Author Topic: Bromination w/NBS  (Read 5762 times)

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Rhodium

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Trifluoromethylation
« Reply #20 on: April 01, 2002, 07:24:00 PM »
Oh, I was thinking of Chemistry Letters, pp. 1719-20 (1981):
Abstract

Regiospecific trifluoromethylation by substitution of the halogen in aromatic halides was achieved by the use of sodium trifluoroacetate and copper(I)iodide. The reaction proceeded smoothly in dipolar aprotic solvents in good to high yields.

Example

A mixture of iodobenzene (5mmol), sodium trifluoroacetate (20mmol), and copper(I)iodide (10mmol) in N-methylpyrrolidone (NMP) (40ml) was heated under argon atmosphere. Evolution of CO2 began at around 140°C. After 4h stirring at 160°C, work-up of the resulting mixture afforded trifluoromethylbenzene in 72% yield (GLC). The reaction can be carried out in glass apparatus under normal pressure.

Iodobenzene => Trifluoromethylbenzene (72%)
m-Bromotoluene => m-Trifluoromethyl-toluene (58%)
2-Bromopyridine => Trifluoromethylpyridine (41%)

Please give me your refs! Do you think it would be best to start with 1,4-dimethoxyiodobenzene or a protected 2C-I for best yields? I am not sure if vilsmeyer formylation (or dichloromethyl methyl ether/TiCl4 formylation) would proceed with good yields on a trifluoromethylated substrate.