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Synlett 2007(13): 2061-2064  
DOI: 10.1055/s-2007-984901
LETTER
© Georg Thieme Verlag Stuttgart · New York

A New Facile Synthesis of 1,1-Dibromo-2-arylethenes

Piotr Pawluć, Grzegorz Hreczycho, Jędrzej Walkowiak, Bogdan Marciniec*
Department of Organometallic Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60780 Poznan, Poland
Fax: +48(61)8291508; e-Mail: marcinb@amu.edu.pl;
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Publication History

Received 23 May 2007
Publication Date:
17 July 2007 (online)

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Abstract

Synthetically useful 1,1-dibromo-2-arylethenes were readily prepared in good yields via double bromodesilylation of the easily accessible 1,1-bis(trimethylsilyl)-2-arylethenes using N-bromo­succinimide under mild conditions.

Key words

1,1-dibromo-1-alkenes - bromodesilylation - halogenation - organometallic reagents - silicon derivatives

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A Typical Procedure for the Synthesis of 1,1-Dibromo-2-arylethenes and Spectroscopic Data of Selected Products: N-Bromosuccinimide (3.55 g, 20 mmol) was added to the solution of the corresponding 1,1-bis(silyl)-2-arylethene (2 mmol) in anhyd MeCN (20 mL) and the suspension was stirred at r.t. for the appropriate time (see Table [1] ). The solvent was then evaporated and the mixture was extracted with n-hexane (50 mL). After extraction with an aqueous solution of Na2S2O3 (5%, 50 mL) the organic layer was concentrated and the crude product was preloaded on to silica. 1,1-Dibromo-2-arylethenes were purified by silica chromatography, eluting with n-hexane-EtOAc (25:1).
1,1-Dibromo-2-(3-methoxyphenyl)ethene (4): yield: 0.514 g, 88%; yellowish oil. 1H NMR (CDCl3): δ = 3.86 (3 H, Me), 6.88-6.96 (m, 2 H), 7.30-7.34 (m, 1 H), 7.60 (s, 1 H, CH=), 7.68-7.72 (m, 1 H). 13C NMR (CDCl3): δ = 55.2 (3 H, Me), 89.6 (=CBr2), 110.3, 121.2, 124.2, 128.8, 129.9 (Ar), 132.8 (CH=), 156.4 (>COMe). MS (EI): m/z (%rel. int.) = 292 (56) [M+], 277 (55), 210 (20), 168 (26), 132 (90), 117 (58), 102 (15), 89 (100), 74 (20), 63 (78). HRMS: m/z [M+ + 2] calcd for C9H8Br2O: 291.8922; found: 291.8916.
1,1-Dibromo-2-(4-nitrophenyl)ethene (6): yield: 0.454 g, 74%; yellow crystals; mp 105-106 °C. 1H NMR (CDCl3): δ = 7.55 (s, 1 H, CH=), 7.68 (d, J = 8.8 Hz, 2 H, Ar), 8.24 (d, J = 8.8 Hz, 2 H, Ar). 13C NMR (CDCl3): δ = 94.3 (=CBr2), 123.3, 129.1, 134.8 (Ar), 138.5 (CH=), 141.4 (>CNO2). MS (EI): m/z (%rel. int.) = 307 (52) [M+], 286 (78), 249 (20), 220 (25), 180 (25), 139 (95), 101 (54), 89 (30), 75 (100), 63 (20), 50 (34). HRMS: m/z [M+ + 2] calcd for C8H5Br2NO2: 306.8667; found: 306.8654.
1,1-Dibromo-2-(4-acetylphenyl)ethene (7): yield: 0.547 g, 90%; yellowish crystals; mp 73-74 °C. 1H NMR (CDCl3): δ = 2.60 (3 H, Me), 7.68 (s, 1 H, CH=), 7.30 (d, J = 8.2 Hz, 2 H, Ar), 7.76 (d, J = 8.2 Hz, 2 H, Ar). 13C NMR (CDCl3): δ = 28.9 (Me), 91.8 (=CBr2), 128.0, 135.6, 147.7 (Ar), 148.9 (CH=), 153.3 (Ar), 196.3 (CO). MS (EI): m/z (%rel. int.) = 304 (25) [M+], 289 (100), 261 (20), 180 (25), 129 (15), 101 (30), 75 (30), 50 (20). HRMS: m/z [M+] calcd for C10H8Br2O: 303.9779; found: 303.9786.
1,1-Dibromo-2-(4-bromophenyl)ethene (8): yield: 0.531 g, 78%; colorless oil. 1H NMR (CDCl3): δ = 7.60 (d, J = 8.6 Hz, 2 H, Ar), 7.52 (s, 1 H, CH=), 7.71 (d, J = 8.6 Hz, 2 H, Ar). 13C NMR (CDCl3): δ = 90.2 (=CBr2), 122.6, 129.8, 132.4, 134.1 (Ar), 135.6 (CH=). MS (EI): m/z (%rel. int.) = 341 (100) [M+], 261 (45), 180 (60), 101 (46), 75 (48), 50 (40). HRMS: m/z [M+ + 2] calcd for C9H5Br3: 339.7921; found: 339.7930.

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Synthesis of 1,4-Bis(2,2-dibromoethenyl)benzene (10): N-Bromosuccinimide (3.55 g, 20 mmol) was added to the solution of 1,4-bis[2,2-bis(trimethylsilyl)ethenyl]benzene (0.418 g, 1 mmol) in anhyd MeCN (50 mL) and the suspension was stirred at r.t. for 24 h. The solvent was then evaporated and the mixture was extracted with n-hexane (50 mL). After extraction with aqueous solution of Na2S2O3 (5%, 50 mL) the organic layer was concentrated and the crude product was preloaded onto silica. 1,4-Bis(2,2-di-bromoethenyl)benzene was purified by silica gel chromatog-raphy, eluting with n-hexane-EtOAc (25:1) (0.397 g, 89%; white crystals; mp 108-109 °C). 1H NMR (CDCl3): δ = 7.39 (s, 2 H, CH=), 7.68 (s, 4 H, Ar). 13C NMR (CDCl3): δ = 90.4 (=CBr2), 128.4, 132.3 (Ar), 136.2 (CH=). MS (EI):
m/z (%rel. int.) = 446 (100) [M+], 365 (12), 286 (30), 206 (18), 126 (48), 63 (25). HRMS: m/z [M+] calcd for C10H6Br4: 445.7162; found: 445.7176.

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Synthesis of 1,4-Bis[2,2-bis(trimethylsilyl)ethenyl] benzene (9): A mixture consisting of palladium(II) acetate (67.0 mg, 0.30 mmol), triphenylphosphine (157.2 mg, 0.6 mmol), silver nitrate (1.70 g, 10 mmol), 1,4-diiodobenzene (5 mmol), 1,1-bis(trimethylsilyl)ethane (10 mmol, 1.72 g), triethylamine (2.80 mL, 20 mmol) and acetonitrile (30 mL) was placed in a 50-mL, two-necked, round-bottomed flask equipped with a magnetic stirring bar and reflux condenser. The suspension was heated in an oil-bath at 80 °C for 2 h. After cooling to r.t., the reaction mixture was added to H2O (50 mL) and extracted with pentane (2 × 30 mL). The combined organic layers were dried (MgSO4) and the crude product obtained was then purified by column chromatog-raphy (silica gel, pentane) to give the pure product (2.01 g, 96%) as white crystals. 1H NMR (CDCl3): δ = -0.01 (s, 18 H, SiMe), 0.18 (s, 18 H, SiMe), 7.12 (s, 4 H, Ar), 7.72 (s, 2 H, =CH). 13C NMR (CDCl3): δ = 0.5 (SiMe), 2.1 (SiMe), 127.4, 141.4 (Ar), 146.3 (CH=), 154.7 (>C=). MS (EI): m/z (%rel. int.) = 418 (10) [M+], 345 (15), 257 (10), 171 (100), 131 (10), 73 (15). HRMS: m/z calcd for C22H42Si4: 418.2363; found: 418.2348.