Ruthenium-catalyzed reductive deamination and tandem alkylation of aniline derivatives

Article abstract of DOI:10.1016/j.jorganchem.2013.06.001

We developed two new catalytic transformations of anilines via oxidative addition of CeN bonds to ruthenium centers. One is ruthenium-catalyzed reductive deaminatoindeamination of N-alkylated oacylanilines. The other one is catalytic coupling of N-alkylated o-acylanilines with olefins giving orthoalkylated aromatic ketones via CeN bond cleavage. This reaction involves a ruthenium hydride species as an intermediate, formed after b-hydride elimination from the ruthenium amide species.

Full text of DOI:10.1016/j.jorganchem.2013.06.001

Journal of Organometallic Chemistry 741-742 (2013) 148e152
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ruthenium-catalyzed reductive deamination and tandem alkylation
of aniline derivatives
*
Tetsuro Koreeda, Takuya Kochi, Fumitoshi Kakiuchi
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
We developed two new catalytic transformations of anilines via oxidative addition of CeN bonds to
ruthenium centers. One is ruthenium-catalyzed reductive deaminatoindeamination of N-alkylated o-
acylanilines. The other one is catalytic coupling of N-alkylated o-acylanilines with olefins giving ortho-
alkylated aromatic ketones via CeN bond cleavage. This reaction involves a ruthenium hydride species as
Received 22 April 2013
Received in revised form
27 May 2013
Accepted 1 June 2013
an intermediate, formed after
b
-hydride elimination from the ruthenium amide species.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Carbonenitrogen bond cleavage
Ruthenium catalyst
Deamination
Tandem deamination/alkylation
1. Introduction
The first catalytic functionalization of unactivated carboneni-
trogen bonds in aniline derivatives was achieved by our group in
2007 [5]. In this reaction, coupling of o-acylanilines with organo-
boronates was catalyzed by RuH2(CO)(PPh3)3 (1) under toluene
refluxing conditions to transform carbonenitrogen bonds into
carbonecarbon bonds (Scheme 1). Our recent studies indicated
that the reaction proceeded via oxidative addition of the carbone
nitrogen bonds, followed by transmetalation with arylboronates
and reductive elimination [6].
Reductive deamination of aniline derivatives is an important
process in organic synthesis, since amino groups show strong
directing effects in electrophilic aromatic substitutions. However,
simple catalytic deamination of unactivated anilines using transi-
tion metal complexes has not been reported [11]. In order to
remove amino groups on the aromatic rings, anilines were nor-
mally converted to more reactive compounds such as diazonium
salts and then reduced [12].
Cleavage of unreactive sp2 carbonenitrogen bonds by transition
metal complexes has been of great interest to many researchers
because of its potential application in development of novel cata-
lytic reactions as well as its relevance to hydrodenitrogenation
processes [1]. Anilines are one of the most common types of
compounds possessing such inert carbonenitrogen bonds, but
there have not been many successful examples of cleavage of aro-
matic carbonenitrogen bonds in anilines by transition metal
complexes [2e6]. As an early example, Fujiwara and coworkers
found that oxidative arylation of olefins with anilines proceeds via
cleavage of carbonenitrogen bonds in the presence of a stoichio-
metric amount of palladium salts [2]. Direct observation of oxida-
tive addition of aromatic carbonenitrogen bonds via was achieved
by Wolczanski and coworkers using tantalum complexes [3], and
Boncella and coworkers also observed a cleavage of a carboneni-
trogen bond of an (N-silyl)arylamido molybdenum complex [4].
Catalytic conversion of inert sp2 carbonenitrogen bonds in anilines
has rarely been achieved, and the carbonenitrogen bonds in these
compounds are usually activated by conversion to more reactive
species such as diazonium salts [7], ammonium salts [8], triazenes
[9], and hydrazines [10].
Here we report that catalytic reductive deamination of o-acy-
lanilines was achieved by simply heating with a ruthenium catalyst.
Tandem reductive deamination/alkylation of the aniline derivatives
was also found to proceed using the ruthenium catalyst in the
presence of olefins.
2. Results and discussion
When N,N-dimethyl-o-acylaniline 2a was treated with 20 mol%
of 1 in toluene at 120 ꢀC for 24 h, the dimethylamino group of 2a
was converted to a hydrogen atom to form pivalophenone (3a) in
* Corresponding author. Tel./fax: þ81 45 566 1591.
E-mail address: kakiuchi@chem.keio.ac.jp (F. Kakiuchi).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.06.001

T. Koreeda et al. / Journal of Organometallic Chemistry 741-742 (2013) 148e152
149
Table 2
R'
R'
cat.
Ruthenium-catalyzed deamination of o-acylanilines.a
O
O
O
O
RuH2(CO)(PPh3)3 (1)
+
R" B
O
toluene, reflux
NR2
R"
R'
R'
[Ru0]
O
R"B(OR"')2
[Ru]
NR2
[Ru]
R"
– R2NB(OR"')2
Entry
2
R1
R2
Yield (%)b
1
2b
2b
2b
2c
2d
2e
Me
Me
H
H
H
H
68
67
76
72
51
24
Scheme 1. Ruthenium-catalyzed coupling of o-acylanilines with organoboronates via
carbonenitrogen bond cleavage.
2c
3d
4
Me
iPr
5
6
e(CH2)4e
Bn
61% yield (Table 1, entry 1). Extension of the reaction time to 48 h
only slightly increased the product yield to 65% (entry 2). Additives
were then screened for the reaction, and cuprous oxide was found
to improve the yield to 76% (entry 3). The reaction temperature was
also examined, and heating in p-xylene at 140 ꢀC led to significant
increase of the yield to 90% (entry 4). At this temperature, addition
of cuprous oxide had little effect on the yield (entry 5). Further
increase of the reaction temperature to 160 ꢀC using mesitylene as a
solvent gave similar results to the reactions in p-xylene at 140 ꢀC
(entries 6 and 7). Lowering the catalyst loading to 10 mol% resulted
in considerable decrease in the yield of 3a (entries 8 and 9).
Therefore, we chose the reaction conditions used for entry 4 for
further investigation.
The ruthenium-catalyzed reductive deamination was also
examined with other o-acylanilines (Table 2). The reaction of N-
methyl-o-acylaniline 2b gave deamination product 3a in 68% yield
(entry 1). In this case, addition of cuprous oxide did not affect the
yield (entry 2), but heating at 160 ꢀC in mesitylene increased the
yield to 76% (entry 3). N-Isopropyl-o-acylaniline 2c and pyrrolidine
derivative 2d can also be transformed into 3a in 72% and 51% yields,
respectively (entries 4 and 5). On the other hand, the reaction of
N,N-dibenzyl-o-acylaniline 2e resulted in the formation of 3a in
24% yield (entry 6). The use of acetyl group as a directing group was
also unsuccessful and the reaction of N,N-dimethyl-o-acetylaniline
under the standard reaction conditions of Table 2 gave only 24%
yield of acetophenone as a product.
Bn
a
Reaction conditions: 2a (0.2 mmol), 1 (0.04 mmol), p-xylene (0.3 mL), 140 ꢀC,
24 h.
b
c
GC yield.
Performed in the presence of cuprous oxide (1 equiv).
Performed in mesitylene at 160 ꢀC.
d
ortho position to the amino group is essential to remove the amino
groups.
In the presence of olefins, tandem reductive deamination/
alkylation can proceed to form carbonecarbon bonds (Table 3) [13].
The reaction of 2a with catalyst 1 in the presence of 3 equiv of
trimethylvinylsilane (4a) gave ortho-alkylated pivalophenone 5a in
73% yield along with a small amount of 3a (entry 1). Addition of
cuprous oxide resulted in decrease in the yield (entry 2). The use of
5 equiv of 4a decreased the yield to 66% (entry 3), while reduction
of the amount of 4a to 1.5 equiv slightly increased the yield to 76%
(entry 4). As one of the possibilities, we propose that the addition of
olefins interferes the coordination of the aromatic ketones to the
ruthenium. The yield of 5a was not improved by performing the
reaction for 48 h (entry 5). The use of 10 mol% of catalyst 1 resulted
in significant lowering of the yield (entry 6). Raising of the reaction
temperature to at 140 ꢀC using p-xylene was effective as well for the
tandem alkylation reaction, and product 5a was obtained in 90%
yield (entry 7). Lowering the catalyst loading to 10 mol% was also
difficult for the reaction at 140 ꢀC, and alkylation product 5a was
obtained in 73% yield even after 48 h (entry 8).
When p-dimethylaminoacylaniline was reacted with catalyst 1
under the reductive deamination conditions, no formation of 3a
was observed. This result indicates that presence of an acyl group at
Table 3
Optimization of ruthenium-catalyzed deamination/alkylation of o-acylaniline 2a.a
Table 1
Optimization of ruthenium-catalyzed deamination of o-acylaniline 2a.a
Entry
4a (equiv)
Solvent
Temp (ꢀC)
Yields (%)b
Entry
Solvent
Temp (ꢀC)
1 (mol%)
Cu2O
Yield (%)b
5a
3a
1
2c
3
4
5
6
7
8
9
Toluene
Toluene
Toluene
p-Xylene
p-Xylene
Mesitylene
Mesitylene
p-Xylene
p-Xylene
120
120
120
140
140
160
160
140
140
20
20
20
20
20
20
20
10
10
None
None
1 equiv
None
1 equiv
None
1 equiv
None
1 equiv
61
65
76
90
89
93
88
61
54
1
3
3
5
1.5
1.5
1.5
1.5
1.5
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
p-Xylene
p-Xylene
120
120
120
120
120
120
140
140
73
68
66
76
74
44
90
73
1
1
1
1
2c
3
4d
5e
6
2
Trace
1
Trace
7
8d,e
a
Reaction conditions: 2a (0.2 mmol), 4a, 1 (0.04 mmol), solvent (0.3 mL), 24 h.
a
b
c
Reaction conditions: 2a (0.2 mmol), 1 (0.04 mmol), cuprous oxide (0.2 mmol, if
GC yield.
added), solvent (0.3 mL), 24 h.
Performed in the presence of cuprous oxide (1 equiv).
Performed for 48 h.
Performed with 10 mol% of 1.
b
d
e
GC yield.
Performed for 48 h.
c

150
T. Koreeda et al. / Journal of Organometallic Chemistry 741-742 (2013) 148e152
t
Next, we investigated the reactivity of olefins and the effect of
Bu
O
D
the alkyl group on the nitrogen atom for the tandem reductive
deamination/alkylation (Table 4). Coupling of 2a with triethylvi-
nylsilane (4b) provided alkylation product 5b in 89% yield (entry 1).
The reaction of 2a with 1-hexene (4c) was not as efficient as that
with vinylsilanes, and gave 43% yield of 5c, which has n-hexyl
group at an ortho position to the carbonyl group, along with
deamination product 3a in 30% yield (entry 2). The alkylation was
also examined with other o-acylanilines. N-Monosubstituted o-
acylanilines 2b and 2c reacted with vinylsilanes 4a and 4b to give
the corresponding alkylation products 5a and 5b in 32e51% yields
(entries 3e6), which are lower than the yields of the reductive
deamination of 2b or 2c (Table 2, entries 1e4). On the other hand,
the tandem alkylation of pyrrolidine derivative 2d using vinyl-
silanes 4a and 4b provided alkylation products 5a and 5b in 63%
and 71% yields, respectively (Table 4, entries 7 and 8), which are
higher than that of the deamination of 2d (Table 2, entry 5).
In order to gain understanding on the reaction mechanism, the
reductive deamination and the tandem alkylation were examined
with a substrate with two CD3 groups on the nitrogen atom (2a-d6)
(Scheme 2). When deuterated substrate 2a-d6 was treated with
catalyst 1 in p-xylene at 140 ꢀC for 24 h, complete transfer of a
deuterium atom of CD3 groups to one of the ortho positions of the
pivalophenone product (3a-d1) was observed. The reaction of 2a-d6
with 1.5 equiv of 4a and catalyst 1 at 140 ꢀC also gave the corre-
sponding alkylation product 5a-dn in 46% yield. In this case,
deuterium incorporation into alkylation product 5a-dn was
observed. The relative hydrogen intensities at benzyl, homobenzyl,
and the ortho position of the carbonyl group were observed with
1.57, 1.46, and 0.68 H, respectively, in the 1H NMR spectrum
(Scheme 2).
20 mol % 1
81% yield
>99% deuterium
incorporation
p-xylene
140 °C, 24 h
t
Bu
3a-d1
0.68 H
(D)H
O
1.46 H
N(CD3)2
t
Bu
1.5 equiv 4a
20 mol % 1
O
2a-d6
H(D)
p-xylene
140 °C, 24 h
SiMe3
H(D)
5a-dn
1.57 H
Scheme 2. The reductive deamination and the tandem alkylation of deuterated N,N-
dimethyl-o-acylaniline 2a-d6.
aromatic ketones by ruthenium catalysts has been reported and is
considered to proceed via oxidative addition of CeO bond followed
by
b-hydride elimination from the ruthenium-methoxide inter-
mediate [14,15]. The tandem alkylation (Fig. 1b) may also start with
oxidative addition of the carbonenitrogen bonds, but this process
may be faster when an olefin coordinates to the ruthenium center.
As a result, olefin-coordinated aryl amido complex C is formed and
reversible b-hydride elimination occurs to give hydrido complex D.
Olefin insertion into the metal-hydrogen bond can proceed in a 1,2-
or 2,1-fashion to form complex E or F, while reductive elimination
to give pivalophenone complex G also competes with the other
processes. The result of the tandem alkylation of deuterated sub-
strate 2a-d6 showed the incorporation of more than one deuterium
atom into at either methylenes or the ortho position of the carbonyl
group, which indicate the reversible conversion between com-
plexes C, D, E, F and G. Irreversible reductive elimination from
complex E is much faster than that from F and ligand dissociation
affords alkylation product 5.
Based on the observations described above, the reductive
deamination and the tandem alkylation of o-acylaniline 2 are
considered to proceed as shown in Fig. 1. The reductive deamina-
tion may be initiated with oxidative addition of the carboneni-
trogen bonds of 2 to form aryl amido complex A, which then
3. Conclusion
undergoes reversible b-hydride elimination and reductive elimi-
In conclusion, catalytic reductive deamination of o-acylaniline
derivatives was achieved by simple treatment with
nation to give complex B, which possess 3 and an imine as ligands.
Dissociation of these ligands provides 3 as a product and re-
generates the catalyst (Fig. 1a). The imine byproduct was detected
by GCeMS analysis for the reaction of N,N-dibenzyl-o-acylaniline
2e (Table 2, entry 6). Demethoxylation at the ortho position of
t
t
t
Bu
Bu
Bu
(a)
O
O
O
H
[Ru]
[Ru]
R'N
[Ru]
R'N
NR'
Table 4
CHR2
CR2
Ruthenium-catalyzed deamination/alkylation of o-acylanilines.a
CHR2
A
2
t
Bu
O
[Ru]
R'N
3a
– [Ru]
H
CR2
B
t
t
Bu
Bu
(b)
H
R''
[Ru]
R''
R''
O
O
Entry
2
R1
R2
4
R3
Yields (%)b
2
5
[Ru]
[Ru]
5
3a
– [Ru]
R'N
C
R'N
E
1
2c
3
4
5
6
7
8
2a
2a
2b
2b
2c
2c
2d
2d
Me
Me
Me
Me
Me
H
H
H
4b
4c
4a
4b
4a
4b
4a
4b
SiEt3
nBu
89 (5b)
43 (5c)
32 (5a)
34 (5b)
46 (5a)
51 (5b)
63 (5a)
71 (5b)
1
30
4
1
4
3
2
1
CR2
CHR2
SiMe3
SiEt3
SiMe3
SiEt3
SiMe3
SiEt3
t
t
Me
Bu
Bu
t
iPr
Bu
R''
O
O
R''
H
iPr
H
R''
O
H
[Ru]
R'N
F
[Ru]
R'N
G
[Ru]
R'N
D
e(CH2)4e
e(CH2)4e
H
CR2
CR2
CR2
a
Reaction conditions: 2 (0.2 mmol), 4 (0.3 mmol), 1 (0.04 mmol), p-xylene
(0.3 mL), 24 h.
b
c
GC yield.
Performed with 5 equiv of 4.
Fig. 1. Possible mechanism of (a) the reductive deamination and (b) the tandem
alkylation of o-acylanilines.

T. Koreeda et al. / Journal of Organometallic Chemistry 741-742 (2013) 148e152
151
RuH2(CO)(PPh3)3 catalyst with heating. In the presence of olefins,
tandem alkylation takes place to form ortho-alkylated piv-
alophenone 5. The reactions are considered to proceed via oxida-
907 m, 861 s, 842 s, 753 s, 690 m, 674 w, 611 w, 598 w, 571 w, 499 w,
472 w, 455 w, 422 w, 412 w, cmꢂ1 1H NMR (CDCl3):
0.01 (s, 9H,
;
d
Si(CH3)3), 0.81e0.86 (m, 2H, ArCH2CH2Si), 1.24 (s, 9H, C(CH3)3),
2.41e2.46 (m, 2H, ArCH2CH2Si), 7.09e7.17 (m, 2H, ArH), 7.24e7.31
tive addition of carbonenitrogen bonds, followed by
b-hydride
elimination from the amido ligand generated. Further mechanistic
studies and application of these reactions are still underway.
(m, 2H, ArH); 13C NMR (CDCl3):
d
ꢂ1.9, 19.2, 27.5, 27.9, 44.8, 124.4,
124.7, 128.7, 128.9, 140.1, 141.5, 215.2; HRMS (ESI) calcd for
[M þ Na]þ (C16H26NaOSi) m/z 285.1651. Found 285.1662.
4. Experimental
4.4.2. Compound 5b
4.1. General information
Pale yellow oil; IR (NaCl): 3861 w, 3850 w, 3063 w, 2953 s, 2909
m, 2874 s, 1688 s, 1600 w, 1477 m, 1461 m, 1416 w, 1392 w, 1364 w,
1276 w, 1237 w, 1185 m, 1084 w, 1015 m, 963 m, 941 w, 809 w, 742 s,
1H and 13C{1H}NMR spectra were recorded using JEOL JNM-
EX400, JNM-A400, and ECX400 spectrometers. Chemical shifts in
1H and 13C{1H}NMR spectra are expressed in ppm relative to re-
499 w, 426 w, cmꢂ1
;
1H NMR (CDCl3):
d
0.54 (q, J ¼ 7.9 Hz, 6H,
SiCH2CH3), 0.83e0.89 (m, 2H, ArCH2CH2Si), 0.95 (t, J ¼ 7.9 Hz, 9H,
SiCH2CH3), 1.24 (s, 9H, C(CH3)3), 2.41e2.46 (m, 2H, ArCH2CH2Si),
7.10e7.17 (m, 2H, ArH), 7.24e7.33 (m, 2H, ArH); 13C NMR (CDCl3):
sidual chloroform (
d d
7.26 for 1H, 77.0 for 13C) or tetramethylsilane
(d
0.00 for 1H and 13C). IR spectra were recorded on a JASCO FT/IR-
410 infrared spectrometer. Gas chromatography (GC) analyses were
d 3.1, 7.4, 14.2, 27.5, 27.9, 44.8, 124.4, 124.7, 128.7, 128.9, 140.1, 141.8,
performed using a CBP-10 capillary column (25 m ꢁ 0.22 mm, film
215.1; HRMS (ESI) calcd for [M þ Na]þ (C19H32NaOSi) m/z 327.2120.
thickness 0.25
m
m). GCMS analyses were performed on a Shimadzu
Found 327.2136.
GCMS-QP2010 gas chromatography mass spectrometer. Flash
chromatography was carried out with Kanto Chemical silica gel
60N. Unless otherwise noted, all reactions performed under nitro-
gen atmosphere.
4.4.3. Compound 5c
Colorless oil; IR (NaCl): 3897 w, 3361 w, 3062 w, 3018 w, 2957 s,
2930 s, 2860 m, 1689 s, 1600 w, 1574 w, 1477 s, 1462 s, 1393 w, 1364
m,1271 w, 1202 w, 1186 m,1126 w, 1030 w, 962 s, 941 m, 751 m, 673
4.2. Solvent and materials
w, 568 w, 453 w, 439 w, 429 w, 417 w, cmꢂ1; 1H NMR (CDCl3):
d
0.88
7.2 Hz, 3H, CH2CH3), 1.19e1.36 (m, 15H, C(CH3)3,
CH2(CH2)3CH3), 1.54e1.62 (m, 2H, ArCH2CH2CH2), 2.42e2.46 (m,
2H, ArCH2CH2), 7.11e7.18 (m, 2H, ArH), 7.24e7.31 (m, 2H, ArH); 13
NMR (CDCl3): 14.1, 22.6, 27.5, 29.4, 31.5, 31.6, 33.7, 44.8, 124.5,
(t,
J
¼
Toluene, p-xylene, and mesitylene were distilled from Na/
benzophenone ketyl. RuH2(CO)(PPh3)3 (1) [13a], 1-[2-(dimethyla-
mino)phenyl]-2,2-dimethyl-1-propaone (2a) [5], 2,2-dimethyl-1-
[2-(methylamino)phenyl]-1-propanone (2b) [5], and 2,2-dimethyl-
1-[2-(1-pyrro-lidinyl)phenyl]-1-propanone (2d) [5] were prepared
by literature methods.
C
d
124.8, 128.5, 129.5, 139.0, 140.6, 215.1; HRMS (ESI) calcd for
[M þ Na]þ (C17H26NaO) 269.1881. Found 269.1869.
Acknowledgments
4.3. Typical procedures
This work was partially supported by the Grants-in-Aid for
Scientific Research from the Japan Society for the Promotion of
Science and the Ministry of Education, Culture, Sports, Science, and
Technology (MEXT) of Japan. This work was partially supported by
the Asahi Glass Foundation. T. Koreeda acknowledges a Research
Fellowships of JSPS for Young Scientists (5293).
4.3.1. Typical procedure for ruthenium-catalyzed deamination of o-
acylanilines: ruthenium-catalyzed deamination of 2a
To a 10 mL Schlenk tube were added in a glove box o-acylaniline
2a (41.5 mg, 0.2 mmol), RuH2(CO)(PPh3)3 (1) (36.7 mg, 0.04 mmol),
and p-xylene (0.3 mL), and the mixture was heated for 24 h in an oil
bath whose temperature adjusted to 140 ꢀC. After the reaction, n-
eicosane (0.1 mmol) was added as an internal standard to the
resulting mixture, which was then analyzed by GC. Column chro-
matography of the crude material (100:1 hexane/EtOAc) afforded
3a as colorless oil (28.4 mg, 87%).
Appendix A. Supplementary data
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.jorganchem.2013.06.001.
4.3.2. Typical procedure for ruthenium-catalyzed alkylation of o-
acylanilines with olefins: ruthenium-catalyzed deamination/
alkylation of 2a with 4a
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975;
To a 10 mL Schlenk tube were added in a glove box o-acylaniline
2a (41.5 mg, 0.2 mmol), RuH2(CO)(PPh3)3 (1) (36.7 mg, 0.04 mmol),
olefin 4a (0.045 mL, 0.3 mmol), and p-xylene (0.3 mL), and the
mixture was heated for 24 h in an oil bath whose temperature
adjusted to 140 ꢀC. After the reaction, n-eicosane (0.1 mmol) was
added as an internal standard to the resulting mixture, which was
then analyzed by GC. Column chromatography of the crude mate-
rial (100:1 hexane/EtOAc) afforded 5a as pale yellow oil (43.1 mg,
82%).
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4.4. Analytical data
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1276 m,1249 s,1185 m,1139 w,1084 w,1044 w, 996 w, 963 s, 942 m,

152
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