Ruthenium/halide catalytic system for C-C bond forming reaction between alkynes and unsaturated carbonyl compounds

Article abstract of DOI:10.1002/adsc.200700371

A ruthenium complex [triruthenium dodecacarbonyl, Ru₃(CO) ₁₂] in the presence of bis(triphenylphosphine)iminium chloride ([PPN]Cl) catalyzes the conjugate addition of terminal alkynes to alkyl acrylates to give high yields of γ,δ-alkynyl esters. On the other hand, the linear codimerization reaction of terminal alkynes with alkyl acrylates proceeds in the presence of a catalytic amount of Ru ₃(CO)₁₂ and lithium iodide to give the corresponding conjugate dienes. These two different types of catalytic carbon-carbon bond forming reactions are controlled only by the nature of halide ions, either a chloride or an iodide, with other conditions being kept almost the same.

Full text of DOI:10.1002/adsc.200700371

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DOI: 10.1002/adsc.200700371
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Ruthenium/Halide Catalytic System for C C Bond Forming
Reaction between Alkynes and Unsaturated Carbonyl Compounds
Takahiro Nishimura,a,* Yosuke Washitake,b and Sakae Uemurab,c,*
a
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
Fax : (+81)-75-753-3988; E-mail: tnishi@kuchem.kyoto-u.ac.jp
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University Katsura, Kyoto
b
606-8510, Japan
c
Present address: Department of Information and Computer Engineering, Faculty of Engineering, Okayama University of
Science, Okayama 700-0005, Japan
E-mail: uemura@ice.ous.ac.jp
Received: July 27, 2007; Revised: October 7, 2007; Published online: November 27, 2007
Dedicated to Professor Jan E. Bäckvall on the occasion of his 60th birthday.
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: A ruthenium complex [triruthenium do- ing conjugate dienes. These two different types of
decacarbonyl, Ru3(CO)12] in the presence of bis(tri- catalytic carbon-carbon bond forming reactions are
phenylphosphine)iminium chloride ([PPN]Cl) cata- controlled only by the nature of halide ions, either a
lyzes the conjugate addition of terminal alkynes to chloride or an iodide, with other conditions being
alkyl acrylates to give high yields of g,d-alkynyl kept almost the same.
esters. On the other hand, the linear codimerization
reaction of terminal alkynes with alkyl acrylates pro-
ceeds in the presence of a catalytic amount of Keywords: alkynes; codimerization; conjugate addi-
Ru3(CO)12 and lithium iodide to give the correspond- tion; conjugate dienes; ruthenium
Introduction
leading studies on the codimerization reaction of al-
kynes with alkenes have been carried out by some re-
The conjugate addition of carbanions to a,b-unsaturat- search groups[9–11] They reported promising results, for
ed carbonyl compounds is one of the most attractive example, for ruthenium-catalyzed codimerization of
[1]
À
methods for constructing a new C C bond. Among a alkynes with acrylamides or alkyl acrylates (Mitsudo/
variety of carbon nucleophiles, terminal alkynes are of Kondo)[9] and for the coupling reaction of unactivated
interest to create the internal alkynes bearing a car- alkenes with unactivated alkynes (Murakami/Ito, Yi,
bonyl functionality. Classical methods for introducing and Tsukuda),[10] and for the intramolecular cycliza-
an alkynyl moiety to organic acceptors by the conju- tion of enynes to give 1,3-dienes (Trost[11a] and
gate addition reaction have used stoichiometric metal Mori[11b]). However, to the best of our knowledge, no
alkynylides.[2] The direct conjugate addition of terminal efficient catalytic system for the codimerization of ter-
alkynes to acceptor alkenes or alkynes would be valua- minal alkynes with acrylates has been reported so far.
ble because of the simple operation and its ability to
We have recently found that Ru3(CO)12 is an effec-
minimize metallic wastes.[3] As for the catalytic direct tive catalyst for the conjugate addition of phenylace-
conjugate addition reaction of terminal alkynes to ac- tylene to ethyl acrylate in the presence of a chloride
ceptor alkenes, a few examples using palladium,[4] ion to give the corresponding g,d-alkynyl esters
copper,[5] rhodium,[6] and ruthenium[7] catalysis have (Scheme 1 (a)).[12] During the course of further work,
been reported. However, these reactions are mostly we also disclosed that the use of an iodide ion in
limited to reactive vinyl ketones and examples of the place of the chloride resulted in the formation of the
reaction with a,b-unsaturated esters are rare.
conjugate dienes from terminal alkynes and ethyl ac-
On the other hand, the catalytic codimerization re- rylate in the presence of the same ruthenium complex
action of alkynes with alkenes giving conjugate dienes (Scheme 1 (b)). Here, we wish to report the rutheni-
is also of interest because of atom economy.[8] The um/halide catalytic system for two different types of
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Scheme 1. Ruthenium-catalyzed reactions of terminal alkynes with alkyl acrylates.
Scheme 2. Conjugate addition of terminal alkynes to ethyl acrylate.
carbon-carbon bond forming reaction controlled by the corresponding ynoates 3n and 3o in good yields
the nature of the halide ion: one is the conjugate ad- (entries 14 and 15). The reaction of an alkenylalkyne
dition of terminal alkynes to ethyl acrylate and the 1p smoothly proceeded to give 3p in 69% yield
other is the linear codimerization between terminal (entry 16). (Trimethylsilyl)acetylene (1g) and 1-octyne
alkynes and ethyl acrylate.
(1r) gave 3g and 3r in 45% and 41% yield, respec-
tively (entries 17 and 18). The use of diyne 1s afford-
ed the corresponding double addition product 3s in
65% yield (entry 19). Reactions of phenylacetylene
(1a) with methyl acrylate (4), butyl acrylate (5), and
Results and Discussion
The conjugate addition of terminal alkynes to alkyl allyl acrylate (6) gave the corresponding addition
acrylates smoothly proceeded to give d,g-alkynyl products 7–9 in 70–86% yield (entries 20–22). The ad-
esters under ruthenium/chloride catalysis. Thus, treat- dition of phenylacetylene to a- or b-substituted acryl-
ment of phenylacetylene (1a) with ethyl acrylate (2) ates such as methyl crotonate and ethyl methacrylate
in the presence of Ru3(CO)12 (2 mol%) and bis(tri- and to a cyclic ester (5,6-dihydro-2H-pyran-2-one),
phenylphosphine)iminium chloride ([PPN]Cl, 10 unfortunately, resulted in the formation of a complex
mol%) in N-methylpyrrolidinone (NMP) at 608C for mixture of unidentified compounds, whereas an alky-
24 h gave ethyl 5-phenylpent-4-ynoate (3a) in 95% noate 10 could also be used as an acceptor in place of
yield (GLC) (Scheme 2).[13] Among several chloride alkyl acrylates to give the addition product enyne 11
sources ([PPN]Cl, Bu4NCl, NaCl, KCl and LiCl) ex- in 63% yield (Scheme 4).
amined, [PPN]Cl, a highly dissociated salt, was re-
As expected from the so-far described results, this
vealed to be most effective.[12] In sharp contrast, the catalytic system could also be applied to the addition
reaction without [PPN]Cl gave only 11% of 3a. Other of terminal alkynes to vinyl ketones under very mild
solvents, such as N,N-dimethylformamide (DMF) and conditions (Scheme 5). Thus, the reaction of 1a with
tetrahydrofuran (THF) could also be employed with- methyl vinyl ketone (12), ethyl vinyl ketone (13), and
out a significant decrease of the product yields.
phenyl vinyl ketone (14) gave the corresponding con-
Results of the reactions of several terminal alkynes jugate addition products 15, 16, and 17 in good to
(Scheme 3) bearing aromatic or vinylic substituents high yields. On the other hand, the addition to b-sub-
(1b–1s) with alkyl acrylates (2, 4–6) are listed in stituted enones such as 3-penten-2-one and 2-cyclo-
Table 1. Aromatic alkynes having either an electron- hexen-1-one was sluggish to give only low yields of
donating or an electron-withdrawing group on the the desired products.
benzene ring gave the corresponding esters in moder-
The g,d-alkynyl carbonyl compounds obtained here
ate to high yields (entries 2–13). It is worth noting are known to be useful intermediates for biologically
that bromo (1e–1g), chloro (1h), cyano (1i and 1j) active compounds.[14] An example of the transforma-
and alkoxycarbonyl (1k–1m) substituents were toler- tion of the g,d-alkynyl ester 9 is shown in Scheme 6.
ated under the present reaction conditions to give the Heating of the solution of 9 in DMF in the presence
corresponding esters in moderate to good yields (en- of Pd
C
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C C Bond Forming Reaction between Alkynes and Unsaturated Carbonyl Compounds
Scheme 3. Scope of the reaction.
Plausible Reaction Pathway
Table 1. Conjugate addition of terminal alkynes to acry-
lates.[a]
Deuterium labeling experiments gave us some infor-
mation about the reaction pathway. Thus, treatment
of phenylacetylene-d (1a-d) with ethyl acrylate (2) in
NMP at 608C for 6 h gave the a-deuteriated alkynyl
ester 3a-d in 40% yield, where 68% of deuterium
was incorporated (Scheme 7). On the other hand, the
reaction of 1a with ethyl acrylate in the presence of
D2O under the same reaction conditions gave 3a-d in
21% yield with >99% deuterium incorporation.[16]
The high deuterium incorporation in the latter reac-
tion clearly shows the presence of a protonolysis step
of some intermediate enolates in the present catalytic
reaction.
Entry Alkyne Acrylate Time
[h]
Product Isolated yield
[%]
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
1r
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
4
5
6
24
24
24
24
42
48
78
42
72
60
48
72
24
24
24
60
60
48
48
24
24
24
3a
3b
3c
3d
3e
3f
3g
3h
3i
89
86
88
65
77
76
77
76
48
60
71
65
80
77
77
69
45
41
65
86
75
70
9
10
11
12
13
14
15
16
17
18
19
20
21
22
3j
3k
3l
The reaction of Ru3(CO)12 with [PPN]Cl has been
known to give several multinuclear ruthenium com-
3m
3n
3o
3p
3q
3r
3s
7
plexes, such as [PPN]
[Ru3(m-Cl)(CO)10], [PPN]
[PPN]2[Ru4(m-Cl)2(CO)11] in equilibrium in the pres-
A
ACHTREUNG
A
G
A
ACHTREUNG
A
N
ence of CO.[17] By taking account of these facts, we
propose the catalytic cycle of the present ruthenium-
catalyzed conjugate addition of phenylacetylene to
ethyl acrylate as shown in Scheme 8. A tetranuclear
1s
1a
1a
1a
8
9
species [PPN]
N
N
Ru3(CO)12 and [PPN]Cl[17] reacts with phenylacety-
lene (1a) to give the complex B.[18] Subsequent attack
of the complex B to ethyl acrylate (2) gives the inter-
mediate enolate C, followed by the protonation with
[a]
Reaction conditions: alkyne
1
(1.0 mmol), acrylate
(5.0 mmol), Ru3(CO)12 (2 mol% to 1), [PPN]Cl (10
mol% to 1), NMP (0.5 mL), at 608C.
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Scheme 4. Addition to ynoate 10.
Scheme 5. Addition of 1a to vinyl ketones.
Scheme 6. Cyclization of g,d-alkynyl esters 9.
Scheme 7. Deuterium labeling experiments.
HCl and ligand exchange with [PPN]Cl to give the chloride ion gave the conjugate dienes instead of the
addition product 3a, regenerating the species A.[19] expected conjugate addition products, alkynyl esters
Actually, we separately confirmed that the ruthenium (Scheme 9). Thus, treatment of phenylacetylene (1a)
complex A generated in situ can catalyze the present with ethyl acrylate (2) in the presence of 2 mol% of
conjugate addition reaction.[20]
Ru3(CO)12 and 10 mol% of lithium iodide in DMF at
608C for 12 h gave a linear codimerized compound,
ethyl 5-phenylpenta-2,4-dienoate (19) in 64% yield
(2E,4Z/2E,4E=74/26) (Table 2, entry 1). Although a
significant difference of the product yields was not
Linear Codimerization
As described above, we demonstrated that the ruthe- observed by changing the kind of iodides (entries 1–
nium/chloride catalytic system is efficient for the 4), the use of lithium iodide gave a slightly higher
direct conjugate addition of terminal alkynes to alkyl yield. In the present linear codimerization, the reac-
acrylates. During the continuation of this work, we tion was much dependent on the type of solvent,
disclosed that the use of an iodide ion in place of a DMF and NMP being revealed to be effective
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C C Bond Forming Reaction between Alkynes and Unsaturated Carbonyl Compounds
Scheme 8. Plausible reaction pathway.
Scheme 9. Codimerization of alkynes with ethyl acrylate.
Table 2. Codimerization of terminal alkynes with acrylates.[a] group gave the dienes 22 and 23 in moderate yields.
This catalytic system could also be applied to the re-
Entry Solvent
Additive Isolated yield [%]
action of an internal alkyne, diphenylacetylene, to
give the corresponding diene 24 in 51% yield.
The codimerization of 1a with other unsaturated
esters such as methyl acrylate, butyl acrylate, and
phenyl acrylate proceeded similarly to give the corre-
sponding dienes (25–27) (Scheme 11). In contrast, the
use of a- or b-substituted acrylates such as methyl
crotonate and ethyl methacrylate gave a complex mix-
ture of unidentified compounds.
1
2
3
4
5
6
7
8
DMF
DMF
DMF
DMF
NMP
MeOH
LiI
NaI
KI
64
62
59
57
61
17
7
A
LiI
LiI
1,2-dimethoxyethane LiI
tetrahydrofuran LiI
6
[a]
Reaction conditions: alkyne 1a (1.0 mmol), ethyl acrylate
2 (5.0 mmol), Ru3(CO)12 (2 mol% to 1a), additive (10
mol% to 1a), solvent (0.5 mL), at 608C for 12 h.
Plausible Reaction Pathway
Two reaction pathways for the present codimerization
(Table 2).[21] As shown in Scheme 10, under the same may be proposed on the basis of the known rutheni-
reaction conditions the use of aromatic alkynes bear- um-catalyzed addition reaction of alkynes to alkenes
ing an electron-donating substituent (Me or MeO) on (Scheme 12).[8a,9a,22] The first one involves the forma-
the benzene ring gave the corresponding dienes 20 tion of ruthenacyclopentane intermediate from an
and 21 in 63% and 70% yields, respectively. The use alkyne, an acrylate and a ruthenium complex, fol-
of aromatic alkynes with bromo and ethoxycarbonyl lowed by b-elimination and successive reductive elim-
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Scheme 10. Scope of the codimerization of alkynes with ethyl acrylate.
Scheme 11. Codimerization of phenylacetylene with acrylates.
Scheme 12. Two plausible reaction pathways for the formation of (2E,4E) and (2Z,4E) isomers.
ination to give the conjugate diene, regenerating the
active ruthenium species (path A). The second one
À
consists of the reaction via the activation of the C H
bond of the acrylate, followed by the insertion of the
alkyne to a produced ruthenium-hydride or rutheni-
um-carbon bond, and then by reductive elimination
(path B). One more plausible pathway is to start from
a ruthenium hydride as an active species, which adds
first to 1a, as shown in Scheme 13.[23] Among these
three possibilities, the last one (Scheme 13) may ex-
plain the formation of both geometrical isomers in
the present catalytic reaction. Thus, the insertion of
an alkyne to a ruthenium-hydride bond gives a vinyl
ruthenium species, followed by carboruthenation to
ethyl acrylate, and then b-hydrogen elimination gives
the isomeric products. On the other hand, the reac-
Scheme 13. A plausible reaction pathway starting from a
tion of deuteriated alkyne (28-d) with ethyl acrylate ruthenium hydride species.
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C C Bond Forming Reaction between Alkynes and Unsaturated Carbonyl Compounds
Scheme 14. Deuterium labeling experiments.
gave dienes 29-d, which consisted of (2E,4E) and cal thin-layer chromatography (TLC) was performed with
silica gel 60 Merck F-254 plates. Column chromatography
was performed with Merck silica gel 60. FT-IR spectra (thin
film for liquids, KBr disk for solids) were recorded on a
Nicolet Impact 400 spectrometer.
(2Z,4E) isomers (Scheme 14). Both isomers were deu-
teriated at the g-position in ca. 70%. These results
suggest that the pathway via a ruthenium vinylidene
complex[10] is at least excluded, because this pathway
should involve the deuterium migration of a terminal
alkyne to the d-position of the diene.
Materials
It has been reported that the reaction of Ru3(CO)12
with [PPN]I in THF at elevated temperature gives
Ru3(CO)12 and bis(triphenylphosphine)iminium chloride
([PPN]Cl) were commercially available and used without
further purification. Bis(triphenylphosphine)iminium iodide
([PPN]I) was prepared from [PPN]Cl and lithium iodide by
the literature method.[24] Terminal alkynes 1a–c, and 1p–r
were purchased and used as received. Terminal acetylenes
1d–o and 1s[25] were synthesized by the literature methods.
a, b-Unsaturated carbonyl compounds were commercially
available except for allyl acrylate, which was prepared ac-
cording to the known procedure from acryloyl chloride and
allyl alcohol.[26] Enyne 11[3a] and g-ketoacetylenes 15[7], 16[2h]
and 17[27] are known compounds
[Ru3(m3-I)(CO)9], which gives some ruthenium hy-
G
dride complexes by the interaction with water.[17c] At
present, however, the active species in this codimeri-
zation is not yet clear, and the possibility of the con-
tribution of a monomeric ruthenium species cannot
also be excluded.
Conclusions
The effective conjugate addition reaction of terminal
alkynes to a,b-unsaturated carbonyl compounds pro-
ceeded under the catalysis of a commercially available
ruthenium complex [Ru3(CO)12] in the presence of
[PPN]Cl. This catalytic system can be carried out
under neutral and mild conditions to give g,d-alkynyl
esters or ketones in good to high yields. On the other
hand, the combination of Ru3(CO)12 and LiI catalyzed
the linear codimerization of alkynes with acrylates to
give conjugate dienes in moderate to good yields.
Typical Procedure for the Conjugate Addition of
Phenylacetylene (1a) to Ethyl Acrylate (2)
A mixture of Ru3(CO)12 (12.8 mg, 0.020 mmol), [PPN]Cl
(57.4 mg, 0.10 mmol) and NMP (0.5 mL) in a 20 mL Schlenk
tube was stirred at 608C under N2. After 15 min,
2
(500.6 mg, 5.0 mmol) and 1a (102.1 mg, 1.0 mmol) were
added and the mixture was stirred at 608C for 24 h. The
mixture was cooled to room temperature and filtered
through a pad of Florisil. The filtrate was concentrated
under vacuum to give an oil, which was subjected to column
chromatography on SiO2 with EtOAc-hexane (2/98) as
eluent furnishing ethyl 5-phenyl-4-pentynoate (3a); colorless
oil; IR (neat): n=1735 (C=O) cmÀ1 1H NMR (300 MHz,
;
Experimental Section
CDCl3): d=1.27 (t, J=7.2 Hz, 3H), 2.58–2.77 (m, 4H), 4.18
(q, J=7.2 Hz, 2H), 7.20–7.50 (m, 5H); 13C NMR (75.5 MHz,
CDCl3): d=14.2, 15.4, 33.7, 60.6, 81.1, 88.0, 123.5, 127.7,
128.2, 131.6, 171.9; anal. calcd. for C13H14O2: C 77.20, H
6.98; found: C 77.45, H 6.94.
When vinyl ketone was used as an acceptor, it was added
at 308C after heating the mixture of Ru3(CO)12 and [PPN]Cl
in DMF at 608C for 15 min.
General Methods
All anaerobic and moisture-sensitive manipulations were
carried out with standard Schlenk techniques under predried
N2. NMR spectra were recorded on JEOL EX-400
(1H NMR, 400 MHz; 13C NMR, 100 MHz), JNM AL-300
(1H NMR, 300 MHz; 13C NMR, 75.5 MHz), and JEOL EX-
270 (1H NMR, 270 MHz, 13C NMR, 67.7 MHz) instruments
for solutions in CDCl3 with Me4Si as an internal standard.
GLC analyses were performed on a Shimadzu GC-14A in-
strument (25 m”0.33 mm, 50 mm film thickness, Shimadzu
fused silica capillary column HiCapCBP-10-S-25–050) with a
flame ionization detector and helium as carrier gas. Analyti-
Typical Procedure for the Codimerization of
Phenylacetylene (1a) with Ethyl Acrylate (2)
A
mixture of Ru3(CO)12 (12.8 mg, 0.020 mmol), LiI
(13.4 mg, 0.10 mmol) and DMF (0.5 mL) in a 20 mL Schlenk
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tube was stirred at 608C under N2. After 15 min,
2
2001, 101, 2067; e) B. M. Trost, Acc. Chem. Res. 2002,
35, 695.
[9] a) T. Mitsudo, S.-W. Zhang, M. Nagao, Y. Watanabe, J.
Chem. Soc., Chem. Commun. 1991, 598; b) T. Mitsudo,
T. Kondo, Synlett 2001, 309.
[10] a) M. Murakami, M. Ubukata, Y. Ito, Tetrahedron Lett.
1998, 39, 7361; b) C. S. Yi, D. W. Lee, Y. Chen, Organo-
metallics 1999, 18, 2044; c) N. Tsukada, H. Setoguchi,
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Soc. 1994, 116, 4268; b) M. Nishida, N. Adachi, K. Ono-
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9158.
(500.6 mg, 5.0 mmol) and 1a (102.1 mg, 1.0 mmol) were
added and the mixture was stirred at 608C for 24 h. The
mixture was filtered through a pad of Florisil. The filtrate
was concentrated under vacuum to give an oil, which was
subjected to column chromatography on SiO2 with EtOAc-
hexane (2/98) as eluent to give the product mixture com-
posed of (2E,4E)-19 and (2Z,4E)-19 (yield: 64.7 mg,
0.32 mmol, 64%). The ratio of geometrical isomers was de-
1
termined by H NMR.
Ethyl 5-phenylpenta-2,4-dienoate [19, (2E,4E)/(2Z,4E)=
G
74/26]:[28] 1H NMR (270 MHz, CDCl3): d= 1.29 (t), 4.22 (q),
5.72 [d, J=11.2 Hz, 1H, (2Z,4E)-isomer], 5.99 [d, J=
15.3 Hz, 1H, (2E,4E)-isomer], 6.72–6.82 [m, 2H, (2Z,4E)-
isomer], 6.85–6.92 [m, 2H, (2E,4E)-isomer], 7.25–7.55 (m),
8.16 [dd, J=15.6, 11.4 Hz, 1H, (2Z,4E)-isomer].
[12] T. Nishimura, Y. Washitake, Y. Nishiguchi, Y. Maeda,
S. Uemura, Chem. Commun. 2004, 1312.
[13] For a review of the halide promotion in reactions of
carbonylruthenium complex, see: G. Lavigne, Eur. J.
Inorg. Chem. 1999, 917.
[14] S. B. Rosenblum, T. Huynh, A. Afonso, H. R. Da-
vis, Jr., Tetrahedron 2000, 56, 5735.
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possible. However, this possibility was excluded by an
experiment where 3a was treated at 608C for 6 h in the
presence of Ru3(CO)12 catalyst and D2O, which showed
no deuterium incorporation into 3a.
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