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A Useful Brominating Reagent

Bromodimethylsulfonium bromide (1) is a brominating reagent for various compounds and its utility has been reported.1) For example, β-keto esters and 1,3-diketones are brominated smoothly at 0 °C to room temperature to afford the corresponding α-bromo derivatives selectively in high yields.2) The notable advantages of this protocol are use of reagent 1, which is less hazardous than molecular bromine, and no added base, Lewis acid, or other catalyst.
Moreover, 1 can be used as a catalyst for protection and de-protection of various functional groups.1) Recently, a mild Beckmann Rearrangement using 1 has been reported.3) According to the report, a wide range of ketoximes are converted into the corresponding amides or lactams in high yields.
Typical Procedure: α-Bromination of β-keto esters and 1,3-diketones2)
Bromodimethylsulfonium bromide (0.278 g, 1.25 mmol) is added to a stirred solution of β-keto ester or 1,3-diketone (1 mmol) in CH2Cl2 (5 mL) at 0–5 °C or room temperature. After 20 min, the reaction mixture is washed with water (10 mL × 2) and extracted with CH2Cl2 (10 mL × 2). The organic layers are combined and dried over anhydrous Na2SO4, and solvents are removed by evaporation in a rotary evaporator to get the crude product.

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