Functionalized α,β-ynones: Efficient ligand for Cu catalyzed Sonogashira-type cross-coupling reaction

Article abstract of DOI:10.1039/c6ra23742h

Under the classic reaction conditions, a large excess of copper catalyst and N, O donor ligands were mandatory for the catalytic cross-coupling of Csp²-Csp bonds. Herein, we wish to report α,β-ynones as σ-, π-electron donating ligands for copper catalyzed Sonogashira-type reaction. As low as 0.25-2.5 mol% of L₁₁ (3-(4-bromophenyl)-1-(4-methoxyphenyl)prop-2-yn-1-one) significantly accelerated the 0.1-1.0 mol% of CuI catalyzed cross-coupling of aryl iodides with terminal alkynes and alkynylcarboxylic acids, respectively. This low-mol% catalyst system showed satisfactory activity and tolerance with 36 examples of substituted alkynes.

Full text of DOI:10.1039/c6ra23742h

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Functionalized α,β-Ynones: Efficient ligand for Cu catalyzed
Sonogashira-type cross-coupling reaction
Received 00th January 20xx,
Accepted 00th January 20xx
‡
[a]
[a]
[a]
[a]
[a]
Xian Wang, Zhenhua Wang, Zunyuan Xie, Guofang Zhang, Weiqiang Zhang* and Ziwei
[a]
DOI: 10.1039/x0xx00000x
Gao*
Under the classic reaction condition, large excess of copper
catalyst and N, O donor ligands were mandatory for the catalytic
2
cross-coupling of Csp -Csp bonds. Herein, we wish to report α,β-
ynones as σ-, π-electron donating ligands for copper catalyzed
Sonogashira-type reaction. As low as 0.25-2.5 mol% of L11 (3-(4-
bromophenyl)-1-(4-methoxyphenyl)prop-2-yn-1-one) significantly
accelerated 0.1-1.0 mol% of CuI catalyzed cross-coupling of aryl
iodides with terminal alkynes and alkynylcarboxylic acids,
respectively. This low-mol% catalyst system showed satisfactory
activity and tolerance with 36 examples of substituted alkynes.
The Sonogashira reaction is a powerful tool for preparing
alkyne compounds, which have been widely applied in the synthesis
1
of natural products, pharmaceuticals, as well as organic materials.
Recently, much attention were attracted to the use of copper
2
3
catalysts, because copper are abundant, economic and less toxic.
Scheme 1. Efficient ligands for Cu-catalyzed Sonogashira reactions.
To enhance the catalytic efficiency of copper catalysts, many hard
donor ligands were employed in Cu-catalyzed Sonogashira
1
9
20
4
Recently, few aromatic ligands, such as Xantphos, pyrene,
reactions. Generally, large excess of multi-dentated ligands such as
2
1
22
5
6
BIMs (bisindoles) and TTCs (triainze trizole) were established as
efficient ligands for Sonogashira cross-coupling reaction with low-
mol% copper loading (Scheme 1). 2.5 mol% aromatic bidentated
phosphine ligands successfully facilitated low-mol% Cu-catalyzed
Sonogashira cross-coupling reaction, in which Xanphos and Dppf
N,N-dimethylglycine (30 mol%), L-proline (10 mol%), 8-
7
8
hydroxyquinoline (20 mol%), rac-BINOL (10 mol%), Choline
9
10
chloride (20 mol%), 6-methylpicolinicacid (10 mol%), diamines
11
12
13
(
10 mol%), 1,10-phenanthroline (20 mol%), DABCO (20 mol%),
1
4
15
N,N-dibenzyl BINAM (20 mol%), diketone (20 mol%), salicylic
16
25
showed excellent activity for 1.0 mol% Cu
aromatic hydrocarbon ligands pyrene enhanced the activity of
Cu(OTf) , affording 52% to 90% yields of alkyne products. BIMs
bearing π-electron-rich aromatic moiety of 4-Chloro-phenyl group
was modulated as powerful ligand for the Cu-catalyzed
2
O. The polycyclic
acid (20 mol%), bis(pyrazolyl)methane(10 mol%) were required
to facilitate Cu-catalyzed cross-coupling reaction of aryl iodides and
terminal alkynes. More recently, C. Bolm et al., observed the ligand
accelerating effect of 20-30 mol% DMEDA (N,N'-dimethyl-ethane-
diamine), by which as low as 0.5 mol% CuI catalyzed cross-coupling
2
a
17
Sonogashira reaction with the yield up to 99%. TTCs with multiply
hard donor sites stabilized catalytic active copper by the diverse
coordination modes and afforded 61% to 96% yields. In light of
these multi-functionalized ligands, particularly the beneficial
accelerating effect of aromatic functional groups for Cu catalysis,
we herein report α,β-ynones as σ-, π-electron donating ligands for
copper catalyzed Sonogashira-type cross-coupling reaction. Ligand
screening experiments of 20 substituted ligands found that L11
containing methoxy- and Br- was the most efficient ligand. In
presence of 2.5 equivalent L11, 1.0 mol% CuI afforded 96% yield,
whilst as low as 0.5mol% of CuI gave 71% yield. An efficient copper
catalyst system of CuI (1.0 mol%)/L11 (2.5 mol%) showed
reactions with decent yields. Until now, the addition of excess
ligands (10-30 mol%) is mandatory to maintain the coupling
18
efficiency for most homogeneous systems. Despite of the ligand-
accelerating effect of these classic ligands, to explore new ligand
system is a promising way to enhance the efficiency of copper
catalysts.
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satisfactory catalytic activity and compatibility in 36 examples of
Sonogashira coupling and decarboxylative coupling, respectively.
b
Entry
CuI
1
L11
0
Yield (%)
1
2
3
4
5
6
7
8
9
a
40
88
94
96
92
89
65
71
50
1
1
1
2
1
2.5
3
1
1
4
1
5
0.5
0.1
1.25
0.25
Reaction conditions: 4-iodo-anisole (0.5 mmol), phenylacetylene (0.6 mmol),
b
1
DMF (3.0 ml), 130 ℃, N
2 2 3
, 24 h, K CO (0.5 mmol). H-NMR yields (average
on three parallel reactions).
The efficiency of α,β-ynone ligands were further investigated
for various Cu loadings. In the control experiment without ligand,
1
.0 mol% CuI gave 40% yield (Table 1, entry 1). The accelerating
Scheme 2. Ligands screening for Cu-catalyzed Sonogashira
reactions.
effect were observed by adding 1.0-5.0 mol% of L11, which
significantly enhanced the catalytic activity of Cu catalyst and
afforded 65%-96% yields (Table 1, entries 2-7). Notably, 2.5 mol%
Reaction conditions: CuI (1.0 mol%), α,β-ynones (4.0 mol%), 4-iodo-anisole (0.5
2 3 2
mmol), phenylacetylene (0.6 mmol), DMF (3.0 ml), K CO ( 0.5 mmol ), 130 ℃, N ,
L
11 gave the highest yield of 96% (Table 1, entries 4), 4.0 mol% and
.0 mol% ligands slightly inhibited the activity of Cu catalyst,
1
2
4 h. H-NMR yields.
5
affording 92% and 89% yield(Table 1, entries 6-7), respectively.
Notably, the ligand accelerating effect was also observed in the sub-
mol% Cu catalyzed reaction. 1.25 mo% L11 and 0.5 mol% CuI
afforded 71% yield (Table 1, entry 8). As low as 0.25 mol% of L11 and
1
In presence of 4.0 mol% ligands (L -L20), 1.0 mol% of CuI
catalyzed cross-coupling reaction of 4-iodoanisole and phenyl-
acetylene were used as a model reaction to evaluate the catalytic
2
6a
efficiency of α,β-ynones.
The simple aromatic α,β-ynone L
, L and L bearing methyl
1
0
.1 mol% of CuI gave 50% yield (Table 1, entry 9).
afforded moderate 50% yield, and L
2
3
4
groups gave 40% to 36% yields. It was reported that chloro-
benezene significantly accelerated transition metal catalyzed C-C
Table 2. Cu-catalyzed Sonogashira cross-coupling reaction of aryl
a
iodides with terminal alkynes
2
3
cross-coupling reaction . Herein, α,β-ynones ligands bearing
halobenzene group were evaluated systematically. Six chlorinated
5 8
α,β-ynones, L to L10 showed the different activity, in which L
bearing 4-OMe on benzoyl group accelerated the reaction with 75%
yield. Interestingly, L11 bearing 4-OMe on benzoyl group and 4-Br on
phenylethenyl group gave the highest yield of 90%. Other ligands
bearing methoxy groups (L12-L18) showed the decent activity and
afforded up to 80% yield. Extra S-donor failed to further enhance
b
Entry
R
1
R
2
Yield (%)
1
2
3
4
5
6
7
8
4-CH O
C6H
96
89
85
83
86
90
76
74
3
5
5
5
5
5
5
4-CH
4-NO
4-C
4-COCH
3
C
6
C
6
C
6
C
6
C
6
H
H
H
H
H
1
the activity of α,β-ynone ligands compared with Ph (L ). L19 and L20
bearing thiophenyl group gave 76% and 34% yield, respectively.
2
These experiments clearly demonstrated that functioinalized α,β-
2
6b,26c
2
H
5
ynones ligands
system accelerated Cu catalyzed cross-coupling
2
of Csp -Csp bonds.
3
4-COOC
2 5
H
Table 1. L11 accelerated cross-coupling of 4-iodoanisole and
a
phenylacetylene
4-CF3
C6H5
C6H5
4-OCF3
2
| J. Name., 2012, 00, 1-3
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PleaseRd So Cn oA t da vd aj un s ct ems argins
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4-Br
COMMUNICATION
also reacted with phenylacetylene in excellent yields, 1-Iodo-
naphthalene was isolated in 63% yield (Table 2, entry 30).
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
C6H5
C6H5
78
72
89
75
73
65
58
56
81
76
70
53
69
63
56
80
63
61
55
74
58
63
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4-Cl
H
C
C
C
C
C
C
C
C
6
6
6
6
6
6
6
6
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
Table 3. CuI-catalyzed decarboxylative coupling reaction of aryl
a
2-CH
2-CH
3
3
O
iodides with alkynylcarboxylic acid
2-CF
2-Cl
3-I
3
b
Entry
R
1
Yield (%)
3-CH
3-CH
3
3
O
1
2
3
4
5
4-CH O
83
80
61
42
58
40
3
4-CH3
H
3-CF3
C6H
5
H
CH
3
(CH
2
)
5
CCH
3-CH O
3
4-CH
4-CH
4-CH
4-CH
4-CH
4-CH
4-CH
3
O
O
O
O
O
O
O
4-CH
3
C
6
H
4
4-NO2
4-Br
3
3
3
3
3
3
4-C
4-C
2
4
H
H
5
9
C
C
6
H
4
4
6
a
6
H
Conditions: CuI (1.0 mol%, 0.0009g), L11 (2.5 mol%, 0.004 g), K CO3 (0.5
2
mmol, 0.0689 g), aryl iodide (0.5 mmol), alkynylcarboxylic acid (0.5 mmol,
b
4-CH
3
OC
6
H
4
0.073 g), DMF (3.0 ml), 130 ℃ , 24 h. Isolated yields.
CH
CH
CH
3
3
3
(CH
(CH
(CH
2
2
2
)
3
4
5
CCH
CCH
CCH
In the past several years, decarboxylative couplings of
alkynylcarboxylic acids have been considered as a sub-category of
Sonogashira coupling reactions since they are readily available and
)
)
2
4
inexpensive. The CuI (1.0 mol%) / α,β-Ynones (2.5 mol%) system
was also suitable for the decarboxylative coupling. We successfully
applied the CuI/L11 catalyst system in the decarboxylative cross-
coupling reaction. The results were summarized in Table 3. The
decarboxylative coupling of alkynylcarboxylic acid with aryl iodides
4-CH O
3-NH C H
2 6
3
4
4-CH
3
O
3 6 4
3-CH C H
3
1-naphthalene
6 5
C H
a
containing electron-donating groups (-OMe or -CH ) gave good
Reaction conditions: CuI (1.0 mol%), L11 (2.5 mol%), K
2
CO
3
(0.5 mmol), DMF
3
b
(
3.0 ml), 130 ℃ , 24 h, aryl iodide (0.5 mmol), alkyne (0.6 mmol). Isolated
yields. The moderate yields were obtained when aryl iodides
yields.
bearing an electron-withdrawing groups (-NO2, -Br) were used.
Conclusions
The scope and limitation of α,β-Ynones/CuI catalyst system
In conclusion, we have disclosed α,β-Ynones as efficient ligand
system for copper catalyzed Sonogashira and decarboxylative cross-
coupling reaction, respectively. The functionalized ligand L11 bearing
bromo- and methoxy- group is the most efficient ligand, by which
were extensively explored with functionalized aryl iodides and
terminal alkynes (Table 2). The cross-coupling reaction displayed
remarkable tolerance towards the substitution pattern and steric
2
6d,26e
effect.
Both electron-rich, electron-neutral or electron-
1
.0 mol% copper catalyzed Sonogashira-type reactions. The catalyst
deficient substituents and sterically encumbering substituents in
the aryl ring gave good results. The aryl iodides containing electron-
system of CuI/L11 were applied for the cross-coupling of both
terminal alkynes and phenylpropiolic acids with various aryl iodides,
respectively. The coupling reactions were compatible with a broad
scope of functional groups and affords products in good to excellent
yields. The activation mechanism of these α,β-ynone ligands is
under investigation.
donating groups (4-OMe, 4-CH
CH ) gave isolated yields of 76% to 96% (Table2, entries 1, 2, 4, 12,
3, 17, 18). When aryl iodides with electron-withdrawn groups (4-
OCF , 4-CF , 4-NO , 4-COCH , 4-COOC , 4-Br, 4-Cl, 4-CF , 2-CF , 2-
Cl, 3-I or 3-CF ) were used, the products were isolated with 56% to
0% yields (Table 2, entries 3, 5-10, 14-16, 19). When 1-octyne, 1-
3 2 5
, 4-C H , 2-CH3, 2-OMe, 3-OMe or 3-
3
1
3
3
2
3
2
H
5
3
3
3
9
Experimental Section
A mixture of aryl iodide (0.5 mmol), aryl alkyne (0.6 mmol), CuI (1.0
heptyne and 1-hexyne were employed instead of phenylacetylene,
the lower yields (63%, 61%, 55%) were obtained (Table 2, entries
mol%), L11 (2.5 mol%), K
Schlenk tube was stirred under a nitrogen atmosphere at 130 ℃for
4 h. After that, the mixture was poured into separating funnel (150
2 3
CO (0.5 mmol), and dry DMF (3.0 ml) in a
2
3 2 5 3 7 3
5-27). When 4-OMe, 4-CH , 4-C H , 4-C H , 3-CH , 3-OMe and 3-
NH phenylacetylene were involved in the coupling reaction, the
2
2
good yields were obtained 69%, 63%, 56%, 80%, 74% and 58%,
respectively (Table 2, entries 21-24, 28-29). Polycyclic compounds
ml) and washed with water (50 ml). And then, it extracted with
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ethyl acetate (3 ×15 ml). The organic layer was dried by anhydrous
MgSO , then filtered and evaporated under vacuum. The residue
2015, 56, 3259-3261.
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Acknowledgements
This work was supported by the 111 Project (B14041), the grant
from National Natural Science Foundation of China (21271124,
7
95-798.
21272186, 21371112), the Fundamental Funds Research for the
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