Copper-Catalyzed Electrophilic Amidation of Organotrifluoroborates with Use of N-Methoxyamides

Article abstract of DOI:10.1002/chem.201901145

A copper-catalyzed electrophilic amidation of aryltrifluoroborates with use of N-methoxyamides is reported. The reaction shows high functional group compatibility derived from two distinct features: 1) the high stability of the N-methoxyamides and 2) the nonbasic mild conditions in the presence of LiCl. The developed method can also be applied to the synthesis of enamides, which are widely distributed in natural products. Preliminary mechanistic studies suggest that the initial step is the transmetalation of the aryltrifluoroborate by the assistance of LiCl, and the resulting aryl copper intermediate provides the anilide through non-S_N2 oxidative addition to the N-methoxyamide and subsequent reductive elimination.

Full text of DOI:10.1002/chem.201901145

A Journal of
Accepted Article
Title: Copper-Catalyzed Electrophilic Amidation of
Organotrifluoroborates Using N-Methoxyamides
Authors: Shona Banjo, Eiko Nakasuji, Tatsuhiko Meguro, Takaaki
Sato, and Noritaka Chida
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To be cited as: Chem. Eur. J. 10.1002/chem.201901145
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Copper-Catalyzed Electrophilic Amidation of
Organotrifluoroborates Using N-Methoxyamides
Shona Banjo, Eiko Nakasuji, Tatsuhiko Meguro, Takaaki Sato,* and Noritaka Chida*[a]
Abstract:
A
copper-catalyzed electrophilic amidation of
group developed a rhodium-catalyzed electrophilic amidation of
alkenylboronic acids with N-pivaloyloxyamides to form
enamides.[5e]
aryltrifluoroborates using N-methoxyamides is reported. The reaction
shows high functional group compatibility derived from two distinct
features: 1) the high stability of the N-methoxyamides, and 2) the non-
basic mild conditions in the presence of LiCl. The developed method
can also be applied to the synthesis of enamides, which are widely
distributed in natural products. Preliminary mechanistic studies
suggest the initial step is the transmetalation of the aryltrifluoroborate
by the assistance of LiCl, and the resulting aryl copper intermediate
provides the anilide through non-SN2 oxidative addition to the N-
methoxyamide and subsequent reductive elimination.
Introduction
The electrophilic amination of organometals is currently a hot
topic in organic chemistry.[1,2] In this reaction, an organometallic
reagent attacks an amino nitrogen atom connected to a leaving
group, forming a carbon-nitrogen bond upon release of the
leaving group, mainly under basic or transition metal-catalyzed
conditions. Recent extensive studies by a number of research
groups have revealed that the electrophilic amination can indeed
be a powerful alternative method to the nucleophilic approach
(Buchwald-Hartwig reaction)[3] and the oxidative approach (Chan-
Lam reaction).[4]
In contrast to the electrophilic amination, the corresponding
amidation has been much less investigated despite the potential
for providing direct access to useful amide functional groups.[5] In
2008, the Liebeskind group reported the first landmark example
of copper-mediated electrophilic amidation of boronic acids.[5a] In
their case, the electrophilic amidation of boronic acid 3 using N-
acetoxyamide 1 provided a variety of anilides 4 (Scheme 1A).
However, the reaction required the use of a stoichiometric amount
of CuTC. They speculated that oxidative addition of N-
acetoxyamide 1 to CuTC to formed stable dimer 2, which resulted
in slow transmetalation and needed the stoichiometric copper salt.
After Liebeskind’s report, Lei documented the electrophilic
amidation of arylboronic acid 3 with N-chloroanilide 5 (Scheme
1B).[5b] Use of the highly reactive N-chloroanilide 5 as an
amidating reagent achieved the first catalytic electrophilic
amidation via a copper amidate complex. Furthermore, the Loh
Scheme 1. Copper-mediated and copper-catalyzed electrophilic amidation of
organoboron reagents.
Although a rhodium catalyst is promising for the electrophilic
amidation of organoborons, our research group focuses on
copper-catalyzed reactions due to the abundant and inexpensive
first-row transition metal. To avoid stoichiometric conditions and
low stability of the amidating reagents,[5a,b] we planned to employ
N-methoxyamide 10[6,7] instead of N-acetoxyamide 1 or N-
chloroanilide 5 (Scheme 1C). Based on Liebeskind’s proposal
shown in Scheme 1A, the relatively stable N-methoxyamide 10
would prevent the first oxidative addition that forms stable dimer
2. Instead, transmetalation of organoboron 8 with the copper salt
might produce organocopper intermediate 9. The resulting 9
could then undergo the electrophilic amidation with N-
methoxyamide 10 to give anilide 4, accompanied by regeneration
of the copper salt. If successful, use of N-methoxyamide 10 would
allow for a catalytic version with the copper salt in contrast to N-
acetoxyamide 1, and allows for the preparation of functionalized
amidating reagents due to the higher stability of 10 than that of
reactive N-chloroanilide 5.
[a]
S. Banjo, E. Nakasuji, T. Meguro, Prof. Dr. T. Sato, Prof. Dr. N.
Chida
Department of Applied Chemistry
Faculty of Science and Technology, Keio University
3-14-1, Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
E-mail: takaakis@applc.keio.ac.jp, chida@applc.keio.ac.jp
Supporting information for this article is given via a link at the end of
the document.
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Table 1. Optimization of electrophilic amidation using N-methoxyamide 11.
Entry[a]
PhBXn
CuXn
Additive
Solvent
Yields [%][b]
12a
13
11
1
14 (1.1 equiv)
15 (1.1 equiv)
16 (1.1 equiv)
17 (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.1 equiv)
18a (1.3 equiv)
18a (1.3 equiv)
18a (1.3 equiv)
18a (1.3 equiv)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuCl2 (10 mol %)
Cu(OAc)2 (10 mol %)
Cu(OTf)2 (10 mol %)
CuTc (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (10 mol %)
CuBr2 (5 mol %)
CuBr (5 mol %)
none
DME
DME
DME
DME
DME
DME
DME
DME
DME
DME
DME
DME
DME
DME
toluene
THF
13
0
0
83
100
40
96
51
76
100
20
89
100
100
87
100
28
38
42
85
16
0
2
none
0
3
none
20
4
40
0
4
none
5
none
36
16
0
13
8
6
none
7
none
0
8
none
38
4
26
3
9
none
10
11
12
13
14
15
16
17
18
19
20
21
22
Cs2CO3 (1.1 equiv)
tBuONa (1.1 equiv)
LiF (1.1 equiv)
CsF (1.1 equiv)
LiCl (1.1 equiv)
LiCl (1.1 equiv)
LiCl (1.1 equiv)
LiCl (1.1 equiv)
LiCl (1.1 equiv)
LiCl (1.3 equiv)
LiCl (1.3 equiv)
LiCl (1.3 equiv)
LiCl (1.3 equiv)
0
0
0
0
12
0
1
0
62
59
53
0
10
3
5
DMF
0
MeCN
MeCN
MeCN
MeCN
MeCN
80
89
93
92
90[c]
4
11
7
0
8
0
CuBr2 (5 mol %)
6[c]
0[c]
[a] N-Methoxyamide 11 (130 mol), PhBXn, CuXn, additive, solvent (0.05 M), 40 °C, 24 h. [b] The yields were determined by 1H NMR with mesitylene as an internal
standard. [c] Yields of isolated products after purification by column chromatography are given.
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Results and Discussion
Our electrophilic amidation was first evaluated using N-
methoxyamide 11 and a variety of phenylborons 14-18a (Table 1).
Treatment of N-methoxyamide 11 and boronic acid 14 with CuBr2
(10 mol %) in DME at 40 °C initiated the electrophilic amidation,
providing anilide 12a in 13% yield (Table 1, Entry 1). While use of
boronic ester 15 resulted in no reaction, boroxin 16 slightly
improved the yield of anilide 12a, but gave primary amide 13 as
the major product in 40% yield (Table 1, Entries 2 and 3). More
nucleophilic potassium phenyltriolborate 17[8] was not effective in
the electrophilic amidation (Table 1, Entry 4). Potassium
trifluoroborate 18a was evaluated as the best organoboron
reagent, giving anilide 12a in 36% yield, along with 13% yield of
primary amide 13 (Table 1, Entry 5). Although the yield was still
low, these results indicated that catalytic electrophilic amidation
was feasible with N-methoxyamide 11. A survey of copper (II)
salts revealed that CuBr2 and Cu(OTf)2 were the most effective
(Table 1, Entries 5-8). The reaction with a catalytic amount of
CuTC, which was the best copper salt in Liebeskind’s method, led
to a low yield (Table 1, Entry 9). We then investigated effects of
additives in the presence of 10 mol % CuBr2. In general, the
effective transmetalation of arylborons to arylcoppers is known to
proceed in the presence of bases such as t-BuONa.[2c-e,9]
However, these bases completely suppressed our electrophilic
amidation (Table 1, Entries 10 and 11). After extensive studies,
we found that the addition of LiCl dramatically enhanced the rate
of the reaction with trifluoroborate 18a, providing anilide 12a in
62% yield (Table 1, Entries 12-14).[10,11] Variation in the reaction
solvent had some effect on the reaction efficiency, and MeCN was
identified as the optimal solvent (Table 1, Entries 15-18). Use of
1.3 equivalents of phenyltrifluoroborate 18a and LiCl resulted in
the complete consumption of N-methoxyamide 11 (Table 1, Entry
19). In contrast, a decrease in the catalyst loading of CuBr2 (5
mol %) was possible, and in fact gave the best result (Table 1,
Entry 20, 12a; 93%). The reactions with CuBr (I) instead of CuBr2
(II) showed identical results in the electrophilic amidation (Table
1, Entry 21). Finally, the optimized conditions provided anilide 12a
and primary amide 13 in 90% and 6% isolated yields after silica
gel column chromatography (Table 1, Entry 22).
Scheme 2. Substrate scope for aryltrifluoroborates in the electrophilic amidation.
Reaction conditions: N-methoxyamide 11 (130 mol), PhBF3–K+ 18a-k (1.3
equiv), CuBr2 (5 mol %), LiCl (1.3 equiv), MeCN (0.05 M), 40 °C, 24 h.
The salient features of our copper-catalyzed electrophilic
amidation are: i) the high stability of the N-methoxyamides
compared with other amidating agents such as N-chloroamides,
and ii) non-basic mild reaction conditions. These seemingly
contradictory properties were solved by addition of LiCl, which
enabled the use of a variety of functionalized N-methoxyamides
(Scheme 3).[12] The reaction was compatible with a MOM ether, a
TBDPS ether, a methyl ester and a Cbz-carbamate (30: 88%; 31:
94%; 32: 89%; 33: 92%). An acidic sulfonamide did not disturb
the electrophilic amidation (34: 91%). One limitation of our
reaction was observed when using the N-methoxybenzamide (35:
14%).[13] In contrast, the reaction of N-methoxyamides having a
double bond proceeded in high yield (36: 90%). A cinnamoyl
derivative did not undergo possible 1,4-addition, but provided
anilide 37 in 81% yield. A terminal alkyne is one of the most
challenging functional groups due to -coordination of the copper
catalyst, and formation of copper acetylide under basic conditions.
However, our mild electrophilic amidation selectively took place in
the presence of a terminal alkyne, affording 38 in 95% yield. The
reaction was applicable to sterically bulkier isopropylamide and
cyclohexylamide (39: 85%; 40: 95%).
With the optimized conditions in hand, the scope of the
electrophilic amidation was investigated for
a range of
aryltrifluoroborates (Scheme 2). The reactions smoothly
proceeded with aryltrifluoroborates containing electron-deficient
groups such as a ketone, an aldehyde and a nitrile (18b: 85%;
18c: 83%; 18d: 89%). An aryl bromide was compatible with this
reaction, highlighting its utility upon further transformation with
other transition metal-catalyzed reactions (18e: 89%). 4-Chloride
and 4-fluoride substituents were well tolerated (18f: 93%; 18g:
88%). The reactions with 4-methylphenyl and 4-methoxyphenyl
substituents provided the corresponding anilides in high yields
(18h: 95%; 18i: 87%). Regardless of the position of the methoxy
group on the phenyl group, the reaction provided the anilides in
good yields (18i: 87%; 18j: 84%; 18k: 79%).
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Scheme 3. Substrate scope for N-methoxyamides in the electrophilic amidation.
Reaction conditions: N-methoxyamide 19-29 (130 mol), PhBF3–K+ 18a (1.3
equiv), CuBr2 (5 mol %), LiCl (1.3 equiv), MeCN (0.05 M), 40 °C, 24 h.
Scheme 4. (A) Representative natural products bearing the enamide motif. (B)
Substrate scope in the electrophilic amidation. Reaction conditions: N-
methoxyamide (65 mol), vinyltrifluoroborate (E)-44 (1.3 equiv), Cu(OAc)2 (10
mol %), LiCl (1.3 equiv), DME (0.03 M), 60 °C, 24 h.
Enamides are widely distributed functional groups in
biologically active natural products such as lobatamide A (41)[14]
Our studies demonstrated that the copper-catalyzed
electrophilic amidation is a useful method for the synthesis of
anilides as well as enamides. To better understand the factors
controlling the scope of the reaction, we conducted control
experiments to elucidate the mechanism. No reaction was
observed without the copper catalyst in the presence or absence
of LiCl (Table 2, Entries 1-3). The reaction without LiCl or with 5
mol % of LiCl resulted in low yields (Table 2, Entries 4 and 5). Use
of 1.3 equivalents of LiCl was essential to promote the
electrophilic amidation, which indicated that LiCl might interact
with phenyl trifluoroborate 18a, not the copper catalyst. Although
we did not determine the exact structure of the activated
intermediate, NMR experiments suggested that addition of LiCl to
phenyl trifluoroborate 18a promoted ligand exchange, leading to
the formation of the reactive intermediate.[18]
and salicylihalamide
A
(42)[15] (Scheme 4A). However,
condensation of a carboxylic acid with an enamine is known to be
difficult due to the instability of the enamine.[5e,16,17] In addition, the
synthesis of enamides requires mild conditions due to the acid-
sensitivity of the enamide itself. If the electrophilic amidation of a
vinyltrifluoroborate is feasible instead of the aryltrifluoroborate,
the enamide moiety could be easily synthesized by the use of
stable N-methoxyamides.
Although a slight modification of the reaction conditions was
needed, electrophilic amidation between N-methoxyamides and
vinyltrifluoroborate (E)-44 proceeded in the presence of Cu(OAc)2
(10 mol %) and LiCl (1.3 equiv), affording enamides 45-47 in
moderate yields
(Scheme 4B).
The reaction with
vinyltrifluoroborates (E)-44 provided enamide (E)-45 in 55% yield
as single diastereomer. Given that most enamide natural products
possess unsaturated amides as shown in Scheme 4A, retention
of the olefin geometries found in the N-methoxyamides is also
crucial in the electrophilic amidation. When using N-
methoxycinnamamide 26, the geometries of both the
vinyltrifluoroborate and the cinnamoyl group were well preserved.
((E,E)-46: 59%). The electrophilic amidation of (E)-44 with N-
methoxyamides (E,Z)-43 provided (E,Z,E)-47, which corresponds
to partial structure of lobatamides A (41), respectively. It is
noteworthy that the electrophilic amidation took place without
affecting oxime ethers found in lobatamide A.
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Table 2. Control experiments: Effects of each reagent.
Entry[a]
CuBr2
LiCl
Yield of 12a [%][b]
1
2
3
4
5
5 mol %
none
1.3 equiv
none
93
0
none
1.3 equiv
none
0
5 mol %
5 mol %
4
5 mol %
11
[a] N-Methoxyamide 11 (130 mol), PhB–F3K+ (1.3 equiv), CuBr2, LiCl,
MeCN (0.05 M), 40 °C, 24 h. [b] The yields were determined by 1H NMR with
mesitylene as an internal standard.
Liebeskind proposed
a possible mechanism involving
oxidative addition of a copper salt to N-acetoxyamide 1 and
subsequent transmetalation (Scheme 1A).[5a] This mechanism
was supported by the control experiment in which N-
acetoxyamide 1 and one equivalent of CuTC were mixed without
phenyl boronic acid, resulting in complete conversion to
PhCONH2 after aqueous work-up. However, this would not apply
to our case because the cleavage of the N-O bond was not
caused by treatment of N-methoxyamide 11 with one equivalent
of copper (II) bromide in the absence of phenyl trifluoroborate 18a
(Scheme 5, eq 1). The Chan-Lam type reaction[4] of primary amide
13 did not take place under the optimized conditions (Scheme 5,
eq 2). Attempted cleavage of the methoxy group in N-
methoxyanilide 48 resulted in no reaction under the optimized
conditions (Scheme 5, eq 3). This control experiment indicated
that 48 was not the reaction intermediate, and excluded the
mechanism involving the Chan-Lam type reaction of N-
methoxyamide 11 and subsequent internal oxidation through the
cleavage of the methoxy group.[19] A radical mechanism via single
electron transfer was also unlikely by the control experiment in the
presence of TEMPO (Scheme 5, eq 4). Electrophilic amidation
using 49 bearing the terminal olefin simply provided enamide 50
in 85% yield without causing the 5-exo radical cyclization
(Scheme 5, eq 5).
Scheme 5. Control experiments to elucidate the reaction mechanism. [a] The
yields were determined by 1H NMR with mesitylene as an internal standard. [b]
Yield of isolated product after purification by column chromatography is given.
Based on the results in the control experiments, three
plausible mechanisms were invoked for our copper-catalyzed
electrophilic amidation (Scheme 6). The first possible mechanism
is the 1,2-rearrangement pathway (path A),[20] which begins with
formation of a copper amidate complex. Transmetalation of the
aryl trifluoroborate generates a borate complex, which undergoes
the 1,2-rearrangement to form an Ar-N bond with expulsion of the
methoxy group. The transmetalation/SN2 pathway (path B) is the
most common mechanism in the electrophilic amination using N-
benzoyloxyamines,[2b-d] and the electrophilic amidation might
follow the same mechanism. LiCl mediated transmetalation from
the trifluoroborate produces an aryl copper intermediate, which
displaces the methoxy group through the SN2 reaction. The
transmetalation/non-SN2 oxidative addition pathway (path C) is
another possible process.[21] Copper (I) species, generated by
disproportionation of copper (II) salts, undergo the
transmetalation of the aryl trifluoroborate to give an aryl copper (I)
intermediate. Oxidative addition of the resulting aryl copper
intermediate to the N-O bond produces an unstable copper (III)
species, which undergoes the reductive elimination to give the
anilide and regenerate the copper (I) salt.
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comparable reaction times and yields. The reaction of a 1:1
mixture of 53 and 55 provided anilides 54 and 56 in 72% and 71%
yields as non-crossover products. Potential crossover products,
anilides 57 and 58 were not observed. These results indicated
that
our
electrophilic
amidation
proceeds
via
the
transmetalation/non-SN2 oxidative addition pathway.
Scheme 6. Three possible mechanisms for the electrophilic amidation using N-
methoxyamides.
To elucidate the possible mechanism for the electrophilic
amidation, compounds 51, 53 and 55 were prepared and
subjected to the optimized conditions, providing anilides 52,[22] 54
and 56 in 49%, 75% and 65% yields, respectively (Scheme 7, eqs
6-8). The 1,2-rearrangement pathway (Scheme 6, path A) was
discarded because compound 51 bearing the N-methyl group
cannot form the amidate complex for the rearrangement. To
differentiate between the SN2-type reaction and the non-SN2
oxidative addition (Scheme 6, paths B and C), the Johnson group
performed an endocyclic restriction test in the copper-catalyzed
electrophilic amination.[2b] Their endocyclic restriction test was
applied to our electrophilic amidation (Scheme 7, eq 9). An
intramolecular SN2 process is prohibited in the electrophilic
amidation of 53 and 55 due to the strained 6-endo-tet transition
state (Scheme 7, eqs 7 and 8). Thus, the mechanism would
discriminate between the intermolecular SN2 pathway involving
two molecules and the intramolecular non-SN2 oxidative addition
pathway. These two mechanisms could be differentiated by a
crossover experiment using compounds 53 and 55 based on the
fact that the reactions of these two substrates showed
Scheme 7. The intramolecular electrophilic amidation to elucidate the reaction
mechanism.
Given the mechanistic insights obtained from the above
experiments, we propose a possible catalytic cycle for our
electrophilic amidation (Scheme 8). The reaction would start with
activation of the aryl trifluoroborate in the presence of LiCl.
Although the structure of the activated borate complex was not
determined,
the
activated
complex
would
undergo
transmetalation under neutral conditions with Cu(I)X, which is
generated by disproportionation of Cu(II)X2. The resulting aryl
copper(I) intermediate could undergo non-SN2 oxidative addition
to the N-methoxyamide, followed by reductive elimination of the
unstable copper (III) species to give the anilide and regenerate
the copper catalyst.
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3702–3705; d) R. P. Rucker, A. M. Whittaker, H. Dang, G. Lalic, Angew.
Chem. Int. Ed. 2012, 51, 3953–3956; Angew. Chem. 2012, 124, 4019–
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11030–11034; h) S. Zhu, N. Niljianskul, S. L. Buchwald, J. Am. Chem.
Soc. 2013, 135, 15746–15749; i) S. L. McDonald, C. E. Hendrick, Q.
Wang, Angew. Chem. Int. Ed. 2014, 53, 4667–4670; Angew. Chem.
2014, 126, 4755–4758; j) S.-L. Shi, S. L. Buchwald, Nature Chem. 2015,
7, 38–44; k) Y. Yang, S.-L. Shi, D. Niu, P. Liu, S. L. Buchwald, Science
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Scheme 8. Proposed mechanism for the electrophilic amidation using N-
methoxyamides.
[3]
For recent selected reviews on the Buchwald-Hartwig coupling, see: a)
D. Prim, J.-M. Campagne, D. Joseph, B. Andrioletti, Tetrahedron 2002,
58, 2041–2075; b) J. F. Hartwig, Synlett 2006, 1283–1294; c) J. F.
Hartwig, Acc. Chem. Res. 2008, 41, 1534–1544; d) D. S. Surry, S. L.
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2, 27–50; f) P. Ruiz-Castillo, S. L. Buchwald, Chem. Rev. 2016, 116,
12564−12649.
Conclusions
We have demonstrated
a
copper-catalyzed electrophilic
amidation of organotrifluoroborates. The high compatibility with a
variety of functional groups was realized due to two factors: 1) the
high stability of the N-methoxyamides, and 2) the addition of LiCl,
which dramatically enhanced the rate of the reaction under non-
basic mild conditions. The electrophilic amidation was also
applicable to the synthesis of enamides, which are challenging
substrates for the classic condensation strategy. Mechanistic
studies indicated that the reaction proceeds via non-SN2 oxidative
addition of an aryl copper (I) species. Elucidation of the detailed
mechanism is currently on-going.
[4]
[5]
For selected reviews on the Chan-Lam coupling, see: a) S. V. Ley and
A. W. Thomas, Angew. Chem. Int. Ed. 2003, 42, 5400–5449; Angew.
Chem. 2003, 115, 5558–5607; b) J. X. Qiao, P. Y. S. Lam, Synthesis
2011, 829–856; c) K. S. Rao, T.-S. Wu, Tetrahedron 2012, 68, 7735–
7754.
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Acknowledgements
This research was supported by a Grant-in-Aid for Scientific
Research (C) from MEXT (15K05436), and the Tobe Maki
scholarship foundation to E. N. Synthetic assistance from Ms.
Kanami Fujita is gratefully acknowledged.
Keywords: Amide • copper catalyst • enamide • electrophilic
reaction • organotrifluoroborate
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Layout 1:
FULL PAPER
A copper-catalyzed electrophilic
amidation of aryltrifluoroborates using
N-methoxyamides is reported. The
reaction shows high functional group
compatibility derived from two distinct
features: 1) the high stability of the N-
methoxyamides, and 2) the non-basic
mild conditions in the presence of
LiCl. The developed method is applied
to the synthesis of enamides, which
are widely distributed in natural
products.
S. Banjo, E. Nakasuji, T. Meguro, T.
Sato,* N. Chida*
Page No. – Page No.
Copper-Catalyzed Electrophilic
Amidation of Organotrifluoroborates
Using N-Methoxyamides
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