A diverse structural behaviour of boronated ortho-phthalaldehydes: A crystal structure of 1,3-dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole

Article abstract of DOI:10.1016/j.jorganchem.2007.03.001

Two isomeric boronated ortho-phthalaldehydes 3- and 4-[B(OH)₂]-1,2-C₆H₃(CHO)₂ have been prepared and their specific behavior in solution under various conditions has been investigated using NMR spectroscopy. The

Full text of DOI:10.1016/j.jorganchem.2007.03.001

Journal of Organometallic Chemistry 692 (2007) 2924–2929
www.elsevier.com/locate/jorganchem
A diverse structural behaviour of boronated ortho-phthalaldehydes:
A crystal structure of
1,3-dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole
*
´
Sergiusz Lulinski , Janusz Serwatowski
Warsaw University of Technology, Faculty of Chemistry, Noakowskiego 3, 00-664 Warsaw, Poland
Received 1 December 2006; received in revised form 21 February 2007; accepted 2 March 2007
Available online 12 March 2007
Abstract
Two isomeric boronated ortho-phthalaldehydes 3- and 4-[B(OH)2]-1,2-C6H3(CHO)2 have been prepared and their specific behavior in
solution under various conditions has been investigated using NMR spectroscopy. The former compound undergoes a ring-chain tau-
tomeric rearrangement to form a cyclic structure of 1,3-dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole predominating in ace-
tone-d6 solution and characterized by X-ray diffraction.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: ortho-Phthalaldehyde (OPA); Arylboronic acids; Ring-chain tautomerism; Benzaldehydes
1. Introduction
aldehyde system is strongly influenced by boronation of the
aromatic ring.
ortho-Phthalaldehyde (OPA) is useful in syntheses of
various carbo- and heterocyclic systems with a fused ben-
zene ring [1]. It also exhibits specific properties due to a
proximity of formyl groups. In the presence of water it is
strongly hydrated to form a cyclic hemiacetal (as a mixture
of cis and trans-isomers) and a geminal diol [2]. Under
alkaline conditions, it is prone to undergo an intramolecu-
lar Cannizzaro reaction to give the anion of 2-(hydroxy-
methyl)benzoic acid [3]. More recently, OPA has been
recognized as the potent antibacterial agent acting due to
the reaction with aminoacids and proteins [4]. Further-
more, the method of determination of trace amounts of
aminoacids is based on their reactions with OPA and its
analogues yielding fluorescent isoindoles [5]. In our contri-
bution we report about novel boronated analogues of
OPA. We demonstrate that the behaviour of ortho-phthal-
2. Results and discussion
The synthesis of boronated ortho-phthalaldehydes is
shown in Scheme 1. It involved a sequence of Br/Li
exchange reactions with alternating formylation/protection
and boronation/deprotection steps. The regioselective Br/
Li exchange proceeds ortho to dimethoxymethyl group [6]
and was a key step in a synthesis of 4-(dihydroxyboryl)-
1,2-phthalaldehyde 4.
1
According to a H NMR analysis, 2 reveals a specific
behaviour in acetone-d6 solution. The spectrum exhibits
only one strong resonance in a low-field range at
10.44 ppm, which can be assigned to the formyl hydrogen.
Another characteristic singlet can be observed at 6.82 ppm.
There are also minor peaks at 10.66 and 10.29 of equal
intensities. In the 13C NMR spectrum a number of reso-
nances is increased indicating the existence of at least two
species in solution. Strong resonances at 191.9 and
97.2 ppm indicate that a more abundant species contains
one formyl group and one quaternized carbon. Based on
*
Corresponding author. Tel.: +4822 2347575; fax: +4822 6282741.
´
E-mail address: serek@ch.pw.edu.pl (S. Lulinski).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.03.001

S. Lulin´ski, J. Serwatowski / Journal of Organometallic Chemistry 692 (2007) 2924–2929
2925
by angles at the boron atom different from 120ꢁ) and less
effective p-bonding between boron and oxygen with respect
to non-annelated analogues [7].
The tautomerism 2-I M 2-II is the next example of spe-
cific processes observed in ortho-functionalized benzaldehy-
des [8] and shows a close analogy with a formation of 3-
hydroxyphthalide from 2-formylbenzoic acid, which is iso-
electronic with 2-formylphenylboronic acid (Scheme 3) [9].
However, it should be stressed that the presence of a formyl
group in a 3-position is required for an equilibrium favour-
ing the cyclic tautomer whereas for 2-formylphenylboronic
acid only a small amount of a cyclic form (ca. 5%) was
detected by 1H NMR analysis in [D6] acetone. Other intra-
molecular cyclizations leading to benzo[c][2,1]oxaboroles
are more entropy-favoured due to elimination of water mol-
ecule [10,11].
The compound 2 crystallizes as a cyclic tautomer 2-II. The
molecular structure is depicted in Fig. 1. The metric features
of the molecule 2-II (Table 1) are similar to those reported
for related 1,3-dihydro-1-hydroxybenzo[c][2,1]oxaborole
[11], and its derivatives [12]. The 3-formyl group is nearly
coplanar with the aromatic ring while the C@O bond
adopts the exo-orientation with respect to the adjacent
boraheterocycle. Apparently, the 3-formyl group impacts
a specific mode of interaction between B(OH)2 and an adja-
cent ortho-CHO group resulting in a destabilization of the
open form 2-I. Presumably, unfavourable steric and
Scheme 1. The synthesis of boronated ortho-phthalaldehydes 2 and 4.
Reagents and conditions: (i): 1. n-BuLi/Et2O (ꢀ70 ꢁC), 2. DMF (ꢀ70 ꢁC),
3. H2SO4 aq., rt, 4. MeOH, CH(OMe)3, H+ (60 ꢁC, 1 h); (ii): 1. n-BuLi/
THF (ꢀ70 ꢁC), 2. (EtO)3B (ꢀ70 ꢁC), 3. H2SO4 aq. (40 ꢁC).
these observations we have formulated the structure of 1,3-
dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole 2-
II (Scheme 2) to be consistent with major resonances in
1H and 13C NMR spectra. Accordingly, smaller peaks
can be assigned to a classical acyclic structure of 2,3-dif-
ormylphenylboronic acid 2-I. Comparison of signal inte-
gration gives a cyclic to acyclic tautomer ratio of 12 at
293 K. Unlike 2, the isomeric compound 4 exists in one
typical acyclic form as evidenced by two formyl hydrogen
1
resonances at 10.50 and 10.45 in the H NMR spectrum,
and corresponding signals of formyl carbons at 193.9 and
193.6 ppm in the 13C NMR spectrum. Moreover, a com-
parison of 11B NMR chemical shifts of 2 and 4 shows a
downfield shift for 2. The difference of d11B values of 2
and 4 is not large (ca. 3–4 ppm). However, both resonances
are clearly distintiguishable as demonstrated by the 11B
NMR spectrum (64.2 MHz) of a mixed sample (see
Fig. 17 in the Supplementary Material). This is in accord
with general observations indicating a deshielding of boron
in five-membered heterocycles containing B–O (and also
B–N) bond due to an increased valence strain (reflected
Scheme 3.
Fig. 1. The molecular structure of 2-II. Displacement thermal ellipsoids
Scheme 2.
are drawn at the 50% probability level.

2926
S. Lulin´ski, J. Serwatowski / Journal of Organometallic Chemistry 692 (2007) 2924–2929
Table 2
dipole–dipole repulsions between adjacent formyl groups
[13] in 2-I result in a partial or even complete deconjuga-
tion between them and the phenyl ring whereas in 2-II
the formyl group is conjugated with the phenyl ring. In
the related 2-formylphenylboronic acid the formyl group
serves as a proton acceptor for B(OH)2 group, thus produc-
ing an approximately planar seven-membered ring due to
an intramolecular hydrogen bond B–OHꢁ ꢁ ꢁO@C [14]. Very
recently, we have found that various 2-formylphenylbo-
ronic acids form reversibly corresponding 1,3-dihydro-
1,3-dihydroxybenzo[c][2,1]oxaboroles. The cyclization is
exerted mainly by the appropriate funcionalization in the
3-position of 2-formylphenylboronic acid; [15] the 3-formyl
group has the strongest impact. It should be noted that the
crystal structure of the cyclic tautomer of related 3-bromo-
2-formylphenylboronic acid was determined but the full
refinement proved difficult due to a crystal disorder [15].
Hence, the structure 2-II is the first precise crystallographic
evidence for the ring-chain tautomerism in 2-form-
ylphenylboronic acids.
a
˚
Hydrogen-bonding geometry (A, ꢁ) for 2-II
d(Hꢁ ꢁ ꢁA)
1.863(14)
d(Dꢁ ꢁ ꢁA)
2.7185(14)
\D–Hꢁ ꢁ ꢁA
173.8(14)
O(2)–H(2)ꢁ ꢁ ꢁO(7)#1
O(5)–H(5)ꢁ ꢁ ꢁO(3)#2
2.044(16)
2.8251(14)
158.7(14)
a
Symmetry codes: #1 x + 1, y ꢀ 1, z; ꢀx + 1, ꢀy + 1, ꢀz.
#2
group. They are paired by cross-linking longer H bonds
between a ring oxygen and a hydrogen from a carbon-
bound hydroxyl group (Table 2). These weaker interac-
tions produce another motif as a cyclic and centrosym-
metric dimer. The C4 atom is asymmetric; molecules in
the chain have the same configuration (i.e., R or S),
whereas molecules in the parallel hydrogen-bonded chain
have the opposite configuration.
We have investigated the effect of a boronic acid group
on a hydration of an ortho-phthalaldehyde system. Upon
addition of 10 wt% of D2O to an acetone-d6 solution of
2, two new characteristic sets of resonances now appear
1
in a H NMR spectrum of 2. The first one is represented
An insight into a crystal structure of 2-II (Fig. 2)
reveals a specific supramolecular assembly due to inter-
molecular hydrogen bonds, of which there are two types
(Table 2). It can be interpreted as an array of infinite
chains formed by shorter and almost linear bridges
between a carbonyl oxygen and a boron-bound hydroxyl
by two singlets at 6.22 and 6.29 ppm of equal intensities.
Based on previous conclusions [2b,13,16], we have assigned
these signals to CH(OH) hydrogens of the cis-isomer of a
cyclic hemiacetal 2a. The second set of slightly less inten-
sive signals comprises two weakly coupled doublets due
to 4JCH–O–CH = 2.0 Hz at 6.52 and 6.62 ppm. Accordingly,
they can be assigned to hemiacetal protons of a trans-iso-
mer 2b. Based on integrations of aforementioned signals
the ratio 2a/2b is ca. 5:4. Further changes are observed in
the aromatic region. The partial assignment of characteris-
tic 13C NMR resonances at 99.9 and 100.2 (2a), 100.8 and
101.2 (2b) was performed by 2D HETCOR (1H,13C) exper-
iment. The overall degree of hydration of 2 in a dilute (ca.
0.05 M) solution in acetone-d6/D2O (90:10) is ca. 0.6 and
decreases only slightly upon heating from 293 to 321 K.
The equilibrium 2-I M 2-II is not significantly affected by
the addition of D2O. However the ratio 2-II/2-I is temper-
ature sensitive and decreases from the value of 14 at 293 K
to 9 at 321 K. Surprisingly, the compound 4 does not
undergo hydration under comparable conditions as indi-
cated by NMR spectra, where no new signals of hemiacetal
hydrogen and carbon atoms could be recorded upon addi-
tion of D2O. The 11B NMR spectrum of a mixed sample
containing 2 and 4 in acetone-d6 changes significantly after
addition of D2O: the well-resolved resonance of 2-II at
31 ppm collapses to leave only a shoulder (see Fig. 18 in
the Supplementary Information), which reflects a reduced
abundance of the cyclic form 2-II under these conditions.
On the contrary, the signal at 28 ppm assigned to 4 remains
essentially unchanged.
Table 1
˚
Selected bond lengths (A) and valence angles (ꢁ) for 2-II
Bond lengths
Bond angles
B(1)–O(2)
B(1)–O(3)
B(1)–C(8)
C(4)–O(3)
C(4)–O(5)
C(6)–O(7)
1.3386(19)
1.3995(18)
1.555(2)
1.4569(17)
1.3938(17)
1.2223(18)
O(2)–B(1)–O(3)
O(2)–B(1)–C(8)
O(3)–B(1)–C(8)
B(1)–O(3)–C(4)
O(5)–C(4)–O(3)
O(5)–C(4)–C(9)
O(3)–C(4)–C(9)
O(7)–C(6)–C(10)
C(9)–C(8)–B(1)
C(13)–C(8)–B(1)
C(8)–C(9)–C(4)
C(10)–C(9)–C(4)
122.48(14)
129.88(14)
107.64(13)
110.84(11)
110.18(12)
111.00(12)
104.87(11)
124.83(14)
105.59(12)
135.44(14)
111.01(12)
126.91(13)
We have investigated the behaviour of boronated ortho-
phthalaldehydes 2 and 4 under moderately alkaline (0.5 M
1
K2CO3/D2O, pH 9–10) aqueous conditions. Clean H and
13C NMR spectra indicate that only one species is present.
There are singlet proton resonances at 10.15 and 6.57 ppm,
to which correspond two 13C NMR signals at 202.7 and
Fig. 2. The crystal packing diagram for 2-II. Hydrogen bonds are marked
by dashed lines.

S. Lulin´ski, J. Serwatowski / Journal of Organometallic Chemistry 692 (2007) 2924–2929
2927
100.6 ppm. All these data are in agreement with a structure
of a cyclic boronate 2c (Scheme 2). Importantly, there are
no signals that could be assigned to anionic forms of
hydrated species 2a–2b. Further confirmation comes from
the 11B NMR spectrum, where a single resonance of a tet-
ravalent boron species appears at 4.5 ppm. A clean forma-
tion of the analogous cyclic anionic species under
moderately alkaline conditions was also observed for 3-flu-
oro-2-formylphenylboronic acid, which also undergoes
ring-chain tautomerism [15]. In practical terms, it seems
advantageous to use such conditions to determine the pur-
ity of various 2-formylphenylboronic acids by NMR as
spectra should be simplified when compared to those
recorded under standard conditions (i.e., without addition
of base).
related aryl(alkoxy)borates precludes a detailed discussion
of this point. However, it is clear that a different interpre-
tation should be formulated to account for the difference
of d11B values for tetravalent borates as unlike their tetra-
valent precursors p-bonding is lacking; moreover, the ring-
strain in 2-II is apparently reduced or removed due to
rehybridization.
3. Conclusions
In conclusion, the boronated ortho-phthalaldehydes
exhibit interesting and diverse properties. The substitu-
ent-dependent tautomeric cyclization is a general structural
feature of functionalized ortho-formylphenylboronic acids,
disturbing their analysis and purity determination. How-
ever, this complication can simply be overcome as under
moderately alkaline conditions only one type of anionic
cyclic boronate is formed. The hydration of phthalalde-
hyde system in 2 and 4 is strongly dependent on the posi-
tion and charge of boron-containing moiety. It is
intriguing that these results are not in line with previous
findings showing that the hydration is stronger for more
electron-deficient benzaldehyde systems. Last but not least,
there is an open field for research focused on the practical
use of boronated analogues of OPA, e.g., as molecular rec-
ognition reagents. Recently, 1,3-dihydro-1-hydrox-
ybenzo[c][2,1]oxaborole has been recognized to show a
strong binding to glucose and methyl a-D-glucopyranoside
[19]. It also proved useful in the Fourier transform ion
cyclotron resonance mass spectrometry analysis of prod-
ucts of formose reaction [20]. We hope that the closely
related species 2-II could also be capable of binding to car-
bohydrates; we are planning to undertake a work in this
field. There is also a wide potential for the use of 2 and 4
as Suzuki coupling partners in the construction of various
systems containing the OPA building block, e.g., for a
potential application as aminoacid receptors [5]. Finally,
considering the microbiological activity of OPA [4] as well
as arylboronic acids [21] and specifically benzo[c][2,1]oxab-
oroles [22], the use of boronated OPAs in this area can be
anticipated as a promising task.
A different situation is observed in alkaline (pH 9–10)
1
solution of 4 in D2O. According to a H NMR spectrum
showing resonances of two formyl groups, a boronate
anion 4a resulting from a simple complexation of boron
by hydroxide is formed (Scheme 4). However, it is accom-
panied by a comparable proportion of another species
characterized by a broad resonance at 6.54 ppm and sepa-
rate multiplets in the aromatic region. We have formulated
it as a boronate anion of a cyclic hemiacetal 4b, i.e., a
hydrated form of 4a. Assuming the hydration of benzalde-
hydes being generally favoured by electron-withdrawing
groups [17], we were again confused as we initially expected
that the hydration of 4a should not occur due to an
increased charge density within the aromatic system upon
boron complexation. The hemiacetal hydrogen as well as
aromatic and hemiacetal carbon resonances of 4b are
strongly broadened. It is indicative of cis M trans intercon-
version occuring within the heterocyclic system quite rap-
idly on the 1H NMR time-scale [2b]. In the 11B NMR
spectrum, a signal with a maximum at 0 ppm, i.e., in the
range typical of metal aryl(alkoxy)borates [18], has a shoul-
der at ca. 1 ppm indicating a detectable difference of 11B
NMR chemical shifts of 4a and 4b. This small difference
cannot be meaningfully interpreted; it is only our hypothe-
sis that it may reflect a change of the electronic character of
the phthalaldehyde system upon hydration, which in turn
slightly affects boron chemical shift. Notably, the boron
atom in the cyclic borate anion 2c exhibits a low field shift
(ca. 3–4 ppm) with respect to those in 4a–4b; this effect is
comparable to that observed for neutral forms 2 and 4.
Unfortunately, the limited number of 11B NMR data for
4. Experimental
All reactions were carried out under an argon atmo-
sphere. Solvents were stored over sodium wire before use.
n-Butyllithium (10 M solution in hexanes), triethyl borate,
N,N-dimethylformamide (DMF), and trimethyl orthofor-
mate were used as received. 1,3-dibromo-2-(dimethoxym-
ethyl)benzene [15] and 1,4-dibromo-2-(dimethoxymethyl)
benzene [6] have been prepared according to the literature
procedures.
The 11B NMR chemical shifts were given relative to
F3B Æ Et2O. The 13C NMR chemical shifts for samples dis-
solved in K2CO3/D2O were calibrated using the value of
168.3 ppm referenced for K2CO3 [23].
Scheme 4.

2928
S. Lulin´ski, J. Serwatowski / Journal of Organometallic Chemistry 692 (2007) 2924–2929
4.1. 1,2-Bis(dimethoxymethyl)-3-bromobenzene (1)
m/cmꢀ1 3428, 3276, 1680, 1468, 964, 704; 1H NMR
((CD3)2CO, 400 MHz) d: 10.68 (1H, s, 2-I), 10.44 (1H, s,
2-II), 10.33 (1H, s, 2-I), 7.98-7.95 (2H, m, 2-II), 7.78 (1H,
t, J 7.5 Hz, 2-I), 7.61 (1H, t, J 7.5 Hz, 2-II), 6.82 (1H, s,
2-II), 3.07 (broad, OH); 11B NMR ((CD3)2CO,
64.2 MHz) d: 32.0; 13C NMR ((CD3)2CO, 100.6 MHz) d:
191.5, 156.9, 138.5, 136.75, 136.67, 136.5, 132.2, 130.9,
130.2, 129.5, 125.7, 97.5. Anal. Calc. for C8H7BO4 (178):
C, 54.00; H, 3.97. Found: C, 53.96; H, 4.03%.
The solution of 1,3-dibromo-2-(dimethoxymethyl)ben-
zene (9.3 g, 30 mmol) in ether (30 mL) was addded to
the solution of BuLi (10 M, 3 mL, 30 mmol) in ether
(50 mL) at ꢀ78 ꢁC. After 15 min stirring DMF (2.9 g,
40 mmol) was added at ꢀ78 ꢁC. The mixture was stirred
for 30 min, then it was allowed to warm to ca. ꢀ50 ꢁC fol-
lowed by hydrolysis with 2 M aq. HCl. The organic layer
was separated followed by evaporation of the solvent
under reduced pressure. To an oily residue, trimethyl
orthoformate (6.4 g, 60 mmol), methanol (10 mL) and a
drop of conc. H2SO4 were added. The mixture was heated
for 1 h at reflux and neutralized with sodium methoxide.
Volatiles were removed under reduced pressure and a res-
idue was distilled in vacuo to give the title compound as
colorless oil (7.3 g, 81%), b.p. 125–130 ꢁC (1 Torr). IR
(film) m/cmꢀ1 2932, 1448, 1372, 1212, 1072, 968; 1H
NMR (CDCl3, 400 MHz) d: 7.67 (1H, dd, J 8.0, 1.5 Hz,
Ph), 7.53 (1H, dd, J 8.0, 1.5 Hz, Ph), 7.22 (1H, td, J 8.0,
0.5 Hz, Ph), 5.96 (1H, s, CH(OMe)2), 5.86 (1H, d,
CH(OMe)2), 3.46 (6H, s, OMe), 3.41 (6H, s, OMe); 13C
NMR (CDCl3, 100.6 MHz) d: 141.1, 134.5, 133.0, 130.3,
127.0, 123.4, 106.7, 101.7, 55.6, 55.3. Anal. Calc. for
C12H17BrO4 (305): C, 47.23; H 5.62. Found: C, 47.57; H
5.51%.
4.4. 4-(Dihydroxyboryl)-1,2-phthalaldehyde (4)
This compound was prepared as described for 2 starting
with 3 (6.1 g, 20 mmol); yield 2.5 g (70%), m.p. 222–225 ꢁC
(dec). IR (KBr) m/cmꢀ1 3420, 1690, 1668, 1336, 1208, 1052,
644; 1H NMR ((CD3)2CO, 400 MHz) d: 10.56 (1H, s,
CHO), 10.51 (1H s, CHO), 8.44 (1H, d, J 1.0 Hz, Ph),
8.28 (1H, dd, J 7.5 and 1.0 Hz, Ph), 7.97 (1H, d, J
7.5 Hz, Ph), 7.86 (s, B(OH)2) and 3.15 (s, B(OH)2); 11B
NMR ((CD3)2CO, 64.2 MHz) d: 28.0; 13C NMR
((CD3)2CO, 100.6 MHz) d: 193.9, 193.6, 140.0, 138.6,
137.3, 136.5, 130.1. Anal. Calc. for C8H7BO4 (178): C,
54.00; H, 3.97. Found: C, 53.81; H, 4.14%.
Crystal structure determination of 2-II.
Details regarding crystal structure determination of 2-II
are given in Table 3.
Single crystals of 2-II were grown by slow evaporation
of a solution of 2 (ca. 0.2 g) in wet ethyl acetate
4.2. 1,2-Bis(dimethoxymethyl)-4-bromobenzene (3)
This compound was prepared starting with 1,4-dib-
romo-2-(dimethoxymethyl)benzene (9.3 g, 30 mmol) as
described for 1. Colorless oil (6.80 g, 75%), b.p. 128–
132 ꢁC (1 Torr); IR (film) m/cmꢀ1 2936, 1356, 1192, 1052,
984; 1H NMR (CDCl3, 400 MHz) d: 7.76 (1H d, J
1.5 Hz, Ph), 7.49–7.44 (2H, m, Ph), 5.65 (1H, s,
CH(OMe)2), 5.63 (1H, s, CH(OMe)2), 3.31 (6H, s, OMe)
and 3.30 (6H, s, OMe); 13C NMR (CDCl3, 100.6 MHz)
d: 137.8, 134.7, 131.2, 129.8, 128.6, 122.6, 100.2, 99.8,
53.15, 53.14. Anal. Calc. for C12H17BrO4 (305): C, 47.23;
H 5.62. Found: C, 47.43; H 5.40%.
Table 3
Crystal data, data collection and refinement parameters for compound 2-
II
Empirical formula
Formula weight
Radiation
C8H7BO4
177.95
Mo Ka (k = 0.71073 A)
100(2)
Monoclinic
P2(1)/n
4
3.8941(2)
8.0550(5)
24.4138(14)
90
94.507(3)
90
763.42(8)
˚
Temperature (K)
Crystal system
Space group
Z (Z0Þ
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c(ꢁ)
4.3. 3-(Dihydroxyboryl)-1,2-phthalaldehyde (2)
3
˚
Volume (A )
A solution of 1 (6.1 g, 20 mmol) in ether (20 mL) was
added dropwise to the solution of BuLi (10 M, 2 mL,
20 mmol) in ether (30 mL) at ꢀ75 ꢁC. After 15 min stirring
B(OEt)3 (3.2 g, 22 mmol) was added at ꢀ75 ꢁC. The mix-
ture was stirred for 30 min, then it was allowed to warm
to ca. ꢀ50 ꢁC followed by hydrolysis with 2 M aq. HCl.
The organic layer was separated followed by evaporation
of the solvent under reduced pressure. Water (10 mL)
and a drop of conc. aq. HCl were added and a mixture
was heated shortly to ca. 60 ꢁC to cleave the acetal protec-
tion followed by removal of methanol in vacuo. A crude
solid product was filtered and washed with cold water
(2 · 5 mL) and toluene (2 · 5 mL) to give the title com-
pound (2.26 g, 64%), m.p. 149–151 ꢁC (dec); IR (KBr)
Absorption coefficient (mmꢀ1
h Range (data collection)
Index range
)
0.122
2.66–28.68
4 6 h 6 5, ꢀ10 6 k 6 10,
ꢀ31 6 l 6 32
7222
1901 (0.0324)
1901/0/145
0.832
R1 = 0.0309, wR2 = 0.0487
R1 = 0.0538, wR2 = 0.0509
+0.195 and ꢀ0.197
Reflections collected
Unique reflections (Rint
Data/restraints/parameters
Goodness-of-fit on F2 a
Final R indices (I > 2rðIÞ)b
R indices (all data)b
)
Largest difference in peak and hole
ꢀ3
˚
(eA
)
2
1=2
a
Goodness of fit S ¼ f½wðF 2o ꢀ F c2Þ ꢂ=ðn ꢀ pÞg where n is the number
of reflections and p is the total number of parameters refined.
b
P
P
P
P
2
2
1=2
R1 ¼ jjF ojꢀjF cjj= jF cj; wR2 ¼ f ½wðF 2o ꢀF c2Þ ꢂ= ½wðF o2Þ ꢂg
.

S. Lulin´ski, J. Serwatowski / Journal of Organometallic Chemistry 692 (2007) 2924–2929
2929
(ca. 15 mL), which was obtained by the addition of a few
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Appendix A. Supplementary material
CCDC 616906 contains the supplementary crystallo-
graphic data for 2-II. These data can be obtained free of
charge
via
http://www.ccdc.cam.ac.uk/conts/retriev-
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Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2007.03.001.
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