Organoiodine-catalyzed oxidative spirocyclization of phenols using peracetic acid as a green and economic terminal oxidant

Article abstract of DOI:10.1071/CH09148

The use of peracetic acid as a green and economical terminal oxidant in fluoroalcohol solvents could provide a practical iodoarene-catalyzed oxidation of phenols to give spirodienones. Acetic acid and water were the only co-products and waste, and thus th

Full text of DOI:10.1071/CH09148

RESEARCH FRONT
Rapid Communication
CSIRO PUBLISHING
Aust. J. Chem. 2009, 62, 648–652
www.publish.csiro.au/journals/ajc
Organoiodine-Catalyzed Oxidative Spirocyclization
of Phenols using Peracetic Acid as a Green
and Economic Terminal Oxidant
Yutaka Minamitsuji,A Daishi Kato,B Hiromichi Fujioka,A Toshifumi Dohi,A,B
and Yasuyuki KitaB,C
AGraduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka,
Suita, Osaka, 565-0871, Japan.
BCollege of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Nojihigashi,
Kusatsu, Shiga, 525-8577, Japan.
CCorresponding author. Email: kita@ph.ritsumei.ac.jp
The use of peracetic acid as a green and economical terminal oxidant in fluoroalcohol solvents could provide a practical
iodoarene-catalyzed oxidation of phenols to give spirodienones. Acetic acid and water were the only co-products and
waste, and thus this catalytic approach utilizing fluoroalcohol media could simplify the reaction workup procedure for
product isolation.
Manuscript received: 13 March 2009.
Final version: 30 April 2009.
OH
Introduction
Iodine(III)
Hypervalent iodine reagents such as phenyliodine diacetate
(PIDA) and phenyliodine bis(trifluoroacetate) (PIFA) have been
widely recognized as extremely useful and environmentally
friendly oxidizing reagents, replacing the highly toxic heavy
metal oxidants, i.e. PbIV, HgII, and TlIII.[1] The recent signif-
icant breakthrough in their application is the fact that useful
stoichiometric organo-oxidants have now been utilized success-
fully in various oxidations by catalytic means.[2] As pioneering
work, we demonstrated in 2005 that m-chloroperbenzoic acid
(mCPBA) is a versatile terminal oxidant to construct an efficient
II to IIII catalytic cycle for the iodoarene-catalyzed oxidations of
phenols.[3] In the same year, Ochiai’s group also reported in the
literature the iodobenzene-catalyzed α-acetoxylation of ketones
using mCPBA in which diacyloxy(phenyl)-λ3-iodanes acted as
real oxidants.[4] With the recent growing interest in greener syn-
thetic processes, the catalytic utilization of hypervalent iodine
reagents is increasing in importance to broaden the utility of
the reagents in organic synthesis, leading to a new route to the
development of organocatalysts.
OAc
Ar
I
AcOH
CO2H
2a
OAc
1
Regeneration
(CF3)2CHOH
(HFIP)
Oxidation
of IIII
O
Cat. ArI(I)
AcOOH
O
O
3a
Scheme 1.
Herein, we report inexpensive and environmentally friendly
peracetic acid (PAA) as the terminal oxidant in the iodoarene-
catalyzed oxidation of phenols 2 to give spirodienones 3, in
which PAA acts as an efficient generator of the reactive arylio-
dine(iii) diacetates 1 from iodoarene catalysts with the aid of
fluoroalcohol solvents (Scheme 1).
Inearlystudies,[3–5] mCPBAinitiallyplayedapivotalroleasa
unique terminal oxidant in catalytic cycles to generate efficiently
the active catalytic iodine(iii) species from iodoarenes in situ.
However, in view of atom economy and cost performance,[6]
mCPBA is not an ideal terminal oxidant for the catalytic strategy.
In addition, commercially available stabilized mCPBA, con-
taining large amounts of water, is potentially explosive in the
absolutely dry form. Accordingly, optimization of the terminal
oxidant to a more favourable one should be the next challenge
to be investigated for the realization of a practical, economical,
safe, and clean organocatalytic process.
Result and Discussion
PAA is known as a safe and environmentally friendly oxidant
that releases non-toxic acetic acid as the co-product. It is com-
mercially available in dilute acetic acid solutions from some
© CSIRO 2009
10.1071/CH09148
0004-9425/09/070648

RESEARCH FRONT
Oxidative Spirocyclization of Phenols
649
Table 1. Optimization of solvent
In the last case, the presence of the electron-withdrawing group
on the aromatic ring clearly inhibited the smooth generation of
the corresponding iodine(iii) by the action of PAA. Thus, the
iodine atom in the catalyst must be moderately activated towards
the terminal oxidant, similarly to the case with mCPBA.[3] No
reaction, needless to say, was observed under the catalyst-free
conditions.
OH
O
Iodobenzene (0.1 equiv.)
AcOOH (5 equiv.)
Solvent, 35°C
OH
O
O
O
2a
3a
With the optimized conditions in hand, we confirmed the ver-
satility of the method using several types of phenol derivatives 2
with 5 mol-% of 4-iodotoluene. It has been established that PAA
could serve as the efficient terminal oxidant in HFIP for the
oxidative C–O bond-forming reaction of phenols 2 to construct
a wide range of spirodienone lactone structures (Table 2). The
oxidative transformation of various phenol derivatives 2 could
indeed occur smoothly in good to excellent yields under short
reaction times. In particular, the acid-sensitive spirodienone that
decomposed in strongly acidic conditions[3a] was obtained in an
acceptable yield under milder conditions (entry f).The less polar
TFE was used for the naphthol derivatives because background
side reactions attributed to the oxidations of the naphthol ring
were dominant in HFIP to give a complex mixture (entry k).
The catalytic conditions with PAA were also compatible with
a nitrogen-containing substrate 4[12] without any optimization
to furnish the spiro C–N bond (Scheme 2). The spirodienone
structures of 3 and 5 are known to exist as the core components
of various biologically active compounds and natural products
and are key intermediates in biosynthetic processes.[13]
Our catalytic method with PAA generates only easily remov-
able acetic acid and water as co-products. This makes the
productisolationstepsimpler, andthealmost-pureproductswere
obtained by a simple aqueous workup. Any tedious purification
procedures such as column chromatography were not necessary,
and the used HFIP could be reused repeatedly after distillation;
these merits would provide a highly practical and environ-
mentally benign method for the organocatalytic oxidation of
phenols.
To determine the existence of hypervalent iodine(iii) species
in the catalytic cycle, we conducted the following experiments
(Scheme 3). In the absence of phenols 2, 4-iodotoluene was
heated with PAA (5 equiv. relative to 4-iodotoluene) in HFIP
(0.25 M) at 35◦C for 1 h. The exclusive formation of the corre-
sponding iodine(iii) could be confirmed this time by isolation
of trivalent 4-(diacetoxyiodo)toluene 1a (90% yield, see Exper-
imental Section) as expected. However, the same operation in
dichloromethane was less effective and partial formation of
1a was detected (1a: 47% yield). These results clearly sug-
gest that HFIP accelerates the formation of the active catalytic
species 1 during the reactions. In addition, the fluoroalcohols can
also facilitate smooth generation of reactive phenoxenium ion
intermediates mediated by the hypervalent iodine(iii) reagents,
leading to the products 3.[14]
Entry
Solvent
Time [h]
Yield of 3a [%]
1A
2
3
4
5
6
7
8
9
CH2Cl2
CH2Cl2
Toluene
THF
CH3CN
MeOH
TFE
24
24
24
24
10
24
3
31
20
33
Trace
8
18
66
82
25
HFIP
NoneB
1
24
A1 equiv. of trifluoroacetic acid was added.
B9% peracetic acid solution was used as solvent.
chemical product companies, or alternatively, is prepared from
hydrogen peroxide and acetic anhydride before use.[7] PAA solu-
tion is frequently employed in industrial-scale oxidations such
as epoxidation or the Baeyer–Villiger reaction. Furthermore, a
0.2–0.3% solution of PAA is widely utilized as a disinfectant in
medical use.
With a commercially available ∼9% (v/v) PAA solution
in acetic acid (net 5 equiv. of PAA was used), we examined
the reaction of 3-(4-hydroxyphenyl)propionic acid 2a using a
10 mol-% amount of iodobenzene (Table 1). The reaction was
performed at ∼35◦C to suitably induce the oxidation ability of
PAA towards iodoarenes.[8] Relying on the optimized reaction
conditions established in the case of mCPBA,[3a] we first started
our survey of the reaction in dichloromethane, which gave only
disappointing results in the obtained yield of 3a (entries 1 and 2).
We therefore next tried to perform the reaction using 2,2,2-
trifluoroethanol (TFE).[3b] At this stage, we noted the remarkable
effect of the fluorinated alcohol solvent[9,10] on the catalytic
phenol oxidation with PAA.
As shown in Table 1, systematic screening of the solvents
was used to verify the yield of the spirodienone product 3a.
Other conventional non-polar or polar solvents such as toluene,
THF, acetonitrile, and methanol were employed with gener-
ally unsatisfactory results (entries 3–6). In contrast, simple
replacement of dichloromethane by TFE remarkably improved
the yield of the obtained product 3a (entry 7). The use of a
more polar and acidic fluoroalcohol, 1,1,1,3,3,3- hexafluoroiso-
propanol (HFIP), as solvent[11] led to a further increase in the
yield to reach 82% (entry 8); the conditions gave the product
3a in a better yield than that under the previously optimized
conditions using mCPBA.[3a] Finally, the PAA solution was also
examined as solvent (entry 9).
Regarding the catalyst, 4-iodotoluene showed the best result
in both turnover number (TON) and turnover frequency (TOF)
in the reaction among those examined. The effect of the
iodoarene catalysts on the reaction of 2a to 3a at 5 mol-%
of the catalysts was established as follows: iodobenzene (1 h,
80%), 4-iodotoluene (1 h, 88%), 4-iodoanisole (5 h, 50%), 4-
fluoroiodobenzene (2 h, 68%), 4-nitroiodobenzene (24 h, 40%).
Conclusions
The main goal of the catalytic approach is to design a practical
and sustainable process by using low-cost and environmentally
friendly terminal oxidants. In the present work, we have estab-
lished PAA as a green and economical terminal oxidant in the
iodoarene-catalyzed oxidation of phenols. When using PAA in
fluoroalcohol media, that is, HFIP and TFE, it functions as
an efficient generator of the active iodine(iii) species 1. The
use of PAA results in the formation of only non-toxic acetic
acid and water, and hence we believe that the present system

RESEARCH FRONT
650
Y. Minamitsuji et al.
Table 2. 4-Iodotoluene-catalyzed spirocyclization of various phenol derivatives 2 using PAA as terminal
oxidant
Conditions: phenols 2 (1 mmol), 4-iodotoluene (5 mol-%), AcOOH (5 equiv.) in HFIP (6 mL) at 35◦C for 1 h
Entry
Phenol 2
Product 3
Yield [%]A
OH
O
R1
R3
R2
R1
R3
R4
R2
O
CO2H
R4
O
R1
R2
R3
R4
a
b
c
d
e
f
H
Me
H
H
H
H
H
H
H
Br
Me
H
H
Me
H
H
H
Me
Me
H
H
H
Me
H
H
H
H
88
72
80
75
83
46
81
97
H
Br
OMe
Br
Br
g
h
O
OH
i
87
O
CO2H
O
O
OH
j
79B
Me
Me
Me
CO2H
O
Me
O
O
OH
kC
62
O
CO2H
O
AIsolated yield of the products 3.
BThe products were obtained as a 51:49 mixture of the diastereoisomers.
C2,2,2-Trifluoroethanol was used as solvent.
OH
O
OAc
I
AcOOH (5 equiv.)
4-Iodotoluene (5 mol-%)
I
AcOOH (5 equiv.)
HFIP, 35°C
OAc
HFIP, 35°C
Ts
N
Ts
HN
1a (90%)
1h
4
5 (69%)
Scheme 3.
(Ts ϭ p-toluenesulfonyl)
Scheme 2.
centimetres. 1H and 13C NMR spectra were recorded on a
JEOL JMN-300 spectrometer operating at 300 MHz in CDCl3
at 25◦C with tetramethylsilane as the internal standard. Data
are reported as follows: chemical shift in ppm (δ), multiplic-
ity (s = singlet, d = doublet, t = triplet, q = quartet, br = broad
singlet, m = multiplet), coupling constant (Hz), and integration.
Elemental analyses were performed by the Elemental Analy-
sis Section of Osaka University. The column chromatography
and TLC were carried out on Merck Silica gel 60 (230–400
mesh) using hexane/AcOEt as eluent; the spots were detected
basis of PAA with fluoroalcohol media could become a valuable
organocatalytic process in line with the recent directions of green
synthesis.
Experimental
Melting points (mp) were measured using a Büchi B-545
apparatus. Infrared spectra (IR) were recorded on a Hitachi
270–50 spectrometer; absorptions are reported in reciprocal

RESEARCH FRONT
Oxidative Spirocyclization of Phenols
651
by UV irradiation (254, 365 nm). The 9% v/v PAA solution was
purchased from Sigma–Aldrich Japan. All commercially avail-
able reagents and solvents were used as received without further
purification.
3g: colourless solid; mp: 103–104◦C. νmax(KBr)/cm−1 2931,
1793, 1685, 1596, 1458, 1419, 1319, 1263, 1218, 1151, 1124,
975. δH (CDCl3, 300 MHz) 1.10 (d, J 6.9, 3H), 2.46 (dd, J 16.5,
11.4, 1H), 2.73–2.93 (m, 2H), 6.45–6.51 (m, 1H), 7.22–7.25
(m, 1H). δC (CDCl3, 75 MHz) 13.8, 35.1, 39.6, 84.7, 123.8,
123.9, 143.7, 146.5, 171.5, 173.3. (Anal. calc. for C10H8Br2O3:
C 35.75, H 2.40, Br 47.57. Found: C 35.71, H 2.45, Br 47.27%.)
3h (diastereomixture):[3] colourless oil. νmax(KBr)/cm−1
2966, 2927, 1793, 1676, 1614, 1421, 1332, 1267, 1209, 1139,
977. δH (CDCl3, 300 MHz) 0.96 (t, J 5.8, 3H), 1.94 (s, 3H),
2.35–2.46 (m, 1H), 2.60–2.83 (m, 2H), 7.20–7.36 (m, 2H). δC
(CDCl3, 75 MHz) 13.4, 13.7, 16.1, 16.2, 35.1, 35.2, 39.2, 39.5,
83.4, 83.6, 126.1, 126.2, 136.3, 136.5, 138.0, 141.4, 143.2, 146.1,
174.0, 174.1, 178.2 (×2).
General Experimental Procedure for Compounds 3
To a stirred solution of 3-(4-hydroxyphenyl)propionic acid
2a (166.2 mg, 1.0 mmol) and catalyst 4-iodotoluene (10.9 mg,
0.05 mmol) in HFIP was added commercially available PAA
solution (9% v/v in acetic acid, 2.2 mL, ∼5 mmol). The reaction
mixture was then stirred for 1 h while the reaction tempera-
ture was maintained at ∼35◦C. After the reaction was complete,
AcOEt was added and the organic layer was washed with water,
saturated aqueous NaHCO3, and then dried over anhydrous
Na2SO4. Evaporation of the solvent under vacuum afforded the
almost pure product, 1-oxaspiro[4,5]deca-6,9-diene-2,8-dione
3a, which was further purified by short column chromatography
on silica-gel to give pure 3a (144.5 mg, 0.88 mmol) in 88% yield.
3a:[3] colourless solid; mp: 106–107◦C. νmax(KBr)/cm−1
3048, 2955, 2930, 2855, 1782, 1678. δH (CDCl3, 300 MHz) 2.37
(d, J 8.3, 2H), 2.78 (d, J 8.3, 2H), 6.28 (d, J 10.0, 2H), 6.85 (d, J
10.0, 2H). δC (CDCl3, 75 MHz) 27.8, 32.1, 78.4, 129.0, 145.5,
175.2, 184.0.
3i: colourless solid; mp: 183–184◦C. νmax(KBr)/cm−1 3057,
1768, 1672. δH (CDCl3, 300 MHz) 6.43 (d, J 10.2, 2H), 6.66 (d,
J 9.9, 2H), 7.31 (d, J 7.5, 1H), 7.64 (td, J 7.2, 0.9, 1H), 7.73
(td, J 7.2, 0.9, 1H), 8.00 (d, J 7.5, 1H). δC (CDCl3, 75 MHz)
80.3, 122.4, 125.5, 126.7, 129.8, 130.6, 135.1, 144.2, 146.4,
168.9, 184.1. (Anal. calc. for C13H8O3: C 73.58, H 3.80. Found:
C 73.57, H 4.00%.)
3j (diastereomixture): colourless solid; mp: 76–77◦C.
νmax(KBr)/cm−1 2970, 2931, 2358, 2339, 1778, 1672, 1633,
1398, 1211, 1147. δH (CDCl3, 300 MHz) 0.97 (t, J 5.1, 3H),
2.09 (s, 3H), 2.37–2.50 (m, 1H), 2.79–2.91 (m, 2H), 6.21 (d, J
1.5, 1H), 6.35 (dd, J 9.0, 2.1, 1H), 6.76 (d, J 10.2). δC (CDCl3,
75 MHz) 13.8, 17.5, 55.8, 38.1, 84.6, 128.9, 130.5, 143.6, 155.2,
174.5, 184.3.
3b: colourless solid; mp: 115–116◦C. νmax(KBr)/cm−1 3535,
2925, 1776, 1676, 1649, 1450, 1396, 1367, 1296, 1226, 1178,
1153, 1109, 1020, 960. δH (CDCl3, 300 MHz) 1.98 (s, 3H), 2.36
(d, J 8.1, 2H), 2.78 (d, J 8.1, 2H), 6.28 (d, J 10.2, 1H), 6.61–
6.63 (m, 1H), 6.82 (dd, J 9.9, 3.3, 1H). δC (CDCl3, 75 MHz)
15.5, 28.0, 32.2, 79.0, 129.0, 136.1, 140.8, 145.2, 175.4, 184.8.
(Anal. calc. for C10H10O3: C 67.41, H 5.66. Found: C 67.32,
H 5.63%.)
3k:[15] colourless solid; mp: 135–136◦C. νmax(KBr)/cm−1
1770, 1672, 1228. δH (CDCl3, 300 MHz) 2.55 (t, J 8.4, 2H),
2.86–3.02 (m, 2H), 6.46 (d, J 10.2, 1H), 7.06 (d, J 10.2, 1H),
7.49–7.57 (m, 2H), 7.68 (dd, J 7.5, 1.5, 1H), 8.15 (dd, J 7.8, 1.2,
1H). δC (CDCl3, 75 MHz) 28.5, 36.6, 80.1, 125.4, 126.8, 128.5,
129.1, 129.7, 133.5, 142.6, 146.4, 175.8, 183.2.
3c: colourless solid; mp: 79–80◦C. νmax(KBr)/cm−1 2970,
1790, 1674, 1633, 1456, 1386, 1344, 1278, 1218, 1147, 1068,
1017, 975. δH (CDCl3, 300 MHz) 1.02 (d, J 6.6, 3H), 2.44 (dd,
J 17.1, 11.7, 1H), 2.62–2.75 (m, 1H), 2.85 (q, J 8.3, 1H), 6.32–
6.40 (m, 2H), 6.79 (d, J 10.2, 2H). δC (CDCl3, 75 MHz) 13.5,
35.4, 39.4, 81.7, 130.2, 142.6, 145.8, 174.4, 184.3. (Anal. calc.
for C10H10O3: C 67.41, H 5.66. Found: C 67.35, H 5.67%.)
3d: colourless solid; mp: 122–123◦C. νmax(KBr)/cm−1 3541,
2968, 2933, 1787, 1672, 1633, 1610, 1460, 1388, 1278, 1257,
1215, 1151, 1068, 1017, 945. δH (CDCl3, 300 MHz) 1.29 (d, J
6.9, 3H), 2.10 (t, J 12.5, 1H), 2.51 (dd, J 13.2, 8.7, 1H), 2.90–2.97
(m, 1H), 6.29 (t, J 10.8, 2H), 6.79 (dd, J 9.9, 3.0, 1H), 6.89 (dd, J
9.9, 3.0, 1H). δC (CDCl3, 75 MHz) 15.4, 34.3, 40.4, 76.1, 128.7,
129.5, 144.9, 146.9, 177.8, 184.1. (Anal. calc. for C10H10O3:
C 67.41, H 5.66. Found: C 67.23, H 5.68%.)
5:[12a] colourless solid; mp: 115–116◦C. νmax(KBr)/cm−1
2879, 1666, 1629, 1344, 1157, 1095. δH (CDCl3, 300 MHz)
2.03–2.09 (m, 4H), 2.43 (s, 3H), 3.69 (t, J 6.9, 2H), 6.17 (d, J
10.2), 6.71 (d, J 10.2), 7.29 (d, J 8.3), 7.67 (d, J 8.3). δC (CDCl3,
75 MHz) 21.6, 23.5, 40.4, 49.1, 63.7, 127.8, 127.9, 129.6, 136.2,
143.9, 150.1, 185.3.
Preparation of 4-(Diacetoxyiodo)toluene 1a in HFIP
with PAA (Scheme 3)
A stirring solution of HFIP (2 mL) containing 4-iodotoluene
(109 mg, 0.5 mmol) and 9% (v/v) PAA solution (2.2 mL,
2.5 mmol) was heated at 35◦C for 1 h. The solvent was evap-
orated, and the resulting oily mixture was washed with water
and then extracted with chloroform. The organic layer contain-
ing the product was dried over anhydrous Na2SO4.After removal
of the solvent, the residue was triturated with hexane to give 4-
(diacetoxyiodo)toluene 1a as a fine powder, which was collected
by filtration (151 mg, 0.45 mmol, 90% yield).
3e: colourless solid; mp: 173–174◦C. νmax(KBr)/cm−1 3051,
1782, 1676, 1643, 1608, 1456, 1419, 1380, 1340, 1296, 1220,
1172, 1140, 1070, 1020, 960. δH (CDCl3, 300 MHz) 2.43 (t, J
8.4, 2H), 2.81 (t, J 6.0, 2H), 6.43 (d, J 10.8, 1H), 6.89 (dd, J 10.2,
3.0, 1H), 7.30 (d, J 3.0, 1H). δC (CDCl3, 75 MHz) 27.7, 31.9,
80.1, 125.8, 127.7, 145.7, 145.8, 174.5, 177.0. (Anal. calc. for
C9H7BrO3: C 44.47, H 2.90, Br 32.87. Found: C 44.31, H 3.02,
Br 32.77%.)
1a: white powder; mp: 107–109◦C (lit.[16] 106–108◦C). δH
(CDCl3, 300 MHz) 1.92 (s, 6H), 2.37 (s, 3H), 7.22 (d, J 7.8,
2H), 7.91 (d, J 7.8, 2H). δC (CDCl3, 75 MHz) 21.1, 22.2, 119.2,
132.5, 135.8, 143.5, 177.2.
3f : colourless solid; mp: 89–90◦C. νmax(KBr)/cm−1 2937,
2909, 2851, 2833, 1770, 1682. δH (CDCl3, 300 MHz) 2.41 (t, J
8.7, 2H), 2.78 (t, J 8.7, 2H), 3.70 (s, 3H), 5.72 (d, J 2.8, 1H), 6.26
(d, J 10.0, 1H), 6.84 (dd, J 10.0, 2.8, 1H). δC (CDCl3, 75 MHz)
28.3, 33.3, 55.2, 80.9, 112.8, 128.2, 145.8, 151.0, 175.2, 179.6.
(Anal. calc. for C10H10O4: C 61.85, H 5.19. Found: C 61.79,
H 5.22%.)
Acknowledgements
The present work was partially supported by a Grant-in-Aid for Scien-
tific Research (A) and for Young Scientists (B), and a grant for Scientific
Research on Priority Areas ‘Advanced Molecular Transformations of Car-
bon Resources’ from the Ministry of Education, Culture, Sports, Science,

RESEARCH FRONT
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Y. Minamitsuji et al.
and Technology, Japan. TD also acknowledges support from the Industrial
Technology Research Grant Program from the New Energy and Industrial
Technology Development Organization (NEDO) of Japan and the Japan
Chemical Innovation Institute (JICC).
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