Ruthenium-catalyzed vinylic substitution reactions with nucleophiles via butatrienylidene intermediates

Article abstract of DOI:10.1021/ja710013y

Novel ruthenium-catalyzed vinylic substitution reactions of vinylic trifluoromethanesulfonates with nucleophiles such as cyclic 1,3-diketones and alcohols have been found to give the corresponding vinylic-substituted products in good to high yields. This catalytic reaction is considered to be a new type of vinylic substitution reaction. Reactions of α-ketoacetylenes with alcohols have also been found to afford the corresponding vinylic ethers in good yields. These catalytic reactions can be explained to proceed by proposing ruthenium-butatrienylidene complexes as key intermediates. We believe that this finding will open up a further aspect of the chemistry of metal-cumulenylidene complexes. Copyright

Full text of DOI:10.1021/ja710013y

Published on Web 02/15/2008
Ruthenium-Catalyzed Vinylic Substitution Reactions with Nucleophiles via
Butatrienylidene Intermediates
Yoshihiro Yamauchi,† Masahiro Yuki,† Yoshiaki Tanabe,† Yoshihiro Miyake,† Youichi Inada,‡
Sakae Uemura,‡,§ and Yoshiaki Nishibayashi*,†
Institute of Engineering InnoVation, The UniVersity of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan, and
Department of Energy and Hydrocarbon Chemistry, Kyoto UniVersity, Nishikyo-ku, Kyoto 615-8510, Japan
Received November 5, 2007; E-mail: ynishiba@sogo.t.u-tokyo.ac.jp
Table 1. Ruthenium-Catalyzed Reactions of 2 with 3 in the
Presence of 1aa
Transition metal complexes of cumulated alkylidenes such as
metal-carbene, -vinylidene, and -allenylidene complexes have
been widely used as versatile organometallic species having a
double bond between a metal and a carbon.1 The metal-carbon
double bond is reactive enough to be employed for many organic
transformations catalytically as well as stoichiometrically.1 In fact,
metathesis of alkenes via metal-carbenes may be one of the most
powerful tools in recent organic synthesis,2 while metal-vi-
nylidenes3 and -allenylidenes4 are also revealed to be the important
organometallic species in various organic transformations of
terminal alkynes. In sharp contrast to the rich chemistry of these
carbene, vinylidene, and allenylidene complexes,1 the chemistry
of higher cumulenylidene complexes is so far limited only to the
isolation and stoichiometric reactions of metal-cumulenylidene
complexes.5,6 We have now found the first example of the
ruthenium-catalyzed novel reactions via metal-butatrienylidene
complexes5 as key intermediates.
Treatment of 2-(1-phenyl-1-buten-3-ynyl) trifluoromethane-
sulfonate (2a), as a mixture of two stereoisomers (isomer ratio 58/
42), with 1,3-cyclopentanedione (3a) (3 equiv to 2a) in the presence
of 3 mol % of [Cp*RuCl(µ2-SMe)]2 (Cp* ) η5-C5Me5; 1a)4 in
ClCH2CH2Cl at room temperature for 30 min gave 3-((E)-1-phenyl-
1-buten-3-yn-2-yloxy)-2-cyclopentenone (4aa) in 91% isolated yield
with a complete selectivity (Scheme 1 and Table 1).7 Interestingly,
3a worked as O-nucleophiles, in sharp contrast to the propargylic
substitution reactions.4c No stereoisomers were detected by 1H
NMR. The molecular structure of 4aa was determined by X-ray
analysis.7,8 The use of the complex bearing a sterically more
demanding SiPr moiety [Cp*RuCl(µ2-SiPr)]2 (1b) did not affect the
yield of 4aa, while that of the corresponding cationic diruthenium
complex [Cp*RuCl(µ2-SMe)2RuCp*(OH2)]OTf (OTf ) OSO2CF3;
1a′) in place of 1a gave 4aa in 69% yield.
a All reactions of 2 (0.30 mmol) with 3 (0.90 mmol) were carried out in
the presence of 1a (0.009 mmol) in ClCH2CH2Cl (8 mL) at room
temperature for 30 min. b The isomer ratio is shown in Supporting
Information. c Isolated yield. d Determined by 1H NMR. e The reaction was
carried out in the presence of 1a (0.015 mmol) for 1 h.
gave the corresponding vinylic ethers (4da and 4ea) in 84 and 89%
isolated yields, respectively (Table 1, runs 10 and 11). Unfortu-
nately, no reaction occurred at all when acyclic 1,3-diketones such
as 2,4-pentanedione and cyclic â-ketoesters such as â-lactones were
used in place of 3. Interestingly, the reaction of 2a with 3d
proceeded smoothly to give the corresponding vinylic ether (4ad)
in 93% isolated yield with an excellent stereoselectivity (E/Z )
98/2) (Table 1, run 12). In addition to cyclic 1,3-diketones, alcohols
can also be employed as nucleophiles for this substitution reaction.
Thus, when the sulfonates 2 were treated with ethanol in the
presence of 5 mol % of 1a at room temperature for 4 h, the
corresponding vinylic ethers (5) were obtained in good yields as a
mixture of stereoisomers (Scheme 2).
Scheme 1
Catalytic reactions of other 2-(1-aryl-1-buten-3-ynyl) trifluo-
romethanesulfonates (2) with cyclic 1,3-diketones (3) were inves-
tigated by using 1a as a catalyst. When 3b was used in place of
3a, lower yields of vinylic ethers (4) were obtained even from the
reactions using a larger amount (5 mol %) of 1a and for a longer
reaction time (1 h) (Table 1, runs 4-6). In contrast, reactions with
3c proceeded smoothly to give 4 in high yields with a complete
selectivity (Table 1, runs 7-9). Reactions of 2d and 2e with 3a
Scheme 2
In order to obtain some information on the reaction pathway,
the following stoichiometric and catalytic reactions were investi-
gated. Treatment of 1a with 1 equiv of 2d in the presence of 2
† The University of Tokyo.
‡ Kyoto University.
i
§ Present address: Okayama University of Science, Okayama, 700-0005, Japan.
equiv of Pr2NEt in ClCH2CH2Cl at room temperature for 20 min
9
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J. AM. CHEM. SOC. 2008, 130, 2908-2909
10.1021/ja710013y CCC: $40.75 © 2008 American Chemical Society

C O M M U N I C A T I O N S
Table 2. Ruthenium-Catalyzed Reactions of 9 with Alcohols in the
Presence of 1a′a
gave the corresponding butenynyl complex (6) in 63% isolated yield
(Scheme 3). The structure of 6 was unambiguously characterized
by X-ray crystallography (Figure S1).7 The complex 6 is considered
to be obtained by nucleophilic attack of a chloride ion to the
γ-carbon of the butatrienylidene complex, which may be generated
in situ from 1a and 2d. A similar mononuclear ruthenium butenynyl
complex has already been obtained and characterized by Selegue
and his co-worker, where the complex was obtained from the
reaction of the corresponding butatrienylidene complex with
trifluoroacetic anhydride.9
Treatment of 6 with 1 equiv of TfOH in the presence of 5 equiv
of NH4Cl gave 710 in 87% yield (Scheme 3). The indene 7 seems
to be produced in situ via Brønsted acid catalyzed intramolecular
Friedel-Crafts-type cyclization of 8 released in situ from 6. These
results indicate that the catalytic reaction might proceed via a
butatrienylidene complex as a key intermediate.11 Furthermore, the
reaction of 2d with 3a in the presence of 3 mol % of 6 at room
temperature for 30 min afforded 4da in 84% yield.
yield of 5
isomer
ratioc
run
Ar of 9
ROH
(%)b
1
2
3
4
5
6
7
8
9
Ph (9a)
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
nPrOH
iPrOH
nBuOH
60 (5aa)
62 (5ba)
59 (5ca)
55 (5da)
49 (5ea)
63 (5fa)
63 (5ab)
53 (5ac)
68 (5ad)
74/26
77/23
79/21
77/23
80/20
71/29
78/22
83/17
77/23
p-MeC6H4 (9b)
p-ClC6H4 (9c)
p-MeOC6H4 (9d)
p-FC6H4 (9e)
2-naphthyl (9f)
Ph (9a)
Ph (9a)
Ph (9a)
a All reactions of 9 (0.30 mmol) with alcohol (15 mL) were carried out
in the presence of 1a′ (0.03 mmol) at 60 °C for 2 h. b Isolated yield.
1
c Determined by H NMR.
Scheme 5.
Scheme 3
as that from 2. In the attempted reactions of 9 with 3, we consider
that no dehydration from E occurs due to a low basicity of 3.
In summary, we have disclosed novel ruthenium-catalyzed
vinylic substitution reactions of vinylic trifluoromethanesulfonates
with nucleophiles which are considered to be a new type of vinylic
substitution reaction,13-15 proceeding via ruthenium-butatrie-
nylidene complexes as key intermediates.16 We believe that this
finding will open up a further aspect of the chemistry of metal-
cumulenylidene complexes.
A proposed reaction pathway is shown in Scheme 4. The initial
step is the formation of a vinylidene complex (A) by the reaction
of 1a with 2, followed by its conversion into a butatrienylidene
complex (B).6 Subsequent attack of a nucleophile on the Cγ atom
of B results in the formation of another vinylidene complex (C).
In the reactions with 3, the steric repulsion between substituents in
both B and 3 might lead to predominant formation of (E)-C. Finally,
the complex C liberates a vinylic-substituted product by reaction
with another 2, regenerating A. We believe that the synergistic effect
in the diruthenium complexes is quite important for the promotion
of this catalytic reaction.4
Supporting Information Available: Experimental procedures,
spectroscopic data, and X-ray data. This material is available free of
charge via the Internet at http://pubs.acs.org.
References
(1) For a recent review, see: Bruneau, C.; Dixneuf, P. H. Angew. Chem.,
Int. Ed. 2006, 45, 2176.
Scheme 4
(2) For a recent review, see: Grubbs, R. H. Angew. Chem., Int. Ed. 2006,
45, 3760.
(3) For a recent review, see: Varela, J. A.; Saa´, C. Chem.sEur. J. 2006, 12,
6450.
(4) For recent examples, see: (a) Yamauchi, Y.; Onodera, G.; Sakata, K.;
Yuki, M.; Miyake, Y.; Uemura, S.; Nishibayashi, Y. J. Am. Chem. Soc.
2007, 129, 5175. (b) Matsuzawa, H.; Miyake, Y.; Nishibayashi, Y. Angew.
Chem., Int. Ed. 2007, 46, 6488. For a review, see: (c) Nishibayashi, Y.;
Uemura, S. Curr. Org. Chem. 2006, 10, 135.
(5) For reviews, see: (a) Touchard, D.; Dixneuf, P. H. Coord. Chem. ReV.
1998, 178-180, 409. (b) Selegue, J. P. Coord. Chem. ReV. 2004, 248,
1543. (c) Bruce, M. I. Coord. Chem. ReV. 2004, 248, 1603. (d) Cadierno,
V.; Gamasa, M. P.; Gimeno, J. Coord. Chem. ReV. 2004, 248, 1627.
(6) Ilg, K.; Werner, H. Chem.sEur. J. 2002, 8, 2812.
(7) See Supporting Information for experimental procedures.
(8) The molecular structure of 4bc was also determined by X-ray analysis.
(9) Lomprey, J. R.; Selegue, J. P. Organometallics 1993, 12, 616.
(10) Cappelli, A.; Galeazzi, S.; Giuliani, G.; Anzini, M.; Donati, A.; Zetta, L.;
Mendichi, R.; Aggravi, M.; Giorgi, G.; Paccagnini, E.; Vomero, S.
Macromolecules 2007, 40, 3005.
(11) The result of the reaction of 2a with EtOD in the presence of 1a also
supports our proposed reaction pathway. See Supporting Information for
details.
(12) Ammal, S. C.; Yoshikai, N.; Inada, Y.; Nishibayashi, Y.; Nakamura, E.
J. Am. Chem. Soc. 2005, 127, 9428.
(13) For reviews, see: (a) Rappoport, Z. Acc. Chem. Res. 1992, 25, 474. (b)
Okuyama, T. Acc. Chem. Res. 2002, 35, 12.
(14) For a recent example, see: Miyauchi, H.; Chiba, S.; Fukamizu, K.; Ando,
K.; Narasaka, K. Tetrahedron 2007, 63, 5940 and references therein.
(15) Okimoto, Y.; Sakaguchi, S.; Ishii, Y. J. Am. Chem. Soc. 2002, 124, 1590.
(16) Separately, we confirmed that no reaction occurred when 2 and 9 bearing
an internal alkyne moiety were used as substrates.
Next, we investigated the reactions of R-ketoacetylenes (9) with
nucleophiles because R-ketoacetylenes are considered to be suitable
substrates to generate butatrienylidene complexes.9 Treatment of
9a in ethanol in the presence of 10 mol % of 1a′ at 60 °C for 2 h
gave the vinylic ether (5aa) in 60% isolated yield as a mixture of
two stereoisomers (Table 2, run 1). Almost the same yield of 5aa
was obtained when 1a was used as a catalyst. The presence of a
substituent at the para-position in the benzene ring of 9a did not
practically influence the yield of 5 (Table 2, runs 2-6). A variety
of alcohols are available as nucleophiles (Table 2, runs 7-9), but
no formation of 4 was observed when reactions of 9 with 3 were
carried out under the same reaction conditions.
These reactions are also considered to proceed via butatrienyli-
dene complexes as key intermediates.9 Dehydration from a vinyli-
dene complex (E) assisted with an alcohol12 may give B (Scheme
5), which is the same reactive intermediate as that in the reactions
of 2 with alcohols (Schemes 2 and 4). In fact, the ratio of stereoiso-
mers of 5 from the reaction of 9 with alcohols is almost the same
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