Pd-Catalyzed C(sp2)-H aminocarbonylation using the Langlois reagent as a carbonyl source

Article abstract of DOI:10.1039/c8ob01421c

A Pd-catalyzed C(sp²)-H aminocarbonylation of aryl carboxamides assisted by an N,S-bidentate directing group was developed, in which cheap and stable sodium trifluoromethanesulfinate was first utilized as a carbonyl source. The reaction can be applicable to a wide range of carboxamides with good functional group tolerance and afford isoindole-1,3-diones in moderate to good yields.

Full text of DOI:10.1039/c8ob01421c

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Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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DOI: 10.1039/C8OB01421C
Organic & Biomolecular Chemistry
Pd-Catalyzed C(sp2)-H Aminocarbonylation Using Langlois Reagent
as Carbonyl Source
Received 00th January 20xx,
Accepted 00th January 20xx
Xiao-Fang Li, Lin-Feng Shi, Xing-Guo Zhang,* Xiao-Hong Zhang*
A Pd-catalyzed C(sp2)-H aminocarbonylation of aryl carboxamides assisted by N, S-bidentate directing group was
developed, in which the cheap and stable sodium trifluoromethanesulfinate was firstly utilized as carbonyl source. The
reaction can be applicable to a wide range of carboxamides with good functional group tolerance and afford isoindole-1,3-
diones in moderate to good yields.
DOI: 10.1039/x0xx00000x
www.rsc.org/
novel approach to isoindole-1,3-dione derivatives bearing methylthio
group.
Introduction
In the past decades, great breakthroughs have been achieved in
Results and discussion
transition-metal-catalyzed C-H carbonylation, which provides a
Table 1. Screening Conditions a
[1]
versatile synthetic method for carbonylated molecules.
Among
O
O
them, the direct Pd-catalyzed C-H carbonylation using carbon
monoxide (CO) as carbonyl source attracted considerable attention.
[2] However, CO gas is difficult to handle, transport and highly toxic,
catalyst
N
CF3SO2Na
N
+
H
oxidant, H2O
S
S
O
1a
[3]
2a
which restricts its usage. Recently, formic acid and its esters,
metal carbonyls, [4] aldehydes, [5] acyl chloride, [6] azodicarboxylates,
Entry
Catalyst
Oxidant (equiv)
Solvent
Yield (%)
[7]
[8]
[9]
2,2-azobisisobutyronitrile (AIBN),
and some solvents
including DMF, nitromethane or CHCl3 were reported to act as CO
sources to construct various carbonyl compounds. Nevertheless, the
development of new CO surrogates by generating CO in-situ for the
carbonylation is still desirable.
1
2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
Cu(OTf)2 (1.0) Dioxane
5
0
Cu(OTf)2(1.0)
Cu(OTf)2(1.0)
Cu(OTf)2(1.0)
Cu(OTf)2(1.0)
DMSO
DCE
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
3
18
21
8
For numerous Pd-catalyzed C–H carbonylation reactions,
directing groups are usually required to realize selectivity of these
4
[10]
5
transformations. Various functional groups, such as amides,
[11]
[12]
[13]
amines,
N-containing heterocycles,
amidines,
hydroxyl
6
Pd(MeCN)2Cl2 Cu(OTf)2(1.0)
32
50
NR
12
33
6
including the phenolic hydroxyl groups, [14] carboxylic acids, [15] and
7
Pd(TFA)2
-
Cu(OTf)2(1.0)
Cu(OTf)2(1.0)
CuCl2(1.0)
[16]
phosphonic/phosphinic acids
have been utilized as directing
groups to realize the C-H carbonylation. However, the 2-
8
methylthioaniline auxiliary was seldom used as the directing-group
9
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
[17]
to construct structurally diverse molecules,
catalyst poisoning by the mercapto group.
presumably due to
As part of our
[18]
10
11
12
13
14 b
15 c
16 d
Cu(BF4)2(1.0)
Cu(NO3)2(1.0)
-
continuing interest in synthesis of sulfur compounds, [19] we herein
wish to report a Pd-catalyzed C(sp2)-H aminocarbonylation of aryl
carboxamides assisted by an N, S-bidentate directing group. The
readily available sodium trifluoromethanesulfinate (CF3SO2Na) was
firstly used as CO surrogate. The unexpected reaction provided a
NR
55
66
77
NR
Cu(OTf)2(1.2)
Cu(OTf)2(1.2)
Cu(OTf)2(1.2)
Cu(OTf)2(1.2)
a Reaction conditions: 1a (0.2 mmol), CF3SO2Na (0.4 mmol), Pd
catalyst (10 mol %), oxidant (1.0 equiv), H2O (4.0 equiv) in
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carboxamides were tested, but no desired products can be
obtained.
solvent (2 mL) at 120°C under air atmosphere for 24 h; Isolated
b
c
d
yield;
CF3SO2Na (2.5 equiv);
CF3SO2Na (2.7 equiv);
Without CF3SO2Na; NR = no reaction.
The reaction of N-(2-(methylthio)phenyl)benzamide 1a with
sodium trifluoromethanesulfinate (CF3SO2Na) was chosen as the
model reaction to optimize the reaction conditions, and the results
were listed in Table 1. Initially, the reaction was conducted in the
presence of 10 mol % Pd(OAc)2, 1 equiv of Cu(OTf)2 and 4.0 equiv
H2O in dioxane at 120 oC for 24 h, but product 2a was isolated only in
5% yield (entry 1). Moreover, the structure of product 2a was
confirmed by X-ray crystallography. Other solvents including DMSO,
DCE and PhCl were also examined, and 21 % yield of product 2a was
obtained in PhCl (entry 4). Encouraged by these results, different
catalysts such as PdCl2, Pd(MeCN)2Cl2 and Pd(TFA)2 were further
screened (entries 5-7). It was found that Pd(TFA)2 was the most
suitable catalyst for the aminocarbonylation and a 50% yield was
obtained (entry 7), the reaction did not work in the absence of
palladium catalyst (entry 8). Subsequently, various oxidants
including CuCl2, Cu(BF4)2 and Cu(NO3)2 were tested, but all gave
worse results than Cu(OTf)2 (entries 9-11). However, the reaction
could not proceed without copper salts (entry 12). The yield was
slightly enhanced to 55 % when the loading of Cu(OTf)2 was
increased to 1.2 equiv (entry 13). Then, various equivalents of
CF3SO2Na were screened (entries 14-16). We were pleased to find
that a 77 % yield was obtained when 2.7 equiv CF3SO2Na was used
(entry 15). Moreover, no carbonylated product was generated in the
absence of CF3SO2Na, which suggested CF3SO2Na actually acted as
the carbonyl source (entry 16).
Table 2. Scope with respect to the aryl carboxamides a
Me
O
O
O
S
S
S
S
S
N
N
N
Me
O
O
O
2a, 77%
2c, 72%
2b, 55%
O
S
O
O
N
S
Me
Me
N
O
N
Et
O
2d, 64%
O
O
2f, 61%
O
Me
2e, 56%
O
S
S
MeO
O
O
N
N
N
MeO
O
O
O
2i, 35%b
2g, 52%
2h, 48%
F
O
O
N
O
N
S
S
S
F
N
F
O
O
O
2k, 49%
2j, 20%
2l, 42%
With the optimal reaction conditions in hand, the substrate
scope of various carboxamides was next investigated. As
shown in Table 2, carboxamides with both electron-donating
O
O
N
O
N
S
S
S
Cl
N
and
electron-withdrawing
groups
underwent
the
Cl
Br
O
2m, 60%
O
O
2n, 58%
O
O
2o, 52%
O
aminocarbonylation smoothly, affording the products 2b
–
2u
in moderate to good yields. Generally, aromatic amides with
electron-donating groups gave the products in higher yields
than those bearing electron-withdrawing groups. For example,
methyl, ethyl and methoxyl carboxamides provided isoindole-
S
S
S
N
N
N
I
F3CO
F3C
O
O
O
2p, 23%b
1,3-diones 2b
– 2h in 48-72 % yields, while fluoro, chloro,
2q, 53%
2r, 45%
bromo, trifluoromethoxy and trifluoromethyl substituents (2j
–
O
O
N
O
N
S
S
S
2r) were isolated in 20-60 % yields. 4-Iodide isoindole-1,3-
dione 2p was also obtained, albeit in a low yield (23%), which
could provide potential handles for further modification. A low
yield was observed in the case of 4-nitro-substituted benzamide
(18%), possibly resulting from the poor solubility of both
N
O2N
Ph
O
O
O
2s, 18%
2t, 56%
2u, 55%
a
Reaction conditions: 1 (0.2 mmol), CF3SO2Na (5.4 mmol),
reactant and product 2s
.
It was noteworthy that
Pd(TFA)2 (10 mol%), Cu(OTf)2 (1.2 equiv) and H2O (4.0 equiv) in
dry PhCl (2 mL) at 120°C under air atmosphere for 24 h; Isolated
yield. b 20 mol % of Pd(TFA)2 was used.
aminocarbonylation of aromatic amides bearing ortho-methyl
and flouro group proceeded well and the corresponding
products 2b and 2j were obtained in 55% and 20 %,
respectively. For meta-substituted amides, such as 3-methyl, 3-
methoxy and 3-fluoro benzamides, the aminocarbonylation
occurred at the less hindered ortho-position, giving the same
Notably, the C-H aminocarbonylation was also compatible with
some substituted 2-thioaniline derivatives with para-methyl, ethoxyl,
chloro and trifluoromethyl moieties, and the targeted products 4a-4d
were isolated in 51-65 % yields (Table 3). In addition, various 2-
alkylthioanlines, such as 2-ethyl and 2-cyclohexylthioaniline were
tolerated well, giving their corresponding products 4e and 4f in 52%
and 61 % yields, respectively. To our delight, when the N-(2-
(phenylthio)phenyl)benzamide 3g was reacted with CF3SO2Na under
standard conditions, the product 4g was isolated in 53 % yield.
products (2d, 2h and 2l) as those para-substituted substrates.
Gratifyingly, 4-phenyl and 2-naphthyl carboxamides also
underwent the reaction smoothly and provided products 2t and
2u in moderated yields. Unfortunately, many heterocyclic
carboxamides including furan, thiophene, and indole
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However, the reaction was totally restrained when methylthio group
(SCH3) was changed to trifluoromethylthio (SCF3, 3h), which
suggested that the electronic property of thio group affected the
aminocarbonylation dramatically.
To probe the reaction mechanism, some control experiments
were conducted as shown in Scheme 1. The reactions of N-
phenylbenzamide 5, N-(quinolin-8-yl)benzamide 7 (assisted by N, N-
bidentate ligand) and N-(2-methoxyphenyl)benzamide 9 (assisted by
N, O- bidentate ligand) with CF3SO2Na were conducted under
standard conditions, no desired products were observed (eqs. 1 , 2
and 3, Scheme 1), which demonstrated that sulfur atom in the N-
phenyl group play an important role for the aminocarbonylation.
When the reaction was conducted under CO atmosphere (CO
balloon) in the absence of CF3SO2Na, 45% yield of the targeted
product 2a was obtained (eq. 4), suggesting the reagent CF3SO2Na
acted as the CO source. Furthermore, 4 equiv of H2O18 was added
into the reaction using the anhydrous chlorobenzene (PhCl) as
solvent, the product 2a was isolated in 72 % yield with the ratio of
O18-2a : O16-2a in 4 : 3 according to the GC analysis and HRMS
results (eq. 5). These results proved that the oxygen atom of
carbonyl group might be derived from the water.
Table 3. Scope with respect to the 2-alkyl(aryl)thioanilines a
Scheme 2. Possible Mechanism
a
Reaction conditions: 1 (0.2 mmol), CF3SO2Na (5.4 mmol),
Pd(TFA)2 (10 mol%), Cu(OTf)2 (1.2 equiv) and H2O (4.0 equiv) in
dry PhCl (2 mL) at 120°C under air atmosphere for 24 h; Isolated
yield.
Scheme 1. Control Experiments
O
O
On the basis of the obtained experimental results and previous
Standard Conditions
eq. 1
eq. 2
N
N
[11f]
report,
a
plausible mechanism is proposed for this
H
CF3SO2Na
5
6, 0%
O
aminocarbonylation (Scheme 2). Initially, (CF3SO2)2Cu is formed in
the reaction of CF3SO2Na with Cu(OTf)2, which is decomposed to
O
O
[20]
release carbene :CF2 accompanied with CuF2 and SO2.
Then, the
Standard Conditions
CF3SO2Na
N
N
H
obtained CF2 carbene reacts with H2O to produce HF and CO in-situ.
[21]
N
In addition, Pd(II) coordinates with 1a to form N,S-chelated
N
O
O
7
8, 0%
intermediate A. Subsequently, the further C-H activation of benzene
ring furnishes the arylpalladium complex B with loss of a HL. Next,
the arylpalladium species B is converted into acylpalladium species C
through a carbonyl insertion. Finally, the nucleophilic displacement of
intermediates C gives the carbonylated product 2a and Pd (0), which
is oxidized by copper (II) salt to regenerate Pd (II) catalyst.
O
O
Standard Conditions
CF3SO2Na
eq.3
N
N
H
O
9
10, 0%
O
O
S
S
O
O
Standard Conditions
CO
N
Many compounds with sulfoxide group moiety have been found
eq.4
eq.5
N
H
[22]
to possess the biological activity.
Thus, the oxidation of the
O
O
2a, 45%
obtained isoindole-1,3-dione 2a was carried out with 3 equiv of m-
[23]
S
S
CPBA in CH2Cl2 at room temperature (Scheme 3, eq. 1),
the
Standard Conditions
CF3SO2Na, H2O18
corresponding sulfoxide 11 was obtained in 85% yield. In addition,
N
N
H
the methylthio group can be easily arylated using diaryliodonium
[24]
O18
2a, 72%, O18 : O16 = 4 : 3
salts under acidic conditions.
When the chloride isoindole-1,3-
dione 2m reacted with diphenyl iodinium trifluoroacetate under
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Scheme 3. Further Elaboration
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Conclusions
In conclusion, we have developed an efficient Pd-catalyzed
C(sp2)-H aminocarbonylation of aryl carboxamides bearing
N,
S-bidentate directing group. A range of carboxamides with
various functional groups underwent this reaction smoothly to
afford the corresponding isoindole-1,3-dione derivatives in
moderate to good yields. Mechanism study revealed that
carbonyl group was derived from the readily available sodium
trifluoromethanesulfinate and water. The reaction represents the
first utilization of Langlois reagent as carbonyl source.
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Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
We thank the National Natural Science Foundation of China (No.
21302144 and 21272177) and Natural Science Foundation of
Zhejiang Province (No. LR15B020002) for financial support.
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4 | J. Name., 2012, 00, 1-3
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