Supported organic catalysts: Synthesis of (E)-nitrostyrenes from nitroalkanes and aromatic aldehydes over propylamine supported on MCM-41 silica as a reusable catalyst

Article abstract of DOI:10.1016/S0040-4039(01)00156-3

MCM-41-supported propylamine showed high catalytic efficiency in the nitroaldol condensation between nitroalkanes and aromatic aldehydes.

Full text of DOI:10.1016/S0040-4039(01)00156-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 2401–2403
Supported organic catalysts: synthesis of (E)-nitrostyrenes from
nitroalkanes and aromatic aldehydes over propylamine supported
on MCM-41 silica as a reusable catalyst
Giuseppina Demicheli,a Raimondo Maggi,a Alessandro Mazzacani,a Paolo Righi,b
Giovanni Sartoria,* and Franca Bigia
aDipartimento di Chimica Organica e Industriale dell’Universita`, Parco Area delle Scienze 17A, I-43100 Parma, Italy
bDipartimento di Chimica Organica ‘A. Mangini’ dell’Universita`, Viale Risorgimento 4, I-40136 Bologna, Italy
Received 30 October 2000; accepted 25 January 2001
Abstract—MCM-41-supported propylamine showed high catalytic efficiency in the nitroaldol condensation between nitroalkanes
and aromatic aldehydes. © 2001 Elsevier Science Ltd. All rights reserved.
Mesoporous MCM-type silicas represent ideal inor-
ganic supports for immobilised catalysts due to their
high surface area and sharply distributed pore dimen-
sions in the mesoporous range1 that allow easy access
to the reagents.2 Organic bases can be anchored to
trimethoxysilane to give solid basic catalysts called
MCM-41-NH2, MCM-41-NHMe and MCM-41-NEt2,
respectively.
All supported catalysts (50 mg) were tested in the
model reaction of benzaldehyde (2.5 mmol) with
nitromethane as the solvent reagent (3 ml). Yields and
selectivities of the corresponding product 3 for all
experiments are reported in Table 1. For comparison,
the reaction was carried out over unfunctionalised
MCM-41 silica.
these
materials
using
the
post-modification
methodology3 or, directly, by co-condensation of con-
veniently functionalised siliceous precursors.4
In connection with our interest in the preparation and
use of solid catalysts for the production of fine chemi-
cals,5 we report here the results of a study on the
catalytic efficiency of aliphatic amines supported on
MCM-41 silica6 for the nitroaldol condensation
between nitroalkanes and aromatic aldehydes to give
(E)-nitrostyrenes.
The inert nature of the amine-free material (entry a)
suggests that the supported amines are responsible for
the activity and whose efficiency follows the trend
primaryꢀsecondary>tertiary (entries b–d), in disagree-
ment with the tabulated basicity order of aliphatic
amines in polar solvents.8
Nitroaldol condensation is routinely performed in the
presence of a wide range of base catalysts. Nitroalco-
hols firstly produced can undergo water elimination to
give nitroalkenes. The intermediacy of imines in the
reaction promoted by primary amines was postulated
even if studies in this area are quite contradictory.7
These features, along with the reported remarkable ease
with which aromatic aldehydes give rise to the sup-
ported imines by reaction with aminopropylsilica,9
allow us to formulate the mechanistic hypothesis
depicted in Scheme 1.
The functional aminopropyl groups were anchored on
MCM-41 silica by the post-modification method3 using
3-aminopropyltriethoxysilane, N-methyl-3-aminopropyl-
The primary step is the condensation of the supported
propylamine 4 with benzaldehyde, which affords the
supported imine 5. Addition of nitromethane (activated
as a nitronate anion) to the carbonꢀnitrogen double
bond via a nitro-Mannich process,10 would give the
relatively unstable supported b-nitroamine 6.11 The
final step is b-scission of 6 that produces nitrostyrene 3
and regenerates the catalyst 4, closing the cycle.12
trimethoxysilane
and
N,N-diethyl-3-aminopropyl-
Keywords: aldol reaction; catalysts; imines; nitrocompounds.
* Corresponding author. Tel.: ++39 0521 905551; fax: ++39 0521
905472; e-mail: sartori@unipr.it
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00156-3

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G. Demicheli et al. / Tetrahedron Letters 42 (2001) 2401–2403
Table 1. Condensation between nitroalkanes and aromatic aldehydes under different conditions
Entry
Catalyst
R
R%
Time (h)
3 Yield (%)
3 Selectivity (%)
a
b
c
d
e
f
g
h
i
MCM-41
H
H
H
H
Me
OMe
NO2
Cl
H
OMe
Cl
H
H
H
H
H
H
H
H
Me
Me
Me
Et
Et
1
1
1
1
1
1
1
1
6
6
6
6
6
–
5
–
a
MCM-41-NEt2
99
81b
99
98
99
99
98
97
98
99
98
97
MCM-41-NHMea
34
98
97
96
98
97
95
95
98
88
92
a
MCM-41-NH2
MCM-41-NH2
MCM-41-NH2
MCM-41-NH2
MCM-41-NH2
MCM-41-NH2
MCM-41-NH2
MCM-41-NH2
a
a
a
a
a
a
j
k
l
a
a
MCM-41-NH2
MCM-41-NH2
Cl
NO2
a
m
a The loading of MCM-41-NEt2, MCM-41-NHMe and MCM-41-NH2 was 1.23, 1.33 and 1.36 mmol N g−1, respectively.
b 1,3-Dinitro-2-phenylpropane was isolated as a by-product.
Scheme 1. A hypothesised catalytic cycle of the MCM-41-NH2-promoted nitroaldol condensation.
In order to support the mechanistic hypothesis depicted
in Scheme 1 and to find out any transformation of the
catalyst occurring during the reaction, FT-IR spectra of
the catalyst (MCM-41-NH2) before and after treatment
with benzaldehyde were compared. The appearance of a
new peak at 1646 cm−1 (CꢁN),13 in addition to the two
peaks at 3357 and 3280 cm−1 (NH2) in the benzaldehyde-
treated catalyst 5, suggests the co-existence of both

G. Demicheli et al. / Tetrahedron Letters 42 (2001) 2401–2403
2403
supported propylamine and benzylidene propylamine.
The FT-IR spectrum of material 5 after further treatment
with nitromethane at 90°C for 1 h was quite similar to
that of the starting MCM-41-NH2. At the same time,
nitrostyrene was detected in the solution by GC analysis.
These data support the mechanism reported in Scheme
1 but, at the same time, do not exclude the co-existence
of the classical one.7b
Navarro, M. T. J. Chem. Soc., Chem. Commun. 1995,
519; (b) Climent, M. J.; Corma, A.; Iborra, S.; Miquel,
S.; Primo, J.; Rey, F. J. Catal. 1999, 183, 76.
3. See for example: Cauvel, A.; Renard, G.; Brunel, D. J.
Org. Chem. 1997, 62, 749.
4. See for example: Fowler, C. E.; Burkett, S. L.; Mann, S.
J. Chem. Soc., Chem. Commun. 1997, 1769.
5. (a) Bigi, F.; Carloni, S.; Maggi, R.; Muchetti, C.; Sartori,
G. J. Org. Chem. 1997, 62, 7024; (b) Bigi, F.; Maggi, R.;
Sartori, G.; Zambonin, E. J. Chem. Soc., Chem. Com-
mun. 1998, 513; (c) Ballabeni, M.; Ballini, R.; Bigi, F.;
Maggi, R.; Parrini, M.; Predieri, G.; Sartori, G. J. Org.
Chem. 1999, 64, 1029; (d) Bigi, F.; Chesini, L.; Maggi, R.;
Sartori, G. J. Org. Chem. 1999, 64, 1033.
Repeated condensation tests were successively performed
for five cycles under the above-reported conditions. The
catalyst was removed after each cycle, washed with
nitromethane and reintroduced into the reactor; a new
batch of benzaldehyde and nitromethane was then added
and the reaction was repeated under the same conditions.
Compound 3 was detected in 98, 95, 95, 90 and 84% yield.
These results show that the catalyst MCM-41-NH2 was
reusable for all the five cycles, showing only a small
lowering of the conversion in the fourth and fifth cycles.
6. For the preparation of MCM-41 silica, see: Beck, J. S.;
Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C.
T.; Schmitt, K. D.; Chu, C. T.-W.; Olson, D. H.; Shep-
pard, E. W.; McCullen, S. B.; Higgins, J. W.; Schlenker,
J. L. J. Am. Chem. Soc. 1992, 114, 10834. X-Ray analyses
of all the MCM-41-supported amines confirmed that
the long-range ordered structure of the inorganic support
was preserved. Moreover, N2-adsorption measurements
showed that the surface area decreases from 1050 to the
average value of 800 m2 g−1 upon anchoring amines.
7. (a) Hurd, C. D.; Strong, J. S. J. Am. Chem. Soc. 1950, 72,
4813; (b) Rosini, G. In Comprehensive Organic Synthesis;
Trost, B. M.; Fleming, I.; Heathcock, C. H., Eds.; Perga-
mon Press: Oxford, 1991; Vol. 2, pp. 321–340; (c) Rosini,
G.; Ballini, R.; Petrini, M.; Sorrenti, P. Synthesis 1985,
515; (d) Ballini, R.; Castagnani, R.; Petrini, M. J. Org.
Chem. 1992, 57, 2160; (e) Ballini, R.; Petrini, M. J. Chem.
Soc., Perkin Trans. 1 1992, 3159.
8. Hall, Jr., H. K. J. Am. Chem. Soc. 1957, 79, 5441.
9. (a) Macquarrie, D. J.; Clark, J. H.; Lambert, A.; Mdoe,
J. E. G.; Priest, A. React. Funct. Polym. 1997, 35, 153; (b)
Clark, J. H.; Macquarrie, D. J. J. Chem. Soc., Chem.
Commun. 1998, 853.
10. Baer, H. H.; Urbas, L. In The Chemistry of Nitro and
Nitroso Groups, Part 2; Patai, S., Ed.; Interscience: New
York, 1970; p. 117.
The reaction has been successfully extended to different
aromatic aldehydes and nitroalkanes giving products 3
in high yield and excellent selectivity.14 In all cases, the
(E)-stereoisomer was the sole product detected (Table 1,
entries e–m).15
In summary, in the present paper we have shown that
aminopropyl silica acts as a heterogeneous organic
catalyst in the nitroaldol condensation between aromatic
aldehydes and nitroalkanes. The results suggest that the
supported primary aminopropyl moiety reacts with the
aldehyde giving an imine intermediate, which in turn
undergoes nitro-Michael attack producing nitrostyrene
as the final product through the unstable supported
nitroamine intermediate 6.
In addition, the use of a supported catalyst that can be
easily removed from the reaction mixture by filtration has
the great advantage of avoiding base-catalysed by-
product formation during the work-up procedure.7b
11. Adams, H.; Anderson, J. C.; Peace, S.; Pennell, A. M. K.
J. Org. Chem. 1998, 63, 9932.
12. Comparative experiments, carried out under homoge-
neous conditions, confirm that the sequential addition
and b-elimination processes between benzylidene propy-
lamine and nitromethane, utilised as solvent–reagent,
occur very easily giving nitrostyrene and 1,3-dinitro-2-
phenylpropane in 80 and 12% yield, respectively, by
heating a 1:1 mixture of reagents at 90°C for 3 hours in
the presence of 5% propylamine.
Acknowledgements
Thanks are due to the Ministero dell’Universita` e della
Ricerca Scientifica e Tecnologica (MURST), Italy, and
to the University of Parma (National Project
‘Stereoselezione in Sintesi Organica. Metodologie ed
Applicazioni’) for financial support. The authors are also
grateful to the Centro Interfacolta` Misure (CIM) for the
use of NMR and mass spectroscopy instruments and to
Mr. Pier Antonio Bonaldi (Lillo) for technical assistance.
13. Texier-Boullet, F. Synthesis 1985, 679.
14. The general procedure for the preparation of nitrostyre-
nes 3 is as follows: A mixture of the selected benzalde-
hyde (2.5 mmol), the selected nitroalkane (3 ml) and
MCM-41-NH2 (50 mg) was stirred at 90°C for the
selected time. The reaction mixture was cooled to rt, the
catalyst removed by filtration and the crude mixture
analysed by GC (SE-30 capillary column). All products
3d–m were characterised (IR, 1H NMR and MS) and
their melting points compared with literature reported
melting points.
References
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