Silicon-tethered cyclocarbonylation of alkynes

Article abstract of DOI:10.1021/ol020099+

(figure presented) Temporary union of alkynes in the Fe(CO)₅-promoted cyclocarbonylation provides a method for carbonylative cross-coupling of alkynes to construct unsymmetrically substituted cyclopentadienones.

Full text of DOI:10.1021/ol020099+

ORGANIC
LETTERS
2002
Vol. 4, No. 17
2837-2840
Silicon-Tethered Cyclocarbonylation of
Alkynes
Anthony J. Pearson* and Jin Bum Kim
Department of Chemistry, Case Western ReserVe UniVersity, CleVeland, Ohio 44106
ajp4@po.cwru.edu
Received May 15, 2002
ABSTRACT
Temporary union of alkynes in the Fe(CO)5-promoted cyclocarbonylation provides a method for carbonylative cross-coupling of alkynes to
construct unsymmetrically substituted cyclopentadienones.
It is known that Fe(CO)5-promoted cyclocarbonylation1 can
provide a method for the construction of five-membered
carbocyclic ring systems, which is potentially useful owing
to the occurrence of such rings in a diverse range of natural
product molecules.2 Although there are a number of examples
of homocoupling via this reaction where two alkynes react
with Fe(CO)5 in CO atmosphere to give the symmetrically
substituted cyclopentadienone-Fe(CO)3 complexes (eq 1),3
no example of cross-coupling of two alkynes has been
reported to the best of our knowledge.
carbonylation makes this reaction intramolecular, thereby
leading to better yield and regioselectivity than are generally
associated with intermolecular reactions. Shibata et al. have
reported a related silicon-tethered diyne homocoupling
promoted by octacarbonyldicobalt.5 Our strategy was first
tested with a simple substrate 1, which was obtained by the
reaction of trimethylsilylpropynol6 with dichlorodiphenylsi-
(3) Hu¨bel, W.; Braye, E. H. J. Inorg. Nucl. Chem. 1959, 10, 250.
Schrauzer, G. N. Chem. Ind. 1958, 1404. Boston, J. L.; Sharp, D. W.;
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W. Aust. J. Chem. 1968, 21, 97. Krespan, C. G. J. Org. Chem. 1975, 40,
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A.; Hudson, G. A. J. Organomet. Chem. 1978, 160, 159. Kno¨lker, H.-J.;
Herber, J.; Mahler, C. H. Synlett. 1992, 1002. For intramolecular cyclo-
carbonylation: Pearson, A. J.; Dubbert, R. A. J. Chem. Soc., Chem.
Commun. 1991, 202. Pearson, A. J.; Shively, R. J., Jr.; Dubbert, R. A.
Organometallics 1992, 11, 4096. Pearson, A. J.; Perosa, A. Organometallics
1995, 14, 5178. Pearson, A. J.; Yao, X. Synlett 1997, 1281. Kno¨lker, H.-J.;
Herber, J. Synlett 1993, 924. Kno¨lker, H.-J.; Baum, E.; Herber, J.
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ReV. 1995, 95, 1253.
We report here a method for cross-coupling of alkynes
via “silicon tethered”4 Fe(CO)5-promoted cyclocarbonylation,
which consists of linking two alkynes into a silyl acetal,
subjecting the resulting diyne to cyclocarbonylation, and
disengaging the metal and the tether moiety. Tethering the
two alkyne reaction partners of Fe(CO)5-promoted cyclo-
(1) Reviews of transition metal-mediated cycloadditions: Ojima, I.;
Tzanmarioudaki, M.; Li, Z.; Donovan, R. J. Chem. ReV. 1996, 96, 635.
Frehauf, H.-W. Chem. ReV. 1997, 97, 523.
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2000, 56, 9259. See also: Sugihara, T.; Wakabayashi, A.; Takao, H.;
Imagawa, H.; Nishizawa, M. Chem. Commun. 2001, 2456. Shibata, T.;
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10.1021/ol020099+ CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/30/2002

lane in the presence of base. The substrate 1, which has two
alkyne reaction units connected by a silyl acetal moiety,
underwent cyclocarbonylation in good yield considering that
the reaction involves seven-membered ring formation.7
Treatment of the resulting cyclopentadienone-Fe(CO)3
complex 2 with Me3NO8 afforded two products, 3 and 4,9
without the known possible problems3 such as dimerization
of cyclopentadienone or migration of one double bond and
accompanying desilylation. Removal of the tether moiety in
3 was completed by treatment with HF (Scheme 1).10 Also,
Scheme 2
Scheme 1
putative intermediate, the tricarbonyl[bis-(η2-alkyne)]iron
complex, may be considered to account for the reactivity
difference between two diastereomers. The tricarbonyl[bis-
(η2-alkyne)]iron complexes,12 which would be formed by the
sequential replacement of two CO ligands by two alkyne
units of the diyne 5, are depicted by RS-9 and SS-9 (Figure
1).
a sterically more demanding substrate 5 was prepared from
trimethysilylacetylene by a one-pot process involving se-
quential treatment with n-BuLi,11 acetaldehyde, and di-
chlorodiphenylsilane. The cyclocarbonylation of diyne 5 over
48 h gave all the possible diastereomers 6a, 6b, and 6c in a
ratio of ca. 1:1:1.2, which gave two diastereomers 7a and
rac-7b after demetalation and concomitant desilylation by
Me3NO treatment (Scheme 2). However, the same reaction
for 24 h gave a 1:1 mixture of 6a and 6b in 44% yield, with
only a trace amount of 6c. Me3NO treatment of this mixture
gave only 7a in 42% yield.
Due to the pseudo 1,3-diaxial interaction between phenyl
and methyl that is unavoidable in SS-9, the formation of SS-9
Scheme 3
The inseparable mixture of Fe(CO)3 complexes 6a, 6b,
and 6c was analyzed by comparison of the 1H NMR spectrum
of the mixture with that of (S,S)-6c, which was synthesized
from commercially available (S)-3-butynol (Scheme 3).
These results indicate that the meso diastereomer of 5
reacts faster than the (S,S)- or (R,R)-diastereomer. The
(7) Pearson, A. J.; Shively, R. J., Jr. Organometallics 1994, 13, 578.
(8) Shvo, Y.; Hazum, E. J. Chem. Soc., Chem. Commun. 1974, 336.
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Solans, X. J. Chem. Soc., Perkin Trans. 1 1987, 2749. Eekhof, J. H.;
Hogeveen, H.; Kellogg, R. M. J. Chem. Soc., Chem. Commun. 1976, 657.
Albers, M. D.; Coville, N. J. Coord. Chem. ReV. 1984, 53, 227.
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Org. Lett., Vol. 4, No. 17, 2002

Scheme 5
Figure 1. Tricarbonyl[bis-(η2-alkyne)]iron complexes (RS-9 and
SS-9) and the diyne 10.
is expected to be slower than that of RS-9. As a result, the
corresponding Fe(CO)3 complex 6c is formed more slowly.
The same reasoning also explains the observation that 10,
which has two additional methyl groups compared to the
substrate 5, did not undergo the cyclocarbonylation but was
recovered unreacted. Diyne 11, which was prepared by the
same method as used for 5, reacted with Fe(CO)5 to give
the inseparable diastereomeric mixture 12. The anticipated
mixture of two diastereomers 13a,b was obtained in ca. 1.1:1
ratio (Scheme 4). The 1H NMR spectrum of the mixture 12
was not useful for determining the ratio of the diastereomers.
We did not examine the potential selectivity of this conver-
sion for a shorter reaction time because of the poorer overall
yield.
Since we found that the silyl acetal moiety is a good tether
for Fe(CO)5-promoted cyclocarbonylation, we prepared the
diynes 16 and 17, which have two different alkyne units
tethered by the silyl acetal moiety, according to the route
depicted in Scheme 5. Monoalkoxylation was accomplished
by using a 5-fold excess of dichlorodiphenylsilane, the excess
of which could be recovered by distillation of the resulting
Scheme 4
(9) Cyclopentadienones are potent synthetic intermediates and used for
the synthesis polycyclic compounds, polymers, and natural products. For a
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Org. Lett., Vol. 4, No. 17, 2002
2839

mixture.13 The addition of another alkynol (814 or 1515) to
the obtained monochlorosilane 14 by using 2,6-lutidine as a
base afforded the diynes 16 and 17, which underwent
cyclocarbonylation to give the mixture of two diastereomers
18a,b and 19a,b, respectively. Treatment of the diastereo-
meric mixtures of the Fe(CO)3 complexes with Me3NO gave
single products 20 and 21.
only the cross-coupled product but also the homocoupled
products and possibly their regioisomers.
In conclusion, we have demonstrated that “silicon-
tethered” Fe(CO)5-promoted cyclocarbonylation can provide
an effective method for carbonylative cross-coupling of
alkynes to furnish cyclopentadienones with variable substit-
uents.
The diols 20 and 21 are equivalent to the products of an
intermolecular version of this reaction that would give not
Acknowledgment. We thank the National Science Foun-
dation for financial support.
(11) Modern Acetylene Chemistry; Stang, P. J., Diederich, F., Eds;
VCH: Weinheim, 1995.
Supporting Information Available: Experimental pro-
cedures, spectroscopic data, copies of 1H NMR and 13C NMR
spectra for new compounds. This material is available free
of charge via the Internet at http://pubs.acs.org.
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