F. Bigi et al. / C. R. Chimie 14 (2011) 685–687
687
Table 3
also demonstrated. A detailed full paper on recyclability
and use of other similar catalytic systems will be published
elsewhere. These types of ionic liquids containing other
desirable metals could pave the way for further develop-
ments in other forms of oxidations. The synthesis of chiral
catalytic ionic liquids for other enantioselective oxidation
reactions, such as epoxidation is currently under way.
Effect of the amount of catalyst, [P6
14]2[WO2(S-mand)2], on
6
6
enantioselective oxidation of methyl phenyl sulfide (Scheme 1).
Entrya
Cat./mol %
Sulfoxide yield/%b
Select./%
ee/%c
1
2
3
1
2
5
10
36
58
100
78
95
95
95
82
a
UHP 1.15 eq., room temperature, CH2Cl2, 1 h.
Yield determined by HPLC.
b
c
Acknowledgment
ee value determined by chiral HPLC.
K.R.S acknowledges EPSRC (Portfolio Partnership
Scheme, grant number EP/D029538/1). C.Q. wishes to
thank the Marie-Curie Foundation for providing a fellow-
ship for her to work at QUILL. We acknowledge
Dr A. Robertson at Cytec for providing phosphonium salts.
Dr J.D. Holbrey is acknowledged for his valuable discus-
sions and Angela Brownlie for her technical support.
Improved results were also obtained adding a small
percentage of ethanol, 2%, to CH2Cl2 and using just 1% of
[P6 6 6 14]2[WO2(S-mand)2] as catalyst, the sulfide conver-
sion increased from 10 to 41%, with 98% of selectivity and
88% of enantiomeric excess (Table 4, entry 2).
As expected, decreasing the reaction temperature
to 10 8C led to an increase of the enantiomeric excess to
96% with 53% sulfoxide yield and 95% selectivity (Table 4,
entry 10). However, a further increase of the reaction
time did not give better results. Different solvent systems
such as tetrahydrofuran (thf), methanol, cyclohexane,
[C4mpyrr][NTf2], water and water with an added phase
transfer reagent were also tested, giving unsatisfactory
results. CH2Cl2-2% EtOH is the solvent system that gave the
best results, as shown in Table 4.
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+
+
hydrophobic [P6
]
and [N1 ]
8 8 8
cations for
6
6
14
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Solvent effects on enantioselective oxidation of methyl phenyl sulfide
(Scheme 1) with [P6
14]2[WO2(S-mand)2].
6
6
Entrya
Solvent
Cat./
Sulfoxide
yield/%b
Select./%
ee/%c
mol %
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1
2
CH2Cl2
1
1
1
1
1
1
1
1
1
1
5
10
41
85
93
8
100
98
100
84
67
84
96
90
85
95
82
95
CH2Cl2-2% EtOH
thf
88
3
< 10
< 10
< 10
< 10
< 10
< 10
< 10
96
4
MeOH
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5
Cyclohexane
[C4mpyrr][NTf2]
H2O
6
51
94
86
76
53
58
7
8
aq. Na[AOT]
Solventless
CH2Cl2-2% EtOH
CH2Cl2
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9
10d
12
95
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a
UHP 1.15 eq., room temperature, 1 h.
Yield determined by HPLC.
ee value determined by chiral HPLC.
10 oC/3 h.
b
c
d