Aluminium-mediated reductive dimerization of aromatic dialdehydes

Article abstract of DOI:10.1039/a808468h

Pinacol coupling reaction of several aromatic dialdehydes 1a-d using inexpensive aluminum powder as a reductive reagent in aqueous NaOH-methanol media afforded dimeric compounds 2a-d as main products, in which only one carbonyl group of 1 was reduced.

Full text of DOI:10.1039/a808468h

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210 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 210^211y
Aluminium-mediated Reductive Dimerization of
Aromatic Dialdehydesy
Daniel A. Sahade,a Takatoshi Kawaji,a Tsuyoshi Sawada,b
Shuntaro Mataka,*b Thies Thiemann,b Ta ke hi t o Ts u kino ki c and
Masashi Tashiroc
aDepartment of Molecular Science and Technology, Graduate School of Engineering Sciences,
b
and Institute of Advanced Material Study, Kyushu University, 6-1 Kasuga Koh-en, Kasuga-shi,
Fukuoka 816-8580, Japan, cCentral Institute for Science,Tohwa University, 1-1-1, Chikushigaoka,
Minami-ku, Fukuoka 815-0036, Japan
Pinacol coupling reaction of several aromatic dialdehydes 1a ^d using inexpensive aluminum powder as a reductive
reagent in aqueous NaOH^methanol media afforded dimeric compounds 2a^d as main products, in which only
one carbonyl group of 1 was reduced.
Pinacol coupling reactions of aromatic aldehydes have been
much used for the preparation of a wide range of vicinal
diols.1 It has been shown that inexpensive aluminium powder
can be used as an e¡ective reagent in the pinacol coupling
reactions of aromatic aldehydes in aqueous media.2 However,
the coupling reactions of aromatic dicarbonyl compounds
have been limited, until now, to the synthesis of macrocyclic
compounds such as porphyrin derivatives3 and cyclophane
compounds.4 There are also some reports concerning the
polymerization of benzene-1,4-dicarbaldehyde to poly-
(1,4-phenylene ethane-1,2-diol) by using Mukaiyama's
reagent.5
When aromatic dialdehydes 1a ^d are treated with alu-
minium powder and an aqueous alkaline solution in
methanol, 1,2-bis(formyl-substituted aryl)ethane-1,2-diols
2a^d are formed as the main products in which only one
carbonyl group of 1 is reduced, the other remaining
unreacted. The diols 2a^d are accompanied by minor
amounts of polymerization products (Scheme 1). The ratios
of ꢀƆ- and meso-isomers of 2a^d were determined by
1H NMR.6 The coupling reactions of the 1,4-dialdehydes
1a and 1d showed a high ꢀƆ-selectivity. However, this was
not the case for the 1,3-dialdehydes 1b,c. One possible expla-
nation for this di¡erence can be the presence of the carbonyl
group in the 4-position of the 1,4-dialdehydes. This carbonyl
group can conjugate e¡ectively with a radical centre to lower
the reactivity of the intermediate formed in the coupling
reaction. Thus, the sterically more favourable ꢀƆ-isomer
may be preferred.7
2,5-Dimethoxybenzene-1,4-dicarbaldehyde8 is sparingly
soluble in methanol and on treatment with aluminium
powder, no coupling product could be obtained, nor could
any starting material be recovered. Under identical con-
ditions naphthalene-1,8-dicarbaldehyde, which exists in an
equilibrium mixture with its hydrated form, also did not give
the expected coupling products. Instead, the product of an
intramolecular Cannizzaro reaction, 1,8-naphthalide,9 was
obtained in high yield (78%).
Only a few reports in the literature deal with speci¢c
reactions on only one carbonyl group of symmetric dial-
dehydes and these contain complicated experimental pro-
cedures or special reaction conditions.10 On treatment
with the Al/NaOH^MeOH reductive system, aromatic di-
aldehydes 1 gave the dimerization products 2, which contain
two hydroxy groups and two formyl functions in the molecu-
le. Owing to their polyfunctionality, 2 could well ¢nd many
applications as starting materials in further syntheses.
Experimental
Mps were determined on a Yanaco MP-500D Micro melting point
apparatus and are uncorrected. IR spectra were recorded on a JASCO
IR 700 infrared spectrometer. 1H and 13C NMR spectra were recorded
on a JEOL JNM-EX 270 (270 MHz) spectrometer using SiMe4 as
internal standard; J values are given in Hz. Mass spectra were recorded
on a JEOL JMS-70 spectrometer. 3-Nitrobenzyl alcohol was used as a
matrix for MS (FAB). Elemental analyses were determined on aYanaco
MT-S CHN Corder apparatus.
OH OH
Al/NaOH(aq)
OHC Ar CHO
OHC Ar
C
C
Ar CHO
MeOH
H
H
2a (65%), 2b (30%)
2c (43%), 2d (40%)
1a–d
Commercially available aluminium powder (mesh 150, Kishida
Chemical Co.) was used as received. Dialdehydes 1a ^b and 1d are com-
mercially available.
5-tert-Butylbenzene-1,3-dicarbaldehyde (1c).öCompound 1c was
prepared by
a A mixture of
Sommelet reaction8 as follows.
a; Ar =
c; Ar =
b; Ar =
3,5-bis(bromomethyl)-tert-butylbenzene11 (3.2 g, 10 mmol), hexa-
methylenetetramine (3.0 g, 21.4 mmol), and aqueous 60% ethanol
(40 ml) was heated under re£ux for 20 h. After it had cooled, the
mixture was extracted with dichloromethane. The organic layer was
dried (MgSO4) and the solvent was evaporated to a¡ord the crude
product which, on column chromatography using hexane^ethyl acetate
(4:1), yielded 1c (1.20 g, 63%) as colourless plates (from hexane), mp
S
d; Ar =
63^64 ꢁC; vmax=cm 2962, 2864, 2732; dH(CDCl3) 1.42 (s, 9 H), 8.19
(s, 3 H), 10.12 (s, 2 H); dC 31.1, 35.2, 129.0, 131.6, 137.0, 153.7, 191.5;
1
Scheme 1
‡
m/z (FAB) (%) 191 (M ‡ H † (Found: C, 75.71; H, 7.47. C12H14O2
requires C, 75.76; H, 7.42%).
General Procedure for Coupling Reaction of 1.öTo a mixture of 1
(5 mmol) and aluminium powder (0.45 g, 16.7 mmol) in methanol
(15 ml), an aqueous 10% NaOH solution (6.7 ml) was added dropwise
during 10 min at room temperature and under mechanical stirring.
After the reaction mixture had been stirred at room temperature
for 80 min, it was ¢ltered and the ¢ltrate was extracted with ethyl
acetate. The extract was washed with water, dried (MgSO4) and evap-
*To receive any correspondence (e-mail: mataka@cm.kyushu-u.
ai.jp).
yThis is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1999 211
orated in vacuo to a¡ord a residue which was chromatographed on
silica gel (Wako gel, C-300) using a mixture of hexane^ethyl acetate
as an eluent, giving 2.
Received, 2nd November 1998; Accepted, 30th November 1998
Paper E/8/08468H
1,2-Bis(4-formylphenyl)ethane-1,2-diol (2a) was eluted with
hexane^ethyl acetate (1:1) as a 4:1-mixture of ꢀƆ and meso-isomers:
colourless prisms (from AcOEt), mp 184^187 ꢁC; vmax=cm 3446,
1
2842, 1686, 1424; dH of ꢀƆ isomer (DMSO-d6† 4.81 (s, 2 H), 5.70
(s, 2 H), 7.35 (d, 2 H, J 8.3), 7.73 (d, 2 H, J 8.3), 9.93 (s, 2 H); dH of
meso-isomer (DMSO-d6) 4.71 (s, 2 H), 5.61 (s, 2 H), 7.46 (d, 2 H, J 7.9),
References
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7.80 (d, 2 H, J 7.9), 9.97 (s, 2 H); m/z (FAB) (%) 271 ꢀM ‡ H , 8) (Found:
C, 70.84; H, 5.32. C16H14O4 requires C, 71.10; H, 5.22%).
1,2-Bis(3-formylphenyl)ethane-1,2-diol (2b) was eluted with
hexane^ethyl acetate (1:1) as a 4:3-mixture of ꢀƆ and meso-isomers:
1
colourless oil; vmax=cm 3446, 2842, 1686; 1424; dH of ꢀƆ isomer
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dH of meso-isomer (DMSO-d6) 4.69 (s, 2 H), 5.56 (s, 2 H), 7.83^7.41
‡
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H, 5.40. C16H14O4Á 16 H2O requires C, 70.32; H, 5.29%).
1,2-Bis(5-tert-butyl-3-formylphenyl)ethane-1,2-diol (2c) was eluted
with hexane^ethyl acetate (4:1) as
a
3:2-mixture of ꢀƆ and
1
meso-isomers; colourless solid, mp 57^60 ꢁC; vmax=cm 3446, 2962,
1698; dH of ꢀƆ-isomer (CDCl3) 1.19 (s, 18 H), 3.10 (s, 2 H), 4.78 (s, 2 H),
7.19^7.78 (m, 6 H), 9.92 (s, 2 H); dH of meso-isomer (CDCl3) 1.22 (s,
18 H), 2.68 (s, 2 H), 5.06 (s, 2 H), 7.19^7.78 (m, 6 H), 9.93 (s, 2 H);
‡
‡
m/z (%) 382 ꢀM , 1), 191 ꢀM /2, 32) (Found: C, 74.76; H, 7.94.
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:
C24H30O4 1=4H2O requires C, 74.49; H, 7.94%).
1,2-Bis(5-formylthiophen-2-yl)ethane-1,2-diol (2d) was eluted with
hexane^ethyl acetate (1:1) as a 5:1-mixture of ꢀƆ and meso-isomers:
colourless solid mp 107^130 ꢁC;
vmax=cm
3422, 1662; dH of
1
ꢀƆ-isomer (DMSO-d6) 5.09 (s, 2 H), 6.43 (s, 2 H), 7.08 (d, 2 H, J 4.0),
7.80 (d, 2 H, J 4.0), 9.79 (s, 2 H); dH of meso-isomer (DMSO-d6) 4.96
(s, 2 H), 6.39 (s, 2 H), 7.14 (d, 2 H, J 3.6), 7.84 (d, 2 H, J 3.6), 9.83 (s,
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‡
2 H); m/z (FAB) (%) 283 ꢀM ‡ H , 15) (Found: C, 51.16; H, 3.68.
C12H10O4S2 requires C, 51.05; H, 3.57%).