Association of Fluorous “Phase-Vanishing” Method with Visible-Light Activation
FULL PAPER
spectrum revealed the presence of 45% of product 2 as determined
ether, 4:1) and found to be 2-bromo-1-methoxy-4-methylbenzene
by comparison with literature data.[23]
(19) (127 mg, 63%).[31]
The Effect of Solvent on the Bromination of 1 by the PV Method:
See Table 1. Bromine (104 µL, 2.02 mmol) was slowly added to oc-
tadecafluorooctane (FC-77) (3 mL) in a glass reactor (19 mm dia-
meter 60 mm length) using a glass syringe. Then a solution of 1
(297 mg, 2.00 mmol) in various solvents (1 mL) or neat was added
carefully to form three distinct phases. Gentle stirring of the bro-
mine and upper organic phase were performed, taking care not to
mix the phases. The fluorous/organic phase border was irradiated
by a 40 W incandescent light bulb. The reaction was run at room
temperature until all the bromine had disappeared and the fluorous
phase had become colourless. The contents of the reactor were then
transferred into a separating funnel, into which 10 mL of CH2Cl2
and 10 mL of 0.01 NaHSO3 were added and the phases sepa-
rated. The lower fluorous phase was recovered and reused without
any observable losses. The organic phase was washed with a satd.
solution of NaHCO3, dried with Na2SO4 and the solvent was evap-
orated. The crude reaction mixture was then analyzed by 1H NMR
spectroscopy and results are presented in Table 1.
Bromination of N-(p-Tolyl)acetamide (20): The product was purified
by preparative thin layer chromatography (SiO2, CH2Cl2/EtOAc,
2:3) and identified as N-(2-bromo-4-methylphenyl)acetamide (21)
(160 mg, 70%).[32]
Acknowledgments
This research was supported by the Ministry of Higher Education,
Science and Technology of the Republic of Slovenia and the Young
Researcher program (A. P.). We thank the European Union
(COST-program “New Fluorous Media and Processes for Cleaner
and Safer Chemistry”, D29/0011/032) and Fluorous Technologies
Inc. Academic Program. We are thankful to the staff of the
National NMR Centre at the National Institute of Chemistry in
Ljubljana for NMR experiments and the Mass Spectrometry Cen-
tre at the JSI.
General Procedure for Phase-Vanishing Bromination of Alkylben-
zenes: In a typical experiment, bromine (160 mg, 1.00 mmol) was
slowly added to octadecafluorooctane (FC-77) (3 mL) in a glass
reactor (19 mm diameter, 60 mm length) using a glass syringe. To
this was added a solution of alkyl benzene (1.00 mmol) in CH2Cl2
(1 mL) to form three distinct phases. Gentle stirring of the bromine
and upper organic phase were performed, taking care not to mix
the phases. The fluorous/organic phase border was then irradiated
(40 W) and the reaction allowed to proceed at room temperature
until the bromine had disappeared and the fluorous phase had be-
come colourless. After the aforementioned workup procedure, the
crude reaction mixture was analyzed by 1H NMR spectroscopy, the
products separated using chromatography and the pure compounds
identified on the basis of comparison with literature data.
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separated by column chromatography (SiO2, petroleum ether/
CH2Cl2, 9:1) and identified as 1-(bromomethyl)-4-tert-butylben-
zene (2) (152 mg, 67%),[23] 1-tert-butyl-4-(dibromomethyl)benzene
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chromatography (SiO2, petroleum ether/CH2Cl2, 9:1). The product
was identified as 1-(bromomethyl)benzene (7) (108 mg, 63%).[25]
Bromination of p-Xylene (8): The products were separated by col-
umn chromatography (SiO2, petroleum ether/CH2Cl2, 1.6:1). The
products were identified as 1-(bromomethyl)-4-methylbenzene (9)
(68 mg, 37%)[26] and 1,4-bis(bromomethyl)benzene (10) (53 mg,
20%).[27]
Bromination of Mesitylene (11): The product was purified by col-
umn chromatography (SiO2, petroleum ether/CH2Cl2, 4:1) and
identified as 2-bromo-1,3,5-trimethylbenzene (12) (74 mg, 37%).[25]
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Bromination of Ethyl 4-Methylbenzoate (13): The product was puri-
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identified as ethyl 4-(bromomethyl)benzoate (14) (72 mg, 30%).[28]
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Bromination of 1-(p-Tolyl)ethanone (15): The products were sepa-
rated by column chromatography (SiO2, CH2Cl2/petroleum ether,
3:1). The products were identified as 2-bromo-1-(4-methylphenyl)
ethanone (16) (149 mg, 70%)[29] and 2,2-dibromo-1-(4-meth-
ylphenyl)ethanone (17) (29 mg, 10%).[30]
Bromination of 1-Methoxy-4-methylbenzene (18): The product was
purified by column chromatography (SiO2, CH2Cl2/petroleum
Eur. J. Org. Chem. 2006, 483–488
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