2,
entries 2 and 3 vs 1). It is clear that the electronic properties of
the para-substituent, on the phenyl group, of methyl or chloro
did not have any significant effect. However, under the same reac-
tion conditions, three kinds of aryl cinnamyl sulfides produced the
corresponding sulfoxides with lower enantioselectivities (Table 2,

Q. Zeng et al. / Tetrahedron: Asymmetry 22 (2011) 717–721
719
entries 4–6 vs 1–3). Cinnamyl phenyl sulfoxide was obtained in
81.5% ee. The enantioselectivities of cinnamyl p-tolyl sulfoxide
and cinnamyl p-chlorophenyl sulfoxide were even lower, 72.0%
and 73.8% ee, respectively. This is probably because the similar
bulky aryl groups on the cinnamyl aryl sulfides decreased the chi-
ral discrimination of chiral vanadyl catalyst 3l.
a magnetic stirrer bar was added 95% ethanol (30 ml), KOH (3.54 g,
0.15 mol), and aromatic thiophenol (0.13 mol). Allyl chloride
(5.80 g, 0.13 mol) was added dropwise to the resulting solution
within 20 min. The mixture was stirred at reflux for an additional
40 min. The mixture was condensed under reduced pressure on a
rotary evaporator. The resulting residue was distributed in diethyl
ether and water. The organic layer was separated, and the aqueous
layer extracted with diethyl ether twice. The combined organic
layer was washed with 2 M aqueous NaOH solution, water, and
then dried over anhydrous K2CO3. The organic layer was condensed
under reduced pressure on a rotary evaporator. The resulting resi-
due was purified on a silica gel column with petroleum ether as an
eluent to give the allyl aryl sulfide.
3. Conclusions
Chiral allyl sulfoxides are of importance, and are mainly synthe-
sized by Andersen’s method. We have developed a vanadium-cat-
alyzed allyl sulfide oxidation protocol. Various vanadyl complexes
of salicylidene amino alcohols were investigated; the vanadyl com-
plex of 3,5-diiodosalicylidene tert-leucinol, purified by column
chromatography was the best catalyst. The effects of the reaction
temperature, the amount of hydrogen peroxide and the amount
of vanadyl catalysts on the sulfide oxidation were examined and
the optimal conditions were obtained. In the presence of 1.6 equiv
of 30% aqueous H2O2 and 3 mol % of chromatography-purified van-
adyl complex of 3,5-diiodosalicylidene tert-leucinol, allyl phenyl
sulfide was oxidized for 16 h inat ice-water bath to give allyl phe-
nyl sulfoxide with 97.3% ee and 57.0% yield. Under the same con-
ditions, other allyl sulfides and cinnamyl sulfides were oxidized
to give the corresponding sulfoxides with good to excellent enanti-
oselectivities and moderate yields.
4.2.1. Allyl phenyl sulfide 1a
Colorless oil 12.3 g (63% yield). 1H NMR (CDCl3, 400 MHz): d
7.35–7.25 (m, 4H), 7.24–7.16 (m, 1H), 5.93–5.83 (m, 1H), 5.16–
5.05 (m, 2H), 3.56–3.53 (m, 2H); 13C NMR (CDCl3, 100 MHz): d
135.9, 133.5, 129.8, 128.7, 126.2, 117.6, 37.1; ESI-MS (MeOH): m/
z = 151 (M+H)+, 173 (M+Na)+.
4.2.2. Allyl 4-tolyl sulfide 1b
Colorless oil 14.5 g (68% yield). 1H NMR (CDCl3, 400 MHz): d
7.27–7.24 (m, 2H), 7.10–7.08 (d, 1H, J = 8.0 Hz), 5.90–5.83 (m,
1H), 5.11–5.02 (m, 2H), 3.51–3.49 (m, 2H), 2.31 (s, 3H); 13C NMR
(CDCl3, 100 MHz): d 136.4, 133.8, 132.0, 130.6, 129.5, 117.4, 37.9,
21.0; ESI-MS (MeOH): m/z = 165 (M+H)+, 187 (M+Na)+.
4. Experimental
4.1. General
4.2.3. Allyl 4-chlorophenyl sulfide 1c
Colorless oil 14.6 g (61% yield). 1H NMR (CDCl3, 400 MHz): d
7.28–7.22 (m, 4H), 5.89–5.79 (m, 1H), 5.13–5.06 (m, 2H), 3.52–
3.50 (m, 2H); 13C NMR (CDCl3, 100 MHz): d 134.3, 133.2, 132.3,
131.3, 128.9, 117.9, 37.4; ESI-MS (MeOH): m/z = 185 (M+H)+, 207
(M+Na)+.
Chemicals were purchased from Aldrich, Acros, Aladdin, or Ke-
long Chemicals Company, and used without further purification.
Silica Gel (300–400 mesh) for column chromatography was used.
The (R)- and (S)-2-amino alcohols were synthesized by reduction
of the corresponding commercially available amino acids as de-
scribed.13 Schiff base ligands and vanadium–Schiff base complexes
3a–3l were prepared according to the literature.8d,9c,g,12a Complex
3l was purified by silica gel chromatography column using a solu-
tion (gradiently from 20:1 to 3:1 (v/v)) of petroleum ether and
ethyl acetate as an eluent. The optical rotation and IR spectrum
of complex 3l could not be taken due to its dark brown color.
The 1H and 13C NMR spectra were consistent with the literature
data.9g
The purities of all synthesized compounds were checked by
thin-layer chromatography (TLC) using various organic solvents.
Melting points were recorded on a Thermo electrothermal melt-
ing-point apparatus. The rotation data were measured on an Amer-
ican Rudolf Autopol IV automatic polarimeter. The IR spectra were
recorded on a Bruker Tensor-27 FT-IR spectrophotometer. 1H and
13C NMR spectra were recorded on a Bruker Advance 400 MHz
NMR spectrometer at 400 and 100 MHz, respectively, using 5 mm
cylindrical tubes. Chemical shifts were referenced to CDCl3 residual
solvent signal (d (1H) = 7.26, d (13C) = 77.0) or internal reference
TMS, with positive values in the low-field direction. Molecular
weights were recorded on an Agilent LC–MS (LC 1100, MS
G1956A) spectrometer equipped with an autosampler. The ee val-
ues were determined by chiral HPLC analysis with a UV–vis detec-
tor (k 254 nm) on a Daicel Chiralcel OD-H analytical column
4.3. Synthesis of aryl cinnamyl sulfides
The general synthesis of aryl cinnamyl sulfides was according to
Guindon’s procedure.15 To a solution of cinnamyl alcohol (2 mmol)
in dry dichloroethane (5 ml) was added dried zinc iodide
(1.2 mmol). Aromatic thiophenol (2 mmol) was then added, and
the mixture was stirred at room temperature for 3 h. The reaction
was quenched with water (4 ml), and the reaction products were
extracted with CH2Cl2 (3 ꢂ 10 ml). The combined organic layer
was washed with 2 M KOH aqueous solution, and dried over anhy-
drous MgSO4. The solution was evaporated under reduced pressure
on a rotary evaporator. The resulting residue was purified on a col-
umn of silica gel (300–400 mesh) with petroleum as the eluent to
give aryl cinnamyl sulfide.
4.3.1. Cinnamyl phenyl sulfide 1d
Pale white solid 0.41 g (91% yield). Mp 76–78 °C [lit. mp. 77–
78].16 1H NMR (CDCl3, 400 MHz): d 7.39–7.36 (m, 2H), 7.32–7.16
(m, 8H), 6.42 (d, 1H, J = 15.7 Hz), 6.24 (dt, 1H, J = 15.7, 7.2 Hz),
3.70 (dd, 2H, J = 7.1, 1.1 Hz); 13C NMR (CDCl3, 100 MHz): d 136.7,
135.8, 132.7, 130.2, 128.8, 128.5, 127.5, 126.4, 126.3, 125.0, 37.1;
ESI-MS (MeOH): m/z = 227 (M+H)+, 249 (M+Na)+.
4.3.2. Cinnamyl p-tolyl sulfide 1e
(250 mm ꢂ 4.6 mm ꢂ 5
lm). Elemental analyses were carried out
on a Carlo Erba 1106 Elemental analyzer.
Pale white solid 0.43 g (89% yield). Mp 66–68 °C [lit. mp. 67–
68 °C].17 1H NMR (CDCl3, 400 MHz): d 7.32–7.18 (m, 7H), 7.08 (d,
2H, J = 8.0 Hz), 6.38 (d, 1H, J = 15.7 Hz), 6.24 (dt, 1H, J = 15.7,
7.1 Hz), 3.65 (d, 2H, J = 7.1 Hz), 2.30 (s, 3H); 13C NMR (CDCl3,
100 MHz): d 136.8, 136.6, 132.5, 131.9, 131.1, 129.6, 128.5, 127.5,
126.3, 125.3, 37.8, 21.0; ESI-MS (MeOH): m/z = 241 (M+H)+, 263
(M+Na)+.
4.2. Synthesis of aryl allyl sulfides
A modified Takaya procedure was adopted to synthesize these
aryl allyl sulfides.14 To a 250 ml round-bottomed -flask fitted with

720
Q. Zeng et al. / Tetrahedron: Asymmetry 22 (2011) 717–721
4.3.3. Cinnamyl p-chlorophenyl sulfide 1f
n-hexane/i-PrOH = 90:10, flow rate = 0.9 ml/min detected at
254 nm): tR = 17.3 min for enantiomer (R), and tR = 20.8 min for
enantiomer (S).
Pale white solid 0.43 g (83% yield). Mp 79–82 °C. 1H NMR
(CDCl3, 400 MHz): d 7.33–7.26 (m, 6H), 7.25–7.17 (m, 3H), 6.40
(d, 1H, J = 15.7 Hz), 6.21 (dt, 1H, J = 15.8, 7.2 Hz), 3.65 (d, 2H,
J = 7.1 Hz), 3.67 (dd, 2H, J = 7.1, 1.2 Hz); 13C NMR (CDCl3,
100 MHz): d 136.5, 134.2, 133.0, 132.5, 131.7, 128.9, 128.5, 127.7,
126.3, 124.6, 37.3; ESI-MS (MeOH): m/z = 261 (M+H)+, 283
(M+Na)+.
4.4.4. (S)-Cinnamyl phenyl sulfoxide 2d
Yellow oil 124 mg (51% yield). Ee 81.5%, ½a D22
¼ ꢀ146:2 (c 0.15,
ꢁ
EtOH). IR (film):
m 3069, 3027, 2926, 1655, 1599, 1450, 1372, 1150,
1050 (S@O), 964 cmꢀ1. 1H NMR (CDCl3, 400 MHz): d 7.62–7.50 (m,
5H), 7.32–7.25 (m, 5H), 6.42 (d, 1H, J = 16 Hz), 6.03–5.95 (m, 1H),
3.75–3.64 (m, 2H); 13C NMR (CDCl3, 100 MHz): d 142.9, 138.4,
136.1, 131.1, 129.0, 128.6, 128.2, 126.5, 124.4, 116.0, 60.7; ESI-
MS (MeOH): m/z = 243 (M+H)+, 265 (M+Na)+. Calcd for C15H14OS
(242.07): C, 74.34, H, 5.82, S, 13.23; found: C, 74.25; H, 5.93; S,
13.14. HPLC (Daicel Chiralcel OD-H 25 cm ꢂ 4.6 mm I.D., n-hex-
ane/i-PrOH = 90:10, flow rate = 0.9 ml/min detected at 254 nm):
tR = 13.2 min for enantiomer (R), and tR = 16.3 min for enantiomer
(S).
4.4. Sulfide oxidation procedure
A typical procedure for the enantioselective oxidation of sul-
fides is as follows. To a 10 ml flask fitted with a magnetic stirrer
bar was added a purified preformed vanadyl complex of 3,5-diiod-
osalicylidene tert-leucinol 3l (0.03 mmol), 2 ml of dichloromethane
and allyl (or cinnamyl) aryl sulfide (1.0 mmol). The flask was put
into an ice-water bath and the mixture was stirred slowly. After
10 min, 30% aqueous H2O2 (1.6 mmol) was added in batches. After
slowly stirring for 16 h, the reaction mixture was quenched with
saturated aqueous NaHSO3, and extracted with CH2Cl2 (3 ꢂ
20 ml). The organic layer was washed with saturated brine, and
dried over anhydrous MgSO4, and then condensed under reduced
pressure on a rotary evaporator. The resulting residue was purified
by a silica gel chromatography column with a solution of petro-
leum ether and ethyl acetate [gradiently from 1:0 to 1:1 (v/v)] as
an eluent to afford the sulfoxide. The enantiomeric excess (ee) of
the sulfoxide was determined with HPLC on a Daicel Chiralcel
4.4.5. (S)-Cinnamyl p-tolyl sulfoxide 2e
Yellow oil 109 mg (43% yield). Ee 72.0%, ½a D22
¼ ꢀ173:5 (c 0.12,
ꢁ
EtOH). IR (film): m 3065, 2967, 1653, 1593, 1370, 1295, 1045 (S@O),
960, 730, 695 cmꢀ1 1H NMR (CDCl3, 400 MHz): d 7.50 (d, 2H,
.
J = 8 Hz), 7.32–7.23 (m, 8H), 6.45 (d, 1H, J = 16 Hz), 6.02–5.94 (m,
1H), 3.68 (d, 2H, J = 8 Hz), 2.42 (s, 3H); 13C NMR (CDCl3,
100 MHz): d 141.6, 139.7, 138.3, 136.1, 129.7, 128.6, 128.1, 126.5,
124.4, 116.2, 60.8, 21.4; ESI-MS (MeOH): m/z = 257 (M+H)+, 279
(M+Na)+. Calcd for C16H16OS (256.09): C, 74.96, H, 6.29, S, 12.51;
found: C, 74.82; H, 6.35; S, 12.41. HPLC (Daicel Chiralcel OD-H
25 cm ꢂ 4.6 mm I.D., n-hexane/i-PrOH = 90:10, flow rate = 0.9 ml/
min detected at 254 nm): tR = 12.5 min for enantiomer (R), and
tR = 15.4 min for enantiomer (S).
OD-H column (250 mm ꢂ 4.6 mm ꢂ 5
lm).
4.4.1. (S)-Allyl phenyl sulfoxide 2a
Pale yellow oil 95 mg (57% yield). Ee 97.3%, ½a D22
¼ ꢀ160:2 (c
ꢁ
0.90, EtOH). IR (film):
m 3055–2910, 1635, 1595, 1475, 1445,
1090, 1045 (S@O), 750, 690 cmꢀ1
.
1H NMR (CDCl3, 400 MHz): d
4.4.6. (S)-Cinnamyl p-chlorophenyl sulfoxide 2f
7.62–7.58 (m, 2H), 7.55–7.48 (m, 2H), 5.70–5.60 (m, 1H), 5.35–
5.18 (m, 2H), 3.60–3.49 (m, 2H); 13C NMR (CDCl3, 100 MHz): d
142.9, 131.1, 129.0, 125.2, 124.3, 123.9, 60.8; ESI-MS (MeOH): m/
z = 167 (M+H)+, 189 (M+Na)+. Calcd for C9H10OS (166.04: C,
65.02; H, 6.06; S, 19.29; found: C, 64.89; H, 6.09; S, 19.26. HPLC
(Daicel Chiralcel OD-H 25 cm ꢂ 4.6 mm I.D., n-hexane/i-
PrOH = 90:10, flow rate = 0.9 ml/min detected at 254 nm):
tR = 11.8 min for enantiomer (R), and tR = 14.2 min for enantiomer
(S).
Yellow oil 130 mg (47% yield). Ee 73.8%, ½a D22
¼ ꢀ189:3 (c 0.11,
ꢁ
EtOH). IR (film):
m 3027, 2973, 1651, 1595, 1494, 1449, 1093, 1041
(S@O), 967, 733, 692 cmꢀ1. 1H NMR (CDCl3, 400 MHz): d 7.57–7.48
(m, 4H), 7.34–7.24 (m, 5H), 6.44 (d, 1H, J = 16 Hz), 6.01–5.93 (m,
1H), 3.74–3.63 (m, 2H); 13C NMR (CDCl3, 100 MHz): d 141.4,
138.8, 137.3, 135.9, 129.3, 128.6, 128.3, 126.5, 125.8, 115.4, 60.7;
ESI-MS (MeOH): m/z = 277 (M+H)+, 299 (M+Na)+. Calcd for
C15H13ClOS (276.03): C, 65.09, H, 4.73, S, 11.58; found: C, 65.21;
H, 4.88; S, 11.49. HPLC (Daicel Chiralcel OD-H 25 cm ꢂ 4.6 mm
I.D., n-hexane/i-PrOH = 90:10, flow rate = 0.9 ml/min detected at
254 nm): tR = 18.5 min for enantiomer (R), and tR = 22.3 min for
enantiomer (S).
4.4.2. (S)-Allyl p-tolyl sulfoxide 2b
Pale yellowish oil 90 mg (50% yield). Ee 89.6%, ½a D22
¼ ꢀ202:1 (c
ꢁ
0.52, EtOH). IR (film):
m 3068, 2975, 1635, 1595, 1490, 1090, 1045
(S@O), 810 cmꢀ1
.
1H NMR (CDCl3, 400 MHz): d 7.50–7.48 (d, 2H,
Acknowledgments
J = 8.0 Hz), 7.33–7.31 (d, 2H, J = 7.8 Hz), 5.68–5.59 (m, 1H), 5.34–
5.18 (m, 2H), 3.58–3.48 (m, 2H), 2.42 (s, 3H); 13C NMR (CDCl3,
100 MHz): d 141.5, 139.6, 129.7, 125.4, 124.3, 123.7, 60.9, 21.4;
ESI-MS (MeOH): m/z = 181 (M+H)+, 203 (M+Na)+. Calcd for
We thank the National Science Foundation of China (Grant Nos.
20672088 and 20705031), Ministry of Human Resources and Social
Security of China, the Science and Technology Bureau of Sichuan
(Grant No. 2011HH0016), the Chengdu Science and Technology Bu-
reau, and Incubation Program for Excellent Innovation Team of
Chengdu University of Technology for financial support. We sin-
cerely thank Mr. Allan Chelashaw, College of Material Science
and Engineering, Donghua University for his help.
C10H12OS (180.06): C, 66.63; H, 6.71; S, 17.79; found: C, 66.58; H,
6.68; S, 17.69. HPLC (Daicel Chiralcel OD-H 25 cm ꢂ 4.6 mm I.D.,
n-hexane/i-PrOH = 90:10, flow rate = 0.9 ml/min detected at
254 nm): tR = 10.6 min for enantiomer (R), and tR = 13.9 min for
enantiomer (S).
4.4.3. (S)-Allyl p-chlorophenyl sulfoxide 2c
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Yellow oil 112 mg (56% yield). Ee 92.7%, ½a D22
¼ ꢀ223:1 (c 0.35,
ꢁ
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