Angewandte
Chemie
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[4] Aldol: a) T. S. Powers, Y. Shi, K. J. Wilson, W. D. Wulff, A. L.
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485.
[5] The methoxy-amine exchange reaction has occasionally served
in the preparation of amino carbenes C (X* = (S)-methoxyme-
thylpyrrolidines): A. Rahm, A. L. Rheingold, W. D. Wulff,
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[6] J. Barluenga, A. Ballesteros, R. Bernardo de la Rffla, J. Santa-
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taken by oxidation with pyridine oxide to 1,3-diphenyl-1-
propynone.
[13] The cycloaddition of carbodienes to chiral ethynyl(amino)-
carbenes of chromium and tungsten derived from (S)-methox-
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with moderate selectivity (d.r. 60:40–86:14).[5]
[14] a) For [4+2] cycloaddition of chiral acetylenic diesters, see: R. N.
Buckle, D. J. Burnell, Tetrahedron 1999, 55, 14829; b) for [2+2]
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[15] For leading papers on asymmetric, catalyzed reactions involving
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dron Lett. 1997, 38, 3981.
[17] CCDC-268919 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from
cam.ac.uk/data_request/cif.
[8] A. Padwa, D. J. Austin, Y. Gareau, J. M. Kassir, S. L. Xu, J. Am.
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[11] The formation of diynyl(amino)carbene complexes by copper-
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tungsten(0) with bromoalkynes is known: C. Hartbaum, H.
Fischer, Chem. Ber. 1997, 130, 1063.
[19] A reviewer pointed out that the cyclization of 13 into 12 could be
seen, not only as an intramolecular Michael-type addition, but
alternatively as an electrocyclization reaction. a) for pseudoper-
icyclic cyclizations of (Z)-1,2,4,6-heptatetraene derivatives, see:
J. Rodríguez-Otero, E. M. Cabaleiro-Lago, Chem. Eur. J. 2003, 9,
1837; b) for torquoselectivity in electrocyclic reactions of 1-aza-
1,3,5-trienes, see: M. J. Walker, B. N. Hietbrink, B. E. Thomas,
IV, K. Nakamura, E. A. Kallel, K. N. Houk, J. Org. Chem. 2001,
66, 6669; c) for a preliminary communication on torquoselec-
tivity in electrocyclic reactions of (Z)-1,2,4,6-heptatetraenes,
see: B. N. Hietbrink, C. A. Merlic, K. N. Houk, Abstract of
Papers, 221st ACS National Meeting, San Diego (CA), 2001,
ORGN-354.
[12] a) The
pentacarbonyl[phenylethynyl(ethoxy)carbene]molyb-
denum(0) complex has been used for kinetic studies, but details
on its preparation and spectral data are not given: R. Pipoh, R.
van Eldik, G. Henkel, Organometallics 1993, 12, 2236; b) Car-
bonylcyclopentadienyl [methoxy(4-methylphenyl)ethynylcar-
bene]nitrosylmolybdenum has been obtained in 12% yield:
K. H. Dötz, C. Christoffers, J. Christoffers, D. Böttcher, M.
Nieger, S. Kotila, Chem. Ber. 1995, 128, 645.
[20] This demetalation procedure will be optimized and the details
publish elsewhere.
[21] For efficient access through 1,4-nucleophilic addition of ketene
silyl acetals to chiral pyridinium salts, see: S. Yamada, C. Morita,
J. Am. Chem. Soc. 2002, 124, 8184.
Angew. Chem. Int. Ed. 2005, 44, 4981 –4983
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