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Nickel-Catalyzed Cross-Coupling of Aryl Redoxactive Esters with Aryl Zinc Reagents Bo-Hao Shih, R. Sidick Basha, and Chin-Fa Lee ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b02913 • Publication Date (Web): 26 Aug 2019 Downloaded from pubs.acs.org on August 26, 2019
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ACS Catalysis
Nickel-Catalyzed Cross-Coupling of Aryl Redoxactive Esters with Aryl Zinc Reagents Bo-Hao Shih,† R. Sidick Basha,† Chin Fa Lee*,†,‡,§ †Department
of Chemistry, National Chung Hsing University, Taichung, Taiwan 402, R.O.C Center for Sustainable Energy and Nanotechnology (RCSEN), Taiwan §Innovation and Development Center of Sustainable Agriculture (IDCSA), Taiwan Supporting Information Placeholder ‡Research
O
O Ar/ Het
R1
O N
O
Ni
O
Aryl NHPI esters +
ZnCl . LiCl
R
R1 new disconnection one-pot
Ar/ Het
O
Ar R
Aryl aryl esters
Ar Arylzinc reagents
ABSTRACT: A nickel-catalyzed aryl–aroyloxyl C(sp2)–O radical cross-coupling reaction conducted using a redox active ester with aryl zinc reagent was developed. This method demonstrates a new disconnection approach for aryl aryl esters formation. In the onepot sequential process, the readily available aryl carboxylic acids can be converted into functionalized aryl aryl esters and heteroaryl esters. This protocol is amenable to the gram scale synthesis. The present method has a wide substrate scope and high functional group tolerance.
KEYWORDS: nickel, cross-coupling, redox-active esters, EPR study, single-electron transfer
The formation of carbon-heteroatom bond serves a vital role in cross-coupling reactions.1-2 Aryl esters are prevalent motifs found in the building blocks of a variety of natural products3,4 and widely used in pharmacological science.5-8 The C–O coupling to esters has been explored using limited routes through transition metal-mediated cross-coupling reactions with proanionic carboxylate chemistry.9-11 The use of crosscoupling reactions with a single-electron transfer process is a widely used and robust strategy that includes two electron metal-mediated coupling reactions.12 Recently, the radical cross-coupling (RCC) reaction catalyzed by transition metals has exhibited a high in demand in chemical synthesis.13-15 However, the limited components were engineered and flourished as coupling partners in RCC reactions. Baran and coworkers have proposed that the unique alkyl redox active esters are decarboxylative coupling partners in the C–C and C– B coupling reactions.16-19 We envisioned the unmapped challenge of the C–O coupling of aryl redox active esters by using arylmetallic reagents (Figure 1A). In this study, a new approach was proposed for C(sp2)–O radical cross-coupling of aryl redoxactive esters with aryl zinc reagents to aryl aryl esters (Figure 1B). The hypothesized mechanism is outlined in Figure 1C. The NiI–X species 1 undergoes transmetalation with aryl
zinc reagent 2 to afford a NiI–aryl species 3. The reduction of aryl NHPI esters 4 from 3 through the single-electron transfer process causes O–N fragmentation of 6. When the NiII–aryl cation 5 is added to the generated benzoyloxyl radical 7 and phthalimide anion A*, the NiIII(aryl)(benzoyloxy)(A*) species 8 is formed. The reductive elimination of 8 provides the product 9 and regenerates the NiI catalyst species 1 (ERP results, see supproting material for the details). At the outset, the redox active ester 4 with 2 in the presence of NiCl2.6H2O with ligand L1 afforded a yield of 54% (Table 1, entry 1). By varying the amount of both NiCl2.6H2O and ligand L2, a higher yield was obtained with 10 mol% NiCl2.6H2O in combination with 20 mol% L2. By further increasing the mol% of nickel, the yield was found to decrease (Table 1, entries 2–5). The reaction with 2,2'-bipyrimidine ligand L3 provides only 8% yield, thus demonstrating that the two bidentate nitrogen ligand species hampered the reaction efficiency. By using the phenanthroline ligand L4, 46% yield was obtained (Table 1, entries 6 and 7). Moreover, we examined the phenanthroline ligand analogs L5–L8. The results revealed that compared with L5 and L8, the aryl substituted L6 and sterically hindered L7 reduce the reaction efficiency and provide lower product yield (Table 1, entries 8–11). Anhydrous
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NiCl2 with ligands L1, L2, L4, and L5 was found to be inefficient (Table 1, entries 12–15). Similarly, Ni(acac)2 with ligands L1 or L2 delivered lower yield. Moreover, Ni(acac)2 with ligands L4 and L5 afforded a product yield of 46% and 48%, respectively (Table 1, entries 16–19). NiF2 with L2 provided a product yield of 33% (Table 1, entry 20). Prefabricated Ni complexes with L2 are ineffective (Table 1, entries 21 and 22). Ni(cod)2 is also active as a Ni source to give the produc in 58% yield (Table 1, entry 23). The Fe–L2 catalyst system could also yield the product but presented a low yield compared with the yield of Ni/L2 (Table 1, entry 24), starting material 4 and biphenyl were detected by GC-MS analysis. From the optimal studies, the Ni–L2 catalyst system is found to be efficient for the C(sp2)–O radical cross-coupling reaction.
trisubstituted methyl 26 and isopropyl 27 were also successfully coupled. The fused aromatic system smoothly afforded product 28 with a 70% yield. Table 1. Optimization of Reaction Conditionsa O N 4 +
A*
O
Ar1
+
M
Ar
Ar
O
Ar1
A* A*
Activating agent
b) This work: C(sp2)-O radical cross coupling O
O
O N
Ar/ Het
R1
O
Ni
O
Aryl NHPI esters
R
+
new disconnection one-pot
ZnCl . LiCl
1
Ar
O
Ar/ Het
R
Aryl aryl esters
Ar
R
Arylzinc reagents c) Hypothesized Ni catalytic cycle:
O Catalyst, Ligand
O
PhZnCl. LiCl 2
O
?
O
O
a) Challenge: O
Page 2 of 6
THF:DMF (3:2), Ar 12 h, 25 C
O 10
entry
Catalyst (mol%)
ligand
yield (%)b
1
NiCl2.6H2O (10)
20 mol% L1
54
2
NiCl2.6H2O (2)
4 mol% L2
51
3
NiCl2.6H2O (5)
10 mol% L2
57
4
NiCl2.6H2O (10)
20 mol% L2
73
5
NiCl2 6H2O (20)
40 mol% L2
50
6
NiCl2.6H2O (10)
20 mol% L3
08
7
NiCl2.6H2O (10)
20 mol% L4
46
8
NiCl2.6H2O (10)
20 mol% L5
54
9
NiCl2 6H2O (10)
20 mol% L6
05
10
NiCl2.6H2O (10)
20 mol% L7
11
11
NiCl2.6H2O (10)
20 mol% L8
47
12
NiCl2 (10)
20 mol% L1
10
13
NiCl2 (10)
20 mol% L2
16
14
NiCl2 (10)
20 mol% L4
12
15
NiCl2 (10)
20 mol% L5
14
16
Ni(acac)2 (10)
20 mol% L1
17
17
Ni(acac)2 (10)
20 mol% L2
19
18
Ni(acac)2 (10)
20 mol% L4
46
19
Ni(acac)2 (10)
20 mol% L5
48
20
NiF2 (10)
20 mol% L2
33
21
NiCl2(PPh3)2 (10)
20 mol% L2
35
22
NiCl2(dppe) (10)
20 mol% L2
23
23
Ni(cod) (10)
20 mol% L2
58
24
Fe(OAc)2 (10)
20 mol% L2
44
.
.
O Ph
9
O
Ar
X
-A* reductive elimination A* O III O L2 Ni Ph Ar 8
[Ar M] 2
I L2Ni X
Transmetalation
1
Nickel Catalytic Cycle
addition A* + Ph
O
7
Ar
O
O N
O Ph
SET
4
OA*
O
Ph O
I 3
II L2Ni Ar 5 O
L2Ni
Ph
OA*
6 O O-N fragmentation
Figure 1. (a) Challenge. (b) New disconnection to C(sp2)-O radical cross-coupling. (c) Hypothesized mechanism of Nicatalysed C(sp2)-O radical cross-coupling. After optimizing the reaction conditions, the varying substrate scope of the arylzinc reagent was evaluated. As shown in Table 2, the reaction with the electron donating substituent at the ortho position such as methyl and methoxy afforded 11 and 12 with a product yield of 59% and 71%, respectively. Similarly, the aryl moiety at the second position delivered 13 with a product yield of 62%. The electron-rich substituents at the meta or para position of the phenylzinc reagent provided the desired products 14–17 with a product yield in the range of 43%–79%. The ortho or para position of the phenyl ring contains strong electron-withdrawing groups such as fluoro, chloro, and trifluoromethyl. These groups were tolerated well and the coupled products 18–22 were obtained with a product yield in the range of 54%–84%. The disubstituents on the phenyl ring, such as methyl 23, fluoro, and methyl or phenyl 24 and 25, provided the products with a moderate to good yield. Moreover,
Reaction performed with 1 equiv of 4, 3 equiv of 2 in 0.16 mmol scale. Isolated yield.
a b
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ACS Catalysis
R1
R1
R2
N
N
1
N
N
N
N
N N R1 =R2 = H, L4 R1 =R2 = OMe, L5 R1 =R2 = Ph, L6
L3
2
R =R = H, L1 R1 =R2 = t Bu, L2
Me N
Me N
Me
L7
Table 2. Scope of the
N L8
Csp2-O
coupling of arylzinc reagentsa
Table 3. One-pot scope of the in situ redox active esters to Csp2-O couplinga
O
O
O
10 mol% NiCl2. 6H2O 20 mol% di-tBubipy
O N 4
O O
ZnCl. LiCl
O
O
10, 73% O
11, 59%
12, 71%
O O
O
Me
O OMe
14, 43%
15, 55%
O
MeO
32, 80%
I
O
O O
O nBu
O
OMe
O
O
Cl 19, 54%
O2N
F
O
O
F3C
CF3
O
39, 59%
O
O O
O
O
S 42, 47%
24, 68%
O
O
O
Me
Me 26, 49%
25, 45% i Pr
O i Pr
O i Pr
Reaction conditions [In situ]: Aryl carboxylic acid (1 equiv), NHydroxyphthalimide (1 equiv), DCC (1 equiv) in DCM at 25 ºC for 12 h, then NiCl2.6H2O (10 mol%), di-tBubpy (20 mol%), arylzinc reagent (3 equiv), THF/DMF (3:2) at 25 ºC for 12 h. bIsolated yield. a
Me
O
F
O
Me
O
Me 23, 37%
40, 50%
F
O
O
Cl
22, 73%
Me
O NH
41, 60%
O
O
O 37, 54%
O
38, 51%
21, 84%
20, 74%
O I
O
O O
O O
O
O 34, 46%
36, 59%
O
F 18, 63%
17, 79%
16, 60%
35, 40%
O
NO2 O
33, 63%
Br
O
31, 49%
O
O
O
13, 62%
O t Bu
30, 77%
O Me
(29-42)b
O
O
O
O
O
O Me
29, 59%
MeO
O Ar1
THF:DMF (3:2), Ar 12 h, 25 C
O O
Me
10 mol% NiCl2. 6H2O 20 mol% di-tBubipy
O
O N
in situ
12 h, Ar, 25 C
Me
O
Ar1
DCC, CH2Cl2
O
O
O
O
CO2H
(10-28)b
O
O
Ar Ar1
THF:DMF (3:2), Ar 12 h, 25 C
PhZnCl .LiCl
NOH
O +
Ar
Me
Me
N
Me
and para positions on the aromatic ring proceeded well and products 29–33 were obtained with a product yield in the range of 49%–80%. Similarly, the electron withdrawing group at the ortho, meta, and para positions reacted smoothly and afforded products 34–39 with moderate to good yields. Moreover, the five- or six-membered heteroaromatic system, such as pyrrole 40, furan 41, and thiophene 42, were compatabile under the present reaction conditions.
R2
The gram scale reaction was performed between 4c and 2 under standard reaction conditions. The desired product 30 was obtained with a 64% yield, thus demonstrating the practicability and scalability of the C(sp2)–O RCC reaction (Scheme 1).
O
O
O Me
28, 70%
27, 67%
O 4c, 3.09 g
Reaction conditions: Phenyl NHPI ester (1 equiv), arylzinc reagent (3 equiv), NiCl2.6H2O (10 mol%), di-tBubpy (20 mol%), THF/DMF (3:2), 25 ºC, 12 h. bIsolated yield. a
Inspired by the above studies, we used our protocol in the one-pot transformation from aryl carboxylic acid. The in situ generated aryl NHPI esters are utilised directly for C(sp2)– O radical cross-coupling to synthesize functionalised aryl aryl esters (Table 3). The electron donating group at the ortho, meta,
30
O N
+
.
ZnCl LiCl 2 (3 equiv)
10 mol% NiCl2. 6H2O 20 mol% di-tBubipy THF:DMF (3:2), Ar 12 h, 25 C [3.09 gram scale]
O Me
O
Me
O O Ph
30, 64% 1.49 g
Scheme 1. C(sp2)-O radical cross-coupling reaction in gram sclae The relative rate of the redox active ester and aryl zinc reagent was investigated (Scheme 2A). The reaction was examined using electronically varied redox active esters with
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the phenyl zinc reagent. The transmetalation process is identical, and the reductive elimination process is solely influenced by electronic properties. The experimental results clearly reveal that reductive elimination highly favors the electron withdrawing behavior. Similarly, the reaction was inspected using the electronically varied aryl zinc reagent (Scheme 2B). The output of the experiment clearly suggests that transmetalation highly favors electron donating properties. Moreover, the electron donating and electron-withdrawing relative rates are higher when transmetalation is conducted than when the phenyl zinc reagent is used. Control experiments were performed to gain insights into the radical cross-coupling reaction. The Ni catalyst and bipyridine ligand are essential for this transformation. There is no influence of light in the reaction, and the reaction solely proceeds at ambient conditions. The use of halides, the Grignard reaction, and triphenyl indium could not successfully conduct this coupling reaction. This result clearly demonstrates the necessity of transmetalation, and there is a specific requirement of zinc in the transmetalation process. The radical cross-coupling reaction profile was investigated (Scheme 2C). The observed result demonstrates that the reaction proceeded smoothly, and the yield of the reaction increased consistently with respect to time. Moreover, no deterrent or dynamic variant of the reaction was observed. Electron paramagnetic resonance (EPR) studies were conducted for the RCC reaction of redox active ester 4, Ni–L2 catalyst, and the 2a solution by using 5,5-dimethyl-1-pyrrolineN-oxide (DMPO) for spin trapping. The generated benzoyloxyl radical 7 was trapped by DMPO and the resulting experimental spectra of the DMPO spin trapping are presented in Scheme 2D. The benzoyloxyl radical assignment is consistent with the Hutchings report20 (Table 4, entry 1). Similarly, the substitued radical spin trapping assignment is represented in Table 4 (entries 2 and 3). A.
Relative rate experiments a) O O
Ph
O N O
.
(1 equiv)
Ph ZnCl LiCl 2 (3 equiv)
X
b)
.
+ X (3 equiv)
B.
Ph
O N
4 (1 equiv) O
.
Ph ZnCl LiCl
O Ph
10 mol% NiCl2. 6H2O
X
20 mol% di-tBubipy
B +
O
THF:DMF (3:2), Ar 12 h, 25 C
O
Ph
10 X = OMe: B:10 = 1:6 X = CF3: B:10 = 4:1
O
O
ZnCl LiCl
O N
4 O (1 equiv)
+
O
O
O
O 10 mol% NiCl2. 6H2O
O
Ph
THF:DMF (3:2), Ar 12 h, 25 C
O Ph
2 (3 equiv)
O
4 O (1 equiv)
+ Ph X (3 equiv)
Scheme 2. Relative rate, control experiments, reaction profile and EPR (performed at room temperature) studies
Table 4. EPR trapping resultsa entry
radicala
g
aN
aH
1
PhCO2•
2.011
12.7
9.1 (1.4)b
2
4-OMePhCO2•
2.010
12.6
9.3 (1.3)b
3
4-CF3PhCO2•
2.010
12.3
9.5 (1.3)b
Trapping agent DMPO was used. bSplitting was observed.
a
In summary, a nickel-catalyzed aryl–aroyloxyl C(sp2)–O radical cross-coupling reaction conducted using a redox active ester with aryl zinc reagent was demonstrated. This method demonstrates a new disconnection approach for aryl aryl esters. In the one-pot sequential process, the readily available aryl carboxylic acids can be converted into functionalized aryl aryl esters and heteroaryl esters. This protocol is amenable to the gram scale synthesis. This method is simple, practical, and convenient. Moreover, it has a wide substrate scope, high functional group tolerance, and good yields. To the best of our knowledge, this is the first report on the use of intermolecular aroyloxyl radicals in the C(sp2)–O radical cross-coupling reaction.
AUTHOR INFORMATION Corresponding Author
Chin-Fa Lee: 0000-0003-0735-5691
Notes
O
The authors declare no competing financial interest.
10 X = OMe: A:10 = 6:1 X = CF3: A:10 = 1.02:1
ASSOCIATED CONTENT 10 mol% NiCl2. 6H2O
O O N
D. EPR study (at room temperature)
ORCID
+
Control experiments
Ph
Reaction profile (formation of 10)
*Email:
[email protected] X
A
20 mol% di-tBubipy
C.
Page 4 of 6
Ph THF:DMF (3:2), Ar 12 h, 25 C X
Supporting Information
O
20 mol% di-tBubipy
O 10
.
X
10
= ZnCl LiCl
w/o NiCl2. 6H2O : 0% w/o di-tBubipy : 0%
w/o NiCl2. 6H2O & di-tBubipy : 0% in dark : 70%
The Supporting Information is available free of charge on the ACS Publications website. Experimental procedures, spectroscopic data and copies of NMR
Br
0%
MgBr
0%
ACKNOWLEDGMENT
InPh2
0%
This work was financially supported by the Ministry of Science and Technology, Taiwan (MOST 107-2113-M-005-019-MY3); National Chung Hsing University; Research Center for Sustainable Energy and Nanotechnology; and the "Innovation and Development Center of Sustainable Agriculture" from The Featured Areas Research Center Program within the framework of
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ACS Catalysis the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan.
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by Redox-Active Esters and Alkylzinc Reagents. Science 2016, 352, 801-805 For Csp3-Csp2 coupling: (a) Chen, T. -G.; Zhang, H.; Mykhailiuk, P. K.; Merchant, R. R.; Smith, C. A.; Qin, T.; Baran, P. S. Quaternary Centers by Nickel‐Catalyzed Cross‐Coupling of Tertiary Carboxylic Acids and (Hetero)Aryl Zinc Reagents. Angew. Chem., Int. Ed. 2019, 58, 2454-2458. (b) Edwards, J. T.; Merchant, R. R.; McClymont, K. S.; Knouse, K. W.; Qin, T.; Malins, L. R.; Vokits, B.; Shaw, S. A.; Bao, D.-H.; We, F.-L.; Zhou, T.; Eastgate, M. D.; Baran, P. S. Decarboxylative Alkenylation. Nature 2017, 545, 213-218. (c) Sandfort, F.; O'Neill, M. J.; Cornella, J.; Wimmer, L.; Baran, P. S. Alkyl−(Hetero)Aryl Bond Formation via Decarboxylative Cross‐Coupling: A Systematic Analysis. Angew. Chem., Int. Ed. 2017, 56, 3319-3323. (d) Toriyama, F.; Cornella, J.; Wimmer, L.; Chen, T.-G.; Dixon, D. D.; Creech, G.; Baran, P. S. RedoxActive Esters in Fe-Catalyzed C–C Coupling. J. Am. Chem. Soc. 2016, 138, 11132-11135. (e) Wang, J.; Qin, T.; Chen, T.-G.; Wimmer, L.; Edwards, J. T.; Cornella, J.; Vokits, B.; Shaw, S. A.; Baran, P. S. Nickel‐Catalyzed Cross-Coupling of Redox‐Active Esters with Boronic Acids. Angew. Chem., Int. Ed. 2016, 55, 9676-9679. (f) Cornella, J.; Edwards, J. T.; Qin, T.; Kawamura, S.; Wang, J. Pan, C-M.; Gianatassio, R.; Schmidt, M.; Eastgate, M. D.; Baran, P. S. Practical NiCatalyzed Aryl–Alkyl Cross-Coupling of Secondary RedoxActive Esters. J. Am. Chem. Soc. 2016, 138, 2174-2177. For Csp3-Csp coupling: Smith, J. M.; Qin, T.; Merchant, R. R.; Edwards, J. T.; Malins, L. R.; Liu, Z.; Che, G.; Shen, Z.; Shaw, S. A.; Eastgate, M. D.; Baran, P. S. Decarboxylative Alkynylation. Angew. Chem., Int. Ed. 2017, 56, 11906-11910. For C-B coupling: (a) Li, C.; Wang, J.; Barton, L. M.; Yu, S.; Tian, M.; Peters, D. S.; Kumar, M.; Yu, A. W.; Johnson, K. A.; Chatterjee, A. K.; Yan, M.; Baran, P. S. Decarboxylative borylation. Science 2017, 356, eaam7355. (b) Wang, J.; Shang, M.; Lundberg, H.; Feu, K. S.; Hecker, S. J.; Qin, T.; Blackmond, D. G.; Baran, P. S. Cu-Catalyzed Decarboxylative Borylation. ACS Catal. 2018, 8, 9537-9542 and references therein. Sankar, M.; Nowicka1, E.; Carter, E.; Murphy, D. M.; Knight, D. W.; Bethell, D.; Hutchings, G. J. The Benzaldehyde Oxidation Paradox Explained by the Interception of Peroxy Radical by Benzyl Alcohol. Nat. Commun. 2014, 5, 3332.
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Graphic Re: Nickel-Catalyzed Cross-Coupling of Aryl Redoxactive Esters with Aryl Zinc Reagents Bo-Hao Shih, R. Sidick Basha, Chin Fa Lee*
A nickel-catalyzed aryl–aroyloxy C(sp2)–O radical cross-coupling reaction conducted using a redox active ester with aryl zinc reagent was developed. This method demonstrates a new disconnection approach for aryl aryl esters formation. In the onepot sequential process, the readily available aryl carboxylic acids can be converted into functionalized aryl aryl esters and heteroaryl esters. This protocol is amenable to the gram scale synthesis. Improtantly, the present method is simple, practical, and convenient. Moreover, it has a wide substrate scope, high functional group tolerance, and good yields. To the best of our knowledge, this is the first report on the use of intermolecular aroyloxy radicals in the C(sp2)–O radical cross-coupling reaction.
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