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Synlett 2005(7): 1142-1146  
DOI: 10.1055/s-2005-865242
LETTER
© Georg Thieme Verlag Stuttgart · New York

Olefin and Enyne Cross-Metathesis - A New Tool for the Synthesis of Alkenyl-substituted Azulenes

Agnieszka Mikusb, Volodymyr Sashuka, Mariusz Kūdzioreka, Cezary Samojowicza, Stanisaw Ostrowski*a,b, Karol Grela*a
a Institute of Organic Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warszawa, Poland
Fax: +48(22)6326681; e-Mail: grela@icho.edu.pl;
b Institute of Chemistry, University of Podlasie, ul. 3 Maja 54, 08-110 Siedlce, Poland
Fax: +48(25)6442045; e-Mail: stan@ap.siedlce.pl;
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Publication History

Received 11 January 2005
Publication Date:
20 April 2005 (online)

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Abstract

A selective synthesis of azulenes with an extended π-electron system by olefin and enyne cross-metathesis is described. Electron-enriched five-membered ring and electron-deficient seven-membered ring of the azulene moiety affected the reaction yield.

Key words

azulene derivatives - olefin and enyne metathesis - ruthenium complexes

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Mkosza, M.; Kêdziorek, M.; Hafner, K.; Ostrowski, S. Eur. J. Org. Chem., in preparation.

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These substrates were prepared either from (1-propynyl)- azulenes via Lindlar reduction (2b → 3a, 2e → 3c) or from the corresponding iodo-derivative via Stille coupling (3b): Sashuk, V. PhD Dissertation, in preparation.

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NMR spectra were recorded with a Varian GEMINI-200 spectrometer operating at 200 MHz for 1H NMR and 50 MHz for 13C NMR. Coupling constants J are expressed in Hz. Mass spectra were measured with an AMD 604 (AMD Intectra GmbH, Germany) spectrometer (EI method). IR spectra were measured with Perkin-Elmer Spectrum 2000 FT-IR spectrometer. TLC analysis was performed on aluminium foil plates pre-coated with silica gel (60F 254, Merck). Silica gel, 230-400 mesh (Merck AG), was used for column chromatography.

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Typical procedure for enyne metathesis with ethylene: A pressure tube (50 mL) was thoroughly flushed with argon and charged with a solution of an azulene derivative 2d (30 mg, 0.097 mmol) and the catalyst 1c (ca. 15 mol%) in anhydrous CH2Cl2 (4 mL). The tube was immersed in liquid nitrogen (ca. -190 °C) and gaseous ethylene was delivered to the tube through rubber septa. Once accumulation of ethylene had occurred, the tube was sealed and the reaction mixture was allowed to reach room temperature. The mixture was stirred under the ethylene gas atmosphere (12 atm) for approximately 44 h. Then it was recooled in liquid nitrogen and the tube was opened. The mixture was allowed to reach room temperature under a stream of argon. The residue was concentrated under reduced pressure and purified by column chromatography (eluent: CHCl3) to give the product 5d as a dark-green solid (blue-green in CHCl3 solution); yield: 15.0 mg (46%); mp 79-81°C. 1H NMR (CDCl3, 200 MHz): d = 8.24 (d, J = 10.8 Hz, 2 H), 7.77 (s, 1 H), 7.24 (d, J = 10.8 Hz, 2 H), 6.64 (dd, J = 17.5,10.9 Hz, 1 H, H-vinyl), 5.46-5.03 (m, 4 H, H-vinyl). 13C NMR (CDCl3, 50 MHz): d = 139.0, 137.9, 135.7, 135.6, 135.0, 127.3, 125.0, 119.1, 118.4, 102.8. MS (EI): m/z (%) = 341 (1), 340 (9), 339 (3), 338 (19), 337 (2), 336 (10) [isotopic M +· ], 310 (5), 260 (1), 259 (6), 258 (6), 257 (6), 256 (5), 179 (16), 178 (100), 177 (18), 176 (20), 175 (2), 153 (1), 152 (11), 151 (10), 150 (15), 149 (3), 126 (3), 125 (4), 124 (2), 123 (1), 89 (10), 88 (8), 87 (3), 76 (11), 75 (10). HR-MS (EI): m/z calcd for C14H10 79Br2, 335.9149; found, 335.9151. Anal. Calcd for C14H10Br2 (338.04): C, 49.74; H, 2.98. Found: C, 50.67; H, 3.49.

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Typical procedure for CM with olefins 4b-e. ( E )-3-(6-Azulenyl)-2-propenyl acetate ( 6c): To a mixture of 3c (21 mg. 0.125 mmol) and olefin 4d (43 mg, 0.250 mmol) in anhydrous CH2Cl2 (6 mL) a solution of 1c (8.4 mg, 10 mol%) in CH2Cl2 (1 mL) was added. The resulting mixture was stirred at 45 °C for 24 h under argon. The solvent was removed under reduced pressure. Flash chromatography (eluent: cyclohexane-EtOAc, 8:2) of the crude dark residue gave 19 mg of 6c (56%) as a dark-blue solid. IR (KBr): 1741, 1735, 1574, 1516, 1477, 1398, 1341, 1243, 1105, 1077, 1026, 961, 860, 782, 759 cm-1. 1H NMR (CDCl3, 200 MHz): δ = 8.28 (d, J = 10.6 Hz, 2 H), 7.85 (apparent t, J = 3.7 Hz, 1 H), 7.35 (d, J = 3.7 Hz, 2 H), 7.27 (d, J = 10.6 Hz, 2 H), 6.84 (d, J = 16.0 Hz, 1 H), 6.48 (dt, J = 16.0, 6.3 Hz, 1 H), 4.80 (dd, J = 6.3, 1.4 Hz, 2 H), 2.14 (s, 3 H, CH3). 13C NMR (CDCl3, 50 MHz): δ = 170.7 (C=O), 144.4, 139.3, 138.0, 137.0, 135.5, 126.9, 121.6, 118.5, 64.8 (CH2), 21.0 (CH3). MS (EI): m/z (%) = 227 (17), 226 (100) [isotopic M +· ], 184 (26), 177 (25), 176 (33), 166 (29), 165 (77), 155 (52), 153 (20), 152 (31), 128 (19), 43 (58); HR-MS (EI): m/z calcd for C15H14O2, 226.0994; found, 226.0999.