Pd-catalyzed amidation of 1,3-diketones with CO and azidesviaa nitrene intermediate

Article abstract of DOI:10.1039/d0cc04565a

An efficient Pd-catalyzed amidation of 1,3-diketones has been developed using carbon monoxide and organic azides. This reaction provides a step-economic approach to produce β-ketoamides from readily available compounds under mild ligand-, oxidant-, and base-free conditions. The mechanistic studies showed that the reaction occurred through anin situgenerated isocyanate intermediate.

Full text of DOI:10.1039/d0cc04565a

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DOI: 10.1039/D0CC04565A
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Pd-Catalyzed Amidation of 1,3-Diketones with CO and Azides via
Nitrene Intermediate
Zheng-Yang Gu,a,b Jie Chenb,c and Ji-Bao Xia*b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
a) Drug molecules containing -ketoamide as a key substructrue
An efficient Pd-catalyzed amidation of 1,3-diketones has been
developed using carbon monoxide and organic azides. This
reaction provides a step-economic approach to produce β-
ketoamides from readily available compounds under mild
ligand-, oxidant-, and base-free conditions. The mechanistic
studies showed that the reaction occurred through an in situ
generated isocyanate intermediate.
OH
O
CF3
OH
O
N
N
H
H3C
N
N
H
S
CH3
CN
Teriflunomide
O
O
Piroxicam
OH
O
OH
O
O
NH2
OH
OH
N
N
H
H
H
O
The β-Ketoamide derivatives are one of the most useful
and reliable synthetic intermediates in chemical industries.
They have been widely used to synthesize organic dyes,
pesticide intermediates, fungicides, and biologically active
compounds.1 Furthermore, β-Ketoamides are broadly
found in drug molecules such as Teriflunomide,2 Piroxicam3
and Lymecycline4 etc., which are used for the treatment of
multiple sclerosis, rheumatoid arthritis and infectious
diseases (Scheme 1a). Several methods have been reported
for the synthesis of β-ketoamides, including the reaction of
amines with ketoesters, acetyl ketenes, isoxazolium salts
and diazonium salts.5 However, these methods are
characterized by one or more of the following limitations,
strict catalytic systems, narrow substrate ranges, excessive
temperatures, or employment of unenvironmentally
reagents. Therefore, the development of novel and
efficient catalytic methods for the synthesis of β-
ketoamides are of great significance and rewarding.
OH
H
HO CH3
N
Lymecycline
H3C
CH3
b) Our previous work: Rh-catalyzed aromatic C(sp2)_H amidation
O
H
R
Rh catalyst
N
Ar
+
CO
+
R
N3
Ar
H
This work
c)
: Pd-catalyzed amidation of 1,3-diketones via carbonylation
O
O
O
O
Pd(OAc)2 (5 mol%)
+
+
R N3
R
CO
N
MeCN, 40 C
(balloon)
H
 selective C C bond cleavage  tandem reaction

C
C & C N formation
 broad scope  mild conditions  ligand-free  oxidant-free  base-free
Scheme 1 Transition-metal-catalyzed formal C–H amidation
with CO and organic azides.
reactions such as addition,7 radical coupling8 and C–H
activation reactions.9 Organic azides have been proved
convenient nitrene precursors, featuring no need of
external oxidant and release of N2 as the only by-product.10
Nitrenes have emerged as useful intermediates for the
formation of C–N bonds in organic synthesis.6 Recently, the
transition-metal-catalyzed nitrene chemistry has attracted
considerable attentions in various nitrogen transfer
In
the
last
decades,
transition-metal-catalyzed
carbonylative reactions have been widely used to
synthesize carbonyl compounds utilizing carbon monoxide
(CO) as a cost-effective C1 source.11 Metal-catalyzed
nitrene coupling reaction with CO to introduce nitrogen
moiety into carbonyl compounds has experienced
considerable growth, but mainly limited to the preparation
of ureas and carbamates.12 In continuation of our interest in
a. College of Textiles and Clothing & Key Laboratory for Advanced Technology in
Environmental Protection of Jiangsu Province, Yancheng Institute of Technology,
Jiangsu, 224003, China.
b. State Key Laboratory for Oxo Synthesis and Selective Oxidation, Center for
Excellence in Molecular Synthesis, Suzhou Research Institute of LICP, Lanzhou
Institute of Chemical Physics (LICP), University of Chinese Academy of Sciences,
Chinese Academy of Sciences, Lanzhou 730000, China. E-mail:jibaoxia@licp.cas.cn
c. Suzhou Kintor Pharmaceuticals, Inc. Suzhou Industrial Park, Suzhou, 215123,
China.
developing
transition-metal-catalyzed
carbonylation
reactions,13 we recently reported a Rh-catalyzed C–H
amidation of simple arenes with CO and azides via metal-
nitrene intermediate (Scheme 1b).14 We hypothesize that
carbonylation of 1,3-diketones with CO and azides would
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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olefin group can survive well under our conditions (3o). Next,
with azidobenzene (2p) as substrate, the corresponding product
be realized through a metal-nitrene intermediate, which
has not been explored yet. Herein, we report an efficient
Pd-catalyzed formal C(sp3)–H amidation of 1,3-diketones to
product β-ketoamides with CO and azides under mild
conditions (Scheme 1c).
View Article Online
DOI: 10.1039/D0CC04565A
3p was obtained in 31% yield with PdCl2 as catalyst in DMA at 70
°C,12b along with 53% yield of 1,3-diphenylurea as a by-product.
Table 2 Substrate scope of organic azidesa
We started by investigating the amidation of
acetylacetone (1a) with CO (balloon pressure) and 4-
methylbenzenesulfonyl azide (2a) in the presence of
various transition-metal catalysts (Table 1). To our delight,
the desired product 3a was obtained in 32% yield with 5
mol% [Rh(cod)Cl]2 as catalyst in MeCN at 80 °C followed by
treatment with acid (Table 1, entry 1). Trace amount of
product could be detected with other metal catalysts, such
as Co(OAc)2, Cu(OAc)2 (Table 1, entries 2-3). When Pd(OAc)2
was used, the yield of 3a was increased to 57% (Table 1,
entry 4). Better results were obtained using Pd(TFA)2 and
Pd(OPiv)2 (Table 1, entries 5-6). Lower yields were obtained
when we examined other solvents (see Table S1 in
Supporting Information). When we increased the amount
of 1a to 1.0 mmol, the yield of product 3a was increased to
87% (Table 1, entry 7). The reaction showed good reactivity
O
O
O
O
Pd(OAc)2 (5 mol%)
+
R
N3
+
R
CO
Me
O
N
MeCN, 40 C, 8 h
then HCl/H2O
Me
Me
(balloon)
H
1a
2
3
3a
3b
R' = Me,
R' = H,
, 82%
, 80%
O
O
O
O
O
S
O
S
O
3c
R' = OMe, , 86%
3d
3e
3f
3g
R' = F,
, 76%
, 71%
, 62%
Me
Me
N
H
Me
N
H
R' = Cl,
R' = Br,
R' =CF3,
b
b
R'
3h
, 95%
, 59%
O
O
O
O
O
O
O
O
O
O
O
S
O
S
S
N
H
Me
N
Me
N
H
H
S
3i
3j
, 55%
3o
, 82%
O
, 74%
O
3k
R = Bn,
R = nBu,
R = nPr,
R = iPr,
, 75%
O
O
O
O
S
66%b
, 71%
3l
,
3m
3n
Me
N
H
Me
N
R
H
, 70%
c
3p
, 31%
o
when reducing temperature to 40 C (Table 1, entry 8).
aReaction conditions: 1a (0.5 mmol), 2 (1.0 mmol), CO (balloon),
Further reducing temperature to 25 oC, only 61% yield of 3a
was obtained (Table 1, entry 9).
Pd(OAc)2 (5 mol%), CH3CN (3 mL), 40 °C, 8 h; then 2N HCl (2 mL), 25
oC, 1 h, isolated yield was provided. 80 °C, 18 h. PdCl2 (5 mol%),
b
c
Table 1 Optimization of the reaction conditionsa
DMA, 70 °C, 12 h.
O
O
O
O
catalyst (5 mol%)
+
+
Ts N3
Ts
CO
(balloon)
Me
N
Table 3 Substrate scope of 1,3-diketonesa
solvent, T., 1 h
then H3O+
Me
Me
H
1a
2a
3a
O
O
O
O
Pd(OAc)2 (5 mol%)
Entry
1
Catalyst
Solvent
MeCN
T (°C)
80
80
80
80
80
80
80
40
Yield (%)[b]
32
+
Ts N3
+
Ts
CO
N
H
MeCN, 40 C, 8 h
then HCl/H2O
Me
(balloon)
[Rh(cod)Cl]2
Co(OAc)2
Cu(OAc)2
Pd(OAc)2
Pd(TFA)2
Pd(OPiv)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
1
2a
3
2
3
4
5
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
trace
trace
57
58
67
87
85 (82)[c]
61
O
O
O
O
O
O
Me
Ts
Me
Me
Ts
N
Ts
N
N
H
H
H
Me
3r
R
b
3s
, 80%
, 76%
R = H,
3t
R = Me, , 86%
3u
R = CN, , 42%
3q
, 71%
O
c
6
7[d]
8[d]
9[d]
O
O
O
O
O
R
Ts
Ts
Ts
N
N
N
H
H
H
X
25
MeO
3v
, 84%
3w
3x
3y
, 71%
, 76%
R = Me,
R = OMe,
, 78%
X = O,
X = S, 3z
aReaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), CO (balloon),
catalyst (5 mol%), solvent (3 mL), 8 h, then 2N HCl (2 mL), 25 oC, 1 h.
bDetermined by 1H NMR analysis using 1,1,2,2-tetrachloroethane as
an internal standard. cIsolated yield. dWith 2a (1.0 mmol).
, 85%
aReaction conditions: 1a (0.5 mmol), 2 (1.0 mmol), CO (balloon),
Pd(OAc)2 (5 mol%), CH3CN (3 mL), 40 °C, 8 h; then 2N HCl (2 mL), 25
oC, 1 h, isolated yield was provided. Heptane-3,5-dione was used.
b
c80 °C, 18 h.
With the optimal reaction conditions in hand, we first
investigated various organic azides 2 for the amidation of 1a
(Table 2). Arylsulfonyl azides with electron-donating groups
(Me, OMe) on the benzene ring showed excellent reactivity,
leading to the desired products 3a–c in 80–86% yields. The
halogen (F, Cl, Br) substituted benzenesulfonyl azides were well
tolerated, and the corresponding products were obtained in
moderated to good yields (3d–f, 62–76%). The 4-
Then, we investigated the scope of 1,3-diketones with azide
2a (Table 3). It was gratifying to observe that heptane-3,5-dione
(1q) reacted well under the standard conditions, affording the
amidation product 3q in 71% yield. Notably, amidation of
unsymmetrical 1,3-diketone 5,5-dimethylhexane-2,4-dione (1r)
generated 3r as the single product in 76% yield via selective C–C
bond cleavage. Similarly, the benzoylacetone (1s) reacted with
2a gave the single product 3s in 80% yield. Furthermore, the p-
Me, p-CN, m-Me and m-MeO substituted benzoylacetones
displayed moderate to good reactivity, affording the
corresponding products 3t–w in 42–86% yields. The 1,3-
diketones containing naphthalene, furan, and thiophene groups,
(trifluoromethyl)benzenesulfonyl azide showed
a
lower
reactivity, delivering the product 3g in 59% yield. The naphthyl
and heteroarylsulfonyl azides also worked very well and the
products 3h–j were obtained in 55–95% yields. The alkylsulfonyl
azides also exhibited good reactivity in this transformation,
producing the target products 3k–o in 66–75% yields. Notably,
2 | J. Name., 2012, 00, 1-3
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Pd(OAc)2 (5 mol%)
were also well tolerated in this reaction, furnishing the products
3x–z in 71–78% yields.
View Article Online
Ts N3
+
CO
Ts NH2
+
Ts NCO
DOI: 10.1039/D0CC04565A
MeCN, 40 C, 4 h
(a)
(balloon)
2a
75%
25%
Next, we evaluated other 1,3-dicarbonyl compounds for this
amidation reaction (Table 4). With cyclic diketone 5,5-
dimethylcyclohexane-1,3-dione (1b) as substrate, we found that
enolate 4a was isolated in 85% yield without C–C bond cleavage
no matter with or without the acidic treatment. Similarly, other
cyclic 1,3-diketones or 1,3-dicarbonyl compound were also
proved reactive, furnishing the corresponding products in good
yields (4b–e, 60–84%). Besides cyclic 1,3-dicarbonyls, the β-
ketoesters, such as methyl 3-oxobutanoate, ethyl 3-
oxobutanoate, and benzyl 3-oxobutanoate, also worked very
well, affording products 4f–h in 68–71% yields. And further
applications of this method were demonstrated in the
Supporting Information (Scheme S1).
Detectd by GC-MS
Pd(OAc)2 (5 mol%)
O
O
O
O
CO (balloon)
O
O
O
+
Ts NH2
Ts NCO
Ts
Ts
(b)
(c)
Me
Me
N
H
MeCN, 40 C, 8 h
then HCl/H2O
N.R.
Me
Me
1a
3a
3a
O
Pd(OAc)2 (5 mol%)
+
N
H
MeCN, 40 C, 8 h
then HCl/H2O
90%
Me
Me
1a
Scheme 2 Control experiments.
Based on the mechanistic studies, a plausible reaction
pathway has been proposed in Scheme 3.15 Initially, the organic
azide 2 undergoes ligand exchange with palladium catalyst to
form intermediate A. Subsequently, the probable palladium
nitrene species B is generated simultaneously with the release
of N2. The insertion of CO into species B affords palladium-
isocyanate complex D via transition state C.15 Then, attack of
Table 4 Substrate scope of other 1,3-dicarbonyl compoundsa
O
O
O
O
Pd(OAc)2 (5 mol%)
Ts
Ts
+
CO
+
Ts N3
N
MeCN, 40 C, 8 h
H
(balloon)
OH
1
2a
4
palladium-isocyanate complex
D with 1,3-diketone as a
O
O
O
O
O
O
O
O
nucleophile leads to intermediate E and regenerates the
palladium catalyst. Next, C–C bond cleavage takes place under
acidic conditions via nucleophilic attack of H2O to the more
Me
Ts
Ts
Ts
N
Me
N
N
N
H
H
H
H
Me
Me
OH
OH
OH
OH
electron-deficient carbonyl group in
E and subsequent
b
4a
4b
4c
4d
, 85%
O
, 71%
, 84%
, 60%
rearrangement, producing enolate 3' along with acetic acid.
Finally, rapid tautomerization of enolate 3' affords more stable
β-ketoamide 3 as the final product.
O
O
O
O
O
O
O
Me
O
Ts
Ts
Ts
Ts
N
N
MeO
N
EtO
Me
4g
N
BnO
N
H
H
H
H
OH
O
H3O+
N
OH
Me
4f
OH
OH
Me
4h
OH
R
R
N3
Pd(OAc)2
Me
N
Me
4e
H
2
, 74%
, 71%
, 70%
, 68%
O
Me
O
O
H2O
E
R
OH
O
O
O
Me
N
H
Me
aReaction conditions: 1a (0.5 mmol), 2 (1.0 mmol), CO (balloon),
Pd(OAc)2 (5 mol%), CH3CN (3 mL), 40 °C, 8 h, isolated yield was
provided. b80 °C, 18 h.
[Pd]
N
[Pd]
N
O
HO
Me
O
Me Me
Pd
Me
1a
N
A
N
C
R
D
R
AcOH
OH
O
O
To understand the reaction mechanism, several control
experiments were performed. We carried out the reaction of
azide 2a with CO catalyzed by Pd(OAc)2, affording 4-
R
N
N2
Me
Me
[Pd]
H
3'
N
R
[Pd]
N
R
C O
methylbenzenesulfonamide
(TsNH2)
and
4-
C
B
O
R
N
methylbenzenesulfonyl isocyanate (TsNCO) in 75% and 25% GC-
yield, respectively (Scheme 2a). It should be noted that no
product was detected in the absence of Pd catalyst for this
reaction. No reaction occurred when Pd-catalyzed amidation of
1a with CO and TsNH2 was carried out (Scheme 2b). It
demonstrates that TsNH2 was not the intermediate. Next, Pd-
catalzyed amidation of 1a with TsNCO was carried out, giving 3a
in 90% NMR yield (Scheme 2c). These results indicate that
TsNCO might be the possible intermediate of this amidation
reaction. In order to verify the role of palladium catalyst in this
reaction, the rate curve experiments were carried out using 1a
and TsNCO with or without Pd(OAc)2 catalyst. The result showed
that Pd-catalyzed reaction is faster than the reaction without
palladium catalyst. This result indicates that palladium catalyst
might work as a Lewis acid catalyst, which accelerates the
amidation reaction of 1,3-diketone with isocyanate
intermediate (details see Figure S1 in Supporting Information).
H
3
CO
Scheme 3 Plausible reaction pathway.
In summary, we have developed a mild and efficient Pd-
catalyzed amidation of 1,3-diketones with CO and organic
azides to produce β-ketoamides. This three-component
carbonylation reaction is realized via metal nitrene
intermediate, which is supported by control experiments.
This strategy provides a simple and step-economic
approach to synthesis β-ketoamides from readily available
compounds without additional ligand, oxidant, or base. The
mechanistic studies have showed that the palladium
catalyst not only promotes the in-situ formation of the
isocyanate intermediate, but also accelerates the
subsequent amidation step as a Lewis acid catalyst.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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Yang and S. J. Ji, J. Org. Chem., 2018, 83, 9364-9369; (c)T.
We are grateful to the financial support provided by
NNSFC (21772208, 21702212), NSFC of Jiangsu Province
(BK20161260, BK20170404), Key Research Program of
Frontier Sciences of CAS (QYZDJSSW-SLH051), Joint Open
Fund of Jiangsu Collaborative Innovation Center for
Ecological Building Material and Environmental Protection
Equipments and Key Laboratory for Advanced Technology
in Environmental Protection of Jiangsu Province (JH201863,
JH201832).
Jiang, Z. Y. Gu, L. Yin, S. Y. Wang and S. J. Ji, JV.ieOwrAgr.ticClehOenmlin.e,
DOI: 10.1039/D0CC04565A
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Conflicts of interest
There are no conflicts to declare.
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