ortho-Selective phenol-coupling reaction by anodic treatment on boron-doped diamond electrode using fluorinated alcohols

Article abstract of DOI:10.1002/chem.200802556

A study was conducted to demonstrate ortho-selective phenol-coupling reaction by anodic treatment on boron-doped diamond electrode using fluorinated alcohols. A protocol for the conversion of neat phenol on boron-doped diamond (BDD) electrodes was also developed for the study. Partial conversion of 30% was carried out to prevent electrochemical incineration and to avoid by-products. It was observed that the free path length of oxyl radicals generated on BDD electrodes were found in the nanometer range. Methanol and other simple alcohols were used in the study on the anodic phenol coupling reaction. It was also found that some amount of methanol disappeared from the electrolysis cell despite cooling the electrolyte. Hexafluoroisopopanol with supporting electrolytes produced a powerful electrolyte system for the anodic coupling reaction of phenols.

Full text of DOI:10.1002/chem.200802556

COMMUNICATION
DOI: 10.1002/chem.200802556
ortho-Selective Phenol-Coupling Reaction by Anodic Treatment on Boron-
Doped Diamond Electrode Using Fluorinated Alcohols
Axel Kirste,[a] Martin Nieger,[b] Itamar M. Malkowsky,[c] Florian Stecker,[c]
Andreas Fischer,[c] and Siegfried R. Waldvogel*[a]
Biphenols are very common motifs in natural products[1]
as well as in technical applications.[2] Recently, biphenols
based on simple methyl-substituted phenols, for example,
2,4-dimethylphenol have drawn significant attention as com-
ponents of highly potent ligand systems.[3–5] The sustainable
synthesis of such biphenols is challenging despite their
rather simple scaffolds. Methyl-substituted phenols are
Scheme 1. Electrochemical oxidation of 1 on BDD anodes.
prone to side reactions and 2,4-dimethylphenol in particular
results in predominantly polycyclic architectures upon
anodic treatment.[6] To circumvent this challenge we devel-
oped a boron-based template strategy[7,8] that can be per-
formed on larger scale.[9] A protocol for the conversion of
neat phenol (1) on boron-doped diamond (BDD) electrodes
was developed in our laboratory.[10] To prevent electrochem-
ical incineration and to avoid by-products only partial con-
version of about 30% is performed.[11] In such cases the
electrochemical transformation is very clean. By using these
particular conditions 2,4-dimethylphenol is converted to the
biphenol (Scheme 1). Other tested phenols gave either no
detectable products or ended up in decomposition, as for ex-
ample, sesamol (3; see Scheme 4). BDD is a very appealing
innovative electrode material that opens up novel synthetic
pathways since alcoxyl or hydroxyl radicals are easily
formed.[12] The free path length of oxyl radicals that are gen-
erated on BDD electrodes is in the nanometer range.[13] Es-
pecially, at high current densities overoxidation is a severe
challenge when a specific product should be formed. There-
fore, BDD electrodes are mostly used for disinfection pur-
poses or waste water treatment.[14]
To overcome this limit and the restriction to the sole sub-
strate 1, studies in our group led to the application of media-
tors. Based on electrochemical incineration of waste water
treatment, alcohols or water can be considered as mediators
which react according to the proposed mechanism
(Figure 1).[15] The synthetic utility of such mediators affords
a high anodic stability and a stabilizing effect onto the
oxygen spin center. We report a significantly enlarged scope
and efficiency for the anodic coupling process of simple phe-
nols on BDD electrodes by fluorinated mediators.
[a] A. Kirste, Prof. Dr. S. R. Waldvogel
Rheinische Friedrich-Wilhelms-Universitꢀt Bonn
Kekulꢁ-Institut fꢂr Organische Chemie und Biochemie
Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany)
Fax : (+49)228-73-9608
Figure 1. Common mechanism for the conversion on BDD anodes.
Methanol and other simple alcohols were applied in our
initial studies on the anodic phenol coupling reaction of 1.[10]
This led to very moderate amounts of 2; a significant
amount of the starting material ended up in polymeric by-
products. Moreover, a decent amount of methanol disap-
peared from the electrolysis cell despite cooling the electro-
E-mail: waldvogel@uni-bonn.de
[b] Dr. M. Nieger
Laboratory of Inorganic Chemistry, University of Helsinki
00014 Helsinki (Finland)
[c] Dr. I. M. Malkowsky, Dr. F. Stecker, Dr. A. Fischer
BASF SE, GCI/E-M311, 67056 Ludwigshafen (Germany)
Chem. Eur. J. 2009, 15, 2273 – 2277
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lyte. Most probably, oxidative degradation yielded more vol-
atile carbonyl derivatives, which open up a non-desired reac-
tion pathway. Consequently, more redox-stable mediators
were investigated, leading to fluorinated alcohols. Previous
studies ruled out simple acids for this transformation.[10] Typ-
ically, tert-butyl alcohol (4) is employed as the inert alcohol
for oxidative transformations. When 4 was used in the con-
version of 1 far less attractive yields were obtained (Table 1,
entry 1).
were necessary to create sufficient ionic conductivity
(Table 1, entry 6). Trifluoroacetic acid (10) and the carboxa-
mide (11) gave under optimized conditions dramatically in-
ferior results for those mediators, revealing that the Brøn-
stedt behavior of 9 is not responsible for the good conver-
sion of 2,4-dimethylphenol (Table 1, entries 7 and 8). The
detailed molecular action of hexafluoroisopropanol (9) has
still to be elucidated and explained, but the beneficial effect
of this highly fluorinated alcohol is well documented in
metal catalysis and oxidation reactions.[16]
Despite the acidic nature of the components, electrolysis
of 1 in hexafluoroisopropanol (9) requires an unusually high
applied voltage across the electrodes. By addition of a sup-
porting electrolyte, the applied voltage can be tremendously
decreased.[17] A collection of different tetraalkylammonium
salts and an imidazolium derivative were employed as sup-
porting electrolyte in the electrolysis of 1 in hexafluoroiso-
propanol (9) (Scheme 3); all gave similar results. Due to the
Table 1. Anodic treatment of 1 using different mediators.[a]
Entry
Mediator
Supporting
electrolyte
T
[8C]
j
A
2
CE
[mAcmÀ2
]
[%][b]
[%][c]
1
2
3
4
5
6
7
8
4
5
6
7
9
8
10
11
12
12
12
12
12
12
14
14
45
45
45
45
45
70
20
100
4.7
4.7
9.5
4.7
4.7
4.7
9.5
9.5
10
26
17
18
47
43
15
5
10
26
17
18
47
43
15
5
[a] Reaction conditions: 2.44 g 1, 30 mL mediator, 0.68 g supporting elec-
trolyte, BDD anode, nickel cathode, Q=1.0 F per mol 1. [b] Determined
from crude product by GC using an internal standard. [c] Current effi-
ciency.
A variety of different fluorinated potential mediators
were tested (Scheme 2). Primary alcohols with fluorous moi-
eties in the b-position, such as 2,2,2-trifluoroethanol (5),
Scheme 3. Tested supporting electrolytes in the anodic conversion of 1.
longer alkyl chains, the cation of 16 modifies the lipophilici-
ty of the anode by insertion in the Helmholtz double layer.
This causes a slight decrease in yield (Table 2, entry 1). Neu-
tral and more polar tetraalkylammonium salts gave the best
results (Table 2, entries 2 and 3), whereas the acidic support-
ing electrolytes led to slightly inferior yields (Table 2, en-
tries 4 and 5). Because of the reproducibility and practicabil-
ity, the ionic liquid 12 was used for further studies.
Scheme 2. Mediators for the oxidation of 1.
2,2,3,3-tetrafluoropraponol (6), or 2,2,3,3,4,4,5,5-octafluoro-
pentanol (7), could be applied but gave only moderate
yields of 2 (Table 1, entries 2–4). A doubling of the current
density led to a decrease in the yield because of an en-
hanced concentration of oxyl spin centers close to the elec-
trode that promotes overoxidations.
Significantly better results were obtained when hexafluor-
oisopropanol (9) was employed as mediator. In a very clean
conversion, 2,4-dimethylphenol (1) is transformed to 2
(Table 1, entry 5). Application of more electric current than
1 F per mole substrate did not improve the yield and quality
of the product 2. A trifluoromethyl group can be replaced
by a phenyl moiety to stabilize the oxyl spin center. Thus,
the fluorinated analogue of phenethyl alcohol 8 provided
comparable results to 9. Higher electrolysis temperatures
The yields and the current efficiency were studied over
the course of the electrolysis under optimized conditions for
Table 2. Anodic treatment of 1 with different supporting electrolytes.[a]
Entry
Supporting
electrolyte
T
[8C]
j
A
2
CE
[mAcmÀ2
]
[%][b]
[%][c]
1
2
3
4
5
16
12
15
14
13
20
45
45
45
45
9.5
4.7
4.7
4.7
4.7
37
47
45
46
43
37
47
45
46
43
[a] Reaction conditions: 2.44 g 1, 0.1m supporting electrolyte in 30 mL
HFIP, BDD anode, nickel cathode, Q=1.0 F per mol 1. [b] Determined
from crude product by GC using an internal standard. [c] Current effi-
ciency.
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Chem. Eur. J. 2009, 15, 2273 – 2277

Anodic Phenol-Coupling Reactions
COMMUNICATION
1 (Figure 2). The chemical yield reached a maximum (ca.
50%) when a current of 1 to 1.3 F was applied per mole 1.
The current efficiency decreases with increasing applied
electric current, indicating that electrochemical decomposi-
tion might occur to some extent. Therefore, application of
1 F electric current per mole substrate represents a reasona-
ble compromise between yield and current efficiency.
Scheme 5. General oxidation of substituted phenols on BDD anodes.
Table 3. Electrochemical synthesis of biphenols.[a]
Entry Substrate Supporting
electrolyte
j
AHCTUNGTRENNUNG
Yield (Product) CE
[mAcmÀ] [%][b] [%][c]
1
2
3
4
5
6
7
17[d]
18[e]
3[f]
12
15
12
12
12
12
12
4.7
4.7
2.8
4.7
4.7
4.7
4.7
22 (23)
41 (24)
74 (25)
13 (26)
30 (27)
24 (28)
30 (29)
22
41
74
13
30
12
30
19
20
21[g]
22
[a] Reaction conditions: 0.02 mol phenol, 0.1m supporting electrolyte in
30 mL HFIP, BDD anode, nickel cathode, Q=1.0 F per mol phenol.
[b] Yield of isolated product. [c] Current efficiency. [d] 0.01 mol phenol.
[e] 0.005 mol phenol. [f] 0.012 mol phenol. [g] 0.04 mol phenol, Q=2.0 F
per mol phenol.
substrates were selectively coupled to the corresponding bi-
phenol (Table 3, entries 4–7). The low yield is reflected by
the electron-deficient nature of the substituents. Despite the
low yield for the fluorinated biphenol 26, it represents the
first direct example for the oxidative coupling of such a fluo-
rinated substrate. The chloro and bromo congeners, 20 and
22, respectively, yielded significantly better results, which
can be attributed to the less deactivating effect of these sub-
stituents. On switching the halogen moiety to position 4,
only the 4-chlorocresol (21) is converted to the biphenol
(Table 3, entry 6). The corresponding 4-fluorocresol is not
converted on BDD electrodes and marks the limit of this
method. Since free radicals are involved in this anodic trans-
formation iodo phenols are not compatible with the proto-
col.
A suitable single crystal of 26 was obtained and the struc-
ture elucidated by X-ray analysis (Figure 3). The molecular
structure of the fluorinated biphenol is specific. Despite the
rather large dipole moment created by the fluoro and hy-
droxyl moieties, the polar groups of both aryls point to the
same side. This spatial arrangement is favored in the solid-
state and dominated by the intramolecular hydrogen bond
between the phenolic oxygen atoms. Since such a seven-
Figure 2. Progress of the conversion of 1 on BDD anode in respect to
current efficiency; ꢄ Yield of 2, * CE.
To elucidate the scope of the elaborated protocol, a varie-
ty of differently substituted phenols were subjected to elec-
trolysis (Scheme 4 and 5). The solubility of the phenolic sub-
strate in the fluorous electrolyte is crucial for the conver-
sion. Therefore, solid substrates (3, 17, 18) had to be electro-
lyzed at 458C and at lower concentrations (Table 3, en-
tries 1–3). Sterically demanding phenol 17 could be
converted in moderate yield (Table 3, entry 1), since alterna-
tive reaction pathways promote complete incineration.[18]
Better results were obtained with 2-naphthol (18),which pro-
vided binol (24) as the sole product (Table 3, entry 2). Most
remarkably, sesamol (3) was anodically coupled in very
good yield (Table 3, entry 3). Without hexafluoroisopropa-
nol (9), anodic conversion of 3 results in only tarry residues
on the BDD electrodes. Furthermore, halogenated phenolic
Figure 3. Molecular structure in the solid state of 3,3’-difluoro-5,5’-di-
methyl-2,2’-biphenol (26); left: top view with indicated hydrogen bond-
ing; right: side view along biaryl axis.
Scheme 4. Converted phenols on BDD anode using 8.
Chem. Eur. J. 2009, 15, 2273 – 2277
ꢃ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2275

S. R. Waldvogel et al.
was recovered in vacuo. The remaining crude product was fractioned by
water (50 mL) and tert-butyl methyl ether (TBME, 50 mL), the layers
were separated and the aqueous layer was extracted with TBME (2ꢄ
30 mL). The combined organic layers were washed with brine (50 mL),
dried (MgSO4), and concentrated in vacuo to give a brown oil. Purifica-
tion by column chromatography and drying under vacuum yielded the
corresponding biphenol as a colorless solid.
membered ring system is not comfortable in plane, the mol-
ecule is twisted around the biaryl axis about 46.58. The mon-
omers form stacks along the a axis, which are linked by in-
termolecular hydrogen bonds. Along the b axis, these stacks
are also linked by intermolecular hydrogen bonding.
In conclusion, hexafluoroisopropanol (9) with supporting
electrolytes creates a powerful electrolyte system for the
anodic coupling reaction of phenols. The scope of BDD
electrodes in organic synthesis has thereby been significantly
enlarged. The protocol is easy to perform and practical.
When only 1 F electric current is applied, a clean reaction
mixture is obtained consisting of products, starting material,
and electrolyte. The protocol is particularly useful for very
electron-rich phenols as well as halogenated substrates. For
the latter biphenols, the access is fast and provides interest-
ing scaffolds for ligand design and catalyst development.
This together with other BDD-generated oxyl spin centers
will be studied with fluorous electrolytes and reported in
due course.
3,3’,5,5’-Tetramethyl-2,2’-biphenol (2): 2,4-Dimethylphenol (1) (2.44 g,
0.02 mol), 12 (0.68 g, 3 mmol), purified by column chromatography (cy-
clohexane/ethyl acetate 98:2; Rf =0.10), yielded
2 (1.15 g, 4.7 mmol,
47%); m.p. 134–1358C (cyclohexane, value in ref. [7]; m.p. 13 58C;
1H NMR (400 MHz, CDCl3): d=2.29 (s, 12H; CH3), 5.09 (s, 2H; OH),
6.88 (s, 2H, 4-H), 7.01 ppm (s, 2H; 6-H).
3,3’,5,5’,6,6’-Hexamethyl-2,2’-biphenol (23): 2,4,5-Trimethylphenol (17)
(1.36 g, 0.01 mol), 12 (0.68 g, 3 mmol), purified by column chromatogra-
phy (cyclohexane/ethyl acetate 95:5; Rf =0.21), yielded 23 (0.31 g,
1.2 mmol, 22%); m.p. 1718C (n-heptane, value in ref. [7]; m.p. 1698C;
1H NMR (300 MHz, CDCl3): d=1.86 (s, 6H; CH3), 2.24 (s, 12H; CH3),
4.03 (s, 2H; OH), 7.01 ppm (s, 2H; 4-H).
1,1’-Binaphthyl-2,2’-ol (24): 2-Naphthol (18) (0.72 g, 0.005 mol), 12
(0.68 g, 3 mmol), purified by vacuum sublimation (1058C, 39 mbar),
yielded 24 (0,30 g, 1.0 mmol, 41%); analytical verification was accom-
plished by comparing to the commercial available substance.
5,5’-DihydroxyACHTUNGTRENNN[UG 6,6’]biACHUTNRTGEG(NNUN benzoACHTNUGTNER[NUGN 1,3]dioxolyl) (25): Sesamol (3) (1.66 g,
0.012 mol), 13 (0.62 g, 3 mmol), the crude product washed with cold
methanol (2ꢄ10 mL), yielded 24 (1.23 g, 4.5 mmol, 74%); m.p. 202–
2038C (cyclohexane, value in ref. [7]; m.p. 2018C; 1H NMR (400 MHz,
CD3OD): d=5.88 (s, 4H; 2-H), 6.46 (s, 2H; 4-H), 6.65 (s, 2H, 7-H),
8.87 ppm (brs, 2H; OH).
Experimental Section
General remarks: All reagents were used in analytical grades. Solvents
were desiccated if necessary by standard methods. BBD (CONDIAS
GmbH, Itzehoe, Germany, 10 mm BDD on Si). Column chromatography
was performed on silica gel (particle size 63–200 mm, Merck, Darmstadt,
Germany) by using mixtures of cyclohexane with ethyl acetate as eluents.
For thin-layer chromatography silica gel 60 sheets on glass (F254, Merck,
Darmstadt, Germany) were used. Melting points were determined with a
Melting Point Apparatus SMP3 (Stuart Scientific, Watford Herts, UK)
and were uncorrected. Microanalysis was performed with a Vario EL III
3,3’-Difluoro-5,5’-dimethyl-2,2’-biphenol (26): 2-Fluoro-4-methylphenol
(19) (2.52 g, 0.02 mol), 12 (0.68 g, 3 mmol), purified by column chroma-
tography (cyclohexane/ethyl acetate 9:1; Rf =0.14), yielded 25 (0.32 g,
1.3 mmol, 13%); m.p. 152–1538C (cyclohexane); 1H NMR (300 MHz,
CDCl3): d=2.32 (s, 6H; CH3), 5.73 (s, 2H; OH), 6.88 (s, 2H, 6-H),
ACTHNUTRGNEUNG
6.96 ppm (d, 3J(H,F)=11.1 Hz, 2H; 4-H); 13C NMR (75 MHz, CDCl3):
1
(Elementar-Analysensysteme, Hanau, Germany). H NMR and 13C NMR
d=20.66 (CH3), 116.07, 126.06, 126.73, 131.02, 138.48, 150.63 ppm;
19F NMR (282 MHz, CDCl3): d=À138.94 ppm; HRMS: calcd for
C14H12F2O2: 250.0805; found: 250.0805; elemental analysis calcd (%) for
C14H12F2O2 (250.08): C 67.20, H 4.83; found: C 66.93, H 4.85.
spectra were recorded at 258C by using a Bruker ARX 300, AMX 300,
or AMX 400 instrument (Analytische Messtechnik, Karlsruhe, Germa-
ny). Chemical shifts (d) are reported in parts per million (ppm) relative
to TMS as internal standard or to traces of CHCl3, [D6]acetone, or
CD3OD in the corresponding deuterated solvents. 19F NMR spectra were
recorded at 258C by using a Bruker AC200 spectrometer with external
calibration relative to CCl3F. Mass spectra were obtained by using a
MAT8200, MAT95XL (Finnigan, Bremen, Germany), or MS50 (Kratos,
Manchester, England) apparatus employing EI and by using a Quattro
LC (Waters-Micromass), or Micro TOF (Bruker) apparatus employing
ESI and HRMS (negative mode). Gas chromatography was performed
with a Shimadzu GC-2010 (Shimadzu, Japan) using a HP 5 column (Agi-
lent Technologies, USA; length: 30 m, inner diameter: 0.25 mm, film:
0.25 mm, carrier gas: hydrogen). GC calibration was accomplished with
analytically pure biphenols (2, 23–29) and pentadecane as internal stan-
dard. Single-crystal X-ray diffraction study was carried out on a Bruker-
Nonius Kappa-CCD diffractometer at 123(2) K using MoKa radiation (l=
0.71073 ꢅ). Direct methods (SHELXS-97)[19] were used for structure so-
lution, and refinement was carried out using SHELXL-97 (full-matrix
least-squares on F2).[19] H atoms were localized by difference electron
density determination and refined by using a riding model (H(O) free).
The absolute structure could not be determined reliably by refinement of
Flackꢆs x-parameter (x=0.0(10)).[20] Graphics DIAMOND 3.0d (Crystal
Impact GbR, Bonn, Germany).
Crystal data of 26: Colorless crystals, C14H12F2O2, M=250.24, crystal size
0.30ꢄ0.12ꢄ0.06 mm, orthorhombic, P212121 (no. 19): a=7.110(1), b=
7.693(1), c=20.923(2) ꢅ, V=1144.4(2) ꢅ3, Z=4, 1calcd =1.452 MgmÀ3, F-
AHCTUNGTRENNUNG
(000)=520, m=0.118 mmÀ1, 11199 reflections (2qmax =508), 2004 unique
[Rint =0.0482], 171 parameters, 2 restraints, R1 (I>2s(I))=0.0405, wR2
(all data)=0.0830, S=1.073, largest difference peak and hole 0.165 and
À0.200 eꢅÀ3. CCDC-710803 (26) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif
3,3’-Dichloro-5,5’-dimethyl-2,2’-biphenol (27): 2-Chloro-4-methylphenol
(20) (2.52 g, 0.02 mol), 12 (0.68 g, 3 mmol), purified by column chroma-
tography (cyclohexane/ethyl acetate 9:1; Rf =0.20), yielded 26 (0.84 g,
3.0 mmol, 30%); m.p. 127–1288C (cyclohexane); 1H NMR (400 MHz,
[D6]acetone): d=2.28 (s, 6H; CH3), 2.95 (s, 2H; OH), 6.97 (s, 2H, 6-H),
7.20 ppm (s, 2H; 4-H); 13C NMR (100 MHz, [D6]acetone): d=21.21
(CH3), 122.74, 128.77, 131.32, 131.95, 132.56, 149.72 ppm; HRMS: calcd
for C14H12Cl2O2: 282.0214; found: 282.0216; elemental analysis calcd (%)
for C14H12Cl2O2·0.5H2O (292.16): C 57.55, H 4.48; found: C 57.76, H 4.33.
5,5’-Dichloro-3,3’-dimethyl-2,2’-biphenol (28): 4-Chloro-2-methylphenol
(21) (5.66 g, 0.04 mol), 12 (0.68 g, 3 mmol), 2.0 F per mole phenol, puri-
fied by column chromatography (cyclohexane/ethyl acetate 95:5; Rf =
0.14), yielded 27 (1.37 g, 4.8 mmol, 24%); m.p. 1608C (cyclohexane);
1H NMR (300 MHz, CDCl3): d=2.29 (s, 6H; CH3), 5.18 (s, 2H; OH),
7.04 (s, 2H, 6-H), 7.19 ppm (s, 2H; 4-H); 13C NMR (75 MHz, CDCl3):
d=16.16 (CH3), 123.02, 125.67, 127.60, 127.95, 131.32, 149.89 ppm;
HRMS: calcd for C14H12Cl2O2: 282.0214; found: 282.0214; elemental
General procedure for the anodic oxidation of substituted phenols: A so-
lution of the corresponding phenol (0.005–0.02 mol) and supporting elec-
trolyte (0.003 mol) in hexafluoroisopropanol (9, 30 mL) was transferred
into a non-divided electrolysis cell equipped with a BDD anode and a
nickel cathode. At 508C, a galvanostatic electrolysis with a current densi-
ty of 2.8–9.5 mAcmÀ2 was performed. After complete reaction (ca. 1 F
per mol phenol), the electrolysis was stopped and hexafluorisopropanol
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Anodic Phenol-Coupling Reactions
COMMUNICATION
analysis calcd (%) for C14H12Cl2O2 (282.02): C 59.39, H 4.27; found: C
59.62, H 4.39.
Siegel, F. Molnar, PCT Int. Appl. WO 2004087314, 2004; e) M.
Bartsch, R. Baumann, D. P. Kunsmann-Keitel, G. Haderlein, T.
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2003033142, 2003.
3,3’-Dibromo-5,5’-dimethyl-2,2’-biphenol (29): 2-Bromo-4-methylphenol
(22) (3.75 g, 0.02 mol), 12 (0.68 g, 3 mmol), purified by column chroma-
tography (cyclohexane/ethyl acetate 95:5; Rf =0.10), yielded 21 (1.12 g,
3.0 mmol, 30%); m.p. 136–1388C (cyclohexane); 1H NMR (300 MHz,
[D6]acetone): d=2.27 (s, 6H; CH3), 3.05 (s, 2H; OH), 6.99 (s, 2H, 6-H),
7.35 ppm (s, 2H; 4-H); 13C NMR (75 MHz, [D6]acetone): d=21.07
(CH3), 112.67, 128.69, 132.57, 133.32, 134.53, 150.63 ppm; HRMS: calcd
for C14H12Br2O2: 369.9210; found: 369.9204; elemental analysis calcd (%)
for C14H12Br2O2·1H2O (390.07): C 43.11, H 3.62; found: C 43.46, H 3.28.
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À
Keywords: C C coupling · electrochemistry · fluorine ·
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Received: December 5, 2008
Published online: January 29, 2009
Chem. Eur. J. 2009, 15, 2273 – 2277
ꢃ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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