Hypervalent iodine(III) sulfonate mediated synthesis of α-thiocynanatoketones in a task-specific ionic liquid [bmim]SCN

Article abstract of DOI:10.1002/jccs.200800179

The task-specific ionic liquid (TSIL) and 1-n-butyl-3-methylimidazolium thiocynanate, ([bmim]SCN) were used as the medium as well as the reactant for the synthesis of α-thiocynanatoketones by the reaction with α-sulfonyloxy aryl ketones. Significant rate enhancements and improved yields have been observed.

Full text of DOI:10.1002/jccs.200800179

1
204
Journal of the Chinese Chemical Society, 2008, 55, 1204-1207
Communication
Hypervalent Iodine(III) Sulfonate Mediated Synthesis of
a-Thiocynanatoketones in a Task-specific Ionic Liquid [bmim]SCN
a
Hsin-Yu Huang (
b
), Huey-Min Wang * (
b
), Rei-Sheu Hou (
),
a
Hui-Ting Cheng (
a
) and Ling-Ching Chen * (
)
Graduate Institute of Pharmaceutical Sciences, College of Pharmacy, Kaohsiung Medical University,
a
Kaohsiung 807, Taiwan, R.O.C.
b
Chung Hwa University of Medical Technology, Tainan 717, Taiwan, R.O.C.
The task-specific ionic liquid (TSIL) and 1-n-butyl-3-methylimidazolium thiocynanate, ([bmim]SCN)
were used as the medium as well as the reactant for the synthesis of a-thiocynanatoketones by the reaction
with a-sulfonyloxy aryl ketones. Significant rate enhancements and improved yields have been observed.
Keywords: Hypervalent iodine; a-Thiocynanatoketones; Ionic liquid.
INTRODUCTION
Recently, ionic liquids have been attracted a consid-
erable attention as an environmental-friendly reaction me-
dia for the various organic transformations. Ionic liquids
can serve as environmentally benign alternatives to the
conventional volatile organic solvents due to their interest-
ing properties such as very low volatility, high chemical
Alkyl thiocyanates are important synthetic precursors
for the preparation of sulphur-containing organic com-
pounds. This functional group can be used as a masked
mercapto group or as a precursor for sulphur-containing
heterocyclic compounds. Additionally, a-thiocyanatoke-
tones are intermediates for a preferred synthetic route to
8
stability, and nonflammability.
1
several types of thiazoles. Thiocyanation is generally car-
The ionic liquid, 1-n-butyl-3-methyl imidazolium
ried out via nucleophilic substitution using thiocyanate an-
ions. The low nucleophilicity of the NCS-ion requires
rather harsh reaction conditions. Metal thiocyanates and
organic halides or sulfonates are generally used to intro-
duce the thiocyanate functionality into an organic mole-
thiocyanate [bmim]SCN was prepared by the anion ex-
9
change of 1-n-butyl-3-methyl imidazolium chloride with
KSCN in acetone for 48 h at room temperature (Scheme
1
I).
0
Hypervalent iodine(III) sulfonates have been received
2
cule. However, the thiocyanate group is not that stable
continuous attention due to their versatile utilities in or-
when heated or under acidic conditions. Chromatography
on silica gel or prolonged heating over 50 °C can cause
intramolecular rearrangement to the thermodynamically
ganic synthesis, ready availability, and relatively non-toxic
11
properties. In view of the easy accessibility of a-[(2,4-di-
nitrobenzene)sulfonyl]oxy ketone intermediates from read-
ily available ketones and hypervalent iodine reagent, [hy-
3
favored isothiocyanate isomers. Furthermore, thiocya-
4
nates have been obtained from alcohols, silyl ethers or
5
droxyl(2,4-dinitrobenzenesulfonyloxy)iodo]benzene
11(o)
6
amines using Ph
3
P(SCN)
2
. However, many drawbacks
(HDNIB).
We now report a facile and efficient method
have been observed for these thiocyanation methodolo-
7
gies.
for the synthesis of a-thiocynanatoketones by the reaction
of a-sulfonyloxy aryl ketones with [bmim]SCN under mild
Scheme I
acetone
Cl + KSCN
SCN + KCl
N
N
N
N
4
8 h, r.t.
[
bmim]SCN

Synthesis of a-Thiocynanatoketones in [bmim]SCN
J. Chin. Chem. Soc., Vol. 55, No. 6, 2008 1205
conditions.
Table 1. Synthesis of a-thiocynanatoketones 3a-i
Entry
Product
Ar
R
Yield (%)
RESULTS AND DISCUSSION
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
Ph
4-MeC H4
H
H
82
86
85
72
75
73
74
80
79
The 2,4-dinitrobenzenesulfonyloxy group located at
the a position to a carbonyl group represents an increas-
ingly important entity in both mechanistic and synthetic or-
ganic chemistry. One reason for this importance is that 2,4-
dinitrobenzenesulfonyloxy group is a good leaving group,
and this accounts for the considerable synthetic utility as-
sociated with these groups in functionalization of carbonyl
compounds.
6
4-MeOC
H
H
6
4
4-ClC H4
6
H
4-BrC H4
6
H
2-Furyl
H
3g
3h
3i
2-Thienyl
H
Ph
Ph
Me
Ph
As shown in Scheme II, our experiments involving
a one-pot procedure for the preparation of a-thiocyana-
toketones (3) by reaction of arylketones (1) with HDNIB
useful alternative to existing methods, since it does not re-
quire a-haloketones or a-tosyloxyketones substrates as
starting materials.
(
2) in CH
mation of a-sulfonyloxy aryl ketone intermediates (2),
bmim]SCN (2 mL) was added to the reaction mixture and
3
CN at 80°C for 1 h. After completion of the for-
EXPERIMENTAL SECTION
[
All melting points are uncorrected. The IR spectra
were recorded on a Shimadzu IR-27 G spectrophotometer.
stirring was continued at room temperature for 10 min to
give the desired a-thiocynanatoketones (3) in good yields.
The results are summarized in the Table 1. When the reac-
tion was carried out by reacting a-sulfonyloxy aryl ketone
1
13
H NMR and C NMR spectra were recorded on a Varian
Unity Plus 400 MHz. Chemical shifts (d) were measured in
ppm with respect to TMS. MS were obtained on a JEOL
JMS D-300 instrument.
(
2a) in ionic liquid, 1-butyl-3-methylimidazolium tetra-
fluoroborate, [bmim]BF with KSCN, the preparation of
-phenyl-2-thiocynanatoethanone (3a) needs stirring for 6
4
1-Phenyl-2-thiocynanatoethanone (3a); Typical proce-
1
dure
h at room temperature. This indicated that the nucleo-
philicity of the SCN anion is much higher in [bmim]SCN
To a solution of acetophenone (1a) (120 mg, 1.0
mmol) in CH CN (20 mL) was added HDNIB (561 mg, 1.2
3
4
compared to KSCN in [bmim]BF .
mmol) and stirred for 1 h at 80 °C. Then [bmim]SCN (2
mL) was added to the reaction mixture and stirring was
continued for 10 min at room temperature. After comple-
tion of the reaction, the reaction mixture was diluted with
water, and the product was extracted with ethyl acetate.
Scheme II
O
O
O
[
bmim]SCN
r. t.
HDNIB
R
R
R
Ar
Ar
CH CN
3
Ar
4
The collected organic fractions were dried over MgSO ,
ODNs
SCN
and the solvent was evaporated under vacuum. The result-
ing residue was chromatographed on silica gel column
eluting with AcOEt: n-hexane (1:1) to give 3a, mp 69-70
1
2
3
O N
2
O
a) Ar= Ph, R= H
12
-1 1
b) Ar= 4-MeC6H4, R= H
c) Ar= 4-OMeC6H4, R=H
d) Ar = 4-ClC6H4, R= H
e) Ar = 4-BrC6H4, R= H
f) Ar = 2-Furyl, R= H
g) Ar = 2-Thienyl, R= H
h) Ar= Ph, R= Me
°C (lit. 71-72 °C). IR (KBr) n: 2150, 1674 cm ; H NMR
CDCl , 400 MHz) d: 4.75 (s, 2H), 7.52-7.56 (m, 2H),
.66-7.70 (m, 1H), 7.93-7.95 (m, 2H); C NMR (CDCl
100 MHz) d: 42.9, 111.8, 128.4, 128.4, 129.1, 129.1, 133.8,
HDNIB = HO
I
O
S
NO2
(
3
O
1
3
7
3
,
DNs = 2,4-dinitrobenzenesulfonyl
+
34.7, 190.7; EI-MS m/z (relative intensity) 177 (M ,
1
0
i) Ar= R= Ph
.47), 105 (100), 76 (21).
In conclusion, we have described a novel and effi-
1-p-Tolyl-2-thiocyanatoethanone (3b)
1
mp 100-102 °C (lit. 102-103 °C). IR (KBr) n: 2152,
3
cient method for the synthesis of a-thiocynanatoketones
using [bmim]SCN as reaction medium as well as reactant.
This new efficient and facile method might be served as a
-1 1
1664 cm ; H NMR (CDCl , 400 MHz) d: 2.48 (s, 3H),
3
4.73 (s, 2H), 7.33 (d, J = 7.6 Hz, 2H), 7.84 (d, J = 8.0 Hz,

1
206 J. Chin. Chem. Soc., Vol. 55, No. 6, 2008
Huang et al.
1
H); C NMR (CDCl
3
2
1
3
, 100 MHz) d: 21.8, 43.0, 128.5,
1,2-Diphenyl-2-thiocyanatoethanone (3i)
2
mp 106-108 °C (lit. 109-110 °C). IR (KBr) n: 2359,
0
28.5, 129.8, 129.8, 131.4, 146.0, 190.3; EI-MS m/z (rela-
+
tive intensity) 191 (M , 0.26), 119 (100), 91 (30).
-1 1
1676 cm ; H NMR (CDCl
3
, 400 MHz) d: 5.95 (s, 1H),
1
-(4-Methoxyphenyl)-2-thiocyanatoethanone (3c)
7.25-7.35 (m, 5H), 7.37-7.41 (m, 2H), 7.50-7.54 (m, 1H),
13
7.90-7.93 (m, 2H); C NMR (CDCl , 100 MHz) d: 76.1,
3
1
mp 120-121 °C (lit. 121 °C). IR (KBr) n: 2147,
4
-1 1
660 cm ; H NMR (CDCl
1
4
2
1
3
, 400 MHz) d: 3.90 (s, 3H),
127.7, 127.7, 128.5, 128.5, 128.6, 128.6, 129.1, 129.1,
.71 (s, 2H), 6.99 (d, J = 8.8 Hz, 2H), 7.90 (d, J = 8.8 Hz,
129.9, 133.4, 133.9, 138.9, 198.9; EI-MS m/z (relative in-
+
tensity) 253 (M , 39), 105 (100), 77 (77).
1
3
H); C NMR (CDCl
3
, 100 MHz) d: 42.9, 55.6, 112.1,
14.3, 114.3, 126.9, 130.9, 130.9, 164.8, 189.1; EI-MS m/z
+
relative intensity) 207 (M , 1), 136 (9), 135 (100), 77 (10).
(
Received July 22, 2008.
1
-(4-Chlorophenyl)-2-thiocyanatoethanone (3d)
1
5
mp 132-134 °C (lit. 135-136 °C). IR (KBr) n: 2065,
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