Ruthenium-catalyzed [1,n]-metallotropic shift (n = 3, 5) of alkynyl carbene complex intermediates

Article abstract of DOI:10.1021/ja0612955

Low-temperature oxygenation of copper(I) complexes of N,N,N-,N-tetraethylpropane-1,3-diamine yields solutions containing both μ-η²:η²-peroxodicopper(II) (P) and bis(μ-oxo)dicopper(III) (O) valence isomers. The P/O equilibrium positio

Full text of DOI:10.1021/ja0612955

Published on Web 06/29/2006
Ruthenium-Catalyzed [1,n]-Metallotropic Shift (n ) 3, 5) of Alkynyl Carbene
Complex Intermediates
Kouichi Ohe,*,† Michinobu Fujita,† Hideyuki Matsumoto,† Yugo Tai,† and Koji Miki†,‡
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto UniVersity, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan, and Nano-Medicine Merger Education Unit, Kyoto UniVersity, Katsura,
Nishikyo-ku, Kyoto 615-8530, Japan
Received February 23, 2006; E-mail: ohe@scl.kyoto-u.ac.jp
Scheme 1
The in situ generation of transient electrophilic carbenoids from
organic compounds with various transition metal complexes is well-
investigated to apply for various inter- or intramolecular carbene
transfer reactions.1,2 We have already demonstrated the in situ
generation of vinylcarbene complexes from propargyl acetates with
several transition metal compounds (Scheme 1).3 Vinylcarbene
complexes generated from secondary and tertiary propargyl car-
boxylates with ruthenium compounds have a rich chemistry that
Scheme 2
combines easy accessibility and high catalytic activity in cycload-
dition reactions with olefins.
Recently, the [1,3] shifts of the carbene center to the remote
alkynyl carbon in free alkynyl carbenes (Scheme 2a)4 and alkynyl
carbene complexes (Scheme 2b)5-10 have been recognized as an
intriguing dynamic organic process (Scheme 2). Since Padwa’s
pioneering work using in situ carbene generation from diazo
Scheme 3
compounds and the rhodium complex for the metallotropic [1,3]-
carbene shift,5 stoichiometric metallotropic [1,3]-shifts of alkynyl
carbene species with transition metal compounds, such as Ti,6 Cr,7
Mo,7 and W,7 have been intensively studied.8 The catalytic
metallotropic [1,3]-carbene shift by ring-closing metathesis (RCM)
of 1,3-diynes to afford π-conjugated enynes and oligoenynes has
been independently developed by Lee et al. and van Otterlo et al.9
We wish to report herein the generation and dynamic behavior of
ruthenium-carbene complexes from oligoynes bearing the prop-
argyl acetate moieties as a carbene trigger and their application to
isomerization of oligoynes.
At first, we examined the generation of carbene complexes from
the symmetrical diynes and a triyne. When the reaction of 2,7-
diacetoxy-2,7-dimethylocta-3,5-diyne (1a) in dichloroethane (DCE)
was carried out in the presence of [RuCl2(CO)3]2 (5 mol %) at 50
°C for 72 h, 3,6-diacetoxy-2,7-dimethylocta-2,6-diene-4-yne (2a)
was obtained in good yield (eq 1).10 Furthermore, when the reaction
of 2,9-diacetoxy-2,9-dimethyldeca-3,5,7-triyne (3) bearing the same
propargyl acetate moieties was carried out, the same type of
isomerization occurred to give 3,8-diacetoxy-2,9-dimethyldeca-2,8-
diene-4,6-diyne (4) in 55% yield (eq 2).11
(1Z,5E)-2,5-diacetoxy-1,6-diphenylhexa-1,5-diene-3-yne (2b) in
47% yield as an isomerized product exclusively (Scheme 3). On
the basis of the stereochemistry of the isomerized product, we pro-
pose one of the most plausible reaction mechanisms for the isom-
erization of oligoynes. The formation of 2b with Z/E-stereochem-
istry can be explained by assuming the generation and the collapse
of the intermediates A and B, respectively, as shown in Scheme
3.12 Since we know that the olefin moiety of a vinylcarbene complex
generated from the secondary propargyl acetate is absolutely Z
(Scheme 1),3a,b the Z-stereochemistry of 2b strongly supports the
generation of the vinylcarbene complex A. Subsequently, the
intermediate A undergoes a [1,3] shift of the carbene center to the
remote alkynyl carbon to form the intermediate B. Finally, the
migratory insertion of an acetate moiety onto the carbene center of
B via the transient structure C takes place to give the product 2b.13
Sterically favored trans configuration of phenyl and ruthenium
moieties followed by migration in the five-membered structure C
is considered to give the E-stereochemistry of 2b.
When we next examined the reaction of 1,6-diacetoxy-1,6-
diphenylhexa-2,4-diyne (1b) bearing the secondary propargyl
acetate moieties in the presence of ruthenium complex, we obtained
Various diynes 1 having symmetrical tertiary and secondary
propargyl carboxylates could participate in the catalytic isomer-
ization via the [1,3]-carbene shift. Furthermore, the addition of an
excess amount of an electron-rich alkene, such as ethyl vinyl ether,
† Department of Energy and Hydrocarbon Chemistry.
‡ Nano-Medicine Merger Education Unit.
9
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J. AM. CHEM. SOC. 2006, 128, 9270-9271
10.1021/ja0612955 CCC: $33.50 © 2006 American Chemical Society

C O M M U N I C A T I O N S
Table 1. Ru-Catalyzed [1,3]-Carbene Shift Using Diynes 1a
Acknowledgment. Dedicated to Professor Kyriacos C. Nicolaou
on the occasion of his 60th birthday. This work was supported by
a Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science and Technology, Japan, the
Nagase Science and Technology Foundation, and the Sumitomo
Foundation.
Supporting Information Available: General procedures and
characterization of new compounds are provided as a PDF file. This
material is available free of charge via the Internet at http://pubs.acs.org.
References
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VCH: Weinheim, Germany, 1999.
a Reaction conditions: substrate 1 (0.50 mmol), ethyl vinyl ether (3.0 equiv),
[RuCl2(CO)3]2 (5.0 mol %), DCE (2.5 mL), at 50 °C for 48 h. b For 72 h; 7%
of starting material was recovered.
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accelerates this isomerization and improves the yields.14 Selected
results are summarized in Table 1. The reactions of 1a, dibenzoate
1c, and dipivalate 1d proceeded smoothly to afford the correspond-
ing products 2a, 2c, and 2d in good yields, respectively. Dicar-
boxylate 1e was isomerized to afford the corresponding product
2e in 89% yield with 1e (7%) recovered. Under the optimized
reaction conditions, the reaction of 1b smoothly proceeded to afford
2b in 84% yield. Electron-withdrawing substituents on the phenyl
rings accelerated the reaction to afford the corresponding products
in excellent yields, while diyne 1i containing an electron-donating
methoxy group gave 2i in a low yield.
When the reaction of unsymmetrical diyne 1j bearing both tert-
iary and secondary propargyl acetate moieties was carried out under
the identical conditions, (E)-2j was obtained as a major product
(eq 3).15 Since both tertiary and secondary propargyl acetates can
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generate carbene complexes, this result shows that the tertiary
propargyl acetate preferentially generates carbene complex, followed
by carbene migration and migratory insertion at the secondary
propargyl acetate moiety.
The isomerization of the diyne 1k bearing primary propargyl
acetate moieties did not occur at all (eq 4). This is consistent with
no reaction of primary propargyl acetate with the ruthenium
complex.3b On the other hand, the reaction of 1l under the same
conditions gave isomerization product 2l (eq 5). The reaction of 1l
(10) The reactions of 1a with 5 mol % of PtCl2 or AuCl(PPh3)/AgSbF6, which
is well-known as one of the most excellent catalysts for catalytic carbene
transfer reactions, also gave the corresponding product 2a in 67 and 47%
yields, respectively.
(11) At present, it is not clear why the yield is increased by the addition of
styrene.
(12) The unsymmetrical structure of 2b could exclude a dicarbene complex D
generated from the 1:2 complexation of 1b and ruthenium complexes.
reveals that the generation of carbene complex took place at the
tertiary propargyl acetate moiety with migration of the carbene
center to give the isomerized product 2l in good yield.
In conclusion, we have demonstrated the ruthenium-catalyzed
isomerization of diynes and triynes by using in situ generation of
transition metal carbene complexes from propargyl carboxylates,
followed by a metallotropic [1,n]-carbene shift (n ) 3, 5) (carbene
walk) of initially generated alkynyl carbene complexes. Further
studies to find the [1,n]-carbene shift (n > 5) as well as to construct
more π-elongated materials by using this protocol are now in
progress in our laboratory.
(13) The similar intramolecular cyclization of ene-carbonyl-carbene complexes
to give furan ring has been reported. See: (a) Ghorai, B. K.; Herndon, J.
W. Organometallics 2003, 22, 3951. (b) Zhang, Y.; Herndon, J. W. J.
Org. Chem. 2002, 67, 4177.
(14) No cyclopropanated product of vinyl ether was observed in each case.
(15) The stereochemistry of product 2j was deduced by nOe experiments. See
Supporting Information.
JA0612955
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