Bis(trifluoroacetoxyiodo)benzene-induced activation of tert-butyl hydroperoxide for the direct oxyfunctionalization of arenes to quinones

Article abstract of DOI:10.1055/s-2004-832843

Various aromatic hydrocarbons were oxidized with bis(trifluoroacetoxyiodo) benzene (PIFA)/tert-butyl hydroperoxide system to afford the corresponding quinones. The reaction conditions and scope have been discussed in detail.

Full text of DOI:10.1055/s-2004-832843

LETTER
2151
Bis(trifluoroacetoxyiodo)benzene-Induced Activation of tert-Butyl
Hydroperoxide for the Direct Oxyfunctionalization of Arenes to Quinones
B
M
is(trifluoroacetoxyiod
u
o)benzene-I
s
t
c
tivatio
a
n
of tert-Bu
f
tyl
H
yd
a
Department of Chemistry, Ataturk University, 25240 Erzurum, Turkey
Fax +90(442)2360948; E-mail: hkilic@atauni.edu.tr
Received 20 April 2004
been reported. Very recently, we have described activa-
tion of hydrogen peroxide by the PIFA (1b) for the perox-
idation of alkenes and aromatic hydrocarbons; the
reactive intermediate has been postulated to be peroxy-
Abstract: Various aromatic hydrocarbons were oxidized with
bis(trifluoroacetoxyiodo)benzene (PIFA)/tert-butyl hydroperoxide
system to afford the corresponding quinones. The reaction condi-
tions and scope have been discussed in detail.
5
iodane 2a. To gain further insight into the chemistry of
Key words: hypervalent iodine, peroxyiodone, aromatic hydrocar-
this peroxide-activation system, we have investigated the
PIFA (1b)/tert-butyl hydroperoxide system. We report
herein the first example of conversion of aromatic hydro-
carbons to quinones using the PIFA/TBHP system.
bon, oxidation, quinone
In spite of extensive studies on the chemistry of hyperva-
lent iodine reagents such as bis(acetoxyiodo)benzene Treatment of PIFA with anhydrous TBHP in methylene
PIDA, 1a) and bis(trifluoroacetoxyiodo)benzene (PIFA, chloride at room temperature leads to the release of oxy-
b), very little is known about peroxyiodanes, probably gen gas and produces iodobenzene. However, the reaction
(
1
because of the fact that they show high tendency to de- of PIFA with TBHP was found to be very slow at –30 °C.
compose. Milas and Plesnicar reported the reaction of Thus, the peroxyiodane 2b generated in situ may serve as
1
bis(acetoxyiodo)benzene (1a) with tert-butyl hydroper- active oxygen source for the oxyfunctionalization of or-
oxide in dichloromethane and proposed the in situ ganic substrates at low temperature. With this aim, the ox-
generation of bis(tert-butylperoxyiodo) benzene (2b) to idation of naphthalene (4a), representing one of the most
be an intermediate, which decomposes homolytically electron-deficient arenes, to 1,4-naphthoquinone (4b) was
6
even at –80 °C to give t-butylperoxy radical and iodo- first studied at –30 °C to optimize the yield. In view of the
2
benzene. This ready decomposition of the (alkylper- solvent effect, five different solvents were selected for a
oxy)iodine can be attributed to the low dissociation screening of the oxidation activity of the present system:
energy of the apical hypervalent peroxy-iodine(III) bond EtOAc, THF, acetone, MeCN and methylene chloride.
and is facilitated by conjugative overlap of the breaking The oxidation in methylene chloride or acetonitrile result-
hypervalent bond with p-orbitals of the aromatic nucleus. ed in the formation of a comparable yield of 4b (Table 1,
Recently, Ochiai and co-workers have reported the syn- entries 4 and 5), while use of ethyl acetate, THF and ace-
thesis and characterization of the first stable crystalline 1- tone gave very poor results. In a control experiment, in
(
tert-butylperoxy)-1,2-benziodoxol-3(1H)-one (3), which which either PIFA or TBHP was excluded, no oxidation
3
oxidizes a number of organic substrates (Figure 1).
Table 1 Oxidation of Naphthalene (4a) with PIFA/TBHP Systema
O
O
I(OCOR)2
I(OOR)2
O
t-BuOO
I
PIFA, TBHP
NaHCO3, solvent
–30 °C, 3 h
1
a R = CH3
b R = CF3
2a R = H
3
4a
4b
O
1
2b R = t-Bu
Entry
Solvent
EtOAc
Acetone
THF
Conversion (%)b Yield (%)c
Figure 1
1
2
3
4
0
0
0
0
Preparative methods of quinones from phenols or phenyl
alkyl ethers using hypervalent iodine reagents have been
reported. However, oxyfunctionalization of aromatic
substrates that have no phenolic hydroxyl or amino sub-
stituents using hypervalent iodine reagents has so far not
4
5
N.d.
30
45
MeCN
CH Cl
35
50
5
2
2
a
Substrate (2 mmol), PIFA (3 mmol), TBHP (10 mmol), NaHCO3
10 mmol), solvent (10 mL), –30 °C, 3 h.
Determined by GC-MS with internal standard.
SYNLETT 2004, No. 12, pp 2151–2154
0
1
.1
0
.2
0
0
4
(
Advanced online publication: 21.09.2004
DOI: 10.1055/s-2004-832843; Art ID: D10004ST
b
c
Isolated yield based on the converted starting material.
©
Georg Thieme Verlag Stuttgart · New York

2
152
M. Catir, H. Kilic
LETTER
occurred or the starting material naphthalene (4a) was re- focused on oxidation activity and regioselectivity of the
covered completely; thus, both components are essential PIFA/TBHP system towards more electron rich-arenes as
for the reaction.
substrates. 2-Methyl-naphthalene (5a), 2,3-dimethyl-
naphthalene (6a), and 2-methoxy-naphthalene (7a) were
chosen as substrates for a comparative study (Table 2, en-
tries 1, 2, and 3). Two tendencies can be seen from
Table 2: (1) The conversion of arene rises with the num-
ber of electron-donating substituents at the aromatic ring
while naphthalene (4a), the most electron-deficient one
among the tested arenes 4a–10a, shows the lowest reac-
tivity [45% 1,4-naphthoquinone (4b) at 50% conversion;
Table 1, entry 5]. Due to its higher reactivity 2-methyl-
Further oxidation of the quinones appears to be responsi-
ble as confirmed through an independent experiment in
which suffered under the condition of run 5 (Table 1).
When 4b was treated with the PIFA/TBHP system under
the identical condition 60% of 4b was recovered after usu-
al extraction and chromatography. The rest was mixture
of other oxidation products, which were not identified.
Working with an optimized condition, our attention was
Table 2 Oxidation of Arenes 5a–10a with PIFA/TBHP Systema
Entry
1
Substrate
Products
Conversion (%)b
90
Yield (%)c
Selectivity (%)
91
d
Me
O
O
5b (55)
d
5
c (5)
Me
Me
5a
O
O
O
O
5
6
7
b
b
b
5c
6c
2
3
4
5
Me
Me
>99
>99
>95
6b (60)e
c (7)e
95
6
Me
Me
Me
Me
6
7
a
a
O
O
O
40e
100
OMe
OMe
O
O
40e
8
a
O
8
9
b
b
9b (40)e
O
O
CO2H
HO2C
>95
>95
d
9
c (20)
9
1
a
9
c
6
30e
O
O
0a
10b
a
Substrate (2 mmol), PIFA (3 mmol), TBHP (10 mmol), NaHCO (10 mmol), CH Cl (10 mL), –30 °C, 3 h.
3
2
2
b
c
d
e
Determined by GC-MS with internal standard.
Yields based on the converted starting material.
Yields determined GC-MS with internal standard.
Isolated yields.
Synlett 2004, No. 12, 2151–2154 © Thieme Stuttgart · New York

LETTER
Bis(trifluoroacetoxyiodo)benzene-Induced Activation of tert-Butyl Hydroperoxide
2153
naphthalene (5a) yields 55% 2-methyl-[1,4]-naphtho-
2 CF3CO2H
7
quinone (vitamin K ) (5b) at 90% conversion. The best
3
quinone yield is obtained for 2,3-dimethyl-naphthalene
(
6a). (2) The high regioselectivities found compare well
8
with known results from the literature. In the case of 2-
1b + t-BuOOH
PhI
2b
methyl-[1,4]-naphthoquinone (5b) a 91:9 ratio for 2- and
6
-methyl-[1,4]-naphthoquinone (5c) and 95:5 for 2,3-
dimethyl-naphthoquinone regioisomers 6b and 6c are ob-
tained. These results remarkably differ from regioselec-
tivities obtained with metal-catalyzed systems. For
instance, in metalloporphyrin-catalyzed oxidation of 5a
selectivity was found to be 53%. The electron-rich arene
OOtBu
OOtBu
O
O
2 t-BuOO
-
t-BuOH
2
-methoxy-naphthalene (7a) was quite succeptible to-
wards oxidation and led exclusively to 2-methoxy-[1,4]-
4a
4b
9
naphthoquinone (7b).
Scheme 1 Proposed mechanism for the generation of t-butylperoxy
radical and oxidation of naphthalene to 1,4-naphthoquinone
Anthracene (8a) gave anthraquinone as the sole product.
In the oxidation of phenanthrene (9a), phenanthrene-9,10-
dione (9b) was obtained as the major product besides bi-
1
0
phenyl-2,2¢-dicarboxylic acid (9c) in a ratio of 65:35.
OOOO
OO
2
Biphenylene (10a) readily undergoes fast conversion to
2
,3-biphenylenequinone (10b)11 and some unidentified
compounds. A plausible reaction mechanism for the gen-
eration of t-butylperoxy radical and oxygen transfer to
naphthalene 4a is displayed in Scheme 1. PIFA (1b) is
converted with TBHP to peroxyiodane 2b by exchanging
two trifluoromethyl acetate groups for two tert-butylper-
oxy groups. The initial step of the decomposition of per-
oxyiodane 2b would involve the homolytic cleavage of
the weak iodine(III)–peroxy bond, generating tert-butyl-
peroxy radical and iodo-benzene. The tert-butylperoxy
radical has been shown to be an efficient radical oxidant
O
+
O2
+
O
H
CH3
t-BuOH
Acetone
Scheme 2 Decomposition mechanism of t-butylperoxy radical
with the highly electrophilic nature for the conversion of References
1
2
sulfides to sulfoxides. Addition of tert-butylperoxy rad-
icals to 4a leads to the intermediary formation of 1,4-bis-
t-butylperoxy-1,4-dihydro-naphthalene, which might
constitute one of the possible reaction pathways. To in-
(
(
1) Moriarty, R. M.; Prakash, O. Acc. Chem. Res. 1986, 19, 244.
2) Milas, N. A.; Plesnicar, B. J. Am. Chem. Soc. 1968, 90, 4450.
(3) (a) Ochiai, M.; Ito, T.; Masaki, Y.; Shiro, M. J. Am. Chem.
Soc. 1992, 114, 6269. (b) Ochiai, M.; Ito, T.; Takahaski, H.;
Nakanishi, A.; Toyorani, M.; Sueda, T.; Goto, S.; Shiro, M.
J. Am. Chem. Soc. 1996, 118, 7716. (c) Ochiai, M.;
1
vestigate the fate of the tert-butylperoxy groups of 2b, H
NMR experiments were carried out in CDCl at room
3
Kajisma, D.; Sueda, T. Tetrahedron Lett. 1999, 40, 5541.
d) Ochiai, M.; Sueda, T.; Fukuda, S. Org. Lett. 2001, 3,
387.
temperature and products were analyzed: Acetone, tert-
butyl alcohol and iodo-benzene were detected. It is a well
known fact that tert-butylperoxy radical undergoes b-scis-
sion yielding acetone and methyl radical or tert-butyl al-
cohol by abstracting a hydrogen atom (Scheme 2).13
(
2
(
4) Tohma, H.; Morioka, H.; Harayama, Y.; Hashizume, M.;
Kita, Y. Tetrahedron Lett. 2001, 42, 6899.
(5) Catir, M.; Kilic, H. Synlett 2003, 1180.
6) General Procedure for Oxidation of Arenes with PIFA/
TBHP System: (Caution! Although we have never
(
Thus, the present study provided the first example of
direct oxyfunctionalization of aromatic hydrocarbons to
quinones using PIFA/TBHP system. This method may be
applied to other arenes. Depending on the reactivity of the
arene, 10 mmol scale may be employed. Further work on
peroxide-activation system is in progress, and the results
of these studies will be reported in the future.
experienced explosion, the oxidation of arenes with TBHP/
PIFA system was carried out behind shields.) To a solution
of arene (2 mmol) and anhyd TBHP (10 mmol) in 10 mL of
CH Cl at –30 °C was added NaHCO (5 mmol). Then, a
freshly prepared solution of PIFA (3 mmol) in 10 mL of
CH Cl was added within 2 h. The temperature was slowly
2
2
3
2
2
increased to r.t. within 1 h. The suspension was filtered and
the solution was washed with sat. NaHCO solution and
3
H O. The organic layer was dried over MgSO and the
2
4
Acknowledgment
solvent was removed at reduced pressure (5 °C/50 mbar).
The products were purified on a silica gel column (40 g) by
eluting with hexane–EtOAc (90:10). First fractions gave
iodobenzene. Further elution afforded analytically pure
quinones. In the case of 5a, 2-methyl- and 6-methyl-1,4-
naphthoquinone could not be separated. Compound 5b was
obtained from the mixture by crystallization from EtOH. The
The Authors are indebted to President of Ataturk University, Prof.
Dr. Yasar Sutbeyaz, for his support to set up a new research labora-
tory and the Department of Chemistry (Ataturk University) for the
financial support of this work and the State Planning Organization
of Turkey (DPT) for purchasing a GC-MS instrument.
Synlett 2004, No. 12, 2151–2154 © Thieme Stuttgart · New York

2
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M. Catir, H. Kilic
LETTER
1
mixture of both naphthoquinones 5b and 5c was also directly
analyzed by H NMR and GC-MS (equipped with a non-
polar column using EI ionization at 70 eV). Compound 5b:
127.5, 127.0, 110.8, 57.3. Compound 10b: H NMR (200
1
13
MHz, CDCl ): d = 6.62 (s, 2 H), 7.73 (s, 4 H). C NMR (50
MHz, CDCl ): d = 180.4, 157.3, 148.6, 136.1, 124.9, 116.8.
(7) Adam, W.; Herrmann, W.-A.; Lin, J.; Saha-Moller, C.-R.;
Fischer, R.-W.; Correia, J. D.-G. Angew. Chem., Int. Ed.
Engl. 1994, 33, 2475.
(8) Song, R.; Sorokin, A.; Bernadou, J.; Meunier, B. J. Org.
Chem. 1997, 62, 673.
(9) Skarzewski, J. Tetrahedron 1984, 40, 4997.
(10) Adam, W.; Ganeshpure, P.-A. Synthesis 1993, 280.
(11) Adam, W.; Balci, M.; Kilic, H. J. Org. Chem. 1998, 63,
8544.
(12) Adam, W.; Haas, W.; Asmus, K.-D. J. Am. Chem. Soc. 1991,
113, 6202.
(13) (a) Howard, J. A. The Chemistry of Peroxides; Wiley: New
York, 1983. (b) Howard, J. A.; Ingold, K. U. J. Am. Chem.
Soc. 1968, 90, 1056.
3
3
1
H NMR (400 MHz, CDCl ): d = 2.18 (d, 3 H, J = 1.5 Hz),
3
6
2
1
.83 (q, 1 H, J = 1.5 Hz), 7.68–7.75 (m, 2 H), 8.01–8.12 (m,
H). 13C NMR (100 MHz, CDCl ): d = 187.5, 186.9, 150.1,
3
37.6, 135.6, 135.5, 134.2, 134.1, 128.5, 128.0, 18.4.
1
Compound 6b: H NMR (200 MHz, CDCl ): d = 2.11 (s, 6
3
H), 7.60–7.64 (AA part of AA¢BB¢ system, 2 H), 8.01–7.97
1
3
(
BB¢ part of AA¢BB¢ system, 2 H). C NMR (50 MHz,
CDCl ): d = 185.6, 144.2, 134.1, 133.0, 127.0, 13.7.
3
1
Compound 6c: H NMR (200 MHz, CDCl ): d = 2.40 (s, 6
3
1
3
H), 6.90 (s, 2 H), 7.82 (s, 2 H). C NMR (50 MHz, CDCl ):
3
d = 186.2, 144.6, 139.4, 130.8, 128.5, 21.1. Compound 7b:
1
H NMR (200 MHz, CDCl ): d = 3.89 (s, 3 H), 6.15 (s, 1 H),
3
1
3
7
.76–7.65 (m, 2 H), 8.12–8.03 (m, 2 H). C NMR (50 MHz,
CDCl ): d = 185.6, 180.9, 161.3, 135.2, 134.2, 132.9, 132.0,
3
Synlett 2004, No. 12, 2151–2154 © Thieme Stuttgart · New York