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Synlett 2008(15): 2287-2290  
DOI: 10.1055/s-2008-1078269
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of Phthalonitriles Using a Palladium Catalyst

Zafar Iqbala, Alexey Lyubimtseva,b, Michael Hanack*a
a Institut für Organische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
Fax: +49(7071)295244; e-Mail: hanack@uni-tuebingen.de;
b Ivanovo State University of Chemistry and Technology, Organic Chemistry Department, F. Engels Str. 7, 153460 Ivanovo, Russian ­Federation
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Received 29 May 2008
Publikationsdatum:
22. August 2008 (online)

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Abstract

An easy synthetic method to obtain phthalonitriles from o-dibromobenzenes under mild conditions in high yields using Zn(CN)2 and a catalytic amount of tris(dibenzylideneacetone)dipalladium and 1,1′-bis(diphenylphosphino)ferrocene is described.

Key words

cyanation - o-dibromobenzenes - palladium - phthalo­nitriles

    References and Notes

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    Synthesis of 1,2-Dibromo-4- tert -butylbenzene ( 2a) To a solution of 1-bromo-4-tert-butylbenzene (8 g, 0.04 mol) in CCl4 (5 mL) in the presence of a small amount of iron powder was added a solution of bromine (9.5 g, 0.12 mol) in CCl4 (4 mL) at 5 ˚C over 10 min. The mixture was stirred at 15 ˚C for 2 h. Solvent was evaporated and product was purified by column chromatography using CH2Cl2-hexane (1:1) as eluent; yield 11 g (92%). ¹H NMR (400 MHz, CDCl3): δ = 7.59 (d, 4 J = 2.3 Hz, 1 H), 7.50 (d, ³ J = 8.4 Hz, 1 H), 7.16 (dd, ³ J = 8.4 Hz, 4 J = 2.3 Hz, 1 H), 1.27 (s, 9 H) ppm. MS (EI): m/z (%) = 291.8 (45) [M]+, 276.8 (100).

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    Synthesis of tert -Butyl-(3,4-dibromophenoxy)dimethylsilane ( 9a) and 3,4-Dibromophenol ( 10a)
    The hydroxy group in 3-bromophenol was protected with tert-butyldimethylsilyl chloride in the presence of imidazole to give tert-butyl(3-bromophenoxy)dimethylsilane quantitatively. [¹²b] ¹H NMR (400 MHz, CDCl3): δ = 7.09-7.04 (m, 2 H), 7.01-6.96 (m, 1 H), 6.79-6.70 (m, 1 H), 0.96 (s, 9 H), 0.18 (s, 6 H) ppm. MS (EI): m/z (%) = 286.0 (20) [M]+, 231.0 (100), which was brominated with NBS. [¹0c] After purification by column chromatography tert-butyl(3,4-dibromophenoxy)dimethylsilane (9a) was obtained in 78% yield. ¹H NMR (400 MHz, CDCl3): δ = 7.41 (d, ³ J = 7.5 Hz, 1 H), 7.10 (d, 4 J = 2.5 Hz, 1 H), 6.64 (dd, ³ J = 7.5 Hz, 4 J = 2.5 Hz, 1 H), 0.95 (s, 9 H), 0.18 (s, 6 H) ppm. MS (EI): m/z (%) = 365.9 (40) [M]+, 308.9 (100). tert-Butyldimeth-ylsilyl group in 9a was deprotected with tetrabutyl-ammonium fluoride [¹²b] to give 3,4-dibromophenol (10a) in 92% yield. ¹H NMR (400 MHz, CDCl3): δ = 7.28 (d, ³ J = 8.6 Hz, 1 H), 7.02 (s, 1 H), 6.55 (d, ³ J = 8.6 Hz, 1 H) ppm. MS (EI): m/z (%) = 252.0 (100) [M]+.

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  • 16a

    Synthesis of 6,7-Dibromo-2,2-dimethylnaphtho[2,3- d ][1,3]dioxole ( 19a)
    To 5.6 g (17.6 mmol) of 2,3-dibromo-6,7-dihydroxy-naphthalene [¹6b] dissolved in toluene (40 mL) toluene and anhydrous acetone (5 mL) was added P2O5 in three portions during 48 h while the reaction mixture was heated at 50 ˚C. The solution was diluted with toluene (50 mL), washed with H2O, 10% NaOH soln, H2O and brine. Combined organic phase was concentrated with a rotary evaporator. Purification of the crude product was carried out by column chromatography using dichloromethane as eluent; yield 3.42 g (57%). ¹H NMR (400 MHz, CDCl3): δ = 7.88 (s, 2 H), 6.87 (s, 2 H), 1.71 (s, 6 H) ppm. MS (EI): m/z (%) = 357.9 (60) [M]+, 342.8 (100).

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7

Synthesis of Substituted Phthalonitriles - General Procedure A 25 mL two-neck round-bottom flask was charged with 1 mmol of o-dibromobenzene in DMAC (2 mL) and PMHS (20 mg) was added at r.t. The reaction mixture was heated to the required temperature (Table  [¹] ) and Pd2 (dba)3 (20 mg, 2 mol%) and DPPF (15 mg, 2.7 mol%) were added. Afterwards, Zn(CN)2 (117 mg, 1 mmol) was added in 4-5 portions during the time mentioned in Table  [¹] till TLC indicated completion of the reaction. The reaction mixture was cooled, diluted with EtOAc and filtered. Filtrate was washed with H2O, dried with MgSO4, and concentrated in vacuo. The crude product was purified by column chromatography using CH2Cl2 as eluent.

11

Synthesis of 1,2-Dibromo-4-acetanilide ( 8a)
3-Bromoacetanilide was brominated with NBS in acetone with catalytic amounts of HCl [¹0c] to give after purification by column chromatography 1,2-dibromo-4-acetanilide (8a) in 90% yield. ¹H NMR (400 MHz, CDCl3): δ = 7.84 (s, 1 H), 7.50 (d, ³ J = 8.8 Hz, 1 H), 7.38 (br s , 1 H), 7.30 (d, ³ J = 8.8 Hz, 1 H), 2.15 (s, 3 H) ppm. MS (EI): m/z (%) = 293.0 (100) [M]+.

17

Compound 19b: ¹H NMR (400 MHz, CDCl3): δ = 8.05 (s, 2 H), 7.10 (s, 2 H), 1.77 (s, 6 H) ppm. MS (EI): m/z (%) = 250.0 (40) [M]+, 235.0 (100), 210.0 (50).