Ruthenium-catalyzed: Ortho -selective CAr-H amination of heteroaryl arenes with di- tert -butyldiaziridinone

Article abstract of DOI:10.1039/c9cc02499a

Application of an oxidative amination reagent (di-tert-butyldiaziridinone) to the Ru₃(CO)₁₂-catalyzed ortho-selective C_Ar-H amination reaction is described. This strategy shows good functional group compatibility with vari

Full text of DOI:10.1039/c9cc02499a

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DOI: 10.1039/C9CC02499A
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Ruthenium-catalyzed ortho-selective C H amination of
Ar
heteroaryl arenes with di-tert-butyldiaziridinone
Received 00th January 20xx,
Accepted 00th January 20xx
a‡
b‡
a
a
a
a
Xue-Ya Gou, Yuke Li, Xin-Gang Wang, Hong-Chao Liu, Bo-Sheng Zhang, Jia-Hui Zhao, Zhao-
a
a
Zhao Zhou, and Yong-Min Liang*
DOI: 10.1039/x0xx00000x
www.rsc.org/
a) Typical amino source for direct C-H amination
An oxidative amination reagent (di-tert-butyldiaziridinone)
applied to the Ru (CO)12-catalyzed ortho-selective CArH amination
DG
DG
DG
3
R1 Pd,Rh,Ir,Ru
Pd,Rh,Ir,Ru
base
R1
H
N
X N
reaction is described. This strategy shows good functional group
compatibility with various phenyl-substituted N-heterocycles,
including biologically active substrates, thus providing a synthetic
potential of this methodology. Mechanistic studies showed that
the reaction process involves an octahedral ruthenium species,
and the carbon monoxide ligand plays a crucial role in the CH
activation.
R2
oxidant
R2
NR1R2
(X=Cl, OR, etc.)
b) This work: direct C-H amination with di-tert-butyldiaziridinone
DG
O
DG
DG
NH2
N
N
NH
t-Bu
t-Bu
t-Bu
R
CO
N
N
N
oxidant free
N
N
S
N
Anilines are ubiquitous building blocks that are widely
employed in synthetic intermediates, natural products,
pharmaceutical agents, and materials science, according to
N
Ru
novel amination reagent
direct C-N bond formation
CO
DG
=
1
N
N
N
O
N
functional groups compatibility
the Retail’s 2016 Top 200 medicines, they exist in the forms of
probable active catalyst
2
Scheme 1 Transition-metal-catalyzed C-H bond amination
1
6 active moieties. Devising improved methods for the high-
3
efficiency construction of CN bonds has been recognized as a
9
particularly important challenge. As one of the transition-
To date, palladium has been the most studied metal in
metal-catalyzed cross coupling reactions between aryl- or transition-metal-catalyzed amination. However, ruthenium is
1
0
alkenyl-(pseudo)halides and nucleophilic reagents, the one-third the cost ($243/mol) of palladium ($879/mol),
4
BuchwaldHartwig
stoichiometric amounts of halide salt by-products. Direct CH
reaction
inevitably
generates showing an evident economic superiority. After Lewis group
1
1
12
pioneered Ru-catalyzed CH activation, Ackermann,
bond amination does not require prefunctionalized arenes, so Dixneuf, Szostak,14 and others have greatly furthered its
it is a highly desirable pathway. Several types of amination progress, especially for the ortho-CH activation of
reagents have been employed in this process, distinguished (hetero)arene. Despite some historical bias regarding the para-
13
5
with the nucleophilic amine source, electrophilic amino substitution within pharmaceutical chemistry, the ortho-CArH
sources without an additional oxidant predominated in terms activation process can expand the chemical space via
of high efficiency (Scheme 1a). In addition, organic azides is distorting planar structures, which makes it superior to the
6
7
15
also an importantly benign amine source. These considerations para and meta ones. However, the ruthenium-catalyzed ortho-
8
led us to envision whether di-tert-butyldiaziridinone, with a CH bond activation has been almost confined to the
1
6
highly strained structure, could act as an amination reagent in introduction of aryl, alkenyl, or alkyl groups, and direct CH
2
the absence of an additional oxidant for direct sp CH amination remains largely unexplored.
1
7
amination.
In 2013, Yu and co-workers first reported an
intermolecular C–H amination with an electrophilic amine
source enabled by ruthenium(II) catalysis. The resulting
amination products are tertiary amines and cannot be
converted to secondary amines in one step via CH
functionalization, and it is also difficult to directly produce
ortho-selective amination products. Therefore, developing a
a. State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou
7
30000, P.R. China. *E-mail: liangym@lzu.edu.cn
b.
Department of Chemistry and Centre for Scientific Modeling and Computation,
Chinese University of Hong Kong, Shatin, Hong Kong, China.
These authors contributed equally.
‡
†
Electronic Supplementary Information (ESI) available: Details on the experimental novel, Ru-catalyzed, chemo-selective amination method, the
procedure, characterization data of all compounds. CCDC of single crystal X-ray
data of compounds:1892347 (3g),1904937 (3m). See DOI: 10.1039/x0xx00000x
products of which contain a naked NH bond, is extremely
This journal is © The Royal Society of Chemistry 20xx
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Journal Name
3
(CO)12-catalyzed electron-donating and electron-drawing groups VaietwtAhrteiclepOanrliane-
challenging. Herein, we have achieved a Ru
ortho-selective CArH amination by employing di-tert- position could produce the mono-aminaDteOdI: 1p0r.o10d3u9c/Cts9C3Cb0−234o99inA
butyldiaziridinone and further conversion can provide good yields (16%−73%). Various synthetically useful functional
functionalized aniline derivatives (Scheme 1b), which groups, such as halogen, nitro, cyano, vinyl, formyl, and
could effectively expand the application and synthetic trifluoromethyl groups, on the phenyl ring were well tolerated.
potential of CH bond amination.
One notable case involved [1,1'-biphenyl]-4-ylmethanol as the
The initial study was carried out with 2-phenylpyridine 1a substrate, which was oxidized to formyl-substituted
and di-tert-butyldiaziridinone 2 catalyzed by the commonly phenylpyridine by 2, and then participated in this reaction. For
used Ru(II) catalytic system ([RuCl (p-cymene)] /DCE). meta-substituted arylpyridines, amination produced on the
2 2
Unfortunately, the desired product 3a was not detected. A less sterically hindered side, furnishing the corresponding
screening of alternative ruthenium catalysts indicated that 3a products 3o3s in good yields. When one of the ortho-
was obtained in a 35% isolated yield when employing positions on the phenyl was occupied, amination on the other
3
Ru (CO)12. A further optimization of the solvents revealed that ortho-position occurred, and 3t was afforded in 45% yields. It
toluene was the most efficient one. Alternative bases were is worth mentioning that the disubstituted arylpyridine
also tested, and MesCOOK (potassium 2,4,6-trimethylbenate) derivate was also tolerant and provided a 44% yield of 3v.
was found to promote the complete conversion of 1a, the Substrates bearing different substituents on the pyridine
yield of 3a was increased to 72% in toluene at 140 °C for 24 h. moiety performed well, and all gave good results (3aa3ae).
No better results were achieved by adding other additives. Furthermore, pyrazole, oxazole, and thiazole were well-
Control experiments demonstrated that Ru (CO)12 was tolerant in the reaction and afforded the products with
3
essential for this reaction, and 3a was obtained in a 34% yield moderate yields (3af3ai). Importantly, the reaction was
in the absence of base, indicated a ruthenium assisted suitable for the C2-selectivity amination of indolic heterocycle
deprotonation of the ortho-CH bond, which is consistent with 3aj. The derivatives of 6-arylpurine were also compatible, and
†
the DFT calculation (see the ESI ).
gave corresponding amination products in 62% and 59% yields,
Under the optimized reaction conditions established, the respectively. In addition, some of the substrates were not
scope and functional group compatibilities of the 2- completely converted, increasing the amount of MesCOOK
arylheterocycles were investigated (Table 1). It was found that
could effectively improve the conversion and yield of the
reaction, such as 3b, 3c, 3h, and others.
Table 1 Substrate scope of pyridine and N-Heterocycle as the DGa
After that, a potential application of the amination product
in this reaction was made. The tert-butyl group of 3a could be
removed by treatment with hydrochloric acid (Scheme 2a),
providing efficient access to a variety of pyridine-substituted
aniline derivatives. N-nitrosoaniline was prepared in a 83%
yield from 3a in one step (Scheme 2b).
To gain a mechanistic insight of this reaction, a series of
control experiments were performed (Scheme 3). Firstly,
intermolecular competition reactions between differently
substituted aryl pyridines indicated that the electron-rich
substrate reacted preferentially (Scheme 3a). Secondly, the
standard reaction was uninhibited in the presence of radical
scavengers such as TEMPO, and this result implied that a
radical process may not be involved in this reaction (Scheme
Ru3(CO)12
O
DG
DG
MesCOOK
N
N
PhMe
t-Bu
t-Bu
40 C, Ar, 24 h
NH
1
t-Bu
3b-3al
1
b-1al
2
43% (57%)b
64%
3
3
3
3
b, R1 = Me, R2 = H,
3k, R1= Vinyl, R2 = H,
c, R1 = OMe, R2 = H, 60%(73%)b
3l, R1= CON(CH3)2, R2 = H, 49%
31%(16%)c
d, R1 = CF3, R2 = H, 72%
3m, R1= COH, R2 = H,
3n, R1= OTBS, R2 = H,
3o, R1= H, R2 = Me,
3p, R1= H, R2 = OMe,
3q, R1= H, R2 = CF3,
3r, R1= H, R2 = Cl,
N
e, R1 = F, R2 = H,
65%
63%
23%
35%(47%)b
H
N
3f, R1 = Cl, R2 = H,
g, R1= Br, R2 = H,
t-Bu
3
52%
70%
43%(54%)b
R2
3h, R1 = CN, R2 = H,
3i, R1 = NO2, R2 = H,
71%
62%(77%)b
54%(66%)b
R1
3
j, R1 = COCH3, R2 = H, 52%(65%)b
3s, R1= H, R2 = Br,
60%
N
N
N
N
H
N
H
H
N
MeO
N
t-Bu
NH
t-Bu
t-Bu
t-Bu
Br
Br
3
2
b). Thirdly, the use of a deuterated co-solvent D O led to H/D
3
u,58%
70%)b
3
t,45%
3v,44%
3aa,60%
3g
(
scrambling solely in the ortho-position, illustrating the
feasibility and reversibility of the CH metalation elementary
step and the tolerance of water in this transformation
R
N
N
O
N
S
3
ab, R = Me,
65%
R = OMe, 70%
R = COCH3, 75%
N
N
3ac
H
H
H
,
N
N
N
H
N
3ad
t-Bu
t-Bu
t-Bu
,
(Scheme 3c). Finally, the intermolecular competition
t-Bu 3ae, R = Cl,
70%
3
af,36%
experiment with
3ag,53%
3ah,49%
(
41%)b
t-Bu
t-Bu
N
H
N
HCl (1.0 mol/L) 1.2 mL
CH3CN, 100 °C, 24 h
N
t-Bu
NH
N
H
N
N
H
N
(a)
N
S
N
N
N
N
N
N
N
NH2
t-Bu
H
N
N
N
t-Bu
O
O
AcO
3
a (0.2 mmol)
4 62% yield
OAc
AcO
HCl (4.8 equiv.)
NaNO2 (1.0 equiv.)
3
ai,30%
3aj,31%
3al,54%
N
N
O
3ak,62%
3m
N
N
(
35%)b
(37%)b
(59%)b
H
(b)
N
a
t-Bu
CH3CN:H2O = 1/2
r.t, 12 h
Reaction conditions: 1 (0.2 mmol), 2 (2.0 equiv.), Ru
3
(CO)12 (5 mol %),
t-Bu
b
MesCOOK (2.0 equiv.), PhMe (2.0 mL), under Ar, 140 °C, 24 h. Isolated yields.
Using 3.0 equiv. of MesCOOK. c [1,1'-biphenyl]-4-ylmethanol as the substrate.
5 83% yield
3a (0.2 mmol)
2
| J. Name., 2012, 00, 1-3
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Scheme 2 Potential application of amination products
In summary, we have presented a Ru
3
(CO)12-catalyzed ortho-
View Article Online
DOI: 10.1039/C9CC02499A
selective CArH amination using di-tert-
a) Intermolecular competition between differently substitued 2-arylpyridine
CO
N
Ru3(CO)12
PhMe, Ar,
N
N
N
N
2
N
N
Ru
Ru3(CO)12 (5 mol %)
H
CO
[RuCl2(CO)3]2
H
N
N
140 °C, 48 h
MesCOOK (2.0 equiv.)
t-Bu
t-Bu
MesCOOK
20% yield
1a
2
2
3a
PhMe, 140 C, Ar, 24 h
A
PhMe, Ar, 140 °C, 24 h
58% yield
1a
OMe
CF3
OMe
CF3
3d
MesCOOK
1c
1d
A
2
2
3a
3c
0
.1 mmol
0.1 mmol
PhMe, Ar, 140 °C, 24 h
70% yield
3
c:3d = 1.6:1
[RuCl2(p-cymene)2]2
(
determined by GC-MS)
b) Radical trapping experiment
MesCOOK
1a
3a
15 mol % A
PhMe, CO, 140 °C, 24 h
O
N
N
MesCOOK
standard conditions
1a
3a
47% yield
H
N
N
N
PhMe, Ar, 140 °C, 24 h
47% yield
t-Bu
t-Bu
t-Bu
TEMPO (2.0 equiv.)
(
a) Ruthenium(II) intermediate A
(b) CO ligand
1a
2
3a
c) H/D exchange experiment
68% yield
Scheme 4 Ruthenium (II) intermediate A and CO ligand studies
O
3 12
Ru (CO) (5 mol %)
N
N
H
CO
MesCOOK (2.0 equiv.)
N
Ru3(CO)12
N
N
D/H
N
N
1a
t-Bu
t-Bu
D O
t-Bu
Ru
PhMe/
2
CO
3a
3a
(
1.8 mL/0.2 mL)
N
CO
Ru
140 C, Ar, 24 h
80%D
t-Bu
D
1a
1a
1a
2
N
N
[D]n-3a
d) KIE study
CO
CO
CO
N
N
N
N
Ru
CO
Ru
t-Bu
O
CO
N
Ru3(CO)12 (5 mol %)
MesCOOK (2.0 equiv.)
N
t-Bu
N
N
D
H
N
N
N
A
CO
N
N
t-Bu
t-Bu
t-Bu
Ru
D5/H5
PhMe, 140 C, Ar, 24 h
KH /KD = 1.5
4
H /D
+
O
4
N
N
t-BuNCO
C
t-Bu
t-Bu
CO
1a/[D]5-1a
2
3a/[D]4-3a
O
(TS2)
N
N
Scheme3 Mechanistic studies
t-Bu
O
t-Bu
t-Bu
2
pathyway c
(TS2)
N
t-Bu
N
t-BuNCO
pathyway a
N
N
N
CO
N
N
Ru
N
Ru
CO
1
1
a and [D
5 H D
]-1a showed a kinetic isotopic effect (KIE) of k /k =
pathyway b
t-Bu
O
B
t-Bu
.5, suggesting that the ortho-CH cleavage might be
E
kinetically relevant (Scheme 3d).
Scheme 5 Proposed mechanism
To further clarify the mechanism, the ruthenium (II)
intermediate A18 was isolated by mixing 1a with 1.0 equiv. of
Ru (CO)12 in PhMe at 140 °C for 48 h under argon. The
3
stoichiometric and catalytic reactions utilizing the
intermediate A worked well and produced 3a in 70% and 47%
yields (Scheme 4), respectively. This result demonstrated the
intermediate nature of the ruthenium (II) complex in this
butyldiaziridinone as an oxidative amination reagent. This
strategy gives an expedient approach to generate synthetically
useful, highly functionalized aniline derivatives. This method
exhibits an excellent functional group compatibility for various
phenyl-substituted N-heterocycles, including biologically active
substrates. Mechanistic studies revealed that an octahedral
ruthenium complex, as the probable active catalyst, is involved
in this reaction, and the carbon monoxide ligand plays an
important role in the CH activation.
catalytic cycle. On the other hand, using [RuCl
catalyst or [RuCl (p-cymene)] as the catalyst under CO
atmospheres could provide good results for the production of
a. This result indicated the importance of carbon monoxide
2 3 2
(CO) ] as the
2
2
3
Financial support was received from the National Natural
Science Foundation of China (21772075, 21532001).
and allowed us to understand valence variation of ruthenium
in the whole catalytic cycle. We speculate that the strong π-
acidic nature of CO as the ligand makes the ruthenium
1
4b, 19
complexes more electrophilic,
which might promote the Conflicts of interest
formation of the ruthenium (II) complex.
There are no conflicts to declare.
Based on mechanistic research detailed above and the
previous related literature, a plausible mechanism is proposed.
The ruthenium (II) intermediate A is formed through Ru
and 1a by CH activation step. After the coordination of A with
3
(CO)12
Notes and references
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1
2
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8
b, 8e
tert-butyl isocyanate
to form Ru-nitrene species C
(
pathway a). The migratory insertion20 of C leads to the
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2
1
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