Abstract
The oxidation of alcohols was carried out with phenyltrimethylammonium tribromide in the presence of a catalytic amount of SbBr3 or CuBr2 . 1,2-Diols, such as hydrobenzoin, were converted into 1,2-diketones or α-ketols without oxidative cleavage of the glycol C-C bond at room temperature. A variety of secondary alcohols were also oxidized to the corresponding carbonyl compounds in a chemoselective manner.
Key words
oxidation - alcohol - phenyltrimethylammonium tribromide - antimony(III) bromide - copper(II) bromide
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37 Benzyl alcohol was recovered in 60-75% yields for 17-24 h. Benzaldehyde dimethylacetal was gradually afforded in 13-32% yields for 48-72 h.
38 A typical procedure is described for the oxidation of meso -hydrobenzoin 1 . To a solution of SbBr3 (18 mg, 0.05 mmol) in MeOH (8 mL) were added pyridine (60 µL) and PTAB (281 mg, 0.75 mmol) at r.t. After stirring for 5 min meso -hydrobenzoin 1 (53 mg, 0.25 mmol) was added. The reaction mixture was treated with 0.5 M aq Na2 S2 O3 after stirring for 16 h at r.t. and extracted with EtOAc. The organic layer was washed by 0.5 M aq Na2 S2 O3 and successively sat. aq NaCl and dried by MgSO4 . After removal of the solvent in vacuo, the residue was purified by column chromatography on silica gel (Wakogel C-200) with CCl4 and CHCl3 (3:1 v/v). Benzil (3 , 50 mg, 0.24 mmol) was obtained in 96% yield.