Lanthanide formamidinates as improved catalysts for the Tishchenko reaction

Article abstract of DOI:10.1002/ejoc.200700827

The tris(formamidinato)lanthanum(III) complexes [La(o-TolForm) ₃(thf)₂] [1; o-TolForm = N,N′-bis(o-tolyl) formamidin-ate], [La(XylForm)₃(thf)] [2; XylForm = N,N′-bis(2,6-dimethylphenyl)formamidinate], and [La(EtForm)₃] [3, EtForm = N,N′-bis(2,6-diethylphenyl)formamidinate] are a new class of precatalysts for the Tishchenko reaction. Their catalytic activity is a result of their high Lewis acidity and the ease with which the ligand spheres can be interchanged. For the dimerization of benzaldehyde to give benzyl benzoate, which is a benchmark reaction, compound 1 is, to the best of our knowledge, the most active catalyst ever reported. On a preparative scale, the reaction can be performed in the absence of solvent. A range of aromatic, heteroaromatic, and aliphatic aldehydes was rapidly converted into the corresponding esters by using catalysts 1-3. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200700827

FULL PAPER
DOI: 10.1002/ejoc.200700827
Lanthanide Formamidinates as Improved Catalysts for the Tishchenko
Reaction
Agustino Zuyls,[a] Peter W. Roesky,*[a] Glen B. Deacon,[b] Kristina Konstas,[b] and
Peter C. Junk*[b]
Keywords: Aldehydes / Homogeneous catalysis / Lanthanum / N ligands / Rare-earth formamidinates
The tris(formamidinato)lanthanum(III) complexes [La(o-Tol-
which is a benchmark reaction, compound 1 is, to the best of
Form)3(thf)2] [1; o-TolForm = N,NЈ-bis(o-tolyl)formamidin- our knowledge, the most active catalyst ever reported. On a
ate], [La(XylForm)3(thf)] [2; XylForm = N,NЈ-bis(2,6-dimeth-
ylphenyl)formamidinate], and [La(EtForm)3] [3, EtForm =
N,NЈ-bis(2,6-diethylphenyl)formamidinate] are a new class
of precatalysts for the Tishchenko reaction. Their catalytic
activity is a result of their high Lewis acidity and the ease
with which the ligand spheres can be interchanged. For the
dimerization of benzaldehyde to give benzyl benzoate,
preparative scale, the reaction can be performed in the ab-
sence of solvent. A range of aromatic, heteroaromatic, and
aliphatic aldehydes was rapidly converted into the corre-
sponding esters by using catalysts 1–3.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
great number of patents derived from it. The Tishchenko
ester of 3-cyclohexenecarbaldehyde is the precursor for the
formation of epoxy resin, which is durable against environ-
mental influences, whereas benzyl benzoate is used as a dye
carrier; other uses of this reaction include the production
of solvents for cellulose derivatives, and it has been used in
the formation of plasticizers and in the food industry.[19]
Traditionally, aluminum alkoxides[20–22] have been used as
homogeneous catalysts for the Tishchenko reaction. More
recently, other catalysts such as boric acid[23] and a few
transition-metal complexes have been used.[24–26] However,
these alternative catalysts are either only reactive under ex-
treme reaction conditions (e.g. boric acid) or they are slow
(e.g. [(C5H5)2ZrH2]),[24] expensive (e.g. [H2Ru(PPh3)2]),[25]
or give low yields (e.g. K2[Fe(CO)4]).[26]
Introduction
Lanthanide organometallic and coordination com-
pounds have undergone significant development in organic
synthesis in recent years. Lanthanide compounds have been
utilized in a great number of synthetic reactions, in both
stoichiometric and catalytic quantities.[1] Lanthanide cat-
ions are considered hard Lewis acids, according to the
hard–soft acid–base (HSAB) classification of Pearson. They
are electrophilic, oxophilic, and redox stable. These proper-
ties, which can be finetuned by variation of the ionic radius
of the lanthanide cation, are the driving force for various
catalytic processes.[2] Thus, lanthanide triflates [Ln(OTf)3]
turned out to be very active catalysts for aldol,[3] Michael,[4]
allylation,[5] Diels–Alder,[6] and glycosylation reactions[7], as
well as for Friedel–Crafts acylations.[8,9] Lanthanide alk-
oxides [Ln(OR)3] have proven to be useful catalysts for the
Meerwein–Ponndorf–Verley reduction[10] and for hydro-
cyanation,[11] whereas lanthanide shift reagents such as
Eu(fod)3 (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-
octanedionate) can be used as catalysts for Diels–Alder[12]
and hetero-Diels–Alder reactions.[13]
Scheme 1.
Recently, it was shown that the lanthanide complexes
[(C5Me5)2LaCH(SiMe3)2][27] and [Ln{N(SiMe3)2}3][14,16] are
the most active catalysts for the Tishchenko reaction be-
cause of their high Lewis acidity and easily interchangeable
ligand spheres. Further advantages of these compounds as
catalysts include the environmentally benign nature of the
metals, their high activity, and their high durability.
[La{N(SiMe3)2}3] is more accessible than [(η5-C5Me5)2La-
CH(SiMe3)2]. Although somewhat less active, [La2-
(tBu2pz)6] (tBu2pz = 3,5-di-tert-butylpyrazolate) can be
readily prepared from La metal and the appropriate pyr-
One of the catalytic transformations that we are inter-
ested in is the so-called Tishchenko reaction (or Claisen–
Tishchenko reaction).[14–16] The Tishchenko reaction, which
has been known for about a century,[17] is the dimerization
of an aldehyde to form the corresponding carboxylic ester
(Scheme 1).[18] Its industrial importance is mirrored in the
[a] Institut für Chemie und Biochemie, Freie Universität Berlin,
Fabeckstraße 34–36, 14195 Berlin, Germany
[b] School of Chemistry, Monash University,
Victoria 3800, Australia
Eur. J. Org. Chem. 2008, 693–697
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
693

A. Zuyls, P. W. Roesky, G. B. Deacon, K. Konstas, P. C. Junk
1
FULL PAPER
azole.[15] Furthermore, very recently the homoleptic bis- characteristic aldehyde proton signal in the H NMR spec-
(trimethylsilyl)amides of the alkaline earth metals trum, provided evidence for the production of benzyl ben-
[M{N(SiMe3)2}2] (M = Ca, Sr, Ba) were reported as precat- zoate. Upon reaction of compound 1 with benzaldehyde in
alysts for the Tishchenko reaction, and they are almost as a 1:5 stoichiometry, the formamidinate ligand was partially
active as the lanthanide compounds.[28]
cleaved off during the catalytic conversion. A comparison
Here, we report a series of tris(formamidinato)lantha- of compounds 1, 2, and 3 (Table 1, Entries 1–3) shows that,
num(III) complexes as precatalysts for the Tishchenko reac- for quantitative turnover, complex 1 exhibited the highest
tion. These compounds are, for most of the conversions de- activity. To rationalize this difference in rate, we suggest
scribed, more active than any other system reported. The that the sterically less hindered complex 1 with two labile
tris(formamidinato)lanthanide(III) complexes were recently thf ligands and the smallest Form ligands is most easily
reported to be accessible from the reaction of N,NЈ-bis- attacked by the aldehyde and thus the initial conversion of
(aryl)formamidines (FormH) with lanthanide metals and the precatalyst is the fastest. The reaction of complex 2 was
bis(pentafluorophenyl)mercury [Hg(C6F5)2] in THF [Equa- repeated on a preparative scale (2.2 g of reactant), in the
tion (1), (R = C6F5)].[29]
absence of solvent, to determine the isolated yield and to
characterize the product fully. The workup of the reaction
was very simple because the product could easily be trans-
ferred by vacuum. The reaction went to completion imme-
diately and thus was faster than the same reaction on an
NMR scale. The fast conversion results from internal heat-
ing of the very exothermic reaction. In contrast to experi-
ments in solution, there is no solvent to dissipate the heat.
(1)
Results and Discussion
Table 1. Tishchenko reaction of benzaldehyde giving benzyl benzo-
ate.
It was shown in our previous studies that the rate of the
catalytic conversion of aldehydes to carboxylic esters de-
pends on the ionic radius of the lanthanide atom involved.
In these studies, derivatives whose central metal possessed
the largest ionic radius were the most active.[14] Therefore,
we focused our studies on the tris(formamidinato)lantha-
num(III) complexes [La(o-TolForm)3(thf)2] [1; o-TolForm =
N,NЈ-bis(o-tolyl)formamidinate], [La(XylForm)3(thf)] [2;
XylForm = N,NЈ-bis(2,6-dimethylphenyl)formamidinate],
and [La(EtForm)3] [3, EtForm = N,NЈ-bis(2,6-diethyl-
phenyl)formamidinate] (Scheme 2). These compounds differ
in their substitution pattern on the aromatic ring and, more
importantly, in the number of thf molecules coordinated to
the central metal.
Scheme 2.
To compare the reaction rates of catalysts 1–3 with those
of other catalysts, the standard reaction of benzaldehyde to
form benzyl benzoate was chosen. The yields were deter-
mined by 1H NMR spectroscopy in C6D6 with approxi-
mately 1 mol-% catalyst at room temperature (Table l). The
[a] Reaction conditions (this work): Catalyst in C6D6. [b] Deter-
mined by H NMR spectroscopy. [c] Isolated yield.
1
Comparison with other lanthanum catalysts such as
turnover frequencies (TOFs) were determined from com- [La{N(SiMe3)2}3] (4) and [(η5-C5Me5)2LaCH(SiMe3)2] (5)
plete conversion.[30] The increase in the intensity of the ben- shows that compounds 1–3 are significantly more active for
zyl group proton signal, concomitant with a decrease in the the conversion of benzaldehyde to benzyl benzoate
694
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 693–697

Lanthanide Formamidinates as Catalysts for the Tishchenko Reaction
(Table 1). Moreover, the commercially available lanthanide Table 2. Results for the catalyzed dimerization of aromatic alde-
hydes.[a]
[31]
[27]
compounds SmI2
and La(OiPr)3
(Table 1, Entries 6
and 7), which are known Tishchenko catalysts, proved to
be inactive for the coupling of benzaldehyde. In contrast,
the homoleptic aryloxide [Sm{O-2,6-(tBu)2-C6H3}3], which
was recently introduced as a catalyst, showed some degree
of activity (Table 1, Entry 8).[32] However, the TOFs and the
yields obtained with the use of the aforementioned catalysts
were significantly lower than those observed for 1–3. In ad-
dition, the recently introduced alkaline earth metal amides,
such as [Ca{N(SiMe3)2}2(thf)2] (6) (Table 1, Entry 9), can-
not compete with the lanthanum catalysts. The use of the
[21,22]
standard aluminum catalyst Al(OiPr)3
under the reac-
tion conditions described above led to a low yield of prod-
uct (Table 1, Entry 10). Even the so-called high-speed
Tishchenko catalysts (2,7-dimethyl-1,8-biphenyldioxy)-
bis[diisopropoxyaluminum(III)] (Table 1, Entry 11) and
(2,7-dimethyl-1,8-biphenyldioxy)bis[dibenzyloxyaluminum-
(III)] (Table 1, Entry 12)[33] or other aluminum-based cata-
lysts (Table 1, Entry 13)[34] did not reach the level of activity
of the lanthanum compounds. All classical transition-metal
catalysts,[23–25] as well as boric acid[22] (Table 1, Entries 14–
18), failed to catalyze the reaction to complete conversion.
Some more recent examples from transition-metal chemis-
try show high yields, but are still slower than the lanthanide
systems (Table 1, Entry 19).[35] In summary, compound 1 is,
to the best of our knowledge, the most active catalyst for
the benchmark Tishchenko reaction of benzaldehyde to
give benzyl benzoate.
[a] Reaction conditions: 0.5–1 mol-% catalyst in C6D6. [b] Deter-
1
mined by H NMR spectroscopy. [c] Ref.[16] [d] Ref.[27] [e] Ref.[28]
[f] Ref.[26]
Table 3. Results for the catalyzed dimerization of aliphatic alde-
hydes.[a]
To study the scope and limitations of compounds 1–3
with respect to the Tishchenko reaction, the reactions of
aromatic, heteroaromatic (Table 2), and aliphatic aldehydes
(Table 3) in the presence of 0.5–1.0 mol-% of the catalysts
were investigated. The reactions were initially performed on
small scale. Unsurprisingly, the intramolecular Tishchenko
reaction of o-phthalaldehyde to form the corresponding lac-
tone gave high yields and was very fast (TOF Ͼ 1500 h–1;
Table 2, Entry 1). Furthermore, the suitability of 1 and 3
for the dimerization of heteroatom-functionalized sub-
strates was investigated by using two substrates that are
known to be difficult to dimerize (Table 2, Entries 2 and
3). Evidently, the heteroatom of the substrate can form a
hemilabile Lewis acid–Lewis base adduct with the catalyst,
[a] Reaction conditions: 0.5–1 mol-% catalyst in C6D6. [b] Deter-
1
mined by H NMR spectroscopy. [c] Isolated yield. [d] Ref.[16] [e]
Ref.[28] [f] Trimers and tetramers were produced as a byproducts,
as determined by GC–MS.
which thus hampers the Tishchenko process, as the required reaction was also repeated on a preparative scale (2.2 g of
aldehyde–catalyst interaction is impeded. Indeed, the poor reactant), in the absence of solvent, and gave a high isolated
reactivity of furfural is well known. Thus, by using an alu- yield.
minum alkoxide or K2[Fe(CO)4]/crown ether catalysts, very
Surprisingly, the dimerization of pivalaldehyde is slower
low yields are observed.[21,26,36] For example, only a 3.4% than expected by using catalysts 1–3, possibly owing to the
yield was obtained by using the K2[Fe(CO)4]/crown ether steric bulk of the substrate (Table 3, Entry 2). In all other
catalysts. In contrast, lanthanum formamidinate is much cases, catalysts 1–3 were superior to compounds 4 and 5.
more reactive (Table 2, Entry 3).
Although complex 1 catalyzed the dimerization of alde-
Both cyclic and noncyclic aliphatic aldehydes were also hydes, with or without an α-H atom, quickly and in high
investigated as potential substrates for the Tishchenko reac- yields, the reaction of butanal at 21 °C gave mostly higher
tion (Table 3). On an NMR scale, quantitative yields were coupling products (Table 3, Entry 4).[22,37,38] Identification
observed for most substrates. As seen for other lanthanum of the products, butyl butyrate and the trimeric and tetra-
catalysts, the dimerization of cyclohexanecarboxaldehyde meric coupling products, which were formed by a tandem
proceeded extremely fast (Table 3, Entry 1) so that the reac- aldol–Tishchenko reaction,[39–41] was established by GC–
tants could not be detected immediately after mixing. This MS.
Eur. J. Org. Chem. 2008, 693–697
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
695

A. Zuyls, P. W. Roesky, G. B. Deacon, K. Konstas, P. C. Junk
FULL PAPER
25 °C): δ = 58.0, 110.8, 111.2, 111.8, 118.3, 143.4, 144.8, 146.4,
149.8, 158.0 ppm.
Summary
Tris(formamidinato)lanthanum(III) complexes 1–3 repre-
sent a new and improved class of Tishchenko catalysts.
Their catalytic activity is a result of their Lewis acidity and
the ease with which the ligand spheres can be interchanged.
For the Tishchenko dimerization of benzaldehyde to benzyl
benzoate, these complexes are, to the best of our knowledge,
the most active catalysts ever reported and their effective-
ness is in the order 1 Ͼ 2 Ͼ 3.
Cyclohexylmethyl Cyclohexanecarboxylate:[24] 1H NMR (400 MHz,
C6D6, 25 °C): δ = 0.80–0.86 (m, 2 H), 0.98–1.09 (m, 6 H), 1.35–
1.67 (m, 11 H), 1.85–1.87 (m, 2 H), 2.16–2.28 (m, 1 H), 3.86 [d,
J(1H,1H) = 2.80 Hz, 2 H, CH2O] ppm. 13C{1H} NMR (100 MHz,
C6D6, 25 °C): δ = 25.7, 26.0, 26.1, 26.6, 29.4, 29.9, 37.5, 43.4, 69.1,
175.4 ppm. C14H24O2 (224.18): calcd. C 74.95, H 10.78; found C
74.33, H 10.62.
Neopentyl Neopentanoate:[24] 1H NMR (400 MHz, C6D6, 25 °C): δ
= 0.79 [s, 9 H, (CH3)3C], 1.45 [s, 9 H, (CH3)3C], 3.71 (s, 2 H, CH2O)
ppm. 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ = 26.4, 27.4, 31.4,
38.9, 73.4, 177.4 ppm.
Experimental Section
2,2-Diphenylethyl Diphenylacetate:[44] 1H NMR (400 MHz, C6D6,
25 °C): δ = 4.15 [t, J(1H,1H) = 7.6 Hz, 1 H, CHPh2], 4.56 [d,
J(1H,1H) = 7.6 Hz, 2 H, CH2O], 4.90 (s, 1 H), 6.90–7.20 (m, 20 H,
Ph) ppm. 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ = 50.0, 57.5,
67.4, 126.8, 127.3,128.5, 128.6, 128.7, 129.0, 139.1, 141.3,
172.0 ppm.
General Considerations: Deuterated solvents were obtained from
Chemotrade Chemiehandelsgesellschaft mbH (all Ն 99 atom-% D)
and they were degassed, dried, and stored in vacuo in resealable
flasks over Na/K alloy. NMR spectra were recorded with a Jeol
JNM-LA 400 FTNMR spectrometer. Chemical shifts were refer-
enced to internal solvent resonances and are reported relative to
tetramethylsilane. Elemental analyses were carried out with an Ele-
mentar vario EL III. All aldehydes were obtained from Sigma-Ald-
rich and were degassed, dried with CaH2, and stored under an
atmosphere of nitrogen in resealable flasks.Catalysts 1–3 were pre-
pared following a literature procedure.[29]
Acknowledgments
This work was supported by the Fonds der Chemischen Industrie
and the Deutsche Forschungsgemeinschaft [DFG Schwerpunkt-
programm (SPP 1166): Lanthanoidspezifische Funktionalitäten in
Molekül und Material], and the Australian Research Council.
General Procedure for the Tishchenko Reaction (NMR-Scale Reac-
tion): Lanthanide complex 1, 2, or 3 was weighed, under a nitrogen
atmosphere, into an NMR tube. C6D6 (≈ 0.7 mL) was condensed
into the NMR tube, and the mixture was frozen to –196 °C. The
reactant was injected onto the solid mixture, and the whole sample
was melted and mixed immediately prior to insertion into the core
of the NMR instrument (t0). For the kinetic measurement the ratio
of reactant to product was calculated by a comparison of the inte-
gration of the CHO with the CH2O signals.
[1] a) T. Imamoto in Lanthanides in Organic Synthesis, Academic
Press, London, 1994; b) G. A. Molander, Chem. Rev. 1992, 92,
29–68; c) G. A. Molander, C. Harris, Chem. Rev. 1996, 96, 307–
338; d) G. A. Molander, J. A. C. Romero, Chem. Rev. 2002,
102, 2161–2186.
[2] R. Anwander in Applied Homogenous Catalysis with Organo-
metallic Compounds (Eds.: B. Cornils, W. A. Herrmann),
Wiley-VCH, Weinheim, 2000.
[3] S. Kobayashi, I. Hachiya, J. Org. Chem. 1994, 59, 3590–3596.
[4] S. Kobayashi, I. Hachiya, M. Araki, H. Ishitani, Tetrahedron
Lett. 1992, 33, 6815–6818.
[5] S. Kobayashi, I. Hachiya, Y. Yamanoi, Bull. Chem. Soc. Jpn.
1994, 67, 2342–2344.
General Procedure for the Tishchenko Reaction (Preparative-Scale
Reaction): Under an atmosphere of nitrogen the catalyst was stirred
in a tempered reaction flask. The reactant (2.2 g) was added di-
rectly to the catalyst and an exothermic reaction was observed.
After 1 d the product was isolated by distillation. [The products
with high TOFs were worked up immediately (see Tables 1 and 2).]
[6] a) S. Kobayashi, I. Hachiya, M. Araki, H. Ishitani, Tetrahedron
Lett. 1993, 34, 3755–3758; b) S. Kobayashi, H. Ishitani, J. Am.
Chem. Soc. 1994, 116, 4083–4084.
[7] A. Kawada, S. Mitamura, S. Kobayashi, Synlett 1994, 545–546.
[8] A. Kawada, S. Mitamura, S. Kobayashi, J. Chem. Soc. Chem.
Commun. 1993, 1157–1158.
Benzyl Benzoate:[24] 1H NMR (400 MHz, C6D6, 25 °C): δ = 5.12
(s, 2 H), 6.95–7.17 (m, 8 H, Ph) 8.05–8.07 (m, 2 H, Ph) ppm.
13C{1H} NMR (100 MHz, C6D6, 25 °C): δ = 66.7, 128.2, 128.4,
128.5, 128.7, 129.9, 132.9, 136.6, 166.1 ppm. C14H12O2 (212.09):
calcd. C 79.22, H 5.70; found C 79.23, H 5.26.
[9] Reviews: a) S. Kobayashi, Synlett 1994, 689–701; b) S. Kobaya-
shi in Transition Metals for Organic Synthesis (Eds.: M. Beller,
C. Bolm), Wiley-VCH, Weinheim, 1998, vol. 2, pp. 285–312; c)
S. Kobayashi, Top. Organomet. Chem. 1999, 2, 63–118.
[10] a) J. L. Namy, J. Souppe, J. Collin, H. B. Kagan, J. Org. Chem.
1984, 49, 2045–2049; b) T. Okano, M. Matsuoka, H. Konishi,
J. Kiji, Chem. Lett. 1987, 181–184.
Phthalide:[42] 1H NMR (400 MHz, C6D6, 25 °C): δ = 4.46 (s, 2 H,
3
3
CH2O), 6.70 [d, J(1H,1H) = 6.70 Hz, 1 H, Ph], 6.95 [t, J(1H,1H)
3
= 7.44 Hz, 1 H, Ph], 7.08 [t, J(1H,1H) = 7.44 Hz, 1 H, Ph], 7.66
[d, 3J(1H,1H) = 6.70 Hz, 1 H, Ph] ppm. 13C{1H} NMR (100 MHz,
C6D6, 25 °C): δ = 69.0, 122.1, 125.4,126.2, 128.7, 133.4, 146.8,
171.0 ppm.
[11] H. Ohno, A. Mori, S. Inoue, Chem. Lett. 1993, 375–378.
[12] M. P. S. Ishar, A. Wali, R. P. Ganghi, J. Chem. Soc. Perkin
Trans. 1 1990, 2185–2194.
[13] S. J. Danishefsky, B. J. Uang, G. Quallich, J. Am. Chem. Soc.
1984, 106, 2453–2455.
[14] H. Berberich, P. W. Roesky, Angew. Chem. 1998, 110, 1618–
1620; Angew. Chem. Int. Ed. 1998, 37, 1569–1571.
[15] G. B. Deacon, A. Gitlits, P. W. Roesky, M. R. Bürgstein, K. C.
Lim, B. W. Skelton, A. H. White, Chem. Eur. J. 2001, 7, 127–
138.
[16] M. R. Bürgstein, H. Berberich, P. W. Roesky, Chem. Eur. J.
2001, 7, 3078–3085.
2-Thienylmethyl 2-Thiophenecarboxylate:[27] 1H NMR (400 MHz,
C6D6, 25 °C): δ = 5.11 (s, 2 H, CH2O), 6.44–6.48 (m, 2 H, aro-
matic), 6.54–6.57 (m, 1 H, aromatic), 6.76–6.80 (m, 2 H, aromatic),
7.56–7.57 (m, 1 H, aromatic) ppm. 13C{1H} NMR (100 MHz,
C6D6, 25 °C): δ = 60.9, 126.9, 127.0, 127.8, 128.6, 132.5, 133.8,
133.9, 138.2, 161.6 ppm.
2-Furylmethyl 2-Furancarboxylate:[43] 1H NMR (400 MHz, C6D6,
25 °C): δ = 4.99 (s, 2 H, CH2O), 5.79–5.81 (m, 2 H, aromatic),
5.92–5.94 (m, 1 H, aromatic) 6.11–6.12 (m, 1 H, aromatic), 6.81–
6.82 (m, 2 H, aromatic) ppm. 13C{1H} NMR (100 MHz, C6D6,
696
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 693–697

Lanthanide Formamidinates as Catalysts for the Tishchenko Reaction
[17] a) L. Claisen, Ber. Dtsch. Chem. Ges. 1887, 20, 646–650; b) W.
Tishchenko, Chem. Zentralbl. 1906, 77, I, 1309.
[18] Recent review: T. Seki, T. Nakajo, M. Onaka, Chem. Lett.
2006, 35, 824–829.
[19] Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed., Wiley-
VCH, Weinheim, 1999.
[20] a) E. G. E. Hawkins, D. J. G. Long, F. W. Major, J. Chem. Soc.
1955, 1462–1468 quoted patents; b) F. R. Frostick, B. Phillips
(Union Carbide & Carbon Corp.), US 2716123, 1953 [Chem.
Abstr. 1953, 50, 7852f].
[21] W. C. Child, H. Adkins, J. Am. Chem. Soc. 1923, 47, 789–807.
[22] a) F. J. Villani, F. F. Nord, J. Am. Chem. Soc. 1947, 69, 2605–
2607; b) L. Lin, A. R. Day, J. Am. Chem. Soc. 1952, 74, 5133–
5135.
[35]
T. Suzuki, T. Yamada, T. Matsuo, K. Watanabe, T. Katoh, Syn-
lett 2005, 9, 1450–1452.
M. Yamashita, Y. Watanabe, T.-A. Mitsudo, Y. Takegami, Bull.
Chem. Soc. Jpn. 1976, 49, 3597–3600.
G. Fouquet, F. Merger, R. Platz, Liebigs Ann. Chem. 1979,
1591–1601.
G. M. Villacorta, J. San Fillipo Jr, J. Org. Chem. 1983, 48,
1151–1154.
Recent reviews: a) J. Mlynarski, Eur. J. Org. Chem. 2006, 4779–
4786; b) R. Mahrwald, Curr. Org. Chem. 2003, 7, 1713–1723;
c) M. Shibasaki, T. Ohshima in Asymmetric Synthesis (Eds: M.
Christmann, S. Bräse), Wiley-VCH, Weinheim, 2007, pp. 141–
146.
Examples of tandem aldol–Tishchenko reaction: a) J. Mlynar-
ski, B. Rakiel, M. Stodulski, A. Suszczynska, J. Frelek, Chem.
Eur. J. 2006, 12, 8158–8167; b) V. Reutrakul, J. Jaratjaroon-
phong, P. Tuchinda, C. Kuhakarn, P. Kongsaeree, S. Prabpai,
M. Pohmakotr, Tetrahedron Lett. 2006, 47, 4753–4757; c) Y.
Horiuchi, V. Gnanadesikan, T. Ohshima, H. Masu, K. Kata-
giri, Y. Sei, K. Yamaguchi, M. Shibasaki, Chem. Eur. J. 2005,
11, 5195–5204; d) V. Gnanadesikan, Y. Horiuchi, T. Ohshima,
M. Shibasaki, J. Am. Chem. Soc. 2004, 126, 7782–7783; e) C.
Schneider, M. Hansch, Chem. Commun. 2001, 1218–1219; f) C.
Delas, O. Blacque, C. Moise, J. Chem. Soc. Perkin Trans. 1
2000, 2265–2270; g) C. Delas, C. Moise, Synthesis 2000, 2, 251–
254; h) L. Lu, H.-Y. Chang, J.-M. Fang, J. Org. Chem. 1999,
64, 843–853; i) P. M. Bodnar, J. T. Shaw, K. A. Woerpel, J. Org.
Chem. 1997, 62, 5674–5675; j) R. Mahrwald, G. Costisella,
Synthesis 1996, 1087–1089; k) F. R. Burkhardt, R. G.
Bergman, C. H. Heathcock, Organometallics 1990, 9, 30–44.
Y. Chen, Z. Zhu, J. Zhang, J. Shen, X. Zhou, J. Organomet.
Chem. 2005, 690, 3783–3789.
[36]
[37]
[38]
[39]
[40]
[23] P. R. Stapp, J. Org. Chem. 1973, 38, 1433–1434.
[24] K.-I. Morita, Y. Nishiyama, Y. Ishii, Organometallics 1993, 12,
3748–3752.
[25] T. Ito, H. Horino, Y. Koshiro, A. Yamamoto, Bull. Chem. Soc.
Jpn. 1982, 55, 504–512.
[26] M. Yamashita, T. Ohishi, Appl. Organomet. Chem. 1993, 7,
357–361.
[27] S. Onozawa, T. Sakakura, M. Tanaka, M. Shiro, Tetrahedron
1996, 52, 4291–4302.
[28] M. R. Crimmin, A. G. M. Barrett, M. S. Hill, P. A. Procopiou,
Org. Lett. 2007, 9, 331–333.
[29] M. L. Cole, G. B. Deacon, C. M. Forsyth, P. C. Junk, K.
Konstas, J. Wang, Chem. Eur. J., DOI: 10.1002/
chem.200700963.
[30] For the definition of TOF, see: J. Takehara, S. Hashiguchi, A.
Fujii, S. Inoue, T. Ikariya, R. Noyori, Chem. Commun. 1996,
233–234.
[41]
[42]
[31] D. A. Evans, A. H. Hoveyda, J. Am. Chem. Soc. 1990, 112,
6447–6449.
M. Mori, K. Chiba, N. Inotsume, Y. Ban, Heterocycles 1979,
12, 921–924.
V. G. Vladimir, A. Howard, J. Org. Chem. 1991, 56, 5159–5161.
T. Ooi, K. Maruoka, H. Yamamoto, Org. Synth. 1995, 72, 95–
103 (1998, Coll. Vol. 9, pp. 356–361).
[32] M. Nishiura, M. Kameoka, T. Imamoto, Kidorui 2000, 36,
294–295.
[33] a) T. Ooi, T. Miura, K. Takaya, K. Maruoka, Tetrahedron Lett.
1999, 40, 7695–7698; b) I. Simpura, V. Nevalainen, Tetrahedron
2001, 57, 9867–9872.
[34] T. Ooi, K. Ohmatsu, K. Sasaki, T. Miura, K. Maruoka, Tetra-
hedron Lett. 2003, 44, 3191–3193.
[43]
[44]
Received: September 5, 2007
Published Online: December 3, 2007
Eur. J. Org. Chem. 2008, 693–697
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
697