Oxidative nucleophilic substitution: Transformation of alkylboronic derivatives

Article abstract of DOI:10.1016/j.tet.2011.09.055

An efficient amidation reaction is described in this paper. Potassium alkyltrifluoroborate salts can be transforming to amides from nitriles in the presence of copper acetate and boron trifluoride. An extension of this reaction allowed the formation of amines, ethers, and C-C bond.

Full text of DOI:10.1016/j.tet.2011.09.055

Tetrahedron 67 (2011) 8615e8621
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Oxidative nucleophilic substitution: transformation of alkylboronic derivatives
*
ꢀ
ꢀ
Clement Cazorla, Estelle Metay, Marc Lemaire
ˇ
ꢀ
ꢀ
ꢁ
ꢀ
Laboratoire de CAtalyse, SYnthese et ENvironnement, Universite de Lyon, UCBL, ICBMS, UMR-CNRS 5246, Campus de la Doua, Batiment Curien-CPE, 3 etage,
43Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2011
Received in revised form 14 September 2011
Accepted 14 September 2011
Available online 21 September 2011
An efficient amidation reaction is described in this paper. Potassium alkyltrifluoroborate salts can be
transforming to amides from nitriles in the presence of copper acetate and boron trifluoride. An ex-
tension of this reaction allowed the formation of amines, ethers, and CeC bond.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Copper acetate
Alkylboronic
Boron trifluoride
Oxidative nucleophilic substitution
Amidation
1. Introduction
aryltrifluoroborate salts with an aniline or an amide mediated by
copper species.10 In this modified-Ullmann condensation potas-
The amide function is one of the most widespread in nature.
Often prepared from an amine and a carboxylic acid, a large choice
of peptide coupling methods is described in the literature.1 Among
these classical approaches, the Ritter reaction appears as an alter-
native for the amide synthesis from alcohols or alkenes.2 However,
this reaction was performed in presence of Lewis acid3 (AlCl3, SnCl4,
Bi(OTf)3, BF3$OEt2, boric acid, etc.) or Brønsted acid4 (concentrated
H2SO4, triflic acid, formic acid or AcOH) at elevated temperatures.
Many efforts were realized during the last decade to develop milder
conditions. For example, Cossy and co-workers reported an iron-
catalyzed Ritter reaction, which provided amides from benzylic
alcohols.5 Very recently, an iodine-catalyzed reaction allows amide
formation from nitriles.6 However, the scope of the reaction is
limited by the requirement of high temperatures (>100 ꢀC).
Another classical approach for the CeN bond formation is the
Ullmann condensation, which was intensively studied to synthe-
size biaryl amine or biaryl ether from halide.7 Since, Chan, Lam, and
Evans have shown that boronic derivatives appear as excellent
partners for the CeN bond formation.8 The formation of C(aryl)eO,
C(aryl)eN, C(aryl)eS bond is performed from reaction between
boronic acids and a phenol, aniline or thiophenol, respectively, in
presence of copper species.9 In 2003, Batey and co-workers de-
veloped the C(aryl)eN bond formation by reaction of a potassium
sium aryltrifluoroborate salts are generally used in excess com-
pared to aniline. However these different studies indicate that
boronic derivatives could be used as precursor for amide synthesis.
Potassium trifluoroborate salts are stable to air, water11 and a vari-
ety of reaction conditions.12 They can be easily prepared from the
corresponding boronic ester or acid. These crystalline derivatives
are easy to handle and can efficiently substitute the corresponding
boronic acids.13 In our laboratory, we were interested in developing
a suitable method for the formation of CeN bond with alkylboronic
derivatives and a nitrogen source. To this end, we have combined
the works of Chan, Lam and Batey with the Ritter reaction to de-
velop a new method of amidation.14 Herein we report a broader
study of this mild and efficient Ritter-type amidation of alkylbor-
onic derivatives with nitriles, proceeding at room temperature. The
mechanistic study drove us to synthesize ethers, amines, and CeC
bond.
2. Results and discussion
In order to reach optimized conditions, potassium 1-
phenylethyltrifluoroborate 1 was considered with benzonitrile
(Scheme 1) in the presence of copper acetate and BF3$OEt2.
The evaluation of different Lewis acids showed that the highest
yield of amidation was reached in the presence of boron trifluoride
(48% in diethyl ether). The formation of the desired product was not
observed with other Lewis acids (TiCl4, AlCl3, ZnCl2, ZrCl4, CeCl3,
and B(Oi-Pr)3). Likewise, the expected amide was not formed when
* Corresponding author. Tel.: þ33 472 44 82 09; fax: þ33 472 43 14 08; e-mail
address: marc.lemaire@univ-lyon1.fr (M. Lemaire).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.09.055

8616
C. Cazorla et al. / Tetrahedron 67 (2011) 8615e8621
O
6). When the expected transformation did not occur, the formation
of 1-phenylethanol was identified. Best conditions were defined as
following: Cu(OAc)2 1 equiv, BF3$OEt2 2 equiv, in 0.5 M of toluene
with 10 equivof nitrile. In order to study the scope and the limitation
of this reaction, different potassium trifluoroborates salts were
prepared according to the literature. More precisely, the preparation
of compound 1 was realized as described by Crudden (Scheme 2).15
CN
BF3K
N
H
2
1
Scheme 1. Amidation of potassium alkyltrifluoroborate salts.
the reaction was carried out without Lewis acid (Table 1, entry 1).
Moreover, in absence of copper acetate, boron trifluoride alone
does not lead to amide formation (Table 1, entry 2). As a conse-
quence, each reagent is necessary for the CeN bond formation. The
amount of each reagent was then studied for optimal reactivity
(Table 1). Nevertheless, reducing the amount of copper decreased
considerably the yield (Table 1, entries 3e6). However the ratio
Cu(OAc)2/BF3$OEt2 seems very important. When the reaction was
realized with benzonitrile as solvent the reaction time was con-
siderably reduced. Indeed, the conversion was complete in 10 min
to afford the corresponding amide, which was detected by GC in
70% yield (Table 1, entry 1). To pursue the optimization condition of
this reaction, the nature of the metal was studied.
1. [Rh(COD)2]BF4,
BF3K
dppp, THF, r.t
2. pinacol, r.t.
O
O
BH
3. KHF2 aq., MeOH
1
81%
Scheme 2. Preparation of potassium 1-phenylethyltrifluoroborate.
In the case of cinnamic substrates, the boronic derivatives were
prepared by the copper-catalyzed addition of bis(pinacolato)
diboron on the conjugated double bond (Scheme 3).16
Table 1
Determination of optimized conditions
O
CN
Toluene 0.5 M
BF3K
N
H
Scheme 3. Synthesis of compound 3.
2
1
Entry Benzonitrile mol % Cu(OAc)2 mol % BF3$OEt2 mol % Yielda (%)
Finally, the Vedejs conditions17 were applied on the commercial
sources of boron derivatives to prepare potassium organo-
trifluoroborate salts 5e10.
The optimized conditions for amidation were applied on the
different homemade potassium organotrifluoroborate salts (Table
3). Acetonitrile was employed as nitrile source and solvent.
These conditions were efficient especially for N-(1-phenylethyl)
acetamide 12, which was isolated in 75% yield after 10 min of re-
action (Table 3, entry 1).
1
2
3
4
5
6
7
8
1000
1000
1000
1000
1000
1000
1000
Solvent 0.5 M
100
d
d
0
0
25
42
15
35
200
20
10
50
10
50
100
100
100
200
200
200
200
70 (1 h)
70 (10 min)b
a
GC yield, internal standard heptadecane.
Reaction was performed without toluene.
b
Different benzylic trifluoroborate salts were studied and the
corresponding amides were formed in 51e66% yields (Table 3,
entries 2e5). In these conditions, trifluoroborate salts 2 and 3 were
oxidized and afforded alcohols as by-products. In these particular
cases, the purification was difficult because amides and alcohols
exhibit similar retention factor values. For compound 3, different
conditions were tested in order to check the formation of the four
membered-ring lactam, unfortunately this product was never
detected. Primary benzylic potassium trifuoroborate salts afforded
the expected amide with good isolated yield (Table 3 entries 4 and
5). Surprisingly, treatment of potassium E-vinyltrifluoroborate 7
with copper acetate and BF3$OEt2 in acetonitrile gives the un-
expected N-(1-phenylethyl)acetamide in 80% yield (Table 4, entry
6). The formation of this product is not in agreement with our
mechanistic hypothesis. However, the monitoring of this reaction
by GCeMS shows the formation of styrene during the reaction. This
compound was then converted into amide by classical Ritter
mechanism, due to the presence of an excess on BF3$OEt2 in the
reaction media. The formation of this product could be explained
by the addition of nitrile on benzylic position following by the re-
duction of the CeB bond. Secondary alkylboronic derivatives seem
to be less reactive since desired amide was isolated in 70% yield
after 86 h of reaction (Table 3, entry 7). tert-Butyltrifluoroborate
potassium salt treated in presence of benzonitrile leads to the
corresponding amide 18 in 56% yields. The reactivity decreases
considerably with primary alkylboronic derivatives. Indeed, po-
tassium octyltrifluoroborate was reduced in alkane and expected
amide was not observed (Table 3, entry 8). The same observation
was done with potassium aryltrifluoroborate salts, the reduction of
starting material was the only reaction (Table 3, entry 9).
Based on results obtained in Table 2 the nature of the metallic
species is important since a lower yield was observed when re-
actions were performed with iron acetate (Table 2, entry 4), man-
ganese acetate (Table 2, entry 8) or cobalt acetate (Table 2, entry 9).
Moreover the nature of the ligand seems to have an influence on the
amide formation. Indeed less than 10% of desired product was ob-
tainedwith chloride oracetylacetonate ligand (Table 2, entries 1, 2, 5,
Table 2
Screening of different metals
Entry
Metala
Yieldb (%)
1
2
3
4
5
6
7
8
FeCl2
3
FeCl3
d
12
36
11
4
Fe(acac)3
Fe(OAc)2
CuCl
CuCl2
Cu(OAc)2
Mn(OAc)2
Co(OAc)2
Co(acac)3
Ni(acac)3
70
38
26
d
19
9
10
11
a
Conditions: potassium trifluoroborate salt (0.5 mmol), benzonitrile (5 mmol),
metal (0.5 mmol), BF3$OEt2 (1 mmol), toluene (1 mL), rt, 15 h.
b
GC yield, internal standard heptadecane.

C. Cazorla et al. / Tetrahedron 67 (2011) 8615e8621
8617
Table 3
Table 4
Reactivity of organotrifluoroborate salts
Reactivity of different nitriles
Metal (1 equiv.),
R
BF3.OEt2 (2 equiv.),
BF3K
N
H
R
CN
Toluene, r.t.
Entry
1
Substrates
Products
Isolated yielda (%)
Entry
1
Substrates
Products
Isolated yielda (%)
75b
1
3
12 75
H3CeCN
12
21
22
23
24
25
26
2
3
13 (51)b
2
3
4
5
6
7
85b
93b
70b
36
4
14 (66)b
4
5
5
6
15 61
16 66
O
BF K
3
N
H
F CO
3
F3CO
56
6
7
12 80
d
7
8
8
9
17 70c
18 56
8
27
28
29
d
57
51
9
9
10
11
19
20
d
d
10
10
11
12
30
31
53
53
a
Conditions: potassium trifluoroborate salt (1 mmol), acetonitrile (2 mL),
Cu(OAc)2 (1 mmol), BF3$OEt2 (2 mmol), rt, 15 h.
b
GCeMS yield.
86 h of reaction.
c
Later, different nitriles were engaged in this amide formation re-
action with potassium 1-phenylethyltrifluoroborate 1. As some ni-
triles studied were solids, the reactionwas carried out in the presence
of toluene as solvent. A series of primary alkylnitriles were tested and
were found to be efficient partners for amide bond formation. The
expected amides were isolated in good yields from 75 to 93%, in 1 h at
room temperature (Table 4, entries 1e4). However, when the alkyl
chain possesses a terminal alkene or alkyne, the isolated yields were
lower and reached only 36 and 56%, respectively (Table 4, entries 5
and 6). In the latter case, no by-products from homo-coupling of al-
kynewere observed thus explaining the moderate yield. In the case of
4-bromoacetonitrile, the expected product 26 (Table 4, entry 7) was
not detected, the only formed product comes from the reduction of
the CeBr bond. Dinitrile substrates were also considered. If no re-
action occurred with malonitrile, glutaronitrile afforded only the
monoamide 27 with a moderate yield of 57%. Substituted aromatic
nitriles were also studied and the presence of electron-withdrawing
group or electron-donating group gave similar results (Table 4, en-
tries 10e12). Moreover, in the case of 4-nitrobenzonitrile (Table 4,
entry 10) a GC analysis revealed the formation 2,3-diphenylbutane
13
32
57
a
Conditions: potassium trifluoroborate salt (1 mmol), nitrile (10 mmol), Cu(OAc)2
(1 mmol), BF3$OEt2 (2 mmol), toluene (2 mL), rt15 h.
b
1 h of reaction.
(dimer) in a 1:1 ratio with expected amide. Finally, the amidation in
the presence of cinnamonitrile was performed in 57% yield.
Based on the results summarized in the different tables, we
were able to propose a mechanism (Scheme 4). While, in the lit-
erature, oxidative processes of boronic derivatives in presence of
transition metal involve a radical intermediate,18 these different
results let us supposed that the mechanism can be compared to the
Ritter reaction with the formation of a carbocation.
Indeed, we believe that the combination of boron trifluoride and
copper acetate generates an oxidative complex, able to reverse the
polarity of the CeB bond and form a carbocation, which react
subsequently with the nucleophilic nitrogen atom of the nitriles.
The corresponding amide is obtained after hydrolysis of the latter

8618
C. Cazorla et al. / Tetrahedron 67 (2011) 8615e8621
Cu+
Cu0
Cu2+
Cu+
aniline were prepared with a good yield of 86% (Table 5, entry 1). In
BF3K
O
the presence of 1-butanol the corresponding ether was isolated in
40% yield (Table 5, entry 2). Alkylation of benzo[b]thiophene should
be performed in these conditions. However, in order to decrease
the formation of by-products, which come from benzothiophene,
only 2 equiv of this reagent were utilized in this case. When N-
methylindole was used, the corresponding product was formed in
a moderate yield. Finally, azides can be prepared by this method-
ology. From both trimethylsilylazide and sodium azide, good con-
versions can be reached. Surprisingly, when alkylamine were used
as substrates, the desired products 38 and 39 were not obtained.
When benzyl acrylate and TEMPO were used as nucleophile, the
formation of the expected products was not observed. Moreover an
experiment, where acetonitrile and TEMPO were in competition
was carried on and only amide formation was observed (Scheme 5).
These examples reinforce our hypothetical mechanism on the
cationic character of this transformation.
Cu(OAc)2,
BF3.OEt2
CH3CN
1
O
O
AcO-
H2O
N
N
H
N
11
Scheme 4. Proposed mechanism for Ritter-type amidation.
intermediate. We suppose that boron trifluoride removed acetate
ligand to form a ‘naked’ copper II species, although the formation of
a difluoroborane species can currently not be excluded.17,19 Thus,
this activated metal would be more reactive for redox reaction and
generate copper metal. The formation of metallic copper is ob-
served in the end of each effective reaction. Moreover, 1 equiv of
copper II is necessary to reach high yields. In fact, when 0.5 equiv
are used the yield do not exceed 42%. Furthermore, the formation of
the carbocation intermediate is supported by the fact that the re-
action did not occur with aryltrifluoroborate salts. Indeed, forma-
tion of carbocation on aryl is much disfavored.
Scheme 5. Determination of a radical intermediate.
From the proposed mechanism, other nucleophiles were en-
gaged with compound 1 in the presence of copper acetate and
boron trifluoride. Results are detailed in Table 5. Amines from
3. Conclusion
Table 5
Reactivity of different nucleophiles
As a conclusion, we have developed an efficient reaction in mild
conditions for amidation of potassium alkyltrifluoroborate salts
from nitriles and mediated by copper acetate and boron trifluoride.
This transformation was realized at room temperature without the
need of adding ligand for the copper. We supposed that the
mechanism involves an oxidative nucleophilic substitution. The
possible formation of a benzylic carbocation intermediate gives
new possibility for the functionalization of boronic derivatives.
Entry
1
Substrates
Products
Yielda (%)
86
33
2
3
4
34
35
36
40
4. Experimental section
4.1. General
61b
,d
35c
NMR spectra were recorded on either a Bruker DRX 300 oper-
ating at 300 MHz and 75 MHz for 1H and 13C acquisitions, re-
spectively, or a Bruker DRX 400 operating at 400 MHz, 100 MHz,
and 376 MHz for 1H, 13C, and 19F acquisitions, respectively. Chemical
shifts are reported in parts per million with the solvent resonance
as the internal standard. Data as reported as follows: s¼singlet,
d¼doublet, t¼triplet, q¼quadruplet, m¼multiplet, and br¼broad,
coupling constant in hertz, integration. High-resolution mass
spectra were obtained on ThermoFinnigan MAT 95 XL spectrome-
ters. Melting points are recorded on melting point apparatus Stuart
SMT 10.
Copper acetate, boron trifluoride etherate (ca. 48% BF3), nitriles
and commercially available boronic derivatives (1-naphthalenb
oronic acid, 1-octylboronic acid, cyclohexylboronic acid, trans-2-
phenylvinylboronic acid, potassium benzyltrifluoroborate, 4-(tri-
fluoromethoxy)benzylboronic acid pinacol ester) were purchased
from Acros or Aldrich and used as received.
5
6
7
8
9
TMSN3
NaN3
36
37
38
39
40
83c
85c
d
d
d
4.2. Synthesis of potassium trifluoroborate salts
10
41
d
4.2.1. Potassium (1-phenylethyl)trifluoroborate [329976-80-9]
(1). In a 250 mL round-bottomed flask, under argon, [Rh(cod)2]
BF4 (394 mg, 0.97 mmol) and dppb (481 mg, 1.17 mmol) were
suspended in anhydrous and deoxygenated THF (75 mL). The sus-
pension was stirred at room temperature until a homogeneous
orange solution was obtained (10 min). Styrene (5.7 mL, 50.0 mmol)
a
Conditions: potassium trifluoroborate salt (1 mmol), Nucleophile (10 equiv),
Cu(OAc)2 (1 mmol), BF3$OEt2 (2 mmol), rt15 h.
b
Only 2 equiv of benzothiophene were used for this reaction.
Determined by GCeMS.
Only 2 equiv of N-methylindole were used for this reaction.
c
d

C. Cazorla et al. / Tetrahedron 67 (2011) 8615e8621
8619
was added to the reaction mixture and the resulting solution was
stirred 10 min at room temperature. Then a solution of cat-
echolborane (6.4 mL, 60.0 mmol) in 25 mL of THF was added
dropwise. The reaction mixture was stirred overnight at room
temperature. Pinacol (12.16 g, 102.90 mmol) was added rapidly in
one batch, and the vessel was flushed with a vigorous flow of argon.
The solution was stirred overnight at room temperature. The sol-
vent was removed and the resulting crude was purified by flash
chromatography (silica gel, cyclohexane/Et2O: 95/5). To the solu-
tion of pinacol ester (40 mmol) in MeOH (100 mL) was added
aqueous potassium hydrogen fluoride (50 mL, 4.5 M, 225 mmol).
The resulting white slurry was stirred at room temperature for
30 min, concentrated in vacuo and dissolved in hot acetone. The
mixture was filtered, the filtrate was concentrated in vacuo and the
residue recrystallised from a minimal amount of ether, to afford
7.1 g (81% yield) of the corresponding potassium trifluoroborate salt
4.3.1. Potassium (4-(trifluoromethoxy)benzyl)trifluoroborate [1201331-
15-8] (6). 1H NMR (400 MHz, DMSO-d6):
d
(ppm): 7.06 (d, J¼8.3 Hz,
2H), 7.0 (d, J¼8.3 Hz, 2H), 1.50 (s, 2H). 13C NMR (100 MHz, DMSO-d6):
d
(ppm): 146.6 (Cq), 144.1 (Cq), 129.6 (2 CH), 120.6 (q, JCeF¼254.5 Hz,
CF3), 119.6 (2 CH). 19F NMR (376 MHz, DMSO-d6):
d
(ppm): ꢁ57.3
(CF3), ꢁ137.5 (BF3K). Mp (Et2O) 173e175 ꢀC (white solid).
4.3.2. Potassium trans-styryltrifluoroborate [201852-49-5] (7). 1H
NMR (400 MHz, DMSO-d6):
2H), 7.10 (t, J¼7.2Hz,2H), 6.46(d, J¼18.1 Hz,1H), 6.17 (dt, J¼18.1, 3.5 Hz,
1H). 13C NMR (100 MHz, DMSO-d6):
(ppm): 140.3 (Cq), 133.2 (CH),
d
(ppm): 7.29 (d, J¼7.3 Hz, 2H), 7.24 (m,
d
133.1 (CH), 128.3 (2 CH), 125.9 (CH), 125.4 (2 CH). 19F NMR (376 MHz,
DMSO-d6):
d
(ppm): ꢁ138.2. Mp (Et2O) >250 ꢀC (white solid).
4.3.3. Potassium cyclohexyltrifluoroborate[446065-11-8] (8). 1H
NMR (400 MHz, DMSO-d6): d (ppm): 1.55 (m, 3H), 1.47 (m, 2H), 1.03
as a white solid. 1H NMR (400 MHz, DMSO-d6):
d
(ppm): 7.03 (m,
(m, 3H), 0.88 (m, 2H), ꢁ0.02 (br,1H). 13C NMR (100 MHz, DMSO-d6):
4H), 6.86 (m, 1H), 1.56 (br, 1H), 1.02 (d, J¼9.8 Hz, 3H). 13C NMR
d
(ppm): 28.9 (2 CH2), 28.4 (2 CH2), 27.7 (CH2). 19F NMR (376 MHz,
(100 MHz, DMSO-d6):
d
(ppm): 152.2 (Cq), 127.6 (CH), 126.8 (CH),
DMSO-d6):
d
(ppm): ꢁ145.5 (white foamy solid).
122.3 (CH), 17.3 (CH3). 19F NMR (376 MHz, DMSO-d6):
ꢁ150.5. Mp (Et2O) 206e207 ꢀC.
d (ppm):
4.3.4. Potassium octyltrifluoroborate [329976-79-6] (9). 1H NMR
(400 MHz, DMSO-d6):
d
(ppm): 1.12 (m, 12H), 0.85 (q, J¼6.9 Hz, 3H),
4.2.2. Potassium
(3-ethoxy-3-oxo-1-phenylpropyl)trifluoroborate
ꢁ0.07 (t, J¼8.3 Hz, 2H). 13C NMR (100 MHz, DMSO-d6):
d (ppm):
(4). CuCl (30 mg, 0.3 mmol), NaOt-Bu (87 mg, 0.9 mmol), and
DPEphos ligand (162 mg, 0.3 mmol) were placed in an oven-dried
Schlenk tube and THF (8 mL) were added under argon. The re-
action mixture was stirred for 30 min at room temperature and then,
bis(pinacolato)diboron (2.79 g, 11 mmol) and THF (6 mL) were
added. The reaction mixture was stirred for 10 min and ethyl cin-
namate (1.68 mL, 10 mmol) was added, followed by MeOH (1.62 mL,
40 mmol). The reaction tube was washed with THF (6 mL), sealed,
and stirred until no starting material was detected by TLC. The re-
action mixture was filtered through a pad of Celite and concentrated.
The crude was purified by silica gel chromatography (cyclohexane/
AcOEt: 95/5). To the solution of pinacol ester (1.0 g, 3.28 mmol) in
MeOH (10 mL) was added aqueous potassium hydrogen fluoride
(5 mL, 4.5 M, 22.5 mmol). The resulting white slurry was stirred at
room temperature for 30 min, concentrated in vacuo and dissolved
in hot acetone. The mixture was filtered, the filtrate was concen-
trated in vacuo and the residue recrystallised from a minimal
amount of ether, to afford 0.73 mg (78% yield) of the corresponding
potassium trifluoroborate salt as a white solid. 1H NMR (400 MHz,
33.24 (CH2), 31.5 (CH2), 29.5 (CH2), 28.9 (CH2), 25.7 (CH2), 25.6
(CH2), 22.2 (CH2), 14.0 (CH3). 19F NMR (376 MHz, DMSO-d6):
d
(ppm): ꢁ137.2. Mp (Et2O) >250 ꢀC (white solid).
4.3.5. Potassium (1-naphthalene)trifluoroborate[166328-07-0] (10).
1H NMR (400 MHz, DMSO-d6):
(ppm): 8.38 (m, 1H), 7.72 (m, 1H),
7.76 (m, 1H), 7.71 (m, 1H), 7.31 (m, 3H). 13C NMR (100 MHz, DMSO-
d6): (ppm): 136.7 (Cq), 133.1 (Cq), 130.3 (Cq), 128.7 (CH), 128.6
d
d
(CH), 127.5 (CH), 125.4 (CH), 125.0 (CH), 124.0 (CH), 123.5 (CH). 19F
NMR (376 MHz, DMSO-d6):
(white solid).
d
(ppm): ꢁ135.5. Mp (Et2O) >250 ꢀC
4.4. General procedure for amide synthesis
To a solution of copper (II) acetate (180 mg, 1 mmol) and po-
tassium organotrifluoroborate (1 mmol) in toluene (2 mL) was
added nitrile (10 mmol). Boron trifluoride (in solution in ether, ca.
48% BF3) was then added. The reaction media was stirred 15 h at
room temperature. The reaction media was poured in 10 mL of
water and extracted with ethyl acetate (3ꢂ5 mL). The combined
organic layers were washed with brine (10 mL) and dried over
MgSO4, filtered, and concentrated under reduce pressure. The
crude was purified by chromatography on silica gel.
DMSO-d6):
d
(ppm): 7.02 (m, 4H), 6.89 (m,1H), 3.81 (q, J¼7.0 Hz, 2H),
2.42 (m, 2H), 1.97 (br, 1H), 0.97 (t, J¼7.0 Hz, 3H). 13C NMR (100 MHz,
DMSO-d6): d (ppm): 174.7 (Cq), 148.6 (Cq), 127.8 (2 CH), 126.8 (2 CH),
122.6 (CH), 58.6 (CH2), 36.8 (CH2), 14.1 (CH3). 19F NMR (376 MHz,
DMSO-d6):
d
(ppm): ꢁ143.5. Mp (Et2O) 147e148 ꢀC.
4.2.3. Potassium (2-cyano-1-phenylethyl) trifluoroborate (3). Using
4.4.1. N-(1-Phenylethyl)benzamide (2) [3480-59-9]. 1H NMR
the same procedure, the title compound was isolated in 92% yield
(300MHz,CDCl3):d(ppm): 7.76e7.78(m, 2H),7.28e7.75 (m, 8H), 6.36
(1.61 g) 1H NMR (400 MHz, DMSO-d6):
d
(ppm): 7.08 (m, 5H), 2.56
(br,1H), 5.34 (q, J¼7.1 Hz,1H),1.60 (d, J¼7.1 Hz, 3H).13C NMR (75 MHz,
(m, 2H), 1.81 (br, 1H). 13C NMR (100 MHz, DMSO-d6):
d
(ppm): 146.6
CDCl3): d (ppm): 166.7 (Cq),134.7 (Cq),143.2 (Cq),131.6 (CH),128.9 (2
(Cq), 127.7 (2 CH), 127.2 (2 CH), 123.6 (CH), 122.5 (Cq), 19.1 (CH2). 19
F
CH),128.7 (2 CH),127.6 (CH),127.0 (2 CH),126.4 (2 CH), 49.3 (CH), 21.8
(ppm):ꢁ144.3. Mp (Et2O) 194e195 ꢀC.
(CH3). HRMS EI: calculated for [C15H15NO]þ ¼225,1154,
ꢃ
NMR (376 MHz, DMSO-d6):
d
found¼225,1146. Mp (MeOH) 122e123 ꢀC (yellow solid).
4.3. General procedure for preparation of potassium
trifluoroborate salt
4.4.2. N-(1-Phenylethyl)acetamide (12) [36065-27-7]. 1H NMR
(300 MHz, CDCl3): d (ppm): 7.27e7.32 (m, 5H), 5.80 (br, 1H), 5.51 (q,
To a solution of boronic acid or pinacol ester (40 mmol) in
methanol (100 mL) was added aqueous potassium hydrogen fluo-
ride (50 mL, 4.5 M, 225 mmol). The resulting white slurry was
stirred at room temperature for 30 min, concentrated in vacuo and
dissolved in hot acetone. The mixture was filtered, the filtrate was
concentrated in vacuo and the residue recrystallised from a mini-
mal amount of ether, to afford the corresponding potassium tri-
fluoroborate salt.
J¼7.1 Hz, 1H), 1.47 (d, J¼7.1 Hz, 3H), 1.42 (s, 3H). 13C NMR (75 MHz,
CDCl3):
d (ppm): 170.4 (Cq), 137.6 (Cq), 128.8 (2 CH), 127.5 (CH),
126.3 (2 CH), 48.9 (CH), 27.0 (CH3), 23.5 (CH3).
4.4.3. N-Benzylacetamide (15) [588-46-5]. 1H NMR (300 MHz,
CDCl3):
2H), 1.94 (s, 3H). 13C NMR (75 MHz, CDCl3):
138.3 (Cq), 128.7 (2 CH), 127.8 (2 CH), 127.5 (CH), 43.7 (CH2), 23.2
d
(ppm): 720e7.28 (m, 5H), 6.15 (br, 1H), 4.34 (d, J¼5.7 Hz,
d
(ppm): 170.2 (Cq),

8620
C. Cazorla et al. / Tetrahedron 67 (2011) 8615e8621
(CH3). HRMS EI: calculated for [C9H11NO]þ ¼149.0841,
found¼149.0838. Mp (MeOH) 61e62 ꢀC (white crystal).
(m, 4H), 1.48 (d, J¼6.8 Hz, 3H). 13C NMR (75 MHz, CDCl3):
d (ppm):
ꢃ
171.0 (Cq),143.2 (Cq),128.8 (2 CH),127.6 (CH),126.2 (2 CH),119.7 (Cq),
48.9 (CH), 35.6 (CH2), 24.9 (CH2), 24.7 (CH2), 21.9 (CH3), 17.1 (CH2)
(yellow oil).
4.4.4. N-(4-(Trifluoromethoxy)benzyl)acetamide
(16). 1H
NMR
(300 MHz, CDCl3):
d
(ppm): 7.28 (d, J¼8.6 Hz, 2H), 7.16 (d, J¼8.6 Hz,
2H), 6.04 (br, 1H), 4.40 (d, J¼5.8 Hz, 2H), 2.00 (s, 3H). 13C NMR
4.4.12. Methyl 4-((1-phenylethyl)carbamoyl) benzoate (30) [925136-
(75 MHz, CDCl3):
d
(ppm): 170.2 (Cq), 148.6 (Cq), 137.2 (Cq), 129.3 (2
89-6]. 1H NMR (300 MHz, CDCl3):
d
(ppm): 8.09 (d, J¼8.5 Hz, 2H),
CH), 121.3 (2 CH), 120.6 (q, JCeF¼254.5 Hz, CF3), 43.0 (CH2), 23.3
7.82 (d, J¼8.5 Hz, 2H), 7.35 (m, 5H), 6.34 (br, 1H), 5.35 (q, J¼6.9 Hz,
(CH3). 19F NMR (282 MHz, CDCl3):
d
(ppm): ꢁ58.4. HRMS EI: cal-
1H), 3.94 (s, 3H), 1.64 (d, J¼6.9 Hz, 3H). 13C NMR (75 MHz, CDCl3):
culated for [C10H10F3NO2]þ ¼233.0664, found¼233.0663. Mp
d (ppm): 166.4 (Cq), 165.8 (Cq), 142.9 (Cq), 138.6 (Cq), 132.9 (Cq),
ꢃ
(MeOH) 122e123 ꢀC (white crystal).
129.9 (2 CH),128.9 (2 CH),127.8 (CH),127.1 (2 CH),126.4 (2 CH), 52.5
(CH), 49.6 (CH3), 21.7 (CH3). EIMS m/z (% relative abundance): 283
(38), 268 (12), 163 (100), 135 (15), 120 (11), 104 (28), 103 (12), 77
(10). Mp (MeOH) 150e151 ꢀC (yellow crystal).
4.4.5. N-(Cyclohexyl)acetamide
(300 MHz, CDCl3): (ppm): 5.61 (br, 1H), 3.73 (m, 1H), 1.88e1.93
(m, 4H), 1.54e1.71 (m, 3H), 1.03e1.37 (m, 6H). 13C NMR (75 MHz,
(17)
[1124-53-4]. 1H
NMR
d
CDCl3):
d
(ppm): 169.4 (Cq), 48.5 (CH), 33.3 (2 CH2), 25.6 (CH2), 24.9
4.4.13. 4-Methyl-N-(1-phenylethyl)benzamide(31) [17537-45-0]. 1H
(2 CH2), 23.6 (CH3). HRMS EI: calculated for [C8H15NO]þ ¼141.1154,
NMR (300 MHz, CDCl3):
d
(ppm): 7.66 (d, J¼8.1 Hz, 2H), 7.20e7.40
ꢃ
found¼141.1147. (white foamy solid).
(m, 7H), 6.30 (br, 1H), 5.32 (q, J¼7.1 Hz, 1H), 2.38 (s, 3H), 1.60 (d,
J¼7.1 Hz, 3H). HRMS ESI: calculated for [C16H17NOþH]þ¼240.1388,
found¼240.1390 (white solid).
4.4.6. N-(1-Phenylethyl)cyclopropanecarboxamide (21) [78172-92-
6]. 1H NMR (300 MHz, CDCl3):
d
(ppm): 7.19e7.28 (m, 5H), 5.94 (br,
1H), 5.08 (q, J¼7.0 Hz,1H),1.42 (d, J¼7.0 Hz, 2H),1.19 (m,1H), 0.90 (m,
2H), 0.65 (m, 2H). 13C NMR (75 MHz, CDCl3):
(ppm): 172.7 (Cq),
4.4.14. N-(1-Phenylethyl)cinnamamide (32) [1004997-26-5]. 1H NMR
d
(300 MHz, CDCl3):
d
(ppm): 7.56 (d, J¼15.6 Hz, 1H), 7.38 (m, 2H),
143.5 (Cq),128.7 (2 CH),127.4 (CH),126.3 (2 CH), 48.9 (CH), 21.9 (CH),
7.23e7.29 (m, 7H), 7.18 (m, 1H), 6.35 (d, J¼15.6 Hz, 1H), 6.01 (br, 1H),
14.9 (CH3), 7.2 (2 CH2). HRMS EI: calculated for [C12H15NO]þ
:
5.21 (q, J¼7.2 Hz,1H),1.48 (d, J¼7.2 Hz, 3H).13C NMR (75 MHz, CDCl3):
ꢃ
189,1154, found¼189.1148. Mp (MeOH) 89e91 ꢀC (white crystal).
d (ppm): 165.1 (Cq),143.2 (Cq),141.3 (Cq),134.9 (CH),129.7 (CH),128.9
(2 CH),128.8 (2 CH),127.9 (2 CH),127.5 (CH),126.4 (2 CH),120.8 (CH),
4.4.7. N-(1-Phenylethyl)dodecanamide (22) [560090-64-4]. 1H NMR
(300 MHz, CDCl3): (ppm): 7.24e7.36 (m, 5H), 5.65 (br, 1H), 5.14 (q,
49.0 (CH), 21.7 (CH3). Mp (MeOH) 136e137 ꢀC (yellow crystal).
d
J¼7.1 Hz, 1H), 2.16 (t, J¼7.6 Hz, 2H), 1.48 (d, J¼7.1 Hz, 3H), 1.24 (m,
4.4.15. N-(1-Phenylethyl)aniline (33) [779-54-4]. 1H NMR (300 MHz,
CDCl3): d (ppm): 7.40 (m, 2H), 7.36 (m, 2H), 7.26 (m, 1H), 7.13 (t,
18H), 0.88 (t, J¼6.7 Hz, 3H). 13C NMR (75 MHz, CDCl3):
d
(ppm):
172.3 (Cq), 143.4 (Cq), 128.8 (2 CH), 127.5 (CH), 126.3 (2 CH), 48.7
(CH), 37.1 (CH2), 32.0 (CH2), 29.7 (CH2), 29.6 (2 CH2), 29.5 (2 CH2),
29.4 (CH2), 25.9 (CH2), 22.8 (CH2), 21.8 (CH3), 14.5 (CH3). HRMS EI:
J¼7.8 Hz, 1H), 6.69 (t, J¼7.3 Hz, 1H), 6.55 (d, J¼7.8 Hz, 2H), 4.53 (q,
J¼6.8 Hz, 1H), 1.55 (d, J¼6.8 Hz, 3H). 13C NMR (75 MHz, CDCl3):
d
(ppm): 147.4 (Cq), 145.3 (Cq), 129.2 (2 CH), 128.7 (2 CH), 127.0 (2
calculated for [C20H33NO]þ ¼303.2562, found¼303.2562. Mp
CH), 122.9 (CH), 117.4 (CH), 113.4 (2 CH), 53.6 (CH), 25.1 (CH3). EIMS
m/z (% relative abundance): 197 (41), 183 (13), 182 (100), 105 (53),
104 (15), 93 (35), 79 (10), 77 (26), 51 (12) (colorless oil).
ꢃ
(MeOH) 180 ꢀC degradation (yellow solid).
4.4.8. 2-Cyclopropyl-N-(1-phenylethyl)acetamide (23) [1201331-51-
2]. 1H NMR (300 MHz, CDCl3):
d
(ppm): 7.20e7.27 (m, 5H), 6.15 (br,
4.4.16. (1-Butoxyethyl)benzene (34) [4157-77-1]. 1H NMR (400 MHz,
1H), 5.11 (q, J¼7.2 Hz, 1H), 2.09 (d, J¼7.1 Hz, 2H), 1.43 (d, J¼7.2 Hz,
CDCl3):
d
(ppm): 7.19e7.27 (m, 5H), 4.32 (q, J¼6.3 Hz, 1H), 3.23 (t,
3H), 0.92 (m, 1H), 0.55 (m, 2H), 0.14 (m, 2H). 13C NMR (75 MHz,
J¼6.6 Hz, 2H),1.47 (m, 2H),1.36 (d, J¼6.3 Hz, 3H),1.28 (m, 2H), 0.82 (t,
CDCl3):
d
(ppm): 171.6 (Cq), 143.4 (Cq), 128.8 (2 CH), 127.4 (CH),
J¼7.3 Hz, 3H). 13C NMR (100 MHz, CDCl3):
d (ppm): 144.5 (Cq), 128.5
126.2 (2 CH), 48.6 (CH), 41.6 (CH2), 22.0 (CH), 7.2 (CH3), 4.7 (2 CH2).
(2 CH),127.4 (CH),126.2 (2 CH), 78.0 (CH), 68.6 (CH2), 39.2 (CH2), 24.3
(CH3), 19.5 (CH2), 14.0 (CH3). EIMS m/z (% relative abundance): 163
(71), 107 (100), 106 (23), 105 (82), 103 (12), 79 (41), 77 (24), 51 (15),
43 (21), 41 (25).
HRMS EI: calculated for [C13H17NO]þ ¼203.1310 found¼203.1307.
ꢃ
Mp (MeOH) 80e82 ꢀC (white crystal).
4.4.9. N-(1-Phenylethyl)hex-5-enamide (24). 1H NMR (300 MHz,
CDCl3):
d
(ppm): 7.18e7.29 (m, 5H), 5.95 (br,1H), 5.70 (m,1H), 5.10 (m,
4.4.17. 3-(1-Phenylethyl)benzo[b]thiophene (35) [114838-47-0]. 1H
1H), 4.91 (m, 2H), 2.09 (t, J¼7.8 Hz, 2H),1.97 (m, 2H),1.66 (m, 2H),1.40
NMR (400 MHz, DMSO-d6):
d
(ppm): 7.94 (d, J¼6.55 Hz, 1H), 7.63 (s,
(d, J¼7.0 Hz, 3H).13C NMR (75 MHz, CDCl3):
d
(ppm): 172.0 (Cq),143.4
1H), 7.61 (m, 1H), 7.26e7.35 (m, 6H), 7.14 (m, 1H), 4.48 (q, J¼7.2 Hz,
(Cq),137.9 (CH),128.7 (2 CH),127.3 (CH),126.2 (2 CH),115.3 (CH), 48.6
(CH), 35.9 (CH2), 33.2 (CH2), 24.8 (CH2), 21.8 (CH3). HRMS CI: calcu-
lated for [C14H19NOþH]þ¼218.1539, found¼218.1528 (yellow oil).
1H), 1.66 (d, J¼7.2 Hz, 3H). 13C NMR (100 MHz, DMSO-d6):
d (ppm):
145.5 (Cq), 140.2 (Cq), 139.9 (Cq), 138.2 (Cq), 128.4 (2 CH), 127.1 (2
CH), 126.1 (CH), 124.2 (CH), 123.8 (CH), 122.9 (CH), 122.3 (CH), 121.9
(CH), 38.5 (CH), 22.3 (CH3). EIMS m/z (% relative abundance): 238
(43), 224 (17), 223 (100), 222 (20), 221 (24) 178 (11).
4.4.10. N-(1-Phenylethyl)hex-5-ynamide (25). 1H NMR (300 MHz,
CDCl3):
d
(ppm): 7.23e7.33 (m, 5H), 6.12 (br, 1H), 5.09 (q, J¼6.9 Hz,
1H), 2.29 (t, J¼7.3 Hz, 2H), 2.22 (m, 2H), 1.95 (t, J¼2.6 Hz, 1H), 1.66
Acknowledgements
(m, 2H), 1.44 (d, J¼6.9 Hz, 3H). 13C NMR (75 MHz, CDCl3):
d (ppm):
171.4 (Cq), 143.3 (Cq), 128.6 (2 CH), 127.3 (CH), 126.1 (2 CH), 83.6
(CH), 69.3 (CH), 48.7 (CH2), 35.1 (CH2), 24.2 (CH2), 21.9 (CH), 17.8
(CH2). HRMS CI: calculated for [C14H17NOþH]þ¼216.1383,
found¼216.1367 (yellow oil).
C.C. thanks the French Ministry for teaching and research
(MESR) for financial support.
References and notes
4.4.11. 5-Cyano-N-(1-phenylethyl)pentanamide
(300 MHz, CDCl3): (ppm): 7.29e7.36 (m, 5H), 5.80 (br, 1H), 5.11 (q,
J¼6.8 Hz, 1H), 2.34 (t, J¼6.8 Hz, 2H), 2.22 (t, J¼6.8 Hz, 2H), 1.66e1.80
(28). 1H
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