In this reaction, the alkyne part of enyne 2 reacts with
ruthenium-carbene complex 1 to give metalacyclobutene
iii. Ring opening of iii gives ruthenium-carbene complex
iv, which reacts with the cycloalkene part intramolecularly
to give ruthenacyclobutane v, which is converted into
ruthenium-carbene complex vi. Thus, a polymer should
obtained. Formally, in this reaction, the double bonds of
ethylene and cycloalkene in 2b are cleaved, and one alkene
carbon in 2b reacts with an alkyne carbon to afford a five-
membered ring, while the other alkene carbon and alkyne
carbon react with the methylene parts of ethylene, respec-
tively.
The enynes 2a and 2c with six- and eight-membered rings
were treated in a similar manner, and the desired ROM-RCM
products 3a and 3c were obtained in 15% and 22% yields,
respectively (Table 1, runs 1 and 3).
5
result from an intermolecular metathesis reaction with 2.
If this reaction were carried out under ethylene gas,
ruthenium-carbene complex vi reacts with ethylene to give
ruthenacyclobutane vii and, as a result, cyclized triene 3
would be formed.
Here, we report the ring-opening and ring-closing met-
atheses (ROM-RCM) of enyne 2 under ethylene gas (Scheme
Table 1. ROM-RCM of Enyne
6
2).
Scheme 2. Our Plan for ROM-RCM of Enyne
run
R
ring size
n
time (h) yielda (%)
2 (%)
1
2
3
4
5
6
Me
Me
Me
H
H
H
6
7
8
6
7
8
1
2
3
1
2
3
2a
2b
2c
2d
2e
2f
24
24
24
4
1
1
15
56
22
78
70
75
75
36
73
0
15
20
a
1
Yields were calculated from H NMR.
We have already reported that the metathesis reaction rate
of an enyne containing a terminal alkyne was slow because
the terminal alkene part of the cyclized product reacts with
the ruthenium-carbene complex. However, a remarkable
effect for metathesis of an enyne containing a terminal alkyne
2 2
When a CH Cl solution of 2b and 10 mol % of 1 was
stirred at room temperature for 24 h under ethylene gas (1
atm), we found that ROM-RCM occurred to afford the five-
membered ring compound 3b in 56% yield along with the
starting material 2b in 36% yield (Scheme 3). When this
3a
was shown under ethylene gas, and the desired cyclized
3
d
product was obtained in high yield. Since this ROM-RCM
of enyne was carried out under ethylene gas, an enyne
containing a terminal alkyne should be applied to the ROM-
RCM of an enyne.
Scheme 3. ROM-RCM of Enyne Containing a Cycloheptene
Moiety
When a CH
cyclohexene part and the terminal alkyne was treated with
0 mol % of 1, surprisingly, triene 3d was obtained in 78%
yield (run 4). The reason for the remarkably higher yield of
d as compared with that of 3a is thought to be the release
of the steric factor for the formation of v in the reaction of
a. The ROM-RCM of enynes 2e and 2f containing a
2 2
Cl solution of enyne 2d containing a
1
3
2
cycloheptene or a cyclooctene ring was carried out in a
similar manner, and the desired trienes 3e and 3f were
obtained in good yields, respectively (runs 5 and 6).
(6) For a recent application of ROM-RCM, see: (a) Zuercher, W. J.;
Hashimoto, M.; Grubbs, R. H. J. Am. Chem. Soc. 1996, 118, 6634. (b)
Chatani, N.; Furukawa, N.; Sakurai, H.; Murai, S. Organometallics 1996,
1
5, 901. (c) F u¨ rstner, A.; Szillat, H.; Gabor, B.; Mynott, R. J. Am. Chem.
reaction was carried out under argon gas instead of ethylene
gas, polymerization occurred and no cyclized product was
Soc. 1998, 120, 8305. (d) Burke, S. D.; Quinn, K. J.; Chen, V. J. J. Org.
Chem. 1998, 63, 8626. (e) Adams, J. A.; Ford, J. G.; Stamatos, P. J.;
Hoveyda, A. H. J. Org. Chem. 1999, 64, 9690. (f) Voigtmann, U.; Blechert,
S. Synhesis 2000, 893. (g) Trost, B. M.; Doherty, G. A. J. Am. Chem. Soc.
2000, 122, 3801. (h) Ovaa, H.; Stragies, R.; van der Malel. G. A.; van
Boom. J. H.; Blechert, S. Chem. Commun. 2000, 1501. (i) F u¨ rstner, A.;
Szillat, H.; Stelzer, F. J. Am. Chem. Soc. 2000, 122, 6785. (j) Stragies, R.;
Blechert, S. J. Am. Chem. Soc. 2000, 122, 9584. (k) Voigtmann, U.; Blechert,
S. Org. Lett. 2000, 2, 3971 and references therein.
(5) If ROM-RCM proceeded first by reaction of the cycloalkene part of
enyne 2 and the ruthenium-carbene complex, a similar reaction pathway
is considered, and the ruthenium-carbene complex would be formed at
the methylene part of the diene moiety of vi, which reacts with 2 to afford
polymer.
1162
Org. Lett., Vol. 3, No. 8, 2001