Copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate)-catalyzed coupling of sodium azide with aryl iodides/boronic acids to aryl azides or aryl amines

Article abstract of DOI:10.1080/00397911.2013.808349

This work reports an efficient protocol for the coupling reaction of aryl iodides/boronic acids with sodium azide to aryl azides/amines in the presence of copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate) Cu(TMHD)₂ catalyst. The Cu(TMHD)₂ catalyst is a structurally well-defined, O-containing, air- and moisture-stable, transition-metal complex and works at mild reaction conditions. It was observed that aryl azides can be reduced further to corresponding aniline derivatives using the same catalyst under basic reaction conditions for a prolonged period. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for the following free supplemental resource(s): Full experimental and spectral details.]

Full text of DOI:10.1080/00397911.2013.808349

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Copper bis(2,2,6,6-Tetramethyl-3,5-
heptanedionate)–Catalyzed Coupling of
Sodium Azide with Aryl Iodides/Boronic
Acids to Aryl Azides or Aryl Amines
Satish R. Lanke a & Bhalchandra M. Bhanage a
a Department of Chemistry , Institute of Chemical Technology ,
Matunga , Mumbai , India
Published online: 20 Nov 2013.
To cite this article: Satish R. Lanke & Bhalchandra M. Bhanage (2014) Copper bis(2,2,6,6-
Tetramethyl-3,5-heptanedionate)–Catalyzed Coupling of Sodium Azide with Aryl Iodides/Boronic
Acids to Aryl Azides or Aryl Amines, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 44:3, 399-407, DOI: 10.1080/00397911.2013.808349
To link to this article: http://dx.doi.org/10.1080/00397911.2013.808349
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Synthetic Communications1, 44: 399–407, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.808349
COPPER BIS(2,2,6,6-TETRAMETHYL-3,5-
HEPTANEDIONATE)–CATALYZED COUPLING OF
SODIUM AZIDE WITH ARYL IODIDES/BORONIC ACIDS
TO ARYL AZIDES OR ARYL AMINES
Satish R. Lanke and Bhalchandra M. Bhanage
Department of Chemistry, Institute of Chemical Technology, Matunga,
Mumbai, India
GRAPHICAL ABSTRACT
Abstract This work reports an efficient protocol for the coupling reaction of aryl iodides/
boronic acids with sodium azide to aryl azides/amines in the presence of copper bis(2,2,
6,6-tetramethyl-3,5-heptanedionate) Cu(TMHD)2 catalyst. The Cu(TMHD)2 catalyst
is a structurally well-defined, O-containing, air- and moisture-stable, transition-metal com-
plex and works at mild reaction conditions. It was observed that aryl azides can be reduced
further to corresponding aniline derivatives using the same catalyst under basic reaction
conditions for a prolonged period.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for the following free supplemental resource(s):
Full experimental and spectral details.]
Keywords Amines; aryl iodides; azidation; boronic acid; copper
INTRODUCTION
Aryl azides and amines are wildly used in chemicals, synthetic intermediates,
natural products, pharmaceuticals, and materials.[1] Aryl azides have found extensive
Received March 28, 2013.
Address correspondence to Bhalchandra M. Bhanage, Department of Chemistry, Institute of
Chemical Technology, Matunga, Mumbai 400019, India. E-mail: bhalchandra_bhanage@yahoo.com;
bm.bhanage@gmail.com
399

400
S. R. LANKE AND B. M. BHANAGE
Scheme 1. Coupling of aryl iodides = boronic acids with sodium azide.
applications in a variety of heterocyclic scaffolds as a photo-affinity labeling agent of
proteins and metal complex syntheses.[2–4] Conventional synthesis of aryl azide is
based on the replacement of the diazonium salt or activated aryl halide with sodium
azide. It has several limitations, such as handling of diazonium salts, particularly
requirement of low temperature, its stability, poor yield, and safety-related con-
cerns.[2,5] Zhu and Ma reported the synthesis of aryl azides from aryl halides using
CuI and proline under basic conditions.[6] Recently, Goriya and Ramana reported
the amine and aryl azide synthesis with additive and Cu(II)=ascorbate-based redox
system.[7] Transition metal–catalyzed coupling of aromatic halides = boronic acids
with sodium azide for synthesis of aryl azides is also reported by using copper-based
catalysts.[8] These methods have one or more drawbacks such as the use of expensive,
toxic catalysts and requirement of specialized ligands, use of strong base, specific
organic solvent, harsh reaction conditions, limited substrate compatibility, and poor
yield of products. Hence, there is scope for the development of a milder protocol for
the synthesis of either aryl azides or direct amines from aryl iodides = boronic acids.
In continuation of our interest in Cu(TMHD)2-catalyzed reactions,[9] herein we
report an efficient multipurpose synthesis of aryl azides and aryl amines from aryl
iodides=boronic acids under base-free and mild reaction conditions respectively
(see Scheme 1). The use of basic reaction conditions gives a one-pot synthesis of ani-
line derivatives for a prolonged reaction time, wherein dimethylformamide (DMF)
acts as a reducing source.[10]
RESULTS AND DISCUSSION
Initially, we have studied the coupling reaction of iodobenzene with sodium
azide in DMF as a model reaction to explore the suitable reaction conditions.
Initially, the catalyst screening studies were performed and different reaction para-
meters such as catalyst loading, solvent effect, the molar ratio of substrate, reaction
time, and temperature were optimized for this transformation. The results obtained
are summarized in Table 1. Based on earlier reaction reports, TMEDA (N,N,N0,
N0-tetramethylethylenediamine) was selected as a ligand in combination with various
metal precursors.[11] Various copper precursors such as CuX (X Br, Cl, I),
=
Cu(OAc)2, and Cu2O provide moderate yields of the desired product (Table 1,

ARYL AZIDES OR AMINES
401
Table 1. Optimization of reaction parameters for azidation of aryl iodides using sodium azidea
Entry
Catalyst
Ligand
Solvent
Yield (%)b
1
2
CuCl
Cu(OAc)2
TMEDA
TMEDA
DMF
DMF
DMF
87
20
3
Cu2O
CuBr
TMEDA
TMEDA
88
75
4
DMF
DMF
5
CuI
Pd(OAc)2
TMEDA
TMEDA
86
6
DMF
DMF
Nr
91
7
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
Cu(TMHD)2
TMEDA
—
—
8
DMF
DMF
THF
93
9
90c
NR
NR
NR
NR
NR
93d
88e
92f
85g
88h
93i
10
11
12
13
14
15
16
17
18
19
20
—
—
MeCN
1, 4-Dioxane
Toluene
DMSO
DMF
—
—
—
—
—
—
DMF
DMF
—
—
DMF
DMF
DMF
—
aReaction conditions: iodobenzene (1 mmol), sodium azide (1.2 mmol), catalyst (0.25 mmol), ligand
(0.50 mmol), solvent (4 ml), temperature (120 ꢀC), reaction time (12 h); NR, no reaction.
bGC yields.
cKOH (3 mmol) product is aniline instead of azide.
dCatalyst (0.20 mmol).
eCatalyst (0.15 mmol).
fTemperature (100 ꢀC).
gTemperature (90 ꢀC).
hReaction time (5 h).
iReaction time (6 h).
entries 1–5). When Cu(TMHD)2 was screened for the model reaction, 93% yield of
the desired product was observed; hence it was used for further studies. We also per-
formed the reaction with palladium acetate but it cannot catalyze the reaction, which
indicates that copper is the only metal that works for the reaction (Table 1, entry 6).
It was noted that when the reaction was carried out in the absence of any catalyst
there is no formation of the product, emphasizing the need for the copper catalyst.
The reaction without addition of any additional ligand shows that Cu(TMHD)2 is
the best catalyst for this reaction and gives very good yield up to 93%. This is because
TMHD itself can act as a ligand (Table 1, entry 8) and it forms a stable chelating
complex. To check whether a base is required for the reaction, we have performed
it using KOH as base and this case we got 90% yield of aniline in 24 h (Table 1,

402
S. R. LANKE AND B. M. BHANAGE
entry 9) instead of azide as a product. In such cases DMF acts as a reducing source in
basic reaction conditions and aniline is a product.[11] From solvent screening studies
it was revealed that DMF is an ideal solvent for this reaction. The reaction was car-
ried out with other protic polar and nonpolar solvents but they did not work. This
may be due to the limited solubility of sodium azide in such solvents, and it also
decomposes under reflux conditions (Table 1, entries 10–14). To obtain the optimum
catalyst, we have performed reactions at 0.25–0.15 equivalents of catalyst loading
and it was observed that reaction works very well at 0.20 equivalent of catalyst
loading, which gives 93% yield of azide product. Further increase in catalyst con-
centration had no significant effect on the yield of the desired product. Also, the
decrease in catalyst concentration decreases the yield of desired product (Table 1,
entries 15 and 16). We have carried out reactions at various temperatures and we
found that 100–110 ꢀC temperature range is sufficient for catalyzing the reaction
(Table 1, entry 17).
Further increases in temperature did not amplify the yield of desired product
and decreases in reaction temperature reduce the yield of product (Table 1, entry
18). Although initially we have performed all reactions for 12 h time study confirms
that 6 h are sufficient to complete the reaction (Table 1, entries 19 and 20). On the
basis of these studies, the optimized reaction conditions for azidation of aryl iodides
using sodium azide are aryl iodides (1 equivalent), sodium azide (1.2 equivalent),
catalyst Cu(TMHD)2 (0.20 equivalent), and solvent DMF (4 ml) at 100–110 ꢀC
for 6 h.
To explore the scope of the Cu(TMHD)2-catalysed azidation reaction to wider
substrate compatibility, various aryl iodides with different substituents were tested
under optimized reaction conditions, and the results are summarized in Table 2. Elec-
tronic variations in the aryl iodides were tested including electron-rich, electron-
deficient, and neutral for the azidation reaction and give good to moderate yields
of the desired products (Table 2, entries 1–11). Iodobenzene reacts efficiently with
sodium azide within 6 h, providing 93% yield of phenyl azide (Table 2, entry 1). Sub-
stituted iodobenzene such as p-iodotoluene, p-iodoanisole, p-iodoaniline, p-iodophe-
nol, p-iodonitrobenzene, and 1-(4-iodophenyl)ethanone react with sodium azide to
provide good to excellent yields of the corresponding products (Table 2, entries
2–7). Electronically deficient aryl iodides need more time for completion of the
reaction, and yields are comparatively lower. In the case of sterically hindered
substrates as well as iodobenzene substituted at the second position, the reaction rate
is slower and these substrates need more time to complete (Table 2, entries 8–10).
1-Iodonaphthalene reacts efficiently with sodium azide within 7 h, providing 84%
yield of respective azide (Table 2, entry 11). Further, we tested the present protocol
for the heterocyclic substrates such as 5-iodo-1H-indole having substitution at
heterocyclic C5 position and 3-iodopyridine has substitution at C3 position gave
a comparatively better yield of the desired product (Table 2, entries 12 and 13).
Furthermore, we also checked the applicability of the methodology for the
amination of iodoaryls in the presence of KOH. In the presence of basic conditions
and longer reaction time, electronically deficient acids directly reduce to the corre-
sponding aniline derivatives. In such cases DMF acts as a reduction source.[10] In this
context we have tested iodobenzene, p-nitroiodobenzene, and 1-(4-iodophenyl)etha-
none in the presence of KOH within the same catalytic system and got appreciable

ARYL AZIDES OR AMINES
403
Table 2. Scope of azidation of various aryl halide with sodium azide catalyzed by Cu(TMHD)2 coupling
reactiona
Entry
1
Substrate
Product
Time (h)
6
Yield (%)b
=
H
=
H
R
R
86
2
3
R¼4-CH3
R¼4-OCH3
R¼4-NH2
R¼4-OH
R¼4-CH3
R¼4-OCH3
R¼4-NH2
R¼4-OH
6
6
90
92
80
89
82
62
62
68
82
4
7
5
8
6
R¼4-NO2
R¼4-COCH3
R¼2- OCH3
R¼2-NH2
R¼2-CH3
R¼4-NO2
R¼4-COCH3
R¼2- OCH3
R¼2-NH2
R¼2-CH3
12
12
12
12
12
7
8
9
10
11
12
7
84
6
72
13
12
20
45
70
14c
H
R
H
=
R
=
15c
16c
R¼4-NO2
R¼4-NO2
24
24
65
60
R¼4-COCH3
R¼4-COCH3
aReaction conditions: aryl iodide (1 mmol), sodium azide (1.2 mmol), catalyst (0.20 mmol), solvent
(4 ml), temperature (100 ꢀC), reaction time (6–12 h).
bGC yields.
cKOH (3 mmol).
yields of aniline derivatives (Table 2, entries 14–16). Hence, current methodology is
also applicable to direct amination of aryl iodides under basic reaction conditions.
Synthesized aryl azides and amines were also analyzed by gas chromatography
(GC), infrared (IR), NMR, and mass spectroscopy.
Considering the excellent results obtained from azidation of aryl iodides, we
used the same copper catalyst system [Cu(TMHD)2] for azidation of aryl boronic
acids (Table 3, entries 1–12). It was observed that the same copper catalyst system
worked very well and tested substrates provide good to excellent yields. Arylboronic
acid, having donating groups, shows better activity than ones containing electron-
withdrawing groups.

404
S. R. LANKE AND B. M. BHANAGE
Table 3. Scope of azidation of various aryl boronic acid with sodium azide catalyzed by Cu(TMHD)2
coupling reactiona
Entry
Substrate
Product
Time (h)
Yield (%)b
1
2
R ¼ H
R ¼ H
6
4
91
92
R ¼ 4-OCH3
R ¼ 4-OCH3
3
R ¼ 4-CH3
R ¼ 4-Cl
R ¼ 4-CH3
R ¼ 4-Cl
7
6
89
75
70
88
80
86
91
90
85
82
75
60
4
5
R ¼ 4-Br
R ¼ 4-Br
6
6
R ¼ 4-OH
R ¼ 3-CH3
R ¼ 3-OCH3
R ¼ 2-OCH3
R ¼ 2-CH3
R ¼ 2-NH2
R ¼ 4-NO2
R ¼ 4-OCH3
R ¼ 4-NO2
R ¼ 4-OH
R ¼ 3-CH3
R ¼ 3-OCH3
R ¼ 2-OCH3
R ¼ 2-CH3
R ¼ 2-NH2
R ¼ 4-NO2
R ¼ 4-OCH3
R ¼ 4-NO2
6
7
6
8
6
9
4
10
11
12
13c
14c
6
6
6
20
24
aReaction conditions: aryl boronic acid (1 mmol), sodium azide (1.2 mmol), catalyst (0.20 mmol), sol-
vent (4 ml), temperature (100 ꢀC), reaction time (6–12 h).
bGC yields.
cKOH (3 mmol).
Furthermore, we also checked the applicability of the methodology for the
amination of boronic acid in the presence of KOH (Table 3, entries 13 and 14).
Synthesized aryl azides and amines were analyzed by GC, IR, NMR, and mass
spectroscopy.
CONCLUSION
In summary, we have developed a simple and wider protocol for the copper-
catalyzed coupling reaction of aryl iodides or arylboronic acid with sodium azide
to aryl azides and aromatic amines in good to excellent yields in short time. The pro-
tocol uses inexpensive, simple copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate)
as the catalyst with structurally well-defined O-containing transition metal complex
as the catalyst system and this works under base-free as well as milder reaction
conditions. The notable advantage of the methodology is excellent tolerance with
a variety of functional groups in good to excellent yield and base-free reaction

ARYL AZIDES OR AMINES
405
conditions. The important observation noted was in basic reaction conditions the
generated aryl azides directly reduces to corresponding aniline derivatives under
the same catalytic system in longer reaction time. In such cases N,N-dimethyl forma-
mide acts as reducing source in basic reaction conditions. The control experiments
show that the crucial roles of Cu(TMHD)2 and N,N-dimethyl formamide in the
methodology.
EXPERIMENTAL
Typical Procedure for the Preparation of Cu(TMHD)2
In a 100-ml, round-bottom flask with spin bar, NaOH (22 mmol) was
dissolved in MeOH (20 ml) with stirring, and the resulting solution was cooled to
rt, followed by addition of TMHD (20 mmol). A solution obtained by dissolving
Cu(NO3)2.6H2O (10 mmol) in MeOH (20 ml) was added to the mixture over a period
of 30 min. The reaction mixture was stirred for 6 h, and resulting precipitate was
filtered, dried, and characterized with differential scanning calorimetry–thermal
gravimetric analysis (DSC-TGA) and NMR analysis. Yield 93%, mp 196–198 ꢀC.
General Procedure for Azidation of Aryl Iodides / Aryl Boronic Acids
In a 10-mL sealed tube with a spin bar, halobenzene (1 mmol) was used, or in
25-ml round-bottom flask with a spin bar equipped with condenser, boronic acid
(1 mmol), was used and DMF (4 ml), sodium azide (1.2 mmol), and Cu(TMHD)2
(0.20 mmol) were added and containers were sealed properly. The reaction mixture
was heated at the 100 ꢀC with stirring for desired time and cooled to room tempera-
ture on completion of the reaction. Then the mixture poured into 15 ml of ice-cold
water and extracted with diethyl ether (3 ꢁ 10 ml). The residue obtained was purified
by column chromatography (silica gel, 60:20 mesh; petroleum ether = ethyl acetate
98:2%) to afford the desired azide products. The organic solution was analyzedby
GC and confirmed by GCMS and NMR. The purity of compounds was determined
by GC-MS analysis. All products are known in the literature.
Representative Spectral Data[6–8]
1
Table 2, entry 1: Azidobenzene. Yellow oil; H NMR (CDCl3, 400 MHz):
d ¼ 7.36 (t, 2H, J ¼ 7.6 Hz), 7.15 (t, 1H, J ¼ 7.6 Hz), 7.05 ppm (d, 2H, J ¼ 7.6 Hz);
13C NMR (CDCl3, 100 MHz): d ¼ 140.13, 128.91, 125.05, 119.17 ppm; MS (EI, 70
ev): m=z (%) ¼ 119.1 (29), 118 (4), 92.1 (10), 91.05 (100), 65.1 (21), 64 (83), 63.05
(43), 62.05 (8), 52.05 (10), 51 (15), 50 (11), 44 (61), 41.05 (16), 39.05 (29), 38.05
(30), 37 (15), 32 (31).
Table 2, entry 3: 1-Azido-4-methoxybenzene. Black oil; 1H NMR
(CDCl3, 400 MHz): d ¼ 6.95 (d, 2H, J ¼ 9.1 Hz), 6.88 (d, 2H, J ¼ 9.1 Hz), 3.77 ppm
(s, 3H); 13C NMR (CDCl3, 100 MHz): d ¼ 157.12, 132.46, 120.12, 115.25,
55.68 ppm; MS (EI, 70 ev): m=z (%) ¼ 149.1 (24), 122.1 (8), 121.1 (100), 106.05
(40), 91.1 (20), 80 (62), 78.05 (71), 64.05 (41), 63.1 (21), 52.05 (62), 51.05 (47).

406
S. R. LANKE AND B. M. BHANAGE
Table 3, entry 3: 1-Azido-4-methylbenzene. Brown oil; 1H NMR (CDCl3,
400 MHz): d ¼ 7.15 (d, 2H, J ¼ 8.1 Hz), 6.93 (d, 2H, J ¼ 8.1 Hz), 2.35 ppm (s, 3H);
13C NMR (CDCl3, 100 MHz): d ¼ 137.26, 134.72, 130.47, 118.97, 20.96 ppm; MS
(EI, 70 ev): m=z (%) ¼ 133.1 (34), 105.1 (100), 104 (65), 78 (68), 77 (46), 65.05 (32),
52.05 (44), 51.05 (37), 50 (23), 44.05 (59), 39 (43), 32.05 (36).
1
Table 3, entry 4: 1-Azido-4-chlorobenzene. Yellow oil; H NMR (CDCl3,
400 MHz): d ¼ 7.29 (d, 2H, J ¼ 8.8 Hz), 6.93 ppm (d, 2H, J ¼ 8.8 Hz); 13C NMR
(CDCl3, 100 MHz): d ¼ 138.77, 130.33, 129.97, 120.40 ppm; MS (EI, 70 ev): m=z
(%) ¼ 153 (24), 127 (32), 125.05 (100), 98.1 (9), 90.05 (95), 89.1 (22), 64 (29), 63.05
(29), 63.05 (83), 62.05 (34), 44.05 (39), 39.1 (27.1), 38 (24).
Table 3, entry 8: 1-Azido-3-methoxybenzene. Black oil; 1H NMR
(CDCl3, 400 MHz): d ¼ 7.23 (t, 2H, J ¼ 8.4 Hz), 6.67 (d, 1H, J ¼ 8.4 Hz), 6.63 (d,
1H, J ¼ 8.4 Hz), 6.53 (s, 1H), 3.77 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d ¼ 160.91, 141.36, 130.54, 111.37, 110.76, 105.03, 55.43.
Table 2, entry, 8 or Table 3, entry 9: 1-Azido-2-methoxybenzene. 1H
NMR (CDCl3, 400 MHz): d ¼ 7.1 (t, 1H, J ¼ 7.4 Hz), 7.02 (d, 1H, J ¼ 7.8 Hz),
6.88–6.96 (m, 2H), 3.87 (s, 3H); 13C NMR (CDCl3, 100 MHz): d ¼ 151.97, 128.43,
125.82, 121.45, 120.41, 112.19, 56.05.
Tables 2 and 3, entry 10: 1-Azido-2-methylbenzene. 1H NMR (CDCl3,
400 MHz): d ¼ 7.22 (t, 1H, J ¼ 7.3 Hz), 7.16 (d, 1H, J ¼ 7.3 Hz), 7.11 (d, 1H,
J ¼ 7.3 Hz), 7.03 (t, 1H, J ¼ 7.4 Hz), 2.2 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d ¼ 138.52, 131.29, 129.73, 127.23, 124.73, 118.05, 17.41.
Table 2, entry 14: Aniline. 1H NMR (CDCl3, 400 MHz): d ¼ 7.21 (t, 2H,
J ¼ 7.6 Hz), 6.82 (t, 1H, J ¼ 7.6 Hz), 6.71 (d, 2H, J ¼ 7.6 Hz), 3.62 (s, 2H); 13C
NMR (CDCl3, 100 MHz): d ¼ 146.47, 129.3, 118.5, 115.1.
Table 2, entry 15, or Table 3, entry 14: 4-Nitroaniline. 1H NMR (CDCl3,
400 MHz): d ¼ 8.05 (d, 2H, J ¼ 8.3 Hz), 6.61(d, 2H, J ¼ 8.3 Hz); 13C NMR (CDCl3,
100 MHz): d ¼ 152.74, 135.64, 126.54, 113.53.
Table 3, entry 13: 4-Methoxyaniline. 1H NMR (CDCl3, 400 MHz): d ¼ 6.73
(d, 2H, J ¼ 8.9 Hz), 6.65 (d, 2H, J ¼ 8.9 Hz), 6.65 (d, 2H, J ¼ 8.9 Hz), 3.73 (s, 3H),
3.42 (s, 2H); 13C NMR (CDCl3, 100 MHz): d ¼ 152.9, 140.07, 116.55, 114.91, 55.86.
Cu(TMHD)2. 1H NMR (CDCl3, 400 MHz): 1.13 (s, 18H), 5.66 ppm (s, 2H).
ACKNOWLEDGMENT
S. R. L. is thankful to the Department of Atomic Energy (ICT-DAE Centre),
Mumbai, India, for a senior research fellowship.
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