High yielding electrophilic amination method for arylcopper reagents

Article abstract of DOI:10.1080/00397911.2017.1295082

The facilitative effect of some P-, N-, S-, and O-donor ligands in the reaction of arylcoppers with acetone O-(mesitylenesulfonyl)oxime was examined to develop a synthesis method for functionalized primary aryl amines under mild reaction conditions. Our research showed that electrophilic amination of monoaryl coppers with ketoximes can be facilitated using appropriate ligand to supply significant increase in the yield. Also, we have seen that this ligand-facilitated method is applicable in terms of arylcopper and ketoxime type and allows synthesis of primary aryl amines in good to high yields easily at room temperature in very short reaction time.

Full text of DOI:10.1080/00397911.2017.1295082

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
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High yielding electrophilic amination method for
arylcopper reagents
Tahir Daşkapan & Semra Çiçek
To cite this article: Tahir Daşkapan & Semra Çiçek (2017): High yielding electrophilic
amination method for arylcopper reagents, Synthetic Communications, DOI:
10.1080/00397911.2017.1295082
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Date: 05 April 2017, At: 01:12

SYNTHETIC COMMUNICATIONS®
http://dx.doi.org/10.1080/00397911.2017.1295082
High yielding electrophilic amination method for
arylcopper reagents
Tahir Daşkapan and Semra Çiçek
Department of Chemistry, Faculty of Science, Ankara University, Ankara, Turkey
ABSTRACT
ARTICLE HISTORY
Received 22 August 2016
The facilitative effect of some P-, N-, S-, and O-donor ligands in the
reaction of arylcoppers with acetone O-(mesitylenesulfonyl)oxime was
examined to develop a synthesis method for functionalized primary
aryl amines under mild reaction conditions. Our researches showed
that electrophilic amination of monoaryl coppers with ketoximes can
be facilitated using appropriate ligand to supply significant increase in
the yield. Also, we have seen that this ligand-facilitated method is
applicable in terms of arylcopper and ketoxime type and allows
synthesis of primary aryl amines in good to high yields easily at room
temperature in very short reaction time.
KEYWORDS
Amination; aryl amines;
ligand; organocopper; oxime
GRAPHICAL ABSTRACT
Introduction
Arylamino group is an important building block in the synthesis of important and useful
chemicals. For this reason, many studies have been made on the development of an
efficient method for the preparation of aryl amines. Nucleophilic amination methods
require harsh reaction conditions that limit their applicability.
Various procedures were given for the preparation of primary anilines by copper-
catalyzed N-arylation of aryl halides with aqueous ammonia.[1–6] Although these methods
allow obtaining primary aryl amines in high yields, they need high reaction temperature
and/or too long reaction time for the success. In addition, some of them require special
catalysts or ligands.
Helquist et al.[7] developed a copper-assisted method for the synthesis of primary
anilines using NaN3 as aminating reagent. Reactions were performed at 100 °C in the
presence of 1 equiv. of CuI or Cu2O, 1.3 equiv. of ligand and 2 equiv. of NaN3. Generally
the reactions were completed in too long reaction times.
CONTACT Tahir Daşkapan
daskapan@science.ankara.edu.tr
Department of Chemistry, Faculty of Science,
Ankara University, Beşevler, Ankara 06100, Turkey.
Supplemental data for this article can be accessed on the publisher’s website.
© 2017 Taylor & Francis

2
T. DAŞKAPAN AND S. ÇIÇEK
Knochel’s group described a procedure for the preparation of primary aryl amines in
high yields by oxidative coupling of aryl amidocuprates at À 78–(À 50)°C in 13 h.[8]
Accordingly, developing a method allowing the synthesis of aryl amines under
milder reaction conditions would be useful. Electrophilic amination is a powerful method
for the synthesis of amines. Various aryl, alkyl, cycloalkyl, and heteroaryl amines have been
easily prepared using suitable aminating agent and organometallic reagent.[9,10]
Organocopper compounds are the most widely used transition metal organometallic
reagents in the field of organic synthesis. They are used not only in the academic
laboratories but also in the industry. This popularity is due to their ability to give reactions
in high chemo, regio, and stereoselectivity and to tolerate broad range of functional
groups.[11–13]
In general, sp3-hybridized nitrogen-based aminating agents were used for the amination
of organocopper reagents.[9,10,14] There have been few reports on the electrophilic
amination of mono-organocoppers. Genét et al.[15–18] have been developed some N-aryl
sulfonyloxycarbamate derivatives as aminating reagents for the synthesis of sensitive
primary amines without any decomposition, and they showed their activity in the
electrophilic amination of aryl and heteroarylcoppers. Bhadra et al.[19] have been showed
iron nanoparticle-catalyzed electrophilic amination of functionalized organocopper for
the synthesis of functionalized tertiary aryl amines.
As far as we know, there have been only two studies about amination of mono-
organocoppers with ketoximes. One of them showed the use of phenylcopper to furnish
aniline in low yield.[20] The other study[21,22] described the preparation of alkylamines
by electrophilic amination of corresponding alkylcoppers with 4,4′-bis(trifluoromethyl)
benzophenone O-methylsulfonyloxime at low temperatures and in the presence of a
coordinating solvent in low to high yields. But synthesis of aryl amines could not be
achieved by this method.
So, the development of a new method for the electrophilic amination of arylcoppers
would be a complementary study in terms of the literature. Previously we described some
electrophilic amination methods for organozinc,[23–25] organomagnesium,[26] and
organocadmium[27] reagents. In this paper, an alternative method for the preparation of
aryl amines including electrophilic amination of functionalized arylcoppers under mild
reaction conditions is described.
Results and discussion
At the first stage of this work we focused on the development of an easily applicable
synthesis method for functionalized primary aryl amines using corresponding arylcopper
reagents. We used acetone O-(2,4,6-trimethylphenylsulfonyl)oxime (1), that we are familiar
with from our previous studies,[23–27] as aminating agent. It can be prepared easily and
stored for a long time without any decomposition. We used the corresponding
functionalized arylmagnesiums prepared in tetrahydrofuran (THF) for the preparation
of arylcoppers, because magnesium was thought to increase the electrophilic character of
the aminating reagent by coordinating with its nitrogen atom.
Aryl amines as the final products were removed from the reaction mixture as their
benzamide derivatives and identified from their melting points,[28–30] Fourier transform
1
infrared (FT-IR) and H NMR analysis.[30–34]

SYNTHETIC COMMUNICATIONS®
3
Scheme 1. Ligand-facilitated electrophilic amination of arylcoppers with ketoximes.
d-Orbitals of arylcopper compounds are low lying and their energies are not sufficient to
give nucleophilic substitution in high yield.[35] In our work, ArCu reacts with ketoxime by
nucleophilic displacement between ArÀ and –OSO2Mes or –OTs (Scheme 1). As is seen in
Table 1, phenylcopper reacted with 1 at room temperature under ligand-free conductions
to give aniline in low yield (Entries 1, 2).
Previously we have observed that copper-catalyzed electrophilic amination of organo-
zinc reagents[25–27] occurred under milder reaction conditions and resulted in higher
yields, by the use of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU). DMPU
is a dipolar aprotic solvent and coordinates to metal ions to increase the nucleophilicity of
Table 1. Optimization of reaction conditions.
Entry
Ligand (%)
Time (min)
PhNH2 (%)
1
2
—
5
30
30
30
5
50
41
30c
70
85
70
82
72
84
70
58
71
71
63
63
65
65
66
51
72
44
—
3
—
4
PPh3, 25
PPh3, 25
PPh3, 15
P(n-Bu)3, 20
P(n-Bu)3, 20
P(n-Bu)3, 10
P(n-Bu)3, 5
P(OEt)3, 25
P(OEt)3, 25
P(OEt)3, 15
P(OEt)3, 10
Ph3PO, 5
Ph3PO, 5
NPh3, 20
NPh3, 5
5
6
5
7
15
5
8
9
15
15
30
15
15
15
15
5
15
15
15
15
5
10
11
12
13
14
15
16
17
18
19
20
21
Me2S, 20
Me2S, 10
Me2S, 10
DMPU, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.
aPhCu/1 ¼ 2.
bYield of amine was isolated as its benzamide derivative.
cDMPU/PhCu ¼ 0.2.

4
T. DAŞKAPAN AND S. ÇIÇEK
their counter ions. For this reason, we added catalytic amount of DMPU to the reaction
mixture. But it led to negative effect on the amination reaction of phenylcopper with 1,
and as seen in Table 1 it caused a further drop in the yield of aniline (Entry 3). After these
results, we decided to add a ligand in a catalytic amount to the reaction mixture. Because in
this way, coordination of the added ligand to Cu-I will make its d-orbitals sufficiently high
for a successful amination reaction.
As is seen in Table 1, addition of PPh3 to reaction mixture supplied a dramatic
increase in the yield of aniline (Entries 4–6). These results have paved the way for a
new synthesis method for functional group containing aryl amines. For this purpose,
we planned to investigate the facilitative effects of various P-, N-, S-, and O-donor
ligands on electrophilic amination of arylcoppers. Our works started with determi-
nation of optimal reaction conditions using reaction of PhCu with 1 as model reaction
(Table 1).
We used three types of P-donor ligands; PPh3, P(n-Bu)3, and P(OEt)3. PPh3 gave the
best result in 5 min when it was used in 25% mol amount (Table 1, entry 5). 10 mol%
of P(n-Bu)3 was enough for high yield of aniline, but the reaction completed in 15 min
(Entry 9). P(OEt)3 showed the lowest facilitative reactivity.
As is seen in Scheme 1, the added donor ligand coordinetes with Cu-I atom and
increases electron density on it. By this interaction, ArCu becomes more susceptible to
react with electrophilic nitrogen atom of ketoxime. Oxidative addition of ArCu to ketoxime
gives a Cu-III complex. Then this complex decomposes to give aryl imine intermediate,
which forms target product following acidic hydrolysis.
P(n-Bu)3 is a soft ligand and strong donor. Therefore, its coordination with Cu-I atom
to facilitate amination reaction is more preferred than that of other two P-donor ligands.
Second, it is a bulky ligand, with three n-Bu- groups in α -position relative to copper atom
and this facilitates decomposition of Cu-III complex to form aryl amine. Hence, as is seen
in Table 1, it increased the yield of aniline from 50 to 82% (Entries 1 and 7). PPh3 is
less donor than P(n-Bu)3 because of -I effect of phenyl groups. So, it is less effective in
facilitation of interaction of ArCu with ketoxime. But it is a bulkier ligand and therefore
it can show more facilitative effect on the formation of aryl amine from Cu-III complex.
As a result, PPh3 allows yield of amine to be as high as P(n-Bu)3 provides. Three etoxy
groups make P(OEt)3 the weakest P-donor ligand. In addition it is not a bulky ligand.
These characteristics make it the least effective P-donor ligand in the electrophilic reaction
of arylcopper reagents with ketoximes.
Coordination of Ph3PO to the copper atom occurs through its oxygen atom. However,
this coordination is not as preferable as coordination with PPh3 or P(n-Bu)3 for Cu-I, a soft
Lewis acid. In addition, Ph3PO, as a hard ligand, increases stability of Cu-III complex
but does not create steric hindrance around Cu-III, since three phenyl groups are not in
α-position relative copper atom (Ph–P–O–Cu). This is not facilitative for decomposition
of Cu-III complex to N-aryl imine. For these reasons, Ph3PO did not show significant
activity in the amination reaction (Table 1, entries 15, 16).
NPh3 is a hard base and the results showed that it is not so effective in the improvement
of aryl amine yield (Table 1, entries 17, 18). Being bulky ligand, it did not provide a
significant benefit in this regard. As in the case of Ph3PO, also in the electrophilic
amination reaction involving NPh3, oxidative addition of arylcopper to ketoxime following
coordination to Cu-I atom appears to be dominant.

SYNTHETIC COMMUNICATIONS®
5
Due to its soft Lewis-base and hard donor feature, Me2S was expected to facilitate the
electrophilic amination of arylcoppers and to greatly increase amine yield. But as is seen
in Table 1, it is not effective as much as P(n-Bu)3 or PPh3. We attributed this to the fact
that Me2S is a small ligand. Thus, it can approach to copper atom more closely and form
a stable complex. Formation of such a complex is easier but its decomposition to give
desired product is more difficult. Consequently, it showed a moderate activity in the
amination of arylcoppers.
Our investigations on finding optimal reaction conditions showed that the molar ratio
of arylcopper to ketoxime must be 2:1. The use of less than 2 mmol of arylcopper led to the
decrease in the yield of amine.
In the second part of this study, the ligand-facilitated electrophilic amination method
that we developed in the first stage was examined whether it is applicable for the synthesis
of functional group bearing aryl amines. For this reason, aminations of various functiona-
lized arylcopper reagents with 1 were performed under optimized reaction conditions. As
is seen in Table 2, all reactions were conducted successfully and functionalized aryl amines
were synthesized in good to high yields.
We observed that this electrophilic amination method was unsuccessful in the
amination of alkyl cycloalkyl and benzylcopper reagents with 1.
Acetone oxime O-tosylate (2) reacted with arylcopper reagents successfully to form
corresponding functionalized aryl amines in good to high yields (Table 3). These results
show that our ligand-facilitated electrophilic amination method is applicable from the
point of ketoxime type.
Table 2. Scope and limitations of ligand-facilitated electrophilic amination of ArCu with 1.
Entry
Ar
Ligand (%)
Time (min)
ArNH2 (%)
1
2
4-CH3OC6H4
4-CH3SC6H4
4-ClC6H4
PPh3, 25
PPh3, 25
5
5
73
74
72
73
76
71
87
81
61
64
73
78
74
65
67
69
60
72
66
55
56
61
55
3
PPh3, 25
5
4
3-ClC6H4
PPh3, 25
5
5
4-FC6H4
1-Naphtyl
2,5-(CH3)2C6H3
4-CH3S–C6H4
4-Cl–C6H4
3-Cl–C6H4
4-F–C6H4
2,5-(CH3)2–C6H4
4-CH3S–C6H4
4-CH3O–C6H4
3-Cl–C6H4
2,5-(CH3)2–C6H4
4-CH3O–C6H4
3-Cl–C6H4
2,5-(CH3)2–C6H4
4-CH3S–C6H4
3-Cl–C6H4
(4-CH3S–C6H4)
4-F–C6H4
PPh3, 25
5
6
PPh3, 25
5
7
PPh3, 25
5
8
P(n-Bu)3, 10
P(n-Bu)3, 10
P(n-Bu)3, 10
P(n-Bu)3, 10
P(n-Bu)3, 10
NPh3, 5
15
15
15
15
15
15
15
15
15
15
15
5
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
NPh3, 5
NPh3, 5
P(OEt)3, 15
P(OEt)3, 15
P(OEt)3, 15
Ph3PO, 5
Ph3PO, 5
Me2S, 10
Me2S, 10
Me2S, 10
5
15
15
15
aArCu:1 ¼ 2:1.
bYield of amine was isolated as its benzamide derivative.

6
T. DAŞKAPAN AND S. ÇIÇEK
Table 3. Scope and limitations of ligand-facilitated electrophilic amination of ArCu with 2.
Entry
Ar
Ligand (%)
Time (min)
ArNH2 (%)
1
2
3-Cl–C6H4
2,5-(CH3)2–C6H4
1-Naphtyl
4-CH3O–C6H4
4-Cl–C6H4
4-F–C6H4
2,5-(CH3)2–C6H4
3-Cl–C6H4
2,5-(CH3)2–C6H4
3-Cl–C6H4
2,5-(CH3)2–C6H4
C6H5
PPh3, 25
PPh3, 25
5
5
67
75
74
75
58
68
69
68
70
68
64
66
55
57
3
PPh3, 25
5
4
P(n-Bu)3, 10
P(n-Bu)3, 10
P(n-Bu)3, 10
NPh3, 5
15
15
15
15
15
15
15
5
5
6
7
8
NPh3, 5
9
P(OEt)3, 15
P(OEt)3, 15
Ph3PO, 5
Me2S, 10
Me2S, 10
Me2S, 10
10
11
12
13
14
15
15
15
3-Cl–C6H4
4-F–C6H4
aArCu/2 ¼ 2.
bYield of amine was isolated as its benzamide derivative.
Conclusion
Our studies revealed that it is possible to conduct the electrophilic amination of
monoaryl coppers with ketoximes successfully in the presence of a suitable ligand. By this
method, functionalized aryl amines were synthesized in high yields at room temperature
and in too short reaction times. Since arylcoppers have high functional group tolerance,
we think this method will be useful for direct insertion of a –NH2 group to an organic
molecule.
This method is an easily applicable method; ligands used as facilitator are simple, stable,
and commercial compounds which do not require special preparation methods.
Experimental
General procedures
All reactions involving organocopper reagents were performed in flame-dried glassware
with standard syringe/cannula techniques[36] under an atmosphere of dry, oxygen-free
argon. Melting points were determined on a Gallencamp capillary melting point. IR spectra
were recorded on a PerkinElmer Spectrum 100 FT-IR (or Shimadzu-brand FT-IR)
spectrometer. 1H NMR spectra were recorded in CDCl3 or DMSO-d6 at room temperature
on a Varian-Mercury 400 MHz (FT)-NMR spectrometer. All chemical shifts were given in
ppm downfield from tetramethylsilane.
Tetrahydrofuran was freshly distilled from solution of sodium/benzophenone under dry
argon. DMPU was distilled under reduced pressure prior to use and kept over molecular
sieves (4 Å 4–8 mesh) and under argon atmosphere. Cu-I iodide was purified prior to use
and stored at dry argon atmosphere.[37]
Magnesium turnings for Grignard reactions (Fischer) were used without any purifi-
cation. Aryl bromides (Sigma-Aldrich) were in high purities and used without any further
purification.

SYNTHETIC COMMUNICATIONS®
7
Arylmagnesium bromides were prepared in THF by conventional standard methods and
their concentrations were determined by the method of Watson and Eastham.[38]
Acetone O-(mesitylenesulfonyl)oxime[39] (1) and acetone oxime O-tosylate[40,41] (2)
were prepared as described in the literature and stored for months without any decompo-
sition. Ligands were commercially available in high purity and used without further
purification.
The final product, aryl amine was isolated as its N-benzoyl derivative that was identified
1
by its melting point,[28–30] FT-IR, and H NMR spectrums.[30–34]
Ligand-facilitated amination reaction of arylcopper reagents with ketoxime
A suspension of CuI (0.762 g, 4 mmol) in anhydrous THF (6 mL) was cooled to À 5 °C
under argon atmosphere and phenylmagnesium bromide (4 mmol) in THF was added
dropwise by a syringe. The reaction mixture was stirred for an additional 15 min, the
cooling bath was removed and the resulting suspension was allowed to warm to room
temperature for 10–15 min. To this mixture, ligand (5–25 mol%), and a solution of acetone
O-(mesitylenesulfonyl)oxime, 1 (2 mmol) in dry THF (3 mL) were added. The reaction
mixture was stirred at room temperature for 5–30 min and then worked up by addition
of concentrated HCl and with stirring at room temperature overnight. The aqueous phase
was washed with diethyl ether (2 � 60 mL), made basic with concentrated NaOH, and the
free aniline was extracted with diethyl ether (3 � 60 mL). The solvent was evaporated and
the crude product was converted to its N-benzoyl derivative by reaction with benzoyl
chloride in the presence of NaOH. The product was recrystallized from ethanol:water
(4:1) mixture. Mp: 160–162 °C (lit.[30] 160 °C); FT-IR (υmax/cmÀ 1): 3342, 3051, 1653
1
(amide, –CO), 1597, 1524, 1453, 1319, 1255, 748, 714, 688, 642. H NMR (400 MHz,
CDCl3, ppm): δH 7.96 (s, 1H), 7.88–7.85 (m, 2H), 7.67–7.64 (m, 2H), 7.56–7.52 (m, 1H),
7.48–7.44 (m, 2H), 7.39–7.34 (m, 2H), 7.17–7.13 (m, 1H).
Funding
Financial support from Ankara University Research Found (Grant No. 09B4240005) is greatly
acknowledged by the authors.
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