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A. Adamczyk-Wozniak et al. / Journal of Molecular Structure 920 (2009) 430–435
431
HO
OH
B
Br
R
R
1
2
(a) R = OCH2CH2OCH3, (b) R = (OCH2CH2)2OCH3, (c) R = OCH2OCH3
Scheme 1. Structures of the investigated compounds.
of 2a is the typical one, compounds 2b and 2c were prepared in sim-
2.2. NMR measurements
ilar manner.
The 1H NMR, 13C NMR and 11B spectra were recorded on Varian
Mercury 400 spectrometer, operating at frequency 400, 100.1 and
128.3 MHz, respectively. Two dimensional spectra were recorded
on Varian Inova 500. The 17O NMR spectra were recorded on Varian
Gemini 300 spectrometer, operating at frequency 40.680 MHz.
Acquisition parameters were as follows: sw = 100 kHz; at = 0.1 s;
2.1.1. 1-Bromo-2-methoxymethoxy-benzene (1c)
o-Bromophenol (10.4 g, 0.06 mol) and p-toluenesulfonic acid
monohydrate (0.06 g) were dissolved in the mixture of dim-
ethoxymethane (25 mL, 0.28 mol) and dichloromethane (120 mL)
and refluxed for 15 h under argon using a Soxhlet containing 4A
molecular sieves (54 g). The reaction mixture was allowed to cool,
neutralized with triethylamine (ca. 0.5 mL), washed twice with
2 M NaOH (25 cm3) and then with water until pH of washings
was neutral. The organic layer was dried over CaCl2. Evaporation
of the solvent afforded the crude oily product which was purified
by vacuum distillation (22% yield). 1H NMR (400 MHz, CDCl3): d:
3.50 (s, 3H), 5.23 (s, 2H), 6.87 (m, 1H), 7.13 (m, 1H), 7.22 (m,
1H), 7.53 ppm (m, 1H).
pw90 = 13.0 ls; pw = 8.0 l
s. All 17O NMR measurements were per-
formed for 0.5 M solutions of compounds studied in acetonitrile at
298 K and referred to external H2O (0.00 ppm).
2.3. X-ray crystallography
The X-ray measurements of compounds 2a–c were performed
at 100 (2) K on a KUMA CCD k-axis diffractometer with graphite–
monochromated Mo K radiation (0.71073 Å). The crystals were
positioned at 62.25 mm from the KM4CCD camera; 664 frames
were measured at 0.9° intervals on a counting time of 30 s, 856
frames were measured at 0.7° intervals on a counting time of
25 s, 1000 frames were measured at 0.6° intervals on a counting
time of 35 s, respectively, for 2a–c. Data reduction and analysis
were carried out with the Kuma Diffraction programs. The data
were corrected for Lorentz and polarization effects but no absorp-
tion correction was applied. Data reduction and analysis were car-
ried out with the Kuma Diffraction (Wrocław, Poland) programmes
[17]. The structure was solved by direct methods [18] and refined
by using SHELXL [19]. The refinement was based on F2 for all
reflections except for those with very negative F2. The weighted
R factor, wR and all goodness-of-fit S values are based on F2. The
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were located from a difference map and were refined iso-
tropically. The atomic scattering factors were taken from the Inter-
national Tables [20]. Crystal structure and structural refinement
are specified in Table 1. Selected bond lengths, bond angles and
torsion angles are given in Table 2. Crystallographic data for the
structure have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication No. CCDC
694828 (2a), 694829 (2b) and 694827 (2c). Copies of the data
can be obtained on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (email: deposit@ccdc.cam.ac.uk).
2.1.2. 2-(2-Methoxy-ethoxy)-phenylboronic acid (2a)
The reaction was carried out under argon protection. Diethyl
ether (30 mL) placed in a three-necked round-bottomed flask,
equipped with a CO2/acetone bath and magnetic stirrer was
cooled down to ꢀ65 oC. n-Butyllithium (10 M in hexanes,
2.5 mL, 0.025 mol) was slowly added to the stirred solvent. 1-
Bromo-(2-methoxy-ethoxy)-benzene (1a) was dropped-in for
10 min while keeping the temperature below ꢀ65 oC. After 1 h
of stirring at that temperature, triethyl borate (4.25 mL,
0.025 mmol) was dropped-in while keeping the temperature be-
low ꢀ65 oC. The stirring was continued for an additional hour at
ꢀ65 oC. After that time the CO2/acetone bath was removed and
H2SO4 (1.5 M, 30 mL) was quickly added while intense stirring.
The temperature rose until about 20 oC. The resulting phases
were separated and the aqueous phase was extracted twice with
diethyl ether (30 mL). The organic phases were combined and
3
about
of the volume of the solvent removed under reduced
4
pressure. Water (50 mL) was added to the remaining liquid
and evaporation was continued for an additional half an hour.
The aqueous phase was removed by decantation. Hexane
(30 mL) was added and the slurry was kept at 4 oC for 11 days.
After that time a white solid was filtered off and dissolved in
acetone with water. On standing at room temperature the sol-
vents slowly evaporated and white solid of the product sepa-
rated (1.15 g, 23.5% yield). Mp 54–57 °C (dec.), 11B NMR
(128.3 MHz, acetone-d6): d: 34.0 ppm. 1H and 13C NMR data
are collected in Table 3.
3. Results and discussion
3.1. Crystal structures
2.1.3. 2-[2-(2-Methoxy-ethoxy)-ethoxy]-phenylboronic acid (2b)
Yield 41.0%, mp 48–53 °C (dec.), 11B NMR (128.3 MHz, acetone-
d6): d: 34.1 ppm. 1H and 13C NMR data are collected in Table 3.
The structures of 2a, 2b and 2c are stabilized by two kinds of
hydrogen bonds. One of the hydroxy groups at the boron atom
forms an intramolecular hydrogen bond with an oxygen atom of
a polyoxa fragment. The other one is involved in an intermolecular
hydrogen bond with a counter pairing molecule. This leads to the
dimer formation (see Figs. 1 and 2), the most common structural
motif observed in crystals of phenylboronic acids [11]. Despite
the similarity of interactions, the crystal packing reveals some
2.1.4. 2-Methoxymethoxy-phenylboronic acid (2c)
Yield 45.2%, mp 66–69 °C (dec.), 1H NMR (400 MHz, acetone-
d6): d: 3.38 (s, 3H), 5.45 (s, 2H), 7.01 (m, 1H), 7.13 (m, 1H), 7.38
(m, 1H), 7.78 ppm (m, 1H), 11B NMR (128.3 MHz, acetone-d6): d:
33.9 ppm.