Highly meso-diastereoselective pinacol coupling of aromatic aldehydes mediated by Al powder/copper sulfate in water

Article abstract of DOI:10.1080/00397910802110198

Pinacol-type coupling reaction products presenting a high meso-diastereoselectivity (the ratio dl/meso was 4/96 up to 1/99) were obtained in fair to good yields (24-69%) using several aromatic aldehydes as starting materials and aluminium powder/copper sulfate as catalysts, in water, under reflux conditions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910802110198

This article was downloaded by: [Pennsylvania State University]
On: 23 February 2013, At: 19:51
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic
Organic Chemistry
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
Highly meso-Diastereoselective
Pinacol Coupling of Aromatic
Aldehydes Mediated by Al
Powder/Copper Sulfate in
Water
a
b
Yoshiharu Mitoma , Iwao Hashimoto , Cristian
c
d
a
Simion , Masashi Tashiro & Naoyoshi Egashira
a
Department of Bioresource Development, School
of Bioresources, Hiroshima Prefectural University,
Shobara, Hiroshima, Japan
b
Department of Industrial Chemistry, Wakayama
National College of Technology, Gobo City, Japan
c
Politehnica University of Bucharest, Faculty
of Applied Chemistry and Material Science,
Department of Organic Chemistry, Bucharest,
Romania
d
National Institute of Advanced Science and
Technology (AIST), Tsukuba, Ibaraki, Japan
Version of record first published: 12 Sep 2008.
To cite this article: Yoshiharu Mitoma , Iwao Hashimoto , Cristian Simion , Masashi
Tashiro & Naoyoshi Egashira (2008): Highly meso-Diastereoselective Pinacol Coupling
of Aromatic Aldehydes Mediated by Al Powder/Copper Sulfate in Water, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 38:19, 3243-3250

To link to this article: http://dx.doi.org/10.1080/00397910802110198
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-
and-conditions
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden.
The publisher does not give any warranty express or implied or make any
representation that the contents will be complete or accurate or up to
date. The accuracy of any instructions, formulae, and drug doses should be
independently verified with primary sources. The publisher shall not be liable
for any loss, actions, claims, proceedings, demand, or costs or damages
whatsoever or howsoever caused arising directly or indirectly in connection
with or arising out of the use of this material.

1
Synthetic Communications , 38: 3243–3250, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802110198
Highly meso-Diastereoselective Pinacol Coupling
of Aromatic Aldehydes Mediated by
Al Powder/Copper Sulfate in Water
1
Yoshiharu Mitoma, Iwao Hashimoto, Cristian Simion, Masashi
2
3
4
Tashiro, and Naoyoshi Egashira
Department of Bioresource Development, School of Bioresources, Hiroshima
Prefectural University, Shobara, Hiroshima, Japan
1
1
2
Department of Industrial Chemistry, Wakayama National College of
Technology, Gobo City, Japan
3
Politehnica University of Bucharest, Faculty of Applied Chemistry and Material
Science, Department of Organic Chemistry, Bucharest, Romania
4
National Institute of Advanced Science and Technology (AIST), Tsukuba,
Ibaraki, Japan
Abstract: Pinacol-type coupling reaction products presenting a high meso-
diastereoselectivity (the ratio dl=meso was 4=96 up to 1=99) were obtained in
fair to good yields (24–69%) using several aromatic aldehydes as starting mate-
rials and aluminium powder=copper sulfate as catalysts, in water, under reflux
conditions.
Keywords: Aqueous media, meso-diastereoselectivity, reductive coupling
INTRODUCTION
Organic syntheses in aqueous media present many advantages in terms
of safety and economical or environmental aspects compared to
[1]
syntheses in organic solvents. Starting from this perspective, we have
Received January 31, 2008.
Address correspondence to Cristian Simion, Politehnica University of
Bucharest, Faculty of Applied Chemistry and Material Science, Department of
Organic Chemistry, Spl. Independentei nr. 313, 060042, Bucharest, Romania.
E-mail: c_simion@chim.upb.ro
3
243

3244
Y. Mitoma et al.
investigated the reduction of some functional groups linked to aromatic
rings using different types of Raney alloys in an aqueous alkaline sol-
[
2]
ution. As a result of prior investigations, we showed that aromatic
aldehydes yielded their corresponding benzyl alcohol, in high yields,
when Raney Ni-Al or Co-Al alloys were used in a tetrahydrofuran
[
2d]
(THF)=water solution with slight addition of alkali.
Interestingly,
the use of Raney Cu-Al alloy, in the same conditions described pre-
viously, also promoted the pinacol coupling reaction between 2 equiva-
lents of aldehyde, in contrast to the use of Raney Ni-Al or Co-Al alloy,
which afforded reduction-type products. Therefore, we decided to inves-
tigate the differences between the reactivities of Raney alloys toward the
behavior of aldehydes in such reaction conditions.
[3]
The well-known pinacol reaction using reductive reagents e.g.,
metals, their salts, or complexes), in different reaction media such as
dry organic solvents, aqueous organic solvents, or simply water, is an
important and convenient method to achieve C-C bond formation in
organic synthesis. In recent decades, several reports have described differ-
ent investigations of pinacol condensation, most of these reports being
[
4]
[5]
related to complex catalysts based on vanadium, titanium, sam-
[10]
[
arium, chromium, indium, manganese, magnesium,
6]
[7]
[8]
[9]
[11]
nickel,
either as
[
12]
[13]
[14]
[15]
[16]
aluminium,
cerium,
niobium,
zinc,
or zirconium,
simple metals or in different types of combinations. Although many dif-
ferent methods have been developed for the pinacol reductive coupling
process, examples of diastereoselective processes are scarce, showing
mostly a dl-stereochemistry of reductive coupling reaction pro-
[
4b,c;5c–i;6a,d;7a–c;8b;9b–e]
ducts.
ples of a meso-diastereoselectivity.
by coupling gave a dl-diastereoisomer, their imine parent compounds
Quite surprinsingly, there are very few exam-
[6a]
Moreover, although the aldehydes
[
4d]
yield a meso-isomer in identical conditions.
To the best of our know-
ledge, no reports have described a highly stereoselective coupling method
in an aqueous solution yielding large amounts of meso-1,2-diols,
although Aspinall et al. presented a 20:80 dl:meso ratio for hydrobenzoin
[
6a]
obtained by reductive coupling of benzaldehyde.
Throughout our investigations of the reduction processes of
aldehydes using the Raney Cu-Al alloy, we found that, along with
the corresponding benzyl alcohol, a low diastereoselective pinacol
coupling reaction of the aromatic aldehydes also occurred. On replac-
ing the Cu-Al alloy with a mixture of Al powder and CuSO and
4
using only water as a solvent (without any alkali), a much higher
diastereoselectivity was obtained, although yields dropped. We report
here a convenient and simple coupling method that yields a highly
meso-diastereoselective coupling product starting from aromatic
aldehydes (Scheme 1).

Pinacol Coupling of Aromatic Aldehydes
3245
Scheme 1. a: R=H, b: R=4ÀCH
À, c: R=4ÀCH
OÀ, d: R=3ÀCH
OÀ,
3
3
3
e: R=2ÀCH OÀ, f: R=4ÀClÀ, g: R=4ÀFÀ.
3
RESULTS AND DISCUSSION
As mentioned previously, we succeedingly found that the use of
Raney Cu-Al alloy in a mixture of an aqueous alkaline solution
and organic solvents as well as in a totally aqueous alkaline media
promoted the pinacol reaction of aromatic aldehyde. Consequently,
the treatment of benzaldehyde 1a with Raney Cu-Al alloy in a 10%
NaOH solution afforded benzylalcohol 2a and hydrobenzoin 3a,
as shown in entry 1 (Table 1). Through a series of experiments, we
investigated the importance of the contribution of each participant
in this process. Therefore, when copper powder was used alone in an
alkaline solution, the transformation of benzaldehyde was complete
Table 1. Reaction of 1a with Raney Cu-Al alloy, Al, Cu, and CuSO
solution without any added organic solvent
4
in aqueous
c
Products (%)
b
Alloy or metal (g) Temp. Time
a
ꢀ
Entry
Additive (g)
( C)
(h)
Solution 1a 2a 3a (dl:meso) 4a
1
2
3
4
5
6
7
Cu-Al alloy=5.0 g
Cu=2.5 g
Al=2.5 g
Al=2.5 g
Cu-Al alloy=5.0 g
rt
rt
rt
1.5 10% NaOH 0 24 67 (46:54)
1.5 10% NaOH 0 52
1.5 10% NaOH 19 0 81 (56:44)
9
48
0
0
0
0
—
Reflux 24
Reflux 1.5
Water
Water
Water
Water
58 9 33 (12:88)
100
86 2 12 (8:92)
86
0
0
—
Al=2.5 g–CuSO
CuSO =1.0 g
4
=1.0 g Reflux 1.5
Reflux
0
13
6
1
0
—
4
a
The reaction conditions were 50 mmol as substrate and 40 ml as solution in
entries 1–7.
b
In entries 1, 3, and 4, the temperature of the reaction solution increased up to
ꢀ
c
9
0 C.
ꢀ
The products were determined by melting point (meso: 139–140 C), GC, and
H NMR spectra. The chemical shifts of methine proton in dl- and meso-isomer
were d 4.73 and 4.83 ppm, respectively.
1

3246
Y. Mitoma et al.
through a simple Cannizzaro reaction (entry 2). When replacing
copper powder with aluminium powder, 3a was obtained in high
yields without any by-product (entry 3), but the dl=meso ratio of 3a
was almost 1:1. No recorded transformations of benzaldehyde 1a
occurred in water at room temperature, even at prolonged reaction
times or at reflux for periods of time up to 120 min (those entries
are not depicted in Table 1). Only when the mixture of benzaldehyde
and Al powder was refluxed in water for 1 day did we notice the pres-
ence of a reductive coupling product in fair yields, but the diastereo-
selectivity was substantially improved (entry 4). Comparing entries
1
–4, we noticed that the presence of copper enhances the formation
of the reactive coupling product, whereas the absence of alkali favors
a high diastereoselectivity. Therefore, we tried the use of Co-Al alloy
in water, but even at reflux conditions there was no transformation of
the starting benzaldehyde (entry 5). The next step was to replace cop-
per with one of its salts to enhance both the yield and the diastereo-
selectivity. The use of Al powder and CuSO4 in water at reflux
allowed aldehyde 1a to transform to the highly meso-diastereo-
selective diol 3a along with the reduced compound 2a. Diol 3a was
ꢀ
identified as the meso-isomer by its melting point (138–140 C, lit.
ꢀ
[17]
37–139 C ) and H NMR spectra. The corresponding diol was
1
1
not obtained at all when only copper sulfate was used; instead, the
corresponding oxidation product, benzoic acid 4a, was formed (para-
doxically in higher yields at a lower temperature). We may conclude
that the reaction in water requires a certain amount of copper sulfate
as a catalyst.
The typical procedure is the following: to a mixture of benzaldehyde
(
10.6 g, 100 mmol) in 50 mL of water, at room temperature, copper sul-
fate 5-hydrate (5.00 g, 20.0 mmol) and aluminium powder (150 mesh,
0.8 g, 400 mmol) were added in one portion. The reaction mixture was
1
stirred vigorously under reflux for 8 h. The mixture was extracted with
ether (3 Â 10 mL). The combined organic layers were washed with brine,
dried over magnesium sulfate, and concentrated. Compound 3a was
obtained in a 51% yield (5.46 g).
Table 2 summarizes the reactions performed using several differ-
ently substituted aromatic aldehydes, 1a–g, and one aliphatic
aldehyde, heptanal 5. The meso-diastereoselectivity is excellent in each
case, even though the yields in reductive coupling product, irrespec-
tive of the nature or position of the substituent, are lower than that
for benzaldehyde.
Taking for a fact that the first step of the reductive coupling process
is the nucleophilic attack of an electron (donated by the metal) at the
[3]
carbon atom of the carbonyl moiety, the electronic effects and the

Pinacol Coupling of Aromatic Aldehydes
3247
Table 2. Effect of substituent on the coupling reaction of aldehydes
a
Products (%)
b
Entry
Substrate
Monoalcohol
Diol
dl=meso-ratio
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
2a (15)
2b (6)
3a (69)
3b (24)
3c (0)
3d (47)
3e (24)
3f (2)
1:99
4:96
—
>99
>99
—
2c (81)
2d (48)
2e (38)
2f (82)
2g (97)
2h (97)
1g
3g (0)
3h (0)
—
—
CH
3
(CH
2
)
5
-CHO
a
Substrate is 5 mmol; the obtained products were identified by GC-MS.
b 1
The dl=meso ratio was determined by H NMR spectra.
electronic densities at this particular atom can explain the lower yields in
runs 2–8 (Table 2). Thus, in run 8, when no coupling occurs, the donor
effect of the aliphatic group enhances the electronic density at the carbon
atom of the carbonyl group. Paradoxically, the same effect (a higher elec-
tronic density) is obtained in runs 6 and 7 because of the powerful
electron-withdrawing effect of the halogen atom (Cl-, respectively F-),
which enhances the conjugation between the aromatic nucleus and
the > C=O double bond, diminishing in the same time the electronic dis-
placement toward the oxygen atom. An interesting situation is that of the
three isomers of anisaldehyde: in m-anisaldehyde, the electron donor
effect of the methoxy group has little or no influence on the electronic
density of the carbon atom in the carbonyl group or on the conjugation
between the aromatic nucleus or the carbon–oxygen double bond (delo-
calization shows high electronic densities on both ortho-carbon atoms).
Consequently, the main effect is the withdrawal effect of the oxygen
atom; the electronic density is subsequently lowered and the reductive
coupling process can occur. In p-anisaldehyde, the negatively charged
atom is located on the quaternary atom in the immediate proximity
of the carbonyl group. An extended conjugation is present, and the
electronic density is therefore very high, which explains the absence of
a reductive coupling product. More interesting is the situation of
o-anisaldehyde: although its behavior should have resembled that of its
para-isomer, the formation of a reductive coupling product can be
explained by an unfavorable limit structure for the extended conjugation,
with two vicinal exocyclic double bonds.

3248
Y. Mitoma et al.
REFERENCES
1
. (a) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice;
Oxford: New York, 1988; (b) Anastas, P. T.; Williamson, T. C. Green
Chemistry: Frontiers in Benign Chemical Syntheses and Processes; Oxford:
New York, 1988.
2
. (a) Tsukinoki, T.; Ishimoto, K.; Tsuzuki, H.; Mataka, S.; Tashiro, M.
Reduction of benzaldehydes with Raney alloys in an alkaline solution. Bull.
Chem. Soc. Jpn. 1993, 66, 3419–3422; (b) Tashiro, M.; Tsuzuki, H.;
Matsumoto, J.; Mataka, S.; Nakayama, K.; Tsuruta, Y.; Yonemitsu, T.
Reductive dechlorination of chloro-phenols and chloro-benzoic acids by
Raney Co-Al alloy in an alkaline deuterium oxide solution and preparation
of deuterated salicylic acids. J. Chem. Res., Synop. 1989, 12, 372–373; (c)
Tashiro, M.; Mataka, S.; Nakamura, H.; Nakayama, K. Preparation of
deuteriated 1-phenylethanols by reductive dehalogenation of the corres-
ponding halogenoacetophenones with Raney alloys in an alkaline deuterium
oxide solution. J. Chem. Soc., Perkin Trans. 1988, 1, 179–181.
3. For review papers, see, for example, (a) Wirth, T. ‘‘New’’ reagents for
the ‘‘old’’ pinacol coupling reaction. Angew. Chem. Int. Ed. Engl. 1996, 35,
61–63; (b) Dushin, R. G. Synthetically useful coupling reactions promoted
by titanium, vanadium, niobium, tungsten, and molybdenum reagents. In
Comprehensive Organometallic Chemistry; L. S. Hegedus (Ed.); Pergamon:
Oxford, 1995; vol. 12, pp. 1071–1095; (c) Imamoto, T. Lanthanoids in
organic synthesis; A. R. Katritzky, O. Meth-Cohn, C. W. Rees (Eds.);
Academic Press: London, 1994, and references cited therein.
4
. (a) Xu, X.; Hirao, T. Vanadium-catalyzed pinacol coupling reaction in water.
J. Org. Chem. 2005, 70, 8594–8596; (b) Hirao, T.; Ogawa, A.; Asahara, M.;
Muguruma, Y.; Sakurai, H. dl-Selective pinacol-type coupling using zinc,
chlorosilane, and catalytic amounts of Cp VCl ; dl-1,2-dicyclohexylethane-
2
2
diol. Org. Synth. 2005, 81, 26; (c) Hirao, T.; Hatano, B.; Imamoto, Y.;
Ogawa, A. A catalytic system consisting of vanadium, chlorosilane, and
aluminum metal in the stereoselective pinacol coupling reaction of benzal-
dehyde derivatives. J. Org. Chem. 1999, 64, 7665–7667; (d) Hatano, B.;
2 2
Ogawa, A.; Hirao, T. Cp VCl -catalyzed meso-selective pinacol coupling
reaction of aldimines in the presence of chlorosilane and zinc metal. J.
Org. Chem. 1998, 63, 9421–9424.
. (a) Wang, K.; Wang, S.-X.; Gao, M.-Z.; Li, J. T. Pinacol coupling of aro-
5
4
matic aldehydes and ketones in ethyl acetate mediated by TiCl -Mg. Synth.
Commun. 2006, 36, 1391–1399; (b) Knoop, C. A.; Studer, A. A new method
for the generation of titanium(III) complexes and its application in pinacol
coupling reactions. Adv. Synth. Catal. 2005, 347, 1542–1546; (c) Chatterjee,
A.; Bennur, T. H.; Joshi, N. N. Truly catalytic and enantioselective pinacol
coupling of aryl aldehydes mediated by chiral Ti(III) complexes. J. Org.
Chem. 2003, 68, 5668–5671; (d) Bensari, A.; Renaud, J.-L.; Riant, O. Enantio-
selective pinacol coupling of aldehydes mediated and catalyzed by chiral
titanium complexes. Org. Lett. 2001, 3, 3863–3865; (e) Yamamoto, Y.;

Pinacol Coupling of Aromatic Aldehydes
3249
Hattori, R.; Miwa, T.; Nakagai, Y.; Kubota, T.; Yamamoto, C.;
Okamoto, Y.; Itoh, K. Diastereoselective inter- and intramolecular pinacol
coupling of aldehydes promoted by monomeric titanocene(III) complex
Cp TiPh. J. Org. Chem. 2001, 66, 3865–3870; (f) Mukaiyama, T.;
2
Kagayama, A.; Igarashi, K. Efficient diastereoselective pinacol reaction
of aliphatic and aromatic aldehydes by combined use of newly utilized
titanium(II) bromide and copper. Chem. Lett. 2000, 336–337; (g) Oshiki, T.;
Kiriyama, T.; Tsuchida, K.; Takai, K. Improved synthesis and crystal structure
3
of TiCl (tmeda)(thf): A highly stereoselective pinacol coupling reagent for aro-
matic aldehydes. Chem. Lett. 2000, 29, 334–336; (h) Gansauer, A.; Bauer, D.
Novel concept for efficient transition-metal-catalyzed reactions: A highly
diastereoselective titanocene-catalyzed pinacol coupling under buffered protic
conditions. J. Org. Chem. 1998, 63, 2070–2071; (i) Clerici, A.; Clerici, L.;
Porta, O. A highly dl-stereoselective pinacolization of aromatic aldehydes
mediated by titanium trichloride in dichloromethane. Tetrahedron Lett.
1996, 37, 3035–3038.
6
. (a) Aspinall, H. C.; Greeves, N.; Valla, C. Samarium diiodide–catalyzed dia-
stereoselective pinacol couplings. Org. Lett. 2005, 7, 1919–1922; (b) Dahlen,
A.; Prasad, E.; Flowers, R. A.; Hilmersson, G. Exploring SmBr
YbI -mediated reactions assisted by microwave irradiation. Chem. Eur. J.
2 2
-, SmI -, and
2
2005, 11, 3279–3284; (c) Matsukawa, S.; Hinakubo, Y. Samarium(II)-
mediated pinacol coupling in water: Occurrence of unexpected disproportio-
nation and action of low-valent samarium as an active species. Org. Lett.
2003, 5, 1221–1223; (d) Pedersen, H. L.; Christensen, T. B.; Enemærke,
R. J.; Daasbjerg, K.; Skrydstrup, T. Ligand effects on the diastereoselecti-
vities of samarium diiodide–promoted pinacol coupling. Eur. J. Org. Chem.
1999, 3, 565–572.
7
. (a) Groth, U.; Jung, M.; Vogel, T. Chromium-catalyzed pinacol-type cross-
coupling: Studies on stereoselectivity. Chem. Eur. J. 2005, 11, 3127–3135; (b)
Takenaka, N.; Xia, G.; Yamamoto, H. Catalytic, highly enantio- and diaster-
eoselective pinacol coupling reaction with a new tethered bis(8-quinolinolato)
ligand. J. Am. Chem. Soc. 2004, 126, 13198–13199; (c) Taniguchi, N.; Hata, T.;
Uemura, M. Enantiomerically pure cyclic trans-1,2-diols, diamines and amino
alcohols by intramolecular pinacol coupling of planar chiral mono-Cr(CO)
3
complexes of biaryls. Angew. Chem., Int. Ed. Engl. 1999, 38, 1232–1235; (d)
F u¨ rstner, A. Carbon–carbon bond formations involving organochromium(III)
reagents. Chem. Rev. 1999, 99, 991–1046, and references cited therein.
8
. (a) Wang, C.; Pan, Y.; Wu, A. InCl
tions of aldehydes and ketones in aqueous media. Tetrahedron 2007, 63,
29–434; (b) Nair, V.; Ros, S.; Jayan, C. N.; Rath, N. P. Indium=indium
3
=Al-mediated pinacol coupling reac-
4
trichloride–mediated pinacol cross-coupling reaction of aldehydes and
chalcones in aqueous media: A facile stereoselective synthesis of substi-
tuted but-3-ene-1,2-diols. Tetrahedron Lett. 2002, 43, 8967–8969; (c) Lim,
H. J.; Keum, G.; Kang, S.-B.; Chung, B.-Y.; Kim, Y. Indium-mediated
pinacol coupling reaction of aromatic aldehydes in aqueous media. Tetra-
hedron Lett. 1998, 39, 4367–4368.

3250
Y. Mitoma et al.
9. (a) Li, J.-T.; Chen, Y.-X.; Chang, R.-X.; Li, T.-S. Pinacol coupling of aro-
matic aldehydes mediated by TiCl -Mn-EtOH under ultrasound irradiation.
3
J. Chem. Res. 2005, 6, 784–786; (b) Mercer, G. J.; Sigman, M. S. Diastereo-
selective synthesis of piperazines by manganese-mediated reductive cycliza-
tion. Org. Lett. 2003, 5, 1591–1594; (c) Li, C.-J.; Meng, Y.; Yi, X.-H.
Manganese-mediated carbon–carbon bond formation in aqueous media:
Chemoselective allylation and pinacol coupling of aryl aldehydes. J. Org.
Chem. 1998, 63, 7498–7504; (d) Rieke, R. D.; Kim, S.-H. New reagent for
reductive coupling of carbonyl and imine compounds: Highly reactive
manganese-mediated pinacol coupling of aryl aldehydes, aryl ketones, and
aldimines. J. Org. Chem. 1998, 63, 5235–5239; (e) Li, C. J.; Meng, Y.; Yi,
X.-H.; Ma, J.; Chan, T.-H. Manganese-mediated reactions in aqueous media:
Chemoselective allylation and pinacol coupling of aryl aldehydes. J. Org.
Chem. 1997, 62, 8632–8633.
1
0. (a) Li, J.-T.; Chen, X.-X.; Li, T.-S. Ultrasound-promoted magnesium-
ammonium bromide-mediated pinacol coupling of aromatic aldehydes and
ketones. Synth. Commun. 2005, 35, 2831–2837; (b) Zhang, W.-C.; Li, C.-J.
Magnesium-mediated carbon–carbon bond formation in aqueous media:
Barbier–Grignard allylation and pinacol coupling of aldehydes. J. Org.
Chem. 1999, 64, 3230–3236.
11. Shi, L.; Fan, C.-A.; Tu, Y.-Q.; Wang, M.; Zhang, F.-M. Novel and efficient
Ni-mediated pinacol coupling of carbonyl compounds. Tetrahedron 2004, 60,
2851–2855.
1
2. (a) Sahade, D. A.; Kawaji, T.; Sawada, T.; Mataka, S.; Thiemann, T.;
Tsukinoki, T.; Tashiro, M. Aluminium-mediated reductive dimerization of
aromatic dialdehydesy. J. Chem. Res. Synop. 1999, 210–211; (b) Tsukinoki,
T.; Kawaji, T.; Hashimoto, I.; Etoh, T.; Sahade, D.-A.; Tashiro, M.
Reductive coupling reaction of carbonyl compounds using Al powder in
10% aq. NaOH=MeOH=THF solution. Eng. Sci. Rep., Kyushu Univ. 1997,
19, 15–18; (c) Khurana, J. M.; Sehgal, A. Rapid pinacolization of carbonyl
compounds with aluminium-KOH. J. Chem. Soc., Chem. Commun. 1994, 5,
71–572.
5
13. Groth, U.; Jeske, M. Diastereoselektive Ce(OiPr)3-katalysierte pinakolkup-
plung von aldehyden. Angew. Chem. 2000, 112, 586–588.
1
4. Arai, S.; Sudo, Y.; Nishida, A. A highly diastereoselective pinacol coupling
reaction of aldehydes and ketones using low-valence niobium generated from
Nb(V). Chem. Pharm. Bull. 2004, 52, 287–288.
1
1
1
5. Tsukinoki, T.; Kawaji, T.; Hashimoto, I.; Mataka, S.; Tashiro, M. Pinacolic
coupling of aromatic carbonyl compounds using Zn powder in aqueous basic
media without organic solvents. Chem. Lett. 1997, 26, 235–236.
6. Lakshmi Kantam, M.; Aziz, K.; Likhar, P. Zirconocene dichloride–catalyzed
pinacol coupling of aromatic aldehydes and ketones. Synth. Commun. 2006,
36, 1437–1445.
7. Rowland, A. T. The determination of the stereochemistry of erythro-1,2-
diphenyl-1,2-ethanediol. J. Chem. Ed. 1983, 60, 1084.