2324
M. M. Mojtahedi et al. / Tetrahedron Letters 50 (2009) 2322–2325
Ph
Ph
Ph
TMSCN
PhCHO
1a
+
Fe3O4 (10 mol%)
NH
3ah
CN
NH2
88%
2h
de=60
Scheme 3.
Table 2
Fe3O4-catalyzed Strecker reaction of benzaldehyde, aniline, and TMSCN in compar-
ison with other methods
100
80
60
40
20
0
Catalyst
Solvent
Yield (%)
Reference
Fe3O4
RhI3
InI3
Montmorillonite
Silica sulfuric acid
NiCl2
—
CH3CN
Et2O
CH2Cl2
CH2Cl2
CH3CN
95
95
95
90
88
92
Present work
Majhi et al.30
Shen et al.27
Yadav et al.29
Chen et al.28
De et al.31
accessible catalyst is presented. After separation of the catalyst
with an external magnet, the reaction products are easily obtained
in good purity by evaporation of the volatiles. A comparison of the
performance of the present catalyst for the Strecker reaction with
some other recent reports27–31 on the condensation of benzalde-
hyde with aniline and TMSCN is shown in Table 2.
1
2
3
4
5
6
7
8
9
10
11
Number of cycles
Figure 1. A typical reaction mixture in the presence or absence of a magnetic field
(top). Efficient recovery of the catalyst (bottom).
Acknowledgment
products within the same time period. Other aromatic aldehydes
bearing electron-withdrawing groups and electron-releasing
groups reacted equally well with various amines under the same
conditions (entries 7–14).
Partial financial support of this work by the Ministry of Science,
Research, and Technology of Iran is gratefully appreciated.
Upon completion of the reactions, the catalyst was recovered
from the reaction mixture simply by applying an external perma-
nent magnet as shown in Figure 1 (top) and the products were iso-
lated in good purity by removing the volatiles under reduced
pressure. Further, the recovered Fe3O4 was reused successfully in
10 subsequent reactions without significant loss of catalytic per-
formance as illustrated in Figure 1 (bottom).
A flame atomic absorption spectroscopy (FAAS) experiment was
designed to study the stability of the Fe3O4 catalyst during the
reaction and the recycling process. Consequently, when a reaction
mixture filtrate was subjected to FAAS analysis, only 0.6 ppm Fe
was detected in the mixture which is equal to 0.1% of the starting
Fe3O4 used for catalysis. This illustrates that Fe3O4 initiates a het-
erogeneous catalytic cycle and does not undergo degradation dur-
ing the reactions allowing its successful reuse.
Supplementary data
Supplementary data associated with this article can be found, in
References and notes
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In the next step, the procedure was further explored by smooth
conversion of the aliphatic aldehydes butyraldehyde or 3-phenyl-
propionaldehyde into their corresponding
a
-aminonitriles 3ga,20
3gf,31 and 3he,20 respectively, in high yields (Scheme 2).
Finally, the diastereoselectivity of the process was examined for
the reaction between (S)-1-phenylethylamine 2h and benzalde-
hyde 1a. Under the above conditions, formation of 3ah24 was ob-
served in 83% yield within 20 min. The 1H NMR spectrum of the
reaction mixture revealed the formation of both possible products
with moderate 4:1 diastereoselectivity (Scheme 3).
17. Mojtahedi, M. M.; Abaee, M. S.; Eghtedari, M. Appl. Organomet. Chem. 2008, 22,
529–532.
In conclusion, an efficient protocol for the rapid room tempera-
ture Strecker reaction using Fe3O4 as an inexpensive and easily
18. Strecker, A. Liebigs. Ann. Chem. 1850, 75, 27–51.
19. Enders, D.; Shilvock, J. P. Chem. Soc. Rev. 2000, 29, 359–373.
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25. For the procedure for the preparation of Fe3O4, see: Kang, Y. S.; Risbud, S.;
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26. Typical procedure: Caution! TMSCN is very toxic and could produce hydrogen
cyanide in contact with water. All operations should be performed with special
care under a well-ventilated fume hood. A mixture of aldehyde (4 mmol),
amine (8 mmol), and Fe3O4 (10 mol % with respect to aldehyde) was stirred at
CN
CN
CN
N
N
N
Ph
3he
3ga
3gf
83%
80%
88%
Scheme 2.