Palladium-Catalyzed Hydrocarbonylative C-N Coupling of Alkenes with Amides

Article abstract of DOI:10.1021/acs.orglett.8b00538

An efficient palladium-catalyzed hydrocarbonylative C-N coupling of alkenes with amides has been developed. The reaction was performed via hydrocarbonylation of alkenes, followed by acyl metathesis with amides. Both intermolecular and intramolecular react

Full text of DOI:10.1021/acs.orglett.8b00538

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Palladium-Catalyzed Hydrocarbonylative C−N Coupling of Alkenes
with Amides
Xibing Zhou,† Guoying Zhang,† Bao Gao,† and Hanmin Huang*,†,‡
†Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, Center for Excellence in Molecular
Synthesis, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, 230026, People’s Republic of China
‡State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, 730000, People’s Republic of China
S
* Supporting Information
ABSTRACT: An efficient palladium-catalyzed hydrocarbony-
lative C−N coupling of alkenes with amides has been
developed. The reaction was performed via hydrocarbonyla-
tion of alkenes, followed by acyl metathesis with amides. Both
intermolecular and intramolecular reactions proceed smoothly
to give either branched or linear amides in high turnover number (3500) with NH4Cl or NMP·HCl as a proton source under the
palladium catalysis. This reaction offers a catalytic convenient approach to deuterated amides when inexpensive NMP·DCl served
as a deuterium source.
mide bonds are among the most important linkages for
functional amides in the presence of imidazole.14 Despite the
1
Athe construction of materials and medicinal molecules. ease of transferring an amine group from the simple DMF, an
interesting question is whether common amides, such as aryl
amides and aliphatic amides derived from aliphatic acids with
long chains, can be used for the hydroaminocarbonylation of
simple alkenes. Inspired by these results and the amide
metathesis reactions,15 as well as our recent results on
carbonylation chemistry,6,16 we have become interested in
employing amides as effective amine sources for the hydro-
carbonylative C−N coupling of alkenes. We anticipated that the
acylpalladium species generated from the hydrocarbonylation
would be trapped by amides through acyl metathesis to give the
desired amides. Herein, we report an efficient and simple
approach to aliphatic amides directly from simple alkenes and
amides in the presence of CO (see Scheme 1). Notably, the
The increasing use of amides in life science and materials
science has motivated the development of efficient method-
ology toward amides.2,3 Among the numerous strategies for the
preparation of amides, transition-metal-catalyzed hydroamino-
carbonylation of simple alkenes and alkynes arguably provides
the most direct access to these compounds from simple
precursors.4 Although Fe, Co, Ni, and Ru had been utilized as
catalyst precursors in this area, these processes required harsh
reaction conditions and resulted in poor chemoselectivity.5 In
contrast, recent studies from our group6 and others7−9 have
demonstrated that the palladium catalytic system, initiated by
palladium-hydride species, could address the above synthetic
problem for delivering the corresponding target amides with
high chemoselectivity and regioselectivity under relative mild
reaction conditions. However, because of the fact that
palladium hydride only can be produced in the relative acidic
conditions,6a some special reaction conditions were required for
simple aliphatic amines. Moreover, the high coordination
abilities of the simple amines to transition metal would inhibit
the desired reaction to some extent, via the formation of
Werner complexes.10 Therefore, the substitution of simple
aliphatic amines in hydroaminocarbonylation by easier-to-
handle synthetic equivalents is of considerable interest.
Scheme 1. Catalytic Hydrocarbonylative C−N Coupling of
Alkenes with Amides
The catalytic transformation of abundant feedstocks into
complex functional molecules is an ongoing challenge that has
significant implications for sustainability of process in the
chemistry industry. Lower-molecular amides, such as N,N-
dimethylformamide (DMF) or N,N-diethylformamide (DMA),
are abundant chemicals, which not only serve as excellent polar
solvents for various reactions, but also act as either electrophilic
or nucleophilic agents for some unique reactions.11−13 In this
context, DMF has long-been served as an effective amine
source for aminocarbonylation of aromatic halides to complex
Received: February 13, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00538
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Table 1. Optimization of Reaction Conditions
b
entry
[Pd]
ligand
DPPB
X·HCl (mol %)
2 (mL)
yield (%)
3aa:4aa
1
2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
PdCl2
NH4Cl (200)
NH4Cl (200)
NH4Cl (200)
NH4Cl (200)
NH4Cl (200)
NH4Cl (200)
NH4Cl (5)
DMA (2)
DMA (2)
DMA (2)
DMA (2)
DMA (3)
DMF (3)
DMF (3)
DMF (3)
DMF (3)
DMA (3)
DMF (3)
DMF (3)
DMF (3)
DMF (3)
DMF (3)
DMA (3)
<5
24
30
96
98
98
62
53
98
7
DPPH
60:40
40:60
12:88
11:89
12:88
16:84
15:85
15:85
8:92
3
DPEPhos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
4
5
6
7
8
NH2OH·HCl (5)
NMP·HCl (5)
NMP·HCl (5)
NMP·HCl (5)
NMP·HCl (5)
NMP·HCl (5)
NMP·HCl (20)
9
10
11
12
87
82
43
98
0
15:85
14:86
95:5
PdOAc2
c
13
Pd(t-Bu3P)2
c
14
Pd(t-Bu3P)2
96:4
c
15
Pd(t-Bu3P)2
c
16
Pd(t-Bu3P)2
NH4Cl (200)
92
91:9
a
Reaction conditions: 1a (1.0 mmol), [Pd] (0.02 mmol), ligand (0.025 mmol), CO (10 atm), 120 °C, 24 h. Yields were determined by GC analysis
b
c
using n-cetane as the internal standard. The ratios (3aa:4aa) were determined by GC-MS and GC analysis of crude product. CO (30 atm).
regioselectivity can be tuned by the appropriate choice of
ligand, and both the linear and branched amides can be
constructed in a regiodivergent manner from a single alkene.
Initially, the hydrocarbonylative C−N coupling of styrene
(1a) with DMA catalyzed by a palladium catalyst was
investigated under 10 atm of CO. Based on our experiences
with palladium-catalyzed hydroaminocarbonylation reactions,6
a series of phosphine ligands were first investigated with NH4Cl
as proton source, which could facilitate the formation of
palladium hydride.6d To our delight, the desired N,N-
dimethylamides was obtained in 96% combined yield with
good regioselectivity for exclusively giving the linear amide 4aa
as the main product when XantPhos was used as a ligand
(Table 1, entries 1−4). Increasing the amount of DMA to 3 mL
could slightly improve the yield of amides to 98% (Table 1,
entry 5). As expected, DMF could also deliver the desired
amides in 98% yield with good regioselectivity under the same
reaction conditions (Table 1, entry 6). We supposed that the H
atom contained in the DMF could be transferred to the final
product via the formation of palladium-hydride species in the
catalytic cycle. Indeed, the reaction could be performed well in
the presence of a catalytic amount of NH4Cl (5 mol % of
NH4Cl; see Table 1, entry 7). Further optimization of the
reaction conditions demonstrated that excellent results were
obtained when a catalytic amount of N-methyl-2-pyrrolidone
hydrochloride (NMP·HCl) was utilized as an additive under
otherwise identical reaction conditions (Table 1, entry 9). A
control experiment demonstrated that only 7% yield was
obtained when DMA was used as an amine source in the
presence of 5 mol % of NMP·HCl (Table 1, entry 10).
Examination of palladium precursors revealed that Pd-
(CH3CN)2Cl2 created the most reactive catalyst for this
transformation to give the linear amides, and other palladium
precursors showed lower activity (Table 1, entries 10 and 11).
To our great delight, using Pd(t-Bu3P)2 as the catalyst, the
regioselectivity was changed to the opposite direction, favoring
the branched amide 3aa in moderate yield with excellent
regioselectivity under 30 atm of CO (Table 1, entry 13).
Increasing the loading of NMP·HCl to 20 mol % led to a
marked improvement in reactivity, giving the amide products in
98% yield with excellent regioselectivity (Table 1, entry 14). As
anticipated, no desired reaction occurred in the absence of acid
(Table 1, entry 15). Similarly, with 2 equiv of NH4Cl, the DMA
could also be transferred to the desired amide 3aa as the main
product with excellent regioselectivity, albeit in a slightly lower
yield (Table 1, entry 16).
With the optimal reaction conditions identified, investigation
into the substrate scope for the present regiodivergent
hydrocarbonylative C−N coupling reaction with a variety of
amides was pursued. As shown in Table 2, the optimized
reaction conditions proved to be effective for treatment of
styrene (1a) with a series of N,N-dimethyl- or N,N-diethyl-
substituted amides 2a−2f affording the corresponding
branched and linear amides in moderate to good yields with
high regioselectivities. The aliphatic amides with long aliphatic
chain 2c or aromatic amide 2d could be smoothly converted to
the desired products in good yields with good to excellent
regioselectivities (see Table 2, entries 3 and 4). Amide 2g
derived from piperidine was less reactive to give the desired
branched and linear adducts in moderate yields with good to
excellent regioselectivities. The reactions with morpholine-
substituted amides 2h and 2i proceeded smoothly, affording the
desired adducts in excellent yields with high regioselectivities,
respectively. Although almost no desired reaction occurred with
N-methyl formamide, 2k and 2l derived from benzylamine and
aniline proved to be efficient partners for the present reaction
and gave the corresponding amides in good yields with good to
excellent regioselectivities. Almost no desired reaction occurred
under the standard reaction conditions when a primary amide
was employed as a coupling partner.
Having confirmed that common amides could be utilized as
effective coupling partners for the present coupling reaction, we
subsequently explored the use of DMF as a coupling partner for
the hydrocarbonylative C−N coupling of a range of alkenes in
the presence of catalytic amount of NMP·HCl. First, various
branched N,N-dimethylamides could be prepared in the
B
DOI: 10.1021/acs.orglett.8b00538
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
a
Table 2. Substrate Scope for Amides
Table 3. Substrate Scope for Branched Amide Synthesis
b
c
entry
1
Ar
3
yield (%)
3:4
C6H5
C6H5
3aa
3aa
3ba
3ca
3da
3ea
3fa
89
70
84
87
80
55
83
65
74
82
77
82
58
71
68
83
96:4
96:4
92:8
90:10
88:12
79:21
92:8
93:7
96:4
91:9
90:10
98:2
98:2
95:5
96:4
98:2
d
2
3
4
4-CH3C6H4
3-CH3C6H4
2-CH3C6H4
2,6-(CH3)2C6H3
4-t-BuC6H4
4-CH3OC6H4
4-EtOC6H4
4-FC6H4
e
5
ef
,
6
7
8
3ga
3ha
3ia
9
10
11
12
13
14
15
16
4-ClC6H4
3ja
4-CH3C(O)C6H4
4-H2N(O)CC6H4
4-HOC6H4
3ka
3la
3ma
3na
3oa
4-MeSC6H4
2-naphthyl
e
a
Reaction conditions: 1 (1.0 mmol), 2a (3 mL), Pd(t-Bu3P)2 (0.02
b
mmol), NMP·HCl (0.2 mmol), CO (30 atm), 120 °C, 24 h. Isolated
yield. The ratios of 3/4, given within parentheses, were determined by
GC-MS and GC analysis of crude product. 1a (30.0 mmol), 2a (30
c
d
e
mL), Pd(t-Bu3P)2 (0.006 mmol), 48 h. Pd(t-Bu3P)2 (0.05 mmol).
f
NMP·HCl (0.5 mmol), CO (50 atm), 140 °C, 48 h.
XantPhos and 5 mol % of NMP·HCl in the presence of 10 atm
of CO (see Table 4). 2-Vinylnaphthalene and styrenes with
various substituents on the para-, meta-, and ortho-position,
such as alkyl-, alkoxy-, acyl-, hydroxy-, carboxyl-, and halogens
can survive to give the desired linear amides 4ba−4pa in 59%−
89% isolated yields with good regioselectivities. The steric
hindered substrates 1d and 1e, as examples of bulky substrates,
favored to transform to the corresponding N,N-dimethylamides
in high yield with excellent regioselectivities. Furthermore,
simple unactivated alkenes are also suitable substrates for this
reaction to give the corresponding linear amides in good yields
and regioselectivities (4qa−4ta) under the slightly modified
reaction conditions. It is worth pointing out that functionalized
aliphatic alkenes, bearing chlorine, ether, ester, and phthalimide
groups, could be successfully converted to the desired linear
amides in 59%−64% isolated yields with good regioselectivities
(4ua−4wa, 4za). Moreover, (+)-β-citronellene (1x) was also
compatible with this novel reaction, in which the reactions
occurred exclusively at the terminal double bond to give the
corresponding linear amides 4xa with partial racemization. It
was noted that norbornylene (1y) can be smoothly transferred
to the amide 4ya in 87% yield with good selectivity.
To understand the reaction mechanism, many control
experiments were conducted. First, the reaction conducted
with 13C-labeling DMF disclosed that the CO incorporated into
the desired amide came from the CO gas (see Scheme 2, eq 1).
In addition, the corresponding ethyl benzoate was detected
after treatment of the carbonylation reaction (the carbonylation
of styrene with N,N-dimethylbenzamide) mixture with EtOH
(Scheme 2, eq 2), indicating that the transacylation occurred in
the catalytic cycle. Inspired by these results, the intramolecular
carbonylation of amide-containing alkenes was investigated. As
expected, a series of lactams with five- to eight-membered rings
were obtained in moderate to good yields (48%−70% yields)
a
Method A: 1a (1.0 mmol), 2 (3.0 mL), Pd(t-Bu3P)2 (0.02 mmol),
b
NH4Cl (2.0 mmol), CO (30 atm), 120 °C, 24 h. Method B: 1a (1.0
mmol), 2 (3.0 mL), Pd(CH3CN)2Cl2 (0.02 mmol), XantPhos (0.025
mmol), NH4Cl (2.0 mmol), CO (10 atm), 120 °C, 24 h. Isolated
yield. The ratios of 3/4, given within parentheses, were determined by
GC-MS and GC analysis of crude product. 2 (10 mmol), anisole (4
mL).
c
d
presence of 30 atm of CO with Pd(t-Bu3P)2 as the catalyst
together with 20 mol % of NMP·HCl as an additive. As shown
in Table 3, in all cases, the present coupling reaction proceeded
smoothly to afford their corresponding branched amides in
moderate to excellent yields with exellent regioselectivities. In
general, both meta- and para-substituted styrenes were
successfully converted into the corresponding amides in good
yields with excellent regioselectivities. However, ortho-sub-
stituted styrenes gave lower yields and regioselectivities,
espescially for disubstituted 1e, which was most likely due to
the steric environment (3ca and 3da). Pleasingly, the 2-
vinylnapthalane (1o) can be applied to this protocol, delivering
the desired product 3oa in 83% yield with perfect
regioselectivity in the present of 5 mol % of Pd(t-Bu3P)2.
Benefiting from the lower coordination ability of DMF, the
gram scale reaction for synthesis of 3aa proceeded smoothly in
the presence of 0.02 mol % of Pd(t-Bu3P)2 to give the desired
amide in 70% yield (3.74 g, see the Supporting Information
(SI)). Notably, this result represents a turnover number
(TON) of 3500, which is among the highest reported for
hydroaminocarbonylation.6,7
Inspired by the above results, we subsequently explored the
substrate scope for the synthesis of linear amides with the
combination of 2 mol % of Pd(CH3CN)2Cl2 with 2.5 mol % of
C
DOI: 10.1021/acs.orglett.8b00538
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
incorporation can improve the overall therapeutic and
metabolic profile of a drug, there is growing interest in
selective deuteration.17 Because of the prevalence of amide in
drug molecules,1 the direct incorporation deuterium into the
amide would be an attractive for drug design. Indeed, with
inexpensive NMP·DCl as a stoichiometric proton source, the
deuterium could be incorporated into the β-position of
branched amide and α-position of linear amide in good yields
by using the present reaction (Scheme 2, eq 4). Moreover, with
DMF-d7 as a coupling partner, the D-labeled amides could be
also prepared in the presence of catalytic amount of NMP·DCl
under the standard reaction conditions (Scheme 2, eq 5).
In summary, we have successfully developed a new and
efficient protocol for catalytic hydrocarbonylative C−N
coupling of alkenes with amides. The reaction proceeded via
palladium-catalyzed hydrocarbonylation of alkenes, followed by
acyl metathesis. Both linear and branched amides can be
obtained in good yields with high regioselectivities by the
appropriate choice of ligands. This direct method is an
improvement on existing amide-metathesis reactions and can
also be employed in the synthesis of deuterated amides with
inexpensive NMP·DCl as a deuterium source. The loading of
the Pd can be lowered to 0.02 mol %. Further investigations on
gaining a detailed mechanistic understanding of this reaction
and the application of this strategy in other reactions are
currently in progress.
Table 4. Substrate Scope for Linear Amide Synthesis
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b00538.
a
Reaction conditions: 1 (1.0 mmol), 2a (3 mL), Pd(CH3CN)2Cl2
(0.02 mmol), Xantphos (0.025 mmol), NMP·HCl (0.05 mmol), CO
(10 atm), 120 °C, 24 h. bIsolated yield. cThe ratios of 4/3 or dr, given
within parentheses, were determined by GC-MS and GC analysis of
Experimental details and full spectroscopic data for all
new compounds (PDF)
d
e
f
crude product. 48 h. NMP·HCl (0.5 mmol), CO (30 atm). PdI2
(0.02 mmol), CO (30 atm). Er was determined by HPLC analysis
with a chiral stationary phase.
g
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: hanmin@ustc.edu.cn.
ORCID
Scheme 2. Control Experiments and Synthetic Applications
Hanmin Huang: 0000-0002-0108-6542
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the National Natural Science
Foundation of China (Nos. 21790333, 21702197 and
21672199), CAS Interdisciplinary Innovation Team, the
Fundamental Research Funds for the Central Universities and
the Anhui Provincial Natural Science Foundation (No.
1708085MB28).
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D
DOI: 10.1021/acs.orglett.8b00538
Org. Lett. XXXX, XXX, XXX−XXX

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