Amination-Oxidation Strategy for the Copper-Catalyzed Synthesis of Monoarylamines

Article abstract of DOI:10.1021/acs.joc.5b02448

A novel approach for the synthesis of monoarylamines from aryl halides is presented. This method employs an inexpensive, nontoxic metal source (copper) and incorporates a stable ammonia surrogate (α-amino acids), obviating the need for special experimental setup or handling of ammonia reagents. This process, which is proposed to proceed via an amination-oxidation sequence, selectively promotes the transformation of a range of aryl and heteroaryl iodides as well as bromides to the corresponding monoarylamines.

Full text of DOI:10.1021/acs.joc.5b02448

Subscriber access provided by UOW Library
Note
An Amination-Oxidation Strategy for the Copper-
Catalyzed Synthesis of Monoarylamines
Christopher Thomas, Marvin Wu, and Kelvin L. Billingsley
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b02448 • Publication Date (Web): 11 Dec 2015
Downloaded from http://pubs.acs.org on December 14, 2015
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Organic Chemistry is published by the American Chemical Society.
1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
An Amination-Oxidation Strategy
for the Copper-Catalyzed Synthesis of Monoarylamines
7
8
9
Christopher Thomas,+ Marvin Wu+ and Kelvin L. Billingsley*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
San Francisco State University, Department of Chemistry and Biochemistry,
San Francisco, CA 94132
+These authors contributed equally to this work.
*Author to whom correspondence should be addressed
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 20
1
2
3
4
Graphical Abstract
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Abstract
A novel approach for the synthesis of monoarylamines from aryl halides is presented.
This method employs an inexpensive, nonꢀtoxic metal source (copper) and incorporates a
stable ammonia surrogate (α−amino acids), obviating the need for special experimental
setup or handling of ammonia reagents. This process, which is proposed to proceed via an
aminationꢀoxidation sequence, selectively promotes the transformation of a range of aryl
and heteroaryl iodides as well as bromides to the corresponding monoarylamines.
ACS Paragon Plus Environment

Page 3 of 20
The Journal of Organic Chemistry
1
2
Metalꢀcatalyzed processes have become fundamental to the drug discovery industry.1
In particular, advancements in palladiumꢀ2 and copperꢀcatalyzed3 carbonꢀnitrogen bond
formation have substantially impacted the design and identification of drug candidates,
with currently >90% of the topꢀselling pharmaceuticals containing at least one nitrogen
atom in their molecular structure.4 Despite the development of myriad methods for the
coupling of alkyl and aryl amines, transformations involving the simplest amine
nucleophile (ammonia)—yielding the corresponding monoarylamine (aniline) products—
are far less common.5 This scarcity of metalꢀcatalyzed amination processes that employ
ammonia has been attributed to several challenges. For example, high concentrations of
ammonia can displace supporting ligands from the metal, resulting in catalyst
deactivation.6 An additional complication associated with these crossꢀcoupling processes
is the ability of the monoarylamine products to further react with equivalents of the
electrophile to form undesired diꢀ and triarylamines byproducts.7
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Despite these limitations, the importance of anilines to numerous fields (e.g.,
pharmaceutical industry, material science and agrochemicals) has led to continued
interest in the development of efficient methods that can prepare these structural
motifs.4,8 In particular, a variety of palladiumꢀbased catalyst systems (Buchwald,9
Hartwig,10 Stradiotto11 and Beller12) have recently been developed that successfully
provide monoarylamine products (Figure 1, Equation 1). These reports, which rely on
the design and application of phosphineꢀderived supporting ligands for palladium,
established the first methods for the direct coupling of ammonia as well as demonstrated
the coupling of typically less reactive electrophiles such as aryl chlorides. Despite these
advancements, the processes still maintain several disadvantages including the significant
cost and inherent toxicity of palladium.13 These constraints have consequently led to the
investigation of other metals and strategies for the synthesis of monoarylamines.
Copper catalysis has emerged as a promising alternative to palladiumꢀbased methods,
and protocols for the amination of aryl iodides and bromides with ammonia have been
realized (Figure 1, Equation 2).14,15 Although copper cannot broadly transform aryl
chlorides to anilines, these systems have several advantages relative to the palladiumꢀ
based counterparts: (1) catalysts are less prone to deactivation, (2) high selectivity for the
monoarylamine product can be obtained when using a large excess of ammonia, (3)
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 20
1
2
3
4
5
6
7
8
9
copper is less toxic than palladium and (4) less expensive metalꢀligand systems are
required. These improvements collectively establish copperꢀcatalyzed methods as an
effective option for the synthesis of monoarylamines. However, copperꢀbased systems
are also plagued by specific technical challenges, which have unfortunately limited their
application. For example, because ammonia is a gas at room temperature, reactions
employing anhydrous ammonia often require highꢀpressure and/or specialized
equipment.16 Liquid ammonia has also been reported as an alternative.17 However, both
of these sources still require special handling and more complex experimental setups.
Recent copperꢀbased methods have attempted to obviate these issues through employing
aqueous ammonia.18 However, the concentration of the ammonia solutions is variable—
decreasing concentrations of the ammonia over time can complicate industrial
applications—and a large excess of amine is typically required to promote monoarylation
without formation of byproducts.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
To address these limitations, we envisioned the development of a copperꢀcatalyzed
process for the efficient synthesis of monoarylamines from aryl halides that employs a
stable, easily handleable ammonia surrogate. Although ammonia equivalents (i.e.,
silylazides,19 benzophenone imine,20 benzylamines21 and others22) have been employed in
metalꢀcatalyzed processes, they have yet to find wide application because the surrogates
generally require subsequent removal steps—after carbonꢀnitrogen bond formation—to
generate the desired free primary amine. Ideally, to obviate these issues, surrogate
ACS Paragon Plus Environment

Page 5 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
moieties would be cleaved postꢀcrossꢀcoupling in the same pot. To this end, we designed
a copperꢀbased catalyst system that allowed for carbonꢀnitrogen bond formation
(amination) followed by oxidation of the resulting Nꢀaryl amine to a Nꢀaryl imine (Figure
1, Equation 3), which is directly hydrolyzed to furnish the desired monoarylamine.
Importantly, this method for the selective synthesis of monoarylamines employs an
inexpensive, nonꢀtoxic metal source (copper) and incorporates a stable ammonia
surrogate (valine), which obviates the need for special handling or experimental setup.
In order to determine the optimal components and parameters for the aminationꢀ
oxidation sequence, we initially examined a variety of copper sources, bases and solvents
for the conversion of 1ꢀiodonaphthalene to the corresponding monoarylamine product, 1ꢀ
aminonaphthalene (1). It was discovered that the nature of the amine source played a
crucial role in the efficiency of the catalytic process. For example, when employing 0.20
equivalents CuI and 1.5 equivalents Cs2CO3 in dimethylsulfoxide (DMSO), a range of
aliphatic and benzyl amines resulted in low conversion of the aryl halide, and no desired
product was detected by gas chromatography (Figure 2). However, amino acidꢀbased
ammonia surrogates were found to be effective for promoting the transformation as
employing 1.2 equivalents of alanine resulted in a 74% yield of 1 (Figure 2). Valine
proved to be ideal as this amine source provided a 100% conversion of the aryl iodide
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 20
1
2
3
4
5
6
7
8
9
with 90% isolated yield of the desired product (Figure 2). The transformation was
selective for the monoarylamine as no diꢀ or triarylamine byproducts were isolated or
detected by gas chromatography. Lower catalyst loadings (<0.20 equivalents CuI) were
also permitted but decreased the overall effectiveness of the transformation as 0.10 or
0.05 equivalents CuI resulted in 65% and 35% yield, respectively, of 1. We speculate
that the success of these αꢀamino acids in the process was because (1) they can
effectively act as a supporting ligand for the metal to prevent catalyst deactivation23 and
(2) they have a greater propensity for oxidation at the tertiary αꢀcarbon.24 Importantly,
valine is a stable, inexpensive, and nonꢀtoxic nitrogen source for the transformation that
allows the procedure to be conducted without special handling or complex experimental
setup.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The substrate scope of the method was examined with a range of aryl iodides, and the
optimized conditions proved to be compatible with several functional groups (Figure 3).
Specifically, aryl iodides bearing trifluoromethyl groups or ketones (1ꢀiodoꢀbis(3,5ꢀ
trifluoromethyl)benzene and 4ꢀiodobenzophenone) successfully furnished the
corresponding monoarylamines 4 and 5 in 79% and 44% yield, respectively. In addition,
ACS Paragon Plus Environment

Page 7 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
the aminationꢀoxidation sequence was tolerant of anilineꢀbased substrates (i.e., 3ꢀ
iodoaniline) as the corresponding diamine 6 could be successfully isolated, albeit in
lower overall yield. The reaction of 1ꢀchloroꢀ4ꢀiodobenzene was also examined. In
agreement with the reactivity trend for oxidative addition of aryl halides, a 45% yield of 3
was obtained without detectable reaction with the aryl chloride; in the examination of a
variety of substrates, we have yet to observe the successful amination of an aryl chloride
group under our standard conditions.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Although aryl bromides are less reactive—than the corresponding iodides—in
copperꢀcatalyzed crossꢀcoupling processes, these substrates are cheaper and more readily
available;25 therefore, these more challenging electrophiles are of considerable
significance in the preparation of monoarylamineꢀderived biologically active compounds
and materials. Importantly, we found that our optimized catalyst system and conditions
were efficient in the aminationꢀoxidation reaction of a range of aryl and heteroaryl
bromides (Figure 3). For example, this method was applicable to orthoꢀsubstituted aryl
bromides as the amination of the sterically hindered aryl halide, 1ꢀbromonaphthalene,
provided a 55% yield of the corresponding monoarylamine 1. In addition, although
electronꢀrich aryl halides are known to be more challenging substrates for copperꢀ
catalyzed carbonꢀnitrogen bondꢀforming processes, 4ꢀbromodiphenylether was applicable
to this methodology. Further, both electronꢀneutral (4ꢀbromobiphenyl) and electronꢀpoor
(4ꢀbromobenzophenone) were successfully converted to the corresponding
monoarylamines 2 and 4 in modest yields (30% and 32%, respectively).
Nitrogenꢀbased heterocycles are ubiquitous in biologically active compounds, but
inclusion of these heterocyclic motifs is often found to be detrimental to catalyst activity
in other systems.26 The aminationꢀoxidation reaction of several nitrogenꢀderived
heteroaryl halides was thus examined (Figure 3). The coupling of orthoꢀsubstituted 4ꢀ
bromoisoquinoline was found to be effective, and a 52% yield of 7 was isolated. In
addition, we were able to demonstrate that an electronꢀrich heterocyclic substrate (i.e., 4ꢀ
bromoꢀNꢀtosylindole) was applicable to the transformation as a 62% isolated yield of 8
was obtained. These results were consistent with the fact that polycyclic aryl halides—
including halonaphthalenes—result in an increased yield of the respective
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 20
1
2
3
4
5
6
7
8
monoarylamine products. This aminationꢀoxidation strategy, which employs a stable and
easily handleable amino acid nitrogen source, therefore offers an effective method for the
conversion of (hetero)aryl iodides and bromides to monoarylamines.
Under the optimized conditions the carbonꢀnitrogen bondꢀforming step must be
conducted under an argon atmosphere followed by introduction of oxygen to promote
imine formation (Figure 4, Entry 1). Interestingly, when argon was employed through
the entire process (no oxygen introduced), only a 45% isolated yield of 1 was obtained
(Figure 4, Entry 2). In addition, if solely oxygen or air atmosphere was utilized for the
duration of the reaction, <10% product was observed (Figure 4, Entries 3ꢀ4). Further,
when an alternative oxidant to molecular oxygen (i.e., 2,2,6,6ꢀtetramethylꢀ1ꢀpiperidinylꢀ
Nꢀoxyl (TEMPO)) was employed in Step 2 of the process, only a 22% yield was isolated.
We propose that this transformation proceeds via an Nꢀaryl imino acid intermediate,
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
which is then hydrolyzed to the desired monoarylamine upon acidic workup.
To
ascertain whether the process proceeds through a Nꢀaryl imino acid intermediate, we
examined the trapping of the imine intermediate with a nucleophilic hydride reagent. In
this event, valine and 1ꢀiodonaphthalene were exposed to the optimized copperꢀcatalyzed
aminationꢀoxidation conditions. Then, as opposed to hydrolytic workup, LiBH4 (4.0
equivalents) and tetrahydrofuran (THF) were added to the crude reaction, and the mixture
was reheated to reflux for 3 h (Figure 4).
This reduction protocol furnished Nꢀnaphthylvaline in a 52% isolated yield—note that
22% of 1ꢀaminonaphthalene was also isolated.
Consistent with our previous
observations, only trace Nꢀnaphthylvaline was found when the amination product mixture
was exposed directly to hydrolytic conditions. This transformation suggests that an Nꢀ
aryl imino acid is formed in situ and the intermediate can be selectively reduced with the
appropriate nucleophile.
ACS Paragon Plus Environment

Page 9 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Copperꢀcatalyzed amine oxidations have been proposed to occur via several
mechanisms including (1) singleꢀelectron transfer (SET) mechanism via a nitrogen
radical cation or (2) initial generation of αꢀcarbonꢀcentered radical intermediate.27 Since
nonꢀenzymatic methods for the oxidation of unprotected α−amino acids to imino acids
are rare,28 we sought to determine whether the Nꢀaryl amino acid furnished by the
amination reaction accelerated the copperꢀcatalyzed oxidation (Figure 5). When
examining the rate of oxidation of valine, Nꢀmethylvaline and Nꢀbiphenylvaline under
optimized conditions, only Nꢀbiphenylvaline efficiently provided the desired Nꢀaryl
imino acid product after 5 h—with other derivatives resulting in trace levels of oxidation.
This result suggests that the α−aryl amino acid amination products are required to initiate
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
oxidation.
The desired oxidation process may further be accelerated through
coordination of the Nꢀaryl amino acid substrate to the metal. Further studies regarding
the mechanism of this reaction and reactivity of the proposed imine intermediate are
underway including extending this methodology to the preparation of α−amino acid
analogues through employing carbon nucleophiles for imine reduction.
Conclusion
In summary, we have designed an aminationꢀoxidation process that successfully
converts (hetero)aryl iodides and bromides to the corresponding monoarylamines. This
copperꢀcatalyzed method provides a mechanistically novel approach to the synthesis of
these important structural motifs. The transformation employs a stable and easily
handleable nitrogen source, valine, and obviates the need for the special handling or
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 20
1
2
3
4
5
6
7
8
9
complex experimental setup. Further, the transformation is selective for the formation of
monoarylamine products without significant diꢀ and triarylamine byproducts observed.
Lastly, we have demonstrated that substitution at nitrogen using an aryl halide initiator
helps facilitate amino acid oxidation.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

Page 11 of 20
The Journal of Organic Chemistry
1
2
3
4
Experimental Section
5
6
7
8
General Considerations. Unless otherwise noted, all reactions were performed under
an argon or oxygen atmosphere in ovenꢀdried glassware. Dimethyl sulfoxide (anhydrous),
valine (reagent grade), copper (I) iodide (purum, ≥99.5%) and cesium carbonate (99%)
were employed. Commercially available aryl iodides and bromides were used without
further purification. Reactions were stirred using Teflonꢀcoated magnetic stirrer bars.
Reactions were monitored via gas chromatography and/or thin layer silica gel
chromatography (TLC) using 0.25 mm silica gel 60F plates with fluorescent indicator.
Plates were visualized under UV light without further staining. Products were purified via
column chromatography using the solvent system(s) indicated. Silica gel 60, 230ꢀ400
mesh, was used for purification.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
All new compounds were characterized by 1H NMR, C NMR, IR spectroscopy and
1
highꢀresolution mass spectrometry. Known compounds were characterized by H NMR
and melting points (for solids) and compared to their literature values. NMR spectra
were measured on a magnetic resonance spectrometer (1H at 500 MHz, 13C at 125 MHz).
1H chemical shifts are reported relative to the residual solvent peak (chloroform = 7.26
ppm) as follows: chemical shift (δ), (proton ID, multiplicity (s = singlet, bs = broad
singlet, d = doublet, bd = broad doublet, ddd = doublet of doublet of doublets, dddd =
doublet of doublet of… etc., ddddd = doublet of doublet of… etc., t = triplet, q = quartet,
13
p = pentet), integration, coupling constant(s) in Hz.). C chemical shifts are reported
13
relative to the residual deuterated solvent C signals (chloroform = 77 ppm). Infrared
spectra were recorded on a FTIR and are reported in wavenumbers (cmꢀ1). Gas
chromatographic analyses were preformed on a gas chromatography instrument with a
FID detector using 25 m x 0.20 mm capillary column with crossꢀlinked methyl siloxane
as a stationary phase.
Optimization of Reaction Conditions (Figure 2). Each ovenꢀdried reaction tube
was equipped with magnetic stir bar and charged with CuI and Cs2CO3 (244 mg, 0.75
mmol). The tubes was capped with a septa and then evacuated and backfilled with
atmosphere #1 (this sequence was carried out three times). DMSO (0.50 mL) was added
via syringe, through the septa, followed by the addition of the 1ꢀiodonaphthalene (127
mg, 73.0 ꢁL, 0.50 mmol) and corresponding amine (0.60 mmol) in a like manner (amines
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 20
1
2
3
4
5
6
7
8
9
that were solids were added with other reagents before evacuation). Each reaction
mixture was heated to 90 °C for 24 h. The reaction mixture was then allowed to cool to
room temperature and then evacuated and backfilled with atmosphere #2 (argon, air or
oxygen). The reaction mixture was reheated to 90 °C for an additional 24 h. The
reaction was cooled to room temperature and dodecane (10 ꢁL) was added to the crude
material as an internal standard. The crude mixture for each reaction was then analyzed
by gas chromatography in order to determine the conversion of 1ꢀiodonaphthalene.
Reactions that resulted in significant conversion of starting material were then purified
via flash chromatography on silica gel to obtain the final isolated yield.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
General Procedure for Aniline Synthesis with Aryl Halides. An ovenꢀdried
reaction tube equipped with magnetic stir bar was charged with CuI (19.0 mg, 0.10
mmol), valine (70.6 mg, 0.60 mmol) and Cs2CO3 (244 mg, 0.75 mmol). The tube was
capped with a septum and then evacuated and backfilled with argon (this sequence was
carried out three times). DMSO (0.50 mL) was added via syringe, through the septum,
followed by the addition of the aryl halide (0.50 mmol) in a like manner (aryl halides that
were solids were added with other reagents before evacuation). The reaction mixture was
heated to 90 °C until aryl halide had been completely consumed, as determined by gas
chromatography (24 h). At this point the reaction mixture was allowed to cool to room
temperature and then evacuated and backfilled with oxygen. The reaction mixture was
reheated to 90 °C for an additional 24 h. The reaction was cooled to room temperature
and partitioned between dichloromethane (1.5 mL) and water (1.5 mL). The solution was
acidified to pH = 1 with conc. HCl (~5 drops, ~0.25 mL) and allowed to stir for 20 min.
Solid sodium bicarbonate was added to neutralize the solution (pH = 7). The aqueous
layer was extracted with dichloromethane, and the combined organic layers were
concentrated. The crude material so obtained was purified via flash chromatography on
silica gel.
1-Aminonaphthalene (1) (halide: iodide).14d 1ꢀIodonaphthalene (127 mg, 73.0 ꢁL,
0.50 mmol) was employed in the reaction using the standard procedure. The crude
product was purified via flash column chromatography on silica gel (10/10/80%
EtOAc/NEt3/Hexanes) to provide the title compound in a 90% yield (65 mg) as a tan
1
solid. H NMR (500 MHz, CDCl3) ≥: δ 7.70ꢀ7.71 (m, 2H), 7.35ꢀ7.37 (m, 2H), 7.16ꢀ7.20
ACS Paragon Plus Environment

Page 13 of 20
The Journal of Organic Chemistry
1
2
(m, 2H), 6.65ꢀ6.67 (d, J = 8.6 Hz, 1H), 3.62 (bs, 2H) ppm. 13C NMR (125 MHz, CDCl3):
δ 142.1, 134.6, 128.8, 126.6, 126.0, 125.0, 123.9, 121.0, 119.2, 109.9 ppm.
4-Aminobiphenyl (2) (halide: iodide).29 1ꢀIodobiphenyl (140 mg, 0.50 mmol) was
employed in the reaction using the standard procedure. The crude product was purified
via flash column chromatography on silica gel (25/10/65% EtOAc/NEt3/Hexanes) to
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
provide the title compound in a 57% yield (48.3 mg) as a colorless solid. H NMR (500
MHz, CDCl3) ≥: δ 7.53ꢀ7.56 (m, 2H), 7.38ꢀ7.44 (m, 4H), 7.26ꢀ7.29 (t, J = 7.2 Hz, 1H),
6.75ꢀ6.78 (d, J = 8.4 Hz, 2H), 3.70 (s, 2H) ppm. 13C NMR (125 MHz, CDCl3): δ 146.7,
141.6, 131.9, 128.9, 128.3, 126.6, 126.5, 115.6 ppm.
4-chloroaniline (3) (halide: iodide).30 1ꢀIodoꢀ4ꢀchlorobenzene (119 mg, 0.50 mmol)
was employed in the reaction using the standard procedure. The crude product was
purified via flash column chromatography on silica gel (30/70% EtOAc/Hexanes) to
1
provide the title compound in a 45% yield (29 mg) as a colorless solid. H NMR (500
MHz, CDCl3) ≥: δ 7.01ꢀ7.03 (d, J = 8.8 Hz, 2H), 6.52ꢀ6.54 (d, J = 8.8 Hz, 2H), 3.57 (bs,
2H) ppm. 13C NMR (125 MHz, CDCl3): δ 144.9, 125.1, 110.3, 104.4 ppm.
4-Aminobenzophenone (4) (halide: iodide).31 4ꢀIodobenzophenone (154 mg, 0.50
mmol) was employed in the reaction using the standard procedure. The crude product
was purified via flash column chromatography on silica gel (40/10/50%
EtOAc/NEt3/Hexanes) to provide the title compound in a 44% yield (43 mg) as a yellow
1
solid. H NMR (500 MHz, CDCl3) ≥: δ 7.63ꢀ7.65 (m, 4H), 7.44ꢀ7.47 (m, 1H), 7.36ꢀ7.39
(m, 2H), 6.61ꢀ6.59 (d, J = 8.5 Hz, 2H), 4.06 (bs, 2H) ppm. 13C NMR (125 MHz, CDCl3):
δ 195.1, 150.8, 138.8, 132.8, 131.2, 129.4, 127.9, 127.5, 113.5 ppm.
3,5-Bis(trifluoromethyl)aniline
Bis(trifluoromethyl)benzene (170 mg, 60.1 ꢁL, 0.50 mmol) was employed in the reaction
using the standard procedure with the following modification. 1ꢀfluoroꢀ2,4ꢀ
(5)
(halide:
iodide).32
1ꢀiodoꢀ3,5ꢀ
dinitrobenzene (25 ꢁL) was added to the combined dichloromethane solution. An aliquot
19
of this solution was then subjected F NMR spectroscopic analysis, which indicated that
91% yield of the desired product.
1,3-Phenylenediamine (6) (halide: iodide).14d 3ꢀIodoaniline (110 mg, 88.6 ꢁL, 0.50
mmol) was employed in the reaction using the standard procedure. The crude product
was purified via flash column chromatography on silica gel (30/10/60%
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 20
1
2
3
4
5
6
7
8
EtOAc/NEt3/Hexanes) to provide the title compound in a 28% yield (15 mg) as a
1
colorless solid. H NMR (500 MHz, CDCl3) ≥: δ 8.28 (t, J = 2.0 Hz, 1H), 7.69 (d, J = 1.9
Hz, 2H), 7.19 (s, 1H), 4.34 (bs, 4H) ppm. 13C NMR (125 MHz, CDCl3): δ 145.0, 126.1,
110.4, 104.5 ppm.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-Aminonaphthalene (1) (halide: bromide).14d 1ꢀBromonaphthalene (103.5 mg, 69.9
ꢁL, 0.50 mmol) was employed in the reaction using the standard procedure. The crude
product was purified via flash column chromatography on silica gel (15/85%
1
EtOAc3/Hexanes) to provide the title compound in a 55% yield (39 mg) as a tan solid. H
NMR (500 MHz, CDCl3) ≥: δ 7.69ꢀ7.74 (m, 2H), 7.35ꢀ7.37 (m, 2H), 7.17ꢀ7.24 (m, 2H),
6.69 (d, J = 7.0 Hz, 1H), 3.62 (bs, 2H) ppm. 13C NMR (125 MHz, CDCl3) ≥: δ 142.3,
134.7, 128.9, 126.5, 126.1, 125.1, 123.9, 121.1, 119.4, 110.0 ppm.
4-Aminobiphenyl (2) (halide: bromide).29 1ꢀBromobiphenyl (116.6 mg, 0.50 mmol)
was employed in the reaction using the standard procedure. The crude product was
purified via flash column chromatography on silica gel (20/10/70%
EtOAc/NEt3/Hexanes) to provide the title compound in a 36% yield (20 mg) as a yellow
1
solid. H NMR (500 MHz, CDCl3) ≥: δ 7.54ꢀ7.58 (m, 2H), 7.41ꢀ7.46 (m, 4H), 7.29ꢀ7.31
(t, J = 7.2 Hz, 1H), 6.77ꢀ6.80 (d, J = 8.4 Hz, 2H), 3.70 (s, 2H) ppm. 13C NMR (125
MHz, CDCl3) ≥: δ 146.7, 141.6, 131.9, 128.9, 128.3, 126.6, 126.4, 115.6 ppm.
4-Aminobenzophenone (4) (halide: bromide).30 4ꢀBromobenzophenone (180.6 mg,
0.50 mmol) was employed in the reaction using the standard procedure. The crude
product was purified via flash column chromatography on silica gel (20/10/70%
EtOAc/NEt3/Hexanes) to provide the title compound in a 32% yield (32 mg) as a yellow
1
solid. H NMR (500 MHz, CDCl3) ≥: δ 7.72ꢀ7.75 (m, 4H), 7.53ꢀ7.57 (t, J = 7.0 Hz, 1H),
7.45ꢀ7.47 (t, J = 7.5 Hz, 2H), 6.67ꢀ6.70 (d, J = 7.9 Hz, 2H), 4.06 (bs, 2H) ppm. 13C NMR
(125 MHz, CDCl3) ≥: δ 195.4, 151.1, 139.2, 133.2, 131.7, 129.7, 128.4, 127.6, 114.0
ppm.
3-Aminoquinoline (7) (halide: bromide).33 3ꢀBromoquinoline (104 mg, 67.9 ꢁL, 0.50
mmol) was employed in the reaction using the standard procedure. The crude product
was purified via flash column chromatography on silica gel (20/10/70%
EtOAc/NEt3/Hexanes) to provide the title compound in a 52% yield (38 mg) as a orangeꢀ
1
red solid. H NMR (500 MHz, CDCl3) ≥: δ 8.42ꢀ8.44 (d, J = 2.8 Hz, 1H) 7.86ꢀ7.89 (d,
ACS Paragon Plus Environment

Page 15 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
J = 8.2 Hz, 1H), 7.49ꢀ7.52 (d, J = 7.6 Hz, 1H), 7.32ꢀ7.38 (m, 2H), 7.16 (d, J = 2.7 Hz,
1H), 3.65 (bs, 2H) ppm. 13C NMR (125 MHz, CDCl3) ≥: δ 142.9, 142.6, 139.6, 129.0,
128.9, 126.9, 125.8, 125.6, 115.1 ppm.
4-Amino-N-tosylindole (8) (halide: bromide).34 4ꢀBromoꢀNꢀtosylindole (175 mg, 0.50
mmol) was employed in the reaction using the standard procedure. The crude product
was purified via flash column chromatography on silica gel (25% EtOAc/Hexanes) to
provide the title compound in a 62% yield (89 mg) as a brown solid. 1H NMR (500
MHz, CDCl3) ≥: δ 7.74ꢀ7.77 (d, J = 8.3 Hz, 2H), 7.47ꢀ7.48 (d, J = 3.7 Hz, 1H), 7.40ꢀ7.44
(d, J = 8.3 Hz, 1H), 7.19ꢀ7.22 (d, J = 8.3 Hz, 2H), 7.08ꢀ7.12 (t, J = 8.1 Hz, 1H), 6.56ꢀ6.58
(d, J = 3.9 Hz, 1H), 6.48ꢀ6.51 (d, J = 7.8 Hz, 1H) 2.32ꢀ2.34 (s, 3H) ppm. 13C NMR (125
MHz, CDCl3): δ 144.0, 139.6, 136.0, 135.4, 129.8, 126.9, 125.7, 124.5, 119.2, 108.2,
105.1, 104.4, 21.5 ppm.
4-Aminodiphenyl ether (9) (halide: bromide).35 4ꢀBromodiphenyl ether (125 mg, 87.5
ꢁL, 0.50 mmol) was employed in the reaction using the standard procedure. The crude
product was purified via flash column chromatography on silica gel (40/10/50%
EtOAc/NEt3/Hexanes) to provide the title compound in a 38% yield (35 mg) as an orange
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
oil. H NMR (500 MHz, CDCl3) ≥: 7.18ꢀ7.121 (m, 2H), 6.90ꢀ6.94 (t, J = 7.1 Hz, 1H),
6.83ꢀ6.86 (d, J = 8.3 Hz, 2H), 6.78ꢀ6.80 (d, J = 8.9 Hz, 2H), 6.58ꢀ6.60 (d, J = 8.80 Hz,
2H) ppm. 3.49 (bs, 2H) ppm. 13C NMR (125 MHz, CDCl3) ≥: δ 148.9, 142.9, 129.8,
122.3, 121.3, 117.5, 116.5, 27.6 ppm.
Reduction of Imino Acid with LiBH4 (Figure 4). An ovenꢀdried reaction tube
equipped with magnetic stir bar was charged with CuI (19.0 mg, 0.10 mmol), valine (70.6
mg, 0.60 mmol) and Cs2CO3 (244 mg, 0.75 mmol). The tube was capped with a septum
and then evacuated and backfilled with argon (this sequence was carried out three times).
DMSO (0.50 mL) was added via syringe, through the septum, followed by the addition of
the 1ꢀiodonaphthalene (127 mg, 73.0 ꢁL, 0.50 mmol) in a like manner. The reaction
mixture was heated to 90 °C for 24 h. The reaction mixture was allowed to cool to room
temperature and then evacuated and backfilled with oxygen. The reaction mixture was
reheated to 90 °C for an additional 24 h. The reaction was cooled to room temperature
and LiBH4 (43.6 mg, 2.00 mmol) and THF (1.00 mL) were added directly to solution.
The reaction was heated to 90 °C for 3 h. The crude product was purified via flash
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 20
1
2
3
4
5
6
7
8
9
column chromatography on silica gel (25% EtOAc/Hexanes) to provide a mixture of 1ꢀ
naphthylvaline in a 52% yield (63 mg) and 1ꢀaminonapthalene 22% yield (16 mg).
Experimental for Oxidation of Valine Derivatives (Figure 5). An ovenꢀdried
reaction tube equipped with magnetic stir bar was charged with CuI (3.8 mg, 0.02 mmol),
valine derivative (0.20 mmol) and Cs2CO3 (97.7 mg, 0.30 mmol). The tube was capped
with a septum and then evacuated and backfilled with oxygen. DMSOꢀD6 (0.20 mL) was
added via syringe, through the septum. The reaction mixture was heated to 90 °C for 5 h.
The reaction mixture was allowed to cool to room temperature and then filtered through a
pad of celite. Each reaction was initially assessed by 1H NMR spectroscopy to determine
conversion of valine derivative. Then, the solution from the oxidation of Nꢀ
biphenylvaline was partitioned between dichloromethane (1.5 mL) and water (1.5 mL).
The solution was acidified to pH = 1 with conc. HCl (~5 drops, ~0.25 mL) and allowed to
stir for 20 min. Solid sodium bicarbonate was added to neutralize the solution (pH = 7).
The aqueous layer was extracted with dichloromethane, and the combined organic layers
were concentrated. The crude product was purified via flash column chromatography on
silica gel (20/10/70% EtOAc/NEt3/Hexanes) to provide Nꢀbiphenylvaline in a 47% yield
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
(15.9 mg) as a yellow solid. H NMR (500 MHz, CDCl3) ≥: δ 7.54ꢀ7.58 (m, 2H), 7.41ꢀ
7.46 (m, 4H), 7.29ꢀ7.31 (t, J = 7.2 Hz, 1H), 6.77ꢀ6.80 (d, J = 8.4 Hz, 2H), 3.70 (s, 2H)
ppm.
Associated Content
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website:
copies of 1H and 13C NMR spectra of all compounds.
Author Information
Corresponding Author
*Email: klbillin@sfsu.edu
Notes
The authors declare no competing financial interest.
ACS Paragon Plus Environment

Page 17 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
Acknowledgements
7
8
9
This research was financially supported by startup funds granted by the College of
Science and Engineering at San Francisco State University.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 20
1
2
3
4
References
5
6
7
8
(1)
(a) Bartholomew, C. H.; Farrauto, R. J. Fundamentals of Industrial Catalytic
Processes; John Wiley & Sons: Hoboken, NJ, 2006. (b) Behr, A.; Neubert, P.
Applied Homogeneous Catalysis; WileyꢀVCH: Weinheim, Germany, 2012.
(a) Surry, D. S.; Buchwald, S. L. Chem. Sci. 2011, 2, 27. (b) Hartwig, J. F. Acc.
Chem. Res. 2008, 41, 1534.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(2)
(3)
Jiang, Y.; Ma, D. Modern Ullmann–Goldberg Chemistry: Arylation of Nꢀ
Nucleophiles with Aryl Halides. In Copper-Mediated Cross-Coupling Reactions;
Evano G.; Blanchard, N., Ed.; John Wiley & Sons, Inc., Hoboken, NJ, 2013;
USA.
(4)
(5)
(6)
Carey, J. S.; Laffan, D.; Thomson, C.; Williams, M. T. Org. Biomol. Chem., 2006,
4, 2337.
(a) Kim, J.; Kim, H. J.; Chang, S. Eur. J. Org. Chem. 2013, 16, 3201. (b)
Klinkenberg, J. L.; Hartwig, J. F. Angew. Chem., Int. Ed. 2010, 50, 86.
Aubin, Y.; Fischmeister, C.; Thomas, C. M.; Renaud, J.ꢀL. Chem. Soc. Rev. 2010,
39, 4130.
(7)
(8)
Enthaler, S. ChemSusChem 2010, 3, 1024.
(a) Wei, Z.; Faul, C. F. J. Macromol. Rapid Commun. 2008, 29, 280. (b)
Rappoport, Z., Ed. The Chemistry of Anilines; John Wiley & Sons: Hoboken, NJ,
2007.
(9)
Surry, D. S.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 10354.
(10) (a) Shen, Q.; Hartwig, J. F. J. Am. Chem. Soc. 2006, 128, 10028. (b) Green, R. A.;
Hartwig, J. F. Org Lett. 2014, 16, 4388.
(11) Lundgren, R. J.; Peters, B. D.; Alsabeh, P. G.; Stradiotto, M. Angew. Chem. Int.
Ed. 2010, 49, 4071.
(12) Schulz, T.; Torborg, C.; Enthaler, S.; Schäffner, B.; Dumrath, A.; Spannenberg,
A.; Neumann, H.; Börner, A.; Beller, M. Chemistry 2009, 15, 4528.
(13) For reviews, see: (a) Ley, S. V.; Thomas, A. W. Angew. Chem. Int. Ed. 2003, 42,
5400. (b) Monnier, F.; Taillefer, M. Angew. Chem. Int. Ed. 2009, 48, 6954.
(14) (a) Lang, F. R.; Zewge, D.; Houpis, I. N.; Volante, R. P Tetrahedron Lett. 2001,
42, 3251. (b) Kim, J.; Chang, S.; Chem. Commun. 2008, 3052. (c) Xia, N.;
ACS Paragon Plus Environment

Page 19 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Taillefer, M. Angew. Chem. Int. Ed. 2009, 48, 337. (d) For the amination of aryl
chlorides under microwave irradiation, see: Xu, H. H.; Wolf, C. Chem. Commun.
2009, 3035. (e) Wu, Z. Q.; Jiang, Z. Q.; Wu, D.; Xiang, H. F.; Zhou, X. G. Eur. J.
Org. Chem. 2010, 1854. (f) Jiao, J.; Zhang, X. R.; Chang, N. H.; Wang, J.; Wei, J.
F.; Shi, X. Y.; Chen, Z. G. J. Org. Chem. 2011, 76, 1180. (g) Thakur, K. G.;
Ganapathy, D.; Sekar, G.; Chem. Commun. 2011, 47, 5076. (h) Ji, P.; Atherton, J.
H.; Page, M. I. J. Org. Chem. 2012, 77, 7471.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(15) For recent reports describing nickelꢀbased systems for the crossꢀcoupling of
ammonia and ammonia surrogates, see: (a) Green, R. A.; Hartwig, J. F. Angew.
Chem. Int. Ed. 2015, 54, 3768. (b) Borzenko, A.; RottaꢀLoria, N. L.; MacQueen,
P. M.; Lavoie, C. M.; McDonald, R.; Stradiotto, M. Angew. Chem. Int. Ed. 2015,
54, 3773.
(16) Lang, F.; Zewge, D.; Houpis, I. N.; Volante, R. P. Tetrahedron Lett. 2001, 42,
3251.
(17) Ji, P.; Atherton, J. H.; Page, M. I. J. Org. Chem. 2012, 77, 7471.
(18) (a) Jiang, L.; Lu, X.; Zhang, H.; Jiang, Y.; Ma, D. J. Org. Chem. 2009, 74, 4542ꢀ
4546. (b) Diao, X.; Wang, Y.; Jiang, Y.; Ma, D. J. Org. Chem. 2009, 74, 7974. (c)
Xia, N.; Taillefer, M. Angew. Chem. Int. Ed. 2009, 48, 337. (d) Wang, D. P.; Cai,
Q.; Ding, K. Adv. Synth. Catal. 2009, 351, 1722. (e) Chen, J.; Yuan, T.; Hao, W.;
Cai, M. Tetrahedron Lett. 2011, 52, 3710. (f) Rao, H. H.; Fu, H.; Jiang, Y. Y.;
Zhao, Y. F. Angew. Chem. Int. Ed. 2009, 48, 1114.
(19) (a) Lee, D.ꢀY.; Hartwig, J. F. Org. Lett. 2005, 7, 1169. (b) Huang, X.; Buchwald,
S. L. Org. Lett. 2001, 3417.
(20) (a) Wolfe, J. P.; Ahman, J.; Sadighi, J. P.; Singer, R. A.; Buchwald, S. L.
Tetrahedron Lett. 1997, 38, 6367. (b) Grasa, G. A.; Viciu, M. S.; Huang, J.;
Nolan, S. P. J. Org. Chem. 2001, 66, 7729.
(21) Lim, C. W.; Lee, S. G. Tetrahedron 2000, 56, 5131.
(22) (a) Gao, X.; Fu, H.; Qiao, R.; Jiang, Y.; Zhao, Y. J. Org. Chem. 2008, 73, 6864.
(b) Zhao, H.; Fu, H.; Qiao, R. J. Org. Chem. 2010, 75, 3311. (c) Barluenga, J.;
Aznar, F.; Valdes, C. Angew. Chem. Int. Ed. 2004, 43, 343. (d) Markiewicz, J. T.;
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 20
1
2
3
4
5
6
Wiest, O.; Helquist, P. J. Org. Chem. 2010, 75, 4887. (e) Tao, C.ꢀZ.; Li, J.; Fu,
Y.; Liua, L.; Guo, Q.ꢀX. Tetrahedron Lett. 2008, 49, 70.
7
8
9
(23) (a) Ma, D.; Cai, Q. Acc. Chem. Res. 2008, 41, 1450ꢀ60. (b) Ma, D.; Zhang, Y.;
Yao, J.; Wu, S.; Tao, F. J. Am. Chem. Soc. 1998, 120, 12459.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(24) (a) Li, Z.; Bohle, S.; Li, C.ꢀJ. Proc. Natl. Acad. Sci. USA 2006, 103, 8928. (b)
Zhao, L.; Baslé, O.; Li, C.ꢀJ. Proc. Natl. Acad. Sci. USA 2009, 106, 4106.
(25) Yang, Y.ꢀX.; Liu, Y.; Zhang, L.; Jia, Y.ꢀE.; Wang, P.; Zhuo, F.ꢀF.; An, X.ꢀT.; Da,
C.ꢀS. J. Org. Chem. 2014, 79, 10696.
(26) (a) Lamberth, C; Dinges, J., Ed. Bioactive Heterocyclic Compound Classes:
Pharmaceuticals; WileyꢀVCH: Weinheim, Germany, 2012. (b) Billingsley, K.;
Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 3358. (c) Duefert, A.; Billingsley,
K.; Buchwald, S. L. J. Am. Chem. Soc. 2013, 135, 12877.
(27) (a) Mahapatra, S.; Hlafen, J. A.; Tolman, W. B. J. Am. Chem. Soc. 1996, 118,
11575. (b) Zhang, C.; Tang, C.; Jiao, N. Chem. Soc. Rev. 2012, 41, 3464.
(28) Stadtman, E. R. Annu. Rev. Biochem. 1993, 62, 797ꢀ821.
(29) Leadbeater, N. E.; Marco, M. Angew. Chem. Int. Ed. 2003, 42, 1407.
(30) Feng, X.; Qu, Y.; Han, Y.; Yu, X.; Bao, M.; Yamamoto, Y. Chem. Commun.
2012, 48, 9468.
(31) Cai, M.; Peng, J.; Hao, W.; Ding, G. Green Chem. 2011, 13, 190ꢀ196.
(32) Myung, B. Y.; Kim, J. S.; Kim, J. J.; Yoon, T. H. J. Poly. Sci.: Part A: Poly.
Chem. 2003, 3361.
(33) Chatterjee, N.; Goswami, A. Org. Biomol. Chem. 2015, 13, 7940.
(34) Wang, X.; Xu, Y.; Mo, F.; Ji, G.; Qiu, D.; Feng, J.; Ye, Y.; Zhang, S.; Zhang, Y.;
Wang, J. J. Am. Chem. Soc. 2013, 135, 10330.
(35) Zhang, Q; Wang, D.; Wang, X.; Ding, K. J. Org. Chem. 2009, 74, 7187.
ACS Paragon Plus Environment