Organic iodine(V) compounds as terminal oxidants in iron(III) phthalocyanine catalyzed oxidation of alcohols

Article abstract of DOI:10.1016/j.tetlet.2008.10.060

The pseudocyclic iodine(V) oxidants, such as esters of iodoxybenzoic acid (IBX-esters) and 2-iodylphenol ethers, can serve as stable and efficient sources of oxygen in catalytic oxidations, and their reactivity is similar to the commonly used thermally unstable and potentially explosive iodosylbenzene. In a specific example, primary or secondary benzylic alcohols are selectively oxidized by isopropyl IBX-ester in the presence of μ-oxo-(tetra-tert-butylphthalocyaninato)iron(III) (0.1 mol equiv) in dichloromethane at room temperature in 0.5-2 h to afford the respective carbonyl compounds in 100% conversion and preparative yields 91-95% after column chromatography.

Full text of DOI:10.1016/j.tetlet.2008.10.060

Tetrahedron Letters 49 (2008) 7410–7412
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Organic iodine(V) compounds as terminal oxidants in iron(III)
phthalocyanine catalyzed oxidation of alcohols
*
*
Ivan M. Geraskin, Matthew W. Luedtke, Heather M. Neu, Victor N. Nemykin , Viktor V. Zhdankin
Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN 55812, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The pseudocyclic iodine(V) oxidants, such as esters of iodoxybenzoic acid (IBX-esters) and 2-iodylphenol
ethers, can serve as stable and efficient sources of oxygen in catalytic oxidations, and their reactivity is
similar to the commonly used thermally unstable and potentially explosive iodosylbenzene. In a specific
example, primary or secondary benzylic alcohols are selectively oxidized by isopropyl IBX-ester in the
Received 18 September 2008
Revised 13 October 2008
Accepted 14 October 2008
Available online 18 October 2008
presence of l-oxo-(tetra-tert-butylphthalocyaninato)iron(III) (0.1 mol equiv) in dichloromethane at room
temperature in 0.5–2 h to afford the respective carbonyl compounds in 100% conversion and preparative
yields 91–95% after column chromatography.
Ó 2008 Elsevier Ltd. All rights reserved.
Hypervalent iodine compounds are used extensively in organic
synthesis as highly selective and environmentally friendly oxidiz-
ing reagents.1 Among these reagents, iodosylbenzene, (PhIO)n, is
particularly important as an oxygen transfer agent that has found
widespread application in catalytic oxygenation reactions after
the discovery of its supreme efficacy as a source of oxygen atoms
for oxidations catalyzed by cytochrome P-450 and by discrete tran-
sition metal complexes.2,3 Despite its usefulness as an oxidant,
practical applications of iodosylbenzene are hampered by its low
solubility in non-reactive media,3 as well as low thermal stability
and explosive properties upon moderate heating.4
t-Bu
t-Bu
t-Bu
N
Fe
Ph
M
N
N
N
N
N
N
N
t-Bu
t-Bu
N
N
N
N
t-Bu
Ph
O
N
Ph
t-Bu
N
N
Fe
N
N
N
N
N
Ph
t-Bu
5, M = Co
6, M = Ru(CO)
4
In this Letter, we report preliminary results on the use of stable
and soluble pseudocyclic hypervalent iodine(V) reagents 1–3
(Fig. 1) as terminal oxidants in biomimetic oxidation of alcohols
catalyzed by the Fe(III) phthalocyanine complex 4 or metal por-
phyrin complexes 5 and 6 (Fig. 2). Complex 4 was prepared using
direct high-temperature reaction between 4-tert-butylphthalonit-
rile and iron(II) acetate as described previously,5 while Co(II) tetra-
phenylporphyrin 5 and Ru(II)-carbonyl tetraphenylporphyrin 6
were used from commercial sources.
Figure 2. Iron(III) phthalocyanine 4 and metal porphyrin complexes 5 and 6.
Isopropyl ester of 2-iodylbenzoic acid 1 was prepared by the
hypochlorite oxidation of the readily available isopropyl ester of
2-iodobenzoic acid and was isolated in the form of a stable, white,
microcrystalline solid.6a Compound 1 is also commercially avail-
able from several chemical companies.6b 2-Iodylbenzamide 27a
and 2-iodylphenol ether 37b were prepared by oxidation of the
respective iodides using dimethyldioxirane. Both reagents are iso-
lated as stable and non-explosive microcrystalline products. The
previously reported X-ray studies of compounds 1–3 revealed the
presence of strong intramolecular IÁ Á ÁO interactions, which par-
tially replace the intermolecular IÁ Á ÁO secondary bonds disrupting
the polymeric structure typical of other ArIO2.6,7 Due to this struc-
tural feature, compounds 1–3 have excellent solubility in non-po-
lar organic solvents and can be used as efficient and convenient
oxidizing reagents.6–8
O
O
O
O
O
O
I
I
I
O
O
OBu
HN
CO2CH3
Oi-Pr
3
2
1
2-iodylphenol ether
IBX amide
IBX ester
Figure 1. Hypervalent iodine(V) oxidants.
We have investigated catalytic oxidation of alcohols to carbonyl
compounds using oxidants 1–3 and complexes 4–6. The use of iod-
osylbenzene in the catalytic oxidation of alcohols in the presence
* Corresponding authors. Tel.: +1 218 726 6902; fax: +1 218 726 7394.
E-mail address: vzhdanki@d.umn.edu (V. V. Zhdankin).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.10.060

I. M. Geraskin et al. / Tetrahedron Letters 49 (2008) 7410–7412
7411
of various transition metal complexes has previously been docu-
mented in the literature.9
solution was analyzed by GC–MS to determine the conversion of
alcohol 7 to the respective carbonyl compound 8. According to
the GC–MS and NMR data, carbonyl compounds 8 and the appro-
priate iodides resulting from the reduction of reagents 1–3 were
the only products formed under these reaction conditions. Dichlo-
romethane was found to be the best solvent; the conversion was
found to be much lower when the oxidation was performed in
In a typical procedure, the oxidation of alcohols was carried out
at room temperature in dry dichloromethane with 0.7 mol equiv
(1.4 equiv of active oxygene) of the iodine(V) reagent and 0.1 equiv
of the appropriate catalyst (Table 1).10 After indicated time, the
catalyst was removed by flash chromatography and the obtained
Table 1
Catalytic oxidation of alcohols 7 to carbonyl compounds 8 using hypervalent iodine reagentsa
R1
R1
reagent 1-3, catalyst
R
O
CH2Cl2
R
OH
8
7
Entry
Reagent
Catalyst
Substrate 7
Conversion (preparative yield) (%)
Time (h)
1a
1b
1c
1d
1e
1f
1
1
1
2
4
5
6
4
4
4
100 (95)
15
100
31
11
68
1
22
1.5
2.5
2
OH
O
3
PhIOb
3
1g
2a
2b
2c
2d
2e
3a
3b
3c
4a
1
1
1
1
3
1
1
1
3
1
None
4
5
6
0
100
0
94
53
24
1.5
48
3
3
168
2
2.5
3
0.5
OH
4
OH
None
55
4
6
4
4
100 (91)
100
54
100
OH
O2N
4b
4c
4d
4e
5
1
1
3
5
6
4
4
4
3
24
1
0.5
1.5
3
100
100
96
OH
PhIOb
1
100
NO2
6a
6b
6c
6d
7
1
1
1
3
1
4
31
5
4
2.5
5.6
3
4c
6
70c
100
31
OH
OH
4
4
24
S
S
OH
8
1
4
20d
3
9a
9b
9c
10a
10b
1
3
4
4
4
100
100
100
22
1
2.5
1
7
3
OH
OH
PhIOb
1
1
4
4c
25c
OH
11
12
1
1
1
4
4
4
11
10
6
8
OH
4.5
3.5
13
OH
a
All oxidations were carried out at room temperature in dry dichloromethane with 0.7 equiv of reagents 1, 2, or 3 and 0.1 equiv of catalyst. Catalyst was removed by flash
chromatography and obtained solution was analyzed by GC–MS.
b
1.5 equiv of PhIO was used.
Oxidations were carried out under reflux conditions.
No products of oxidation on sulfur were observed.
c
d

7412
I. M. Geraskin et al. / Tetrahedron Letters 49 (2008) 7410–7412
toluene or acetonitrile. The results of the oxidations are summa-
rized in Table 1.
Fund, administered by the American Chemical Society (Grant
PRF-45510-GB-3).
Using benzylic alcohols as model substrates, we have found that
IBX-ester 1 is the most efficient stoichiometric oxidant in the cata-
lytic oxidation reactions. Indeed, the oxidation of 4-methoxybenzyl
alcohol using oxidant 1 at room temperature in the presence of
Fe(III) phthalocyanine complex 4 (10 mol %) affords the respective
aldehyde in a 100% conversion (95% isolated yield after chromato-
graphy) after 1 h of stirring at room temperature (Table 1, entry
1a). The conversion is much lower when reagents 2 and 3 are em-
ployed for the oxidation of benzylic alcohols under similar condi-
tions using the same catalyst 4 (entries 1d, 1e, 2d, 3c, 4d, and
6d). Iron(III) phthalocyanine complex 4 and ruthenium(II)-car-
bonyl tetraphenylporphyrin 6 are the most efficient catalysts in
these oxidations. The oxidations in the presence of Ru(II) complex
6 (entries 1c, 2c, 3b, 4c, and 6c) proceed only slightly slower com-
pared to the Fe(III) complex 4 (entries 1a, 2a, 3a, 4a, 5, and 6a,b),
while the Co(II) tetraphenylporphyrin 5 did not show any signifi-
cant catalytic effect (entries 1b, 2b, and 4b). The availability and
low cost of iron(III) complex 4 as compared those of to the ruthe-
nium porphyrin 6 clearly make it a potentially useful reagent for
biomimetic catalytic transformations.
The oxidation of alcohols with reagent 1 in the absence of cat-
alyst proceeds extremely slow and shows measurable conversion
to the aldehyde only after 4–7 days of stirring at room temperature
(entries 1g and 2e).11 The sulfur-containing benzylic alcohols (en-
tries 7 and 8) show significantly lower reactivity in the catalytic
oxidations, and the oxidation of organic sulfur to sulfoxide or sul-
fone is not observed under these conditions. The allylic alcohol
demonstrates about the same reactivity in the catalytic oxidations
(entries 9a,b), while the aliphatic substrates are much less reactive
(entries 10–13).
References and notes
1. (a) Moriarty, R. M.; Prakash, O. Hypervalent Iodine in Organic Chemistry:
Chemical Transformations; Wiley-Interscience, 2008; (b) Wirth, T., Ed.;
Hypervalent Iodine Chemistry: Modern Developments in Organic Synthesis.
[In: Top. Curr. Chem., 2003; 224], 2003; (c) Varvoglis, A. Hypervalent Iodine in
Organic Synthesis; Academic Press: London, 1997; (d) Koser, G. F. Adv.
Heterocycl. Chem. 2004, 86, 225–292; (e) Zhdankin, V. V. Sci. Synth. 2007, 31a,
161–234; (f) Ladziata, U.; Zhdankin, V. V. ARKIVOC 2006, ix, 26–58; (g) Ochiai,
M. Coord. Chem. Rev. 2006, 250, 2771–2781; (h) Ochiai, M. Chem. Rec. 2007, 7,
12–23; (i) Deprez, N. R.; Sanford, M. S. Inorg. Chem. 2007, 46, 1924–1935; (j)
Tohma, H.; Kita, Y. Adv. Synth. Catal. 2004, 346, 111–124; (k) Kita, Y.; Fujioka, H.
Pure Appl. Chem. 2007, 79, 701–713; (l) Quideau, S.; Pouysegu, L.; Deffieux, D.
Synlett 2008, 467–495; (m) Togo, H.; Sakuratani, K. Synlett 2002, 1966–1975;
(o) Feldman, K. S. ARKIVOC 2003, vi, 179–190.
2. (a) Groves, J. T.; Nemo, T. E.; Myers, R. S. J. Am. Chem. Soc. 1979, 101, 1032–
1033; (b) Moro-oka, Y. Catal. Today 1998, 45, 3–12; (c) Moro-oka, Y.; Akita, M.
Catal. Today 1998, 41, 327–338; (d) Noyori, R. Asymmetric Catalysis in Organic
Synthesis, Wiley, New York, 1994.
3. (a) Moriarty, R. M.; Kosmeder, J. W.; Zhdankin, V. V. ‘Iodosylbenzene’ in
Encyclopedia of Reagents for Organic Synthesis, Wiley, Chichester, 2004; (b)
Stang, P. J.; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123–1178; (c) Zhdankin, V. V.;
Stang, P. J. Chem. Rev. 2002, 102, 2523–2584.
4. Drying iodosylbenzene at elevated temperatures should be avoided; a violent
explosion of 3.0 g PhIO upon drying at 110 °C in vacuum has recently been
reported: McQuaid, K. M.; Pettus, T. R. R. Synlett 2004, 2403–2405.
5. (a) Nemykin, V. N.; Addei-Maanu, C.; Koposov, A. Y.; Tretyakova, I. N.; Polshyn,
E. V. J. Porphyrins Phthalocyanines 2006, 10, 793; (b) Nemykin, V. N.; Chernii, V.
Y.; Volkov, S. V.; Bundina, N. I.; Kaliya, O. L.; Li, V. D.; Lukyanets, E. A. J.
Porphyrins Phthalocyanines 1999, 3, 87–98.
6. (a) Zhdankin, V. V.; Koposov, A. Y.; Litvinov, D. N.; Ferguson, M. J.; McDonald,
R.; Luu, T.; Tykwinski, R. R. J. Org. Chem. 2005, 70, 6484–6491; (b) Zhdankin, V.
V.; Litvinov, D. N.; Koposov, A. Y.; Luu, T.; Ferguson, M. J.; McDonald, R.;
Tykwinski, R. R. Chem. Commun. 2004, 106–107; (c) According to SciFinder
Scholar, compound 1 (Benzoic Acid, 2-iodyl, 1-methylethyl ester, Registry
number 674776-90-0) is currently available from three chemical companies:
AAT Pharmaceutical, LLC (USA), Atlantic SciTech Group, Inc. (USA), and
SinoChemexper Company (China).
IBX ester 1 and iodosylbenzene show similar reactivity in the
oxidation of same substrates in the presence of Fe(III) phthalocya-
nine complex 4 as catalyst (compare entries 1a and 1f, 4a and 4e,
9a and 9c). Both iodosylbenzene and reagent 1 are commercially
available or can be conveniently prepared from common precur-
sors. However, in contrast to the insoluble, thermally unstable
and potentially explosive iodosylbenzene,3,4 reagent 1 is soluble
in organic solvents, can be stored for extended periods at room
temperature, and is not explosive. The results of our comparative
studies (Table 1) confirm that IBX ester 1 can be effectively used
as a stoichiometric oxidant in biomimetic oxidations catalyzed
by metal porphyrin or phthalocyanine complexes.
7. (a) Zhdankin, V. V.; Koposov, A. Y.; Netzel, B. C.; Yashin, N. V.; Rempel, B. P.;
Ferguson, M. J.; Tykwinski, R. R. Angew. Chem., Int. Ed. 2003, 42, 2194–2196; (b)
Koposov, A. Y.; Karimov, R. R.; Geraskin, I. M.; Nemykin, V. N.; Zhdankin, V. V. J.
Org. Chem. 2006, 71, 8452–8458.
8. Koposov, A. Y.; Zhdankin, V. V. Synthesis 2005, 22–24.
9. (a) Yang, Z. W.; Kang, Q. X.; Quan, F.; Lei, Z. Q. J. Mol. Catal. A 2007, 261, 190–
195; (b) Vatele, J.-M. Synlett 2006, 2055–2058; (c) Adam, W.; Gelalcha, F. G.;
Saha-Moeller, C. R.; Stegmann, V. R. J. Org. Chem. 2000, 65, 1915–1918; (d)
Mueller, P.; Godoy, J. Tetrahedron Lett. 1981, 22, 2361–2364.
10. Typical procedure: To a vigorously stirred solution of reagents 1–3 (0.08 mmol)
and catalysts 4–6 (0.011 mmol) in dry dichloromethane (3 ml), the appropriate
alcohol (0.11 mmol) was added. The resulting solution was stirred at room
temperature for the indicated time (Table 1). A portion of the crude reaction
mixture (0.1 ml) was passed through 1 cm of silica gel suspended in a pasteur
pipet and washed with the mixture of hexane and ethyl acetate 3:2 (1 ml). The
obtained solution was analyzed by GC–MS.
11. It was previously reported that reagents 1 and 3 do not oxidize alcohols in
dichloromethane at room temperature in the absence of acids or Lewis
acids.6,7b IBX-amide 2 can effectively oxidize alcohols without catalysts,7a and
in fact the addition of Fe(III) phthalocyanine complex 4 does not lead to any
improvement of oxidative reactivity of reagent 2 (entry 1d of Table 1).
Acknowledgments
This work was supported by a research Grant from the National
Science Foundation (Grant CHE-0702734) and Petroleum Research