Homogeneous Enantioselective Pauson–Khand-Type Cyclization
COMMUNICATIONS
none was found to be unsuccessful (Table 2, entry 9), References and Notes
probably due to the coordination of the thiophene moi-
ety to the metal center which rendered the metal com-
plex coordinatively saturated.
[1] a) I. U. Khand, G. R. Knox, P. L. Pauson, W. E. Watts, J.
Chem. Soc. Chem. Commun. 1971, 36; b) I. U. Khand,
G. R. Knox, P. L. Pauson, W. E. Watts, M. I. Foreman,
J. Chem. Soc. Perkin Trans. 1 1973, 977.
These reaction conditions were also used to explore
other nitrogen- and carbon-tethered enynes (Table 2,
entries 10–13). Excellent isolated yields were obtained
and high ee values were observed either in N- or C-teth-
ered substrates withalkyl substitution (instead of a phe-
nyl group) (Table 2, entries 10–13).
In summary, we have developed an interesting homo-
geneous system for the efficient decarbonylation and
cascaded asymmetric Pauson–Khand-type cyclizations
in a relatively non-toxic alcoholic medium. In the pres-
ence of the axially chiral (S)-BisbenzodioxanPhos li-
gand, O-, N- and C-tethered cyclopentenones were ob-
tained withgood to excellent ees in this cooperative
dual catalysis. Interestingly, the electronic influence of
the substrate was found to be responsible for the enan-
tioselectivity of the product.
[2] For reviews on PKR, see: a) N. Jeong, in: Transition Met-
als In Organic Synthesis: Building Blocks and Fine
Chemicals, (Eds.: M. Beller, C. Bolm), Wiley-VCH,
Weinheim, 1998, Vol. 1, p. 560; b) Y. K. Chung, Coord.
Chem. Rev. 1999, 188, 297; c) S. L. Buchwald, F. A. Hicks,
in: Comprehensive Asymmetric Catalysis, Vol. II, (Eds.:
E. N. Jacobsen, A. Pfaltz, H. Yamamoto), Springer, Ber-
lin, Heidelberg, 1999, p. 491; d) K. M. Brummond, J. L.
Kent, Tetrahedron 2000, 56, 3263; e) A. J. Fletcher,
S. D. R. Christie, J. Chem. Soc. Perkin Trans. 1 2000,
1657; f) M. R. Rivero, J. Adrio, J. C. Carretero, Eur. J.
Org. Chem. 2002, 2881; g) S. T. Ingate, J. Marco-Contelle,
˜
Org. Prep. Proced. Int. 1998, 30, 121; h) L. V. R. Bonaga,
M. E. Krafft, Tetrahedron 2004, 60, 9795; i) D. Strübing,
M. Beller, in: Transition Metals In Organic Synthesis:
Building Blocks and Fine Chemicals, (Eds.: M. Beller,
C. Bolm), 2nd edn., Wiley-VCH, Weinheim, 2004, Vol.
1, p. 619; j) K. H. Park, Y. K. Chung, Synlett 2005, 545;
for most recent review on intermolecular PKR, see:
k) S. E. Gibson, N. Mainolfi, Angew. Chem. Int. Ed.
2005, 44, 3022.
Experimental Section
General Procedures for Asymmetric Pauson–Khand-
type Cyclization of Various Enynes
[3] For recent selected pharmaceutical/biological examples,
see: a) T. F. Jamison, S. Shambayati, W. E. Crowe, S. L.
Schreiber, J. Am. Chem. Soc. 1994, 116, 5505; b) K. M.
Brummond, D. Gao, Org. Lett. 2003, 5, 3491; c) B. Jiang,
M. Xu, Angew. Chem. 2004, 116, 2597; Angew. Chem. Int.
Ed. 2004, 43, 2543; d) J. Velcicky, A. Lanver, J. Lex, A.
Prokop, T. Wieder, H.-G. Schmalz, Chem. Eur. J. 2004,
10, 5087; for most recent applications, see: e) J. D. Win-
kler, E. C. Y. Lee, L. I. Nevels, Org. Lett. 2005, 7, 1489;
f) A. Lanver, H.-G. Schmalz, Eur. J. Org. Chem. 2005,
1444; for a recent review, see: g) J. Blanco-Urgoiti, L.
[Rh(COD)Cl]2 (4.4 mg, 9.0 mmol), (S)-BisBenzodioxanPhos
(11.5 mg, 18.0 mmol), aldehyde (0.45 mmol, 1.5 equivs. with re-
spected to enyne) and Teflon-coated magnetic stirrer bar
(3 mmꢀ10 mm) were charged to a Teflon-lined screw-capped
vial on the bench-top at room temperature with continuous
stirring. The enyne (0.3 mmol) was then added. These vials
were evacuated and backfilled withnitrogen (3 cycles), fol-
lowed by the addition of unpurified tert-amyl alcohol
(0.2 mL, 1.5 M, from benchgrade 4-L bottle, prior bubbled
withnitrogen for 2 min). The reaction mixtures were magneti-
cally stirred in a preheated 1008C (ꢂ38C) oil bathfor 36 hours
(reaction times were unoptimized for eachsubstrate). The vials
were allowed to reach room temperature. Diethyl ether or eth-
yl acetate (~2 mL) was added. The crude reaction mixtures
were directly purified by column chromatography on silica
gel using hexane/ethyl acetate mixture as the eluent to afford
the chiral bicyclic cyclopentenones. The enantiomeric excess
of the products were determined by chiral HPLC analysis using
Chiralcelꢂ columns.
´
´
˜
Anorbe, L. Perez-Serrano, G. Domínguez, J. Perez-Cas-
tells, Chem. Soc. Rev. 2004, 33, 32.
[4] For recent reviews on catalytic PKR, see: a) S. E. Gib-
son, A. Stevenazzi, Angew. Chem. 2003, 115, 1844; An-
gew. Chem. Int. Ed. 2003, 42, 1800; b) B. E. Hanson,
Comments Inorg. Chem. 2002, #41#23, 289.
[5] For recent enantioselective Co-catalyzed PKR withCO
gas, see: a) S. J. Sturla, S. L. Buchwald, J. Org. Chem.
1999, 64, 5547; b) S. J. Sturla, S. L. Buchwald, J. Org.
Chem. 2002, 67, 3398; c) K. Hiroi, T. Watanabe, R. Kawa-
gishi, I. Abe, Tetrahedron Lett. 2000, 41, 891; d) K. Hiroi,
T. Watanabe, R. Kawagishi, I. Abe, Tetrahedron: Asym-
See Supporting Information for the preparation of enyne
substrates, detailed characterization data and chiral HPLC
conditions for the optically active cyclopentenones.
`
metry 2000, 11, 797; e) X. Verdaguer, M. A. Pericas, A.
Riera, M. A. Maestro, J. Mahía, Organometallics 2003,
22, 1868; f) D. Konya, F. Robert, Y. Gimbert, A. E.
Greene, Tetrahedron Lett. 2004, 45, 6975; g) X. Verda-
Acknowledgements
We thank the University Grants Committee Areas of Excellence
Scheme in Hong Kong (Project No. AoE/P-10/01) and The
Hong Kong Polytechnic University Area of Strategic Develop-
ment Fund for financial support of this study. We thank Miss
Yi Sha Cheng for her initial preparation of some enyne substrate
precursors.
´
´
guer, A. Lledo, C. Lopez-Mosquera, M. A. Maestro,
`
M. A. Pericas, A. Riera, J. Org. Chem. 2004, 69, 8053;
for a most recent reference, see: h) S. E. Gibson,
K. A. C. Kaufmann, J. A. Loch, J. W. Steed, A. J. P.
White, Chem. Eur. J. 2005, 11, 2566.
Adv. Synth. Catal. 2005, 347, 1750 – 1754
ꢁ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
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