Synthesis of 3-aryloxy-2-iodoemodines by oxidation of emodin with (diacetoxyiodo)arenes

Article abstract of DOI:10.1002/ejoc.200300317

Hypervalent iodine oxidation of emodin (1) with various (diacetoxyiodo)arenes 2a-f in potassium hydroxide/methanol leading to 3-aryloxy-1,8-dihydroxy-2-iodo-anthraquinones 4a-f is reported. Mechanistic studies showed reaction via iodonium ylides. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejoc.200300317

FULL PAPER
Synthesis of 3-Aryloxy-2-iodoemodines by Oxidation of Emodin with
(Diacetoxyiodo)arenes
Katja S. Daub,[a] Bernd Habermann,[a] Thilo Hahn,[b] Lars Teich,[a] and Kurt Eger*[a]
Dedicated to Professor Peter Welzel, Universität Leipzig, on the occasion of his 65th birthday
Keywords: Oxidation / Natural products / Ylides / Iodine / Emodin
Hypervalent iodine oxidation of emodin (1) with various (di-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
acetoxyiodo)arenes 2a−f in potassium hydroxide/methanol Germany, 2004)
leading to 3-aryloxy-1,8-dihydroxy-2-iodo-anthraquinones
4a−f is reported. Mechanistic studies showed reaction via
iodonium ylides.
Introduction
The use of hypervalent iodine reagents in organic syn-
thesis has become popular during the last three
decades.[1Ϫ5] Depending on the substrate, hypervalent iod-
ine oxidation with (diacetoxyiodo)benzene (DIB) and pot-
assium hydroxide in methanol leads to different classes of
substances. Where 2,4-dihydroxyacetophenones are in-
volved, oxidation with DIB yields 2-hydroxy-3-iodo-4-
phenoxyacetophenones by rearrangement of iodonium yl-
ides.[6,7] We tried to use this reaction in our survey on deriv-
atization of emodin (1,3,8-trihydroxy-6-methylanthraqui-
none, 1), whose ‘‘left wing’’ has a structural similarity to
2,4-dihydroxyacetophenone (Scheme 1). Emodin occurs in
different plants (rhubarb, aloe) and is a widespread dye in
fungi and lichens. It belongs to the anthraquinones as do
daunorubicin and mitoxantrone, which are some of the
most powerful cytostatics. Emodin possesses diuretic[8] and
vasodilatory[9] effects as well as antineoplastic,[10,11] anti-
biotic[12,13] and antiviral[14,15] activity. It is a tumor cell
growth inhibitor[16] and is also supposed to sensitize cancer
cells.[17] Thus, emodin sensitizes HER/neu-overexpressing
cancer cells to chemotherapeutic agents such as cisplatin,
doxorubicin, etoposide and paclitaxel.[18] This paper reports
on the hypervalent iodine oxidation of emodin (1) with vari-
ous (diacetoxyiodo)arenes 2aϪf via iodonium ylides 3aϪf
to 3-aryloxy-2-iodo-emodines 4aϪf (Scheme 1). In contrast
[a]
Institut für Pharmazie, Fakultät für Biowissenschaften,
Pharmazie und Psychologie, Universität Leipzig,
Brüderstraße 34, 04103 Leipzig, Germany
Fax: (internat.) ϩ49-(0)341-9736709
E-mail: eger@uni-leipzig.de
[b]
Institut für Anorganische Chemie, Universität Leipzig,
Johannisallee 29, 04103 Leipzig, Germany
Scheme 1
894
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200300317
Eur. J. Org. Chem. 2004, 894Ϫ898

Synthesis of 3-Aryloxy-2-iodoemodines
FULL PAPER
sensitivity to oxidation and lowered solubility in many sol-
vents. Their biological activity is under investigation.
Results and Discussion
Emodin (1) oxidation was carried out with DIB and vari-
ous methylated (diacetoxyiodo)arenes 2aϪf to produce 3-
aryloxy-1,8-dihydroxy-2-iodoemodines 4aϪf (Table 1).
2aϪf could be obtained by oxidation of the respective iodo-
benzene derivatives with sodium perborate in acetic acid
according to McKillop.[19] A mechanistic pathway similar
to the oxidation of 2,4-dihydroxyacetophenones with DIB
for the reaction of emodin (1) to 4aϪf with various (diace-
toxyiodo)arenes 2aϪf is outlined in Scheme 2. We assume
that (diacetoxyiodo)arenes [ArI(OAc)2] are converted into
(dimethoxyiodo)arenes [ArI(OMe)2] under highly alkaline
conditions (KOH in MeOH),[20] while emodin changes into
the corresponding emodinate I in situ. (Dimethoxyiodo)-
arenes attack emodin at position 2 to form intermediates II
followed by formation of the iodonium ylides 3aϪf. The
orange-red-colored iodonium ylides finally rearrange to 3-
aryloxy-2-iodoemodines 4aϪf, which is probably due to an
intermediary spiro-Meisenheimer complex III as suggested
by Spyroudis et al. where 2,4-dihydroxyacetophenones are
involved.[21] Using the absorption maximum of the yellow-
Scheme 2. Mechanistic pathway of formation of 3-aryloxy-2-iodo-
emodines 4aϪf
colored aryloxyiodoemodins 4aϪf (λmax. [acetone]
ϭ
437 nm), the migration of the aryl group could be followed
by UV/Vis spectroscopy (Figure 1). Owing to the fast re-
arrangement of the iodonium ylides 3aϪf into the corre-
sponding iodoethers 4aϪf, even at low temperature (1Ϫ10
°C), clean isolation of the zwitterionic iodonium ylides
3aϪf was not possible. However, emodin (1) is a much more
complex molecule than 2,4-dihydroxyacetophenone; it con-
tains a 1,4-benzoquinone moiety and presents many more
mesomeric opportunities, so other mechanistic pathways
may also be available. The position of the aryl substituent
in 4aϪf could not be elucidated by NMR experiments since
no coupling between 4-H and C-1Ј was observed. However,
the structure could be unambiguously verified by X-ray dif-
fraction analysis (Figure 2). Thiophene derivatives 2g and
2h yielded multicomponent mixtures; no products could
be isolated.
Figure 1. Monitoring the rearrangement from 3b to 4b in acetone
by UV/Vis spectroscopy
Conclusion
Table 1. Oxidation of emodin with various (diacetoxyiodo)arenes
ArI(OAc)2 2aϪf
In summary, 3-aryloxy-2-iodoemodines 4aϪf were syn-
thesized for the first time. Their structures were conclusively
determined by X-ray diffraction analysis. The potential of
these highly functionalized compounds as biologically ac-
tive substances is under investigation.
Ar
ArϪI(OAc)2 2 Product 4 Yield 4
(%)
Benzene
a
b
c
d
e
f
a
b
c
d
e
f
21
32
5
16
23
22
2,6-Dimethylbenzene
3,5-Dimethylbenzene
2,4,6-Trimethylbenzene
2,3,5,6-Tetramethylbenzene
2,3,4,5,6-Pentamethylbenzene
Experimental Section
General: Melting points were measured in open capillaries in an oil
bath and are corrected. IR spectra were obtained in KBr disks
Eur. J. Org. Chem. 2004, 894Ϫ898
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895

K. S. Daub, B. Habermann, T. Hahn, L. Teich, K. Eger
FULL PAPER
Figure 2. X-ray crystallographic structures of 4d and 4e
using a PerkinϪElmer FT-IR PC 16 spectrophotometer. 1H NMR
(Diacetoxyiodo)arene 2c: Yield 2.2 g (63%), m.p. 142Ϫ148 °C. 1H
NMR (CDCl3): δ ϭ 2.00 (s, 6 H, COCH3), 2.38 (s, 6 H, CH3), 7.20
and 13C NMR spectra were recorded with a Bruker DRX
(400 MHz) instrument. 13C-HMBC and 13C-HMQC were observed (s, 1 H, 4-H), 7.72 (s, 2 H, 2-H, 6-H) ppm. 13C NMR (CDCl3): δ ϭ
with a Bruker DRX (600 MHz) instrument. EI MS was performed 20.43 (COCH3), 21.36 (CH3), 121.39 (C-4), 132.57 (C-2, C-6),
with a Bruker Daltonics mass spectrometer operating at 70 eV.
MALDI-TOF-MS was performed with a Perspective Biosystems
Voyager-DETM RP. Colorimetric measurements were carried out
with a PerkinϪElmer Lambda 16 UV/Vis spectrophotometer. TLC
was performed using Merck silica-gel 60 F254 plates and column
chromatography using Merck Kieselgel 60 (0.063Ϫ0.200 mm).
133.76 (C-1), 141.10 (C-3, C-5), 176.40 (COCH3) ppm.
1
(Diacetoxyiodo)arene 2d: Yield 2.5 g (67%), m.p. 160Ϫ163 °C. H
NMR (CDCl3): δ ϭ 1.98 (s, 6 H, COCH3), 2.37 (s, 3 H, 4-CH3),
2.72 (s, 6 H, 2-CH3, C6-CH3), 7.12 (s, 2 H, 3-H, 5-H) ppm. 13C
NMR (CDCl3): δ ϭ 20.43 (COCH3), 21.22 (4-CH3), 26.76 (2-CH3,
6-CH3), 129.00 (C-1), 129.72 (C-3, C-5), 141.37 (C-2, C-6), 176.40
(COCH3) ppm.
(Diacetoxyiodo)arenes 2bϪh: (Diacetoxyiodo)arenes were prepared
by oxidation of iodoarenes with sodium perborate in glacial acetic
acid using the procedure described by McKillop et al.[22] These
authors have previously described the synthesis of 2b and 2e. The
synthesis of 2c and 2d by iodoarene oxidation with peracetic acid
was reported by Shah et al.[23] The pentamethylbenzene derivative
2f is a new compound. Since no NMR spectroscopic data have
been generated from any of these compounds until now, these data
are listed below. Thiophene derivative 2g and the new compound
2h were prepared using the procedure described by Togo et al.[24]
These heterocyclic derivatives are less stable than the (diacetoxy-
iodo)benzene derivatives 2aϪf, so that 5-methylthiophene deriva-
tive 2h decomposes even at room temperature.
(Diacetoxyiodo)arene 2e: Yield 2.2 g (58%), m.p. 150Ϫ157 °C. 1H
NMR (CDCl3): δ ϭ 1.97 (s, 6 H, COCH3), 2.36 (s, 6 H, 3-CH3, 5-
CH3), 2.65 (s, 6 H, 2-CH3, 6-CH3), 7.15 (s, 1 H, 4-H) ppm. 13C
NMR (CDCl3): δ ϭ 20.37 (COCH3), 21.72 (3-CH3, 5-CH3), 24.58
(2-CH3, 6-CH3), 135.55 (C-4), 135.93 (C-3, C-5), 136.10 (C-1),
176.44 (COCH3) ppm.
(Diacetoxyiodo)arene 2f: Yield 3.3 g (85%), m.p. 137Ϫ140 °C. 1H
NMR (CDCl3): δ ϭ 1.99 (s, 6 H, COCH3), 2.32 (s, 3 H, 4-CH3),
2.36 (s, 6 H, 3-CH3, 5-CH3), 2.75 (s, 6 H, 2-CH3, 6-CH3) ppm. 13
C
NMR (CDCl3): δ ϭ 17.52 (4-CH3), 18.75 (3-CH3, 5-CH3), 20.45
(COCH3), 26.29 (2-CH3, 6-CH3), 134.35 (C-1), 134.55, 136.59 (C-
3, C-5, C-2, C-6), 176.44 (COCH3) ppm.
General Procedure: Sodium perborate tetrahydrate (16.9 g,
110 mmol) was added to a solution of iodoarene (10 mmol) in gla-
cial acetic acid (90 mL) in portions over a time of 20 min. The
mixture was heated to 50 °C and stirred at this temperature for 6 h.
The product was extracted with dichloromethane (3 ϫ 50 mL). The
organic phase was washed with water (2 ϫ 100 mL), dried with
anhydrous Na2SO4, and filtered. The solvent was evaporated under
reduced pressure. The crude product was purified by crystallization
from hexane.
(Diacetoxyiodo)arene 2g: Yield 1.1 g (34%), m.p. 112Ϫ119 °C (de-
composition). H NMR (CDCl3): δ ϭ 2.02 (s, 6 H, COCH3), 2.75
(d, J ϭ 3.6 Hz, 1 H, 3-H), 7.12Ϫ7.15 (m, 1 H, 4-H), 7.64 (d, J ϭ
5.4 Hz, 1 H, 5-H) ppm. 13C NMR (CDCl3): δ ϭ 20.37 (COCH3),
106.33 (C-2), 128.64, 134.87, 139.07 (C-3, C-4, C-5), 177.01
(COCH3) ppm.
1
(Diacetoxyiodo)arene 2h: Yield 1.2 g (35%). 1H NMR (CDCl3): δ ϭ
2.04 (s, 6 H, COCH3), 2.68 (s, 3 H, CH3), 6.82 (d, J ϭ 3.8 Hz, 1
1
H, 4-H) 7.63 (d, J ϭ 3.8 Hz, 1 H, 3-H) ppm. H NMR ([D6]ace-
1
(Diacetoxyiodo)arene 2b: Yield 2.0 g (57%), m.p. 151Ϫ153 °C. H
tone): δ ϭ 1.95 (s, 6 H, COCH3), 2.72 (s, 3 H, CH3), 6.97 (d, J ϭ
3.9 Hz, 1 H, 4-H), 7.80 (d, J ϭ 3.9 Hz, 1 H, 3-H) ppm.
NMR (CDCl3): δ ϭ 1.93 (s, 6 H, COCH3), 2.70 (s, 6 H, CH3),
7.22Ϫ7.31 (m, 3 H, Har) ppm. 13C NMR (CDCl3): δ ϭ 20.43
(COCH3), 26.99 (CH3), 128.14 (C-3, C-5), 132.54 (C-4), 133.04 (C-
1), 141.49 (C-2, C-6), 176.40 (COCH3) ppm.
3-Aryloxy-1,8-dihydroxy-2-iodo-6-methylanthraquinones 4a؊f. Gen-
eral Procedure: A solution of KOH (280 mg, 5 mmol) and emodin
896
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2004, 894Ϫ898

Synthesis of 3-Aryloxy-2-iodoemodines
FULL PAPER
(270 mg, 1 mmol) in methanol (25 mL) was added to a solution of
CH3), 6.74 (s, 1 H, 4-H), 6.95 (s, 1 H, 4Ј-H), 7.08 (s, 1 H, 7-H),
(diacetoxyiodo)arene 2aϪf (1 mmol) and stirred at 0 °C for 4 h. 7.52 (s, 1 H, 5-H), 11.93 (s, 1 H, 8-OH), 13.30 (s, 1 H, 8-OH), 13.30
Acetone (250 mL) was added, and the solution was stirred at 30
(s, 1 H, 1-OH) ppm. 13C NMR (CDCl3): δ ϭ 12.58, 19.76, 22.26
°C for 24 h. The reaction’s progress was monitored by TLC. After
(CH3), 84.01 (C-2), 104.98 (C-4), 110.72 (C-9a), 113.23 (C-8a),
completion of the reaction, the organic solvent was removed by 121.38 (C-5), 124.78 (C-7), 126.15 (C-2Ј, C-6Ј), 129.47 (C-4Ј),
rotary evaporation at reduced pressure. The residue was suspended
in a solvent mixture of petroleum ether/ethyl acetate/acetic acid
(20/20/1) and filtered. The filtrate was evaporated under reduced
pressure and purified by column chromatography and/or recrystal-
lization.
133.01, 135.15 (C-4a, C-10a), 149.03 (C-6), 150.24 (C-1Ј), 162.65,
163.91, 164.10 (C-OH), 181.66 (C-10), 190.61 (C-9) ppm.
1,8-Dihydroxy-2-iodo-6-methyl-3-(2,3,4,5,6-pentamethylphenoxy)-
anthraquinone (4f): Yield 120 mg (22%), m.p. 300Ϫ305 °C, yellow
plates. UV (CHCl3): λmax. ϭ 440 nm. IR (KBr): ν˜ ϭ 3429, 2923,
1675, 1625 cmϪ1. MS calculated for C26H23IO5 [M]: 542.37,
MALDI-MS [M]Ϫ found: 542.3. 1H NMR (CDCl3): δ ϭ 2.02 (s, 6
H, 3Ј-CH3, 5Ј-CH3), 2.24 (s, 6 H, 2Ј-CH3, 6Ј-CH3), 2.27 (s, 3 H,
4Ј-CH3), 6.74 (s, 1 H, 4-H), 7.09 (s, 1 H, 7-H), 7.52 (s, 1 H, 5-H),
11.95 (s, 1 H, 8-OH), 13.32 (s, 1 H, 1-OH) ppm. 13C NMR
(CDCl3): δ ϭ 13.42, 18.53, 28.23, 22.30 (CH3), 84.13, 105.15,
110.66 (C-9a), 113.23 (C-8a), 121.36 (C-5), 124.78 (C-7), 125.66 (C-
2Ј, C-6Ј), 134.31 (C-4Ј), 134.94 (C-3Ј, C-5Ј), 133.01, 135.11 (C-4a,
C-10a), 148.15 (C-6), 148.15 (C-6), 148.97 (C-1Ј), 162.61, 163.88,
164.38 (C-0 H), 181.74 (C-10), 190.57 (C-9) ppm.
1,8-Dihydroxy-2-iodo-6-methyl-3-phenoxyanthraquinone (4a): Yield
100 mg (21%), m.p. 263Ϫ264 °C, yellow plates. UV (acetone):
λmax. ϭ 433 nm. IR (KBr): ν˜ ϭ 3423, 1672, 1625, 1560 cmϪ1. MS
calculated for C21H13IO5 [M]: 472.24, MALDI-MS [M]Ϫ found:
1
472.2. H NMR (CDCl3): δ ϭ 2.45 (s, 3 H, CH3), 6.84 (s, 1 H, 4-
H), 7.47 (s, 1 H, 5-H), 7.21Ϫ7.23 (m, 3 H, 2Ј-H, 6Ј-H, 7-H), 7.37
(d, J ϭ 7.6 Hz, 1 H, 4Ј-H), 11.93 (s, 1 H, 8-OH), 13.32 (s, 1 H, 1-
OH) ppm. 13C NMR (CDCl3): δ ϭ 22.27 (CH3), 84.21 (C-2),
103.95 (C-9a), 107.47 (C-4), 111.03 (C-8a), 120.60 (C-2Ј, C-6Ј),
121.57 (C-5), 124.83 (C-7), 125. 89 (C-4Ј), 125.89 (C-4Ј), 130.45 (C-
3Ј, C-5Ј), 132.10, 132.97 (C-4a, C-10a), 149.29 (C-6), 153.97 (C-1Ј),
164.67, 163.91, 167.69 (CϪOH), 181.15 (C-10), 190.51 (C-9) ppm.
¯
Crystallographic Data. 4d: Crystal system: triclinic; space group P1;
˚
˚
˚
a ϭ 8.088(1) A, b ϭ 9.759(1) A, c ϭ 14.451(1) A, α ϭ 76.13(1)°,
3
˚
3-(2,6-Dimethylphenoxy)-1,8-dihydroxy-2-iodo-6-methylanthra-
quinone (4b): Yield 160 mg (32%), m.p. 302Ϫ304 °C, yellow plates.
UV (acetone): λmax. ϭ 436 nm. IR (KBr)1: ν˜ ϭ 3425, 1663, 1633,
1522 cmϪ1. MS calculated for C23H17IO5 [M]: 500.29, MALDI-MS
βϭ 75.24(1)°, γ ϭ 70.40(1)°, V ϭ 1024.1(2) A , Z ϭ 2, ρcalcd.
ϭ
1.668 g·cmϪ3, collected reflections 6504; unique reflections 4697;
number of parameters 347; R1 ϭ 0.0340; wR2 0.0800 for [I Ͼ 2σ(I)].
˚
¯
4e: Crystal system: triclinic; space group P1; a ϭ 6.898(1) A, b ϭ
1
[M ϩ Na]ϩ found: 523.3. H NMR (CDCl3): δ ϭ 2.13 (s, 6 H, 2Ј-
˚
˚
8.513(1) A, c ϭ 18.367(2) A, α ϭ 88.94(1)°, β ϭ 84.53(1)°, γ ϭ
73.25(1)°, V ϭ 1028.0(2) A , Z ϭ 2, ρcalcd. ϭ 1.707 g·cmϪ3, col-
3
˚
CH3, 6Ј-CH3), 2.44 (s, 3 H, 6-CH3), 6.78 (s, 1 H, 4-H), 7.10 (s, 1
H, 7-H), 7.16 (s, 3 H, 3Ј-H, 4Ј-H, 5Ј-H), 11.94 (s, 1 H, 8-OH), 13.32
(s, 1 H, 1-OH) ppm. 13C NMR (CDCl3): δ ϭ 16.28, 22.27 (CH3),
84.13 (C-2), 104.62 (C-4), 110.89 (C-9a), 113.23 (C-8a), 121.46 (C-
5), 124.81 (C-7), 126.46 (C-4Ј), 129.48 (C-3Ј, C-5Ј), 130.64 (C-2Ј,
C-6Ј), 132.99, 135.23 (C-4a, C-10a), 149.13 (C-6), 150.48 (C-1Ј),
162.69, 163.64, 163.94 (C-OH), 181.53 (C-10), 190.67 (C-9) ppm.
lected reflections 5950; unique reflections 4323; number of para-
meters 364; R1 ϭ 0.0340; wR2 0.0800 for [I Ͼ 2σ(I)]. The structures
of 4d and 4e were solved by the direct method using the SHELXL-
97 program.[25] All hydrogen atoms were located and refined iso-
tropically, all non-hydrogen atoms were refined anisotropically.
CCDC-189425 and -189426 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; Fax: (international) ϩ 44-1223-336-033;
E-mail: deposit@ccdc.cam.ac.uk].
3-(3,5-Dimethylphenoxy)-1,8-dihydroxy-2-iodo-6-methylanthra-
quinone (4c): Yield 25 mg (5%), m.p. 252Ϫ254 °C, yellow plates.
UV (acetone): λmax. ϭ 437 nm. IR (KBr): ν˜ ϭ 3440, 1675, 1625,
1560 cmϪ1. MS calculated for C23H17IO5 [M]: 500.29, MALDI-MS
1
[M ϩ Na]ϩ found: 523.3. H NMR (CDCl3): δ ϭ 2.34 (s, 6 H, 3Ј-
CH3, 5Ј-CH3), 2.44 (s, 3 H, 6-CH3), 6.73 (s, 2 H, 2Ј-H, 6Ј-H), 6.91
(s, 1 H, 7-H), 7.10 (s, 1 H, 4-H), 7.13 (s, 1 H, 4Ј-H), 7.57 (s, 1 H,
4Ј-H), 11.94 (s, 1 H, 8-OH), 13.32 (s, 1 H, 1-OH) ppm.
Acknowledgments
1,8-Dihydroxy-2-iodo-6-methyl-3-(2,4,6-trimethylphenoxy)-
anthraquinone (4d): Yield 82 mg (16%), m.p. 257Ϫ258 °C, yellow
plates. UV (acetone): λmax. ϭ 437 nm. IR (KBr): ν˜ ϭ 3425, 2918,
1670, 1622, 1554 cmϪ1. MS calculated for C24H19IO5 [M]: 514.32,
MALDI-MS [M ϩ H]ϩ found: 515.3. 1H NMR (CDCl3): δ ϭ 2.07
(s, 6 H, 2Ј-CH3, 6Ј-CH3), 2.33 (s, 3 H, 3Ј-CH3), 2.44 (s, 3 H, 6-
CH3), 6.79 (s, 1 H, 4-H), 7.10 (s, 1 H, 7-H), 7.26 (s, 2 H, 3Ј-H, 5Ј-
H), 11.94 (s, 1 H, 8-OH), 13.32 (s, 1 H, 1-OH) ppm. 13C NMR
(CDCl3): δ ϭ 16.33, 21.02, 22.39 (CH3), 84.21 (C-2), 104.85 (C-4),
110.87 (C-9a), 113.38 (C-8a), 121.56 (C-5), 124.81 (C-7), 130.22 (C-
3Ј, C-5Ј), 130.30 (C-4Ј), 133.15, 135.32 (C-4a, C-10a), 136.08 (C-
2Ј, C-6Ј), 148.43 (C-6), 149.23 (C-1Ј), 162.80 (C-3), 164.04 (C-1, C-
8), 181.72 (C-10), 190.78 (C-9) ppm.
The authors are grateful to Fonds der Chemischen Industrie and
Deutsche Forschungsgemeinschaft (DFG) Graduiertenkolleg
‘‘Mechanistische und Anwendungsaspekte nichtkonventioneller
Oxidationsreaktionen’’ for financial support. We thank Prof.
Joachim Sieler for generating X-ray crystallographic data from 4e
and for technical support.
[1]
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[2]
P. S. Stang, V. V. Zhdankin, Chem. Rev. 1996, 96, 1123Ϫ1178.
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Chem. Int. Ed. 2000, 39, 2525Ϫ2529.
1,8-Dihydroxy-2-iodo-6-methyl-3-(2,3,5,6-tetramethylphenoxy)-
anthraquinone (4e): Yield 121 mg (23%), m.p. 281Ϫ283 °C, yellow
plates. UV (CHCl3): λmax. ϭ 440 nm. IR (KBr): ν˜ ϭ 3440, 2920,
1670, 1625 cmϪ1. MS calculated for C25H21IO5 [M]: 528.35,
MALDI-MS [M ϩ H]ϩ found: 529.4. 1H NMR (CDCl3): δ ϭ 1.97
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