Highly efficient RuCl3-catalyzed disproportionation of (diacetoxyiodo)benzene to iodylbenzene and iodobenzene; leading to the efficient oxidation of alcohols to carbonyl compounds

Article abstract of DOI:10.1016/j.tetlet.2006.06.100

(Diacetoxyiodo)benzene (DIB) selectively oxidizes primary and secondary alcohols to the respective carbonyl compounds in the presence of RuCl₃ (0.8-1.0 mol %) at room temperature in aqueous acetonitrile. This reaction proceeds via an initial instantaneous Ru-catalyzed disproportionation of DIB to iodobenzene and iodylbenzene with the latter acting as the actual stoichiometric oxidant toward alcohols.

Full text of DOI:10.1016/j.tetlet.2006.06.100

Tetrahedron Letters 47 (2006) 6305–6308
Highly efficient RuCl3-catalyzed disproportionation
of (diacetoxyiodo)benzene to iodylbenzene and iodobenzene;
leading to the efficient oxidation of alcohols to carbonyl compounds
Mekhman S. Yusubov,a Ki-Whan Chi,b Joo Yeon Park,b
Rashad Karimovc and Viktor V. Zhdankinc,*
aThe Siberian State Medical University, 2 Moskovsky trakt, 634050 Tomsk, Russia and The Tomsk Polytechnic University,
30 Lenin st., 634050 Tomsk, Russia
bUniversity of Ulsan, 680-749 Ulsan, Republic of Korea
cDepartment of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, Minnesota 55812, USA
Received 25 May 2006; revised 16 June 2006; accepted 19 June 2006
Available online 17 July 2006
Abstract—(Diacetoxyiodo)benzene (DIB) selectively oxidizes primary and secondary alcohols to the respective carbonyl compounds
in the presence of RuCl3 (0.8–1.0 mol %) at room temperature in aqueous acetonitrile. This reaction proceeds via an initial instan-
taneous Ru-catalyzed disproportionation of DIB to iodobenzene and iodylbenzene with the latter acting as the actual stoichiometric
oxidant toward alcohols.
Ó 2006 Elsevier Ltd. All rights reserved.
During the past decade hypervalent iodine compounds
have attracted a significant interest as mild, selective and
environmentally benign reagents in synthetic organic
chemistry.1 It has also been found that transition metals
have a dramatic catalytic effect on some oxidations
with hypervalent iodine reagents.1–4 In particular,
iodosylbenzene is widely used as an oxidant in the tran-
sition metal catalyzed epoxidation of alkenes and
hydroxylation of hydrocarbons.1 Likewise, (diacetoxy-
iodo)arenes are efficient oxidizers in the Pd(OAc)2-cata-
lyzed selective acetoxylations of arene and alkene C–H
bonds.2 The catalytic effect of transition metals on the
synthetically important reaction of oxidation of alcohols
by hypervalent iodine reagents has been less investi-
gated.3,4 It has been demonstrated that benzylic and
allylic alcohols can be oxidized by iodosylbenzene to
the corresponding carbonyl compounds in the presence
of (salen)Cr(III) complex (15 mol %) and 4-phenylpyri-
dine N-oxide (30 mol %).3 Mueller and Godoy reported
in 1981 that several complexes of ruthenium can cata-
lyze the oxidation of alcohols to carbonyl compounds
and carboxylic acids using excess iodosylbenzene as
the oxidizer in dichloromethane solution at room tem-
perature.4 In the present letter we want to report a sim-
ple and highly efficient RuCl3-catalyzed selective
oxidation of alcohols to carbonyl compounds by
(diacetoxyiodo)benzene (DIB). We have also received
experimental evidence that this reaction proceeds via
an initial instantaneous Ru-catalyzed disproportion-
ation of DIB to iodobenzene and iodylbenzene with
the latter acting as the actual stoichiometric oxidant
toward alcohols.
We have found that the addition of RuCl3 (0.8–1.0
mol %) to the solution of equimolar amounts of (diacet-
oxyiodo)benzene and an alcohol at room temperature in
aqueous acetonitrile results in an instantaneous interac-
tion with the formation of a precipitate which then
slowly completely dissolves after stirring for 0.5–24 h
(reaction time varies for specific alcohols). NMR spectra
of the reaction mixtures indicated in each case an almost
quantitative conversion of alcohol to the respective carb-
onyl compound. The aldehydes and ketones (2) formed
from the oxidation of each alcohol (1) were further con-
verted to the 2,4-dinitrophenylhydrazone derivatives (3)
and identified by comparison of their melting points
with the ones reported in the literature data (Scheme
Keywords: Hypervalent iodine; (Diacetoxyiodo)benzene; Iodylbenzene;
Oxidation; Catalysis.
*
Corresponding author. Tel.: +1 218 7266902; fax: +1 218 7267394;
e-mail: vzhdanki@d.umn.edu
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.06.100

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M. S. Yusubov et al. / Tetrahedron Letters 47 (2006) 6305–6308
1).5 The preparative yields and melting points of
2,4-dinitrophenylhydrazones 3 obtained from alcohols
1 are summarized in Table 1.
crystalline precipitate that forms immediately after addi-
tion of RuCl3 to the solution of (diacetoxyiodo)benzene
and an alcohol in aqueous acetonitrile. Based on the
NMR data and melting point (229 °C, expl), this initial
product was identified as iodylbenzene, PhIO2. Further
investigation has revealed that alcohol (1) is not
To clarify the nature of the actual oxidizing species in
this reaction, we have isolated and identified the micro-
PhI(OAc)2 (1 equiv)
RuCl3 (0.8-1 mol%), rt
R1
R2
R1
R2
R1
2,4-(NO2)2C6H3NHNH2
O
2,4-(NO2)2C6H3NHN
OH
MeCN/H2O (5:1)
H2SO4, H2O
R2
3
2
1
Scheme 1.
Table 1. RuCl3-catalyzed oxidation of alcohols to carbonyl compounds by (diacetoxyiodo)benzene
Entry
Alcohol 1
Time (h)
Yield of 3a (%)
Mp of 3 (lit. mp) (°C)
Ref.
1
2
3
(+)-Menthol
3-Phenyl-1-propanol
1-Octanol
2.0
0.5
1.5
92
94
71
146–148 (145)
156–157 (152–153)
100–102 (100–101.5)
6
7
7
OH
4
1.5
96
256–258 (256.5–257.5)
8
9
5
6
PhCH2OH
1.0
1.5
95
241–242 (239–240)
Oil
79b
—
c
OH
7
1.5
2.5
5.0
1.5
0.5
90
93
73
88
82
147–148 (146–147)
157–159 (157–162)
259–261 (258.5–259.5)
239–241 (242)
10
7
OH
OH
8
OH
9
11
12
7
N
OH
10
11
S
OH
256–257 (258–259)
MeO
OH
12
13
14
9.3
6.0
24
70d
37e
62d
292–293 (293–294)
146–148 (148–150)
168–170 (164–166)
9
NO2
OH
13
14
OH
a Isolated yields of 2,4-dinitrophenylhydrazones.
b Yield of aldehyde (2) measured by GC.
c Aldehyde was identified by MS (M+ = 140.12).
d About 20% of unreacted alcohol present according to 1H NMR.
e Formation of black tar was observed in this reaction.

M. S. Yusubov et al. / Tetrahedron Letters 47 (2006) 6305–6308
6307
RuCl3 (0.4 mol %), rt
2PhI(OAc)2 + 4H2O
PhIO2 + PhI + 4AcOH
MeCN/H2O (5:1)
Scheme 2.
(i) PhIO2 (0.5 equiv), RuCl3 (1 mol %)
MeCN/H2O (5:1), rt
Ph
H
PhCH2OH
2,4-(NO2)2C6H3NHN
(ii) 2,4-(NO2)2C6H3NHNH2, H2SO4
4 (92%)
Scheme 3.
involved in the initial step of this reaction. The addition
of a catalytic RuCl3 (0.4 mol %) to a solution of (diacet-
oxyiodo)benzene in aqueous acetonitrile at room tem-
perature results in an instantaneous quantitative
disproportionation of DIB to a 1:1 mixture of iodobenz-
ene and iodylbenzene according to NMR data (Scheme
2). This unique and highly efficient disproportionation
can be conveniently performed in a preparatory scale
affording analytically pure PhIO2 in a moderate isolated
yield.15
latter acting as the actual stoichiometric oxidant toward
alcohols.
Acknowledgments
The authors gratefully acknowledge the National Sci-
ence Foundation for support of this work through
research Grant (CHE 0353541), NSF-MRI award (CHE
0416157) and University of Ulsan Research Fund 2006.
When this reaction is performed in the presence of an
alcohol, the initially formed iodylbenzene further acts
as the stoichiometric oxidant slowly converting alcohol
to the carbonyl compound. In a special experiment, ben-
zyl alcohol was oxidized with PhIO2 (0.5 equiv) in the
presence of RuCl3 (1 mol %) under conditions identical
to the reaction of (diacetoxyiodo)benzene (Table 1,
entry 5). The reaction (Scheme 3) was complete in
40 min affording the expected 2,4-dinitrophenylhydr-
azone 4 in a 92% isolated yield.16 This example (Scheme
3) illustrates that PhIO2 can serve as an efficient oxidizer
in the Ru-catalyzed oxidations of alcohols. In practical
use, however, the readily available and safe (diacetoxy-
iodo)benzene is a more convenient oxidizer compared
to the explosive and unavailable from commercial
sources iodylbenzene.
References and notes
1. (a) Hypervalent Iodine Chemistry; Wirth, T., Ed.; Springer:
Berlin, 2003; (b) Varvoglis, A. Hypervalent Iodine in
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Tohma, H.; Kita, Y. Adv. Synth. Catal. 2004, 346, 111; (d)
Wirth, T. Angew. Chem. Int. Ed. 2005, 44, 3656; (e)
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(f) Zhdankin, V. V. Curr. Org. Synth. 2005, 2, 121; (g)
Ladziata, U.; Zhdankin, V. V. ARKIVOC 2006, ix, 26.
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3. Adam, W.; Gelalcha, F. G.; Saha-Moeller, C. R.;
Stegmann, V. R. J. Org. Chem. 2000, 65, 1915.
It is known from the literature that RuCl3 as well as
other ruthenium salts and complexes can catalyze the
oxidation of alcohols with various stoichiometric oxi-
dants.17 For example, the H2O2–RuCl3 system can
non-selectively oxidize alcohols to carbonyl compounds
and carboxylic acids at 80 °C.18 It has been proposed in
particular that the oxo ruthenium complexes of a lower
oxidation state are involved as the active intermediates
in these catalytic cycles.18 We assume that the similar
intermediate oxo ruthenium complexes are responsible
for the oxygen transfer steps in the mechanisms of dis-
proportionation of iodine(III) species and oxidation of
alcohols.
4. Mueller, P.; Godoy, J. Tetrahedron Lett. 1981, 22, 2361.
5. General procedure for the RuCl3-catalyzed oxidation of
alcohols: To a solution of alcohol 1 (0.5 mmol) and
(diacetoxyiodo)benzene (161 mg, 0.5 mmol) in 1 mL of
aqueous acetonitrile (MeCN–H2O, 5:1) an aqueous solu-
tion of RuCl3 (8.0–10 lL of 0.5 M solution; 0.004–0.005
mmol) was added under stirring at room temperature. An
instantaneous formation of a cotton-like, off-white, pre-
cipitate was observed. The reaction mixture was stirred
until the complete dissolution of the initial precipitate (see
Table 1 for reaction times) and then 4–5 mL of a standard
solution of 2,4-dinitrophenylhydrazine (prepared from 3 g
2,4-DNP, 15 mL concd H2SO4, 70 mL EtOH, and 20 mL
H2O) was added. The precipitate of 2,4-dinitrophenylhydr-
azone 3 was filtered, washed with water, dried, and
recrystallized from 95% ethanol. Melting points and yields
of 2,4-dinitrophenylhydrazones 3 are listed in Table 1.
6. Allen, C. F. H. J. Am. Chem. Soc. 1930, 52, 2955.
7. Omura, K.; Swern, D. Tetrahedron 1978, 34, 1651.
8. Rinehart, K. L., Jr.; Gustafson, D. H. J. Org. Chem. 1960,
25, 1836.
In conclusion, we have found a simple and highly effi-
cient procedure of RuCl3-catalyzed selective oxidation
of alcohols to carbonyl compounds using (diacetoxy-
iodo)benzene. We have also received experimental
evidence that this reaction proceeds via an initial instan-
taneous Ru-catalyzed disproportionation of (diacetoxy-
iodo)benzene to iodobenzene and iodylbenzene with the
9. Jones, L. A.; Mueller, N. L. J. Org. Chem. 1962, 27, 2356.

6308
M. S. Yusubov et al. / Tetrahedron Letters 47 (2006) 6305–6308
10. Doering, W. v. E.; Denney, D. B. J. Am. Chem. Soc. 1955,
77, 4619.
(m, 3H); 13C NMR (DMSO-d6) d 150.8 (C-IO2), 131.7,
129.1, 126.6.
11. Newman, M. S.; Caflish, E. G., Jr. J. Am. Chem. Soc.
1958, 80, 862.
12. Dunn, F. W.; Waugh, T. D.; Dittmer, K. J. Am. Chem.
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Krezo, L. M. Dokl. Akad. Nauk SSSR 1969, 186, 1325.
15. Experimental procedure for RuCl3-catalyzed disproportion-
ation of (diacetoxyiodo)benzene: To a solution of (diacet-
oxyiodo)benzene (161 mg, 0.5 mmol) in 1 mL of aqueous
acetonitrile (MeCN–H2O, 5:1) an aqueous solution of
RuCl3 (4 lL of 0.5 M solution; 0.002 mmol) was added via
a syringe under stirring at room temperature. An imme-
diate formation of a white microcrystalline precipitate of
PhIO2 was observed. After additional stirring for 5 min,
the precipitate was filtered, washed with cold aqueous
acetonitrile (MeCN–H2O, 5:1), and dried to afford 36 mg
(61%) of iodylbenzene, mp 229–230 °C (expl), IR (KBr):
731, 713 (IO2);19 1H NMR (DMSO-d6) d 7.92 (m, 2H) 7.59
16. RuCl3-catalyzed oxidation of benzyl alcohol with iodylbenz-
ene: To a mixture of benzyl alcohol (108 mg, 1 mmol) and
iodylbenzene (161 mg, 0.5 mmol) in 1 mL of aqueous
acetonitrile (MeCN–H2O, 5:1) an aqueous solution of
RuCl3 (10 lL of 0.5 M solution; 0.005 mmol) was added
under stirring at room temperature. The reaction mixture
was stirred for 40 min until the complete dissolution of
iodylbenzene and then 9 mL of a standard solution of 2,4-
dinitrophenylhydrazine was added. The precipitate was
filtered, washed with water, and dried to afford 263 mg
(92%) of 1-benzylidene-2-(2,4-dinitrophenyl)hydrazine 4,
mp 241–242 °C (lit.9 239–240 °C).
17. For key references on ruthenium-catalyzed oxidations of
alcohols see: Marko, I. E.; Giles, P. R.; Tsukazaki, M.;
Chelle-Regnaut, I.; Urch, C. J.; Brown, S. M. J. Am.
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2001, 6, 881.