Synthesis of dihydroquinolinones via iridium-catalyzed cascade C-H amidation and intramolecular aza-Michael addition

Article abstract of DOI:10.1039/C8CC09751H

An iridium-catalyzed annulation of chalcones with sulfonyl azides via cascade C-H amidation and intramolecular aza-Michael addition was developed, affording a variety of 2-aryl-2,3-dihydro-4-quinolones in moderate to good yields. This reaction features ea

Full text of DOI:10.1039/C8CC09751H

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
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DOI: 10.1039/C8CC09751H
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Synthesis of dihydroquinolinones via iridium-catalyzed
cascade C-H amidation and intramolecular aza-Michael
addition
Received 00th January 20xx,
Accepted 00th January 20xx
Changduo Pan,*a,b Zhenkun Yang,a Hao Xiong,b Jiangang Teng,b Yun Wanga,b and Jin-Tao Yu*b
DOI: 10.1039/x0xx00000x
www.rsc.org/
An iridium-catalyzed annulation of chalcones with sulfonyl azides vulnerable arylamines were used as essential substrates with
via cascade C-H amidation and intramolecular aza-Michael limited substrate scopes. As a result, more general, clean, and
addition was developed, affording a variety of 2-aryl-2,3-dihydro- efficient methods are required for the direct construction of 2-
4-quinolones in moderate to good yields. This reaction features aryl-2,3-dihydro-4-quinolone derivatives from readily available
with the easy operation, readily available starting materials, and starting materials.
the cascade formation of two C-N bonds in one pot.
Quinolones are a class of compounds with broad antibiotic
properties.1 In particular, 2-aryl-2,3-dihydro-4-quinolones,
namely the azaflavanones, have been received more concern
due to their unique bioactivities, such as antimalarial activity,
cytotoxic activity against a panel of human tumor cell lines and
potent cross-species microRNA inhibitors.2 Besides, they also
serve as key intermediates in the synthesis of many
biologically active natural products.3 Thus the synthesis of
quinolones from readily available starting materials is highly
desirable. Traditionally, the construction of 2,3-dihydro-4-
quinolone skeleton could be accessed via intermolecular Fries-
type rearrangement of aryl β-lactams catalyzed by Bronsted or
Scheme 1. Approaches for the synthesis of 2-aryl-2,3-dihydro-
4-quinolones.
Lewis acids,4 PPA-promoted intramolecular Friedel-Crafts
acylation of 3-(arylamino)propanoic acids or esters,5 Michael
addition of 2-alkenoylanilines in the presence of proper bases,6
Direct C-H amidation was proved to be convenient approach
and the palladium-catalyzed intermolecular cyclizations.7 In
for the C-N bond formation with high atom-economy.11 In
2012, Chang pioneered the direct C-H amidation employing
sulfonyl azides as the N-sources with gaseous nitrogen as a
clean by-product.12 Subsequently, Chang’s13 and other
groups14,15 deeply demonstrated the organic azides-involved
direct C-H amidation as the reliable and efficient method for
the construction of C-N bonds. Additionally, chalcones, which
can be conveniently synthesized from aryl aldehydes and 1-
arylethanones via Claisen-Schmidt condensation, are an
important class of compounds that exhibit a broad range of
biological activities in the area of anticancer, antidiabetic, anti-
HIV, and anti-inflammatory.16 The β-H activation or ortho-C−H
bond activation of chalcones were selectively achieved under
transition-metal catalyzed conditions.17 However, sequential
ortho-C−H bond activation and aza-Michael addition in one pot
has never been reported. In this paper, we aimed to
accomplish the annulation of chalcone with sulfonyl azide via
the
case
of
2-aryl-2,3-dihydroquinolin-4-ones,
the
condensation of o-aminoacetophenones and aryl aldehydes in
the presence of certain organocatalysis was frequently
employed (Scheme 1, eq 1).8 In addition, intramolecular aza-
Michael addition of o-aminochalcones was also utilized in the
successfully construction of this structure under the catalysis
of transition-metals9 or organocatalysts (Scheme 1, eq 2).10
However, throughout those above mentioned approaches,
either intermolecular or intramolecular reactions, odorous and
a.School of Chemical and Environmental Engineering, Jiangsu University of
Technology, Changzhou 213001, P. R. China
b.School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced
Catalytic Materials & Technology, Changzhou University, Changzhou 213164, P. R.
China
E-mail: panchangduo@jsut.edu.cn; yujintao@cczu.edu.cn
Electronic
Supplementary
Information
(ESI)
available].
See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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ortho-C−H bond amidation and then to fulfill the aza-Michael phenyls, were all well tolerated. Next, theVieswuAbrtsictlietOunelinnet
DOI: 10.1039/C8CC09751H
addition in one pot for the construction of 2-aryl-2,3-dihydro- influences on aryls adjacent to carbonyl of chalcones were
4-quinolones with high atom- and step-economical (Scheme 1, tested. Methyl, halo, and methoxycarbonyl at para-position of
eq 3).
phenyl all reacted smoothly to generate the products in good
yields (3la 3qa, 74-55% yields). The tolerance of halo produced
opportunities for further derivations (3ea 3ha 3ma 3pa 3ua).
-
Table 1. Screening the optimized reaction conditions.a
-
,
-
,
Specially, iodo remains innocent under this Ir-catalyzed
condition to produce 3pa in 55% yield. Notably, steric
hindrance had negative influence on this reaction, for
chalcones with ortho-substituents generated the products in
Entry
Catalyst
[Cp*RhCl2]2
[Ru(p-cymene)Cl2]2
[Cp*IrCl2]2
Additive
AgSbF6
AgSbF6
AgSbF6
AgNTf2
AgBF4
Solvent
DCE
Yield (%)b
trace
trace
26
lower yields (3ra
& 3sa). In order to investigate the selectivity
1
2
of this reaction, meta-substituted substrates 1t and 1u were
subjected to the reaction, leading to the corresponding
products in moderate yields with excellent regioselectivities
DCE
3
DCE
(3ta & 3ua). In addition, if the β-aryl was replaced by alkyl (1v),
4
[Cp*IrCl2]2
DCE
30
2-alkyl-2,3-dihydroquinolin-4(1H)-one (3va) could be obtained
in moderate yield. Other sulfonyl azides, such as
benzenesulfonyl azide, 4-methoxybenzenesulfonyl azide, 4-
chlorobenzenesulfonyl azide were also proved to be efficient
N-sources, leading to the corresponding dihydroquinolin-
5
[Cp*IrCl2]2
DCE
trace
38(49)b
0
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
6
[Cp*IrCl2]2
DCM
Toluene
MeCN
MeOH
DCM
7
[Cp*IrCl2]2
8
[Cp*IrCl2]2
trace
7
63c(77)d
4(1H)-ones in good to moderate yields (3ab-3ad).
9
[Cp*IrCl2]2
Figure 1. Scope of the Ir-catalyzed cascade amidation and aza-
Michael addition reactions a
10
[Cp*IrCl2]2
a
Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), catalyst (5
o
b
mol%), additive (20 mol%) in solvent (2 mL) at 100 C for 12 h. At
120 C. Adding HOAc (1 equiv), 120 C. Adding PivOH (1 equiv) ,
120 oC.
o
c
o
d
To achieve our goals, we started to screen the reaction
conditions for the cascade amidation and aza-Michael addition
of chalcone (1a) with tosyl azide (2a) using Rh(III) as the
catalyst and AgSbF6 as the additive (Table 1, Entry 1). However,
only trace amount of product was detected, even after we
switched the catalyst to Ru(II) (Table 1, Entry 2). To our delight,
the desired product 2-phenyl-1-tosyl-2,3-dihydroquinolin-
4(1H)-one (3aa) was obtained in 26% yield when catalyzed by
[Cp*IrCl2]2 (Table 1, Entry 3). Encouraged by this result, other
reaction parameters were then extensively investigated to
further optimize the reaction. For example, AgNTf2 was better
silver source than AgBF4 (Table 1, Entries 4 & 5). Other solvents,
such as DCM, toluene, acetonitrile, and methanol were tested,
and the results indicated that DCM was the best choice (Table
o
1, Entries 6-9). Elevate the temperature to 120 C resulted in
higher yield (Table 1, Entry 6). The yields increased remarkably
after adding one equivalent amount of acid. Product 3aa was
isolated in 77% yield in the presence of pivalic acid (Table 1,
Entry 10).
After the establishment of the optimized reaction conditions,
the substrates scope of this cascade amidation and aza-
Michael addition reaction was investigated as listed in Figure 1.
As expected, chalcones with different substituents on aryls
adjacent to alkenyl have little influence on the efficiency of
this reaction, leading to the corresponding 2-aryl-2,3-dihydro-
a
Reaction conditions: 1 (0.2 mmol), 2 (0.4 mmol), [Cp*IrCl2]2 (5
o
mol%), AgNTf2 (20 mol%), PivOH (1 equiv) in DCM (2 mL) at 120 C
for 12 h, isolated yields.
4-quinolone products in good yields (3aa−3ka, 85−65% yields).
Interestingly, if NaOAc was employed in the model reaction
instead of pivalic acid, only ortho-amidation occurred, no
cyclisation product was detected at all. Other chalcones with
Electron donating groups, such as methyl, tert-butyl, and
phenyl, or electron withdrawing groups, such as halo, nitro,
and methoxycarbonyl, at either meta- or para-position of
2 | J. Name., 2012, 00, 1-3
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different substituents all gave the amidation products in good
COMMUNICATION
According to the mechanistic experiments aVniedw AlirttieclreaOtnulirnee
to moderate yields in the presence of AgSbF6 as the silver reports,13,15 a possible mechanistic pathway is proposed in
DOI: 10.1039/C8CC09751H
source (Figure 2, 4a
-
4f). This result was similar to Chang’s.17f
Scheme 3. First, the treatment of a dimeric iridium species
with AgNTf2 and PivOH generates the active Ir(III) catalyst,
which induces the ortho-C−H bond cleavage of 1a to produce
Figure 2. Scope of the Ir-catalyzed cascade amidation and aza-
Michael addition reactions a
cyclometalated Ir(III) complex
coordination of the tosyl azide to
A
A
.
Subsequently, the
forms Ir-species . The
leads to intermediate with
the releasing of byproduct N2. Then, protodemetalation of
provides another Ir-coordinated intermediate Finally,
intramolecular nucleophilic 1,4-addition of gives compound
and regenerates the active Ir complex. Product 3aa was
B
C
following migratory insertion of
B
C
D
.
D
E
formed from E after enol–keto tautomerization.
a
Reaction conditions: 1 (0.2 mmol), 2a (0.4 mmol), [Cp*IrCl2]2 (5
o
mol%), AgSbF6 (20 mol%), NaOAc (1 equiv.) in DCE (2 mL) at 100 C
for 12 h, isolated yields.
Control experiments were conducted to investigate the
mechanism of this reaction as listed in Scheme 2. Product
3aa could be isolated in 89% yield from 4a catalyzed by
[Cp*IrCl2]2 in the presence of AgNTf2 (Scheme 2, eq a).
However, no product was formed in the absence of any
transition-metal catalysts (Scheme 2, eq b). The cyclisation
could occur under the catalysis of either [Cp*IrCl2]2 or AgNTf2,
while the yields were lower than under the catalysis of Ir-Ag
system (Scheme 2, eqs c & d vs eq a). These results indicated
that the amidation product 4a was the reaction intermediate
and metal-catalyst was essential for the aza-Michael addition
step. Besides, AgNTf2 may play important role in the
deprotonation process of 4a to form the sulfamide anion with
enhanced nucleophilicity for the following aza-Michael
addition.
Scheme 3. Proposed mechanism.
In summary, we have developed a cascade ortho-C-H
amidation and intramolecular aza-Michael addition with
chalcones and sulfonyl azides. A variety of 2-aryl-2,3-dihydro-
4-quinolones with different substituents on aryls were
obtained in moderate to good yields under standard
procedure. This reaction features with the easy operation,
readily available starting materials, and the cascade formation
of two C-N bonds in one pot. This procedure represents as an
effective tool for the convenient synthesis of pharmaceutically
promising heterocyclic compounds.
We thank the National Natural Science Foundation of China
(21602086 and 21672028), and Jiangsu Key Laboratory of
Advanced Catalytic Materials & Technology (BM2012110) for
financial supports. Wang thanks Postgraduate Research &
Practice Innovation Program of Jiangsu Province (SJCX18_1000)
for financial supports.
Notes and references
1
A. S. Wagman and M. P. Wentland, In Comprehensive
Medicinal Chemistry II; Taylor, J. B., Triggle, D. J., Eds.;
Elsevier: Amsterdam, 2006; Vol. 7, pp 567-596.
Scheme 2. Mechanism studies.
This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C8CC09751H
An iridium-catalyzed annulation of chalcones with sulfonyl azides via cascade C-H amidation and
aza-Michael addition is developed to provide 2-aryl-2,3-dihydro-4-quinolones.
O
O
[Cp*IrCl2]2, AgNTf2
PivOH, DCM, 120 o
R
Ar'SO2N3
Ar
R
C
N
Ar
H
SO2Ar'