Ruthenium(IV)-catalyzed markovnikov addition of carboxylic acids to terminal alkynes in aqueous medium

Article abstract of DOI:10.1021/om1010325

The dimeric bis(allyl)ruthenium(IV) complex [{RuCl(μ-Cl)( η³:η³-C₁₀H₁₆)}₂] (C₁₀H₁₆ = 2,7-dimethylocta-2,6-diene-1,8-diyl) (5) and several mononuclear species trans-[RuCl₂(η³: η³-C₁₀H₁₆)(L)] (L = two-electron-donor ligand) (6) derived from 5 have been checked as catalysts for the addition of carboxylic acids onto terminal alkynes using water as a green reaction medium. The best results in terms of activity and regioselectivity were obtained with the mononuclear derivative trans-[RuCl₂(η³: η³-C₁₀H₁₆)(PPh₃)] (6a), which was able to promote the selective Markovnikov addition of both aromatic and aliphatic carboxylic acids to a large variety of terminal alkynes, enynes, and diynes as well as propargylic alcohols. In this way, a wide number of enol esters and β-oxo esters could be synthesized in moderate to good yields under mild conditions (60 °C) in an aqueous medium.

Full text of DOI:10.1021/om1010325

852 Organometallics 2011, 30, 852–862
DOI: 10.1021/om1010325
Ruthenium(IV)-Catalyzed Markovnikov Addition of Carboxylic Acids
to Terminal Alkynes in Aqueous Medium
ꢀ
Victorio Cadierno,* Javier Francos, and Jose Gimeno*
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Departamento de Quımica Organica e Inorganica, Instituto Universitario de Quımica Organometalica
“Enrique Moles” (Unidad Asociada al CSIC), Universidad de Oviedo, E-33071 Oviedo, Spain
Received November 2, 2010
The dimeric bis(allyl)ruthenium(IV) complex [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (C10H16 = 2,7-dimeth-
ylocta-2,6-diene-1,8-diyl) (5) and several mononuclear species trans-[RuCl2(η3:η3-C10H16)(L)] (L =
two-electron-donor ligand) (6) derived from 5 have been checked as catalysts for the addition of
carboxylic acids onto terminal alkynes using water as a green reaction medium. The best results in
terms of activity and regioselectivity were obtained with the mononuclear derivative trans-[RuCl2-
(η3:η3-C10H16)(PPh3)] (6a), which was able to promote the selective Markovnikov addition of both
aromatic and aliphatic carboxylic acids to a large variety of terminal alkynes, enynes, and diynes as
well as propargylic alcohols. In this way, a wide number of enol esters and β-oxo esters could be
synthesized in moderate to good yields under mild conditions (60 °C) in an aqueous medium.
Introduction
Among the different metal sources used to promote the
addition of carboxylic acids to terminal alkynes,1,2 ruthe-
nium catalysts have been the most widely studied, due to
their high efficiency and tolerance to functional groups.5,6 In
addition, some of them allow the control of the regio- and
stereoselectivity of this transformation, leading preferentially
to one of the three possible enol ester isomers (see Scheme 1).
Thus, while the catalytic systems bis(η5-cyclooctadienyl)-
ruthenium/PR3,7 [RuCl2(η6-arene)(PR3)],8 and [{Ru(μ-O2CH)-
(CO)2(PPh3)}2]9 are known to promote the addition toward
Transition-metal-catalyzed addition of heteroatom-hydrogen
bonds to alkynes has become one of the most powerful tools
in synthetic organic chemistry, since it allows the straightfor-
ward preparation of a wide variety of functionalized unsa-
turated compounds of enormous interest from academic and
industrial points of view.1 In particular, the direct addition of
carboxylic acids to terminal alkynes is an elegant and useful
method for preparing enol esters (Scheme 1),1,2 which are
valuable intermediates for carbon-carbon and carbon-
heteroatom bond formation,3 and also have specific indus-
trial applications as monomers for the production of several
polymers and copolymers.4
(5) Pioneering work on ruthenium-catalyzed addition of carboxylic
acids to alkynes was done by Rotem and Shvo using [Ru3(CO)12] as
catalyst: Rotem, M.; Shvo, Y. Organometallics 1983, 2, 1689.
(6) Specific reviews on the ruthenium-catalyzed addition of car-
boxylic acids to alkynes are available: (a) Bruneau, C. In Metal
Vinylidenes and Allenylidenes in Catalysis: From Reactivity to Applica-
tions in Synthesis; Bruneau, C., Dixneuf, P. H., Eds.; Wiley-VCH: Weinheim,
Germany, 2008; p 313. (b) Bruneau, C. In Handbook of C-H Transformations:
Applications in Organic Synthesis; Dyker, G., Ed.; Wiley-VCH: Weinheim,
Germany, 2005; Vol. 1, p 72. (c) Fischmeister, C.; Bruneau, C.; Dixneuf,
P. H. In Ruthenium in Organic Synthesis; Murahashi, S.-I., Ed.; Wiley-VCH:
Weinheim, Germany, 2004; p 189.
*To whom correspondence should be addressed. E-mail: vcm@
uniovi.es (V.C.); jgh@uniovi.es (J.G.).
(1) For general reviews, see: (a) Alonso, F.; Beletskaya, I. P.; Yus, M.
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Angew. Chem., Int. Ed. 2004, 43, 3368. (c) Hintermann, L. Top. Organo-
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ꢀ
ꢀ
(4) Vinyl acetate, the monomeric precursor of poly(vinyl acetate) and
poly(vinyl alcohol), is undoubtedly the most popular representative.
Industrial production of vinyl acetate is presently based on the addition
of acetic acid to ethylene catalyzed by Pd(II) under oxidative conditions:
(a) Wittcoff, H. A.; Reuben, B. G. In Industrial Organic Chemicals;
Wiley-Interscience: New York, 1996; p 109. For polymerization reactions of
ꢀ
acetoxystyrenes, see: (b) Montheard, J. P.; Camps, M.; Seytre, G.; Guillet, J.;
Dubois, J. C. Angew. Makromol. Chem. 1978, 72, 45.
r
pubs.acs.org/Organometallics
Published on Web 01/20/2011
2011 American Chemical Society

Article
Organometallics, Vol. 30, No. 4, 2011 853
Figure 1. Proposed intermediates in the Ru-catalyzed additions of carboxylic acids to terminal alkynes.
Scheme 1. Catalytic Addition of Carboxylic Acids to Terminal Alkynes
the Markovnikov product 3, the bis(allyl)ruthenium(II)
complexes [Ru(η3-2-C3H4Me)2{κ2(P,P)-Ph2P(CH2)nPPh2}]
(n = 1-4), described by Dixneuf and co-workers,10 are able
to reverse the selectivity, affording almost exclusively the Z
isomer of the alk-1-en-1-yl esters 4.11,12 It is presently well
established that the different regioselectivity relies on the
ability of ruthenium fragments to control the π-alkyne vs
vinylidene rearrangement favoring either the Markovnikov
(π-alkyne coordination) or the anti-Markovnikov (vinylidene
ruthenium intermediate) addition of the carboxylate anion
(see Figure 1).6
water on the rate and endo/exo selectivity of Diels-Alder
reactions,13 the development of organic transformations in
aqueous media has become one of the major cornerstones in
modern chemistry.14 This fact is also attributed to the
increasing academic and industrial interest in fulfilling the
principles of “Green Chemistry”,15 since water is the most
convenient solvent that one can imagine in terms of cost,
availability, safety, and environmental impact.16,17 Although
the hydrophobic character of most organic compounds has
(13) (a) Rideout, D. C.; Breslow, R. J. Am. Chem. Soc. 1980, 102,
7816. (b) Breslow, R.; Maitra, U.; Rideout, D. C. Tetrahedron Lett. 1983, 24,
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(d) Grieco, P. A.; Yoshida, K.; Garner, P. J. Org. Chem. 1983, 48, 3137.
(e) Breslow, R.; Maitra, U. Tetrahedron Lett. 1984, 25, 1239.
On the other hand, since the discoveries made by Breslow
and Grieco in the early 1980s on the positive effect of
(14) See for example: (a) Li, C.-J. Chem. Rev. 1993, 93, 2023. (b)
Lubineau, A.; Auge, J.; Queneau, Y. Synthesis 1994, 741. (c) Li, C.-J.; Chan,
T. H. In Organic Reactions in Aqueous Media; Wiley: New York, 1997.
(10) (a) Doucet, H.; Martin-Vaca, B.; Bruneau, C.; Dixneuf, P. H. J.
Org. Chem. 1995, 60, 7247. (b) Doucet, H.; Derrien, N.; Kabouche, Z.;
Bruneau, C.; Dixneuf, P. H. J. Organomet. Chem. 1998, 551, 151.
(c) Doucet, H.; Hofer, J.; Derrien, N.; Bruneau, C.; Dixneuf, P. H. Bull.
Soc. Chim. Fr. 1996, 133, 939. (d) Emme, I.; Bruneau, C.; Dixneuf, P. H.;
Militzer, H.-C.; de Meijere, A. Synthesis 2007, 3574.
€
(d) Lindstrom, U. M. Chem. Rev. 2002, 102, 2751. (e) Li, C.-J. Chem. Rev.
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2005, 105, 3095. (f) Andrade, C. K. Z.; Alves, L. M. Curr. Org. Chem. 2005,
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C. I.; Yao, X.; Li, Z.; Li, C. J. Chem. Rev. 2007, 107, 2546. (i) Organic
€
(11) Although other ruthenium-based catalysts able to orient the
addition towards the anti-Markovnikov products 4 are known, they are
in general less active and/or stereoselective than Dixneuf’s catalysts. In
other cases, the 3 vs 4 selectivity was found to be strongly dependent on
the nature of the terminal alkyne, carboxylic acid, and/or solvent
employed. See for example: (a) Gemel, C.; Trimmel, G.; Slugovc, C.;
Kremel, S.; Mereiter, K.; Schmid, R.; Kirchner, K. Organometallics
1996, 15, 3998. (b) Melis, K.; Samulkiewicz, P.; Rynkowski, J.; Verpoort, F.
Tetrahedron Lett. 2002, 43, 2713. (c) Opstal, T.; Verpoort, F. Tetrahedron
Lett. 2002, 43, 9259. (d) Melis, K.; Vos, D. D.; Jacobs, P.; Verpoort, F. J.
Organomet. Chem. 2003, 671, 131. (e) Melis, K.; Verpoort, F. J. Mol. Catal.
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Dragutan, V.; Verpoort, F. Adv. Synth. Catal. 2005, 347, 1721 and references
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Practice; Oxford University Press: Oxford, U.K., 1998. (b) Anastas, P. T.;
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(c) Matlack, A. S. In Introduction to Green Chemistry; Marcel Dekker:
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(16) See, for example: (a) Nelson, W. M. In Green Solvents for
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(17) We note that the “green” nature of water (as a solvent for organic
synthesis) is not absent of controversy. See for example: Blackmond,
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2007, 46, 3798.
~
cited therein. (i) Pelagatti, P.; Bacchi, A.; Balordi, M.; Bolano, S.; Calbiani, F.;
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(12) It is also interesting to note that, just by adding coordinating
amines to the reaction media, the regioselectivity shown by complexes
[RuCl2(η6-arene)(PR3)] can be completely reversed, leading predomi-
nantly to enol esters (Z)-4 instead of their expected isomers 3: Goossen,
L. J.; Paetzold, J.; Koley, D. Chem. Commun. 2003, 706.

854 Organometallics, Vol. 30, No. 4, 2011
Cadierno et al.
been considered as a major drawback for a long time, it is
nowadays well documented that even when the reaction
medium is completely heterogeneous an enhancement of
the reactivity and/or selectivity can be observed by using
water as solvent.18,19 Following this general trend, the search
of metal catalysts for organic reactions in water has also
attracted growing interest in recent years,20 a wide variety
of highly efficient and selective synthetic protocols con-
ducted in aqueous media being already available for prac-
tical uses.14,20 As far as the catalytic addition of carboxylic
acids to terminal alkynes is concerned, despite the great
interest of this atom-economical transformation in synthesis,
up to now no general protocols have been reported in aqueous
Figure 2. Structures of the bis(allyl)ruthenium(IV) complexes 5
and 6.
media,21 probably owing to the competitive hydration of the
alkynes in water to give carbonyl derivatives.22,23
In the context of our current work dealing with the
catalytic applications of ruthenium complexes in aqueous
media,24 we have reported that the commercially available
bis(allyl)ruthenium(IV) dimer [{RuCl(μ-Cl)(η3:η3-C10H16)}2]
(5; C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl)25 is able
to catalyze efficiently and selectively the [2 þ 2 þ 2] cyclo-
trimerization of alkynes in water without observation of
hydration side reactions.26 This fact prompted us to explore
the potential of dimer 5 and its mononuclear derivatives
trans-[RuCl2(η3:η3-C10H16)(L)] (6 in Figure 2), easily acces-
sible by cleavage of the chloride bridges of 5 with two-
electron-donor ligands,27 as catalysts for the addition of
carboxylic acids to terminal alkynes in aqueous media.
Herein we describe the successful application of the mono-
nuclear complex trans-[RuCl2(η3:η3-C10H16)(PPh3)] in the
selective Markovnikov addition of a large variety of car-
boxylic acids to terminal alkynes, enynes, diynes, and pro-
pargylic alcohols. We must note that, despite the plethora of
ruthenium complexes used to date to promote these catalytic
transformations, high-oxidation-state Ru(IV) derivatives
have been completely neglected.
(18) The term “on water”, introduced by Sharpless and co-workers, is
commonly used in the literature to refer to organic reactions proceeding
in aqueous suspension: Narayan, S.; Muldoon, J.; Finn, M. G.; Fokin,
V. V.; Kolb, H. C.; Sharpless, K. B. Angew. Chem., Int. Ed. 2005, 44,
3275.
(19) For recent reviews on organic synthesis “on water”, see: (a)
Chanda, A.; Fokin, V. V. Chem. Rev. 2009, 109, 725. (b) Butler, R. N.;
Coyne, A. G. Chem. Rev. 2010, 110, 6302.
(20) See for example: (a) Kalck, P.; Monteil, F. Adv. Organomet.
Chem. 1992, 34, 219. (b) Herrmann, W. A.; Kohlpaintner, C. W. Angew.
Chem., Int. Ed. Engl. 1993, 32, 1524. (c) Aqueous Organometallic
ꢀ
ꢀ
Chemistry and Catalysis; Horvath, I. T., Joo, F., Eds.; Kluwer: Dordrecht,
The Netherlands, 1995. (d) Aqueous-Phase Organometallic Catalysis:
Concepts and Applications; Cornils, B.; Herrmann, W. A., Eds.; Wiley-
VCH: Weinheim, Germany, 1998. (e) Hanson, B. E. Coord. Chem. Rev.
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1999, 185-186, 795. (f) Aqueous Organometallic Catalysis; Horvath, I. T.,
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Joo, F., Eds.; Kluwer: Dordrecht, The Netherlands, 2001; (g) Pinault, N.;
Bruce, D. W. Coord. Chem. Rev. 2003, 241, 1.
(21) The use of water-saturated organic solvents has led in some cases
to a beneficial impact on the reaction rates. See ref 8i and: (a) Willem,
Q.; Nicks, F.; Sauvage, X.; Delaude, L.; Demonceau, A. J. Organomet.
Chem. 2009, 694, 4049. (b) In the context of a more general study, one
example in water, i.e. the addition of benzoic acid to 4-ethynylanisole
catalyzed by [RuHCl(CO)(PCy3)2], has been described.11k
(22) Catalytic transformations of alkynes in water have been recently
reviewed: (a) Chen, L.; Li, C.-J. Adv. Synth. Catal. 2006, 348, 1459. (b) Li,
C.-J. Acc. Chem. Res. 2010, 43, 581.
(23) The metal-catalyzed hydration of terminal alkynes to afford
aldehydes (anti-Markovnikov addition) or ketones (Markovnikov ad-
dition) is a well-known and widely studied transformation of significant
synthetic utility. For reviews on this topic see ref 1 and: Hintermann, L.;
Labonne, A. Synthesis 2007, 1121.
Results and Discussion
Our investigations started with the evaluation of the
catalytic activity of the dimer [{RuCl(μ-Cl)(η3:η3-C10H16)}2]
(5) in the addition of benzoic acid (2a) to 1-hexyne (1a)
(Scheme 2). Initial exploratory experiments were performed
at 60 °C using equimolar amounts of the substrates (1 M in
water) and a ruthenium loading of 2 mol %. Under these
conditions, in the absence of any cocatalyst, the reaction
proceeded to 89% overall GC yield in 24 h, producing a
mixture of the three possible 1/1 adducts with low selectivity
(3aa/(E)-4aa/(Z)-4aa ratio 3/2/4). Remarkably, neither for-
mation of carbonyl compounds derived from the hydration
of the CtC bond of 1-hexyne nor alkyne oligomers were
detected by GC/MSD of the crude reaction mixture.
Although a significant rate enhancement was observed upon
addition of different bases (M2CO3, MOH, and amines), the
selectivity of the addition process remained in all cases low
and formation of minor amounts of dimerization products of
1-hexyne was observed in general. As a representative ex-
ample, in the presence of 4 mol % of Na2CO3, a conversion
of 92% could be reached after only 4 h of heating, leading to
a 3aa/(E)-4aa/(Z)-4aa mixture (75% GC ield in 2/3/3 ratio)
(24) (a) Cadierno, V.; Garcıa-Garrido, S. E.; Gimeno, J. Chem.
Commun. 2004, 232. (b) Cadierno, V.; Crochet, P.; García-Garrido, S. E.;
Gimeno, J. Dalton Trans. 2004, 3635. (c) Cadierno, V.; García-Garrido,
S. E.; Gimeno, J.; Nebra, N. Chem. Commun. 2005, 4086. (d) Cadierno, V.;
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García-Garrido, S. E.; Gimeno, J.; Varela-Alvarez, A.; Sordo, J. A. J. Am.
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Chem. Soc. 2006, 128, 1360. (e) Díaz-Alvarez, A. E.; Crochet, P.; Zablocka,
M.; Duhayon, C.; Cadierno, V.; Gimeno, J.; Majoral, J. P. Adv. Synth. Catal.
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2006, 348, 1671. (f) Crochet, P.; Díez, J.; Fernandez-Zꢀumel, M. A.; Gimeno,
J. Adv. Synth. Catal. 2006, 348, 93. (g) Cadierno, V.; Francos, J.; Gimeno, J.;
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N. Chem. Eur. J. 2007, 13, 6590. (i) Díaz-Alvarez, A. E.; Crochet, P.;
Zablocka, M.; Duhayon, C.; Cadierno, V.; Majoral, J. P. Eur. J. Inorg. Chem.
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(l) Cadierno, V.; Crochet, P.; Francos, J.; García-Garrido, S. E.; Gimeno,
J.; Nebra, N. Green Chem. 2009, 11, 1992. (m) Cadierno, V.; Francos, J.;
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c0gc00417k).
(25) Available from Strem Chemicals, Inc. (catalogue number 44-
0203). Alternatively, complex 5 can be easily prepared by reacting an
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3
M. C.; Colombo, A.; Allegra, G. Tetrahedron Lett. 1965, 47, 4187.
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Geyser, S.; Podewils, F.; Turpin, G. C.; Ernst, R. D. Inorg. Synth. 2004,
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(26) (a) Cadierno, V.; Garcıa-Garrido, S. E.; Gimeno, J. J. Am.
Chem. Soc. 2006, 128, 15094. (b) Cadierno, V.; Francos, J.; García-Garrido,
S. E.; Gimeno, J. Green Chem. Lett. Rev. 2010, in press.
(27) For a comprehensive review on the chemistry of [{RuCl(μ-Cl)-
(η3:η3-C10H16)}2] (5), see: Cadierno, V.; Crochet, P.; Garcıa-Garrido,
S. E.; Gimeno, J. Curr. Org. Chem. 2006, 10, 165.

Article
Organometallics, Vol. 30, No. 4, 2011 855
Scheme 2. Catalytic Addition of Benzoic Acid (2a) to 1-Hexyne (1a)
Scheme 3. Synthesis of the Mononuclear Bis(allyl)ruthenium-
(IV) Derivatives 6a-s
the π-alkyne-to-vinylidene rearrangement is favored when
the terminal alkyne coordinates in an equatorial position of the
neutral [RuCl2(η3:η3-C10H16)] ruthenium fragment (Figure 3).
In contrast, when nonlabile ligands are present, coordina-
tion of the alkyne occurs in the axial position of the cationic
ruthenium(IV) complex [RuCl(η3:η3-C10H16)(L)]þ, in which
such a rearrangement is disfavored.30 The best results in
terms of activity and regioselectivity were obtained with the
mononuclear derivative [RuCl2(η3:η3-C10H16)(PPh3)] (6a),
which was able to generate the enol ester 3aa in 96% GC
yield after only 3 h of heating (entry 1). However, from the
data obtained, there is no apparent relationship between the
steric and/or electronic nature of the auxiliary ligand L and
the catalytic activity observed.
It is important to note that, with the exception of the water-
soluble complexes trans-[RuCl2(η3:η3-C10H16)(TPPMS)] (6b;
TPPMS = 3-(diphenylphosphino)benzenesulfonate sodium
salt) and trans-[RuCl2(η3:η3-C10H16){P(OR)3}] (R = Me (6i),
Et (6j), iPr (6k)), all the rest of these mononuclear ruthenium-
(IV) complexes are completely insoluble in water. Accord-
ingly, a two-phase water/organic product system was formed
in all cases, with the ruthenium catalyst remaining mainly in
the organic phase (an emulsion is formed by stirring the cat-
alytic reaction mixture). In light of the possibilities offered by
surfactants to perform catalytic organic reactions in water,
facilitating the solubility of both the metal catalyst and the
reactants,31 we decided to explore the catalytic addition of
benzoic acid (2a) to 1-hexyne (1a) in aqueous micelles using
the most active complex, trans-[RuCl2(η3:η3-C10H16)(PPh3)]
(6a). In this regard, the commercially available sodium dodecyl
sulfate (SDS) and cetyltrimethylammonium bromide (CTABr)
were used as surfactants, the reactions being performed in
aqueous 0.01 M solutions (Table 2, entries 2 and 3).32
Although the reaction media were now completely homo-
geneous, longer reaction times were required to attain similar
conversions and selectivities (entries 2 and 3 vs entry 1).33
Interestingly, the use of organic solvents, regardless of their
and the corresponding tail-to-tail and head-to-tail dimers of
1-hexyne (17% GC yield).28 The use of either lower tem-
peratures or catalyst loadings did not lead to a higher
selectivity for the process, also negatively affecting the reac-
tion rate (no catalytic activity was observed below 35 °C).
In the search for a more selective catalyst, a series of mono-
nuclear derivatives trans-[RuCl2(η3:η3-C10H16)(L)] (6a-s)
was synthesized by cleavage of the chloride bridges of dimer
5 with phosphines (6a-h), phosphites (6i-l), nitriles (6m,n),
amines (6o,p), carbon monoxide (6q), and isocyanides (6r,s)
(see Scheme 3).29 We expected that the catalytic process
might be improved in terms of activity as well as regioselec-
tivity (Markovnikov/anti-Markovnikov addition) via the
influence of these ligands, featuring different electronic and
steric properties.
The ability of these mononuclear species to promote the
addition of benzoic acid (2a) to 1-hexyne (1a) in water was
then evaluated (Scheme 2). Table 1 provides a summary of
the results obtained on performing the catalytic reactions at
60 °C with a ruthenium loading of 2 mol %.
As shown in Table 1, all the mononuclear complexes
checked were found to be active catalysts, providing enol
esters 3aa and 4aa in moderate to good yields after 3-24 h of
heating. In general, a higher selectivity toward the Markov-
nikov product was observed, as compared to that found for
the dimeric precursor [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (5). The
anti-Markovnikov adducts (E/Z)-4aa were only predomi-
natly formed from complexes 6m-p, containing a labile
nitrile or amine ligand. These results seem to indicate that
(30) One reviewer suggested that anti-Markovnikov addition of the
carboxylic acid to the vinylidene ligand can proceed in an intramolecular
fashion. Although this reaction pathway cannot be totally discarded, we
must note that the use of the benzoate complex [RuCl{κ2(O,O)-
O2CPh)}(η3:η3-C10H16)] (its preparation and characterization are de-
scribed in the Experimental Section) as catalyst resulted in remarkably
lower yields, without improving the selectivity toward the anti-Markov-
nikov product 4aa. Thus, under the same reaction conditions, only 33%
conversion was observed after 24 h of heating, giving to a 3aa/(E)-
4aa/(Z)-4aa mixture in ca. 1/1/1 ratio. This fact suggests that coordina-
tion of the benzoate anion to ruthenium does not occur during the
catalytic event.
(31) See, for example: (a) Dwards, T.; Paetzold, E.; Oehme, G.
Angew. Chem., Int. Ed. 2005, 44, 7174. (b) Zhang, J.; Meng, X.-G.; Zheng,
X.-C.; Yu, X.-Q. Coord. Chem. Rev. 2009, 253, 2166. (c) Cavarzan, A.;
Scarso, A.; Strukul, G. Green Chem. 2010, 12, 790.
(32) The critical micelle concentrations of CTABr and SDS are 9 ꢀ
10-4 and 8 ꢀ 10-3 M, respectively. The use of 0.01 M solutions of these
surfactants assures the correct formation of micelles: (a) Fendler, J. H.;
Fendler, E. J. In Catalysis in Micellar and Macromolecular Systems;
Academic Press: New York, 1975. (b) Furton, K.; Norelus, A. J. Chem.
Educ. 1993, 70, 254. Under these reaction conditions both the organometallic
catalyst 6a and the organic substrates are completely soluble in the aqueous
phase.
(28) (a) Competitive dimerization of the alkyne has been previously
observed in related ruthenium-catalyzed addition processes. See, for
example, refs 8i, 11d, and 21a. Formation of dienyl esters (alkyne/
carboxylic acid 2/1 adducts) was not detected by GC/MSD: (b) Le Paih,
ꢀ
J.; Monnier, F.; Derien, S.; Dixneuf, P. H.; Clot, E.; Eisenstein, O. J. Am.
Chem. Soc. 2003, 125, 11964.
(29) With the exception of 6h (see the Experimental Section), the
preparation of these mononuclear complexes has been previously de-
scribed in the literature. In all cases equatorial adducts are exclusively
formed: (a) Head, R. A.; Nixon, J. F.; Swain, J. R.; Woodard, C. M. J.
Organomet. Chem. 1974, 76, 393. (b) Cox, D. N.; Roulet, R. J. Chem. Soc.,
Chem. Commun. 1988, 951. (c) Cox, D. N.; Roulet, R. Inorg. Chem. 1990,
29, 1360. (d) Cox, D. N.; Small, R. W. H.; Roulet, R. J. Chem. Soc., Dalton
Trans. 1991, 2013. (e) Steed, J. W.; Tocher, D. A. J. Organomet. Chem.
1994, 471, 221. (f) Wache, S.; Herrmann, W. A.; Artus, G.; Nuyken, O.; Wolf,
D. J. Organomet. Chem. 1995, 491, 181. (g) Glander, S. C.; Nuyken, O.;
Schattenmann, W. C.; Herrmann, W. A. Macromol. Symp. 1998, 127, 67.
€
(h) Werner, H.; St€uer, W.; Jung, S.; Weberndorfer, B.; Wolf, J. Eur. J. Inorg.
Chem. 2002, 1076. (i) See also refs 24d, 24o, and 24q.

856 Organometallics, Vol. 30, No. 4, 2011
Cadierno et al.
Table 1. Addition of Benzoic Acid (2a) to 1-Hexyne (1a) Catalyzed by the Mononuclear Ruthenium(IV)
Complexes trans-[RuCl2(η3:η3-C10H16)(L)] (6a-s) in Watera
entry
cat.
time (h)
conversn (%)b
yield of 3aa (%)b
yield of 4aa (%)b,c
1
2
3
4
5
6
7
8
6a (L = PPh3)
3
4
3
4
5
24
6
9
3
3
99
99
98
96
97
94
99
87
92
97
85
78
76
65
37
81
75
89
91
96
92
94
94
79
79
95
81
88
95
83
63
23
21
12
22
64
63
68
3 (2:3)
7 (3:2)
4 (2:3)
6b (L = TPPMS)
6c (L = P(p-Tol)3)
6d (L = PPh2Me)
6e (L = PPhMe2)
6f (L = PMe3)
6g (L = PiPr3)
2 (1:1)
18 (1:8)
18 (5:4)
4 (1:3)
6 (1:2)
4 (1:1)
6h (L = PBn3)
9
6i (L = P(OMe)3)
6j (L = P(OEt)3)
6k (L = P(OiPr)3)
6l (L = P(OPh)3)
6m (L = NCMe)
6n (L = NCPh)
6o (L = NH2Ph)
6p (L = py)
10
11
12
13
14
15
16
17
18
19
2 (1:1)
2 (1:1)
3
24
24
24
24
24
24
24
24
15 (1:1)
53 (3:2)
44 (3:2)
25 (1:1)
59 (1:1)
11 (3:2)
26 (1:1)
23 (1:1)
6q (L = CO)
6r (L = CNBn)
6s (L = CNCy)
a Reactions performed under a N2 atmosphere at 60 °C using 1 mmol of 1-hexyne, 1 mmol of benzoic acid, 0.02 mmol of the corresponding ruthenium
complex, and 1 mL of water. b Conversion and yields determined by GC (uncorrected GC areas). c E/Z ratios are given in brackets (GC determined).
(2p; entry 16) to 1a. Remarkably, several common functional
groups were tolerated and remained unaffected using this
aqueous procedure: i.e., halide, ether, cyanide, alkene, and
alcohol. Concerning the aromatic substrates (entries 1-10),
no influence of the electronic properties of the aryl rings on
the efficiency of the process was observed. The generality of
this addition process was also confirmed by using a variety of
other aliphatic (1b-l; entries 17-27) and aromatic terminal
alkynes (1m,n; entries 28 and 29), as well as 1,3-enynes (1o,p;
entries 30 and 31), the addition of benzoic acid (2a) to these
substrates leading to the high-yield formation of enol esters
3ba-3pa (73-97% GC yields; 60-88% isolated yields). As a
general trend, faster reactions and higher yields were reached
with aliphatic alkynes in comparison to the aromatic al-
kynes. In the case of methyl propargyl ether (1j; entry 25) a
long reaction time (24 h) and a higher ruthenium loading (3
mol %) was also required to attain a high conversion. We
must note that, in all the reactions given in Table 3, the
formation of minor amounts of the corresponding anti-
Markovnikov addition products was detected by GC.
Figure 3. π-Alkyne-to-vinylidene equilibrium: (a) coordination
in the equatorial position; (b) coordination in the axial position.
polarity or hydrogen-bonding capacity (entries 4-11), also
reduced considerably the catalytic activity of 6a (a homo-
geneous reaction medium was in all cases observed). A
Although the content of these products in the crude reaction
mixtures was in general less than 10%, this amount was
significantly higher when the aromatic alkynes phenylacety-
similar behavior was observed in the absence of solvent
lene and 4-methoxyphenylacetylene were used as substrates
(17-23%; entries 28 and 29).34 Solvent removal and chro-
matographic workup on silica gel provided analytically pure
(entry 12). All these results clearly indicate that the “on-
water” effect (trans-phase H-bonding interactions of water
with transition states and reactants) plays a key role in this
samples of all enol esters 3aa-3pa, whose identity was
catalytic transformation.19b
In order to evaluate the scope of the catalytic activity of
assessed by comparison of their 1H and 13C{1H} NMR data
with those previously described in the literature and by their
trans-[RuCl2(η3:η3-C10H16)(PPh3)] (6a) in water, the addi-
tion of a number of other carboxylic acids to 1-hexyne (1a)
fragmentation in GC/MSD (characterization data for new
compounds are included in the Experimental Section).
was explored. Thus, as shown in Table 3, using the same
To further demonstrate the synthetic utility of the complex
trans-[RuCl2(η3:η3-C10H16)(PPh3)] (6a), we next examined
reaction conditions employed in the preparation of 3aa
(entry 1), related enol esters 3ab-3ap could prepared in good
the coupling reactions of benzoic acid (2a) with diynes
to excellent yields (83-98% GC yields; 70-90% isolated yields)
by addition of other aromatic (2b-j; entries 2-10), aliphatic
(34) This fact is in accord with the higher tendency of aromatic
(2k-o; entries 11-15) and R,β-unsaturated carboxylic acids
views on the chemistry of transition-metal vinylidene complexes, see: (a)
alkynes to undergo the π-alkyne-to-vinylidene rearrangement. For re-
(33) This negative effect is particularly marked for CTABr, probably
due to the presence of an excess of bromide anions in the reaction
medium that compete with the alkyne for coordination to the metal
center.
Bruce, M. I. Chem. Rev. 1991, 91, 197. (b) Puerta, M. C.; Valerga, P. Coord.
Chem. Rev. 1999, 193-195, 977. (c) Wakatsuki, Y. J. Organomet. Chem.
2004, 689, 4092. (d) Cadierno, V.; Gamasa, M. P.; Gimeno, J. Coord. Chem.
Rev. 2004, 248, 1627. (e) Lynnam, J. M. Chem. Eur. J. 2010, 16, 8238.

Article
Organometallics, Vol. 30, No. 4, 2011 857
Table 2. Addition of Benzoic Acid (2a) to 1-Hexyne (1a) Catalyzed by the Mononuclear Ruthenium(IV) Complex trans-[RuCl2(η3:η3-
C10H16)(PPh3)] (6a) in Different Solvent Mediaa
entry
solvent
time (h)
conversn (%)b
yield of 3aa (%)b
yield of 4aa (%)b,c
1
2
3
4
5
6
7
8
H2O
3
5
99
99
88
90
10
43
56
15
88
57
92
80
96
93
82
83
7
37
48
12
82
53
87
74
3 (2:3)
6 (2:4)
6 (2:4)
7 (2:5)
3 (1:2)
6 (1:5)
8 (2:6)
3 (1:2)
6 (2:4)
4 (1:3)
5 (1:4)
6 (1:5)
SDS(aq) (0.01 M)
CTABr(aq) (0.01 M)
CH2Cl2
THF
MeOH
EtOH
MeCN
dioxane
toluene
24
24
24
24
24
24
24
24
24
24
9
10
11
12
n-hexane
None
a Reactions performed under an N2 atmosphere at 60 °C using 1 mmol of 1-hexyne, 1 mmol of benzoic acid, 0.02 mmol of complex 6a, and 1 mL of the
appropriate solvent. b Conversion and yields determined by GC (uncorrected GC areas). c E/Z ratios are given in brackets (GC determined).
Table 3. Addition of Carboxylic Acids to Terminal Alkynes Catalyzed by the Mononuclear Ruthenium(IV) Complex trans-[RuCl2(η3:η3-
C10H16)(PPh3)] (6a) in Watera
entry
alkyne 1 (R1)
acid 2 (R2)
Ph (2a)
time (h)
conversn (%)b
product 3; yield (%)c
1
2
3
4
5
6
7
8
nBu (1a)
3
2
2
3
3
3
3
6
6
1
6
7
7
5
6
5
6
5
3
3
6
4
3
5
24
5
99
99
99
99
99
99
99
99
99
99
98
99
94
99
99
99
99
99
99
99
99
99
99
99
95
99
99
90
99
99
99
3aa; 96 (82)
3ab; 92 (80)
3ac; 95 (85)
3ad; 98 (90)
3ae; 94 (83)
3af; 95 (81)
3ag; 84 (73)
3ah; 96 (87)
3ai; 96 (85)
3aj; 83 (70)
3ak; 90 (80)
3al; 96 (84)
3am; 84 (72)
3an; 91 (82)
3ao; 92 (83)
3ap; 91 (80)
3ba; 94 (86)
3ca; 97 (85)
3da; 95 (83)
3ea; 94 (86)
3fa; 86 (78)
3ga; 96 (85)
3ha; 94 (85)
3ia; 94 (86)
3ja; 89 (77)
3ka; 91 (79)
3la; 96 (88)
3ma; 73 (60)
3na; 76 (61)
3oa; 90 (81)
3pa; 98 (87)
nBu (1a)
2-C6H4F (2b)
2-C6H4Cl (2c)
3-C6H4Cl (2d)
3-C6H4Br (2e)
3-C6H4OMe (2f)
4-C6H4Cl (2g)
4-C6H4CN (2h)
4-C6H4CHdCH2 (2i)
C6F5 (2j)
n-C6H13 (2k)
n-C7H15 (2l)
CH2Cy (2m)
CH2CH2Ph (2n)
(S)-CH(OH)Ph (2o)
(E)-CHdCHPh (2p)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
nBu (1a)
nBu (1a)
nBu (1a)
nBu (1a)
nBu (1a)
nBu (1a)
9
nBu (1a)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25d
26
27
28
29
30
31
nBu (1a)
nBu (1a)
nBu (1a)
nBu (1a)
nBu (1a)
nBu (1a)
nBu (1a)
nPr (1b)
n-C6H13 (1c)
n-C8H17 (1d)
n-C1i0H21 (1e)
CH2 Pr (1f)
CH2Cy (1g)
CH2-c-C5H9 (1h)
CH2Ph (1i)
CH2OMe (1j)
tBu (1k)
Cy (1l)
Ph (1m)
4-C6H4OMe (1n)
C(Me)dCH2 (1o)
c-C6H9 (1p)e
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
3
24
24
7
7
a Reactions performed under an N2 atmosphere at 60 °C using 1 mmol of the corresponding alkyne and carboxylic acid, 0.02 mmol of complex 6a, and
1 mL of water. b Determined by GC. c Determined by GC (uncorrected GC areas; isolated yields are given in parentheses). The differences between
conversions and yields correspond to the anti-Markovnikov products present in the reaction media. d Reaction performed with a ruthenium loading of 3
mol %. e c-C6H9 = 1-cyclohexenyl.
(Scheme 4). Thus, when commercially available 1,6-hepta-
diyne (4a), 1,7-octadiyne (4b), and 1,8-nonadiyne (4c) were
used as starting materials and the catalytic reactions were
performed in the presence of 2 equiv of 2a, the corresponding
gem-dienol diesters 7aa-7ca were regioselectively formed
(91-95% GC yields; 83-89% isolated yields) after 10 h of
heating at 60 °C in the presence of 2 mol % of complex 6a.
Albeit in lower yields due to the competitive formation of
7aa-7ca, the monoaddition products 8aa-8ca could also be
synthesized using 6a just by performing the catalytic reac-
tions with a diyne/benzoic acid ratio of 1.3/1 (details are
given in the Experimental Section). All these results clearly
demonstrate the extraordinary synthetic potential of trans-
[RuCl2(η3:η3-C10H16)(PPh3)] (6a). However, we must note
that all attempts made to promote the addition of benzoic
acid to alkynes bearing an internal CtC bond (i.e., 3-hexyne

858 Organometallics, Vol. 30, No. 4, 2011
Scheme 4. Catalytic Addition of Benzoic Acid to Terminal Diynes
Cadierno et al.
Scheme 5. β-Oxo Ester Formation by Addition of Carboxylic
Acids to Terminal Propargylic Alcohols
accepted mechanism for this transformation involves the
initial Markovnikov addition of the carboxylic acid to the
alkynol CtC bond,37 followed by an intramolecular trans-
esterification step.38 The high selectivity shown by
trans-[RuCl2(η3:η3-C10H16)(PPh3)] (6a) toward the forma-
tion of Markovnikov adducts starting from terminal alkynes
prompted us to study the suitability of this catalyst to
generate β-oxo esters in water. In this context, we should
note that the compatibility of this coupling process with the
use of an aqueous medium has been recently demonstrated
by us, employing the hydrophilic ruthenium(II) complex
[RuCl2(η6-C6H6)(TPPMS)] as catalyst.24m
We were pleased to find that treatment of several terminal
propargylic alcohols 9a-s with 1 equiv of benzoic acid (2a),
in water at 60 °C and in the presence of 6a (2 mol %), resulted
in the formation of the desired β-oxo esters 10aa-10sa,
which were isolated in 52-88% yield after appropriate
chromatographic workup (see Table 4; details are given in
the Experimental Section). The wide scope of this aqueous
transformation was assessed by using both aliphatic and
aromatic secondary (9b-l; entries 2-12) and tertiary alky-
nols (9m-s; entries 13-19), as well as propargylic alcohol
itself (9a; entry 1). Furthermore, as shown in Figure 4, the
process was not restricted to benzoic acid, since the catalytic
addition of 2-chlorobenzoic acid (2c), pentafluorobenzoic
acid (2j), heptanoic acid (2k), and 3-cyclopentylpropionic
acid (2r) to 1-phenyl-2-propyn-1-ol (9d) also took place,
affording the β-oxo esters 10dc, 10dj, 10dk, and 10dr, respec-
tively, in moderate to good yields (47-90%).
and 4-octyne) using 6a were unsuccessful.35 In all cases, the
starting materials were recovered unchanged ever after pro-
longed heating at 100 °C (24 h) in the presence of 5 mol %
of 6a.
The catalytic addition of carboxylic acids 2 to terminal
propargylic alcohols 9 promoted by ruthenium complexes is
a well-known process that provides a straightforward and
atom-economical route of access to synthetically useful
β-oxo esters 10 (Scheme 5).7a,11k,m,24m,36 The generally
(35) Although rare, ruthenium-catalyzed additions of carboxylic
acids to internal alkynes are known. See, ref 5 and: (a) Rotem, M.;
Shvo, Y. J. Organomet. Chem. 1993, 448, 189. (b) Kabouche, A.;
Kabouche, Z.; Bruneau, C.; Dixneuf, P. H. J. Soc. Alger. Chim. 1999, 9,
In general, the catalytic activity of trans-[RuCl2(η3:η3-
C10H16)(PPh3)] (6a) turned out to be somewhat lower than
that shown by the hydrophilic complex [RuCl2(η6-C6H6)-
(TPPMS)].24m However, it is worth noting that the addition of
benzoic acid to tertiary aromatic alkynols HCtCC(OH)Ar2
(Ar = 4-C6H4F (9m), 4-C6H4Cl (9n)) gave rise to the β-oxo
esters 10ma and 10na as the major reaction products (entries
13 and 14 of Table 4), in contrast with the catalytic activity of
[RuCl2(η6-C6H6)(TPPMS)],24m which resulted in the almost
exclusive formation of the alkene products H2CdCAr2 via
hydrolysis of the highly reactive allenylidene intermediate
[Ru]dCdCdCAr2 generated by dehydration of the alkynol.39
However, we must note that formation of minor amounts of
€
€
ꢁ
141. (c) Karabulut, S.; Ozt€urk, B. O; Imamoglu, Y. J. Organomet. Chem.
2010, 695, 2161. We assume that in our case the greater steric hindrance
between the internal-alkyne substituents and the ancillary triphenylphosphine
ligand prevent the coordination of the CtC bond to the metal center.
(36) (a) Devanne, D.; Ruppin, C.; Dixneuf, P. H. J. Org. Chem. 1988,
53, 925. (b) Bruneau, C.; Kabouche, Z.; Neveux, M.; Seiller, B.; Dixneuf,
P. H. Inorg. Chim. Acta 1994, 222, 154. (c) Darcel, C.; Bruneau, C.; Dixneuf,
P. H.; Neef, G. J. Chem. Soc., Chem. Commun. 1994, 333. (d) Costin, S.;
Rath, N. P.; Bauer, E. B. Adv. Synth. Catal. 2008, 350, 2414. (e) Heitt, N. P.;
Lynam, J. M.; Welby, C. E.; Whitwood, A. C. J. Organomet. Chem. 2011,
696, 378.
(37) Ruthenium-catalyzed anti-Markovnikov additions of car-
boxylic acids to terminal propargylic alcohols are rare: (a) Picquet,
ꢀ
M.; Fernandez, A.; Bruneau, C.; Dixneuf, P. H. Eur. J. Org. Chem. 2000,
2361. (b) Berger, S.; Haak, E. Tetrahedron Lett. 2010, 51, 6630.
(38) One reviewer suggested that an alternative mechanism involving
an initial ruthenium-catalyzed propargylic substitution of the hydroxyl
group of the alkynol by carboxylate, followed by intramolecular attack
of carboxylate CdO to C-2 and hydrolysis, could be operative in these
transformations. This reaction pathway has been discarded, since the
independently synthesized propagylic benzoate HCtCCHPh(O2CPh)
remained unchanged after 12 h of heating in water at 60 °C in the
presence of 6a (2 mol %): Huang, X.; de Haro, T.; Nevado, C. Chem.
Eur. J. 2009, 15, 5904.
(39) For reviews on the chemistry of transition-metal allenylidene
complexes, see: (a) Bruce, M. I. Chem. Rev. 1998, 98, 2797. (b) Cadierno,
V.; Gamasa, M. P.; Gimeno, J. Eur. J. Inorg. Chem. 2001, 571. (c) Cadierno,
V.; Crochet, P.; Gimeno, J. In Metal Vinylidenes and Allenylidenes in
Catalysis: From Reactivity to Applications in Synthesis; Bruneau, C.,
Dixneuf, P. H., Eds.; Wiley-VCH: Weinheim, Germany, 2008; p 61. (d)
Cadierno, V.; Gimeno, J. Chem. Rev. 2009, 109, 3512. (e) Cadierno, V.;
García-Garrido, S. E. Top. Organomet. Chem. 2010, 30, 151.

Article
Organometallics, Vol. 30, No. 4, 2011 859
Table 4. Addition of Carboxylic Acids to Terminal Propargylic Alcohols Catalyzed by the Mononuclear Ruthenium(IV) Complex
trans-[RuCl2(η3:η3-C10H16)(PPh3)] (6a) in Watera
entry
propargylic alcohol 9
time (h)
conversn (%)b
product 10; yield (%)b
1
2
3
4
5
6
7
8
R1 = R2 = H (9a)
24
21
24
24
20
22
15
20
22
22
22
20
24
24
24
7
74
87
99
99
99
97
98
80
99
99
99
99
77
83
88
99
72
80
74
10aa; 74 (67)
10ba; 87 (78)
10ca; 99 (83)
10da; 93 (80)
10ea; 94 (83)
10fa; 94 (81)
10ga; 94 (86)
10ha; 72 (60)
10ia; 87 (79)
10ja; 84 (71)
10ka; 76 (62)
10la; 82 (73)
10ma; 62 (56)
10na; 68 (61)
10oa; 72 (64)
10pa; 99 (88)
10qa; 72 (65)
10ra; 74 (63)
10sa; 65 (52)
R1 = H, R2 = Me (9b)
R1 = H, R2 = Bn (9c)
R1 = H, R2 = Ph (9d)
R1 = H, R2 = 2-C6H4Cl (9e)
R1 = H, R2 = 3-C6H4Cl (9f)
R1 = H, R2 = 4-C6H4Cl (9g)
R1 = H, R2 = 2-C6H4OMe (9h)
R1 = H, R2 = 3-C6H4OMe (9i)
R1 = H, R2 = 4-C6H4OMe (9j)
R1 = H, R2 = 1-Napht (9k)
R1 = H, R2 = 2-Napht (9l)
R1 = R2 = 4-C6H4F (9m)
R1 = R2 = 4-C6H4Cl (9n)
R1 = Me, R2 = Ph (9o)
9
10
11
12
13
14
15
16
17
18
19
R1R2 = -(CH2)4- (9p)
R1R2 = -(CH2)5- (9q)
22
24
24
R1R2 = -(CH2)6- (9r)
R1R2 = -(CH2)7- (9s)
a Reactions performed under an N2 atmosphere at 60 °C using 1 mmol of the corresponding propargylic alcohol, 1 mmol of benzoic acid, 0.02 mmol of
complex 6a, and 1 mL of water. b Yields determined by GC (uncorrected GC areas; isolated yields are given in parenthses). The differences between
conversions and yields correspond to the olefinic side products CH2dCR1R2 present in the reaction media.
using the readily available mononuclear bis(allyl)ruthenium-
(IV) complex trans-[RuCl2(η3:η3-C10H16)(PPh3)] (6a) under
mild thermal conditions (60 °C). This is the first efficient
synthetic protocol of enol esters performed in water as a
green reaction medium.40 The process is based on the selec-
tive Markovnikov addition of both aromatic and aliphatic
carboxylic acids to the alkynes. The synthetic methodology is
also feasible for propargylic alcohols and compares well with
the catalytic activity of [RuCl2(η6-C6H6)(TPPMS)] previously
reported by us.24m
Experimental Section
Reactions were performed under an atmosphere of nitrogen
using vacuum-line and standard Schlenk techniques. All reagents
were obtained from commercial suppliers and used without
further purification with the exception of the compounds [{RuCl-
(μ-Cl)(η3:η3-C10H16)}2] (5),25 trans-[RuCl2(η3:η3-C10H16)(PPh3)]
(6a),29a trans-[RuCl2(η3:η3-C10H16)(TPPMS)] (6b),24o trans-[RuCl2-
Figure 4. Structure of β-oxo esters 10dc, 10dj, 10dk, and 10dr.
(η3:η3-C10H16){P(p-Tol)3}] (6c),24d trans-[RuCl2(η3:η3-C10H16)-
(PPh2Me)] (6d),24d trans-[RuCl2(η3:η3-C10H16)(PPhMe2)] (6e),24d
olefinic side products was observed in many of the reactions
given in Table 4.
trans-[RuCl2(η3:η3-C10H16)(PMe3)] (6f),24d trans-[RuCl2(η3:η3-
C10H16)(PiPr3)] (6g),29h trans-[RuCl2(η3:η3-C10H16){P(OMe)3}]
(6i),29b,d trans-[RuCl2(η3:η3-C10H16){P(OEt)3}] (6j),29g trans-
Conclusion
[RuCl2(η3:η3-C10H16){P(OiPr)3}] (6k),29g trans-[RuCl2(η3:η3-
C10H16){P(OPh)3}] (6l),29f trans-[RuCl2(η3:η3-C10H16)(NCMe)]
In brief, we have reported the catalytic addition of car-
boxylic acids onto terminal alkynes, enynes, and diynes by
(6m),29c trans-[RuCl2(η3:η3-C10H16)(NCPh)] (6n),29g trans-[RuCl2-
(η3:η3-C10H16)(NH2Ph)] (6o),29e trans-[RuCl2(η3:η3-C10H16)-
(py)] (6p),29c trans-[RuCl2(η3:η3-C10H16)(CO)] (6q),29a trans-
[RuCl2(η3:η3-C10H16)(CNBn)] (6r),24q and trans-[RuCl2(η3:η3-
(40) Preliminary studies indicate that more classical areneruthenium(II)
complexes are also operative catalysts for this transformation in
aqueous media. As an example, under the same reaction conditions
C10H16)(CNCy)] (6s),24q which were prepared by following the
methods reported in the literature. Flash chromatography was
employed in this work, the complex [RuCl2(η6-p-cymene)(PPh3)] (2mol%)
performed using Merck silica gel 60 (230-400 mesh). Infrared
is able to generate the enol ester 3aa, by selective Markovnikov addition of
spectra were recorded on a Perkin-Elmer 1720-XFT spectrom-
benzoic acid (2a) to 1-hexyne (1a), in 94% GC yield after 4 h of heating (to
be compared with entry 1 in Table 1). Full details will be presented in due
course.
eter. The C, H, and N analyses were carried out with a Perkin-
Elmer 2400 microanalyzer. GC (FID detection) measurements

860 Organometallics, Vol. 30, No. 4, 2011
Cadierno et al.
were made on Hewlett-Packard HP6890 equipment using a Su-
pelco Beta-Dex column (30 m length; 250 μm diameter). GC/
MSD measurements were performed on Agilent 6890N equip-
ment coupled to a 5973 mass detector (70 eV electron impact
ionization) using a HP-1MS column. NMR spectra were re-
corded on a Bruker DPX300 instrument at 300 MHz (1H), 121.5
MHz (31P), or 75.4 MHz (13C) using SiMe4 or 85% H3PO4 as
standard. DEPT experiments have been carried out for all the
compounds reported in this paper. The numbering for protons
and carbons of the 2,7-dimethylocta-2,6-diene-1,8-diyl skeleton
is as follows:
mixture was stirred at 60 °C for the time indicated in Table 3.
The course of the reaction was monitored by regular sampling
and analysis by GC (FID detection). After elimination of the
solvent under reduced pressure, chromatographic workup of the
crude reaction mixtures over silica gel, using an ethyl acetate-
hexane mixture (1/100 v/v) as eluent, provided pure samples of
enol esters 3aa-3pa. The identities of known compounds were
1
assessed by comparison of their H and 13C{1H} NMR data
with those previously described in the literature5,7-9,11 and by
their fragmentation in GC/MS. Characterization data for the
novel enol esters synthesized in this work are as follows.
1-Hexen-2-yl 2-Fluorobenzoate (3ab). Orange oil. Yield: 80%
(0.177 g). IR (neat, cm-1): ν 1664 (m, CdC), 1740 (s, CdO). 1H
NMR (CDCl3): δ 0.90 (t, 3H, 3JHH = 7.1 Hz, CH3), 1.36 and
1.52 (m, 2H each, CH2), 2.33 (t, 2H, 3JHH = 7.4 Hz, CH2), 4.82
2
and 4.87 (d, 1H each, JHH = 1.3 Hz, dCH2), 7.18 (m, 2H,
CHarom), 7.52 and 7.97 (m, 1H each, CHarom) ppm. 13C{1H}
NMR (CDCl3): δ 13.8 (s, CH3), 21.9, 28.5, and 33.0 (s, CH2),
101.4 (s, dCH2), 117.0 (d, JCF = 22.2 Hz, CHarom), 118.2
2
2
3
(d, JCF = 9.5 Hz, Carom), 123.9 (d, JCF = 3.8 Hz, CHarom),
3
132.2 (s, CHarom), 134.8 (d, JCF = 8.9 Hz, CHarom), 156.5
1
(s, dC), 162.0 (d, JCF = 260.7 Hz, Carom), 162.3 (d, JCF
3
=
3.5 Hz, CdO) ppm. MS (EI 70 eV): m/z 222 (Mþ, 1%), 165 (2),
123 (100), 95 (20).
1-Hexen-2-yl 2-Chlorobenzoate (3ac). Yellow solid. Yield:
Synthesis of trans-[RuCl2(η3:η3-C10H16)(PBn3)] (6h). Triben-
zylphosphine (0.609 g; 2 mmol) was added, at room tempera-
ture, to a solution of [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (5) (0.616 g;
1 mmol) in 20 mL of dichloromethane. After the mixture was
stirred for 10 min, the solvent was removed under vacuum and
the resulting yellow solid residue washed with hexanes (3 ꢀ 10
mL) and dried in vacuo. Yield: 84% (1.029 g). Anal. Calcd for
RuC31H37Cl2P: C, 60.78; H, 6.09. Found: C, 60.89; H, 6.13. IR
(KBr, cm-1): ν 480 (w), 706 (s), 723 (m), 764 (m), 786 (m), 842 (s),
919 (w), 1029 (w), 1070 (w), 1238 (w), 1383 (m), 1450 (s), 1494 (s),
1600 (m), 2854 (w), 2917 (m), 2970 (w), 2998 (w), 3057 (w).
85% (0.203 g). IR (Nujol, cm-1): ν 1666 (m, CdC), 1744
1
3
(s, CdO). H NMR (CDCl3): δ 0.91 (t, 3H, JHH = 7.1 Hz,
CH3), 1.37 and 1.52 (m, 2H each, CH2), 2.35 (t, 2H, JHH =
7.1 Hz, CH2), 4.83 and 4.88 (s, 1H each, dCH2), 7.32 (m, 1H,
3
3
CHarom), 7.43 (m, 2H, CHarom), 7.87 (d, 1H, JHH = 7.7 Hz,
CHarom) ppm. 13C{1H} NMR (CDCl3): δ 13.8 (s, CH3), 22.0,
28.5, and 32.9 (s, CH2), 101.5 (s, dCH2), 126.6, 131.1, 131.5, and
132.8 (s, CHarom), 129.6 and 133.9 (s, Carom), 156.6 (s, dC),
163.7 (s, CdO) ppm. MS (EI 70 eV): m/z 238 (Mþ, 1%), 139
(100), 111 (20), 75 (10).
1
31P{1H} NMR (C6D6): δ 10.3 (s) ppm. H NMR (CD2Cl2): δ
2.28 (s, 6H, CH3), 2.31 (m, 2H, H4 and H6), 3.23 (m, 2H, H5 and
H7), 3.50 (d, 2H, 3JHP = 3.5 Hz, H2 and H10), 3.67 (d, 6H, 2JHP
=
1-Hexen-2-yl 3-Chlorobenzoate (3ad). Yellow oil. Yield: 90%
(0.214 g). IR (neat, cm-1): ν 1667 (m, CdC), 1737 (s, CdO). 1H
NMR (CDCl3): δ 0.90 (m, 3H, CH3), 1.35 and 1.47 (m, 2H each,
8.7 Hz, PCH2), 4.54 (d, 2H, 3JHP = 9.3 Hz, H1 and H9), 5.43 (m,
2H, H3 and H8), 7.11 (m, 15H, Ph) ppm. 13C{1H} NMR (C6D6):
δ 20.2 (s, CH3), 32.3 (d, 1JCP = 20.0 Hz, PCH2), 36.1 (s, C4 and
C5), 64.0 (d, 2JCP = 5.9 Hz, C1 and C8), 107.1 (d, 2JCP = 9.6 Hz,
C3 and C6), 122.9 (s, C2 and C7), 126.4, 128.5, and 130.8 (s, CH of
Ph), 135.6 (d, 2JCP = 16.8 Hz, C of Ph) ppm.
3
CH2), 2.32 (t, 2H, JHH = 7.4 Hz, CH2), 4.83 and 4.85 (s, 1H
each, dCH2), 7.38, 7.52, and 7.94 (m, 1H each, CHarom), 8.03
(d, 1H, 4JHH = 1.4 Hz, CHarom) ppm. 13C{1H} NMR (CDCl3):
δ 13.8 (s, CH3), 22.0, 28.5, and 32.9 (s, CH2), 101.4 (s, dCH2),
127.9, 129.7, 129.8, and 133.2 (s, CHarom), 131.5 and 134.5
(s, Carom), 156.5 (s, dC), 163.4 (s, CdO) ppm. MS (EI 70 eV):
m/z 238 (Mþ, 1%), 139 (100), 111 (25), 75 (10).
Synthesis of [RuCl{K2(O,O)-O2CPh)}(η3:η3-C10H16)]. Sodium
benzoate (0.050 g; 0.324 mmol) was added, at room temperature,
to a solution of [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (5) (0.100 g; 0.162
mmol) in 10 mL of acetone. After the mixture was stirred for 24 h,
the solvent was removed under vacuum, the resulting purple solid
residue was extracted with dichloromethane (ca. 20 mL), and the
extract was filtered over Kieselguhr. Concentration of the resulting
solution (ca. 2 mL) followed by the addition of hexanes (ca. 30 mL)
precipitated a purple solid, which was washed with hexanes (5 ꢀ 5
mL) and vacuum-dried. Yield: 72% (0.092 g). Anal. Calcd for
RuC17H21O2Cl: C, 51.84; H, 5.37. Found: C, 51.98; H, 5.46. IR
(KBr, cm-1): ν 482 (w), 686 (m), 715 (m), 801 (m), 841 (w), 863 (s),
936 (w), 1023 (s), 1096 (m), 1261 (m), 1420 (s), 1444 (s), 1491 (m),
1507 (m), 1601 (m), 2854 (w), 2920 (m), 2962 (w). 1H NMR
(C6D6): δ 1.78 and 2.12 (s, 3H each, CH3), 2.00 (m, 4H, H4, H5, H6
and H7), 3.37 and 4.33 (m, 1H each, H3 and H8), 3.57 and 4.50 (s,
1H each, H2 and H10), 4.88 and 5.65 (s, 1H each, H1 and H9), 7.03
(m, 3H, Ph), 8.89 (d, 2H, 3JHH = 7.6 Hz, Ph) ppm. 13C{1H} NMR
(C6D6): δ 18.1 and 18.6 (s, CH3), 31.5 and 33.4 (s, C4 and C5), 85.6
and 85.9 (s, C1 and C8), 91.7 and 93.0 (s, C3 and C6), 118.0 and
123.7 (s, C2 and C7), 129.5 and 134.1 (s, CH of Ph), 132.2 (s, C of
Ph), 182.7 (s, O2CPh) ppm.
1-Hexen-2-yl 3-Bromobenzoate (3ae). Yellow oil. Yield: 83%
(0.235 g). IR (neat, cm-1): ν 1667 (m, CdC), 1732 (s, CdO).
1H NMR (CDCl3): δ 0.91 (t, 3H, 3JHH = 7.4 Hz, CH3), 1.36 and
1.50 (m, 2H each, CH2), 2.32 (t, 2H, 3JHH = 7.4 Hz, CH2), 4.84
and 4.85 (s, 1H each, dCH2), 7.33, 7.68, and 7.71 (m, 1H each,
4
CHarom), 8.20 (d, 1H, JHH = 2.0 Hz, CHarom) ppm. 13C{1H}
NMR (CDCl3): δ 13.7 (s, CH3), 22.0, 28.5, and 33.0 (s, CH2),
101.4 (s, dCH2), 122.5 and 131.8 (s, Carom), 128.4, 129.9, 132.8,
and 136.1 (s, CHarom), 156.6 (s, dC), 163.3 (s, CdO) ppm. MS
(EI 70 eV): m/z 284 (Mþ, 1%), 183 (100), 155 (25), 76 (20).
1-Hexen-2-yl 3-Methoxybenzoate (3af). Orange oil. Yield:
81% (0.190 g). IR (neat, cm-1): ν 1666 (m, CdC), 1732 (s, CdO).
1H NMR (CDCl3): δ 0.91 (t, 3H, 3JHH = 7.3 Hz, CH3), 1.37 and
1.52 (m, 2H each, CH2), 2.34 (t, 2H, 3JHH = 7.4 Hz, CH2), 3.85
(s, 3H, OCH3), 4.83 and 4.85 (s, 1H each, dCH2), 7.12 and 7.67
(d, 1H each, 3JHH = 7.5 Hz, CHarom), 7.36 (dd, 1H, 3JHH = 7.5
and 7.5 Hz, CHarom), 7.59 (s, 1H, CHarom) ppm. 13C{1H} NMR
(CDCl3): δ 13.8 (s, CH3), 22.1, 28.7, and 33.1 (s, CH2), 55.4 (s,
OCH3), 101.3 (s, dCH2), 114.3, 119.8, 122.3, and 129.5 (s,
CHarom), 131.2 and 159.6 (s, Carom), 156.8 (s, dC), 164.6 (s,
CdO) ppm. MS (EI 70 eV): m/z 234 (Mþ, 5%), 178 (5), 135
(100), 107 (20), 92 (10), 77 (10).
General Procedure for the Addition of Carboxylic Acids to
Terminal Alkynes Catalyzed by trans-[RuCl2(η3:η3-C10H16)-
(PPh3)] (6a). Under a nitrogen atmosphere, water (1 mL), the
corresponding terminal alkyne (1 mmol) and carboxylic acid
(1 mmol), and the ruthenium catalyst 6a (11 mg, 0.02 mmol)
were introduced into a sealed tube and the resulting reaction
1-Hexen-2-yl 4-Cyanobenzoate (3ah). Yellow oil. Yield: 87%
(0.199 g). IR (neat, cm-1): ν 1667 (m, CdC), 1738 (s, CdO), 2232
(m, CtN). 1HNMR(CDCl3):δ0.89 (t, 3H, 3JHH =7.4Hz, CH3),

Article
Organometallics, Vol. 30, No. 4, 2011 861
1.32-1.49 (m, 4H, CH2), 2.32 (t, 2H, 3JHH = 7.1 Hz, CH2), 4.85
1-Decen-2-yl Benzoate (3da). Yellow oil. Yield: 83% (0.216 g).
3
1
(s, 2H, dCH2), 7.76 and 8.17 (d, 2H each, JHH = 8.5 Hz,
IR (neat, cm-1): ν 1667 (m, CdC), 1733 (s, CdO). H NMR
CHarom) ppm. 13C{1H} NMR (CDCl3): δ 13.7 (s, CH3), 22.0,
28.5, and 32.9 (s, CH2), 101.7 (s, dCH2), 116.6 and 117.8
(s, CtN and Carom), 130.3 and 132.2 (s, CHarom), 133.6
(s, Carom), 156.4 (s, dC), 163.0 (s, CdO) ppm. MS (EI 70 eV):
m/z 229 (Mþ, 10%), 172 (5), 130 (100), 102 (30), 83 (10).
1-Hexen-2-yl 4-Vinylbenzoate (3ai). Orange solid. Yield: 85%
(0.195 g). IR (Nujol, cm-1): ν 1630 and 1666 (m, CdC), 1731 (s,
CdO). 1H NMR (CDCl3): δ 0.92 (t, 3H, 3JHH = 7.1 Hz, CH3),
1.39 and 1.50 (m, 2H each, CH2), 2.34 (t, 2H, 3JHH = 7.1 Hz,
(CDCl3): δ 0.87 (br, 3H, CH3), 1.27-1.54 (m, 14H, CH2), 2.34
(t, 2H, 3JHH = 7.1 Hz, CH2), 4.84 and 4.86 (s, 1H each, dCH2),
3
7.44-7.59 (m, 3H, CHarom), 8.09 (d, 2H, JHH = 7.4 Hz,
CHarom) ppm. 13C{1H} NMR (CDCl3): δ 14.0 (s, CH3), 22.6,
26.5, 28.9, 29.1, 29.3, 31.7, and 33.4 (s, CH2), 101.2 (s, dCH2),
128.4, 129.8, and 133.2 (s, CHarom), 156.8 (s, dC), 164.7 (s,
CdO) ppm; Carom not observed. MS (EI 70 eV): m/z 260 (Mþ,
1%), 105 (100), 77 (20).
1-Dodecen-2-yl Benzoate (3ea). Yellow oil. Yield: 86% (0.248 g).
IR (neat, cm-1): ν 1666 (m, CdC), 1733 (s, CdO). H NMR
1
CH2), 4.83 and 4.86 (s, 1H each, dCH2), 5.40 (d, 1H, 3JHH
=
11.1 Hz, CHdCH2), 5.87 (d, 1H, 3JHH = 17.6 Hz, CHdCH2),
3
(CDCl3): δ 0.88 (t, 3H, JHH = 6.2 Hz, CH3), 1.26 (m, 14H,
3
CH2), 1.52 (m, 2H, CH2), 2.35 (t, 2H, 3JHH = 7.4 Hz, CH2), 4.84
and 4.86 (s, 1H each, dCH2), 7.44-7.58 (m, 3H, CHarom), 8.08
(d, 2H, 3JHH = 8.4 Hz, CHarom) ppm. 13C{1H} NMR (CDCl3):
δ 14.0 (s, CH3), 22.6, 26.5, 29.0, 29.2, 29.3, 29.5 (2C), 31.8 and
33.4 (s, CH2), 101.2 (s, dCH2), 128.4, 129.8, and 133.2 (s, CHarom),
156.8 (s, dC), 164.6 (s, CdO) ppm; Carom not observed. MS
(EI 70 eV): m/z 288 (Mþ, 1%), 105 (100), 77 (15).
6.75 (dd, 1H, JHH = 17.6 and 11.1 Hz, CHdCH2), 7.48 and
8.04 (d, 2H each, 3JHH = 8.5 Hz, CHarom) ppm. 13C{1H} NMR
(CDCl3): δ 13.8 (s, CH3), 22.0, 28.6, and 33.1 (s, CH2), 101.2
(s, dCH2), 116.6 (s, CHdCH2), 126.1 and 130.2 (s, CHarom),
128.9 and 142.2 (s, Carom), 135.9 (s, CHdCH2), 156.7 (s, dC),
164.4 (s, CdO) ppm. MS (EI 70 eV): m/z 230 (Mþ, 5%), 131
(100), 103 (20), 77 (15).
1-Hexen-2-yl Pentafluorobenzoate (3aj). Orange oil. Yield:
70% (0.206 g). IR (neat, cm-1): ν 1670 (m, CdC), 1753 (s,
CdO). 1H NMR (CDCl3): δ 0.91 (t, 3H, 3JHH = 7.1 Hz, CH3),
1.37 and 1.50 (m, 2H each, CH2), 2.32 (t, 2H, 3JHH = 7.1 Hz,
CH2), 4.87 and 4.91 (br, 1H each, dCH2) ppm. 13C{1H} NMR
(CDCl3): δ 13.6 (s, CH3), 21.9, 28.2, and 32.7 (s, CH2), 102.0
(s, dCH2), 116.9 (s, Carom), 133.4 (s, dC), 135.9-147.0
(m, CFarom), 156.2 (s, CdO) ppm. MS (EI 70 eV): m/z 294
(Mþ, 1%), 276 (5), 224 (5), 195 (100), 167 (20), 117 (10).
1-Hexen-2-yl Heptanoate (3ak). Yellow oil. Yield: 80% (0.170 g).
4-Methyl-1-penten-2-yl Benzoate (3fa). Yellow oil. Yield: 78%
(0.159 g). IR (neat, cm-1): ν 1666 (m, CdC), 1732 (s, CdO). 1H
3
NMR (CDCl3): δ 0.97 (d, 6H, JHH = 6.8 Hz, CH3), 1.85
(m, 1H, CH), 2.23 (d, 2H, 3JHH = 7.1 Hz, CH2), 4.83 and 4.90
(s, 1H each, dCH2), 7.44-7.59 (m, 3H, CHarom), 8.07 (d, 2H,
3JHH = 7.7 Hz, CHarom) ppm. 13C{1H} NMR (CDCl3): δ 22.2
(s, CH3), 25.8 (s, CH), 42.8 (s, CH2), 102.5 (s, dCH2), 128.4,
129.8, and 133.2 (s, CHarom), 155.5 (s, dC), 164.6 (s, CdO) ppm;
Carom not observed. MS (EI 70 eV): m/z 204 (Mþ, 1%), 105
(100), 77 (30).
1
IR (neat, cm-1): ν 1665 (m, CdC), 1755 (s, CdO). H NMR
3-Cyclohexyl-1-propen-2-yl Benzoate (3ga). Yellow oil. Yield:
85% (0.207 g). IR (neat, cm-1): ν 1666 (m, CdC), 1734 (s,
3
(CDCl3): δ 0.85 and 0.87 (t, 3H each, JHH = 7.1 Hz, CH3),
=
1.28-1.46 (m, 10H, CH2), 1.60 (m, 2H, CH2), 2.17 (t, 2H, 3JHH
1
CdO). H NMR (CDCl3): δ 0.94 (m, 2H, CH2), 1.21 (m, 3H,
3
6.9 Hz, CH2), 2.35 (t, 2H, JHH = 7.7 Hz, CH2), 4.66 and 4.68
(d, 1Heach, 2JHH =1.3Hz, dCH2) ppm. 13C{1H} NMR (CDCl3):
δ 13.7 and 13.8 (s, CH3), 21.9, 22.3, 24.8, 28.5, 28.6, 31.3, 32.9, and
34.3 (s, CH2), 100.8 (s, dCH2), 156.5 (s, dC), 171.9 (s, CdO) ppm.
MS (EI 70 eV): m/z 212 (Mþ, 1%), 142 (5), 113 (100), 85 (40), 55
(20), 43 (60).
CH2), 1.52 (m, 1H, CH), 1.65-1.85 (m, 5H, CH2), 2.26 (d, 2H,
3JHH = 7.1 Hz, CH2), 4.82 and 4.92 (s, 1H each, dCH2),
3
7.45-7.60 (m, 3H, CHarom), 8.10 (d, 2H, JHH = 7.6 Hz,
CHarom) ppm. 13C{1H} NMR (CDCl3): δ 26.2, 26.4, 33.0, and
41.5 (s, CH2), 35.3 (s, CH), 102.5 (s, dCH2), 128.5, 129.9, and
133.2 (s, CHarom), 130.0 (s, Carom), 155.2 (s, dC), 164.6 (s, CdO)
ppm. MS (EI 70 eV): m/z 244 (Mþ, 1%), 187 (10), 105 (100), 77
(30).
1-Hexen-2-yl Octanoate (3al). Yellow oil. Yield: 84% (0.190 g).
1
IR (neat, cm-1): ν 1665 (m, CdC), 1757 (s, CdO). H NMR
3
(CDCl3): δ 0.86 and 0.88 (t, 3H each, JHH = 7.1 Hz, CH3),
=
3-Cyclopentyl-1-propen-2-yl Benzoate (3ha). Yellow oil. Yield:
85% (0.196 g). IR (neat, cm-1): ν 1664 (m, CdC), 1732 (s, CdO).
1H NMR (CDCl3): δ 1.20 and 1.80 (m, 2H each, CH2), 1.55 (m,
4H, CH2), 2.05 (m, 1H, CH), 2.34 (d, 2H, 3JHH = 7.1 Hz, CH2),
4.84 and 4.87 (s, 1H each, dCH2), 7.42-7.59 (m, 3H, CHarom),
1.26-1.48 (m, 12H, CH2), 1.65 (m, 2H, CH2), 2.18 (t, 2H, 3JHH
3
7.7 Hz, CH2), 2.36 (t, 2H, JHH = 7.3 Hz, CH2), 4.67 and 4.69
(s, 1H each, dCH2) ppm. 13C{1H} NMR (CDCl3): δ 13.7 and 13.9
(s, CH3), 22.0, 22.5, 24.9, 28.5, 28.8, 28.9, 31.5, 32.9, and 34.3
(s, CH2), 100.8 (s, dCH2), 156.5 (s, dC), 171.9 (s, CdO) ppm. MS
(EI 70 eV): m/z 226 (Mþ, 1%), 142 (5), 127 (90), 109 (10), 98 (10),
57 (100), 43 (40).
3
8.09 (d, 2H, JHH = 8.3 Hz, CHarom) ppm. 13C{1H} NMR
(CDCl3): δ 25.0, 32.3, and 39.7 (s, CH2), 37.2 (s, CH), 101.9
(s, dCH2), 128.4, 129.8, and 133.2 (s, CHarom), 156.3 (s, dC), 164.6
(s, CdO) ppm; Carom not observed. MS (EI 70 eV): m/z 230 (Mþ,
1%), 173 (5), 105 (100), 77 (20).
1-Hexen-2-yl Cyclohexylacetate (3am). Orange oil. Yield: 72%
(0.161 g). IR (neat, cm-1): ν 1665 (m, CdC), 1755 (s, CdO). 1H
NMR (CDCl3): δ 0.87 (t, 3H, 3JHH = 7.3 Hz, CH3), 1.08 (m, 2H,
1-Cyclohexylvinyl Benzoate (3la). Yellow oil. Yield: 88%
(0.203 g). IR (neat, cm-1): ν 1660 (m, CdC), 1732 (s, CdO).
1H NMR (CDCl3): δ 1.24 (br, 6H, CH2), 1.69-1.96 (m, 4H,
CH2), 2.44 (br, 1H, CH), 4.83 (br, 2H, dCH2), 7.43-7.58 (m, 3H,
3
CH2), 1.27-1.74 (m, 13H, CH2 and CH), 2.16 (t, 2H, JHH
=
3
6.9 Hz, CH2), 2.36 (t, 2H, JHH = 7.5 Hz, CH2), 4.65 and 4.66
(s, 1H each, dCH2) ppm. 13C{1H} NMR (CDCl3): δ 13.7 (s, CH3),
21.9, 25.0, 28.5, 31.0, 32.3, 32.9, and 33.6 (s, CH2), 39.5 (s, CH),
100.7 (s, dCH2), 156.5 (s, dC), 171.9 (s, CdO) ppm. MS (EI
70 eV): m/z 226 (Mþ, 1%), 142 (10), 125 (100), 107 (100), 97 (20),
79 (50), 69 (20), 55 (90).
3
CHarom), 8.10 (d, 2H, JHH = 7.4 Hz, CHarom) ppm. 13C{1H}
NMR (CDCl3): δ 25.9, 26.0, and 30.6 (s, CH2), 41.7 (s, CH), 99.6
(s, dCH2), 128.4, 129.9, and 133.2 (s, CHarom), 160.6 (s, dC),
164.8 (s, CdO) ppm; Carom not observed. MS (EI 70 eV): m/z 230
(Mþ, 1%), 105 (100), 77 (20).
1-Hexen-2-yl (E)-3-Phenylacrylate (3ap). Yellow oil. Yield:
80% (0.184 g). IR (neat, cm-1): ν 1636 and 1666 (m, CdC), 1732
1-Cyclohexenylvinyl Benzoate (3pa). Yellow oil. Yield: 87%
(0.198 g). IR (neat, cm-1): ν 1626 and 1651 (m, CdC), 1740
(s, CdO). 1H NMR (CDCl3): δ 1.59, 1.73, 2.10, and 2.26 (m, 2H
each, CH2), 4.84 and 5.08 (d, 1H each, 2JHH = 1.0 Hz, dCH2),
5.99 (br, 1H, dCH), 7.45-7.60 (m, 3H, CHarom), 8.15 (m, 2H,
CHarom) ppm. 13C{1H} NMR (CDCl3): δ 21.7, 22.2, 24.6, and
25.2 (s, CH2), 100.1 (s, dCH2), 125.9 (s, dCH), 128.5, 129.9, and
133.3 (s, CHarom), 129.6 and 130.2 (s, CdCH and Carom), 153.9
(s, dC), 164.8 (s, CdO) ppm. MS (EI 70 eV): m/z 228 (Mþ,
10%), 210 (5), 105 (100), 77 (30).
1
3
(s, CdO). H NMR (CDCl3): δ 0.94 (t, 3H, JHH = 7.2 Hz,
CH3), 1.39 and 1.51 (m, 2H each, CH2), 2.31 (t, 2H, JHH =
3
7.2 Hz, CH2), 4.80 and 4.83 (s, 1H each, dCH2), 6.50 and 7.76
(d, 1H each, 3JHH = 16.0 Hz, dCH), 7.40 (br, 3H, CHarom), 7.55
(br, 2H, CHarom) ppm. 13C{1H} NMR (CDCl3): δ 13.9 (s, CH3),
22.2, 28.7, and 33.2 (s, CH2), 101.1 (s, dCH2), 117.7 and 145.9
(s, dCH), 128.1, 128.9, and 130.5 (s, CHarom), 134.2 (s, Carom),
156.7 (s, dC), 165.1 (s, CdO) ppm. MS (EI 70 eV): m/z 202
(Mþ - Et, 5%), 131 (100), 103 (30), 77 (20).

862 Organometallics, Vol. 30, No. 4, 2011
Cadierno et al.
Catalytic Synthesis of Dienol Diesters 7aa-7ca. Under a
nitrogen atmosphere, water (1 mL), the corresponding diyne
(1 mmol), benzoic acid (0.244 g, 2 mmol), and the ruthenium
catalyst 6a (11 mg, 0.02 mmol) were introduced into a sealed
tube and the resulting reaction mixture was stirred at 60 °C for
10 h. After elimination of the solvent under reduced pressure,
chromatographic workup of the crude reaction mixtures over
silica gel, using an ethyl acetate-hexane mixture (1/100 v/v) as
eluent, provided pure samples of dienol diesters 7aa-7ca in
83-89% yield. The identity of 7aa and 7ba was assessed by
comparison of their 1H and 13C{1H} NMR data with those
previously described in the literature11k,41 and by their fragmen-
tation in GC/MS. Characterization data for the novel dienol
diester 7ca are as follows. Yellow oil. Yield: 86% (0.313 g). IR
and 133.3 (s, CHarom), 156.4 (s, dC), 164.7 (s, CdO) ppm; Carom
not observed. MS (EI 70 eV): m/z 242 (Mþ, 1%), 120 (5), 105
(100), 77 (20).
General Procedure for the Addition of Carboxylic Acids to
Terminal Propargylic Alcohols Catalyzed by trans-[RuCl2(η3:η3-
C10H16)(PPh3)] (6a). Under a nitrogen atmosphere, water
(1 mL), the corresponding propargylic alcohol (1 mmol) and
carboxylic acid (1 mmol), and the ruthenium catalyst 6a (11 mg,
0.02 mmol) were introduced into a sealed tube and the resulting
reaction mixture was stirred at 60 °C for the time indicated in
Table 4 and Figure 3. The course of the reaction was monitored
by regular sampling and analysis by GC (FID detection). After
elimination of the solvent under reduced pressure, chromato-
graphic workup of the crude reaction mixtures over silica gel,
using an ethyl acetate-hexane mixture (1/10 v/v) as eluent,
provided pure samples of the β-oxo-esters 10aa-10dr. The
identity of known compounds was assessed by comparison of
their 1H and 13C{1H} NMR data with those previously described
in the literature24m,36a,36d,42 and by their fragmentation in GC/
MS. Characterization data for the novel β-oxo esters synthe-
sized in this work are as follows.
(neat, cm-1): ν 1667 (m, CdC), 1732 (s, CdO). 1H NMR
3
(CDCl3): δ 1.45-1.61 (m, 6H, CH2), 2.35 (t, 4H, JHH
=
7.1 Hz, CH2), 4.83 and 4.87 (d, 2H each, 2JHH = 1.4 Hz, dCH2),
7.43-7.61 (m, 6H, CHarom), 8.07 (m, 4H, CHarom) ppm.
13C{1H} NMR (CDCl3): δ 26.2, 28.3, and 33.3 (s, CH2), 100.5
(s, dCH2), 128.4, 129.8, and 133.2 (s, CHarom), 156.4 (s, dC),
164.7 (s, CdO) ppm; Carom not observed. MS (EI 70 eV): m/z 259
(Mþ - PhCO, 5%), 120 (5), 105 (100), 77 (20).
1,1-Bis(4-fluorophenyl)-2-oxopropyl Benzoate (10ma). Yellow
oil. Yield: 56% (0.205 g). IR (neat, cm-1):ν1716 (s, CdO). 1HNMR
(CDCl3): δ 2.18 (s, 3H, CH3), 7.06 (m, 4H, CHarom), 7.51-7.66
Catalytic Synthesis of Enol Esters 8aa-8ca. Under a nitrogen
atmosphere, water (1 mL), the corresponding diyne (1.3 mmol),
benzoic acid (0.122 g, 1 mmol), and the ruthenium catalyst 6a
(11 mg, 0.02 mmol) were introduced into a sealed tube and the
resulting reaction mixture was stirred at 60 °C for 6 h. After
elimination of the solvent under reduced pressure, chromato-
graphic workup of the crude reaction mixtures over silica gel,
using an ethyl acetate-hexane mixture (1/100 v/v) as eluent,
provided pure samples of the novel enol esters 8aa-8ca. Char-
acterization data are as follows.
1-Hepten-6-yn-2-yl Benzoate (8aa). Yellow oil. Yield: 59%
(0.126 g). IR (neat, cm-1): ν 1667 (m, CdC), 1733 (s, CdO),
2118 (w, CtC), 3302 (m, tCH). 1H NMR (CDCl3): δ 1.77, 2.27,
and 2.48 (m, 2H each, CH2), 1.97 (br, 1H, tCH), 4.88 and 4.91
(s, 1H each, dCH2), 7.44-7.61 (m, 3H, CHarom), 8.08 (d, 2H,
3JHH = 8.1 Hz, CHarom) ppm. 13C{1H} NMR (CDCl3): δ 17.6,
25.3, and 32.3 (s, CH2), 68.9 (s, tCH), 83.5 (s, tC), 102.2
(s, dCH2), 128.4, 129.9, and 133.3 (s, CHarom), 155.4 (s, dC), 164.6
(s, CdO) ppm; Carom not observed. MS (EI 70 eV): m/z 214
(Mþ, 1%), 105 (100), 77 (30).
3
(m, 7H, CHarom), 8.16 (d, 2H, JHH = 7.2 Hz, CHarom) ppm.
13C{1H} NMR (CDCl3): δ 25.0 (s, CH3), 89.4 (s, C), 115.6
(d, 3JCF = 21.9 Hz, CHarom), 129.2, 130.4, and 134.4 (s, CHarom),
129.7 (s, Carom), 130.7 (d, JCF = 8.7 Hz, CHarom), 135.1 (br,
2
C
arom), 162.9 (d, 1JCF = 248.5 Hz, CHarom), 165.6 (s, OCdO),
202.4 (s, CdO) ppm. MS (EI 70 eV): m/z 323 (Mþ - COMe,
1%), 201 (10), 123 (10), 105 (40), 77 (50), 43 (100).
1,1-Bis(4-chlorophenyl)-2-oxopropyl Benzoate (10na). Yellow
oil. Yield: 61% (0.243 g). IR (neat, cm-1): ν 1714 (s, CdO).
1H NMR (CDCl3): δ 2.16 (s, 3H, CH3), 7.33 (m, 4H, CHarom),
3
7.51-7.67 (m, 7H, CHarom), 8.13 (d, 2H, JHH = 8.5 Hz,
CHarom) ppm. 13C{1H} NMR (CDCl3): δ 24.7 (s, CH3), 88.7
(s, C), 128.4, 128.7, 129.6, 129.8, and 133.9 (s, CHarom), 129.1,
134.5, and 137.2 (s, Carom), 165.0 (s, OCdO), 201.5 (s, CdO)
ppm. MS (EI 70 eV): m/z 355 (Mþ - COMe, 5%), 199 (5), 139
(10), 105 (100), 77 (20).
1-Acetylcyclooctyl Benzoate (10sa). Colorless oil. Yield: 52%
(0.143 g). IR (neat, cm-1): ν 1716 (s, CdO). 1H NMR (CDCl3): δ
1.58-1.63 (m, 10H, CH2), 2.11-2.31 (m, 4H, CH2), 2.12 (s, 3H,
CH3), 7.44-7.62 (m, 3H, CHarom), 8.06 (m, 2H, CHarom) ppm.
13C{1H} NMR (CDCl3): δ 21.3, 24.8, 27.7, and 29.3 (s, CH2),
23.6 (s, CH3), 89.2 (s, C), 128.4, 129.7, and 133.3 (s, CHarom),
165.5 (s, OCdO), 206.9 (s, CdO) ppm; Carom not observed. MS
(EI 70 eV): m/z 231 (Mþ - COMe, 19%), 105 (100), 77 (30).
1-Octen-7-yn-2-yl Benzoate (8ba). Yellow oil. Yield: 63%
(0.144 g). IR (neat, cm-1): ν 1666 (m, CdC), 1732 (s, CdO),
2117 (w, CtC), 3301 (m, tCH). 1H NMR (CDCl3): δ 1.63 (m,
4H, CH2), 1.94 (t, 1H, 4JHH = 2.6 Hz, tCH), 2.20 and 2.37 (m,
2H each, CH2), 4.86 and 4.88 (s, 1H each, dCH2), 7.44-7.61 (m,
3
3H, CHarom), 8.07 (d, 2H, JHH = 8.5 Hz, CHarom) ppm.
13C{1H} NMR (CDCl3): δ 18.1, 25.4, 27.6, and 32.8 (s, CH2),
68.5 (s, tCH), 84.0 (s, tC), 101.7 (s, dCH2), 128.4, 129.9, and
133.3 (s, CHarom), 129.7 (s, Carom), 156.1 (s, dC), 164.7 (s, CdO)
ppm. MS (EI 70 eV): m/z 228 (Mþ, 1%), 105 (100), 77 (20).
1-Nonen-8-yn-2-yl Benzoate (8ca). Yellow oil. Yield: 70%
(0.169 g). IR (neat, cm-1): ν 1662 (m, CdC), 1730 (s, CdO),
2116 (w, CtC), 3303 (m, tCH). 1H NMR (CDCl3): δ 1.53 (m,
6H, CH2), 1.93 (t, 1H, 4JHH = 2.5 Hz, tCH), 2.18 and 2.35 (m,
2H each, CH2), 4.84 and 4.86 (s, 1H each, dCH2), 7.44-7.61 (m,
Acknowledgment. Financial support from the Spanish
MICINN (Projects CTQ2006-08485/BQU, CTQ2010-
14796/BQU, and CSD2007-00006) and the Gobierno del
Principado de Asturias (FICYT Project IB08-036) is acknowl-
edged. J.F. thanks the MICINN and the European Social
Fund for the award of a Ph.D. grant.
Supporting Information Available: Figures giving the 1H and
13C{1H} NMR spectra of all new enol esters and β-oxo esters
synthesized in this work. This material is available free of charge
via the Internet at http://pubs.acs.org.
3
3H, CHarom), 8.08 (d, 2H, JHH = 8.4 Hz, CHarom) ppm.
13C{1H} NMR (CDCl3): δ 18.2, 25.9, 27.9, 28.1, and 33.2 (s,
CH2), 68.3 (s, tCH), 84.3 (s, tC), 101.5 (s, dCH2), 128.4, 129.8,
(41) (a) Yamaguchi, I.; Osakada, K.; Yamamoto, T. Macromolecules
1994, 27, 1112. (b) Kabouche, A.; Kabouche, Z.; Bruneau, C.; Dixneuf, P. H.
J. Chem. Res., Miniprint 1999, 1247; J. Chem. Res., Synop. 1999, 249.
(42) (a) Stevens, C. L.; Malik, W.; Pratt, R. J. Am. Chem. Soc. 1950,
72, 4758. (b) Rubin, M. B.; Inbar, S. J. Org. Chem. 1988, 53, 3355.