Ruthenium-catalyzed C-H amination of aroylsilanes

Article abstract of DOI:10.1039/d1ob00935d

Acylsilane represents a valuable synthon in synthetic chemistry. We report on ruthenium(ii)-catalyzedortho-C-H amination of aroylsilanes to provide facile access to synthetically useful imidobenzoylsilanes and tosyl-amidobenzoylsilanes. The protocols, with broad substrate scope and excellent functional group tolerance, are enabled with the weak chelation-assistance of acylsilaneviaC-H cyclometallation.

Full text of DOI:10.1039/d1ob00935d

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Ruthenium-catalyzed C–H amination of
aroylsilanes†
Cite this: Org. Biomol. Chem., 2021,
9, 6313
1
a
a
a
a
a
a
b
Feifei Yu, Wenzhou Shen, Yaling Sun, Yilei Liao, Shuqi Jin, Xiunan Lu, Rui He,*
b
a
a,b
Liangjun Zhong,* Guofu Zhong
and Jian Zhang
*
Received 13th May 2021,
Accepted 24th June 2021
Acylsilane represents a valuable synthon in synthetic chemistry. We report on ruthenium(II)-catalyzed
ortho-C–H amination of aroylsilanes to provide facile access to synthetically useful imidobenzoylsilanes
and tosyl-amidobenzoylsilanes. The protocols, with broad substrate scope and excellent functional group
tolerance, are enabled with the weak chelation-assistance of acylsilane via C–H cyclometallation.
DOI: 10.1039/d1ob00935d
rsc.li/obc
N-tosyloxyphthalimide as the amino group source under
ruthenium catalysis (Scheme 1a). The Chang group demon-
Introduction
8
a
Widely occurring nitrogen-containing molecules in drugs, strated ruthenium-catalyzed C–H amination of aromatic
9
n
natural products and materials have attracted much attention amides and ketones using sulfonyl azides (Scheme 1b). The
for the development of efficient and mild amination reac- Sahoo group developed ortho-C–H amidation of aromatic
1
9h,i
tions. Transition metal-catalyzed C–N bond formation reac- ketones/sulfoximine using sulfonyl azides.
tion represents one of the most efficient methods using been reports concerning oxidative C–H amination employing
There have also
1
1a,b
simple raw chemicals. One powerful method is the catalytic free aryl/alkyl amines, demonstrated by the Chang
and
1
1c
cross-coupling reaction of aryl- or alkenyl (pseudo) halides Yu groups.
and amines represented by palladium-catalyzed Buchwald– Organosilicon molecules have been used as key building
Hartwig amination. Another more straightforward and atom blocks for the synthesis of drugs, natural products and
2
1
3
economical strategy is C–H amination which can directly materials. Acylsilanes are distinct from other carbonyl com-
functionalize a hydrocarbon bond to obviate the preinstalla- pounds in which silicone and oxygen atoms are directly bound
3
14
tion of a reactive group. There are also some other to the same carbon atom, and they are very versatile and can
4
approaches such as C–H insertion catalysis and photoredox be used in many organic transformations, such as reactions
catalysis via a single electron transfer pathway. In the past with various nucleophiles via a [1,2]-Brook rearrangement,
two decades, an appealing method with excellent site-selecti- siloxycarbene insertion by photochemical reactions, and
5
15
1
6
vity is the use of chelation-assisted C–H bond function-
6
alization proceeding by
a C–H cyclometallation event.
Arylamines are widely occurring and essential structural frag-
7
ments in pharmaceutical compounds, and a series of
transition-metal-catalyzed ortho-C–H aminations have been
developed with the assistance of suitable directing groups
7
c
such as amide, pyridyl, pyrimidyl or ketone groups, employ-
8
ing amino sources such as hydroxyl amine derivatives,
9
10
azides, N-fluoro-benzenesulfonimide (NFSI), free amines/
anilines and others. For example, the Ackermann group
1
1
12
reported
a C–H imidation of aromatic ketones using
a
College of Materials, Chemistry and Chemical Engineering, Hangzhou Normal
University, Hangzhou 311121, China. E-mail: zhangjian@hznu.edu.cn
b
Department of Stomatology, The Affiliated Hospital of Hangzhou Normal University,
Hangzhou Normal University, Hangzhou, 310015, China. E-mail: zymdxx@163.com,
heruiminli@sina.com
†
Electronic supplementary information (ESI) available: Experimental pro-
cedures, characterization data, and NMR spectra. See DOI: 10.1039/d1ob00935d
Scheme 1 Related Ru-catalyzed aromatic C–H amidation/alkenylation.
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a
transition-metal-catalyzed cross-coupling reactions via C–Si Table 1 Optimization of catalytic conditions using phthalimide
1
7
bond cleavage. Moreover, acylsilanes have been demon-
1
8
strated to be valuable in complex molecule synthesis. In the
past decade, aromatic C–H functionalization using acylsilane
as a directing group has attracted limited attention due to its
weak coordinating and steric bulk, as well as easy decompo-
1
9,20
sition properties.
Acylsilane-directed C–H alkenylation has
1
9a
19b
b
been realized by the Bolm group and us (Scheme 1c). The Entry
Ag salt
Additive
Solvent
Yield (%)
Bolm group also reported an iridium-catalyzed ortho-amin-
1
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
6
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
2
2
2
2
2
2
2
2
2
2
2
2
THF
8
6
0
0
2
0
ation of aroylsilane using azides. However, there is still high
demand to develop ruthenium-catalyzed C–H amination due
to the complement of both the substrate and reaction type,
which also provide new insight for exploring novel ligand-con-
trolled reactions. Moreover, inexpensive ruthenium complexes
may facilitate its potential application in synthetic chemistry.
Given the high synthetic value of acylsilanes and our continu-
2
3
4
5
6
7
8
9
1
6
6
6
6
6
6
Dioxane
MeOH
Toluene
DCE
9
DCM
15
<5
20
0
<5
22
41
77
0
<5
46
0
31
32
0
HCCl
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
3
AgBF
Ag CO
4
2
3
0
AgOAc
AgOTf
AgNTf
AgNTf
—
AgNTf
AgOTf
AgNTf
AgNTf
AgNTf
AgNTf
1
9b,c,21
ous interest in directed C–H functionalizatoin,
we report 11
12
13
14
2
on ruthenium-catalyzed aromatic C–H amination using azides
and N-hydroxyphthalimides (PhthN-OTs) to afford unique ami-
noaroylsilanes, which represent key intermediates in the syn- 15
2
Ag
Ag
—
2
O
O
2
2
c
d
e
f
16
17
18
19
20
Cu(OAc)
2
thesis of various heteroarenes such as indoles, quinolines, qui-
2
2
2
2
Ag
Ag
Ag
Ag
2
O
2
O
2
O
2
O
2
2
nazolines and diazepines (Scheme 1d).
g
a
Unless otherwise noted, the reactions were carried out using 1a
(5 mol%), Ag salt
20 mol%), and an additive (50 mol%), in a solvent (1 mL) at 90 °C for
Results and discussion
(
2 2
0.2 mmol), 2a (0.4 mmol), [Ru(p-cymene)Cl ]
(
1
At the outset, we examined the reaction between aroylsilane 1a
b
c
d
8 h. Isolated yields. 2.5 mol% [Ru(p-cymene)Cl ] used. RuCl was
2 2 3
e
and O-Ts N-hydroxyphthalimide 2a using the complex [Ru(p- used as the catalyst. [Ru(benzene)Cl2] was used as the catalyst.
2
f
g
[
RhCp*Cl
2 2 2 2
] was used as the catalyst. [IrCp*Cl ] was used as the
cymene)Cl ] as the catalyst and AgSbF as the additive with
2
2
6
catalyst.
the assistance of copper acetate (Table 1). Representative sol-
vents such as THF, dioxane, MeOH, toluene, DCE, DCM and
CHCl were examined, and DCM was demonstrated to be the
3
best one, producing 3aa in 15% yield (entries 1–7). Next, we of acetic acid also led to comparable results (entry 11). These
2
3
turned to examine different silver additives such as AgBF
4
,
results exhibited an acetate-assisted C–H metalation regime.
Ag CO , AgOAc, AgOTf and AgNTf , and AgNTf greatly Finally, the amount of NaOAc was investigated, and 40 mol%
2
3
2
2
improved the C–H amination reaction to afford 3aa in 41% of NaOAc was found to be the best (entries 12 and 13).
yield (entries 8–12). Interestingly, if Ag
O was used instead of Unfortunately, the reaction using lower catalyst loading only
copper acetate, the product yield increased to 77% (entry 13). led to 31% yield (entry 14). Different Ru-, Rh- and Ir-based cat-
Notably, both AgNTf and Ag
O are mandatory to the reaction alysts have been investigated, but none of them led to better
entries 14 and 15). However, the reaction using 2.5 mol% cata- results (entries 15–18).
lyst loading only led to 46% yield (entry 16). Some other Ru-,
With the two optimal conditions in hand, we turned to the
Rh- and Ir-based complexes have been examined, but none of evaluation of their utility by examining the influence of the
them led to satisfactory results (entries 17–20).
aromatic substitution pattern. To our satisfaction, a wide
2
2
2
(
If the optimal conditions from Table 1 were applied to the range of aroylsilanes 1 bearing various electron-donating and
reaction of aroylsilane 1a and tosylazide 4a, a trace amount of electron-withdrawing groups smoothly provided the ortho-C–H
product was detected (Table 2, entry 1). While the usage of amination products 3 with the assistance of weakly coordinat-
AgOAc remarkably promoted the reaction, the employment of ing acylsilane, although increased catalyst loading was
simple copper acetate further improved the reaction to afford required in some cases (Table 3). The robustness of the ruthe-
the corresponding tosylamide 5aa in 40% yield (entries 2 and nium(II)-catalyzed C–H amination protocol was reflected by the
3
). Some other silver salts such as Ag CO , AgOAc, AgOTf and good tolerance of valuable functional groups, including meth-
2 3
AgBF
4
were tested, but none of them could improve the reac- oxyl, fluoro, chloro, bromo, trifluoromethyl and trifluoro-
tion (entries 4–7). As increasing the amount of copper acetate methoxyl substituents (3ab–3am). These features demon-
failed to improve the reaction, some other simple carboxylate strated the protocol to be instrumental for further synthetic
salts such as NaOAc, KOAc and KOPiv were tried, and all of diversification of thus obtained imidobenzoylsilanes 3. Other
them remarkably promoted the transformation, with NaOAc benzoylsilanes bearing different silyl groups such as the tri-
showing the best results (entries 8–10). Interestingly, addition ethylsilyl group were also converted, leading to 3an in moder-
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a
a
Table 2 Optimization of reaction conditions using azides
Table 3 Substrate scope of amination using phthalimide
b
Entry
Ag salt
Additive
Ag
Base/acid
Yield (%)
1
2
3
4
5
6
7
AgSbF
AgSbF
AgSbF
6
2
O
—
—
—
—
—
—
—
NaOAc
KOAc
KOPiv
HOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
<5
27
40
<5
<5
<5
27
68
58
53
53
79
70
31
0
6
6
AgOAc
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Ag CO
2 3
AgOAc
AgOTf
AgBF
4
c
8
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
AgSbF
6
d
9
6
6
6
6
6
6
6
6
6
6
e
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
f
g
h
i
j
k
l
31
32
70
m
a
Unless otherwise noted, the reactions were carried out using 1a
(5 mol%), Ag salt
40 mol%), and an additive (100 mol%), in a solvent (1 mL) at 90 °C
2 2
(0.2 mmol), 4a (0.4 mmol), [Ru(p-cymene)Cl ]
(
b
c
d
for 12 he. Isolated yields. NaOAc (30 mol%) added. KOAc (30 mol%)
f
g
added. KOPiv (30 mol%) added. HOAc (30 mol%) added. NaOAc
h
i
(40 mol%) added. NaOAc (50 mol%) added. 2.5 mol% [Ru(p-
j
k
cymene)Cl
]
2 2
used. RuCl
3
was used as the catalyst. [Ru(benzene)Cl
]
2 2
a
l
Reaction conditions: 1 (0.2 mmol), 2a (0.4 mmol), [Ru(p-cymene)Cl
(5 mol%), AgNTf (20 mol%), and Ag O (50 mol%), in dichloro-
methane (1 mL) at 90 °C for 18 h. The yields indicated are isolated
2 2
]
was used as the catalyst. [RhCp*Cl
]
2 2
was used as the catalyst.
m
2
2
[
2 2
IrCp*Cl ] was used as the catalyst.
b
c
yields. [Ru(p-cymene)Cl
2 2 2
] (10 mol%) was used for 24 h. Cu(OAc)
was used instead of Ag O for 24 h.
2
ate yield using Cu(OAc) instead. Unfortunately, heterocycles
2
such as thiophene showed no reactivity under the catalytic
conditions.
observed, thereby showing a reversible five-membered C–H
Next, the substrate scope of C–H amination using azide was cyclometallation (Scheme 2a). However, if aroylsilane 1a
investigated (Table 4). Aroylsilanes bearing various para- and reacted with 2a under cond. A in the presence of D O, 79%
meta-substituents at the aromatic core reacted well with azide ortho-deuterium incorporation was observed in recovered 1a-d,
a to deliver the corresponding tosyl amides in moderate to as well as 6% deuterium incorporation into the product 3aa,
2
4
good yields, regardless of their electron-donating or electron- showing that the C–H activation is more competitive than the
withdrawing properties (53%–79% yields for 5ab–5an). The amination process (Scheme 2b). Kinetic isotope effect (KIE)
utility of this protocol was demonstrated by the tolerance of a experiments were performed to demonstrate the ortho-C–H
2
4
wide range of functionalities such as alkyl, aryl, methoxyl, activation to be the rate-determining step (Scheme 2c).
fluoro, chloro, bromo, trifluoromethyl and trifluoromethoxyl Moreover, an intermolecular competition experiment of
substituents. Notably, a benzoylsilane bearing meta-f substitu- aroylsilanes 1x and 1y revealed the electron-rich one to be
ent reacted well to afford para-C–H amination with excellent more reactive, which can be explained by a base-assisted
regio-selectivity (5am). Interestingly, although a methylthio internal electrophilic substitution-type (BIES) mechanism
2
5
substituted substrate led to decreased reactivity presumably (Scheme 2d).
due to strong S-coordination to the metal center, its sulfone
derivative delivered the desired product in 60% yield (5ao and
When substrate 1a was subjected to Cond. B containing
2
O with or without azide 4a, complete D% incorporation in
D
5
ap). Reaction of substrates with bulkier silyl groups such as recovered 1a–d and significant ortho H/D exchange in 3aa also
triethylsilyl (TES) resulted in the aniline product 5aq in 60% implied a very fast and reversible cyclometallation event
yield. (Scheme 3a and b). KIE experiments showed that C–H acti-
After that, some control experiments were performed to vation was not included in the rate-determining step
2
4
gain mechanism insights. If aroylsilane 1a was subjected to C– (Scheme 3c). A competition experiment of aroylsilanes 1x
H amination under Cond. A with D O in the absence of an and 1y also demonstrated the electron-rich one to be converted
2
amination reagent, 69% ortho-deuterium incorporation was more easily (Scheme 3d).
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a
Table 4 Substrate scope of amination using azide
Scheme 3 Deuterium-labelling/competition experiments (Cond. B).
a
Reaction conditions: 1 (0.2 mmol), 4 (0.4 mmol), [Ru(p-cymene)Cl
(40 mol%), Cu(OAc) (1.0 equiv.), and NaOAc
40 mol%), in dichloromethane (1 mL) at 90 °C for 12 h. The yields
2 2
]
(5 mol%), AgSbF
6
2
(
indicated are isolated yields.
Scheme 4 Investigation of differently substituted O-arylsufonyl
N-hydroxyphthalimides.
8
a
treatment with hydrazine to provide free aniline 6 in 52%
yield with the acylsilane motif intact (eqn (1)). Schmidt reac-
tion of alkyl azide with acyl silanes 3aa and 5aa successfully
affords amides 7 and 8 in good yields (eqn (2)). Treatment of
acylsilane 5aa with KF gives the corresponding benzaldehyde 9
in 79% isolated yield (eqn (3)). The successful gram-scale syn-
Scheme 2 Deuterium-labelling/competition experiments (Cond. A).
2
6
Substituents on the aromatic moiety attached to sulfone of thesis of 5aa showed the robustness of the protocol (eqn (4)).
imidating reagents 2 were investigated under Cond. A, Based on these experimental results and previous reports,
3
showing that the OTs are the best leaving group (Scheme 4). plausible mechanisms are illustrated in Scheme 5. The ruthe-
Notably, the phthalimide group can be readily removed by nium(II)-catalyzed C–H nitrogenation commenced via a revers-
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Acknowledgements
We gratefully acknowledge the National Natural Science
Foundation of China (NSFC) (21672048 and 81570989),
Natural Science Foundation of Zhejiang Province (ZJNSF)
(LY19B020006), Major Project of Hangzhou Health Science
and Technology Plan (Z20200046), and Key Subject of
Stomatology in Hangzhou for financial support.
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