Catalytic Oxidation of Silyl Enol Ethers to 1,2-Diketones Employing Nitroxyl Radicals

Abstract

A novel and efficient method for the preparation of 1,2-diketones is reported. A series of α-diketones were readily prepared by the nitroxyl-radical-catalyzed oxidation of silyl enol ethers using magnesium monoperoxyphthalate hexahydrate (MMPP⋅6H₂O) as the co-oxidant.

Key words

oxidation - catalysis - enols - diketones - nitroxyl radical

• References and Notes

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• 16 General Procedure for the Catalytic Oxidation of Silyl Enol Ether to 1,2-Diketone: To a solution of MMPP⋅6H₂O (565 mg, 0.994 mmol), Nor-AZADO (18 mg, 0.133 mmol) and LiBF₄ (124 mg, 1.33 mmol) in MeCN (6.6 mL) was added dropwise a solution of 7a (206 mg, 0.663 mmol) in MeCN (6.6 mL) over 4 h and stirred for 2 h at r.t. Solutions of 5% aq NaHCO₃ (5 mL) and 20% aq Na₂S₂O₃ (5 mL) were added and the aqueous layer was extracted with CH₂Cl₂. The organic layer was dried over Na₂SO₄ and concentrated under reduced pressure. The residue was purified by silica gel column chromatography to afford 8a (120 mg, 0.571 mmol, 86%)