Cobalt-catalyzed 1,4-hydrovinylation of styrenes and 1-aryl-1,3-butadienes

Article abstract of DOI:10.1021/ol901064p

The application of aryl-substituted starting materials such as styrene and 1-aryl-substituted 1,3-butadiene derivatives in the cobalt-catalyzed 1,4-hydrovinylation reaction has been investigated. The use of unsymmetrical α,ω-dienes in the hydrovinylation

Full text of DOI:10.1021/ol901064p

ORGANIC
LETTERS
2009
Vol. 11, No. 15
3322-3325
Cobalt-Catalyzed 1,4-Hydrovinylation of
Styrenes and 1-Aryl-1,3-butadienes
Gerhard Hilt,* Michael Danz, and Jonas Treutwein
Fachbereich Chemie, Philipps-UniVersita¨t Marburg, Hans-Meerwein-Strasse,
35043 Marburg, Germany
hilt@chemie.uni-marburg.de
Received May 25, 2009
ABSTRACT
The application of aryl-substituted starting materials such as styrene and 1-aryl-substituted 1,3-butadiene derivatives in the cobalt-catalyzed
1,4-hydrovinylation reaction has been investigated. The use of unsymmetrical r,ω-dienes in the hydrovinylation with 1-aryl-1,3-butadiene led
chemoselectively to the 1:1 or the 1:2 adducts depending on the stoichiometry of the starting materials.
The transition-metal-catalyzed hydrovinylation reaction is an
excellent example for an atom economic transformation
leading to the formation of a new carbon-carbon bond. Two
very successful procedures can be distinguished. First, simple
olefins such as styrene or norbornene derivatives are
converted in a transition-metal-catalyzed 1,2-hydrovinylation
reaction with ethene to the corresponding adducts.1 Second,
the 1,4-hydrovinylation of 1,3-dienes with terminal alkenes
leads to 1,4-diene products.2 Alongside diverse methodologi-
cal investigations,2b-d we were able to utilize the cobalt-
catalyzed 1,4-hydrovinylation reaction of a terminal alkene
as the key step in the short synthesis of moenocinol.3
In a recent report, Ritter described the first application of
low-valent iron complexes in the regioselective 1,4-hydrovi-
nylation of 1,3-dienes.4 Of considerable interest is the fact
that the 1,4-hydrovinylation of allyl benzene with 2,3-
dimethyl-1,3-butadiene (Scheme 1) led to different results
Scheme 1. Cobalt- and Iron-Catalyzed 1,4-Hydrovinylation of
Allylbenzene with 2,3-Dimethyl-1,3-butadiene
(1) For reviews on hydrovinylations, see: (a) Grabulosa, A.; Muller, G.;
Ordinas, J. I.; Mezzetti, A.; Maestro, M. A.; Font-Bardia, M.; Solans, X.
Organometallics 2005, 24, 4961. (b) RajanBabu, T. V. Chem. ReV 2003,
103, 2845. See also: (c) Saha, B.; Smith, C. R.; RajanBabu, T. V. J. Am.
Chem. Soc. 2008, 130, 9000. (d) Shirakura, M.; Suginome, M. J. Am. Chem.
Soc. 2008, 130, 5410. (e) Saha, B.; RajanBabu, T. V. J. Org. Chem. 2007,
72, 2357. (f) Zhang, A. B.; RajanBabu, T. V. J. Am. Chem. Soc. 2006,
128, 54. (g) Zhang, A.; RajanBabu, T. V. Org. Lett. 2004, 6, 1515. (h)
Zhang, A.; RajanBabu, T. V. Org. Lett. 2004, 6, 3159. (i) Kumareswaran,
R.; Nandi, M.; RajanBabu, T. V. Org. Lett. 2003, 5, 4345. (j) RajanBabu,
T. V.; Nomura, N.; Jin, J.; Nandi, M.; Park, H.; Sun, X. J. Org. Chem.
2003, 68, 8431. (k) Park, H.; RajanBabu, T. V. J. Am. Chem. Soc. 2002,
124, 734. (l) Bogdanovi, B.; Pauling, H.; Wilke, G.; Meister, B.; Henc, B.
Angew. Chem., Int. Ed. 1972, 11, 1023.
when the applied transition metal was varied. While under
cobalt catalysis, the branched product 1 with a 1,4-diene
(2) (a) Sanchez, R. P.; Connell, B. T. Organometallics 2008, 27, 2902.
(b) Hilt, G.; Luers, S.; Schmidt, F. Synthesis 2004, 634. (c) Hilt, G.; Luers,
S. Synthesis 2002, 609. (d) Hilt, G.; du Mesnil, F. X.; Lu¨ers, S. Angew.
Chem., Int. Ed. 2001, 40, 387.
(3) Hilt, G.; Treutwein, J. Chem. Commun 2009, 1395.
(4) Moreau, B.; Wu, J. Y.; Ritter, T. Org. Lett. 2009, 11, 337.
10.1021/ol901064p CCC: $40.75
Published on Web 07/07/2009
 2009 American Chemical Society

subunit is formed,2 and the iron-catalyzed process led to the
formation of 2 with a 1,5-diene subunit after double bond
migration under the reaction conditions. In this respect, the
two methodologies are complementary, each leading to
different products when starting from identical educts.5 A
significant exception is observed when utilizing styrene
derivatives. These are excellent starting materials in the iron-
catalyzed process, and under cobalt catalysis, the 1,4-
hydrovinylation of styrenes was observed with a very low
rate.
conversion was far from completion. The reaction of
2-vinyl thiophene led to the desired hydrovinylation
product in acceptable yield, and for no obvious reason
the linear product of type 4 was the only isomer isolated.
The characterization of the products was complicated by
the fact that the separation of the unreacted starting
materials from the branched products 3 and the linear
products 4 to give analytically pure samples could be
accomplished in only two cases. Therefore, only a limited
number of examples were investigated as shown in
Scheme 2.
We then focused our attention upon the application of
1-aryl-substituted 1,3-butadienes as starting materials in the
1,4-hydrovinylation process.6 The starting materials can be
easily generated from aromatic aldehydes by a Wittig
olefination with allyl triphenyl phosphonium bromide as a
mixture of E/Z-1,3-dienes in good yields. The cobalt-
catalyzed conversion of these 1,3-dienes with terminal olefins
led to the formation of products of type 5 (Scheme 3). The
Inspired by the report by Ritter we reinvestigated the
cobalt-catalyzed 1,4-hydrovinylation of styrene derivatives
with 2,3-dimethyl-1,3-butadiene (eq 1, Scheme 2). To our
Scheme 2
.
Cobalt- and Iron-Catalyzed Hydrovinylation of
Styrene Derivatives
Scheme 3. Cobalt-Catalyzed 1,4-Hydrovinylation of
1-Aryl-Substituted 1,3-Butadienes
good to excellent yields indicate that both isomers of the
E/Z-mixture are well accepted as starting materials. Because
complete conversion of the 1,3-diene is observed, it follows
that the cobalt catalyst converts both isomers to a single 1,2-
disubstituted and Z-configured double bond in 5. Also, the
reaction times were drastically reduced, and the complete
conversions eliminate purification problems. The newly
formed carbon-carbon bond was generated exclusively at
the less hindered side of the 1,3-diene, and with nonactivated
alkenes only branched products of type 5 were observed.
The results of this investigation are summarized in Table 1.
Besides the exomethylene double bond generated from the
terminal alkene, the internal double bond from the 1,3-diene
was generated exclusively as the Z-isomer. Both electron-
donating as well as electron-withdrawing substituents on the
aryl substituent gave equally good results, and several terminal
alkenes were applied successfully (entries 1-5). Also, interest-
ing results were obtained for the application of 1,5-hexadiene
(entries 6 and 7). The bisadduct 5g could be obtained as a single
isomer in quantitative yield utilizing an excess of the 1,3-diene.
The monoadduct 5f was obtained in a good 77% yield when
an excess of the 1,5-hexadiene was used accompanied by 17%
5g. The application of a ferrocenyl-substituted 1,3-diene (entry
8) gave the hydrovinylation product 5h in good yields with no
interference by the redox-active ferrocene subunit. As prototypes
of heterocyclic compounds, the N-tosylated heterocyclic-
regret, the reaction rates were rather low, and mostly
incomplete conversions were encoutered (eq 2). Also, the
two possible regioisomers 3 and 4 concerning the newly
formed carbon-carbon bond were formed generally as a
mixture in the range of 6.0:1.0 to 1.0:8.4.
Electronically different styrene derivatives were used
to investigate electronic effects upon the regiochemisty
of the hydrovinylation process. Electron-withdrawing
substituents such as the trifluoromethyl-substituted arene
substituent slightly favored the formation of the linear
product of type 4. The branched product of type 4 was
strongly preferred when electron-donating substituents
such as in the methoxy-substituted benzene derivatives
were used. Of considerable interest is the application of
the 2-chloro-substituted styrene. In this case, the branched
product of type 3 was clearly favored, although the
(5) For regio- and stereodivergent reactions, see: (a) Webster, R.; Boing,
C.; Lautens, M. J. Am. Chem. Soc. 2009, 131, 444. (b) Lu, Z.; Ma, S. Angew.
Chem. 2008, 120, 264; Angew. Chem., Int. Ed 2008, 47, 258. (c) Graening,
T.; Schmalz, H.-G. Angew. Chem. 2003, 115, 2684; Angew. Chem., Int. Ed
2003, 42, 2580. (d) Trost, B. M.; Crawley, M. L. Chem. ReV. 2003, 103,
2921. (e) Trost, B. M.; Lee, C. B. Catalytic Asymmetric Synthesis II; Ojima,
I., Eds.; Wiley-VCH: 2000, 593. (f) PfaltzA.; Lautens, M. ComprehensiVe
Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.;
Springer: 1999; Vol. 2, p 833. (g) Helmchen, G. J. Organomet. Chem. 1999,
576, 203. (h) Johannsen, M.; Jørgensen, K. A. Chem. ReV. 1998, 98, 1689.
(i) Trost, B. M.; Van Vranken, D. L. Chem. ReV. 1996, 96, 395. (j) Frost,
C. G.; Howarth, J.; Williams, J. M. J. Tetrahedron:Asymmetry 1992, 3,
1089.
(6) For an application of 1-aryl-substituted 1,3-dienes in cobalt-catalyzed
Diels-Alder reactions, see: Hilt, G.; Danz, M. Synthesis 2008, 2257.
Org. Lett., Vol. 11, No. 15, 2009
3323

substituted 1,3-dienes were applied with moderate to good
success in the synthesis of 5i/5j (entries 9 and 10). In these
cases, it seems evident that the tosyl functionality reduces the
reactivity of the 1,3-diene when attached in proximity to the
diene subunit as illustrated by the reduced yield of 5i. Also, a
1-aryl-3-alkyl-substituted 1,3-diene could be applied in the
reaction (entry 11) with an acceptable yield of the adduct 5k.
The transformation to give 5f indicates that the aryl-
substituted 1,3-diene is quite reactive and is mostly consumed
in the reaction. This intriguing result encouraged us to
investigate the question if an unsymmetrical R,ω-diene as
starting material could react chemoselectively. For this
purpose, readily available bisallyl ethers of type 6 with one
substituent (R) in the allylic position were utilized in the
cobalt-catalyzed 1,4-hydrovinylation reaction (Scheme 4).
Table 1. Results of the Cobalt-Catalyzed 1,4-Hydrovinylation
Reaction with 1-Aryl-Substituted 1,3-Dienesa
Scheme 4. Chemoselective Cobalt-Catalyzed
1,4-Hydrovinylation Reaction of Bisallyl Ether Derivatives
The results for the generation of products of type 7 are
summarized in Table 2. It was anticipated that the chemose-
Table 2. Results of the Cobalt-Catalyzed 1,4-Hydrovinylation
Reaction Utilizing Bisallyl Ethers
a Ar ) 4-methoxyphenyl. b Catalyst system: CoBr2(1,2-bisdiphenylphos-
phinoethane) 10 mol %; zinc dust 20 mol %; zinc iodide 20 mol %, CH2Cl2,
rt, overnight.
a Catalyst system: CoBr2(1,2-bisdiphenylphosphinoethane) 10 mol %;
zinc dust 20 mol %; zinc iodide 20 mol %, CH2Cl2, rt, overnight. b Excess
of the 1,5-hexadiene (3.0 equiv) was used. c Excess of the 1,3-diene (3.0
equiv) was used. d Twice the amount of the catalyst system (footnote a)
was used. e Half the amount of the catalyst system (footnote a) was used.
lectivity would be dependent on the steric bulk of the
substituent R of the bisallyl ether 6. The hydrovinylation
3324
Org. Lett., Vol. 11, No. 15, 2009

reaction took place selectively at the less hindered allyl
subunit even with the methyl group, which represents the
smallest substituent used in our study.
was realized utilizing 20 mol % of the cobalt catalyst, and the
product 8 was isolated in 72% yield over the two consecutive
reactions performed in a one-pot procedure (Scheme 5). In this
case, the isolated yield of 8 was even higher than that of the
monoadduct 7c which is formed as an intermediate in this
protocol.
The products of type 7 were isolated as single isomers in
good to excellent yields utilizing a slight excess (1.1 equiv)
of 1-(4-methoxyphenyl)-1,3-butadiene which was used as the
test system in this investigation. The monoadduct 7b with
the geminal dimethyl subunit did not react with another aryl-
1,3-diene even when 3 equiv of the diene was applied.
Accordingly, a sequential process was envisaged for the other
hydrovinylation products such as 7a where the monoadducts
were then converted in another hydrovinylation reaction with
a different 1,3-diene such as 2,3-dimethyl-2,3-butadiene to
generate tetraene products of type 8 (Scheme 5). This procedure
In conclusion, we have demonstrated that aryl substituents
are accepted without difficulties on the 1,3-diene substrate,
whereas vinyl heteroaromatic and styrene derivatives gave
mixtures and incomplete conversions. For the application of
styrene, the iron-catalyzed procedure by Ritter is superior
at the moment. However, a chemoselective 1,4-hydroviny-
lation reaction could be performed with an unsymmetrical
bisallyl ether as a divalent substrate. Accordingly, a sequen-
tial transformation of these substrates generated the tetraene
product 8 selectively. The triene and tetraene products
generated by our method show potential as interesting
substrates for other transformations such as alkene metath-
esis, hydroboration, or hydroformylation reactions, perhaps
to permit elucidation of their chemoselectivity and reactivity
when several differently substituted double bonds are present
in a single substrate.
Scheme 5. Sequential Chemoselective Cobalt-Catalyzed
1,4-Hydrovinylation Reaction of Unsymmetrical Bisallyl Ether
Derivatives
Supporting Information Available: Experimental pro-
cedures and full characterization of the compounds 5a-5k,
7a-7d, and 8. This material is available free of charge via
the Internet at http://pubs.acs.org.
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