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DOI: 10.1055/s-2008-1078269
Synthesis of Phthalonitriles Using a Palladium Catalyst
Publication History
Publication Date:
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
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1a
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10a
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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10b
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12a
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]+. -
12b
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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). -
16b
Youssev TE.Hanack M. J. Porphyrins Phthalocyanines 2002, 6: 571
References and Notes
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]+.
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).