Reaction of zirconacyclopentadienes with CO in the presence of n-BuLi. Selective formation of cyclopentenone derivatives from two alkynes and CO [4]

Full text of DOI:10.1021/ja982570t

1094
J. Am. Chem. Soc. 1999, 121, 1094-1095
of n-BuLi showed an interesting reactivity toward CO. In this
paper we would like to report the cyclopentenone formation by
the reaction of zirconacyclopentadienes with CO in the presence
of n-BuLi. This is the first example of a CO insertion reaction of
zirconacyclopentadienes which gives the cyclopentenones.
The reaction was carried out as follows. Typically, to a solution
of zirconacyclopentadiene 1a (1 mmol) in THF was added n-BuLi
(1 mmol) at -78 °C. After the mixture was stirred for 1 h, CO
(1 atm) was introduced to the mixture at -78 °C. The mixture
Reaction of Zirconacyclopentadienes with CO in the
Presence of n-BuLi. Selective Formation of
Cyclopentenone Derivatives from Two Alkynes and
CO
Tamotsu Takahashi,* Shouquan Huo, Ryuichiro Hara,
Yoshinori Noguchi, Kiyohiko Nakajima,† and Wen-Hua Sun
Catalysis Research Center and Graduate School of
Pharmaceutical Sciences, Hokkaido UniVersity
Sapporo 060, Japan
Department of Chemistry, Aichi UniVersity of Education
Igaya, Kariya 448, Japan
ReceiVed July 20, 1998
Cyclopentenones are very useful intermediates for organic
synthesis. It is well-known that three components, namely an
alkyne, an alkene, and CO, provide cyclopentenone derivatives
with transition metal compounds.1 However, use of two alkynes
and CO for preparation of cyclopentenones is very rare. (eq 1).
was stirred at -78 °C under a slightly positive pressure of CO
for 1 h and quenched with 3 N HCl at -78 °C. Cyclopentenone
2a was obtained in 88% yield (75% isolated yield) as a mixture
of trans and cis isomers in a ratio of 5.5 to 1. No formation of
cyclopentadienone was detected. The results are shown in Table
1 and the following points are noteworthy. Without n-BuLi 1a
did not give any CO insertion products under CO (1 atm)
atmosphere, and the starting compound 1a remained unreacted.
The use of n-BuMgCl instead of n-BuLi did not give the product.
Deuteriolysis of the resulting mixture instead of hydrolysis
afforded dideuterated 2a-D in 72% isolated yield with >95% of
Only several examples have been reported with Co,2,3 Rh,2 Ir,2
and Ni.4 Moreover, there is no report for the selective preparation
of cyclopentenones from two different alkynes and CO.
Recently we have reported several reactions of zirconacyclo-
pentadienes,5 which can be selectively prepared from two
alkynes.6 However, it is known that zirconacyclopentadienes are
inert toward the CO insertion reactions. Under usual conditions
as used for zirconacyclopentanes and zirconacyclopentenes, the
CO insertion reaction of zirconacyclopentadienes does not
proceed. Therefore, to develop a coupling reaction of two alkynes
and CO, some different approach is required. It was reported that
the reaction of Cp2Zr(CO)2 with an excess of diphenylacetylene
in a sealed vessel at high temperature gave a cyclopentadienone
as a minor product, but not a cyclopentenone.7 Recently, Jordan
reported a coupling reaction of two alkynes and CO using
zirconocene cation complexes under mild conditions.8 This
reaction gave divinyl ketones.8 During the course of our study,
we found that a mixture of zirconacyclopentadienes and 1 equiv
deuterium incorporation. This indicates that one of two double
bonds of the diene moiety was reduced to a single bond during
the hydrolysis. Zirconacyclopentadienes 1b-d afforded similar
results. The products 2b-d were obtained in good to high yields
as a mixture of trans and cis isomers. The structure of the trans
isomer of 2d was determined by X-ray crystallography. It is
noteworthy that when two different alkynes, diphenylacetylene
and 3-hexyne, were used for this reactionsin other words, when
unsymmetrical zirconacyclopentadiene 1e was useds
cyclopentenone 2e was selectively formed. No formation of a
positional isomer of the double bond 3 was detected. The double
bond originated from 3-hexyne was reduced to a single bond
selectively. Similar site selectivity was expected for indanone
formation. As expected, zirconaindene 1f-g9 gave 2f-g selec-
tively by this reaction. For terminal alkynes, unfortunately, the
reaction was not selective.
* Address correspondence to this author at Hokkaido University.
† Aichi University of Education.
(1) (a) Schore, N. E. In ComprehensiVe Organic Synthesis; Trost, N. M.,
Fleming, I., Paquette, L. A., Eds.; Pergamon Press: Oxford, U.K., 1991; Vol.
5, p 1037. (b) Pauson, P. L. Tetrahedron 1985, 41, 5855. (c) Pauson, P. L.
Aspects of a Modern Interdisciplinary Field. In Organometallics in Organic
Synthesis; De Meijere, A., Dieck, H. T., Eds.; Springer: Berlin, 1988; p 233.
(2) Hong, P.; Mise, T.; Yamazaki, H. Bull. Chem. Soc. Jpn. 1990, 63, 247-
248.
(3) Schore, N. E.; La Belle, B. E.; Knudsen, M. J.; Hope, H.; Xu, X.-J. J.
Organomet. Chem. 1984, 272, 435-446.
(4) (a) Mueller, G. P.; MacArtor, F. L. J. Am. Chem. Soc. 1954, 76, 4621-
4622. (b) Best, W.; Fell, B.; Schmitt, G. Chem. Ber. 1976, 109, 2914-2920.
(5) For carbon-carbon bond formation of zirconacyclopentadienes, see:
(a) Takahashi, T.; Kotora, M.; Kasai, N.; Suzuki, N. Organometallics 1994,
13, 4183-4185. (b) Takahashi, T.; Kotora, M.; Xi, Z. J. Chem. Soc., Chem.
Commun. 1995, 361-362. (c) Takahashi, T.; Hara, R.; Nishihara, Y.; Kotora,
M. J. Am. Chem. Soc. 1996, 118, 5154-5155. (d) Kotora, M.; Umeda, C.;
Ishida, T.; Takahashi, T. Tetrahedron Lett. 1997, 38, 8355-8358. (e)
Takahashi, T.; Sun, W.-H.; Xi, C.; Kotora, M. Chem. Commun. 1997, 2079-
2080. (f) Takahashi, T.; Xi, Z.; Yamazaki, A.; Liu, Y.; Nakajima, K.; Kotora,
M. J. Am. Chem. Soc. 1998, 120, 1672-1680. (g) Takahashi, T.; Sun, W.-H.;
Xi, C.; Ubayama, H.; Xi, Z. Tetrahedron 1998, 54, 715-726. (h) Kotora,
M.; Xi, C.; Takahashi, T.Tetrahedron Lett. 1998, 39, 4321-4324.
(6) For review for the CO insertion reaction of zirconacyclopentanes or
zirconacyclopentenes, for example, see: Negishi, E. In ComprehensiVe
Organic Synthesis; Trost, B. M., Fleming, I., Eds; Pargamon: Oxford, U. K.,
1991; Vol. 5, pp 1163-1184 and references therein.
To understand the reaction, the reaction mixture of 1a, n-BuLi,
and CO was investigated by NMR study. The NMR study of the
resulting mixture after CO insertion indicated the formation of
4a in 87% NMR yield. 13C NMR of 4a showed a methine carbon
(9) (a) Erker, G. J. Organomet. Chem. 1977, 134, 189. (b) Erker, G.; Kropp,
K. J. Am. Chem. Soc. 1979, 101, 3659. (c) Kropp, K.; Erker, G. Organome-
tallics 1982, 1, 1246. (d) Buchwald, S. L.; Watson, B. T.; Huffman, J. C. J.
Am. Chem. Soc. 1986, 108, 7411-7413.
(7) Sikora, D. J.; Rausch, M. D. J. Organomet. Chem. 1984, 276, 21-37.
(8) Guram, A. S.; Guo, Z.; Jordan, R. F. J. Am. Chem. Soc. 1993, 115,
4902-4903.
10.1021/ja982570t CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/20/1999

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 5, 1999 1095
Table 1. Formation of Cyclopentenones from
Scheme 1
Zirconacyclopentadienes and CO in the Presence of n-BuLia
cyclization of 9 affords 10 as observed for the CO insertion
reactions of zirconacyclopentanes5 or zirconacyclopentenes.6 Since
the cyclopentadienyl anion is more stable, transformation of 10
proceeds to produce 4a which was observed by NMR. Hydrolysis
of 4a affords 2a via 11 and 12 as shown in Scheme 1. The ratio
of trans and cis isomers was dependent on the conditions of
protonation reactions. Selective reduction of double bonds
originated from 2-butyne and 3-hexyne in 1f-g was attributed
to an aromatic ring system. The reason for the site selectivity for
2e is not clear yet, but it can be explained by predominant
protonation at the benzyl carbon to afford 13, which finally
produces 2e.
Further investigation of the reactivity of 7 led us to an
interesting reaction. When phenylacetylene was added instead of
CO to the mixture of 1a (or 1b) and n-BuLi at -78 °C,
unexpected butylated diene 14a (or 14b) was obtained in 96%
yield (or 98% yield). A similar reaction proceeded when hexyl-
a The reactions were carried out in THF. n-BuLi (1 equiv) was added
at -78 °C. The mixture was treated with CO at -78 °C under slight
positive pressure. Cyclopentenones were obtained after hydrolysis.b GC
yields are in parentheses.
at 111.01 ppm assigned to Cp and four signals at 40.38, 36.92,
30.80, and 14.21 ppm assignable to a Bu group attached to
zirconium. These four carbon signals are consistent with the Bu
group of Cp2Zr(Bu)(OMe), which shows four carbons at 40.34,
36.01, 29.87, and 14.27 in its 13C NMR spectrum.10 The 13C NMR
spectrum of 4a also showed three signals at 100.92, 106.83, and
146.62 ppm assignable to five ring carbons of a symmetrical
cyclopentadienyl anion. The reaction of 4a with EtBr for 1 h at
0 °C gave an ethylated cyclopentenone 5 in 59% GC yield (44%
isolated yield) along with the formation of its isomers. In the
case of use of MeLi instead of BuLi the formation of a similar
type of complexes 4b-d was observed.
The following is a plausible mechanism of this reaction
(Scheme 1). n-BuLi coordinates to zirconium of zirconacyclo-
pentadiene 1a to produce zirconium-ate complex 6.11 This
compound is in equilibrium with 7. In fact, the reaction of a
mixture of 1a and n-BuLi with CBrCl3 afforded 3-bromo-4,5-
diethylocta-3,5-diene in 72% yield after hydrolysis. Since zir-
conacyclopentadiene 1a is inert toward CBrCl3, it suggests that
an alkenyllithium moiety is formed in 7. The real structure of 7
is not clear yet. It might contain multicenter bonds between
zirconium, carbon, and lithium. However, we tentatively use this
conventional structure here for intermediate 7.
lithium was used instead of n-BuLi, and the hexylated product
14c was formed in 78% yield. With use of deuterated phenyl-
acetylene, monodeuterated diene 14a-D was formed in high yield
with >99% deuterium incorporation. This result suggests that the
alkenyllithium moiety in 7 was protonated with phenylacetylene
and reductive coupling of a Bu (or hexyl ) group and a dienyl
group occurred. The coupling reaction on zirconocene of an alkyl
group such as a butyl group and a hexyl group with an alkenyl
group is unprecedented.
Although we must await further investigation to elucidate the
reaction mechanism, it is clear that the ate complexes prepared
from zirconacyclopentadienes and alkyllithium show novel in-
teresting reactivities and provide a useful preparative method of
cyclopentenones from two alkynes and CO. Further investigation
of the reactions of the zirconacyclopentadienes and alkyllithium
system is now in progress.
The reaction of 7 with CO gives 8, and the alkenyllithium
moiety in 8 attacks the CO on zirconium to produce 9. Subsequent
(10) Nishihara, Y.; Aoyagi, K.; Hara, R.; Suzuki, N.; Takahashi, T. Inorg.
Chim. Acta 1996, 252, 91-99.
(11) Reaction of zirconacyclopentanes with organolithium compounds,
see: (a) Luker, T.; Whitby, R. J. Tetrahedron Lett. 1994, 35, 785-788. (b)
Luker, T.; Whitby, R. J. Tetrahedron Lett. 1994, 35, 9465-9469. (c) Luker,
T.; Whitby, R. J. Tetrahedron Lett. 1995, 36, 4109-4112. (d) Gordon, G. J.;
Whitby, R. J. Synlett 1995, 77. (e) Fillery, S.; Gordon, G. J.; Luker, T.; Whitby,
R. J. Pure Appl. Chem. 1997, 69, 639-644. (f) Kondakov, D. Y.; Negishi, E.
J. Chem. Soc., Chem. Commun. 1996, 963.
Supporting Information Available: All experimental details and
crystallographic data, positional and thermal parameters, and lists of bond
lengths and angles for 2d (PDF). This material is available free of charge
via the Internet at http://pubs.acs.org.
JA982570T