Catalytic double addition of diazo compounds to alkynes: Synthesis of functional conjugated dienes [8]

Full text of DOI:10.1021/ja000790c

7400
J. Am. Chem. Soc. 2000, 122, 7400-7401
dienes and thus to show the formal bis-carbene character of
alkynes RsCtCsR T RsC(:)sC(:)sR.
Catalytic Double Addition of Diazo Compounds to
Alkynes: Synthesis of Functional Conjugated Dienes
Now we report a novel, selective catalytic synthesis of new
substituted 1,4-bistrimethylsilylbuta-1,3-dienes, by the combina-
tion of two molecules of trimethylsilyldiazomethane and one of
alkyne, catalyzed by RuCl(cod)C5Me5 (eq 1). The stereoselective
formation of these functional conjugated dienes results from the
ruthenium-catalyzed selective creation of two carbon-carbon
double bonds via double dimerization of a 1,2 bis-carbene
precursor with another carbene source.
Jacques Le Paih, Sylvie De´rien, Ismail O¨ zdemir,† and
Pierre H. Dixneuf*
Organome´talliques et Catalyse: Chimie et
Electrochimie Mole´culaires, UMR 6509 CNRS-UniVersite´ de
Rennes, Campus de Beaulieu, F-35042 Rennes, France
ReceiVed March 6, 2000
A major challenge in organic synthesis deals with the discovery
of one-pot, several-step reactions selectively leading to the
formation of several carbon-carbon bonds under mild conditions.
Metal-catalyzed reactions of diazo compounds have shown an
important contribution in this area, and still offer a strong potential
in synthesis.1 Catalytic additions of diazo compounds to alkynes,
especially with Rh2(OAc)4 catalyst, afford either cyclopropene
intermediates2 or reactive vinylcarbenoid species promoting C-C
bond formations in cascade.3-5 On the other hand, ruthenium
precatalysts have recently shown efficiency in the activation of
diazoalkane derivatives for their dimerization,6 cyclopropanation,7
or ring-opening metathesis,8 but to our knowledge, no example
of ruthenium-catalyzed addition of diazo compounds to alkynes
has been reported yet. As ruthenium-carbene species are well
known to easily generate, on reaction with an alkyne, alkenyl-
carbene-ruthenium species,9 and as it was recently shown that
two cis carbene ligands can be accommodated on a Cp*(Cl)Ru
moiety (Cp* ) C5Me5),10,11 we have investigated the possibility
of coupling alkenylcarbene-ruthenium, in situ generated from
diazoalkane derivative and alkyne, with a second equivalent of
carbene species arising from diazoalkane in order to produce
The reaction of 1.25 mmol of phenylacetylene with 2.4 equiv
of trimethylsilyldiazomethane (2 M in hexane), in the presence
of 5 mol % of catalyst precursor RuCl(cod)C5Me512 (A) in 2 mL
of dioxane, affords the 1,4-bistrimethylsilylbutadiene 1 after 6 h
1
at 60 °C in 72% yield (eq 2). H NMR and NOE experiments
showed Z stereoselectivity for the trisubstituted double bond,
whereas the disubstituted double bond is formed with an E/Z
stereoselectivity in the ratio 70/30. The bulky, electron-rich
precursor A appears to be a selective catalyst for this reaction,
whereas RuCl3‚xH2O, (PPh3)3RuCl2, [(p-cymene)RuCl2]2, (p-
cymene)RuCl2(PCy3), and Cp*RuBr2(η3-C4H7) do not catalyze
it at all.
Consequently, the catalyst precursor A and the above reaction
conditions (dioxane, 60 °C) have been selected to study the
activation of a variety of alkynes.13 1-Ethynylcyclohexene affords
after 5 h the 1,4-bistrimethylsilylbutadiene derivative 2 in 80%
yield (E/Z ) 89/11) (eq 2). The reaction has also been extended
to various disubstituted alkynes, and the 1,4-bistrimethylsilyl-
butadienes 3 and 4 have been obtained in 56 and 30% yield,
respectively (eq 3). Only one isomer has been observed by NMR
* To whom correspondence should be addressed. Phone: +33 299286280.
Fax: +33 299286939. E-mail: pierre.dixneuf@univ-rennes1.fr.
† Permanent address: Ino¨nu U¨ niversitesi Fen-Edebiyat Faku¨ltesi, 44280
Malatya, Turkey.
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for these tetrasubstituted dienes. NOE experiments and selective
13C NMR decoupling show that this isomer has both substituents
in the cis position on each double bond. Hex-3-yne affords the
(E,E)-1,4-bistrimethylsilylbutadiene 5 (R ) R′ ) Et) in 72% yield.
(12) Fagan, P. J.; Mahoney, W. S.; Calabrese, J. C.; Williams, I. D.
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(13) The alkyne (2.5 mmol) and trimethylsilyldiazomethane (2.4 equiv)
are stirred in dioxane (2-4 mL) in the presence of catalyst A (0.125 mmol)
at 60 °C for 5-6 h. The solvent is evaporated under vacuum, and the products
are isolated by column chromatography over silica gel. The isolated yields
are based on the alkyne. All compounds were fully characterized by
spectroscopic methods. Selected data for 1: isomer Z,E, 1H NMR (200 MHz,
CDCl3) δ -0.16 (9H, s), 0.09 (9H, s), 5.44 (1H, d, J ) 18 Hz), 5.88 (1H, d,
J ) 1 Hz), 6.75 (1H, dd, J ) 18 Hz, J ) 1 Hz), 7.10-7.13 (2H, m), 7.28-
7.35 (3H, m); isomer Z,Z, 1H NMR (200 MHz, CDCl3) δ -0.09 (9H, s), 0.13
(9H, s), 5.59 (1H, d, J ) 14 Hz), 5.88 (1H, d, J ) 1 Hz), 6.87 (1H, dd, J )
14 Hz, J ) 1 Hz), 7.19-7.24 (2H, m), 7.28-7.35 (3H, m). Selected data for
3: 1H NMR (200 MHz, CDCl3) δ -0.2 (9H, s), 0.05 (9H, s), 2.04 (3H, s),
5.24 (1H, s), 5.93 (1H, s), 7.02-7.14 (2H, m), 7.26-7.38 (3H, m).
10.1021/ja000790c CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/18/2000

Communications to the Editor
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7401
Methyl propargyl alcohol also reacts in the presence of 2.4 equiv
of trimethylsilyldiazomethane to give the 1,4-bistrimethylsilyl-
butadiene 6 (R ) CH2OH, R′ ) Me) in very good yield (95%),
thus showing that the reaction tolerates a hydroxy functional
group. The reactivity of a conjugated diyne such as bistrimeth-
ylsilylbutadiyne has been examined to clear up the regioselectivity
of the addition (1,2; 1,4 or 1,2 plus 3,4). In the presence of 4.8
equiv of trimethylsilyldiazomethane, this 1,3-diyne reacts as a
monoalkyne, and only one CtC bond was transformed to give
the tetrasilylated dienyne 7 (48%) (eq 4), a useful molecule for
the search of functional unsaturated carbon-rich molecules and
networks.14 This catalytic reaction offers a new route to selectively
build functional 1,3-dienes useful in synthesis as the vinylsilane
moiety can be easily converted into a variety of functionalities.15
Scheme 1
is shown in Scheme 1. As trimethylsilyldiazomethane is known
to give a RudCHSiMe3 species with a coordinatively unsaturated
ruthenium complex,8 the coordination of the alkyne and one
molecule of trimethylsilyldiazomethane to the ruthenium center
is expected, on displacement of the cod ligand, to give the
ruthenium-carbene intermediate B. Classical coupling of the
carbene and triple bond should afford the intermediate C and then
the unsaturated ruthenium vinyl carbene derivative D. Addition
of a second molecule of N2CHSiMe3 on D may lead to species
E, and then to the coordinated diene F by coupling of both carbene
species, or directly via addition on species D.
This formation of 1,4-bisfunctional buta-1,3-dienes constitutes
an alternative route, with the advantageous presence of reactive
vinylsilane moieties, to terminal 1,3-dienes from alkynes and
ethene via catalytic ene/yne metathesis.16
The above catalytic reaction constitutes an unusual crossover
2:1 coupling between diazoalkanes and a substantial wide range
of alkynes. It represents a novel example of a one-pot, mild,
ruthenium-catalyzed reaction combining three substrates into only
one, with release of only two molecules of dinitrogen, via selective
CdC coupling. Moreover, we have shown that it was possible to
selectively create two C-C double bonds and to produce only
one stereoisomer of 2,3-disubstituted 1,4-trimethylsilyl-1,3-dienes
from disubstituted alkynes.
The efficiency of the reaction depends on the nature of the
solvent, despite the presence of hexane in the reaction mixture,
and the temperature. After 6 h at 60 °C the reaction of
phenylacetylene carried out in dichloromethane, dimethylforma-
mide, hexane, tetrahydrofuran, and dioxane leads to the diene 1
in 15, 40, 52, 64, and 72% yield, respectively. The reaction
performed in dioxane at room temperature for 20 h affords only
25% of the corresponding diene. This low yield could be explained
by the observation that, at room temperature, RuCl(cod)C5Me5
dimerizes phenylacetylene and leads to a biscarbene derivative10,11
which is not a catalyst for this reaction.
Ethyldiazoacetate is less reactive than trimethylsilyldiazo-
methane and requires more drastic reaction conditions. After 20
h at 100 °C in dioxane (4 mL), in the presence of 5 mol % of
catalyst precursor A, phenylacetylene with 2.4 equiv of ethyl-
diazoacetate affords the butadiene 8 in 64% yield as a mixture
of isomers (eq 5).
A possible mechanism for this selective formation of 1,4-
bistrimethylsilylbutadiene derivatives 1-7 from simple alkynes
Acknowledgment. The authors are grateful to C. Bruneau and B.
Cetinkaya for stimulating discussions, the MENRT for a thesis grant to
J.L.P., the CNRS for an associate research position to I.O¨ ., the University
of Malatya, and the COST programm (D12/0025/99) and the CNRS-
TU¨ BITAK programm.
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Supporting Information Available: Spectroscopic data for com-
1
pounds 1-7 and H and 13C NMR spectra for the selected compound 4
(PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
JA000790C
(16) (a) Kinoshita, A.; Sakakibara, N.; Mori, M. J. Am. Chem. Soc. 1997,
119, 12388. (b) Smulik, J. A.; Diver, S. T. J. Org. Chem. 2000, 65, 1788.