Efficient conversion of ketones to α-tosyloxyketones with m-chloroperbenzoic acid and p-toluenesulfonic acid in the presence of catalytic amount of IL-supported PhI in [emim]OTs

Article abstract of DOI:10.1055/s-2007-984914

Various ketones were smoothly converted into the corresponding α-tosyloxyketones with MCPBA and p-toluenesulfonic acid in the presence of a catalytic amount of ionic-liquid (IL)-supported PhI in room temperature ionic liquid, [emim]OTs. Moreover, the pres

Full text of DOI:10.1055/s-2007-984914

2168
LETTER
Efficient Conversion of Ketones to a-Tosyloxyketones with m-Chloro-
perbenzoic Acid and p-Toluenesulfonic Acid in the Presence of Catalytic
Amount of IL-Supported PhI in [emim]OTs
C
onversio
u
nof
K
etones
n
to
a
-
Tosylox
n
yketones osuke Akiike, Yukiharu Yamamoto, Hideo Togo*
Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
E-mail: togo@faculty.chiba-u.jp
Received 14 June 2007
fore, these solvents have been successfully used in
Abstract: Various ketones were smoothly converted into the corre-
sponding a-tosyloxyketones with MCPBA and p-toluenesulfonic
acid in the presence of a catalytic amount of ionic-liquid (IL)-sup-
ported PhI in room temperature ionic liquid, [emim]OTs. Moreover,
Friedel–Crafts reaction,9 hydrogenation,10 Diels–Alder
reactions,11 Heck, Suzuki, Sonogashira, and olefin-meta-
thesis reactions,12 Michael additions,13 oxidation,14 con-
the present ionic-liquid reaction media containing a catalytic densation reaction,15 formation of imines,16 1,2-
rearrangement,17 esterification of carboxylic acids and
amount of IL-supported PhI could be reused for the same a-tosyl-
carboxylates,18 Williamson ether synthesis,19 and
oxylation of ketones and thiazoles directly, keeping good yields.
Grignard reaction.20 Recently, we also reported highly ef-
Key words: ionic liquid, IL-supported PhI, a-tosyloxyketone,
ketone, MCPBA, p-toluenesulfonic acid, thiazole, catalyst
ficient esterification of carboxylic acids and phosphonic
acids with trialkyl orthoacetate in ionic liquid,21 and de-
methylation of N,N-dimethylanilines with phenyl chloro-
Synthetic use of hypervalent iodines for organic synthesis formate in various ionic liquids.22
has been studied widely.1 Among these hypervalent io-
dines, [(hydroxy)(tosyloxy)iodo]benzene (HTIB, Koser’s
Here, we would like to report an oxidative conversion of
ketones into a-tosyloxyketones with MCPBA and p-tolu-
enesulfonic acid in the presence of a catalytic amount of
ionic-liquid (IL)-supported PhI. As IL-supported PhI cat-
alysts, ionic liquids A (oil), B (mp 126–128 °C), C (mp
170–172 °C), and D (mp 149–150 °C) were prepared to
reagent) is an efficient and sole reagent for the direct a-
tosyloxylation of ketones.2 a-Tosyloxyketones are very
important strategic precursors for the construction of
various heteroaromatics such as thiazoles, oxazoles,
selenazoles, imidazoles, pyrazoles, benzofurans, and
see their reactivity and reusability (Figure 1). Then, a-to-
syloxylation of acetophenone in the presence of a catalytic
lactones.2 We have also studied synthetic uses of
[(hydroxy)(tosyloxy)iodo]arenes,
1-(arenesulfonyl-
amount of IL-supported PhI (10 mol%) A in typical room-
temperature ionic liquids (2 mL), such as butylmethyl-
imidazolium hexafluorophosphate ([bmim]PF6), butyl-
methylimidazolium tetrafluoroborate ([bmim]BF4),
ethylmethylimidazolium tosylate([emim]OTs), and butyl-
methylpyrrolidinium bis(trifluoromethanesulfonyl)imide
([bmpy]NTf2), with MCPBA and p-toluenesulfonic acid
was carried out to give a-tosyloxyacetophenone in 41%,
oxy)benziodoxolones, and poly[4-(hydroxy)(tosyloxy)io-
do]styrene for the construction of thiazoles, imidazoles,
imidazo[1.2-a]pyridines, and 2,1-benzothiazines.3 Re-
cently, PhI-catalyzed efficient a-acetoxylation of ketones
with m-chloroperbenzoic acid (MCPBA) in AcOH in the
presence of BF3·OEt2 and water was reported to provide
the corresponding a-acetoxyketones in moderate isolated
yields,4 and hypervalent iodine(III)-catalyzed oxidative
cyclization of b-(4-hydroxyaryl)propanoic acids with
MCPBA was also reported to give the corresponding
spirolactones.5 We also reported a direct one-pot prepara-
tion of various [(hydroxy)(sulfonyloxy)iodo]arenes from
iodoarenes with MCPBA and sulfonic acids at room tem-
perature,6 and PhI-catalyzed a-tosyloxylation of ketones
with MCPBA and p-toluenesulfonic acid.7 On the other
hand, today, ionic liquids have become very popular as
organic reaction media due to the promotion of ionic reac-
tions and recyclable reaction media.8 Thus, these solvents
possess interesting and useful advantages for organic
reactions such as negligible vapor pressure, low flamma-
bility, high thermal stability, and easy reusability. There-
+
O
N
N
Me
I
I
Br–
A
B
+
N
N
Me
O
Br–
+
N
N
Me
O
Br-
I
O
C
D
+
N
N
Me
I
Br–
SYNLETT 2007, No. 14, pp 2168–2172
0
3
.0
9
.2
0
0
7
Advanced online publication: 20.07.2007
DOI: 10.1055/s-2007-984914; Art ID: U05707ST
© Georg Thieme Verlag Stuttgart · New York
Figure 1 IL-supported PhI A–D

LETTER
Conversion of Ketones to a-Tosyloxyketones
2169
0%, 82%, and 51% yields, respectively. When B was used of the ethyl acetate extract with aqueous saturated
instead of A, in [bmim]PF6, [bmim]BF4, [emim]OTs, and NaHCO3. The recovered ionic-liquid reaction media con-
[bmpy]NTf2, a-tosyloxyacetophenone was obtained in taining a catalytic amount of IL-supported PhI A, B, C, or
65%, 0%, 83%, and 56% yields, respectively. Thus, D could be reused for the same a-tosyloxylation of ketone
[emim]OTs showed the best reactivity among these four with MCPBA and p-toluenesulfonic acid, keeping good to
room-temperature ionic liquids. Then, a-tosyloxylation of moderate yields of a-tosyloxyketone as shown in Table 2
various ketones with MCPBA and p-toluenesulfonic acid until the third time. Naturally, when iodobenzene instead
in the presence of a catalytic amount (10 mol%) of ionic of IL-supported PhI A–D in [emim]OTs was used, the
liquid A, B, C, or D was carried out in [emim]OTs. As recovered ionic-liquid reaction medium could not be re-
shown in Table 1, various a-tosyloxyketones were effi- used due to the lack of iodobenzene.
ciently prepared in good to moderate yields from the reac-
tion of ketones under the same conditions. Moreover, after
the extraction of a-tosyloxyketones and byproduct
(MCBA) with ethyl acetate from the reaction mixture,
Table 2 a-Tosyloxylation of Ketone with MCPBA in Recovered
Ionic-Liquid Reaction Media
O
O
MCPBA (1.3 equiv),
a-tosyloxyketones could be simply obtained by washing
PTSA·H2O (1.1 equiv)
CH2
OTs
Me
A, B, C, or D (0.1 equiv),
[emim]OTs (2 mL)
50 °C, 5 h
Table 1 a-Tosyloxylation of Ketones with IL-Supported PhI
MCPBA (1.3 equiv)
PTSA·H2O (1.1 equiv)
O
O
Iodoarene
Yield (%)
R'
OTs
R'
R
R
A, B, C, or D (0.1 equiv),
1st
82
76
78
78
84
2nd
3rd
73
36
74
69
0
[emim]OTs (2 mL), 50 °C, 5 h
A
82
71
80
78
<1
Entry Product
Yields (%)a
B
A
B
C
D
C
O
D
1
82
83
80
39
67
70
48
67
PhI
OTs
O
A plausible reaction pathway for the present IL-supported
PhI-catalyzed a-tosyloxylation of ketones is shown in
Scheme 1. Finally, after the formation of a-tosyloxy-
acetophenone in the present reaction system, thioamides
i.e., thioacetoamide and thiobenzamide, were added to the
reaction mixture of [emim]OTs to provide the corre-
sponding thiazoles in good to moderate yields as shown in
Table 3. Especially, IL-supported PhI A showed the best
reactivity. Moreover, after the extraction of thiazoles with
ethyl acetate, the recovered ionic-liquid reaction media
containing a catalytic amount of IL-supported PhI A could
be reused for the same direct preparation of thiazoles,
keeping good to moderate yields until the third time as
shown in Table 4.
2
60
58
OTs
OTs
Me
O
3
77
76
Cl
O
4
65
70
72
71
OTs
O2N
O
O
5
6
83b
81b
75b
75b
63b
52b
70b
56b
OTs
OTs
In conclusion, various ketones were smoothly converted
into the corresponding a-tosyloxyketones with MCPBA
and p-toluenesulfonic acid in the presence of a catalytic
amount of IL-supported PhI in [emim]OTs. The present
ionic liquid reaction media containing a catalytic amount
of IL-supported PhI could be reused for the same a-tosyl-
oxylation of ketones, keeping good to moderate yields.
Moreover, thiazoles could be directly obtained from the
ketone without isolation of a-tosyloxyketones, and the
ionic-liquid reaction media containing a catalytic amount
of IL-supported PhI could be reused for the same prepara-
tion of thiazoles.
O
7
57
57
64
66
61
62
69
53
OTs
O
8
OTs
Further synthetic study using IL-supported PhI in ionic
liquids is under way in this laboratory.
a Isolated yield.
b PTSA·H2O (5.0 equiv) was used.
Synlett 2007, No. 14, 2168–2172 © Thieme Stuttgart · New York

2170
J. Akiike et al.
LETTER
OH
R'
O
Table 4 Direct Preparation of Thiazoles in Recovered Ionic-Liquid
Reaction Media
R'
R
R
R
S
O
MCPBA (1.3 equiv),
PTSA·H2O (1.1 equiv), 50 °C, 5 h
1)
Me
TsO–
N
O
2) RC(S)NH2 (1.1 equiv), 80 °C, 2 h
O
R'
R
R'
OTs
A (0.1 equiv), [emim]OTs (2 mL)
R
I
IL
OH2
+
Yield (%)
R
1st
72
66
2nd
67
3rd
56
OH
I
Me
Ph
IL
I
IL
73
52
OTs
mixture was stirred for 5 h at 50 °C. After the reaction, a-tosyloxy-
acetophenone was isolated as the same procedure mentioned above.
Typical Experimental Procedure for Preparation of Thiaozles23
To a mixture of acetophenone (1 mmol, 120 mg), A (0.1 mmol, 43.7
mg), and PTSA·H2O (1.1 mmol, 209 mg) in [emim]OTs (2 mL) was
added MCPBA (65% purity, 1.3 mmol, 345 mg). The obtained mix-
ture was stirred for 5 h at 50 °C under an argon atmosphere. Then,
thioacetoamide (1.1 mmol, 75.1 mg) was added to the reaction mix-
ture, and the obtained mixture was warmed for 2 h at 80 °C. Then
the reaction mixture was extracted with EtOAc (20 × 2 mL). The
extract was washed with aq sat. NaHCO3 solution once and dried,
and the solvent was removed to provide crude 2-methyl-4-phenyl-
thiazole (purity: >90%). Pure 2-methyl-4-phenylthiazole was
obtained in 72% yield by the treatment of flash column chromatog-
raphy (eluent: hexane–EtOAc = 9:1). When the ionic-liquid reac-
tion medium was reused, it was dried by vacuum pump for 2 h at r.t.
to remove volatile materials. Then acetophenone (1 mmol, 120 mg),
PTSA·H2O (1.1 mmol, 209 mg), and finally MCPBA (65% purity,
1.3 mmol, 345 mg) were added to the ionic liquid, and the obtained
mixture was stirred for 5 h at 50 °C. Then thioacetoamide (1.1
mmol, 75.1 mg) was added to the reaction mixture, and the obtained
mixture was warmed for 2 h at 80 °C. After the reaction, the mixture
was extracted with EtOAc (20 × 2 mL). The extract was washed
with aq sat. NaHCO3 solution once and dried, and the solvent was
removed to provide 2-methyl-4-phenylthiazole.
MCPBA, PTSA·H2O
MCBA
Scheme 1 Reaction pathway for IL-supported PhI-catalyzed
a-tosyloxylation of ketones
Table 3 Direct Preparation of Thiazoles Using Thioamides
R
S
O
MCPBA (1.3 equiv),
PTSA·H2O (1.1 equiv), 50 °C, 5 h
1)
Me
N
2) RC(S)NH2 (1.1 equiv), 80 °C, 2 h
A, B, C, or D (0.1 equiv),
[emim]OTs (2 mL)
Iodoarene
Yield (%)
R = Me
R = Ph
66
A
B
C
D
72
37
58
62
63
62
Acknowledgment
66
Financial support of a Grant-in-Aid for Scientific Research on
Priority Areas from the Ministry of Education, Science, Sports and
Culture of Japan is gratefully acknowledged.
Typical Experimental Procedure for Preparation of a-
Tosyloxyketones23
References and Notes
To a mixture of acetophenone (1 mmol, 120 mg), A (0.1 mmol, 43.7
mg) and PTSA·H2O (1.1 mmol, 209 mg) in [emim]OTs (2 mL) was
added MCPBA (65% purity, 1.3 mmol, 345 mg). The obtained mix-
ture was stirred for 5 h at 50 °C under an argon atmosphere. Then,
the reaction mixture was extracted with EtOAc (20 × 2 mL). The
extract was washed with aq sat. NaHCO3 solution once and dried,
and the solvent was removed to provide crude a-tosyloxyacetophe-
none (purity: >90%). Pure a-tosyloxyacetophenone was obtained in
82% yield by the treatment of flash column chromatography (elu-
ent: hexane–EtOAc = 3:1). When the ionic-liquid reaction medium
was reused, it was dried by vacuum pump for 2 h at r.t. to remove
volatile materials. Then, acetophenone (1 mmol, 120 mg), PT-
SA·H2O (1.1 mmol, 209 mg), and finally MCPBA (65% purity, 1.3
mmol, 345 mg) were added to the ionic liquid, and the obtained
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Commun. 2005, 325. (b) Handy, S. T. J. Org. Chem. 2006,
71, 4659. (c) Law, M. C.; Wong, K.; Chen, T. H. Chem.
Commun. 2006, 2457.
(21) Yoshino, T.; Imori, S.; Togo, H. Tetrahedron 2006, 62,
1309.
(22) Imori, S.; Togo, H. Synlett 2006, 2629.
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J. Akiike et al.
LETTER
(23) a-Tosyloxyketones
(s, 2 H), 7.37 (d, J = 8.3 Hz, 2 H), 7.83 (d, J = 8.3 Hz, 2 H),
8.03 (d, J = 8.9 Hz, 2 H), 8.32 (d, J = 8.9 Hz, 2 H).
a-Tosyloxypropiophenone
a-Tosyloxyacetophenone
Mp 90 °C (lit.2h 90–91 °C). IR (KBr): 1180, 1360, 1715
cm–1. 1H NMR (400 MHz, CDCl3): d = 2.45 (s, 3 H), 5.27 (s,
2 H), 7.35 (d, J = 8.5 Hz, 2 H), 7.47 (t, J = 8.2 Hz, 2 H), 7.61
(t, J = 8.2 Hz, 1 H), 7.84 (d, J = 8.2 Hz, 2 H), 7.85 (d, J = 8.2
Hz, 2 H).
Mp 68 °C (Lit.24 68–69 °C). IR (KBr): 1170, 1370, 1700
cm–1. 1H NMR (400 MHz, CDCl3): d = 1.60 (d, J = 7.0 Hz,
3 H), 2.41 (s, 3 H), 5.79 (q, J = 7.0 Hz, 1 H), 7.29 (d, J = 8.1
Hz, 2 H), 7.46 (t, J = 7.2 Hz, 2 H), 7.60 (t, J = 7.2 Hz, 1 H),
7.75 (d, J = 7.2 Hz, 2 H), 7.88 (d, J = 8.1 Hz, 2 H).
Thiazoles
a-Tosyloxy-p-methylacetophenone
Mp 80 °C (lit.24 82–83 °C). IR (KBr): 1170, 1350, 1700
cm–1. 1H NMR (400 MHz, CDCl3): d = 2.41 (s, 3 H), 2.45 (s,
3 H), 5.24 (s, 2 H), 7.26 (d, J = 8.1 Hz, 2 H), 7.35 (d, J = 8.2
Hz, 2 H), 7.74 (d, J = 8.1 Hz, 2 H), 7.86 (d, J = 8.2 Hz, 2 H).
a-Tosyloxy-p-chloroacetophenone
2-Methyl-4-phenylthiazole
Mp 64 °C (lit.25 67 °C). IR (KBr): 1600 cm–1. 1H NMR (400
MHz, CDCl3): d = 2.78 (s, 3 H), 7.31 (s, 1 H), 7.32 (t, J = 7.5
Hz, 1 H), 7.41 (t, J = 7.5 Hz, 2 H), 7.87 (d, J = 7.5 Hz, 2 H).
2,4-Diphenylthiazole
Mp 123 °C (lit.24 125 °C). IR (KBr): 1190, 1360, 1710 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.46 (s, 3 H), 5.21 (s, 2 H),
7.35 (d, J = 8.4 Hz, 2 H), 7.45 (d, J = 8.6 Hz, 2 H), 7.80 (d,
J = 8.6 Hz, 2 H), 7.84 (d, J = 8.4 Hz, 2 H).
Mp 167 °C (lit.26 168 °C). IR (KBr): 1600 cm–1. 1H NMR
(400 MHz, CDCl3): d = 7.27 (t, J = 7.5 Hz, 1 H), 7.35–7.45
(m, 6 H), 7.75 (m, 2 H), 8.05 (d, J = 6.8 Hz, 2 H).
(24) Khanna, M. S.; G rag, C. P.; Kapoor, R. P. Tetrahedron Lett.
1992, 33, 1495.
a-Tosyloxy-p-nitroacetophenone
Mp 137 °C (lit.24 130–131 °C). IR (KBr): 1180, 1340, 1710
cm–1. 1H NMR (400 MHz, CDCl3): d = 2.47 (s, 3 H), 5.25
(25) Kar, J. N.; Acharya, R. C.; Rout, M. K. J. Org. Chem. 1973,
38, 2164.
(26) Ishida, M.; Nakanishi, H.; Kato, S. Chem. Lett. 1984, 1691.
Synlett 2007, No. 14, 2168–2172 © Thieme Stuttgart · New York

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