Palladium-catalyzed and copper-mediated cross-coupling reaction of aryl- or alkenylboronic acids with acid chlorides under neutral conditions: Efficient synthetic methods for diaryl ketones and chalcones at room temperature

Article abstract of DOI:10.1016/j.tet.2013.01.058

Palladium-catalyzed cross-coupling reaction of aryl- or alkenylboronic acids with acid chlorides in the presence of copper(I) thiophene-2-carboxylate (CuTC) as an activator in diethyl ether at room temperature under strictly non-basic conditions affords the diaryl ketones or chalcones in moderate to excellent yields. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on the aromatic ring are compatible.

Full text of DOI:10.1016/j.tet.2013.01.058

Tetrahedron 69 (2013) 2565e2571
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Palladium-catalyzed and copper-mediated cross-coupling reaction
of aryl- or alkenylboronic acids with acid chlorides under neutral
conditions: efficient synthetic methods for diaryl ketones and
chalcones at room temperature
Daisuke Ogawa, Keita Hyodo, Masato Suetsugu, Jing Li, Yoshiaki Inoue,
Mamoru Fujisawa, Masayuki Iwasaki, Kentaro Takagi, Yasushi Nishihara
*
Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku,
Okayama 700-8530, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium-catalyzed cross-coupling reaction of aryl- or alkenylboronic acids with acid chlorides in the
presence of copper(I) thiophene-2-carboxylate (CuTC) as an activator in diethyl ether at room temper-
ature under strictly non-basic conditions affords the diaryl ketones or chalcones in moderate to excellent
yields. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent
on the aromatic ring are compatible.
Received 28 December 2012
Received in revised form 16 January 2013
Accepted 21 January 2013
Available online 1 February 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Palladium
Copper
Cross-coupling
Ketones
Chalcones
1. Introduction
Unsymmetrical diaryl ketone and chalcone motifs are important
building blocks to construct natural products and pharmaceuti-
cals.1 For example, as shown in Fig. 1, sulisobenzone is an important
class of unsymmetrical diaryl ketones used as UV absorbers in some
sunscreens that protects the skin from UV lights.1a Optically active
(S)-ketoprofen is a nonsteroidal anti-inflammatory drug with ap-
proximately 160 times the anti-inflammatory potency of aspirin.1b
On the other hand, sofalcone is one of the chalcone derivatives,
which is used as an anti-ulcer with mucosa protective effect and
isolated from the root of the Chinese medicinal plant Sophora
subprostrata.1c Rottlerin (ROT) is widely used as an inhibitor toward
protein kinase C-delta.1d
Since Haddach and McCarthy have reported the palladium-
catalyzed cross-coupling reaction of acid chlorides with arylbor-
onic acids under basic conditions for the synthesis of diaryl ke-
tones,2 the analogous reactions have been developed for
a construction of diaryl ketone3 and chalcone4,5 derivatives. These
Fig. 1. Examples of representative diaryl ketones and chalcones.
coupling reactions involve several advantageous features relative to
FriedeleCrafts acylation6 or carbonylative SuzukieMiyaura7 and
MizorokieHeck type reactions8,9 of aryl halides in the presence of
carbon monoxide: mild reaction conditions, high regioselectivity,
and compatibility with various functional groups. In addition,
organoboronic acids are non-toxic and stable toward heat, air, and
* Corresponding author. Tel./fax: þ81 86 251 7855; e-mail address: ynishiha@
okayama-u.ac.jp (Y. Nishihara).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.01.058

2566
D. Ogawa et al. / Tetrahedron 69 (2013) 2565e2571
Table 2
moisture. Although numerous reports described the coupling of
organoboron compounds with carboxylic acid derivatives under
basic conditions,10,11 to the best of our knowledge, there are no
reports describing the synthesis of diaryl ketones or chalcones by
cross-coupling reaction of organoboronic acids with acid chlorides
under neutral conditions. We herein report the Pd-catalyzed cross-
coupling reaction of aryl- or alkenylboronic acids with acid chlo-
rides, which proceeds with an assistance of copper(I) thiophene-2-
carboxylate (CuTC) under non-basic and mild reaction conditions
(room temperature), leading to various diaryl ketones and
chalcones.12
Solvent effect on cross-coupling reaction of 1a with 2aa
Entry
Solvent
Temp (ꢀC)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
THF
DME
65
65
57
59
51
72
Bu2O
THP
65
80
1,4-dioxane
Et2O
100
25
72
2. Results and discussion
78 (97)c
toluene
DMF
65
65
37
0
2.1. Cross-coupling reaction of arylboronic acids 1 with acid
chlorides 2
DMSO
methanol
65
25
0
0d
Our initial investigation started with a cross-coupling reaction
of phenylboronic acid (1a) with benzoyl chloride (2a) as model
substrates in the presence of 5 mol % of Pd(dba)2 plus 10 mol % of
PPh3 as the catalyst and 1 equiv of various copper compounds in
THF at 65 ꢀC for 12 h.13 The results obtained are shown in Table 1.
Benzophenone (3a) was obtained in the presence of various copper
halides in 39e52% yields (Table 1, entries 1e3). Both Cu(OAc)2 and
CuOAc were found to be inferior (Table 1, entries 4 and 5). To our
delight, when we used copper(I) thiophene-2-carboxylate (CuTC),
the desired product 3a was formed in 57% yield (Table 1, entry 6).
The similar copper compounds, such as CuFC and CuPC showed low
activity. In all cases, the reaction gave rise to the formation of a little
amount of 4-chlorobutyl benzoate and biphenyl, presumably de-
rived from homocoupling of 1a. Formation of 4-chlorobutyl ben-
zoate was attributed to Pd-mediated reaction of 2a with THF as the
reactant.14 The similar boiling point and polarity of 4-chlorobutyl
benzoate would be a drawback for an isolation of the desired 3a.
Therefore, we screened other solvents for the reaction of 1a with
2a by using CuTC as an additive, as shown in Table 2. Reactions
proceeded in ethereal solvents, such as 1,2-dimethoxyethane (DME)
and Bu2O in moderate yields (Table 2, entries 2 and 3). Reactions in
higher temperature increased the yield (Table 2, entries 4 and 5).
Surprisingly, diethyl ether as the solvent significantly suppressed
the side reactions and the reaction preceded at room temperature in
78% yield (Table 2, entry 6). However, the yield of the reaction in less
polar toluene decreased to 37% (Table 2, entry 7). Unfortunately,
a
Reaction conditions: 1a (0.1 mmol), 2a (0.15 mmol), Pd(dba)2 (5 mol %), PPh3
(10 mol %), and CuTC (0.1 mmol) for 12 h.
b
GC yields.
c
A GC yield is shown in parenthesis under the following conditions: ratio of 1a/
2a¼2:1, reaction time; 3 h.
d
Methyl benzoate was formed in 59% yield.
reactions in DMF or DMSO did not afford 3a at all (Table 2, entries 8
and 9). When methanol was used as the solvent, methyl benzoate
was formed in 59% yield (Table 2, entry 10). Diethyl ether seems to
play an important role as the low concentration of CuTC and boronic
acid 1a in the reaction system is favorable to avoid excess amounts of
activated organoboron species leading to homocoupling during the
reaction, thereby giving rise to biphenyl as a byproduct. Further
examination revealed that the reaction was completed within 3 h
and 1a/2a¼2:1 ratio gave superior yield (97%).
Finally, we explored various catalyst systems and the results are
summarized in Table 3. When we employed Pd(PPh3)4, 3a was
obtained in lower yield (60%, Table 3, entry 2) presumably due to
suppression of catalytic reaction rate by the presence of excess PPh3
ligands. Although P(OPh)3 and P(2-furyl)3 in combination with
Pd(dba)2 gave satisfactory yields (Table 3, entries 3 and 4), P(t-Bu)3
and PMe3 as the ligand and Pd(dba)2 alone gave poor results (Table
3, entries 5e7). As the other palladium catalyst precursor, Pd(OAc)2
with PPh3 afforded 3a in 71% yield, albeit along with 8% yield of
biphenyl as the byproduct (Table 3, entry 8). Palladium catalyst
containing bidentate phosphine ligand, such as PdCl2(dppf) gave
Table 1
Table 3
Effect of Cu compounds for cross-coupling reaction of 1a with 2aa
Cross-coupling reaction of 1a with 2a using various catalyst systemsa
Entry
Catalyst
Yieldb (%)
Entry
Copper compound
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
Pd(dba)2/2 PPh3
Pd(PPh3)4
97
60
92
72
14
0
1
2
3
4
5
6
7
8
CuCl
CuBr
CuI
52
39
45
34
42
57
39
41
Pd(dba)2/2 P(OPh)3
Pd(dba)2/2 P(2-furyl)3
Pd(dba)2/2 P(t-Bu)3
Pd(dba)2/2 PMe3
Pd(dba)2
Cu(OAc)2
CuOAc
CuTC
6
CuFCc
CuPCd
Pd(OAc)2/2 PPh3
71
15
<1
PdCl2(dppf)c
Ni(cod)2
a
Reaction conditions: 1a (0.1 mmol), 2a (0.15 mmol), Pd(dba)2 (5 mol %), PPh3
a
(10 mol %), and copper compound (0.1 mmol) in THF at 65 ꢀC for 12 h.
Reaction conditions: 1a (0.2 mmol), 2a (0.1 mmol), catalyst (5 mol %) and CuTC
b
GC yields.
(0.1 mmol) in Et2O (3 mL) at room temperature for 3 h.
c
b
CuFC¼copper(I) furan-2-carboxylate.
GC yields.
d
c
CuPC¼copper(I) pyridine-2-carboxylate.
dppf¼1,10-bis(diphenylphosphino)ferrocene.

D. Ogawa et al. / Tetrahedron 69 (2013) 2565e2571
2567
poor results, along with 6% yield of biphenyl (Table 3, entry 9).
Ni(cod)2 was completely ineffective as the catalyst (Table 3, entry
10). Deletion of Pd(dba)2 yielded no product, confirming the re-
quirement for a palladium catalyst for this cross-coupling reaction.
The use of catalytic (10 mol %) and substoichiometric (50 mol %)
amounts of CuTC for the reaction of 1a with 2a afforded 3a in 7%
and 44% yields, respectively, whereas the use of excess (200 mol %)
amounts of CuTC did not disturb the reaction progress. Thus, we
employed a stoichiometric amount (100 mol %) of CuTC as the
optimal conditions.
A series of cross-coupling reactions of arylboronic acids 1aeg
with acid chlorides 2aej were conducted and the results are
summarized in Table 4. The reactions of 1a with acid chlorides
bearing electron-donating (Table 4, entries 2 and 3) and electron-
withdrawing groups proceeded in good to excellent yields (Table
4, entries 4e6). Acid chlorides 2g and 2h, having heteroatomatics,
such as 2-furyl and 2-thienyl groups, afforded the corresponding
cross-coupled products 3g and 3h in 73% and 82% yields, re-
spectively (Table 4, entries 7 and 8). Alkyl- and alkenyl-substituted
acid chlorides 2i and 2j underwent the reactions to give 3i and 3j in
moderate yields (Table 4, entries 9 and 10). On the other hand, the
reaction of 2a with arylboronic acids 1beg bearing various func-
tional groups similarly underwent the cross-coupling reactions in
up to 96% yield (Table 4, entries 11e16). However, a sterically hin-
dered arylboronic acid, 2,6-dimethylphenylboronic acid, com-
pletely retarded the reaction of 2a and gave no desired product.
In order to demonstrate an advantageous feature of the present
cross-coupling reaction under neutral conditions, the reaction of 1a
with 4-(chloromethyl)benzoyl chloride was subjected to compare
with the result of the reported basic conditions,3b as shown in
Scheme 1. In the presence of a stoichiometric amount of CuTC at
room temperature in Et2O, chemoselective cross-coupling occurred
to generate 4-chloromethylbenzophenone (3q) as a sole product in
77% isolated yield (81% GC yield). In a sharp contrast, under basic
conditions with K3PO4 gave the formation of 3q in 43% yield, with
other multiple products including 4-benzylbenzophenone (7%),
indicating that phenylation toward a chloromethyl group also
proceeded under basic conditions. a-Aryl nitriles are versatile in-
termediates for the synthesis of carboxylic acids, amides, primary
amines, aldehydes, and heterocycles. They can also have biological
activity as exemplified by medicinal compounds, such as anas-
trozole.15 A chemoselective reaction allowed us to perform the
subsequent cyanation of 3q with NaCN to generate 4 in 51% yield.
2.2. Cross-coupling reaction of alkenylboronic acids 5 with
acid chlorides 2
We next progressed to employ alkenylboronic acids as coupling
partners to give chalcones. The cross-coupling reactions of various
alkenylboronic acids 5 with acid chlorides 2 were investigated
under the optimized conditions. The results obtained are shown in
Table 5. The reaction of (E)-styrylboronic acid (5a) with various acid
chlorides 2 bearing electron-neutral and -withdrawing groups
afforded the chalcone derivatives 3j and 6aec in moderate yields
(Table 5, entries 1e4). Acid chlorides 2g and 2h having hetero-
aromatic rings, such as 2-furyl and 2-thienyl groups afforded the
corresponding products 6d and 6e in 70% and 85% yields, re-
spectively (Table 5, entries 5 and 6). Although the reaction of 5a
with 4-methoxybenzoyl chloride (2k) gave low yield of 6f even in
prolonged reaction time (45%, Table 5, entry 7), the reaction of 5a
with 4-methylbenzoyl chloride (2l) yielded 82% yield of 6g (Table 5,
entry 8). Alkenylboronic acid 5b bearing a methoxy group in the
para-position underwent the cross-coupling reaction with acid
chlorides 2a and 2e to give 6h and 6i, respectively, in good yields
(Table 5, entries 9 and 10). In addition, the reaction of alkenylbor-
onic acid bearing an electron-withdrawing trifluoromethyl group
with acid chlorides 2a, 2k, and 2l proceeded and gave the corre-
sponding cross-coupled products 6j, 6k, and 6l in moderate to good
yields (Table 5, entries 11e13). The reactions of an alkyl-substituted
alkenylboronic acid 5d with aroyl and heteroaromatic acid chlo-
rides underwent the cross-coupling reactions in good yields (Table
5, entries 14 and 15). Unfortunately, the reaction of an acid chloride
2i bearing an alkyl group gave a poor result (24%, Table 5, entry 16).
It seems that the low isolated yields of products 6 contain a certain
amount of technical loss due to the difficulty to isolate the desired
products from the dibenzylideneacetone (DBA) ligand.
Table 4
Cross-coupling reactions of arylboronic acids 1 with acid chlorides 2a
Entry
Boronic acid (R1)
Acid chloride (R2)
Product
Yieldb (%)
1c
2c
3
Ph (1a)
Ph (2a)
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
78
78
87
76
93
75
73
82
47
52
87
71
76
82
80
96
3-MeC6H4 (2b)
4-n-BuC6H4 (2c)
4-O2NC6H4 (2d)
4-ClC6H4 (2e)
4-NCC6H4 (2f)
2-Furyl (2g)
2-Thienyl (2h)
n-C7H15 (2i)
(E)-PhCH]CH (2j)
Ph (2a)
4
5c
6c
7
8
9
10
11
12
13
14
15
16
4-MeC6H4 (1b)
4-MeOC6H4 (1c)
2-MeOC6H4 (1d)
4-CF3C6H4 (1e)
4-BrC6H4 (1f)
4-MeCOC6H4 (1g)
a
Reaction conditions: arylboronic acid 1 (2 mmol), acid chloride 2 (1 mmol),
Pd(dba)2 (5 mol %), PPh3 (10 mol %), and CuTC (1 mmol) in Et2O (30 mL).
b
2.3. Reaction mechanism
Isolated yields.
c
Reaction time is 1 h.
We propose a reaction mechanism shown in Scheme 2. Oxida-
tive addition of acid chlorides 2 to the Pd(dba)2/PPh3 catalyst
Scheme 1.

2568
D. Ogawa et al. / Tetrahedron 69 (2013) 2565e2571
Table 5
Cross-coupling reactions of alkenylboronic acids 5 with acid chlorides 2a
Entry
Alkenylboronic acid (R1)
Acid chloride (R2)
Product
Yieldb (%)
1
2
3
4
Ph (5a)
Ph (2a)
3j
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
75
62
60
64
70
85
45
82
65
74
73
71
66
89
81
24
4-O2NC6H4 (2d)
4-ClC6H4 (2e)
4-NCC6H4 (2f)
2-Furyl (2g)
2-Thienyl (2h)
4-MeOC6H4 (2k)
4-MeC6H4 (2l)
Ph (2a)
4-ClC6H4 (2e)
Ph (2a)
4-MeOC6H4 (2k)
4-MeC6H4 (2l)
Ph (2a)
5
6
7c
8
9
4-MeOC6H4 (5b)
4-F3CC6H4 (5c)
10
11
12
13
14
15
16
n-C6H13 (5d)d
2-Furyl (2g)
n-C7H15 (2i)
a
Reaction conditions: boronic acid (1 mmol), acid chloride (0.5 mmol), Pd(dba)2 (5 mol %), PPh3 (10 mol %), and CuTC (0.5 mmol) in Et2O (15 mL).
Isolated yield.
Reaction time was 6 h.
Pd(dba)2 (10 mol %), PPh3 (20 mol %), reaction time was 7 h.
b
c
d
Scheme 2. A plausible mechanism for Pd-catalyzed and Cu-mediated cross-coupling reaction of organoboronic acids with acid chlorides.
generates an acylpalladium(II) chloride complex. Subsequent
accelerates the polarization of the palladiumechlorine bond, while
the hard carboxylate counterion activates the CeB bond of the
organoboronic acids via a six-membered ring. Although the re-
action with other copper salts, such as CuCl, CuBr, CuI, CuOAc, and
transmetalation of the organic group on aryl- or alkenylboronic
acid (1 or 5) to palladium takes place at the PdeCl bond. CuTC
seems to play dual important roles as an activator: the soft Cu(I) ion

D. Ogawa et al. / Tetrahedron 69 (2013) 2565e2571
2569
Cu(OAc)2 have been examined, inefficient reaction occurred, be-
4.2. Reaction of phenylboronic acid (1a) with benzoyl chlo-
cause they cannot construct such a six-membered ring. Compared
to the analogous copper compounds like CuFC and CuPC showed
the lower activity, implying that the thiophene moiety would also
play a role to activate the organoboronic acid by a coordination to
boron.
The measurement of X-ray diffraction (XRD) pattern analysis of
the copper residue, after completion of the reaction of phenyl-
boronic acid (1a) with 2-furoyl chloride (2g) in the presence of
100 mol % of CuTC, indicated that a part of new peaks was found
identical with those of CuCl (7). As a result, we found that both
CuTC and organoboronic acids are critical to the smooth trans-
metalation, presumably due to the presence of a hydrogen bond
between the carbonyl oxygen in CuTC and a hydroxy group of the
organoboronic acids.
ride (2a) in the presence of a Pd catalyst and CuTC in THF
(Table 1, entry 6)
Phenylboronic acid (1a) (12.2 mg, 0.1 mmol), CuTC (19.1 mg,
0.1 mmol), Pd(dba)2 (2.9 mg, 0.005 mmol), and PPh3 (2.6 mg,
0.01 mmol) were placed in 20 mL Schlenk tube. After a vacuum and
argon cycle three times, dry THF (1 mL) and benzoyl chloride (2a)
(17.3 mL, 0.15 mmol) were added at room temperature. The reaction
mixture was heated at 65 ꢀC for 12 h. Yields of a desired cross-coupled
product 3a (57%, based on 1a), biphenyl (7%, based on 1a), and 4-
chlorobutyl benzoate (18%, based on 2a) were detected by GC using
n-dodecane (23 m C
L, 0.1 mmol) as an internal standard. The 1H and 13
{1H} NMR data of 4-chlorobutyl benzoate were identical to a com-
mercially available authentic sample. 1H NMR (300 MHz, CDCl3):
Attempt to demonstrate the reactions by using relatively labile
phenylboronates PhB(OR)2 [(OR)2¼eOCH2CH2Oe, eOCH2CMe2
CH2Oe, and eOCHMeCH2CHMeOe] with 2a was failed even after
48 h at room temperature.
d
1.91e1.95 (m, 4H), 3.58e3.62 (m, 2H), 4.33e4.37 (m, 2H), 7.40e7.46
(m, 2H), 7.53e7.55 (m,1H), 8.02e8.05 (m, 2H).13C{1H} NMR (75 MHz,
CDCl3): 26.0, 29.1, 44.4, 64.0, 128.3, 129.4, 130.1, 132.9, 166.4.
d
4.3. General procedure for synthesis of unsymmetrical ke-
tones by the cross-coupling reaction of arylboronic acids with
acid chlorides
3. Conclusion
In conclusion, we have successfully developed a preparative
synthetic method for the generation of ketones and chalcones from
the cross-coupling reactions of acid chlorides with arylboronic
acids or alkenylboronic acids in the presence of Pd(dba)2 and
a stoichiometric amount of CuTC as a neutral activator. These re-
actions proceed under neutral conditions at room temperature
within 3 h. It is remarkable that diethyl ether as the solvent effects
the transformation of boronic acids into ketones, forming a car-
bonecarbon bond through the cross-coupling by the activation
with CuTC. These reactions are synthetically useful methods for
syntheses of ketones and chalcones from a viewpoint of non-toxic,
tolerant of many functional groups, and mild conditions. Further
application of this method to the synthesis of natural products and
pharmaceuticals is in progress.
4.3.1. Benzophenone (3a).18 To phenylboronic acid (1a, 244 mg,
2 mmol), CuTC (191 mg, 1 mmol), Pd(dba)2 (29 mg, 0.05 mmol), and
PPh3 (26.2 mg, 0.1 mmol), were added dry Et2O (30 mL) and benzoyl
chloride (2a,116 mL,1 mmol) at rt and the reaction was monitored by
GC and TLC. After completion of the reaction, the reaction mixture
was passed briefly through a Celite pad. Further, the pad was washed
with Et2O (2ꢁ10 mL). The combined organics were concentrated
with a rotary evaporator to give a viscous oil or solid. The residue
was purified by flash column chromatography on silica gel (hexane/
EtOAc¼9:1, Rf¼0.47), benzophenone (3a) (142 mg, 0.78 mmol, 78%)
was obtained as awhite solid.1H NMR (300 MHz, CDCl3):
d 7.46e7.51
(m, 4H), 7.56e7.62 (m, 2H), 7.79e7.83 (m, 4H).
4.3.2. 3-Methylbenzophenone (3b).19 1H NMR (300 MHz, CDCl3):
2.43 (s, 3H), 7.34e7.43 (m, 2H), 7.45e7.51 (m, 2H), 7.56e7.59 (m,
d
4. Experimental section
4.1. General
2H), 7.61e7.64 (m, 1H), 7.79e7.83 (m, 2H).
4.3.3. 4-n-Butylbenzophenone (3c).20 1H NMR (300 MHz, CDCl3):
d
0.95 (t, J¼7.2 Hz, 3H), 1.39 (m, 2H), 1.65 (m, 2H), 2.70 (t, J¼7.5 Hz,
All the reactions were carried out under an Ar atmosphere using
standard Schlenk techniques. Glassware was dried in an oven
(130 ꢀC) and heated under reduced pressure before use. For thin
layer chromatography (TLC) analyses throughout this work, Merck
precoated TLC plates (silica gel 60 GF254, 0.25 mm) were used. Silica
gel column chromatography was carried out using Silica gel 60 N
2H), 7.26e7.30 (m, 2H), 7.44e7.55 (m, 2H), 7.54e7.60 (m, 1H),
7.73e7.79 (m, 2H), 7.79e7.82 (m, 2H).
4.3.4. 4-Nitrobenzophenone (3d).21 1H NMR (300 MHz, CDCl3):
d
7.50e7.56 (m, 2H), 7.63e7.68 (m, 1H), 7.79e7.83 (m, 2H),
7.92e7.96 (m, 2H), 8.33e8.37 (m, 2H).
(spherical, neutral, 40e100
mm) from Kanto Chemicals Co., Ltd.
NMR spectra (1H, 13C{1H}, and 19F{1H}) were recorded on Varian
INOVA-600 (600 MHz) or Mercury-300 (300 MHz) spectrometers.
CHCl3: 7.26 ppm for 1H NMR and CDCl3: 77.0 ppm for 13C{1H} NMR
were used as internal standards. GC analyses were performed on
a Shimadzu GC-14A equipped with a flame ionization detector
using Shimadzu Capillary Column (CBP1-M25-025) and Shimadzu
C-R6A-Chromatopac integrator. The GC yields were determined
using suitable hydrocarbon internal standards. GC/MS analyses
were carried out on a SHIMADZU GC-17A equipped with a SHI-
MADZU QP-5050 GCeMS system. XRD patterns were measured
with Rigaku X-RAY DIFFRACTIOMETER RAD-1C.
4.3.5. 4-Chlorobenzophenone (3e).22 1H NMR (300 MHz, CDCl3):
d
7.45e7.52 (m, 4H), 7.58e7.63 (m, 1H), 7.75e7.80 (m, 4H).
4.3.6. 4-Cyanobenzophenone (3f).23 1H NMR (300 MHz, CDCl3):
d
7.49e7.54 (m, 2H), 7.61e7.67 (m, 1H), 7.77e7.81 (m, 4H),
7.86e7.89 (m, 2H).
4.3.7. 2-Furyl phenyl ketone (3g).24 1H NMR (300 MHz, CDCl3):
d
6.59 (dd, J¼3.3, 1.5 Hz, 1H), 7.22e7.24 (m, 1H), 7.46e7.52 (m, 2H),
7.56e7.62 (m, 1H), 7.70e7.71 (m, 1H), 7.95e7.99 (m, 2H).
Boronic acids 1a, 1d, and 1g and 1b, 1c, 1e, and 1f were pur-
chased from Aldrich Chemical Co. and Tokyo Chemical Industry Co.,
respectively, and used as received. Dehydrated diethyl ether was
purchased from Kanto Chemicals Co., Ltd. Copper(I) thiophene-2-
4.3.8. Phenyl 2-thienyl ketone (3h).25 1H NMR (300 MHz, CDCl3):
d
7.15 (dd, J¼3.9,1.2 Hz,1H), 7.47e7.52 (m, 2H), 7.57e7.62 (m,1H), 7.63
(dd, J¼3.9, 1.2 Hz, 1H), 7.71 (dd, J¼5.1, 1.2 Hz, 1H), 7.85e7.88 (m, 2H).
17
carboxylate (CuTC)16 and Pd(dba)2 were synthesized according
4.3.9. 1-Phenyl-1-octanone (3i).26 1H NMR (300 MHz, CDCl3):
to the literature procedures.
d
0.88 (t, J¼7.2 Hz, 3H), 1.29e1.40 (m, 8H), 1.73 (quint, J¼7.2 Hz, 2H),

2570
D. Ogawa et al. / Tetrahedron 69 (2013) 2565e2571
2.96 (t, J¼7.2 Hz, 2H), 7.43e7.49 (m, 2H), 7.53e7.58 (m, 1H),
7.95e7.98 (m, 2H).
benzoyl chloride (2a, 58 mL, 0.5 mmol) at room temperature. The
reaction was monitored by GC and TLC. After completion of the
reaction, the reaction mixture was passed briefly through a Celite
pad. Further, the pad was washed with Et2O (2ꢁ10 mL). The com-
bined organics were concentrated with a rotary evaporator to give
viscous oil. The residue was purified by preparative TLC on silica gel
(hexane/EtOAc¼10:1, Rf¼0.33) to give 3j (78 mg, 0.38 mmol, 75%)
4.3.10. (E)-1,3-Diphenyl-2-propen-1-one (3j).27 1H NMR (300 MHz,
CDCl3):
1H), 8.01e8.06 (m, 2H).
d
7.40e7.45 (m, 3H), 7.48e7.67 (m, 6H), 7.83 (d, J¼15.7 Hz,
4.3.11. 4-Methylbeonzophenone (3k).28 1H NMR (300 MHz, CDCl3):
as a white solid. 1H NMR (300 MHz, CDCl3):
d 7.40e7.45 (m, 3H),
d
2.44 (s, 3H), 7.27e7.29 (m, 2H), 7.44e7.50 (m, 2H), 7.55e7.60 (m,
7.48e7.67 (m, 6H), 7.83 (d, J¼15.7 Hz, 1H), 8.01e8.06 (m, 2H).
1H), 7.71e7.74 (m, 2H), 7.77e7.80 (m, 2H).
4.6.2. (E)-1-(4-Nitrophenyl)-3-phenyl-2-propen-1-one
(6a).34 1H
4.3.12. 4-Methoxybenzophenone (3l).28 1H NMR (300 MHz, CDCl3):
NMR (300 MHz, CDCl3): 7.43e7.51 (m, 4H), 7.65e7.68 (m, 2H), 7.85
d
d
3.87 (s, 3H), 6.93e6.98 (m, 2H), 7.46e7.49 (m, 2H), 7.53e7.58 (m,
(d, J¼15.6 Hz, 1H), 8.13e8.17 (m, 2H), 8.34e8.38 (m, 2H).
1H), 7.73e7.77 (m, 2H), 7.80e7.85 (m, 2H).
4.6.3. (E)-1-(4-Chlorophenyl)-3-phenyl-2-propen-1-one (6b).9 1H
NMR (300 MHz, CDCl3): d 7.42e7.52 (m, 6H), 7.63e7.67 (m, 2H),
4.3.13. 2-Methoxybenzophenone (3m).28 1H NMR (300 MHz,
CDCl3):
d
3.73 (s, 3H), 7.00 (d, J¼8.3 Hz, 1H), 7.04 (dt, J¼7.5, 0.9 Hz,
7.83 (d, J¼15.6 Hz, 1H), 7.95e7.99 (m, 2H).
1H), 7.35e7.58 (m, 5H), 7.80e7.83 (m, 2H).
4.6.4. (E)-4-(3-Phenylacryloyl)benzonitrile (6c).4 1H NMR (300
MHz, CDCl3): d 7.41e7.49 (m, 4H), 7.63e7.66 (m, 2H), 7.78e7.85 (m,
4.3.14. 4-(Trifluoromethyl)benzophenone
(3n).29 1H
NMR
(300 MHz, CDCl3):
(m, 2H), 7.79e7.83 (m, 2H), 7.88e7.91 (m, 2H). 19F{1H} NMR
(282 MHz, CDCl3):
ꢂ63.5.
d
7.48e7.54 (m, 2H), 7.61e7.66 (m,1H), 7.74e7.77
3H), 8.06e8.10 (m, 2H).
d
4.6.5. (E)-1-(2-Furyl)-3-phenyl-2-propen-1-one (6d).35 1H NMR
(300 MHz, CDCl3):
d 6.58e6.60 (m, 1H), 7.33e7.48 (m, 5H),
4.3.15. 4-Bromobenzophenone (3o).30 1H NMR (300 MHz, CDCl3):
7.46e7.52 (m, 2H), 7.58e7.70 (m, 5H), 7.76e7.79 (m, 2H).
7.63e7.66 (m, 3H), 7.88 (d, J¼15.6 Hz, 1H).
d
4.6.6. (E)-3-Phenyl-1-(2-thienyl)-2-propen-1-one (6e).36 1H NMR
(300 MHz, CDCl3): d 7.18e7.21 (m,1H), 7.40e7.46 (m, 4H), 7.64e7.70
(m, 3H), 7.84e7.89 (m, 2H).
4.3.16. 4-Acetylbenzophenone (3p).31 1H NMR (300 MHz, CDCl3):
2.66 (s, 3H), 7.47e7.52 (m, 2H), 7.59e7.65 (m, 1H), 7.78e7.81 (m,
d
2H), 7.84e7.87 (m, 2H), 8.04e8.07 (m, 2H).
4.6.7. (E)-1-(4-Methoxyphenyl)-3-phenyl-2-propen-1-one (6f).9 1H
4.4. Synthesis of 4-chloromethylbenzophenone (3q)32
NMR (300 MHz, CDCl3):
d
3.88 (s, 3H), 6.98 (d, J¼9.0 Hz, 2H),
7.40e7.42 (m, 3H), 7.55 (d, J¼15.9 Hz, 1H), 7.63e7.66 (m, 2H), 7.81
Following the general procedure, to phenylboronic acid (1a)
(488 mg, 4 mmol), CuTC (382 mg, 2 mmol), Pd(dba)2 (58 mg,
0.10 mmol), and PPh3 (52.4 mg, 0.20 mmol), were added dry diethyl
ether (60 mL) and a solution of 4-(chloromethyl)benzoyl chloride
(378 mg, 2 mmol) in 5 mL of diethyl ether at room temperature. The
suspension was stirred at room temperature for 3 h. After purifi-
cation by column chromatography on silica gel (hexane/ethyl
acetate¼9:1, Rf¼0.46), 3q (358 mg,1.55 mmol, 77%) was obtained as
a pale yellow oil. Bp: 200e210 ꢀC/4.1 Torr. 1H NMR (300 MHz,
(d, J¼15.9 Hz, 1H), 8.03e8.06 (m, 2H).
4.6.8. (E)-3-Phenyl-1-(4-methylphenyl)-2-propen-1-one (6g).4 1H
NMR (300 MHz, CDCl3):
7.40e7.43 (m, 3H), 7.55 (d, J¼15.6 Hz, 1H), 7.62e7.66 (m, 2H), 7.82
(d, J¼15.6 Hz, 1H), 7.94e7.97 (m, 2H).
d
2.43 (s, 3H), 7.30 (d, J¼7.8 Hz, 2H),
4.6.9. (E)-3-(4-Methoxyphenyl)-1-phenyl-2-propen-1-one
(6h).37 1H NMR (300 MHz, CDCl3):
d
3.85 (s, 3H), 6.93 (d, J¼6.9 Hz,
CDCl3):
d
4.60 (s, 2H), 7.42e7.48 (m, 4H), 7.53e7.59 (m, 1H),
2H), 7.42 (d, J¼15.6 Hz, 1H), 7.47e7.62 (m, 5H), 7.79 (d, J¼15.6 Hz,
7.56e7.78 (m, 4H). 13C{1H} NMR (75 MHz, CDCl3):
d 45.2, 128.1,
1H), 8.01e8.03 (m, 2H).
128.2, 129.8, 130.2, 132.4, 137.1, 137.2, 141.5, 195.7.
4.6.10. (E)-1-(4-Chlorophenyl)-3-(4-methoxyphenyl)-2-propen-1-
4.5. Synthesis of 2-(4-benzoylphenyl)acetonitrile (4)33
one (6i).38 1H NMR (300 MHz, CDCl3):
d 3.85 (s, 3H), 6.93 (d,
J¼8.7 Hz, 2H), 7.35 (d, J¼15.6 Hz, 1H), 7.45 (d, J¼8.4 Hz, 2H), 7.59 (d,
Diaryl ketone 3q (115 mg, 0.5 mmol) and sodium cyanide
(49 mg, 1.0 mmol) were dissolved in 1,4-dioxane/H2O¼7:3 (15 mL).
The mixture was heated under reflux for 2 h, during which the
organic product appeared as a separate layer. The cooled reaction
mixture was extracted with EtOAc (2ꢁ10 mL). The combined or-
ganics were concentrated with a rotary evaporator to give yellow
solid. After purification by column chromatography on silica gel
(hexane/ethyl acetate¼2:1, Rf¼0.46) 4 (57 mg, 1.3 mmol, 51%) was
J¼8.7 Hz, 2H), 7.78 (d, J¼15.6 Hz, 1H), 7.95 (d, J¼8.4 Hz, 2H).
4.6.11. (E)-3-{(4-(Trifluoromethyl)phenyl)}-1-phenyl-2-propen-1-
one (6j).39 1H NMR (300 MHz, CDCl3):
d 7.49–7.76 (m, 6H), 7.60 (d,
J¼15.6 Hz, 1H), 7.81 (d, J¼8.4 Hz, 2H), 8.02–8.06 (m, 2H). 19F{1H}
NMR (282 MHz, CDCl3):
d
ꢂ63.2.
4.6.12. (E)-1-(4-Methoxyphenyl)-3-{4-(trifluoromethyl)phenyl}-2-propen-
1-one (6k).40 1H NMR (300 MHz, CDCl3):
obtained as pale yellow solid. 1H NMR (300 MHz, CDCl3):
d
3.84
d
3.89 (s, 3H), 6.99 (d, J¼8.7 Hz,
(s, 2H), 7.44e7.51 (m, 4H), 7.57e7.63 (m, 1H), 7.76e7.82 (m, 4H).
2H), 7.58e7.67 (m, 3H), 7.72e8.03 (m, 3H), 8.05 (d, J¼8.7 Hz, 2H).
4.6. General procedure for synthesis of chalcones by the
cross-coupling reaction of alkenylboronic acids with acid
chlorides
4.6.13. (E)-1-(4-Methylphenyl)-3-{(4-(trifluoromethyl)phenyl)}-2-
propen-1-one (6l).39 1H NMR (300 MHz, CDCl3):
d 2.45 (s, 3H), 7.31
(d, J¼8.1 Hz, 2H), 7.33e7.82 (m, 6H), 7.95 (d, J¼8.1 Hz, 2H). 19F{1H}
NMR (282 MHz, CDCl3)
d
ꢂ63.2.
4.6.1. (E)-Chalcone (3j).4 To (E)-styrylboronic acid (1a, 148 mg,
1 mmol), CuTC (95 mg, 0.5 mmol), Pd(dba)2 (14 mg, 0.0025 mmol),
and PPh3 (13 mg, 0.05 mmol), were added dry Et2O (15 mL) and
4.6.14. (E)-1-Phenyl-2-nonen-1-one (6m).41 1H NMR (300 MHz,
CDCl3):
0.89 (t, J¼6.9 Hz, 3H), 1.25e1.40 (m, 6H), 1.47e2.35 (m, 2H),
d

D. Ogawa et al. / Tetrahedron 69 (2013) 2565e2571
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2.31 (qd, J¼5.7, 1.2 Hz, 2H), 6.87 (dt, J¼15.3, 1.2 Hz, 1H), 7.07 (dt,
J¼15.3, 6.9 Hz, 1H), 7.43e7.49 (m, 2H), 7.52e7.58 (m, 1H), 7.91e7.95
(m, 2H).
4.6.15. (E)-1-(2-Furyl)-2-nonen-1-one (6n). FTIR (KBr, cmꢂ1): 3443
(w), 2955 (m), 2928 (s), 2857 (m), 1667 (s), 1622 (s), 1566 (m), 1466
(s), 1395 (w), 764 (s). 1H NMR (300 MHz, CDCl3)
d
0.89 (t, J¼6.6 Hz,
3H), 1.25e1.39 (m, 6H), 1.46e1.56 (m, 2H), 2.30 (qd, J¼7.2, 1.8 Hz,
2H), 6.55 (dd, J¼3.6, 1.8 Hz, 1H), 6.79 (dt, J¼15.6, 1.5 Hz, 1H),
7.11e7.24 (m, 2H), 7.61 (d, J¼1.5 Hz, 1H). 13C{1H} NMR (75 MHz,
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CDCl3, rt): d 14.0, 22.5, 28.1, 28.9, 31.6, 32.7, 112.3, 117.4, 124.8, 146.4,
149.4, 153.4, 178.2. MS (EI, m/z (relative intensity)): 206 (Mþ, 5), 191
(1), 177 (5), 163 (4), 149 (25), 138 (9), 123 (38), 110 (90), 95 (100), 77
(16), 67 (10). Anal. Calcd for C13H18O2: C, 75.69; H, 8.80%. Found: C,
75.75; H, 8.46%.
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Following the general procedure, to phenylboronic acid (1a)
(244 mg, 2 mmol), CuTC (191 mg, 1 mmol), Pd(dba)2 (29 mg,
0.05 mmol), and PPh3 (26.2 mg, 0.1 mmol), were added dry diethyl
ether (30 mL) and 2-furoyl chloride (2g) (99 mL, 1 mmol) at room
temperature. The reddish brown suspension was stirred at room
temperature for 5 h. The mixture involving a brown precipitate was
filtered off and washed with diethyl ether. The resulting solid was
dried under reduced pressure to give a brown powder (152 mg),
which was subjected to the XRD analysis. Residue with 100 mol % of
CuTC: 2
47.45 (35), 56.27 (18), 61.38 (18), 73.53 (13). CuCl (measured): 2
(relative intensity) 28.55 (100), 33.09 (3), 47.46 (21), 56.30 (10),
59.05 (2), 69.36 (3), 76.64 (4). CuCl:43
(relative intensity) 28.59
q (relative intensity) 28.54 (100), 36.42 (74), 42.28 (26),
q
2q
(100), 33.03 (8), 47.43 (55), 56.29 (30), 69.34 (6), 76.58 (10), 88.34
(8), 95.30 (6), 107.13 (2), 114.58 (4), 128.16 (4).
Acknowledgements
The authors gratefully thank Ms. Megumi Kosaka and Mr.
Motonari Kobayashi at the Department of Instrumental Analysis,
Advanced Science Research Center, Okayama University for the
measurements of elemental analyses and the SC-NMR Laboratory
of Okayama University for the NMR spectral measurements. We are
grateful to Professor Hideki Taguchi at Okayama University for the
XRD measurements.
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Supplementary data
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Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2013.01.058.
These data include MOL files and InChiKeys of the most important
compounds described in this article.
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43. XRD pattern of CuCl is available from International Centre for Diffraction Data
(ICDD).