Copper-catalyzed cascade addition/cyclization: Highly efficient access to phosphonylated quinoline-2,4(1H,3H)-diones

Article abstract of DOI:10.1039/c5ob00617a

A novel and facile Cu-catalyzed addition/cyclization cascade of o-cyanoarylacrylamide was developed. The process exhibits significant functional group tolerance, and provides an efficient and straightforward pathway for the synthesis of various phosphonyl

Full text of DOI:10.1039/c5ob00617a

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Copper-Catalyzed Cascade Addition/Cyclization:
Highly Efficient Access to Phosphonylated Quinoline-
2,4(1H,3H)-diones
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
Ya-Min Li,* Shi-Sheng Wang, Fuchao Yu, Yuehai Shen, Kwen-Jen Chang
DOI: 10.1039/x0xx00000x
www.rsc.org/
A novel and facile Cu-catalyzed addition/cyclization cascade including Pd(II),12 Rh(I)13 and Ni(II).14 Another type of this
of -cyanoarylacrylamide was developed. The process transformation is radical addition. In general, radical additions to
o
exhibits significant functional group tolerance, and provides polar nitrile groups are not efficient because highly unstable iminyl
an efficient and straightforward pathway for the synthesis radicals are generated.15 Nonetheless, this radical addition might be
of various phosphonylated quinoline-2,4(1H,3H)-diones.
successful if the unstable iminyl radical intermediate can be
effectively trapped.16 A number of metal reagents were successfully
employed for the radical addition of nitrile. However, most of them
Organophosphorus compounds can be found in a wide range of
biochemistry, medicinal chemistry, photoelectric materials, catalysis
and organic synthesis.1 In light of their importance, the development
of efficient C − P bond-forming method for the construction of
phosphorus compounds is still a research focus up to now. In general,
C−P bond formation relies on several classic reactions,2 for example,
electrophilic phosphor reagents such as R2P(O)Cl with carbon
nucleophile,2a Michaelis–Arbuzov reaction,2b,2c and addition of
phosphines to carbon–carbon multiple bonds via radical or ionic
pathways.2d Alone with the rapid development of organometallic
chemistry, transition-metal-catalyzed coupling reactions3 and alkene,
alkyne functionalization4 were developed as powerful strategies for
C–P bond formation. However, most studies in this field focused on
classic one-bond-forming reactions, very few P-containing cascade
reactions have been reported,4e–j which can offer more
environmentally benign and atom-economical processes. Therefore,
the development of new transition-metal-catalyzed cascade reactions
to build the C–P bond is highly desirable.
are the early transition metal complexes such as titanium16a-c
,
samarium16d,e and manganese.16f Herein, we describe a novel Cu-
catalyzed cascade addition/cyclization reaction, where the
cyclization was accomplished by an intramolecular addition of the
carbon radical to the nitrile (Scheme 1). This transformation
provides an efficient protocol for the synthesis of valuable
phosphonylated quinoline-2,4(1H,3H)-diones.
Quinoline-2,4-dione derivatives are a highly valuable class of
heterocyclic compounds with remarkable biological activities such
as antiplatelet, antibiotics, and herbicidal activities.17 Therefore, the
development of a sustainable and atom-economic method for the
synthesis of quinoline-2,4-dione derivatives is in demand.
The nitrile group is widely used in synthetic organic chemistry.
For example, addition reactions to nitriles provided great
opportunities for the synthesis of ketones. This addition reaction can
be classified into two major types depending on the mechanism. The
reaction can be initiated by the insertion of nitrile group from metal
nucleophile such as Grignard reagents5 and lithium reagents.6 Many
reports showed that the insertion of nitrile groups was carried out by
stoichiometric early transition metal complexes, such as titanium,7
zirconium,8 scandium,9 molybdenum10 and tungsten.11 In recent
years, catalytic insertion of nitriles was also reported, and different
late transition metal catalysts have been developed for this insertion
Scheme 1 Cu-catalyzed addition/cyclization cascade
To begin our study, anthranilonitrile-derived N-(2-cyanophenyl)-
N-methylmethacrylamide
(1a)
and
readily
available
diphenylphosphine oxide were selected as the model substrates for
the optimization of reaction conditions. When the reaction was
performed in the presence of a stoichiometric amount of CuCl in
CH3CN at 100 °C, the reaction afforded the desired quinoline-2,4-
dione (2a) in 72% isolated yield (Table 1, entry 1). Encouraged by
this result, the reaction conditions of this cascade were further
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optimized. However, when the loading of CuCl was decreased to 10
mol %, the corresponding product (2a) was obtained only in 21%
yield (entry 2). Metal nitrates are commonly used as efficient
additives in C−P bond-forming reactions.4f–j Indeed, in the present
reaction, the addition of Mg(NO3)2·6H2O significantly improved the
conversion of the starting material, and the yield increased to 84%
(entry 3). Different Cu and Ag salts such as CuBr, CuI, Cu2O, CuO,
CuCl2, CuBr2, Cu(OAc)2, Cu(acac)2, Ag2CO3 and AgNO3 were
screened; CuBr2 gave the best yield (93%) of 2a (entries 4–13). The
additive also exerted a significant influence on the reaction. When
Cu(NO3)2·3H2O, Ce(NO3)3·6H2O, and Zr(NO3)4·5H2O were
investigated as the additive, the yield decreased (entries 14–16).
Furthermore, the loading of Mg(NO3)2·6H2O could be decreased to
0.3 equiv and still provided an excellent yield (entry 17). The
reaction also occurred at a lower temperature (80 °C), albeit in a
lower yield (entry 18). Finally, other solvents such as toluene, DMF,
DMSO, and 1,4-dioxane were screened, and the results indicate that
this reaction proceeded most efficiently in CH3CN (entry 17 vs.
entries 19–22). Control tests showed that no reaction occurred in the
Table 2 Substrate scope a,b
.
absence of either CuBr2 (entry 23) or Mg(NO3)2 6H2O (entry 24).
Table 1 Reaction conditions screeninga
yield (%) b
entry
catalyst (mol %) additive (equiv)
1
2
3
4
5
6
7
8
CuCl (100)
CuCl (10)
CuCl (10)
CuBr (10)
CuI (10)
-
-
72
21
84
84
trace
69
73
67
93
73
76
43
82
31
64
24
94
81
48
56
51
67
0
.
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Mg(NO3)2 6H2O (0.5)
Cu(NO3)2 3H2O (0.5)
Ce(NO3)3 6H2O (0.5)
Zr(NO3)4 5H2O (0.5)
Mg(NO3)2 6H2O (0.3)
Mg(NO3)2 6H2O (0.3)
.
.
.
Cu2O(10)
CuO(10)
.
.
CuCl2 (10)
CuBr2 (10)
Cu(OAc)2 (10)
Cu(acac)2 (10)
Ag2CO3 (10)
AgNO3 (10)
CuBr2 (10)
CuBr2 (10)
CuBr2 (10)
CuBr2 (10)
CuBr2 (10)
CuBr2 (10)
CuBr2 (10)
CuBr2 (10)
CuBr2 (10)
-
.
9
.
10
11
12
13
14
15
16
17
18c
19d
20e
21f
22g
23
24
.
.
a Unless otherwise noted, all the reactions were carried out in the presence of
.
0.30 mmol of 1a–1v, HP(O)R32 (2.0 equiv), 10 mol % catalyst and 0.3 equiv
.
b
Mg(NO3)2·6H2O in 3.0 mL CH3CN at 100 °C under N2. Yield of the
.
isolated product.
.
.
With the optimized reaction conditions (Table 1, entry 17), the
substrate scope and limitations of the addition/cyclization cascade
were investigated, and the results are summarized in Table 2.
Initially, different protecting groups on the N atom were evaluated:
N-(2-cyanophenyl)-N-acrylamides bearing methyl and benzyl
protecting groups participated well in this transformation; however,
the reactions of acetylated and unprotected substrates failed (2a–2c).
Next, the effect of substituents at the N-aryl moiety was investigated
(2d–2q). The electronic properties of the substituents had no
significant influence on the efficiency of the reaction. Both electron-
donating and -withdrawing substituents were tolerated in this
cascade, and most of the substrates were successfully converted into
the desired products in good to excellent yields. However, the steric
.
.
Mg(NO3)2 6H2O (0.3)
Mg(NO3)2 6H2O (0.3)
Mg(NO3)2 6H2O (0.3)
Mg(NO3)2 6H2O (0.3)
Mg(NO3)2 6H2O (0.3)
-
.
.
.
.
CuBr2 (10)
0
a Reaction conditions: 1a (0.30 mmol), HP(O)Ph2 (0.60 mmol), catalyst,
b
and additive in solvent (3.0 mL) at 100 °C for 10 h under N2. Isolated
yield. c 80 °C. d Toluene was used as the solvent. DMF was used as the
e
solvent. f DMSO was used as the solvent. g 1,4-Dioxane was used as the
solvent.
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hindrance effect was obvious on the transformation reactivity. For coordinate with N-(2-cyanophenyl)-N-acrylamides 1a to form
example, N-(3-bromo-2-cyanophenyl)-N-methylmethacrylamide, intermediate B, the electrophilic phosphonyl radical attacks the
bearing a Br atom at the ortho position of the nitrile group, afforded carbon–carbon double bond of B to afford the corresponding
the corresponding product 2f in 38% yield, whereas the substrate nucleophilic carbon-centered radical C. Next, an intramolecular
containing a Br atom at the meta position of the nitrile group addition of the alkyl radical to the coordinated nitrile affords imine
afforded the corresponding product 2j in 91% yield. Notably, halo D, which is then hydrolyzed by H2O to provide the desired product
functional groups such as Cl and Br were well tolerated in the 2a and release the copper species.
reaction, thus offering opportunities for further modification at the
halogenated positions. The substrates with two substituents on the
benzonitrile moieties also reacted well with Ph2P(O)H (2p and 2q).
Next, the effect of the substituents on olefins was evaluated. A series
of α-substituted olefins bearing different functional groups such as
benzyl, phenyl, ester, and phthalimide were compatible with the
optimal conditions, affording the desired products 2r − 2u in
moderate to good yields. Heterocyclic substrate pyridineacrylamide
also underwent the reaction smoothly, affording product 2v in 91%
yield. Unlike diphenylphosphine oxide, the reaction of diethyl
phosphite failed under the standard conditions. However, the
reaction proceeded when AgNO3 was used as the catalyst to afford
2w in 59% yield. It is worth noting that the reaction was also readily
scaled up with similar efficiency. For instance, the reaction at the 6.0
mmol scale afforded the corresponding product 2a in 87% yield. (see
the ESI†).
Scheme 3 Possible mechanism of addition/cyclization cascade
In summary, novel Cu-catalyzed cascade
addition/cyclization reaction was developed, where the
cyclization was accomplished by an intramolecular addition of
the carbon radical to the nitrile. This radical mediated cascade
reaction is not only efficient and general, but also functional
group compatible. This protocol provides a practical synthetic
method for the construction of phosphonylated quinoline-
In order to probe the possible mechanism of the cascade reaction,
several radical-trapping experiments were carried out (Scheme 2).
When the reactions were conducted in the presence of 1.5 equiv of
2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as the radical
scavenger, the reaction progress was remarkably suppressed, and
only trace amounts of the desired products were detected, even after
longer reaction times. The addition of 1,1-diphenylethylene led to a
complete reaction, yielding the alkenyl diphenylphosphine oxide 3 in
19% yield. Furthermore, the reaction of diene 4 afforded cyclized
product 5 under the optimized conditions. These results suggest that
the transformation may involve a radical process.
a
2,4(1H,3H)-diones. Further investigation of the reaction
mechanism and synthetic applications are underway.
Financial support from the National Natural Science
Foundation of China (No. 21402071) and the Foundation of
Kunming University of Science and Technology (No.
KKSY201426046) is greatly appreciated.
Notes and references
Faculty of Life Science and Technology, Kunming University of Science and
Technology, Kunming 650500, P. R. China. E-mail: liym@kmust.edu.cn.
†
Footnotes should appear here. These might include comments
relevant to but not central to the matter under discussion, limited
experimental and spectral data, and crystallographic data.
Electronic Supplementary Information (ESI) available: Experimental
procedures, characterization of new compounds, copies of 1H, 13C, 31P
and 19F NMR spectra. See DOI: 10.1039/c000000x/
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