Catalytic activity of palladium acyclic diaminocarbene complexes in the synthesis of 1,3-diarylpropynones via Sonogashira reaction: Cross- versus homo-coupling

Article abstract of DOI:10.1016/j.tetlet.2013.02.086

Sonogashira cross-coupling of aryl acetylenes and aroyl chlorides catalyzed by palladium(II) acyclic diaminocarbene complexes was investigated. Reactions were carried out with 0.04 mol % of the catalysts, all of which demonstrated high stability and activ

Full text of DOI:10.1016/j.tetlet.2013.02.086

Tetrahedron Letters 54 (2013) 2369–2372
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Tetrahedron Letters
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Catalytic activity of palladium acyclic diaminocarbene complexes
in the synthesis of 1,3-diarylpropynones via Sonogashira reaction:
cross- versus homo-coupling
a
b
b
b
Dmitry S. Ryabukhin , Viktor N. Sorokoumov , Elizaveta A. Savicheva , Vadim P. Boyarskiy ,
b
a,b,
⇑
Irina A. Balova , Aleksander V. Vasilyev
Saint-Petersburg State Forest Technical University, Institutsky per. 5, 194021 Saint-Petersburg, Russia
a
b
Department of Chemistry, Saint-Petersburg State University, Universitetsky pr. 26, 198504 Saint-Petersburg, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Sonogashira cross-coupling of aryl acetylenes and aroyl chlorides catalyzed by palladium(II) acyclic dia-
minocarbene complexes was investigated. Reactions were carried out with 0.04 mol % of the catalysts, all
of which demonstrated high stability and activity in air. The influence of the reaction conditions (temper-
ature, time, amount of catalyst, solvent) and the structures of the starting compounds on the ratios of
cross- (1,3-diarylpropynones) and homo-coupling (1,4-diarylbutadiynes) products was elucidated. The
yields of 1,3-diarylpropynones reached 95–98%.
Received 19 November 2012
Revised 11 February 2013
Accepted 27 February 2013
Available online 7 March 2013
Keywords:
Palladium acyclic diaminocarbene
complexes
Ó 2013 Elsevier Ltd. All rights reserved.
Sonogashira coupling
1
1
,3-Diarylpropynones
,4-Diarylbutadiynes
a
,b-Acetylene ketones (propynones) are of significant impor-
of aryl acetylenes with aroyl chlorides (Scheme 1, route a).9,10
This route was discovered by Sonogashira in 1977 in his seminal
tance because of their wide use in organic synthesis as bifunc-
tional three-carbon building blocks. For example, they are
employed in the preparation of heterocycles, biologically active
1
0a
work.
Later, non-palladium procedures for this reaction were
1
11
12
described. Another pathway is the aroylation of copper or
lithium derivatives of aryl acetylenes (Scheme 1, route b). Other
compounds, carbocycles,3 functionalized enone systems, etc.
Propynones were applied effectively in the synthesis of unsym-
metrical 1-aryl(hetaryl/vinyl) buta-1,3-diynes using the Fritsch–
Buttenberg–Wiechell rearrangement according to Tykwinski
et al.5 In particular, intramolecular cyclization of 1,3-diarylpropy-
nones in Bronsted superacids resulted in the formation of 3-aryl
2
4
13
methods are the reactions of aroyl chlorides or amides with
1
4
15
16
arylethynyl stannanes, boranes, or stibines in both palla-
1
4a,16
14b,15
dium-catalyzed
or non-palladium versions
(Scheme 1,
route c). Other syntheses are based on carbonylative coupling
1
7a–c
of aryl acetylenes (or their derivatives) with aryl halides,
tri-
6
17d
17e
indenones, which could be easily photo-dimerized into cyclobu-
flates,
route d).
The most common palladium catalysts for the Sonogashira reac-
amines,
or triarylantimony(V) diacetate (Scheme 1,
tane structures.7 Hydroarylation of the acetylene bond of 1,3-
diarylpropynones in superacids leads to 1,3,3-triaryl substituted
17f
8
18
propenones. Oxidative dimerization of these acetylene ketones
tion are PdCl
2
3
(PPh )
2
or Pd(PPh
3
)
4
.
More recently, attention has
2 3 2 2 2
using the PbO –CF CO H–CH Cl system is a simple one-pot
been paid to palladium aminocarbene species as catalysts for versa-
1
9
method to prepare synthetically difficult tetraaroyl ethylenes,
which are used as precursors of pyridazine and 2,3,6,7-tetraaz-
anaphthalene derivatives.9
Several approaches have been developed for the preparation
of 1,3-diarylpropynones using acetylenes (Scheme 1). One of
the most effective methods is palladium-catalyzed cross-coupling
tile organic transformations, including the Sonogashira synthesis
2
0a
20b,c
of dialkylacetylenes,
enes,
alkylarylacetylenes,
and alkylarylbutadiynes.20c
Based on our studies on the preparation and chemical reac-
diarylacetyl-
20b,d–g
9
a
6
–9
tions
of 1,3-diarylpropynones, herein we report a synthesis of
these substrates via the palladium acyclic diaminocarbene com-
plex catalyzed Sonogashira coupling of arylacetylenes with aroyl
chlorides. This is the first example of the use of such palladium
species in the synthesis of acetylene ketones.
⇑
Corresponding author. Tel.: +7 812 6709352; fax: +7 812 6709390.
E-mail address: aleksvasil@mail.ru (A.V. Vasilyev).
0
040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.02.086

2
370
D. S. Ryabukhin et al. / Tetrahedron Letters 54 (2013) 2369–2372
Me
Cl
C
But
N
Cl
N
Me
Cl
Cl
C
Pd
C
N
Pd
C
Cl
C
C
Me
N
N
HN
NH
Pd
H
Cl
Pd
C
NH
H
Ph
N
N
N
N
C
But
C
NH
II
C
N
Me
Ph
Ph
Ph
O
2
N
I
III
IV
O
O
"
Pd" or
Ar
H
Cl
Ar
Y
X
non"Pd"
"
Pd"
Ar'
Ar'
route c Y = SnBu , SnCl , BF , SbPh
route a
3
3
2
2
O
X = Cl, NMe2
Ar
Ar'
non"Pd"
"
Pd"
O
route b
route d
Ar
M
X
Ar
Z
CO
X Ar'
Ar'
Z = H, CO H, SiMe
2
3
M = Cu, Li
X = Cl, OEt, NMe(OMe)
X = I, Br, OTf, NH , SbAr' (OAc)
2
2
2
Scheme 1.
Four complexes (I–IV) have been studied as catalysts in the de-
ucts. In this study we also investigated the selectivity of complexes
I–IV toward cross- and homo-couplings.
scribed reaction. Acyclic diaminocarbene complexes I–III are read-
ily available from palladium(II) isonitrile complexes by addition of
the corresponding N-nucleophiles to a CN triple bond.19 The com-
plexes II and III were obtained recently and tested in Sonogashira
cross-coupling of acetylenes with iodoarenes.20c Complex I was
synthesized analogously by reaction of isonitrile complex IV with
To study and compare the catalytic activity complexes I–IV, we
chose the reaction of phenyl acetylene (1a) with benzoyl chloride
6
b,9
(2a) using complexes I–IV instead of PdCl
2
(Table 1). The ratio
of the two reaction products, 1,3-diphenylpropynone (3a) (the
cross-coupling product) and 1,4-diphenylbutadiyne (4a) (the
2
1
1
p-nitrophenylhydrazine. Starting complex IV was also tested in
homo-coupling product), was determined by H NMR spectroscopy
2
3
the presence of secondary amines to investigate the possibility of
and GC–MS after work-up of the reaction mixtures.
2
2
the in situ generation of catalytic Pd-aminocarbene species.
First of all, experiments with each aminocarbene complex were
It is known that the Pd/Cu catalyzed cross-coupling is usually
accompanied by competitive homo-coupling, which leads to the
formation of butadiynes from terminal acetylenes. Thus, it is nec-
essary to use an excess of the terminal acetylene and to separate
the target cross-coupling products from homo-coupling by-prod-
carried out under argon at 20 °C according to the procedure previ-
9
a
ously developed by us. In the presence of only 0.04 mol % of cat-
alysts I–IV the reactions were rapid. However even under an inert
atmosphere and using THF or benzene as the solvents, diph-
enylbutadiyne 4a was formed as the major product (Table 1, en-
18
Table 1
Reaction of phenyl acetylene (1a) with benzoyl chloride (2a): catalysts, conditions, yields, and ratios of reaction products 3a and 4a
O
O
Catalyst "Pd"
Ph
H
Cl
2a
Ph
Ph
Ph
PPh (1 mol%), CuI (2 mol%),
Ph
3
Ph
Et N (1.5 eq)
3
1a
3a
4a
Entry
Catalyst (mol %)
Reaction conditions
Yield of 3a + 4a (%)
Ratio of 3a:4a
Solvent
THF
Atmosphere
Temperature (°C)
Time (h)
1
2
3
4
5
6
7
8
9
I (0.04)
I (1)
Argon
Argon
Argon
Argon
Argon
Argon
Air
Air
Air
Air
Air
20
20
20
20
20
20
20
20
20
20
20
60
60
60
60
60
7
5
1
24
5
24
12
24
24
24
24
1
93
87
52
91
75
91
95
89
86
93
98
98
94
98
90
96
44:56
20:80
7:93
50:50
9:91
C
6
H
6
II (0.04)
III (0.04)
IV (1)
IV (0.04) + NHEt
I (0.04)
II (0.04)
III (0.04)
III (1)
IV (0.04) + NHEt
I (0.04)
THF
C
C
6
H
H
6
6
6
2
(20 mg)
(20 mg)
(20 mg)
THF
6:94
C
C
C
C
C
C
C
C
C
C
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
6
6
6
6
6
6
6
6
6
59:41
28:72
13:87
15:85
44:56
67:33
77:23
89:11
80:20
72:28
1
1
1
1
1
1
1
0
1
2
3
4
5
6
2
Air
Air
Air
Air
II (0.04)
III (0.04)
IV (0.04)
1
1
1
1
IV (0.04) + NHEt
2
Air

D. S. Ryabukhin et al. / Tetrahedron Letters 54 (2013) 2369–2372
2371
Table 2
Reactions of aryl acetylenes 1a–e with benzoyl chlorides 2a–c
"
3
Pd" (0.04 mol%), PPh (1 mol%),
O
O
CuI (2 mol%), Et N (1.5 eq)
3
R
H
Cl
R
C
6
H
6
, air, 60 oC, 1 h
3
b-g
a,b
1a-e
2a-c
R'
R'
R
R
4
Entry
Substituents in 1–4
Initial compounds
Catalyst
Reaction products
0
R
R
Alkyne
Chloride
Ketone
Diyne
Yield of 3 + 4 (%)
Ratio of 3a:4a
1
2
3
4
5
6
H
H
Me
MeO
Br
Me
NO
H
H
H
1a
1a
1b
1c
1d
1e
2b
2c
2a
2a
2a
2a
II
II
I
I
II
II
3b
3c
3d
3e
3f
4a
4a
—
—
—
89
92
95
98
97
90
23:77
38:62
100:0
100:0
100:0
77:23
2
NO
2
H
3g
4b
tries 1–6). Increasing the amount of the catalyst from 0.04 to
species and the different stabilities of the so-formed reaction inter-
mediates under the various reaction conditions investigated (ar-
gon, oxygen, temperature, solvent). This complex problem of Pd-
catalyzed couplings has been discussed, and the formation of a
‘cocktail’-like mixture of the catalysts in such reactions was
1
mol % (Table 1, entry 2) did not change the situation significantly.
Next, experiments were performed under similar conditions at
0 °C in air (Table 1, entries 7–11) with the use the benzene as
2
the solvent. Previously it was shown that complexes II and III dem-
onstrated high catalytic activity in Sonogashira cross-couplings of
acetylenes with iodoarenes in air.2 Surprisingly, despite the fact
that the homo-coupling product prevailed, the amount of the het-
ero-coupling product 3a, except that from the reaction catalyzed
by III (Table 1, entries 9 and 10), was increased. We assume that
benzene favors formation of the cross-coupling product (compare
entries 1 and 7 or 3 and 8, Table 1). It was also noted that complete
conversion of the starting compounds required more time (up to
2
4
proposed.
0c
In conclusion, palladium acyclic diaminocarbene complexes can
be used as catalysts in Sonogashira cross-couplings to give 1,3-
diarylpropynones. Compared to other similar syntheses of 1,3-
6
b,9
diarylpropynones, where PdCl
(0.9 mol %)
2
(2 mol %)
2 3 2
or PdCl (PPh )
1
0b
were used, in this study the quantity of complexes
I–III was extremely low 0.04 mol %. Also the palladium acyclic dia-
minocarbene complexes reacted in air, yielding the target 1,3-
diarylpropynones in yields up to 95–98%. The scope, limitations,
and mechanistic aspects of this reaction are currently under
investigation.
2
4 h).
In the subsequent experiments, the temperature was increased
to 60 °C. Under these conditions, all the reactions were complete in
one hour. Moreover the increased temperature led to an inversion
in the ratio of the homo- and hetero-coupling products and higher
yields of the latter were observed (Table 1, entries 12–16). The
complexes I–III showed approximately equal catalytic activity.
The isonitrile compound IV could also be used as a catalyst (Table 1,
entry 15), or with addition of Et NH (Table 1, entries 6, 11 and 16).
2
It should also be mentioned that the increased temperature had a
beneficial effect on the reactions catalyzed by complexes II and III
Acknowledgements
The authors thank the Russian Foundation for Basic Research
(Grants RFBR: 11-03-00048-a, Federal Grant-in-Aid Program
‘‘Human Capital for Science and Education in Innovative Russia’’
for 2009-2013: agreement No. 14.B37.21.0794 from 03.09.2013,
12-03-00311-a), the Ministry of Education and Science of the
Russian Federation (Grant MKh-504.2011.3 of President of Russian
Federation), and Saint-Petersburg State University (Research Grant
12.38.14.2011) for financial support of this work.
(Table 1, entries 13 and 14 vs entries 8 and 9).
Having developed favorable conditions for the preparation of
1
1
,3-diarylpropynones (Pd-catalyst 0.04 mol %, air, 60 °C, benzene,
hour), we next explored the reaction of aryl acetylenes 1a–e
2
3
and aroyl chlorides 2a–c with the complexes I and II (Table 2).
References and notes
Acetylene substrates 1b–d with electron-donating (Me, MeO) or
the weakly electron-withdrawing Br groups reacted with benzoyl
chloride (2a) to form exclusively the ketones 3d–f without any of
the corresponding 1,4-diarylbutadiynes (Table 2, entries 3–5). On
the other hand, even acetylene 1e, bearing a strong electron-
1
.
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2
.
2
accepting NO substituent, gave propynone 3g as the major reac-
tion product and diyne 4b as a minor product (Table 2, entry 6).
Reactions of substituted aroyl chlorides 2b,c led to ketones 3b,c
and diyne 4a with a predominant formation of the latter (Table 2,
entries 1 and 2).
3. (a) Wang, J.-C.; Ng, S.-S.; Krische, M. J. J. Am. Chem. Soc. 2003, 125, 3682–3683;
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The formation of diynes, as products of homo-coupling, is one
1
8
outcome of the catalytic cycle of the Sonogashira reaction. In
our study, the formation of large amounts of diynes 4a,b revealed
deep mechanistic problems related to the abilities of copper acet-
ylides and aroyl chlorides to coordinate with catalytic palladium
5.
(a) Eisler, S.; Tykwinski, R. R. In Acetylene Chemistry: Chemistry, Biology, and
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.
.
4
9
1
1
1
0. (a) Tohda, Y.; Sonogashira, K.; Hagihara, N. Synthesis 1977, 777–778; (b) Cox, R.
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21. Characterization of complex I: 1H NMR (CDCl
3
, d): 9.90 (s, 1H, C@NHN), 8.10 (d,
2Harom., J = 8.7 Hz), 7.75 (s, 1H, ArNH), 7.05 (d, 1H, NH, J = 10.2 Hz), 6.90 (d,
2Harom., J = 8.7 Hz), 4.44 (m, 1H, CH), 4.01 (m, 1H, CH), 2.20–1.24 (m, 20H,
ꢀ
1
10CH
2
). IR (KBr,
m
, cm ): 2934–2856 (C–H); 2230 (C„N); 1330 (NO
2
). HRMS:
+
+
ꢀ
5
2, 1498–1502.
2. (a) Sladkov, A. M.; Golding, I. R. Zh. Org. Khim. Russ. J. Org. Chem. 1967, 3, 1338;
b) Normant, J. F.; Bourgain, M. Tetrahedron Lett. 1970, 11, 2659–2662.
ESI -MS, found: 514.1092 [M-Cl] ; calcd for C20
H
29ClN
5
O
2
Pd: 514.1049. ESI -
ꢀ
1
1
MS, found: 548.08 [MꢀH] ; calcd for C20
H28Cl N O Pd: 548.07.
2 5 2
(
22. Larkin, G. A.; Scott, R. P.; Wallbridge, M. G. H. J. Organomet. Chem. 1972, 37,
C21–C23.
3. (a) Trost, B. M.; Schmidt, T. J. Am. Chem. Soc. 1988, 110, 2301–2303; (b)
Backvall, J.-E.; Nilsson, Y. I. M.; Andersson, P. G.; Gatti, R. G. P.; Wu, J.
Tetrahedron Lett. 1994, 35, 5713–5716; (c) Yim, S. J.; Kwon, C. H.; An, D. K.
Tetrahedron Lett. 2007, 48, 5393–5395.
23. General procedure for the coupling of aryl acetylenes with aroyl chlorides. Catalyst
(0.04 mol %, as 0.35–0.5 ml aliquot of THF or benzene solutions), PPh
3
(8 mg,
1 mol %), CuI (11 mg, 2 mol %), and Et N (1.5 equiv) were added to a solution of
3
1
4. (a) Logue, M. W.; Teng, K. J. Org. Chem. 1982, 47, 2549–2553; (b) Shchelkunov,
S. A.; Sivolobova, S. A.; Muldahmetov, Z. M. Russ. J. Org. Chem. 1997, 33, 1182–
the aryl acetylene (3 mmol) and aroyl chloride (3 mmol) in benzene (10 ml)
under stirring at 60 °C. The mixture was stirred at 60 °C for 1 h, then cooled to
1
186.
room temperature, and diluted with CHCl
washed with H O (20 ml), aqueous NaHCO
(20 ml), and dried over Na SO . After evaporation of the solvent under vacuum,
3
(100 ml). The organic layer was
1
1
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2
3
solution (2 ꢁ 10 ml), and H
2
O
2
4
1
4
143–4146.
the residue was analyzed by H NMR and GC–MS. Individual reaction products
were separated by column chromatography on silica gel (eluent hexanes/
EtOAc). 1,3-Diarylpropynones 3a–g were previously obtained and
characterized by ourselves.6
1
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Ahmed, M. S. M. A.; Mori, A. Org. Lett. 2003, 5, 3057–3060; (c) Park, A.; Park, K.;
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b,9
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