Dehydroascorbic acid (DHAA) capped magnetite nanoparticles as an efficient magnetic organocatalyst for the one-pot synthesis of α-aminonitriles and α-aminophosphonates This article is dedicated to memory of Majid Shahriari

Article abstract of DOI:10.1016/j.tetlet.2013.09.032

A dehydroascorbic acid capped magnetite (DHAA-Fe₃O₄) catalyst is prepared and used for the one-pot synthesis of α-aminonitriles and α-aminophosphonates. Different derivatives of these compounds are synthesized in good yields.

Full text of DOI:10.1016/j.tetlet.2013.09.032

Accepted Manuscript
Dehydroascorbic acid (DHAA) capped magnetite nanoparticles as an efficient
magnetic organocatalyst for the one-pot synthesis of α-aminonitriles and α-
aminophosphonates
Dariush Saberi, Samaneh Cheraghi, Samaneh Mahdudi, Jafar Akbari, Akbar
Heydari
PII:
S0040-4039(13)01586-4
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.09.032
TETL 43532
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
11 April 2013
22 August 2013
11 September 2013
Please cite this article as: Saberi, D., Cheraghi, S., Mahdudi, S., Akbari, J., Heydari, A., Dehydroascorbic acid
(DHAA) capped magnetite nanoparticles as an efficient magnetic organocatalyst for the one-pot synthesis of α-
aminonitriles and α-aminophosphonates, Tetrahedron Letters (2013), doi: http://dx.doi.org/10.1016/j.tetlet.
2013.09.032
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Dehydroascorbic acid (DHAA) capped
magnetite nanoparticles as an efficient magnetic
organocatalyst for the one-pot synthesis of α-
aminonitriles and α-aminophosphonates
Dariush Saberi, Samaneh Cheraghi, Samaneh Mahdudi, Jafar Akbari, Akbar Heydari*

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Dehydroascorbic acid (DHAA) capped magnetite nanoparticles as an efficient
magnetic organocatalyst for the one-pot synthesis of α-aminonitriles and α-
aminophosphonates
Dariush Saberi, Samaneh Cheraghi, Samaneh Mahdudi, Jafar Akbari, Akbar Heydari*
Chemistry Department, Tarbiat Modares University, P.O. Box 14155-4838 Tehran, Iran, Fax: (+98)-21- 82883455; phone: (+98)-21-82883444; email:
heydar_a@modares.ac.ir
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A dehydroascorbic acid capped magnetite (DHAA-Fe3O4) catalyst is prepared and used for the
one-pot synthesis of α-aminonitriles and α-aminophosphonates. Different derivatives of these
compounds are synthesized in good yields.
2009 Elsevier Ltd. All rights reserved.
Available online
Keywords:
Dehydroascorbic acid
Organocatalyst
magnetite nanoparticles
α-aminonitriles
α-aminophosphonates
Nitrogen-containing compounds such as amines, α-
aminonitriles, α-aminophosphonates, etc., are very common
substrates in organic synthesis. α-Aminonitriles constitute a class
of compounds some of which display anticancer, antibacterial,
antifungal and antiviral activities.1 They also serve as efficient
precursors for the synthesis of natural and unnatural α-amino
acids.2 α-Aminophosphonic acids act as antibiotics,3 herbicides,4
pharmacological agents5 and enzyme inhibitors.6 Owing to their
widespread applications, the synthesis of these compounds has
gained a great deal of attention. Among all the procedures
leading to these compounds, three-component condensation
reactions are very attractive. In this context, the addition of
nucleophiles to in situ generated C=N bonds has emerged as an
extremely useful tool for the synthesis of such nitrogen-
containing molecules. Two renowned approaches in this field are
the Strecker reaction7 and Kabachnik–Fields reaction.8 In the
former, condensation of a carbonyl compound (generally an
aldehyde), an amine and a cyanide ion source leads to the direct
one-pot synthesis of α-aminonitriles. In the latter, which is the
most frequently used for the synthesis of α-aminophosphonates,
an amine, an aldehyde and a di- or tri-alkyl phosphite react in a
one-pot fashion in the presence of either a Lewis acid or a
Brønsted acid. As is common for classical Strecker reactions, an
aqueous solution of KCN is used as the cyanide source which
poses difficulties, especially in the work-up stage. Thus a number
of alternative cyanide sources have been introduced to overcome
problems associated with using KCN.9 Among these,
trimethylsilyl cyanide (TMSCN) was found to be a promising
choice, due to its nature as an effective, easily-handled, and
relatively safe cyanation reagent.10 It is noteworthy that TMSCN
is able to transfer the cyanide ion only in the presence of a
catalyst. Hence, different types of catalysts have been developed
including various Lewis and Brønsted acids such as Yb(OTf)3,11a
Cu(OTf)2,11b BiCl3,11c RuCl3,11d Sc(OTf)3,11e K2PdCl4,11f
11j
GdCl3.6H2O,11g InI3,11h CeCl3,11i ZrCl4 K4[Fe(CN)6]11k and p-
toluenesulfonic acid,11l which catalyze homogeneously the
Strecker reaction. Incidentally, several heterogeneous catalysts
have also been proposed, which are more advantageous in terms
of catalyst/product separation.12 Similarly, diverse catalytic
systems for the synthesis of α-aminophosphonates have been
reported,13 but most of them suffer from at least one of the
following disadvantages: harsh reaction conditions, air
sensitivity, the use of stoichiometric, toxic and relatively
expensive reagents or catalysts, poor product yields, long
reaction times and tedious separation procedures. To compensate
for these deficiencies, numerous endeavors have been made
giving rise to satisfactory results in terms of efficiency and rate of
the reaction, but still two major problems remained. Firstly, the
presence of a metal (free or complex) as the catalyst, hence
posing environmental problems and as an impurity in the final
product. Secondly, the matter of recycling and reusability of the
catalyst. Other shortcomings include the low selectivity of most
of the catalysts. Thus, green, selective and metal-free catalytic
systems, which can be easily recycled are still required for these
reactions.
The emergence of organocatalysts has interested chemists by
virtue of them often being waste-free, environmentally benign,
easily-handled, and highly efficient.14 Nevertheless, developing
such catalysts is a challenging issue.
Herein, we introduce Vitamin C (in its oxidized form, DHAA)
as a green and biocompatible organocatalyst which can promote
the three-component coupling reactions of aldehydes (ketones),
amines (both primary and secondary), and TMSCN or dimethyl
phosphite to afford of α-aminonitriles and α-aminophosphonates.
To avoid problems arising during separation of the catalyst from

2
Tetrahedron
the reaction medium, and also to facilitate the purification
unsaturated aldehyde such as cinnamaldehyde, produced
excellent yields, without any decomposition or polymerization
(Table 2, entries 4 and 7). Aliphatic aldehydes were also used,
which afforded very good yields under these conditions (Table 2,
entries 5 and 6). The cyclic amine, morpholine, gave a high yield
of product in a short time (Table 2, entry 15).
process, DHAA is mounted on magnetite nanoparticles. In this
way, a reusable magnetic organocatalyst is formed, which is
easily separated from the reaction medium simply by applying an
external magnet.
DHAA-capped magnetite nanoparticles (DHAA-Fe3O4) were
synthesized according to a previously reported procedure.15
Briefly, a 0.1 M Fe(OH)3 colloidal solution was prepared by
adding 10 mL of FeCl3.6H2O aqueous solution to 20 mL of a
0.45 M NaHCO3 solution, and the obtained solution stirred for 30
minutes. Subsequently, 10 mL of an aqueous solution of vitamin
C in a molar ratio of 1:6 was added gradually to the Fe3+. The
mixture was stirred for another 10 minutes and then transferred
into a steel-lined Teflon autoclave to a volume of 50 mL and the
autoclave kept at 150 °C for 4 hours. The particles were washed
three times with water and ethanol and then collected by
centrifugation (0.42 mmol DHAA/g catalyst). It is worth
mentioning that in this synthetic process, not only does vitamin C
act as the reducing agent by its C=C bond being oxidized, but
also its oxidation product (dehydroascorbic acid, DHAA) serves
as a stabilizer and capping ligand due to the interactions of its
carbonyl groups with FeOx particles.15
Table 2: Strecker reaction of various aldehydes or ketones
and amines in the presence of DHAA-Fe3O4 as the catalyst a
Time
(min)
15
Yield
(%)b
90
Entry
R
R1
R2
Ref.
1
2
Ph
Ph
Ph
H
H
11g
12b
4-Me-C6H4
4-MeO-
C6H4
45
80
3
Ph
H
30
92
12b
4
5
6
7
8
Ph
Ph
Ph
Ph
Ph
PhCH=CH
C3H7
H
H
H
H
H
80
30
60
100
100
60
45
30
180
180
180
78
83
75
82
85
90
83
90
80
11i
13h
11g
11d
16
11k
11f
16
iPr
furan-2-yl
cyclohexyl
9
Ph
R1,R2= (CH2)5
10
11
12
13
14
4-Me-C6H4
4-MeO-C6H4
4-Br-C6H4
4-I-C6H4
4-O2N-C6H4
RNH2 =
O(CH2CH2)2
NH
Ph
Ph
Ph
Ph
Ph
H
H
H
H
H
11f
-
17
78
<10c
To assess the efficacy of the synthesized catalyst, the one-pot
reaction between benzaldehyde, aniline and TMSCN was carried
out in the presence of vitamin C (17.6 mg, 10 mol%), in EtOH as
the solvent, at room temperature, which gave rise to
approximately 20% conversion after 3 hours. Much to our
surprise, when DHAA-Fe3O4 (20 mg, 0.9 mol% DHAA) was
used as the catalyst, the reaction went to completion in 15
minutes and 90% of the product was isolated. To investigate the
role of Fe3O4 as a catalyst, the same reaction was performed in
the presence of Fe3O4 (23 mg, 10 mol%), which resulted in a
90% yield after 150 minutes. Next, the effects of the solvent and
catalyst loading were investigated (Table 1). The best results
were obtained when the reaction was conducted in EtOH with 20
mg of the catalyst.
15
Ph
H
60
85
11c
16
Ph
Ph
Me
180
trace
11k
aReaction conditions: aldehyde or ketone (1 mmol), amine
(1.2 mmol), TMSCN (1.2 mmol), catalyst (20 mg), room
temperature.18 bIsolated yield. cConversion
In the case of 4-nitroaniline, due to its low nucleophilicity,
only 10 mol% of the starting material was converted into the
corresponding product after 3 hours (Table 2, entry 14). By
applying these conditions to cyclohexanone, a 90% yield of the
corresponding product was obtained (Table 2, entry 9). In
contrast, in the case of acetophenone the progress of the reaction
was negligible (Table 2, entry 16).
Table 1: The effect of the solvent and catalyst loading on the
As a second target, we explored the effectiveness of DHAA-
Strecker reactiona
Fe3O4 as
a reusable catalyst for the generation of α-
Amount of Cat.
Yield
(%)b
90
68
80
70
75
50
60
aminophosphonates (Scheme 2).
Entry
Solvent
Time (min)
(mg)
20
20
20
20
20
20
20
10
25
1
2
3
4
5
6
7
8
9
EtOH
CH2Cl2
CH3CN
H2O
DMSO
toluene
THF
15
60
60
60
60
60
60
15
15
Scheme 2: Kabachnik–Fields reaction in the presence of the
DHAA-Fe3O4 catalyst.
EtOH
EtOH
70
90
The reaction between dimethyl phosphite and the in situ
generated imine from benzaldehyde and aniline was chosen as a
model system. Having screened parameters such as solvent,
temperature and amount of catalyst loading (Table 3), the
following conditions offered the maximum yield of product:
aldehyde (1 mmol), amine (1 mmol), dimethyl phosphite (1
mmol), catalyst (20 mg), 40 °C, and solvent-free conditions.
aReaction conditions: benzaldehyde (1 mmol), aniline (1.2
mmol), TMSCN (1.2 mmol), room temperature. bIsolated yield.
Having established optimum conditions, a series of α-
aminonitriles was synthesized by reacting various aldehydes or
ketones and amines with TMSCN in the presence of DHAA-
Fe3O4 in EtOH in order to showcase the broad scope and
generality of this method (Scheme 1).
Several α-aminophosphonates were prepared (Table 4).
Simple aldehydes and acid-sensitive aldehydes such as
thiophene-2-carbaldehyde and cinnamaldehyde underwent the
reaction with aniline and dimethyl phosphite to produce the
corresponding α-aminophosphonates. Several other aniline
derivatives were coupled with benzaldehyde and dimethyl
phosphite to give good yields of the desired products.
Cyclohexanone also underwent this one-pot reaction with aniline
and dimethyl phosphite to give the desired product in good yield
(Table 4, entry 10).
Scheme 1: Strecker reaction in the presence of the DHAA-Fe3O4
catalyst
Irrespective of the aldehyde used, the reaction proceeded to
furnish the corresponding product with varying degrees of
success (Table 2). Substituted aromatic aldehydes provided good
results. Acid-sensitive heterocycles such as furfural and an

3
Table 3: Optimization of the reaction conditions for the
Kabachnik–Fields reaction catalyzed by DHAA-Fe3O4
intermediate through generation of hydrogen bonds between the
a
hydroxyl groups of DHAA and the oxygen atom of the carbonyl
group. In the presence of the magnetic catalyst, the imine carbon
is attacked by cyanide to give the product. This mechanism is
thought to also occur in the formation of α-aminophosphonates.
Catalyst
(mg)
20
20
20
Time
(h)
3.5
3.5
3.5
Entry
Temp.
Solvent
Yield (%)b
1
2
3
4
40
40
40
40
EtOH
CH2Cl2
H2O
CH3CN
Solvent-
free
Solvent-
free
Solvent-
free
40
60
40
50
A
more significant issue is that the catalyst used is
enantiomerically pure and so it is possible that the cyanide ion
attack on both sides of the imine is not equal. Consequently, the
reaction may be enantioselective. Although this is a very
important issue, unfortunately it was not possible to examine this
aspect in detail.
20
3.5
5
6
7
8
9
40
r.t.
60
40
40
20
20
20
15
25
2
2
2
2
2
93
10
93
70
95
Solvent-
free
Solvent-
free
aReaction conditions: benzaldehyde (1 mmol), aniline (1 mmol),
dimethyl phosphite (1 mmol). bIsolated yield
Table 4: Kabachnik–Fields reaction of various aldehydes or
ketones and amines in the presence of DHAA-Fe3O4 as the
catalyst.a
Time Yield
Entry
R1
R
Ref.
(h)
2
2
2
1
2
2
2
(%)b
93
91
90
95
80
80
90
83
1
2
3
4
5
6
7
8
Ph
4-Me-C6H4
4-Cl-C6H4
4-MeO-C6H4
thien-2-yl
PhCH=CH
Ph
Ph
Ph
Ph
Ph
Ph
13n
13e
13n
13l
13r
13r
13s
13d
Scheme 3: A plausible mechanism for the one-pot synthesis of α-
Ph
aminonitriles catalyzed by DHAA-Fe3O4
4-Me-C6H4
4-Br-C6H4
RNH2 =
O(CH2CH2)2NH
Ph
2
Finally, a comparative study of this catalytic system with
other recent reports on one-pot reactions between benzaldehyde,
aniline and TMSCN was undertaken, which revealed that our
catalyst was comparable with others in terms of the reaction time
and yields, but required less catalyst (Table 5).
9
Ph
R1CHO =
2
75
13t
10
Ph
2
85
13t
cyclohexanone
aReaction conditions: aldehyde (1 mmol), amine (1 mmol),
dimethyl phosphite (1 mmol), solvent-free, 40 °C.18 bIsolated
yield
Table 5: A comparison of the efficiency of DHAA-Fe3O4 with
several reported procedures on the condensation of benzaldelyde,
aniline, and TMSCN
The reusability of the catalyst was also tested in the reaction
between benzaldehyde, aniline and TMSCN. When the stirring
was stopped, the catalyst was adsorbed onto the surface of the stir
bar. The nanoparticles were then washed with EtOH, air-dried
and used directly for the next reaction without further
purification. The DHAA-Fe3O4 nanoparticles could be recovered
and reused 6 times without any significant loss of the catalytic
activity (Figure 1).
Catalyst
loading
Time
(min)
Yield
(%)a
Entry
1
Catalyst
Ref.
19
sulfamic
acid
20 mol%
240
90
2
3
4
5
6
Ph3P/DEAD
Ga-TUD-1
oxalic acid
K2PdCl4
RhI3
100 mol%
4 mol%
20
30
60
12
10
98
95
97
95
95
20
21
10 mol%
10 mol%
2 mol%
22
11f
23
Montmorillo
nite KSF
DHAA-
Fe3O4
7
8
1 g
150
15
90
90
12b
Present
work
0.9 mol%
In conclusion, we have shown that DHAA supported on
magnetite nanoparticles can act as novel, effective,
Figure 1: Reusability of the DHAA-Fe3O4 catalyst in the
Strecker reaction between benzaldehyde, aniline and TMSCN.
Reaction time: 15 min.
a
heterogeneous and biocompatible organocatalyst for the one-pot
synthesis of α-aminonitrile and α-aminophosphonate derivatives
from commercially available starting materials. Various
aldehydes and ketones and amines gave the corresponding
products in high yields. Recovery of the catalyst was simple
using a magnet, allowing its reuse without significant loss of its
catalytic activity (over 6 cycles).
A plausible mechanism for the one-pot, three-component
condensation reaction of aldehydes, amines and TMSCN to
produce α-aminonitriles in the presence of DHAA-Fe3O4 is
shown in Scheme 3. According to this mechanism, DHAA-Fe3O4
nanoparticles catalyze the in situ formation of the imine

4
Tetrahedron
1713; (g) Olah, G.A.; Mathew, T.; Panja, C.; Smith, K.; Prakash,
G.K.S. Catal. Lett. 2007, 114, 1.
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We are thankful to Tarbiat Modares University for partial
support of this work
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and the progress of the reaction was monitored by TLC. After stirring
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surface of the stir bar and was separated from the solution. The
product was obtained by evaporation of the volatiles under reduced
pressure and the residue purified by column chromatography, if
necessary. All the products are known. The identity of the products
was confirmed by comparison of their spectroscopic data with
literature data.
General procedure for the synthesis of α-aminophosphonates:
To a 10 mL round-bottomed flask were added sequentially the
aldehyde (1.0 mmol), amine (1 mmol), dimethyl phosphite (1.0
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