Catalytic hypervalent iodine oxidation using 4-iodophenoxyacetic acid and oxone: oxidation of p-alkoxyphenols to p-benzoquinones

Article abstract of DOI:10.1248/cpb.57.252

A catalytic hypervalent iodine oxidation of p-alkoxyphenols using 4-iodophenoxyacetic acid (1a) and Oxone was developed. Reaction of p-alkoxyphenol (2) with a catalytic amount of 1a in the presence of Oxone as a co-oxidant in 2,2,2-trifluoroethanol-water (1: 2) gave the corresponding p-quinone (3) in excellent yield without special operation. The substituent effect on iodobenzene ring in the oxidation was observed; p-alkoxy is the most effective, with the series following the approximate order p-RO>p-Me, o-MeO, m-MeO>H2H. And remarkable solvent effects were observed.

Full text of DOI:10.1248/cpb.57.252

252
Chem. Pharm. Bull. 57(3) 252—256 (2009)
Vol. 57, No. 3
Catalytic Hypervalent Iodine Oxidation Using 4-Iodophenoxyacetic Acid
and Oxone®: Oxidation of p-Alkoxyphenols to p-Benzoquinones
Takayuki YAKURA,* Yuan TIAN, Yû YAMAUCHI, Masanori OMOTO, and Tatsuya KONISHI
Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama; Sugitani, Toyama 930–0194, Japan.
Received October 21, 2008; accepted December 25, 2008; published online January 5, 2009
A catalytic hypervalent iodine oxidation of p-alkoxyphenols using 4-iodophenoxyacetic acid (1a) and Oxone®
was developed. Reaction of p-alkoxyphenol (2) with a catalytic amount of 1a in the presence of Oxone® as a co-
oxidant in 2,2,2-trifluoroethanol–water (1 : 2) gave the corresponding p-quinone (3) in excellent yield without spe-
cial operation. The substituent effect on iodobenzene ring in the oxidation was observed; p-alkoxy is the most ef-
fective, with the series following the approximate order p-ROꢀp-Me, o-MeO, m-MeOꢀHꢀo-CO2H. And re-
markable solvent effects were observed.
Key words hypervalent iodine; 4-iodophenoxyacetic acid; Oxone®; p-alkoxyphenol; p-benzoquinone
Hypervalent iodine compounds, trivalent iodine com- methoxyphenol (2a) and an equimolar amount of Oxone® in
pounds such as phenyliodine(III) diacetate (PIDA) and acetonitrile–water (2 : 1) at room temperature gave the corre-
phenyliodine(III) trifluoroacetate (PIFA) and pentavalent io- sponding p-benzoquinone (3a), but the reaction was sluggish
dine reagents such as Dess–Martin periodinane (DMP) and and the yield of 3a was only 13% along with 78% of recov-
o-iodoxybenzoic acid (IBX), have been used extensively in ered starting 2a after 24 h. Next, we examined reactions of
recent organic synthesis because of their low toxicity, ready 2a in the presence of several iodoarenes as a catalyst (Chart
availability and easy handling.1—15) However, these reagents 1). Table 1 presents the results. According to the procedure
are highly expensive. And stoichiometric amounts of iodine reported by Vinod,28) a mixture of 2a, 0.2 equivalents (eq) of
reagents are required to produce equimolar amounts of or- 2-iodobenzoic acid, and 1 eq of Oxone® in acetonitrile–water
ganic iodine waste. Moreover, pentavalent iodine reagents was heated at 70 °C for 19 h to give a complicated mixture
are potentially explosive. To overcome these disadvantages, (entry 2). However, a similar reaction at room temperature
catalytic hypervalent iodine oxidations16—18) using m- suggested catalytic activity of iodoarene to give 3a in 39%
chloroperbenzoic acid (m-CPBA),19—27) Oxone® (2KHSO5· yield (entry 3). Iodobenzene gave better result (entry 4).
30)
KHSO4·K2SO4),28,29) and H2O2 as a co-oxidant have been Methyl and methoxy groups on the benzene ring showed
reported recently.
Development of efficient methods for synthesis of p-
quinone and p-quinone derivatives is an important subject in
synthetic organic chemistry because they are structural com-
ponents of numerous natural products and useful synthetic
intermediates.31—36) A convenient procedure for p-quinones
Chart 1
was hypervalent iodine oxidation of p-alkoxyphenols using
PIFA.37) Reactions of p-alkoxyphenols with an equimolar
Table 1. Oxidation of 2a with 1 and Oxone®a)
amount of PIFA in a 2 : 1 mixture of acetonitrile and water at
room temperature gave the corresponding p-quinones in ex-
cellent yield.
1
Entry
Time (h) Yield of 3a (%)
As part of our study for development of practical and envi-
ronmentally benign oxidation, we report a mild, efficient and
practical procedure for catalytic hypervalent iodine oxidation
of p-alkoxyphenols to p-quinones using a catalytic amount of
4-iodophenoxyacetic acid (1a) and Oxone® as a co-oxidant38)
in 2,2,2-trifluoroethanol–water.
X
(eq)
1
2c)
3
4
5
6
7
8
9
10
11
12
13
14
15
16
none
24
19
24
24
24
24
24
17
24
22
21
40
24
9
13 (78)b)
6 (4)b)
39 (6)b)
64 (24)b)
77 (14)b)
71 (14)b)
77 (4)b)
90
o-CO2H
o-CO2H
H
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.5
1.0
0.2
p-Me
o-OMe
m-OMe
p-OMe
p-OCOCH3
p-OMOM
p-OCH2CO2Me
p-O(CH2)3CO2Me
p-OMe
Results and Discussion
We chose Oxone® as an environmentally safe co-oxidant
for a catalytic hypervalent iodine oxidation of p-alkoxyphe-
nols because Oxone® is an inorganic and water-soluble oxi-
dant with a low order of toxicity, moreover, it is commer-
cially available and inexpensive.39) Oxone® has been already
used as a co-oxidant under heating conditions in the catalytic
IBX oxidation by Vinod28) and Giannis29) groups, independ-
ently. Because alkoxyphenols have high reactivity under oxi-
dation conditions, we first investigated the oxidative ability
of Oxone® itself.40) A mixture of 2-pivaloyloxymethyl-4-
54 (40)b)
92
94
86
73 (18)b)
92
p-OMe
p-OMe
5
94
p-OCH2CO2H
19
99
a) Reactions were carried out in the presence of 1 eq of Oxone® in CH3CN–H2O
(2 : 1) at room temperature. b) Parentheses are recovery of 2a. c) Reaction was car-
ried out at 70 °C.
∗ To whom correspondence should be addressed. e-mail: yakura@pha.u-toyama.ac.jp
© 2009 Pharmaceutical Society of Japan

March 2009
253
Table 2. Oxidation of 2a with 1a and Oxone®a)
dioxane gave almost similar results (entries 7—9), 2,2,2-tri-
fluoroethanol (TFE) was found to be the best co-solvent (en-
tries 10—14).22,30,42) In TFE–H2O (1 : 2) the completion of a
similar reaction of 2a required only 20 min (entry 10), al-
though 1 : 5 mixture of TFE and H2O lengthened the reaction
time longer (entry 11). Using 0.05 eq of 1a with 4 eq of
Oxone® gave a satisfactory result (entry 12), although a simi-
lar reaction with 1 eq of Oxone® was not completed after
28 h (entry 13). With only 0.01 eq of 1a and 4 eq of Oxone®,
the reaction was finished after 13 h to give 3a in quantitative
yield in TFE–H2O (1 : 2) (entry 14).
Variety of p-alkoxyphenols (2b—i) were oxidized with
0.05 eq of 1a and 4 eq of Oxone® in TFE–H2O (1 : 2) to the
corresponding p-quinones. Results are presented in Table 3
with our preliminary results reported in ref. 38. In all cases
TFE–H2O was suprerior to CH3CN–H2O as a solvent system.
Reactions of simple p-methoxy, p-ethoxy, and p-butoxyphe-
nols (2b—d) respectively gave p-benzoquinone (3b) in high
Entry
1a (eq)
Oxone (eq)
Solvent
Time (h)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.05
0.05
0.01
1
CH3CN–H2O (2 : 1)
CH3CN–H2O (2 : 1)
CH3CN–H2O (2 : 1)
CH3CN–H2O (2 : 1)
CH3CN–H2O (2 : 1)
CH3CN–H2O (1 : 2)
Acetone–H2O (1 : 2)
THF–H2O (1 : 2)
1,4-Dioxane–H2O (1 : 2)
TFE–H2O (1 : 2)
TFE–H2O (1 : 5)
TFE–H2O (1 : 2)
TFE–H2O (1 : 2)
19
48
8 db)
10
6
1
4
4
1
0.33
2
0.75
28b)
13
0.7
0.5
2
4
4
4
4
4
4
4
4
1
4
TFE–H2O (1 : 2)
a) Reactions were carried out at room temperature. b) Reaction was not finished.
enhanced reactivity of iodoarene (entries 5—8). Especial- yield (entries 1—3). This oxidation system was also effective
ly, when 0.2 eq of 4-iodoanisole was used as a catalyst, the for phenols bearing a bulky substituent at the ortho position
reaction was completed within 17 h to give 2a in 90% (entries 4, 5). tert-Butyldiphenylsilyloxy (TBDPSO) and
yield (entry 8). Acetoxy group, however, decreased reac- azide groups were tolerable under the reaction conditions
tivity of iodoarene (entry 9). Other iodobenzenes having (entries 6, 7). Oxidation of phenol having succinimide group
p-alkoxy group such as p-OMOM, p-OCH2CO2Me, and p- (2i) proceeded with high yield (entry 8). In all cases, 1a was
O(CH2)3CO2Me are also effective to catalyze the oxidation of recovered in good yield (75—85%) and it can be used for the
2a to 3a (entries 10—12). These results show that the elec- oxidation again after recrystallization.
tron-donating alkoxy group at the para position on the
Based on the remarkable acceleration of the oxidation of
benzene ring would increase the catalytic efficiency of phenols by addition of only a small amount of iodoarene and
iodoarene, in contrast to the reported results using m- documented examples of the reactions of iodoarene and
30)
CPBA19,20) and H2O2 as a co-oxidant. Slower reaction was Oxone®, which produce pentavalent iodine species,43—48) it
observed using 0.1 eq of 4-iodoanisole (entry 13). However, was suggested that iodine(V) species, generated in situ, was
larger amounts (0.5—1 eq) led to decreased reaction times included in this oxidation as the active catalyst. However,
with similar yields of 3a (entries 14, 15).
formation of pentavalent iodine species requires a higher
Although p-alkoxyiodobenzenes gave satisfactory results, temperature (70 °C) than that in the oxidation of 2 with 1a
the reactions unfortunately required careful purification by and Oxone®. Therefore, it would be possible that trivalent io-
column chromatography to separate the product quinone and dine species is formed and acts as an oxidant. Both pentava-
the recovered catalyst. Therefore, we selected 4-iodophe- lent and trivalent iodines react with phenols, but oxidized
noxyacetic acid (1a), which is prepared easily from 4- products were different in some cases.49—52) For example, re-
iodophenol41) and which is commercially available, in the action of p-methoxyphenol with IBX provided 4-methoxy-
hope of finding more practical catalyst because 1a has an 1,2-benzoquinone,53) in contrast to the reaction with PIFA
electron-donating group at the para position and is soluble in giving p-quinone.37) Although it remains unclear whether io-
alkaline solution. A similar reaction of 2a with 0.2 eq of 1a dine(V) or iodine(III) species was formed during the reac-
in the presence of 1 eq of Oxone® proceeded smoothly to af- tion,54) a possible catalytic cycle for this oxidation is shown
ford pure 3a in 99% yield and 75% of recovered 1a without in Chart 2. Oxone® oxidizes 1a to a hypervalent species;
column chromatography (entry 16).
chemical behaviors suggest that trivalent species would be
We next investigated influences of the amounts of Oxone®, more likely than pentavalent one. It oxidizes p-alkoxyphenol
1a, and solvent systems (Table 2). In all cases, except for en- to give the p-quinone and 1a. Iodoarene (1a) would be re-ox-
tries 3 and 13, starting 2a was completely consumed and idized by Oxone® to a hypervalent species. Iodoarenes with
quinone 3a was given in quantitative yield. The reactions electron-donating substituents such as alkoxy and methyl
were monitored by thin-layer chromatography. The reaction groups may be more easily oxidized by Oxone® to cause
was completed within longer 48 h when 0.2 eq of 1a and 0.7 rapid reactions, whereas an electron-withdrawing substituent
eq of Oxone® was used in the reaction of 2a (entry 2). A sim- such as carboxyl group may decrease the reactivity of
ilar reaction using 0.5 eq of Oxone® was not finished after iodoarene against the oxidant.
several days (entry 3). On the other hand, use of 2 or 4 eq of
Oxone® decreased the reaction times to 10 and 6 h, respec- Conclusion
tively (entries 4, 5). Remarkable solvent effects42) were ob-
A novel and practical catalytic method was developed for
served in this catalytic hypervalent iodine oxidation system hypervalent iodine oxidation of phenol derivatives using 1a.
(entries 6—10). The reaction was accelerated by addition of Reaction of p-alkoxyphenol (2) with a catalytic amount of 1a
water. The reaction of 2a with 0.2 eq of 1a and 4 eq of in the presence of Oxone® as a co-oxidant in TFE–water
Oxone® in CH3CN–H2O (1 : 2) was completed within 1 h (1 : 2) gave the corresponding p-quinones (3) in excellent
(entry 6). Although acetone, tetrahydrofuran (THF), and 1,4- yield without special operation. The substituent effect on

254
Vol. 57, No. 3
Table 3. Catalytic Hypervalent Iodine Oxidation of 2 with 1a and Oxone®a)
in TFE–H2O (1 : 2)
in CH3CN–H2O (2 : 1)b,c)
Entry
Phenol
Quinone
Time (h)
Yield (%)
Time (h)
Yield (%)
1
2
3
0.5
0.5
0.5
78
97
88
16
17
17
80
79
77
4
5
1
3
Quant
Quant
24
23
53
80
6
7
8
3
Quant
95
24
22
40
96
0.5
2
92
98
89d)
a) Reactions were carried out using 0.05 eq of 1a and 4 eq of Oxone® at room temperature. b) Our preliminary results in ref. 38. c) 0.2 eq of 1a and 1 eq of Oxone® were
used. d) 0.4 eq of 1a was used.
trometers, tetramethylsilane as an internal standard. 13C-NMR spectra were
determined with Varian Gemini 300 (75 MHz) and JEOL JNM-FX270
(67.5 MHz) spectrometers. All 13C-NMR spectra were determined with com-
plete proton decoupling. High resolution MS were determined with JEOL
JMS-GCmate and JEOL JMS-AX505HAD instruments. 4-Iodophenoxy-
acetic acid (1a) was purchased from Tokyo Chemical Industry (TCI) Co.,
Ltd. and used after recrystallization from diethyl ether–hexane, and Oxone®
was available from Wako Pure Chemical Industries, Ltd. and used as re-
ceived. Phenols (2b—g) were commercially available. Other phenols (2a,
2g, 2h, 2i) were prepared from 2-hydroxymethyl-4-methoxyphenol by the
usual methods.
2-Hydroxy-5-methoxybenzyl 2,2-Dimethylpropanoate (2a): Colorless
crystals, mp 66.5—67 °C (ethyl acetate–hexane). IR (KBr) cmꢁ1: 3363,
1
1686, 1510, 1469, 1432. H-NMR (270 MHz, CDCl3) d: 1.19 (9H, s), 3.77
(3H, s), 5.07 (2H, s), 6.78—6.96 (3H, m), 7.50 (1H, s). 13C-NMR
(67.5 MHz, CDCl3) d: 27.1 (3), 38.9, 55.8, 63.4, 116.5 (2), 118.6, 122.5,
149.3, 153.3, 180.9. Anal. Calcd for C13H18O4: C, 65.53; H, 7.61. Found: C,
Chart 2
65.46; H, 7.33. HR-MS m/z: 238.11718 (Calcd for C13H18O4 (Mꢂ):
238.12051).
2-(tert-Butyldiphenylsilyloxymethyl)-4-methoxyphenol (2g): A colorless
iodobenzene ring in the oxidation was observed; p-alkoxy is
the most effective, with the series following the approximate
oil. IR (neat) cmꢁ1: 3399, 1499, 1465, 1428. 1H-NMR (270 MHz, CDCl3) d:
1.07 (9H, s), 3.68 (3H, s), 4.84 (2H, s), 6.34 (1H, d, Jꢃ2.7 Hz), 6.75 (1H,
order p-ROꢀp-Me, o-MeO, m-MeOꢀHꢀo-CO2H. And re-
markable solvent effects were observed. This oxidation sys-
tem has the following features. The first is that reaction pro-
ceeds under mild conditions. The second is that Oxone® is an
inorganic, water-soluble, commercially available, and inex-
pensive with low toxicity. The third is that solubility of 1a in
alkaline solution facilitates its recovery.
dd, Jꢃ8.6, 2.9 Hz), 6.85 (1H, d, Jꢃ8.6 Hz), 7.35—7.50 (6H, m), 7.61 (1H,
s), 7.65—7.72 (4H, m). 13C-NMR (67.5 MHz, CDCl3) d: 19.1, 26.7 (3),
55.7, 66.5, 112.4, 114.1, 117.2, 124.6, 127.9 (4), 130.1 (2), 132.0 (2), 135.5
(4), 150.2, 152.8. HR-MS m/z: 392.17912 (Ccalcd for C24H28O3Si (Mꢂ):
392.18078).
2-Azidomethyl-4-methoxyphenol (2h): A colorless oil. IR (neat) cmꢁ1
:
1
3331, 1514, 1446, 1435. H-NMR (270 MHz, CDCl3) d: 3.77 (3H, s), 4.39
(2H, s), 5.11 (1H, br s), 6.75—6.80 (3H, m). 13C-NMR (67.5 MHz, CDCl3)
d: 51.0, 55.8, 114.9, 115.4, 116.9, 122.6, 148.0, 153.7. HR-MS m/z:
179.06662 (Calcd for C8H9N3O2 (Mꢂ): 179.06948).
Experimental
2-(2-Hydroxy-5-methoxybenzyl)isoindole-1,3-dione (2i): Pale yellow
crystals, mp 161—162 °C (ethyl acetate–ether). IR (KBr) cmꢁ1: 3328, 1765,
1697, 1617, 1501, 1434, 1400. 1H-NMR (300 MHz, CDCl3) d: 3.75 (3H, s),
Melting points are uncorrected. IR spectra were recorded using JASCO
FT/IR-460 Plus spectrophotometer. H-NMR spectra were determined with
Varian Gemini 300 (300 MHz) and JEOL JNM-FX270 (270 MHz) spec-
1

March 2009
255
eral procedure, 2i (50 mg, 0.18 mmol) was treated with 1a (2.5 mg,
0.0088 mmol) and Oxone® (434 mg, 0.71 mmol) in TFE–H2O (1 : 2, 2 ml)
to give 2-(3,6-dioxocyclohexa-1,4-dienylmethyl)isoindole-1,3-dione (3i)55)
(46 mg, 98%) as yellow needles, mp 169—172 °C (ethyl acetate–hexane). IR
(neat) cmꢁ1: 1767, 1711, 1659, 1467, 1419, 1391. 1H-NMR (270 MHz,
CDCl3) d: 4.72 (2H, d, Jꢃ1.9 Hz), 6.37 (1H, q, Jꢃ2.2 Hz), 6.75 (1H, dd,
Jꢃ10.3, 2.2 Hz), 6.83 (1H, d, Jꢃ10.3 Hz), 7.75—7.93 (2H, m), 7.87—7.93
(2H, m). 13C-NMR (67.5 MHz, CDCl3) d: 28.9, 123.6 (2), 131.1, 131.6,
134.4 (3), 136.4 (2), 142.4, 167.3 (2), 186.0, 186.5. HR-MS m/z: 267.04932
(Calcd for C15H9NO4 (Mꢂ): 267.05316).
4.80 (2H, s), 6.79 (1H, dd, Jꢃ8.8, 3.0 Hz), 6.91 (1H, d, Jꢃ8.8 Hz), 6.94 (1H,
t, Jꢃ3.0 Hz), 7.51 (1H, s), 7.70—7.75 (2H, m), 7.82—7.88 (2H, m). 13C-
NMR (75 MHz, CDCl3) d: 37.2, 55.8, 115.9, 116.1, 119.2, 122.9, 123.6 (2),
131.6, 134.3 (3), 148.6, 153.4, 168.8 (2). Anal. Calcd for C16H13NO4: C,
67.84; N, 4.94; H, 4.63. Found: C, 67.53; N, 5.25; H, 4.66. HR-MS m/z:
283.08138 (Calcd for C16H13NO4 (Mꢂ): 283.08446).
Catalytic Hypervalent Iodine Oxidation of 2a, General Procedure
A
suspension of 2a (1.0 g, 4.2 mmol), 1a (58 mg, 0.2 mmol) and Oxone®
(1.03 g, 16.8 mmol) in TFE–H2O (1 : 2, 42 ml) was stirred at room tempera-
ture for 45 min. The mixture was diluted with ethyl acetate and washed with
water. The organic layer was then washed with aqueous saturated sodium bi-
carbonate solution and dried, concentrated to give pure 3,6-dioxocyclohexa-
1,4-dienylmethyl 2,2-dimethylpropanoate (3a) (931 mg, quant) as yellow
crystals; mp 71—72 °C (ethyl acetate–hexane). IR (KBr) cmꢁ1: 1735, 1658,
1484, 1459, 1440. 1H-NMR (270 MHz, CDCl3) d: 1.27 (9H, s), 4.99 (2H, d,
Jꢃ1.9 Hz), 6.64—6.68 (1H, m), 6.74—6.88 (2H, m). 13C-NMR (75 MHz,
CDCl3) d: 27.2 (3), 38.9, 59.4, 131.1, 136.5, 136.6, 143.6, 177.5, 186.1,
186.9. Anal. Calcd for C12H14O4: C, 64.85; H, 6.35. Found: C, 64.71; H,
5.86. HR-MS m/z: 222.08846 (Calcd for C12H14O4 (Mꢂ): 222.08921). The
alkaline solution was acidified by 10% hydrochloric acid solution and ex-
tracted with ethyl acetate. The organic layer was dried and concentrated to
give recovered 1a (44 mg, 76%). It can be used after recrystallization from
diethyl ether–hexane.
Acknowledgments The authors wish to thank Professor Yasuyuki Kita
for helpful discussion.
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Catalytic Hypervalent Iodine Oxidation of 2b Following the general
procedure, 2b (124 mg, 1 mmol) was treated with 1a (14 mg, 0.05 mmol) and
Oxone® (2.46 g, 4 mmol) in TFE–H2O (1 : 2, 10 ml) to give 1,4-benzoquinone
(3b) (84 mg, 78%) as yellow crystals, which was directly identical to the
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and Oxone® (738 mg, 1.2 mmol) in TFE–H2O (1 : 2, 3 ml) to give 3b (31 mg,
97%) as yellow crystals.
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6754 (2007).
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(1998).
Catalytic Hypervalent Iodine Oxidation of 2d Following the general
procedure, 2d (50 mg, 0.3 mmol) was treated with 1a (4 mg, 0.015 mmol)
and Oxone® (738 mg, 1.2 mmol) in TFE–H2O (1 : 2, 3 ml) to give 3b (29 mg,
88%) as yellow crystals.
Catalytic Hypervalent Iodine Oxidation of 2e Following the general
procedure, 2e (180 mg, 1 mmol) was treated with 1a (14 mg, 0.05 mmol) and
Oxone® (2.46 g, 4 mmol) in TFE–H2O (1 : 2, 10 ml) to give 2-tert-butyl-1,4-
benzoquinone (3e) (163 mg, quant) as orange crystals, which was directly
identical to the commercial sample supplied by TCI CO., Ltd.
Catalytic Hypervalent Iodine Oxidation of 2f Following the general
procedure, 2f (292 mg, 1 mmol) was treated with 1a (14 mg, 0.05 mmol) and
Oxone® (2.46 g, 4 mmol) in TFE–H2O (1 : 2, 10 ml) to give 2,5-bis-(1,1-di-
methylbutyl)-1,4-benzoquinone (3f) (276 mg, quant) as yellow crystals, mp
61—62 °C (hexane). IR (KBr) cmꢁ1: 1648, 1597, 1470, 1461, 1449, 1366.
1H-NMR (270 MHz, CDCl3) d: 0.84 (6H, t, Jꢃ7.0 Hz), 0.97—1.15 (4H, m),
1.22 (12H, s), 1.65—1.74 (4H, m), 6.42 (2H, s). 13C-NMR (67.5 MHz,
CDCl3) d: 14.6 (2), 18.4 (2), 27.4 (4), 38.1 (2), 43.1 (2), 134.9 (2), 153.5
(2), 188.3 (2). Anal. Calcd for C18H28O2: C, 78.21; H, 10.21. Found: C,
78.41; H, 10.14. HR-MS m/z: 276.20919 (Calcd for C18H28O2 (Mꢂ):
276.20893).
Catalytic Hypervalent Iodine Oxidation of 2g Following the gen-
eral procedure, 2g (59 mg, 0.15 mmol) was treated with 1a (2 mg,
0.0075 mmol) and Oxone® (369 mg, 0.6 mmol) in TFE–H2O (1 : 2, 1.5 ml)
to give 2-(tert-butyldiphenylsilyloxymethyl)-1,4-benzoquinone (3g) (57 mg,
quant) as yellow solid, mp 76—79 °C (ethyl acetate–hexane). IR (KBr)
cmꢁ1: 1656, 1598, 1470, 1428. 1H-NMR (270 MHz, CDCl3) d: 1.10 (9H, s),
4.58 (2H, d, Jꢃ2.4 Hz), 6.68 (1H, d, Jꢃ10.0 Hz), 6.73 (1H, dd, Jꢃ10.0,
2.2 Hz), 7.04 (1H, q, Jꢃ2.4 Hz), 7.36—7.49 (6H, m), 7.60—7.73 (4H, m).
13C-NMR (67.5 MHz, CDCl3) d: 19.4, 26.9 (3), 59.9, 127.8 (4), 129.9 (2),
130.5, 132.4 (2), 135.3 (4), 136.3, 136.4, 147.9, 186.9, 187.5. HR-MS m/z:
376.14506 (Calcd for C23H24O3Si (Mꢂ): 376.14948).
Catalytic Hypervalent Iodine Oxidation of 2h Following the general
procedure, 2h (48 mg, 0.27 mmol) was treated with 1a (4 mg, 0.013 mmol)
and Oxone® (659 mg, 1.07 mmol) in TFE–H2O (1 : 2, 2.7 ml) to give 2-
azidomethyl-1,4-benzoquinone (3h) (42 mg, 95%) as yellow needles, mp
65—66.5 °C (ethyl acetate–hexane). IR (KBr) cmꢁ1: 1661, 1637, 1602,
1425, 1361. 1H-NMR (300 MHz, CDCl3) d: 4.29 (2H, d, Jꢃ1.4 Hz), 6.75—
6.84 (3H, m). 13C-NMR (75 MHz, CDCl3) d: 48.5, 132.6, 136.3, 136.7,
142.6, 186.1, 186.6. Anal. Calcd for C7H5N3O2: C, 51.54; H, 3.09; N, 25.76.
Found: C, 51.63; H, 3.45; N, 24.99; HR-MS m/z: 163.03585 (Calcd for
C7H5N3O2 (Mꢂ): 163.03818).
36) Review: Owton W. M., J. Chem. Soc., Perkin Trans. 1, 1999, 2409—
Catalytic Hypervalent Iodine Oxidation of 2i Following the gen-

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