Asymmetric michael addition catalyzed by aluminum lithium bis-(R)-binaphthoxide

Article abstract of DOI:10.1023/A:1013131621384

Enantiomerically pure aluminum lithium bis-(R)-binaphthoxide [(R)-ALB] was synthesized and used to catalyze asymmetric Michael addition of diethyl malonate to ethyl crotonate.

Full text of DOI:10.1023/A:1013131621384

Russian Journal of Organic Chemistry, Vol. 37, No. 9, 2001, pp. 1287 1288. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 9, 2001,
pp. 1354 1356.
Original Russian Text Copyright
2001 by Tabatabaeian, Mamaghani, Pourahamad.
Asymmetric Michael Addition
Catalyzed by Aluminum Lithium Bis-(R)-binaphthoxide*
K. Tabatabaeian, M. Mamaghani, and A. Pourahamad
Chemistry Department, Faculty of Science, Guilan University, P.O.Box 1914, Rasht, Iran
e-mail: taba@cd.gu.ac.ir
Received April 4, 2001
Abstract Enantiomerically pure aluminum lithium bis-(R)-binaphthoxide [(R)-ALB] was synthesized and
used to catalyze asymmetric Michael addition of diethyl malonate to ethyl crotonate.
One of the most fascinating aspects of modern
organic chemistry is the synthesis of optically active
chiral compounds which play an important role in
medicine, agriculture, food industry, and manufacture
of liquid crystals [1]. Among methods available for
preparing such compounds, catalytic asymmetric
synthesis has attracted the most attention. Although
catalytic antibodies or structurally modified enzymes
are now becoming accessible [2], molecular catalysts
observed in enzymatic processes involving metal ion
cocatalysis [5].
Chiral bidentate ligands based on the 1,1 -binaph-
thalene system have achieved remarkable success in
asymmetric synthesis, ensuring in many cases a high
enantioselectivity (>90%) [6]. This success has
focused on a more convenient synthesis of the homo-
chiral 1,1 -binaphthalene-2,2 -diol (BINOL) ligand
and a chiral building block for preparation of atropo-
(
in particular homogeneous) have a great advantage isomeric chiral molecules possessing a C axis of
2
because their structures can be modified to improve
their efficiency.
symmetry.
The present communication describes the develop-
Many catalytic asymmetric syntheses with organo- ment of the use of heterobimetallic asymmetric catal-
metallic compounds have been carried out [3]. The
respective characteristics, chemical reactivities and
Lewis acidities, play crucial role in the key steps.
yst, namely aluminum lithium bis-(R)-binaphthoxide
[(R)-ALB], in a new asymmetric Michael reaction
(Scheme 1). For this purpose, racemic 1,1 -binaph-
thalene-2,2 -diol was synthesized [7] and resolved by
L-proline [8]. The procedure was repeated several
times until a high optical purity (ee > 97%) was
achieved. The ligand thus obtained was used in the
preparation of (R)-ALB.
The use of amphoteric Zr(OBu-t) for developing
4
a new class of basic asymmetric catalysts [4] led to
the development of exciting heterobimetallic asym-
metric catalysts with conceptually new chemical
reactivities [5]. Heterobimetallic asymmetric catalysts
efficiently promote a number of reactions through the
synergistic cooperation between two different metals
and a chiral template in a manner analogous to that
In order to extend the catalytic application of
(R)-ALB, asymmetric Micheal addition of diethyl
malonate to ethyl crotonate was accomplished in
Scheme 1.
_
*
___________
The original article was submitted in English.
1
070-4280/01/3709-1287$25.00 2001 MAIK Nauka/Interperiodica

1
288
TABATABAEIAN et al.
Scheme 2.
accordance with Scheme 2. The addition product was
chloric acid. The product was extracted into ethyl
acetate (3 100 ml), and the organic phase was
washed with a solution of sodium carbonate and dried
over anhydrous sodium sulfate. The solvent was
removed on a rotary evaporator, and the residue was
purified by column chromatography on silica gel
using petroleum ether ethyl acetate (4:1) as eluent.
We isolated 0.96 g (3.5 mmol, 70%) of the target
2
6
isolated in 70% yield as a dense oil, [ ]D = 15
c = 1, CHCl ). It was analytically pure (according to
(
3
1
the GLC and H NMR data).
The results of the present work provide further
insight to the extension of studies initiated by Shiba-
saki and co-workers [9] on the use of heterobimetallic
catalysts in asymmetric synthesis and encourage more
research in this field.
Michael adduct as a dense oil, [ ]2 = 15 (c = 1,
6
D
1
CHCl ). IR spectrum (neat), , cm : 2950, 1730,
3
1
1
1
300 1000. H NMR spectrum (CDCl ), , ppm:
EXPERIMENTAL
3
d (3H, CH , J = 5.6 Hz), 1.15 m (9H, OCH CH ,
3
2
3
J = 5.1 Hz), 2.1 2.7 m (3H, CHCH ), 3.3 d (1H, CH,
The IR spectra were recorded on a Shimadzu 470
spectrometer. The H NMR spectra were obtained
2
1
J = 6.1 Hz), 4.1 m (6H, OCH CH ). Mass spectrum,
2
3
+
on a Bruker instrument operating at 80 MHz in the
Fourier transform mode; tetramethylsilane was used
as internal reference. GLC analysis was performed
on a Buck Scientific 910 instrument. The mass spectra
were run on a Sisons Trio-1000 mass spectrometer
coupled with a Sisons 8000 gas chromatograph. The
optical rotations were measured on a Polax-Atago
polarimeter (cell length 10 cm). The melting points
were determined using an Electrothermal instrument
and are incorrected. Silica gel 60 GF254 (Merck) was
used for column chromatography. The solvents were
dried by standard methods prior to use.
m/z (Irel, %): 229 (9.3) [M OEt] , 201 (24.4), 187
52), 183 (100), 139 (12.6), 115 (30.7), 87 (59.8),
(
7
3 (25.6), 45 (33.45), 42 (35).
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2
3
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9
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ethyl crotonate, 0.8 g (5 mmol) of diethyl malonate,
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(
1
1
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 9 2001