A Novel Efficient Synthesis of α-Keto Triflates

Article abstract of DOI:10.1081/SCC-120026318

The direct and efficient synthesis of α-keto triflates by the reaction of aromatic ketones with thallium(III) triflate is decribed.

Full text of DOI:10.1081/SCC-120026318

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A Novel Efficient Synthesis of α-Keto Triflates
a
a
Jong Chan Lee & Yong Chan Lee
a
Department of Chemistry , Chung-Ang University , Seoul, Korea
Published online: 19 Aug 2006.
To cite this article: Jong Chan Lee & Yong Chan Lee (2003) A Novel Efficient Synthesis of α-Keto Triflates, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:22, 3943-3946, DOI:
10.1081/SCC-120026318
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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 22, pp. 3943–3946, 2003
A Novel Efficient Synthesis of a-Keto Triflates
Jong Chan Lee* and Yong Chan Lee
Department of Chemistry,
Chung-Ang University, Seoul, Korea
ABSTRACT
The direct and efficient synthesis of a-keto triflates by the reaction of
aromatic ketones with thallium(III) triflate is decribed.
Key Words: Ketones; Sulfonates; Thallium(III); Triflates.
The a-keto triflates have attracted considerable attention in both
physical and synthetic organic chemistry mainly based on the intrinsically
[
1–3]
super leaving ability of trifluoromethanesulfonate ester (triflate) group.
Preparation of a-keto triflates have been generally achieved by the reaction
[
4]
of a-diazo ketones with trifluoromethanesulfonic acid or treatment of
[
1,5]
a-hydroxy ketones with trifluorosulfonic anhydride.
In addition, the
reaction of trimethylsilyl enol ethers with iodosobenzene in the presence
*Correspondence: Jong Chan Lee, Department of Chemistry, Chung-Ang
University, Seoul 156-756, Korea; E-mail: jclee@cau.ac.kr.
3
943
DOI: 10.1081/SCC-120026318
Copyright & 2003 by Marcel Dekker, Inc.
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Lee and Lee
of trimethylsilyl trifluoromethane sulfonate had been reported as a
[
6]
convenient alternative for the synthesis of a-keto triflates. However,
the preparation of required a-diazo ketones, a-hyrdoxy ketone, and
trimethylsilyl enol ether precursors limits the utility of these reactions.
Therefore, development of facile and direct method for the preparation
of a-keto triflates will be quite useful for their further synthetic
applications. Although there are few reports that deal with the Ritter
type reactions of intermediary a-keto triflates with nitrile solvents to
[7,8]
give substituted oxazoles,
there has been no report on the synthesis
and isolation of a-keto triflates formed from ketones. Recognizing the
lack of direct method leading to a-keto triflates, we thought that
thallium(III) triflate could be appropriate for the introduction of
triflate group to alpha position of carbonyl groups. This prediction
was based on the successful results obtained from thallium(III)
[
9,10]
sulfonate mediated a-sulfonyloxylation reaction of ketones.
Now we
wish to report here, thallium(III) triflate mediated direct synthetic method
for the a-keto triflates starting from ketones. Thallium(III) nitrate
trihydrate was reacted with trifluoromethanesulfonic acid (3.0 equiv.) in
aectonitrile to give thallium(III) triflate. After evaporation of solvent, the
residue was dissolved in dichloromethane and a ketone (1.0 eqiuv.)
was added to the reaction solution. The reaction of various ketones
with thallium(III) triflate at reflux for 2–4 h cleanly provided the corre-
sponding a-keto triflates (Sch. 1). Representative examples are shown in
Table 1. All of the reactions proceeded smoothly in satisfactory yields. It is
important to note that most of the reactions, except for cyclohexanone,
are almost quantitative in view of no starting ketones remained after the
reactions. The somewhat lower isolated yields are results of the loss of
the reactive products during the work-up procedures. All a-keto triflates
products exhibited spectral data consistent with assigned structures in the
literature.
In conclusion, the present report is the first to deal with the direct
conversion of ketones to the corresponding a-keto triflates. We believe
this new and facile protocol should find wide utilities particularly for the
reaction of a-keto triflates with various nucleophiles.
O
O
Tl(OTf)3
CH Cl
R2
R2
R1
R1
O
2
2
O S O
CF3
reflux, 2 - 4 h
Scheme 1.

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a-Keto Triflates
3945
Table 1. Synthesis of a-keto triflates from ketones.
1
2
R
a
Entry
R
Yield (%)
1
2
3
4
5
6
7
Ph
p-MeC
H
83
78
72
82
78
75
57
6
H
4
H
H
6 4
p-ClC H
Ph
p-MeC H
CH3
CH3
6
4
p-ClC
-(CH ) -
6
H
4
CH
3
2 4
a
Isolated yield.
EXPERIMENTAL
1
H NMR spectra were recorded on a Varian 2000 (300 MHz)
spectrometer. IR spectra were recorded with a Jasco FT/IR 5300 spectro-
photometer.
General Procedure
Thallium nitrate trihydrate (1.0 mmol) and trifluoromethanesulfonic
acid (3.0 mmol) were dissolved in acetonitrile (20 mL) and reaction mixture
was stirred for 10 min at room temperature to give thallium(III) triflate.
The acetonitrile was evaporated and the resulting residue was dissolved in
20 mL of dichloromethane. To the solution of thallium(III) triflate, a
ketone (1.0 mmol) was added and the mixture was stirred for 2–4 h
with reflux. The solvent was evaporated and the residue was washed
with hexane (2 ꢀ 20 mL), cold water (2 ꢀ 20 mL), and dried over MgSO .
4
After evaporation of the solvent, the residue was purified with column
chromatography (silica gel, ethyl acetate:hexane ¼ 1:2) to give pure
a-keto triflate.
ACKNOWLEDGMENTS
This research was supported by the Chung-Ang University research
grants in 2003.

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2
3
. Creary, X. J. Am. Chem. Soc. 1984, 106, 5568.
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33, 1495.
Received in Japan April 9, 2003