Direct aerobic carbonylation of C(sp2)-H and C(sp3)-H bonds through Ni/Cu synergistic catalysis with DMF as the carbonyl source

Article abstract of DOI:10.1021/jacs.5b01671

The direct carbonylation of aromatic sp² and unactivated sp³ C-H bonds of amides was achieved via nickel/copper catalysis under atmospheric O₂ with the assistance of a bidentate directing group. The sp² C-H func

Full text of DOI:10.1021/jacs.5b01671

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Communication
Direct Aerobic Carbonylation of C(sp2)-H and C(sp3)-H Bonds
through Ni/Cu Synergistic Catalysis with DMF as the CO Source
Xuesong Wu, Yan Zhao, and Haibo Ge
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 27 Mar 2015
Downloaded from http://pubs.acs.org on March 28, 2015
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Direct Aerobic Carbonylation of C(sp2)-H and C(sp3)-H Bonds
through Ni/Cu Synergistic Catalysis with DMF as the CO Source
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Xuesong Wu, Yan Zhao, and Haibo Ge*
Department of Chemistry and Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, IN 46202
(USA)
Supporting Information Placeholder
atmospheric O2.6 On the basis of these studies, it is believed that
ABSTRACT: The direct carbonylation of aromatic sp2 and unꢀ
selective oxidation of NꢀmethylꢀNꢀalkyl substituted amides could
activated sp3 C−H bonds of amides was achieved via nickꢀ
be reached, and the in situ generated iminium ion intermediates
el/copper catalysis under atmospheric O2 with the assistance of a
could then act as highly reactive electrophiles for the nucleophilic
bidentate directing group. The sp2 C−H functionalization showed
addition of an organometallic species. Following this process,
high regioselectivity and good functional group compatibility.
aerobic oxidative intramolecular dehydrogenative cyclization
The sp3 C−H functionalization showed high siteꢀselectivity by
(IDC) could occur to provide succinimides as the products
favoring the C−H bonds of αꢀmethyl groups over those of the αꢀ
[Scheme 1 (2)]. On the basis of recent reports of nickelꢀcatalyzed
methylene, βꢀ or γꢀmethyl groups. Moreover, this reaction showed
bidentate ligandꢀdirected C−H functionalization of arenes and
alkanes,7 herein, we report the chelationꢀassisted siteꢀselective
a predominant preference for functionalizing the αꢀmethyl over αꢀ
carbonylation of C(sp2)−H and C(sp3)−H bonds via nickel/copper
phenyl group. Mechanistic studies revealed that nickel/copper
synergistic catalysis is involved in this process.
synergistic catalysis with N,Nꢀdimethylforamide (DMF) as the
carbonyl source under atmospheric O2.8 It is noteworthy that this
reaction represents the first example of nucleophilic addition to a
carbonꢀheteroatom double bond via nickelꢀcatalyzed C−H funcꢀ
tionalization on sp2 carbons. Additionally, it is the first example
Transition metalꢀcatalyzed C−H functionalization has experienced
a tremendous development over the past decade.1 This method
of transition metalꢀcatalyzed siteꢀselective nucleophilic addition
reactions of unactivated C(sp3)−H bonds. Moreover, the use of
allows for the direct derivatization of (hetero)arenes and alkanes
two distinct metals as the synergistic catalysts in an sp3 C−H
in a highly siteꢀselective manner by avoiding the prefunctionalizaꢀ
tion in the classic coupling reactions. Within this reaction class,
direct carbonylation has attracted considerable attention in recent
years due to the prevalent presence of the carbonyl group in orꢀ
ganic molecules [Scheme 1 (1)].2 For example, Pd, Co, Rh, or Ruꢀ
catalyzed processes have been well established on sp2 carbons.3
Additionally, direct carbonylation of C(sp3)−H bonds has been
demonstrated with Pd, Rh, or Ru catalysis.4 Despite a powerful
strategy, the use of toxic CO (mainly at high pressure) associated
with somewhat troublesome gas handling procedure limits the
application of this method. Therefore, it would be highly desirable
if nontoxic and inexpensive reagents, preferably the organic solꢀ
vents, could serve as the carbonyl source.
functionalization process is rare.
Table 1. Optimization of Reaction Conditionsa
Scheme 1. Transition MetalꢀCatalyzed Direct Carbonylation of
sp2 and sp3 carbons
aReaction conditions: 1a (0.2 mmol), Ni source (10 mol%), Cu
Cooperꢀcatalyzed aerobic cross dehydrogenative coupling reacꢀ
tions of amines have been well studied.5 Very recently, intramoꢀ
lecular dehydrogenative cyclization reactions of hydrazones have
also been demonstrated in our group with copper catalysis under
source (20 mol%), base, additive (1.0 eq), O2 (1 atm), 3.0 mL of
o
b
solvent, 160 C, 24 h. Yields and conversions are based on 1a,
1
determined by HꢀNMR using dibromomethane as the internal
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c
d
functional groups including methoxyl, methyl, halogen (F, Cl and
standard. Isolated yields. At 140 °C. TBAB = Tetrabutylammoꢀ
nium bromide. TBAI = Tetrabutylammonium iodide. TBAPF6 =
Tetrabutylammonium hexafluorophosphate. THAB = Tetrahepꢀ
tylammonium bromide. Q = 8ꢀquinolinyl.
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Br), cyano, trifluoromethyl, and nitro groups are compatible with
the catalytic conditions (2aꢀj). In addition, substrates with an elecꢀ
tronꢀwithdrawing group on the benzene ring gave lower yields
compared with those with an electronꢀdonating group. Considerꢀ
ing that a nucleophilic addition step might be involved in the proꢀ
cess, the above observed results are not surprising since an elecꢀ
tronꢀwithdrawing group decreases the nucleophilicity of the in
situ generated nucleophile. Furthermore, it was found that the
benzene ring could also be effectively replaced by naphthalene
moiety (2k and 2l). Unfortunately, heteroaromatic substrates
failed to provide any desired products.9
Our investigation began with direct carbonylation of Nꢀ
(quinolinꢀ8ꢀyl)benzamide (1a) in DMF via nickel/copper bimetalꢀ
lic catalysis under atmospheric oxygen (Table 1). After an extenꢀ
sive screening of the catalysts, the desired product, 2ꢀ(quinolinꢀ8ꢀ
yl)isoindolineꢀ1,3ꢀdione (2a) was obtained in 23% yield by the
combination of catalytic amounts of NiI2 and Cu(acac)2 with 1
equivalent of Na2CO3 as the base (entry 8). Next, the screening of
the base was carried out, and it turned out that Li2CO3 is optimal,
providing 2a in 37% yield (entry 11). Interestingly, a higher yield
was then observed with reduced amounts of Li2CO3, indicating
that the base might compete with the substrate for the metal coorꢀ
dination (entry 12). Further optimization showed that this reaction
could be significantly improved by the addition of a quaternary
ammonium salt, presumably due to the increased solubility of the
reagents and intermediates by this ammonium salt (entries 13ꢀ16).
It was also noticed that both a nickel and copper catalyst are reꢀ
quired for this process, suggesting that this reaction is performed
via a synergistic catalysis (entries 17 and 18).
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Table 3. Scope of Aliphatic Amidesa,b
Table 2. Scope of Aromatic Amidesa,b
aReaction conditions: 3 (0.2 mmol), NiBr2 (10 mol%), Cu(acac)2
(20 mol%), Na2CO3 (0.3 eq), TBAPF6 (1.5 eq), O2 (1 atm), 5.0
mL of DMF, 160 oC, 24 h. bIsolated yield.
Next, we carried out the substrate scope study on aliphatic amꢀ
ides (Table 3). As expected, good yields were obtained with 2,2ꢀ
disubstituted propanamides bearing either the linear or cyclic
chains under modified reaction conditions (4aꢀl). As shown in the
previous studies,4,7 this reaction showed a high siteꢀselectivity by
preferring the methyl group over the methylene groups including
the relatively reactive benzyl group (4f). Furthermore, a predomiꢀ
nant preference of functionalizing the βꢀC−H over γꢀ or δꢀC−H
bonds of methyl groups was also observed, indicating that the
formation of a fiveꢀmembered ring intermediate in the cyclometꢀ
alation step is favored over the sixꢀ or sevenꢀmembered ring inꢀ
termediates. Moreover, with the 2ꢀphenylꢀsubstituted substrate,
sp3 C−H functionalization of the methyl group is preferred over
the sp2 C−H functionalization (4e). It should be mentioned that a
quaternary α–carbon is required for this reaction because subjecꢀ
tion of amides 5ꢀ8 to the reaction conditions did not afford any
desired products. Additionally, 2,2ꢀdiethylꢀNꢀ(quinolinꢀ8ꢀ
yl)butanamide (9) failed this reaction, suggesting that the forꢀ
mation of a sixꢀmembered cyclometalated intermediate is not
feasible under the current reaction conditions.
aReaction conditions: 1 (0.2 mmol), NiI2 (10 mol%), Cu(acac)2
(20 mol%), Li2CO3 (0.4 eq), THAB (1.0 eq), O2 (1 atm), 3.0 mL
of DMF, 160 oC, 24 h. bIsolated yield.
Following the above studies, we then carried out the investigaꢀ
tion on the reaction mechanism. It has been reported that DMF
could release carbon monoxide at high temperature, and thus the
With the optimized conditions in hand, the scope study of aroꢀ
matic amides was carried out. As shown in Table 2, a variety of
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released CO could potentially participate in this process as the
carbonyl source.10 To clarify this, DMF(13C=O) was used as the
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Scheme 4. Deuterium Labeling Experiments of C(sp2)−H Activaꢀ
tion
solvent to replace regular DMF (Scheme 2). It was found that
only trace amount of [13C]ꢀ2a was obtained from the reaction,
indicating that the incorporated carbonyl group mainly comes
from the methyl group. On the basis of these results, we then carꢀ
ried out some control experiments with a series of Nꢀcontaining
solvents. Not surprisingly, the reaction could be performed with
an Nꢀmethyl solvent such as N,Nꢀdimethylacetamide or Nꢀ
methylpyrrolidone. In an Nꢀethyl solvent (diethylformaide), only a
small amount of 2a was obtained, presumably arisen from the
insertion of CO generated from the solvent upon heating.
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In contrast, a first order kinetic isotope effect was observed
with 3c in the sp3 C−H functionalization process, indicating that
the cyclometalation step of an aliphatic amide is the rateꢀ
determining step (Scheme 5). Interestingly, an apparent H/D exꢀ
change also occurred with the product. Furthermore, subjection of
[D2]ꢀ4c into the standard reaction conditions provided 4c in 90%
yield. These results suggested that the observed H/D exchange of
the product [D2]ꢀ4c has arisen from the formation of an enolate
ion followed by protonation.
Scheme 2. Control Experiments and Isotope Studies of Aromatic
Substrates
Scheme 5. Deuterium Labeling Experiments of C(sp3)−H Activaꢀ
tion
To gain more insights on the reaction mechanism, several poꢀ
tential intermediates (10ꢀ13) were then synthesized and subjected
to the reaction conditions (Scheme 3). Among these substrates,
only 2ꢀ((dimethylamino)methyl)ꢀNꢀ(quinolinꢀ8ꢀyl)benzamide (12)
afforded the desired product, suggesting that an NꢀmethylꢀNꢀ
methylenemethanaminium species is involved in this process as a
reactive nucleophile.
On the basis of the above observations and the previous reꢀ
ports,7 a plausible catalytic cycle is proposed (Scheme 6). It is
believed that this process is initiated from coordination of amide 1
to a NiII species followed by a ligand exchange step under basic
conditions to give the nickel complex A. Then, cyclometalation of
A occurs via either sp2 or sp3 C−H bond activation to generate the
intermediate B. It is noteworthy that sp2 C−H bond cleavage is a
reversible step while sp3 C−H bond cleavage is an irreversible
step as discussed in Schemes 3 and 4. Concurrently, an Nꢀmethylꢀ
Nꢀmethylenemethanaminium species C is generated in situ from
DMF via a sequential decarbonylation, nucleophilic addition, and
elimination process under copper catalysis with oxygen as the
external oxidant.11 Nucleophilic addition of the intermediate B to
the iminium ion intermediate C provides the intermediate D. Oxiꢀ
dation of intermediate D followed by intramolecular nucleophilic
addition gives rise to the intermediate F which then produces the
product 3 or 4 via oxidation and hydrolysis.
Scheme 3. Control Experiments of Aromatic Substrates
A deuteriumꢀlabeling experiment was then carried out to furꢀ
ther probe the reaction mechanism of aromatic amides (kinetic
isotope effect), and an apparent H/D exchange was observed for
[D5]ꢀ1a (Scheme 4). This suggests that C−H bond cleavage
should be a reversible step in the sp2 C−H functionalization proꢀ
cess.
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application of this transformation is currently undergoing in our
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laboratory.
Scheme 6. Plausible Reaction Mechanism
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ASSOCIATED CONTENT
Supporting Information
Experimental details including characterization data, copies of 1H
and 13C NMR spectra. This material is available free of charge via
the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
geh@iupui.edu
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
We gratefully acknowledge NSF CHEꢀ1350541 and Indiana Uniꢀ
versityꢀPurdue University Indianapolis for financial support.
To further broaden the synthetic utility of this process, ringꢀ
opening reactions of succinimide 4j were carried out (Scheme
7).4d Treatment of 4j under acidic conditions provided the hydroꢀ
lyzed product 1ꢀ(carboxymethyl)cyclopentaneꢀ1ꢀcarboxylic acid
(14) in 85% isolated yield. On the other hand, selective alcoholyꢀ
sis of 4j occurred with NaOMe in MeOH at room temperature,
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affording
methyl
2ꢀ(1ꢀ((2ꢀ(pyridinꢀ2ꢀyl)propanꢀ2ꢀ
yl)carbamoyl)cyclopentyl)acetate (15) in 74% yield. Furthermore,
the quinolinꢀ8ꢀyl moiety of 2l could also be readily removed by
treatment with ammonia, affording the corresponding naphꢀ
thalimide derivative 16.12
Scheme 7. Derivatization of Succinimides
In summary, a direct carbonylation of C−H bonds of aromatic
or aliphatic amides was developed through nickel/copper synerꢀ
gistic catalysis under atmospheric oxygen with DMF as the CO
source. The sp2 C−H bond functionalization process was featured
with high regioselectivity and a good compatibility with a broad
range of functional groups. The sp3 C−H bond functionalization
process showed a predominant preference for the αꢀmethyl groups
over the αꢀmethylene and βꢀ or γꢀ methyl groups. Furthermore, the
preference of functionalizing the sp3 C−H bond of the αꢀmethyl
group over the sp2 C−H bond of the αꢀphenyl group was also
observed. Mechanistic studies suggested that this reaction is perꢀ
formed via nickel/copper synergistic catalysis with the nickel
species initiating the C−H activation of an amide to generate a
nucleophile and DMF providing an electrophile by the copper
species. Interestingly, it was found that C−H bond cleavage of
aromatic amides is a reversible step while C−H bond cleavage of
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activation on sp3 carbons is a more challenging process compared
with sp2 carbons. The detailed mechanistic study and potential
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