First iron-catalyzed synthesis of oximes from styrenes

Article abstract of DOI:10.1039/b900326f

Aryl-substituted olefins react with t-butyl nitrite and sodium borohydride in the presence of iron(ii)phthalocyanine to give oximes in moderate to high yields.

Full text of DOI:10.1039/b900326f

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First iron-catalyzed synthesis of oximes from styreneswz
Saisuree Prateeptongkum,a Irina Jovel,a Ralf Jackstell,a Nadine Vogl,b
Christoph Weckbeckerb and Matthias Beller*a
Received (in Cambridge, UK) 7th January 2009, Accepted 2nd February 2009
First published as an Advance Article on the web 25th February 2009
DOI: 10.1039/b900326f
Aryl-substituted olefins react with t-butyl nitrite and sodium
borohydride in the presence of iron(II)phthalocyanine to give
oximes in moderate to high yields.
Table 1 Iron-catalyzed synthesis of oximesa
The development of general methods for the formation of
carbon–nitrogen bonds from olefins is an important challenge
in organic synthesis.1 For some years we have been interested
in this area and reported advancements in catalytic
hydroamination,2 and hydroaminomethylations.3 Recently,
we also showed that NO can be used as a practical amination
reagent for the non-catalytic synthesis of nitro olefins.4 Based
on this work, we got attracted in catalytic conversions of
olefins and NO or NO-releasing reagents. Herein, we wish to
report the first iron-catalyzed synthesis of oximes from olefins
by employing a biomimetic iron phthalocyanine complex
catalyst and easily available reagents (NaBH4 and t-BuONO).5,6
Until now, few studies have been performed on the catalytic
nitrosation of olefins applying nitric oxide or alkyl nitrites in
the presence of various reductants.7 In general, cobalt com-
plexes were used as catalysts in these reactions. However,
Sugamoto and co-workers reported the utilization of
iron(III) meso-tetraphenylporphine chloride [Fe(TPP)Cl] for
nitrosation.7f Unfortunately, this complex showed no catalytic
activity using t-BuONO.
Fe(Pc) NaBH4
Entry (mol%) (equiv.) Solvent
Conv. Yield
(%)c
t/h (%)b
1
2
3
4
5
6
7
8
20
20
20
20
20
10
5
1
1
1
1.5
1.5
1.5
1.5
2
2
2
2
2
DME-i-PrOHe
i-PrOH
DME
24 19
24 14
24 32
12
10
30
6
Toluene-i-PrOHe 24 12
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
24 98
24 99
24 97
24 98
24f
32
33
58
66
83
(79)
27
39
9
3
3
98
99
10d
2
11
12
1
0.5
1.2
2
EtOH
EtOH
3
53
24 75
a
Reaction conditions: 1 mmol of styrene and 2.5 mmol of t-BuONO
b
in 4 mL of solvent at room temperature under Ar. Determined by
c
GC after the reaction. Determined by GC after workup; isolated
d
yield is given in parenthesis. The reaction was performed in auto-
e
clave with additional 10 bar of H2. The ratio for mixed solvents is 1:1
f
v/v. Trace of 1-phenylethylamine is observed by GC after the reaction.
For our initial experiments, the reaction of styrene with tert.
butyl nitrite in the presence of iron phthalocyanine complex
(Fe(Pc)) was chosen as a model. Selected results of the
optimization of reaction conditions are summarized in
Table 1. First tests showed only low conversion of the olefin.
However, a survey of solvents indicated that high activity is
observed in EtOH using NaBH4 as reductant. Notably, higher
catalyst concentration as well as prolonged reaction time led to
decomposition of the product (Table 1, entries 5–9). In
addition, some complexation between the initially formed
nitrosoalkane and the iron centre of catalyst might occur,8 and
side-products such as 2,3-diphenylbutane and ethylbenzene,
which resulted from reduction of styrene,9 are detected by GC
in up to 20%. This is in agreement with the work of Eckert
et al. who demonstrated that oxime 2 can be reduced to
1-phenylethylamine in the presence of a large amount of
catalyst and NaBH4.10 However, under our conditions only
traces of 1-phenylethylamine are observed (Table 1, entry 5).
The best yield of 2 is obtained when the reaction was
performed in the presence of 10 bar H2 (Table 1, entry 10).
A survey of different metal phthalocyanines (Table 2, entries
1–3) showed that the iron complex is by the far the most active
and selective catalyst for the model reaction. Noteworthy, also
vitamin B12 and the cobalt complex Co(DH2)(py)Cl showed
significant activity (Table 2, entries 4–5). Moreover, using
different nitrogen ligands in the presence of 10 mol% FeCl3
or FeCl2 gave the corresponding product in 5–61% yield
(Table 2, entries 7–14). The best result was achieved when
the reaction was performed in the presence of terpyridine L1
(Table 2, entry 8). In general, monodentate (L6) and bidentate
ligands (L5) exhibited much lower activity compared to
tridentate ligands (L1–L4).
a Leibniz-Institut fur Katalyse e.V. an der Universita¨t Rostock,
¨
Albert-Einstein-Str. 29a, 18059 Rostock, Germany.
E-mail: matthias.beller@catalysis.de; Fax: +49-381-1281-51113
b Evonik Degussa GmbH, Health and Nutrition, Rodenbacher
Chaussee 4, 63457 Hanau, Germany
w Electronic supplementary information (ESI) available: General pro-
cedure, characterization data for compounds 2, 4a–4k and 5 and 1H
and 13C NMR spectra of compounds 2, 4a–4k and 5. See DOI:
10.1039/b900326f
z This article is part of a ChemComm ‘Catalysis in Organic Synthesis’
web-theme issue showcasing high quality research in organic chem-
istry. Please see our website (http://www.rsc.org/chemcomm/organic
webtheme2009) to access the other papers in this issue.
With respect to the mechanism, we propose that oxime
formation proceeds similarly compared to the reaction in the
presence of cobalt complexes (Scheme 1).7 Remarkably, at the
initial stage of the reaction hydrogen evolution is observed.
Moreover, B(OEt)3 is detected by GC. Key step in the
ꢀc
This journal is The Royal Society of Chemistry 2009
1990 | Chem. Commun., 2009, 1990–1992

Table 2 Variation of catalysts and ligandsa
Table 3 Scope and limitationsa
Conv.
(%)b
Yield
(%)c
Entry Olefin
1
Product
97
95
65
69
2
Ligand
(equiv./catalyst)
Conv. Yield
3
4
92
99
56
83
Entry
Catalyst (mol%)
(%)d
(%)e
1
2
3
4
5
6
7
8
Co(Pc)b (10)
Mn(Pc)b (10)
Ni(Pc)b (10)
Vit B12 (1)
Co(DH2)(py)Clc (10)
FeCl3 (1)
FeCl2 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
—
—
—
—
12
39
2
2
9
o1
44
22
16
55
61
5
73
55
43
97
94
29
99
99
76
44
55
—
L1 (2)
L1 (2)
L1 (2)
—
L2 (2)
L3 (2)
L4 (2)
L5 (3)
L6 (4)
5
6
98
99
73
86
9
10
11
12
13
14
46
32
34
7
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
8
a
Reaction conditions: 1 mmol of styrene, 2 mmol of NaBH4 and
2.5 mmol of t-BuONO in 4 mL of EtOH, 3 h at room temperature under
7
8
97
59
88
b
Ar. Pc = phthalocyanine. DH2 = dimethylglyoxime, py = pyridine.
c
Determined by GC after the reaction. e Determined by GC after work-up.
d
100
9
85
60
40
44
10
Scheme 1 Proposed reaction mechanism.
11
100
32
mechanism is the formation of the s-alkyliron(III)
complex A, which reacts with t-BuONO to afford the
corresponding oxime.
12
61–100 61–100
Finally, the scope and limitations of the reaction were
investigated by employing various olefins (Table 3). For
convenience the reactions were performed without additional
hydrogen pressure. Different para- and meta-substituted
styrene derivatives gave the desired products in good yields
(Table 3, entries 1–2 and 4–6), while ortho-substituted
substrates afforded the corresponding oximes in somewhat
lower yields (Table 3, entries 3 and 7). In addition, 2-vinylpyri-
dine showed high activity and selectivity, leading to 4h in 88%
yield (Table 3, entry 8). 1,2-Disubstituted aryl olefins (3i–3k)
a
Reaction conditions: 3 mmol of olefin, 1 mol% of Fe(Pc), 6 mmol of
NaBH4 and 7.5 mmol of t-BuONO in 18 mL of EtOH, 3 h at room
b
temperature under additional 10 bar of H2. Determined by GC after
c
the reaction. Isolated yield.
were converted to the corresponding oximes (4i–4k) in
moderate yields (Table 3, entries 9–11). In the case of 3k,
3-phenyl-2-isoxazoline (5) is formed from the cyclization of
ꢀc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 1990–1992 | 1991

oximate anion of 4k11 as a minor product (14% yield). It
should be noted that all products are conveniently isolated by
chromatography.
Chem., 2006, 4, 826; (c) L. Routaboul, C. Buch, H. Klein,
R. Jackstell and M. Beller, Tetrahedron Lett., 2005, 46, 7401;
(d) A. Moballigh, A. Seayad, R. Jackstell and M. Beller, J. Am.
Chem. Soc., 2003, 125, 10311; (e) P. Eilbracht, L. Barfacker,
¨
In summary, we have developed the first iron-catalyzed
synthesis of oximes from olefins. Noteworthy, the reaction
proceeds in the presence of a convenient iron complex and
inexpensive reagents.
C. Buss, C. Hollmann, B. E. Kitsos-Rzychon, C. L. Kranemann,
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5 For recent reviews on iron-catalyzed reactions see: (a) C. Bolm,
J. Legros, J. Le Paih and L. Zani, Chem. Rev., 2004, 104, 6217;
(b) S. Enthaler, K. Junge and M. Beller, Angew. Chem., Int. Ed.,
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6 Some recent iron-catalyzed reactions of olefins: (a) G. Anilkumar,
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Notes and references
1 For some reviews see: (a) J. J. Brunet, N. C. Chu and
M. Rodriguez-Zubiri, Eur. J. Inorg. Chem., 2007, 4711;
(b) A. V. Lee and L. L. Schafer, Eur. J. Inorg. Chem., 2007,
2243; (c) R. Severin and S. Doye, Chem. Soc. Rev., 2007, 36,
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507; (g) S. Doye, Synlett, 2004, 1653; (h) J. Seayad, A. Tillack,
C. G. Hartung and M. Beller, Adv. Synth. Catal., 2002, 344, 795;
(i) M. Beller, C. Breindl, M. Eichberger, C. G. Hartung, J. Seayad,
O. Thiel, A. Tillack and H. Trauthwein, Synlett, 2002, 1579.
2 Some recent examples from our group: (a) K. Alex, A. Tillack,
N. Schwarz and M. Beller, ChemSusChem, 2008, 1, 333;
(b) A. Tillack, V. Khedkar, J. Jiao and M. Beller, Eur. J. Org.
Chem., 2005, 5001; (c) V. Khedkar, A. Tillack, C. Benisch,
J.-P. Melder and M. Beller, J. Mol. Catal. A: Chem., 2005, 241,
175; (d) V. Khedkar, A. Tillack, M. Michalik and M. Beller,
Tetrahedron Lett., 2004, 45, 3123; (e) A. Tillack, H. Jiao,
I. Garcia Castro, C. G. Hartung and M. Beller, Chem.–Eur. J.,
2004, 10, 2409; (f) M. Beller, J. Seayad, A. Tillack and H. Jiao,
Angew. Chem., Int. Ed., 2004, 43, 3368; M. Beller, J. Seayad,
A. Tillack and H. Jiao, Angew. Chem., 2004, 116, 3448;
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3 (a) A. Moballigh, C. Buch, L. Routaboul, R. Jackstell, H. Klein,
A. Spannenberg and M. Beller, Chem.–Eur. J., 2007, 13, 1594;
(b) K.-S. Mueller, F. Koc, S. Ricken and P. Eilbracht, Org. Biomol.
ꢀc
This journal is The Royal Society of Chemistry 2009
1992 | Chem. Commun., 2009, 1990–1992