Cp?CoIII-catalyzed formal [4+2] cycloaddition of benzamides to afford quinazolinone derivatives

Article abstract of DOI:10.1039/c9cc07173c

A Cp?Co^III-catalyzed arene C-H bond amidation/annulation of benzamides was developed to afford quinazolinone derivatives in one-pot with high yields and broad substrate scope. This method could be applied to the synthesis of quinazolinone drugs and late-stage modification of natural products.

Full text of DOI:10.1039/c9cc07173c

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Cp*CoIII-catalyzed formal [4+2] cycloaddition of
benzamides to afford quinazolinone derivatives†
Cite this: Chem. Commun., 2019,
55, 13840
Jingshu Yang,‡a Xiao Hu,‡a Zijie Liu,bc Xueyuan Li,a Yi Dong
*
and Gang Liu
*
bc
a
Received 13th September 2019,
Accepted 22nd October 2019
DOI: 10.1039/c9cc07173c
rsc.li/chemcomm
A Cp*CoIII-catalyzed arene C–H bond amidation/annulation of
benzamides was developed to afford quinazolinone derivatives in
one-pot with high yields and broad substrate scope. This method
could be applied to the synthesis of quinazolinone drugs and late-
stage modification of natural products.
As a very important drug fragment, 2-alkyl-modified quinazolinone
is commonly found in many classic drug structures,1 which has
led to increasing interest in its efficient synthesis (Fig. 1).2
Although some traditional methods have been reported, most of
these methods suffer from limited substrate scope, such as
requiring the use of ortho-functionalized anilines and ortho-pre-
activation (halogenation) of benzoic acid derivatives, or using
harsh reaction conditions or multiple-step sequences (Fig. 2A
and B).3 Thus, it is strongly desired to develop a convenient, easily
applied, and highly efficient approach to build 2-alkyl-substituted
quinazolinone scaffolds from simple starting materials to allow for
synthesis of diverse quinazolinone drugs.
Fig. 1 Selected 2-alkyl modified quinazolinone scaffold drugs.
C–H activation is a synthetic strategy in organic synthesis
that is straightforward, step economical, and highly efficient.
More importantly, it is suitable for late-stage modification of
complex natural product analogs or drug derivatives.4 Recently,
Li, Zhu, and Glorius developed a C–H amidation/annulation of
imidates to afford 4-ethoxyquinazoline scaffolds followed by
acidification to give 2-alkyl-modified quinazolinone, but this
indirect C–H activation method has two separate steps (Fig. 2C).5
Clearly, it is challenging for C–H amidation6/annulation of
a School of Pharmaceutical Sciences, Tsinghua University, Haidian District,
Beijing 100084, China. E-mail: gangliu27@tsinghua.edu.cn
b State Key Laboratory of Bioactive Substance and Function of Natural Medicines,
Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking
Union Medical College, Beijing 100050, China. E-mail: dongyi@imm.ac.cn
c Beijing Key Laboratory of Active Substances Discovery and Druggability
Evaluation, Institute of Materia Medica, Chinese Academy of Medical Sciences
and Peking Union Medical College, Beijing 100050, China
Fig. 2 Synthetic methods to prepare quinazolinone.
benzamide to build a 2-alkyl-modified quinazolinone skeleton
in one step.7 Very recently, C–H amidation/annulation of a
N-OMe-substituted benzamide catalyzed by an expensive
RhIII-catalyst was reported by Cheng,8 but this only produced
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9cc07173c
‡ These authors contributed equally.
13840 | Chem. Commun., 2019, 55, 13840--13843
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Table 1 Cp*CoIII-catalyzed selective ortho C–H amidation of benzamidea
2-aryl-modified quinazolinones and the expensive Rh-catalyst is
not economic for industrial synthesis. Moreover, this method is
not applicable to strongly electron-deficient benzamide substrates
and N-alkyl-substituted amides, which limits its application in the
synthesis of a diverse range of quinazolinone drugs (Fig. 2D).
Over the past few decades, investigation of the first-row
transition-metal-catalyzed reactions has been a hot research
topic because these metals are cheap and have high natural
abundance.9 In recent years, the Cp*CoIII complex has been
widely employed in C–H activation as a powerful and inexpen-
sive catalyst.10 However, the excellent yield (e.g., 495%) or good
applicable ability to substrates with strong electron-withdrawing
groups (e.g., NO2) remains challenging for Cp*CoIII-catalyzed
C–H activation. Here, we report on a Cp*CoIII-catalyzed arene
C–H amidation/annulation using 1,4,2-dioxazol-5-one as an
amidating reagent to efficiently build a 2-alkyl-modified quina-
zolinone skeleton with broad substrate scope and excellent
yield.11 Importantly, this method is very convenient for the
synthesis of quinazolinone drugs and late-stage modification of
benzamide natural product derivatives.
Entry
R
Ag salt
Solvent
3/30, Yieldb/%
1
2
3
4
5
6
7
8
H
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgBF4
AgOAc
AgOTf
AgNTf2
—
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DMF
Toluene
1,4-Dioxane
DCE
3aa/3aa0, 0/12
3ba/3ba0, 0/0
3ca/3ca0, 0/63
3da/3da0, 37/0
3ea/3ea0, 50/0
3ea/3ea0, 15/0
3ea/3ea0, 13/0
3ea/3ea0, 67/0
3ea/3ea0, 99/0
3ea/3ea0, 18/0
3ea/3ea0, 0/0
3ea/3ea0, 28/0
3ea/3ea0, 13/0
3ea/3ea0, 17/0
3ea/3ea0, 19/0
3ea/3ea0, 76/0
Ms
tBu
Me
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
9
10
11
12
13
14c
15d
16e
DCE
DCE
a
Reaction conditions: 1 (0.2 mmol), 2a (0.24 mmol), [Cp*Co(CO)I2]
Initially, this amide-directed arene C–H amidation/annula-
tion to afford quinazolinones was investigated using free amino
benzamide and 3-methyl-1,4,2-dioxazol-5-one in the presence
of 5 mol% [Cp*Co(CO)I2], 10 mol% AgSbF6, and 1.0 equivalent
of Zn(OAc)2 in DCE at 120 1C overnight. Unfortunately only the
C–H amidation product was isolated in 12% yield, and no desired
annulation product was obtained (entry 1). Testing with different
N-auxiliary groups showed that Me and OMe had excellent selec-
tivities and produced the desired quinazolinones in 37% and 50%
yields, respectively (entries 4 and 5). Considering the ease of
removal of OMe and diverse derivatization of quinazolinone, we
chose it as the optimum N-protected group. Next, the effect of
silver salts on the reaction was investigated, and AgNTf2 gave an
excellent yield of the desired quinazolinone product (99% yield,
entry 9). When the reaction was carried out in DMF, no reaction
occurred. In toluene or 1,4-dioxane, only the C–H amidation
product was obtained in low yield. The use of NaOAc or
Cu(OAc)2 instead of Zn(OAc)2 resulted in a sharp decrease in the
yield of the desired product, which is probably because Zn(OAc)2
played the powerful role of a Lewis acid which would cooperate
with Cp*CoIII to improve the electrophilicity of the carbonyl group
and facilitate the nucleophilic addition.12 Decreasing the reaction
temperature to 100 1C gave an isolated yield of 76%, which showed
that a temperature of 120 1C was necessary for this C–H amidation/
annulation (Table 1).
(5.0 mol%), Ag salt (10 mol%), Zn(OAc)2 (1.0 equivalent), solvent (2.0 mL),
b
c
d
120 1C. Isolated yield. NaOAc instead of Zn(OAc)2. Cu(OAc)2 instead
e
of Zn(OAc)2. 100 1C instead of 120 1C. DCE = dichloroethane, Ms =
t
methanesulfonyl, and Bu = tert-butyl.
Scheme 1 Amide substrate scope and isolated yields. Reaction condi-
tions: 1 (0.2 mmol), 2 (0.24 mmol), [Cp*Co(CO)I2] (5.0 mol%), AgNTf2
(10 mol%), Zn(OAc)2 (1.0 equivalent), DCE (2.0 mL), and 120 1C. a 10 mol%
The aryl amide scope for this Cp*CoIII-catalyzed formal [4+2]
cycloaddition was investigated under the optimized conditions.
The Cp*CoIII-catalyzed C–H amidation/annulation of N-OMe-
substituted benzamide could support gram-scale synthesis with
[Cp*Co(CO)I2], 20 mol% AgNTf2, Zn(OAc)2 (3.0 equivalents), and
(2.0 equivalents) were used.
2
a good yield (Scheme 1). Other alkyls, such as methyl-, n-butyl-, a high catalytic performance. Excellent reaction performance
and benzyl-substituted benzamides, could also be smoothly was achieved for benzamides substituted with strong electron-
converted into the target quinazolinone products. Aryl amides withdrawing groups (e.g., NO2 or CF3), which demonstrates that
substituted with electron-donating or -withdrawing groups this C–H activation method has good substrate scope and
were effective for this C–H amidation/annulation and gave the application in quinazolinone synthesis. It is worth noting
corresponding quinazolinone derivatives in good to excellent that this Cp*CoIII-catalyzed C–H amidation/annulation showed
yields, which implied that this Cp*CoIII catalytic system showed excellent site-selectivity in the high catalytic activity system.
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For meta-substituted arylamides, the reaction showed excellent be transformed into the corresponding quinazolinone analog 47
site-selectivity for the C–H bond with little steric hindrance, and in excellent yield by this C–H activation method.
no C–H activation products from other C–H bonds or di-activation
To explore the mechanism of this C–H amidation/annulation,
products were detected by LC-MS. When para-substituted aryl- hydrogen/deuterium (H/D) exchange and kinetic isotope effect
amides were employed for this reaction, the mono-activated product (KIE) experiments were conducted. The deuterium exchange
was obtained in high yield with high selectivity, and only a small experiments showed slight H/D exchange at the ortho-position
amount of the di-activated product was obtained. This reaction also of the amide group (10% D) and no exchange at any other
efficiently generated the desired quinazolinones from the substrates positions (Scheme 3A). This implies that the phenyl C(sp2)–H
with multiple substituents. Other aryl amides, such as naphthamide activation is irreversible. The intermolecular KIE experiment
or benzo[d]oxazole amide, could be used to synthesize the corres- gave a relatively small value (kH/D = 1.2), indicating that the
ponding quinazolinones. Except for 3-methyl-1,4,2-dioxazol-5-one, rate-determining process was likely not the C(sp2)–H bond
other 1,4,2-dioxazol-5-ones substituted with primary- and secondary- cleavage, but the subsequent steps possibly (Scheme 3B). In fact,
alkyl, or aryl could be utilized by this method to afford the Cp*CoIII catalysts could significantly promote some C–H activa-
corresponding quinazolinones in good yields, but tertiary-alkyl (e.g. tion reactions which were already set up by Cp*RhIII catalysts,16
tBu) and alkenyl 1,4,2-dioxazol-5-one did not work.
which might be related to the large difference in the electro-
Importantly, this Cp*CoIII-catalyzed arene C–H functionaliza- negativity between Co and Rh.17 This might be the reason why
tion method could be utilized in derivatization of the quinazoline the C–H activation step is not the rate-determining process in
skeleton, synthesis of quinazolinone drugs or natural products, some Co-catalyzed C–H activation reactions.
and late-stage modification of natural product derivatives. The
On the basis of our experimental results, a mechanism for this
OMe group could be removed by Pd/C-catalytic hydrogenation to arene C(sp2)–H amidation/annulation is proposed in Scheme 3C.
give free amino quinazolinone analog 35 (Scheme 2A), which First, the active cobalt catalyst cationic [Cp*CoIIII] is generated in
could undergo further functionalization to conveniently afford the the presence of [Cp*Co(CO)I2] and AgNTf2 in situ. This coordinates
natural product schizocommunin 36 and quinazolinone drug with 1a and undergoes concerted metalation–deprotonation to give
diproqualone 37. Similarly, demethoxy quinazolinone 39 could cobaltacycle I. Subsequent coordination with 2a gives intermediate
be transformed into an antimetabolite drug 41 (Raltitrexed)13 and II, followed by intramolecular migratory insertion to generate the
a quinazoline skeleton inhibitor of the bacterial cell division CoIII-amido species III with CO2 extrusion. Finally, protonation
protein FtsZ 38.14 Deprotection of quinazolinone 28 could afford regenerates the [Cp*CoIII] catalyst for a new catalytic cycle, and
compound 42 in one step, followed by a Mitsunobu reaction to simultaneously results in the synthesis of the arene C(sp2)–H
give tri-cyclic deoxyvasicinone 43, which is a key intermediate for amidation product 3ea0, which undergoes intramolecular dehydra-
the synthesis of the quinazolinone structural drug (ꢀ)-vasicinone tion to give the desired quinazolinone product 3ea.
44.15 In addition, the natural product estrone derivative 46 could
In summary, an arene C–H amidation/annulation with a
cobalt catalyst was developed to prepare 2-alkyl-substituted
quinazolinones. This method is attractive because it has high
yield and broad substrate scope. In addition, it allows for the
convenient synthesis of quinazolinone scaffold natural products
or drugs and late-stage modification of complex molecular
Scheme 2 Synthetic application of the Cp*CoIII-catalyzed C–H activation
method.
Scheme 3 Mechanism studies.
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and development.
We gratefully acknowledge the financial support from the
National Natural Science Foundation of China (81773575 and
81703329) and the Non-profit Central Research Institute of
Chinese Academy of Medical Sciences (2019-RC-HL-008).
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