Rhenium-catalyzed insertion of nonpolar and polar unsaturated molecules into an olefinic C-H bond

Article abstract of DOI:10.1021/ol900962v

Treatment of olefins bearing a directing group with α,β- unsaturated carbonyl compounds, alkynes, or aldehydes in the presence of a catalytic amount of a rhenium complex, [ReBr(CO)₃(thf)]₂ gave γ,δ-unsaturated carbonyl compounds, die

Full text of DOI:10.1021/ol900962v

ORGANIC
LETTERS
2009
Vol. 11, No. 12
2711-2714
Rhenium-Catalyzed Insertion of
Nonpolar and Polar Unsaturated
Molecules into an Olefinic C-H Bond
Yoichiro Kuninobu,* Yasuo Fujii, Takashi Matsuki, Yuta Nishina, and
Kazuhiko Takai*
DiVision of Chemistry and Biochemistry, Graduate School of Natural Science and
Technology, Okayama UniVersity, Tsushima, Kita-ku, Okayama 700-8530, Japan
kuninobu@cc.okayama-u.ac.jp; ktakai@cc.okayama-u.ac.jp
Received May 1, 2009
ABSTRACT
Treatment of olefins bearing a directing group with r,ꢀ-unsaturated carbonyl compounds, alkynes, or aldehydes in the presence of a catalytic
amount of a rhenium complex, [ReBr(CO)3(thf)]2 gave γ,δ-unsaturated carbonyl compounds, dienes, and allyl silyl ethers, respectively. This
reaction proceeds via C-H bond activation, insertion of unsaturated molecules into the formed rhenium-carbon bond, and then reductive
elimination (or transmetalation in the case of aldehydes).
Olefins are fundamental functional groups in organic com-
pounds. Complex organic molecules can be constructed by
functionalizing olefin moieties of substrates. For example,
the Mizoroki-Heck reaction,1 Fujiwara-Moritani reaction,2
and olefin metathesis,3 are well-known as preparative
methods. Alternatively, multisubstituted olefins can be
synthesized from alkenes in a direct and efficient manner
via olefinic C-H bond activation. There have been several
reports on such transformations: alkylation via intermolecu-
lar4 and intramolecular5 insertion of an alkene into a C-H
bond, and acylation via successive insertion of carbon
monoxide and alkene.6 However, there have been fewer
reports on olefin functionalizations via C-H bond activation
compared with functionalizations of aromatic compounds.7,8
In addition, it has been difficult to insert polar unsaturated
molecules into an olefinic C-H bond. We report herein
rhenium- and manganese-catalyzed insertion of nonpolar and
polar unsaturated molecules into a C-H bond of olefins with
a directing group.
Treatment of 2-(1-cyclohexenyl)pyridine (1a) with
2-ethylhexyl acrylate (2a) in the presence of a catalytic
(6) Chatani, N.; Ishii, Y.; Ie, Y.; Kakiuchi, F.; Murai, S. J. Org. Chem.
1998, 63, 5129–5136.
(1) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009–
3066.
(7) There have been several reports on ruthenium- and rhodium-catalyzed
transformations via C-H bond activation. (a) Kakiuchi, F.; Murai, S. Top.
Organomet. Chem. 1999, 3, 47–79. (b) Guari, Y.; Sabo-Etienne, S.;
Chaudret, B. Eur. J. Inorg. Chem. 1999, 1047–1055. (c) Dyker, G. Angew.
(2) Jia, C.; Piao, D.; Oyamada, J.; Lu, W.; Kitamura, T.; Fujiwara, Y.
Science 2000, 287, 1992–1995.
(3) (a) Fu¨rstner, A. Angew. Chem., Int. Ed. 2000, 39, 3012–3043. (b)
Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18–29.
(4) (a) Kakiuchi, F.; Tanaka, Y.; Sato, T.; Chatani, N.; Murai, S. Chem.
Lett. 1995, 679–680. (b) Trost, B. M.; Imi, K.; Davies, I. W. J. Am. Chem.
Soc. 1995, 117, 5371–5372. (c) Kakiuchi, F.; Sato, T.; Igi, K.; Chatani, N.;
Murai, S. Chem. Lett. 2001, 386–387. (d) Lim, Y.-G.; Kang, J.-B.; Lee,
K.; Kim, Y. H. Heteroatom Chem. 2002, 13, 346–350.
(5) Fujii, N.; Kakiuchi, F.; Yamada, A.; Chatani, N.; Murai, S. Chem.
Lett. 1997, 425–426.
Chem., Int. Ed. 1999, 38, 1698–1712.
(8) We have reported on rhenium- and manganese-catalyzed transforma-
tions via C-H bond activation. (a) Kuninobu, Y.; Kawata, A.; Takai, K.
J. Am. Chem. Soc. 2005, 127, 13498–13499. (b) Kuninobu, Y.; Nishina,
Y.; Shouho, M.; Takai, K. Angew. Chem., Int. Ed. 2006, 45, 2766–2768.
(c) Kuninobu, Y.; Inoue, Y.; Takai, K. Chem. Lett. 2006, 35, 1376–1377.
(d) Kuninobu, Y.; Kikuchi, K.; Takai, K. Chem. Lett. 2008, 37, 740–741.
(e) Kuninobu, Y.; Nishina, Y.; Matsuki, T.; Takai, K. J. Am. Chem. Soc.
2008, 130, 14062–14063
.
10.1021/ol900962v CCC: $40.75
Published on Web 05/26/2009
 2009 American Chemical Society

amount of a rhenium complex, [ReBr(CO)3(thf)]2, in
toluene at 135 °C for 24 h promoted a conjugate addition-
type reaction, and yielded γ,δ-unsaturated ester 3a in 91%
yield (eq 1).9,10 This result shows that the rhenium complex,
[ReBr(CO)3(thf)]2, promoted the activation of the olefinic
C-H bond.8a-c
were polymerized in the presence of a catalytic amount
of [ReBr(CO)3(thf)]2. By the reaction of an olefinic
compound with no substituents, 1b, with acrylate 2a, only
Z isomer 3b was formed in low yield (entry 1), and the
polymerization of 1b occurred. When olefinic substrates
with a methyl group at the R- or ꢀ-position, 1c and 1d,
were used, the reaction proceeded well, and ꢀ-alkylated
products 3c and 3d were obtained in 76 and 77% yields
(entries 2 and 3). In entry 2, 3c was produced as a mixture
of Z and E isomers.
The selection of a directing group of olefinic substrates 1
is important to promote the reaction (Table 2). When acrylate
Table 2. Investigation of Several Directing Groupsa
The reaction also proceeded when acyclic olefinic
compounds were used as substrates (Table 1). In these
Table 1. Investigation of Olefins 1a
a 1 (1.0 equiv), 2, 4 (1.0 equiv). b Isolated yield. Yield determined by
1H NMR is reported in parentheses. c The ratios of E and Z isomers are
given in square brackets. d 6a (1.0 equiv, 8 h) and HSiEt3 (1.0 equiv, 8 h)
were added three times, MS4A, 115 °C.
a 2a (1.0 equiv). b Isolated yield. Yield determined by 1H NMR is
reported in parentheses. c The ratios of Z and E isomers are given in square
brackets.
2a or alkyne 4a was employed as an unsaturated molecule,
a pyridyl group was effective as a directing group; however,
imidazolyl and oxazolinyl groups were ineffective (entries
1-6). On the other hand, an imidazolyl group promoted the
reaction in the case of aldehyde 6a (entry 8).11 However,
investigations, a rhenium complex, Re2(CO)10, was em-
ployed as a catalyst because the olefinic substrates 1b-1d
(9) This reaction also proceeded using a rhenium complex, Re2(CO)10
or ReBr(CO)5, as a catalyst, and 3a was formed in 73 and 81% yields,
respectively. A rhodium complex, RhCl(PPh3)3, also produced 3a in 50%
yield. However, manganese complexes, Mn2(CO)10 and MnBr(CO)5, and a
ruthenium complex, RuH2(CO)(PPh3)3, did not promote the reaction.
(10) Colby, D. A.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc.
(11) Silyl ether 7a was decomposed slightly during the isolation process.
Therefore, the isolated yield was decreased compared with 1H NMR
yield.
2006, 128, 5604–5605
.
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Org. Lett., Vol. 11, No. 12, 2009

Table 3. Reactions between Olefins 1 and Unsaturated
Molecules 2, 4, and 6a
Scheme 1
.
Proposed Mechanism for the Formation of Allyl
Silyl Ethers
pyridyl and oxazolinyl groups had no promotion abilities
(entries 7 and 9).
R,ꢀ-Unsaturated ketone 2b and R,ꢀ-unsaturated amide 2c
also afforded the corresponding γ,δ-unsaturated ketone 3e
and γ,δ-unsaturated amide 3f in 91 and 47% yields,
respectively (Table 3, entries 1 and 2). Olefinic C-H
functionalization also proceeded using alkynes (Table 3,
entries 3-6). By the reaction of 2-(1-cyclohexenyl)pyridine
(1a) with diphenylacetylene (4a), diene 5a was provided in
96% yield (Table 3, entry 3). In this reaction, the product
was obtained as a mixture of E and Z isomers. A rhodium
complex, RhCl(PPh3)3, also promoted the insertion of alkyne
4a into a C-H bond of olefin 1a, and diene 5a was obtained
in 86% yield [E:Z ) 88:12]. Dialkyl acetylene 4b also gave
the corresponding diene 5b, however, the yield of 5b was
low (Table 3, entry 4).12 Although there have been several
examples of internal alkyne insertion into a C-H bond, only
a few examples of terminal alkyne insertion has been
reported.10 As a result of investigating the insertion of
terminal alkynes, we found the insertion of phenylacetylene
(4c) and 1-dodecyne (4d) into a C-H bond of olefin 1a
produced tetrasubstituted dienes 5c and 5d in 96% yields,
respectively (Table 3, entries 5 and 6). Next, we tried to
insert polar unsaturated molecules, such as aldehydes.13
Although benzaldehyde (6a) did not insert into a C-H bond
of olefin 1a at all, the insertion reaction proceeded when an
imidazolyl group was used as a directing group (Table 3,
entry 7). This reaction is a vinyl Grignard-type reaction, and
generated an allyl silyl ether 7a in 80% yield (Table 3, entry
7). A manganese catalyst, MnBr(CO)5, also promoted the
insertion of an aldehyde into an olefinic C-H bond. By the
reaction of olefin 1e with benzaldehyde (6a) and hydrosilane
in the presence of a catalytic amount of a manganese com-
plex, MnBr(CO)5, provided the corresponding silyl ether 7a
in 46% yield (Table 3, entry 8).14 Aryl aldehydes bearing
a 1 (1.0 equiv), 2, 4, 6 (1.0 equiv). b Isolated yield. Yield determined
by 1H NMR is reported in parentheses. c The ratios of E and Z isomers are
given in square brackets. d 2c (1.2 equiv). e 4b (1.5 equiv). f 4 (0.75 equiv,
12 h) was added two times. g Re2(CO)10 (5.0 mol %) was used as a catalyst.
h 6 (1.0 equiv, 8 h) and HSiEt3 (1.0 equiv, 8 h) were added three times,
MS4A, 115 °C. i MnBr(CO)5 (5.0 mol %) was used as a catalyst; 115 °C,
19 h. j 6e (1.0 equiv, 16 h) and HSiEt3 (1.0 equiv, 16 h) were added three
times, MS4A, 115 °C.
(12) For the insertion of internal alkynes into an olefinic C-H bond,
see: (a) Yotphan, S.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc.
2008, 130, 2452–2453. (b) Colby, D. A.; Bergman, R. G.; Ellman, J. A.
J. Am. Chem. Soc. 2008, 130, 3645–3651.
(13) For rhenium-catalyzed insertion of aldehydes into an aromatic C-H
bond, see: (a) Kuninobu, Y.; Nishina, Y.; Nakagawa, C.; Takai, K. J. Am.
Chem. Soc. 2006, 128, 12376–12377. (b) Kuninobu, Y.; Nishina, Y.; Takai,
K. Tetrahedron 2007, 63, 8463–8468.
Org. Lett., Vol. 11, No. 12, 2009
2713

an electrodonating or withdrawing group, 6b and 6c, also
yielded the corresponding silyl ethers 7b and 7c in 81 and
87% yields, respectively (Table 3, entries 9 and 10). A silyl
ether 7d was afforded in 79% yield using thiophene-2-
carbaldehyde (6d) (Table 3, entry 11). Primary and secondary
aliphatic aldehydes, 6e and 6f, also provided the correspond-
ing silyl ethers, 7e and 7f, in 65 and 52% yields, respectively
(Table 3, entries 12 and 13).
unsaturated carbonyl compounds) or (3-b) silyl protection
via the formation of dihydrogen (in the case of aldehydes).
We have succeeded in rhenium-catalyzed functionalization
of olefins via the insertion of unsaturated molecules into a
C-H bond of an olefin moiety. In these transformations, R,ꢀ-
unsaturated carbonyl compounds, alkynes, and aldehydes can
be employed as unsaturated molecules. As a result, γ,δ-
unsaturated carbonyl compounds, dienes, and allyl silyl ethers
are obtained. We hope that this result will give a useful
insight into synthetic organic chemistry.
The proposed mechanism for the insertion of unsaturated
molecules into an olefinic C-H bond is as follows (Scheme
1: represented by the reaction of aldehydes): (1) oxidative
addition of an olefinic compound to a rhenium or manganese
center (C-H bond activation); (2) insertion of an unsaturated
molecule into the rhenium-carbon or manganese-carbon
bond. At the next step, there are two pathways: (3-a)
reductive elimination (in the case of acetylenes and R,ꢀ-
Acknowledgment. Financial support from the Ministry
of Education, Culture, Sports, Science, and Technology of
Japan is gratefully acknowledged.
Supporting Information Available: General experimental
procedure, characterization data for γ,δ-unsaturated carbonyl
compounds 3, dienes 5, and allyl sily ethers 7. This material
is available free of charge via the Internet at http://pubs.acs.org.
(14) For manganese-catalyzed insertion of aldehydes into an aromatic
C-H bond, see: (a) Kuninobu, Y.; Nishina, Y.; Takeuchi, T.; Takai, K.
Angew. Chem., Int. Ed. 2007, 46, 6518–6520.
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