Synlett 2005(5): 0805-0808  
DOI: 10.1055/s-2005-863746
LETTER
© Georg Thieme Verlag Stuttgart · New York

Cyclopentenones from a Novel [4+1]Cocyclization of Methylenecyclopropanes with Fischer Carbenechromium Complexes [1]

Takuya Kurahashia, Yao-Ting Wua, Kathrin Meindlb, Stephan Rühlb, Armin de Meijere*a
a Institut für Organische und Biomolekulare Chemie der Georg-August-Universität Göttingen, Tammannstraße 2, 37077 Göttingen, Germany
Fax: +49(551)399475; e-Mail: Armin.deMeijere@chemie.uni-goettingen.de;
b Institut für Anorganische Chemie der Georg-August-Universität Göttingen, Tammannstraße 4, 37077 Göttingen, Germany
Further Information

Publication History

Received 13 January 2005
Publication Date:
09 March 2005 (online)

Abstract

Fischer carbenechromium complexes react with methylenecyclopropanes and bicyclopropylidene in an unprecedented manner. All four carbon atoms of the methylenecyclopropane moiety along with carbon monoxide are incorporated with the formation of three new C-C σ-bonds to give substituted cyclopentenone derivatives in moderate (33-58% for methylenecyclopropanes) to good yields (65-72% for bicyclopropylidene).

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Representative Procedure.
To a solution of the carbene complex 2-Me (271 mg, 1 mmol) in MeOH (10 mL) was added methylenecyclo-propane 1a (130 mg, 1 mmol) and H2O (48 mg, 3 mmol). The screw-cap vial was sealed and heated at 70 °C for 24 h. The cooled reaction mixture was diluted with Et2O (20 mL) and stirred under air for 6 h. Filtration through Celite and purification by column chromatography (hexane-Et2O, 4: 1) gave 3a-Me (127 mg, 0.55 mmol, 55%) as a pale yellow oil. R f = 0.41 (hexane-Et2O, 4: 1). 1H NMR (500 MHz, CDCl3): δ = 1.26 (t, J = 7.0 Hz, 3 H), 1.45 (d, J = 6.5 Hz, 3 H), 2.74 (d, J = 18.5 Hz, 1 H), 3.17 (dd, J = 18.5, 7.0 Hz, 1 H), 3.54 (q, J = 7.0 Hz, 2 H), 3.65 (dd, J = 7.0, 3.0 Hz, 1 H), 4.34 (q, J = 6.5 Hz, 1 H), 6.18 (m, 1 H), 7.15 (m, 2 H), 7.31 (m, 3 H). 13C NMR (125 MHz, CDCl3): δ = 15.4, 19.8, 37.1, 51.9, 64.8, 74.6, 126.9, 127.5, 128.1, 128.8, 139.5, 181.9, 208.4. IR (neat): 3061, 3028, 2977, 2931, 2872, 1700, 1617, 1496, 1455, 1373, 1252, 1159, 1100, 871, 756, 701, 634 cm-1. MS: m/z (%) = 232/231/230 (1/16/100) [M+], 229 (1) [M+ - 1], 185 (69) [M+ - EtO], 157 (58), 129 (68), 91 (84). Anal. Calcd for C15H18O2: C, 78.23; H, 7.88. Found: C, 78.08; H, 7.60. Spectroscopic data of the minor diastereomer (R f = 0.37): 1H NMR (500 MHz, CDCl3): δ = 1.15 (t, J = 7.0 Hz, 3 H), 1.29 (d, J = 7.0 Hz, 3 H), 2.44 (dd, J = 18.5, 2.5 Hz, 1 H), 2.99 (dd, J = 18.5, 7.0 Hz, 1 H), 3.28 (qd, J = 7.0, 2.5 Hz, 1 H), 3.40 (qd, J = 7.0, 2.0 Hz, 1 H), 3.81 (qd, J = 7.0, 1.5 Hz, 1 H), 3.98 (dt, J = 7.0, 2.0 Hz, 1 H), 6.33 (m, 1 H), 7.16 (m, 2 H), 7.28 (m, 3 H). 13C NMR (125 MHz, CDCl3): δ = 15.3, 20.0, 46.0, 46.7, 64.5, 73.4, 127.1, 127.4, 128.5, 129.1, 141.0, 184.8, 208.3. The diastereomeric ratio was determined according to the integrals of distinguishable signals in the 1H NMR spectrum of the crude product mixture: major isomer δ = 6.18 (m, 1 H); minor isomer δ = 6.33 (m, 1 H).

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Compound 3a-Ph: C20H20O2, triclinic crystals of space group P-1, unit cell dimensions: a = 5.804 (4), b = 11.023 (4), c = 12.772 (4) Å, α = 94.72 (3), β = 100.79 (4), γ = 91.16 (4)°, V = 799.4 (6) Å3, 7814 reflections. Compound 3g-Ph: C16H18O2, triclinic crystals of space group P-1, unit cell dimensions: a = 7.253 (2), b = 11.094 (2), c = 17.226 (2) Å, α = 75.77 (2), β = 81.14 (2), γ = 75.59 (2)°, V = 1294.9 (5) Å3, 16431 reflections. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-255973 (3a-Ph) and CCDC-258435 (3g-Ph). Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[fax: +44 (1223)336033; email: deposit@ccdc.cam.ac.uk].