Simple direct synthesis of [bis(trifluoroacetoxy)iodo]arenes

Article abstract of DOI:10.1055/s-2006-942543

A modified procedure for the direct synthesis of hypervalent [bis(trifluoroacetoxy)iodo]arenes is described. It avoids the use of hazardous reagents with the workup being only an aqueous extraction. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942543

PRACTICAL SYNTHETIC PROCEDURES
3153
Simple Direct Synthesis of [Bis(trifluoroacetoxy)iodo]arenes
Simple
Direct
S
.
ynthesis of
[
K
Bis(trifluoroacetox
e
y)iodo]are
r
nes i Page, Thomas Wirth*
School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, UK
Fax +44(29)20876968; E-mail: wirth@cf.ac.uk
Received 26 May 2006; revised 27 June 2006
PSP
No70
Abstract: A modified procedure for the direct synthesis of hypervalent [bis(trifluoroacetoxy)iodo]arenes is described. It avoids the use of
hazardous reagents with the workup being only an aqueous extraction.
Key words: hydrogen peroxide, hypervalent compounds, iodine, oxidation
CF3
ligand
R
exchange
Ar
I
O
O
O
R
Ar
I
O
direct
synthesis
Ar
I
CF3
1
Scheme 1 Indirect and direct synthesis of [bis(trifluoroacetoxy)iodo]arenes 1
Hypervalent iodine compounds are now established re- A commonly used procedure is the ligand-exchange reac-
agents in organic synthesis. Their use as mild and efficient tion using (diacetoxyiodo)arenes and trifluoroacetic acid.4
oxidants is important, but many more applications of The success of this method is related to the electronic
these compounds have emerged recently. They range properties of the (diacetoxyiodo)arene – the reaction rate
from the formation of carbon–carbon bonds in phenol- of electron-poor substrates can be very low. Other indirect
coupling reactions or as benzyne precursors in the gener- methods include the reaction of (dichloroiodo)arenes with
ation of carbon–heteroatom bonds to the activation of car- silver trifluoroacetate5 or the reaction of iodosylarenes
bon–hydrogen bonds. Depending on the substrate, with trimethysilyl trifluoroacetate.6
rearrangements or fragmentations can also be induced by
The direct oxidation of iodoarenes, however, is still a
these reagents.1 They are an alternative to metal-contain-
more convenient method, although the choice of oxidants
ing reagents due to their low toxicity, stability, ease of
has to take into account the structure and the electronic
handling, and high efficiency. Although first reports on
properties of the iodoarene. Deactivated iodoarenes can
the catalytic use of hypervalent iodine reagents have re-
be oxidized by either nitric acid7 or sodium percarbonate8
cently appeared in the literature,2 most of the applications
together with trifluoroacetic anhydride. The oxidation
still rely on stoichiometric quantities of these compounds.
with trifluoroperacetic acid seems to be most convenient,
Of practical importance are hypervalent iodine com-
but requires 80% hydrogen peroxide, which is dangerous
pounds with halides (chloride, fluoride) and acetoxy or
and not commercially available.9 Very recently, the use of
trifluoroacetoxy groups as ligands. Among the growing li-
potassium persulfate with trifluoroacetic acid anhydride
brary of hypervalent iodine compounds are [bis(trifluoro-
was reported by Kitamura et al. in an efficient synthesis of
acetoxy)iodo]arenes 1, ArI(OCOCF3)2, originally
prepared by Yagupolskii et al.3 They have been applied as
potent and often chemoselective oxidants, and have a
broad appeal throughout organic synthesis.
[bis(trifluoroacetoxy)iodo]arenes.10 Herein we report the
direct synthesis of [bis(trifluoroacetoxy)iodo]arenes 1 us-
ing in situ generated trifluoroperacetic acid and describe a
variation of the procedure reported by Zhdankin and
Several methods have been published for the synthesis of Stang.9
[bis(trifluoroacetoxy)iodo]arenes. These reagents (1) can
The solubility of hydrogen peroxide is higher in organic
be prepared either by an indirect route, usually by a
ligand-exchange reaction on an already-oxidized io-
dine(III) compound, or by direct oxidation from aryl io-
dide precursor molecules.
solvents than in water.11 Consequently, urea can be re-
moved from solutions of the commercially available hy-
drogen peroxide–urea adduct in organic solvents by
extraction with water. The remaining solution of hydro-
gen peroxide in an organic solvent can then, after drying,
react with trifluoroacetic anhydride to generate trifluoro-
peracetic acid. If this reaction is performed in the presence
of an aryl iodide, the corresponding hypervalent [bis(tri-
SYNTHESIS 2006, No. 18, pp 3153–3155
x
x.
x
x
.
2
0
0
6
Advanced online publication: 02.08.2006
DOI: 10.1055/s-2006-942543; Art ID: T08406SS
© Georg Thieme Verlag Stuttgart · New York

3154
T. K. Page, T. Wirth
PRACTICAL SYNTHETIC PROCEDURES
Method A: 1. H2O2⋅urea, removal of urea
mation of trifluoroperacetic acid takes place around
–30 °C, as shown by low-temperature NMR studies of hy-
drogen peroxide–trifluoroacetic anhydride mixtures.
2. –40 °C, (F3C–CO)2O
Method B: 1. H2O2⋅urea, –40 °C, (F3C–CO)2O
2. removal of urea
In conclusion, we have improved an existing procedure
and avoided the use of hazardous 80% hydrogen peroxide
by replacement with hydrogen peroxide–urea adduct.
This method allows the synthesis of hypervalent iodine re-
agents at low temperatures and should be applicable to a
wide range of iodoarenes.
Ar
I
Ar I(OCOCF3)2
1
Scheme 2
fluoroacetoxy)iodo]arenes are obtained in good yields as
shown in Table 1 and described in general procedure A.
As an alternative to this protocol, a mixture of the hydro-
gen peroxide–urea adduct and trifluoroacetic anhydride [Bis(trifluoroacetoxy)iodo]arenes 1; General Procedure,
Method A
can be used directly for the generation of trifluoroperace-
tic acid. In the presence of an iodoarene, the hypervalent
iodine species 1 are generated, but the urea has to be re-
moved after the reaction. This protocol (general procedure
B) is therefore only suitable for hypervalent iodine com-
pounds that tolerate subsequent aqueous workup. The for-
H2O2·urea (216 mg, 2.29 mmol) was dissolved in a minimum
amount of deionized H2O (0.5 mL) and extracted with CH2Cl2
(3 × 6 mL). The combined organic phases were dried (Na2SO4) and
filtered to give a soln of H2O2 in CH2Cl2. This soln was cooled to
–40 °C and trifluoroacetic anhydride (1.27 mL, 9.17 mmol) was
added dropwise. After 30 min, the iodoarene (0.91 mmol) was add-
ed to the soln and the mixture stirred at –40 °C for a further 7 h. The
soln was warmed up to r.t. and stirred for 1 h. The solvent was re-
moved under reduced pressure to yield the corresponding [bis(tri-
fluoroacetoxy)iodo]arene.
Table 1 Direct Synthesis of [Bis(trifluoroacetoxy)iodo]arenes 1
[Bis(trifluoroacetoxy)iodo]arenes 1
Method
B
Yield (%)
96
[Bis(trifluoroacetoxy)iodo]arenes 1; General Procedure,
Method B
1a
1b
I(OCOCF3)2
Trifluoroacetic anhydride (1.27 mL, 9.17 mmol) was added drop-
wise to a stirred soln of H2O2·urea (216 mg, 2.29 mmol) in CH2Cl2
(4 mL) at –40 °C. After 30 min, the appropriate iodoarene (0.91
mmol) was added, and the resulting soln stirred at –40 °C for 7 h.
The soln was warmed up to r.t. and stirred for 1 h. The soln was
quickly washed with a small quantity of H2O, the organic phase sep-
arated, dried (MgSO4) and the solvent removed under reduced pres-
sure to yield the corresponding [bis(trifluoroacetoxy)iodo]arene.
B
A
91
65
I(OCOCF3)2
I(OCOCF3)2
1c
F
F
F
F
Spectroscopic data for known compounds can be found in the liter-
ature: 1a,10 1e,10 1b,12 1c,4b 1d,7b 1f,9 1i.13
1d
A
95
F
I(OCOCF3)2
1g
1H NMR (500 MHz, CDCl3): d = 2.04 (m, 2 H, CH2CHOMePh),
2.95 (m, 1 H, ArCH2), 3.08 (m, 1 H, ArCH2), 3.19 (s, 3 H, CH3),
4.15 (dd, J = 8.0, 2.8 Hz, 1 H, CH2CHOMe), 7.10–7.31 (m, 6 H,
ArH), 7.5 (d, J = 8.2 Hz, 1 H, ArH), 7.58 (t, J = 7.6 Hz, 1 H, ArH),
8.21 (d, J = 8.14 Hz, 1 H, ArH).
1e
1f
A
A
90
81
F
I(OCOCF3)2
I(OCOCF3)2
F3C
13C NMR (125.7 MHz, CDCl3): d = 35.5 (CH2CHOMe), 39.3
(ArCH2), 56.6 (OCH3), 83.4 (CH2CHOMe), 112.9 (q, JCF = 288 Hz,
CF3), 126.5, 126.8, 128.5, 128.7, 129.5, 131.1, 134.6 (CI), 138.3,
141.0, 144.5, 161.0 (q, JCF = 40 Hz, COCF3).
OMe
Ph
1g
1h
B
B
59
26
I(OCOCF3)2
CN
1h
1H NMR (500 MHz, CDCl3): d = 4.30 (s, 2 H, CH2), 7.57 (t, J = 7.7
Hz, 1 H, ArH), 7.87 (t, J = 7.6 Hz, 1 H, ArH), 7.98 (d, J = 7.7 Hz,
1 H, ArH), 8.40 (d, J = 7.9 Hz, 1 H, ArH).
I(OCOCF3)2
O
13C NMR (125.7 MHz, CDCl3): d = 27.5 (CH2), 112.6 (q, JCF = 289
Hz, CF3), 115.2 (CN), 126.2 (CI), 130.7, 131.9, 134.0, 135.4, 138.2,
161.3 (q, JCF = 41 Hz, COCF3).
1i
A
50a
O
I
OCOCF3
Acknowledgment
a Determined by NMR.
We thank the School of Chemistry, Cardiff University, for suppor-
ting this work.
Synthesis 2006, No. 18, 3153–3155 © Thieme Stuttgart · New York

PRACTICAL SYNTHETIC PROCEDURES
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Direct Synthesis of [Bis(trifluoroacetoxy)iodo]arenes
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Synthesis 2006, No. 18, 3153–3155 © Thieme Stuttgart · New York