Toluene → 4-(5-Bromo-2-methylphenyl)-2,2,6,6-tetramethylpyran-3,5-dione

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Reaction Steps

To a mixture of 2,2,6,6-tetramethylpyran-3,5-dione (6.00 g, 35.29 mmol) and N,N-dimethylaminopyridine (21.62 g, 177.21 mmol) is added anhydrous chloroform (200 ml), followed by stirring at room temperature until dissolution. To this solution is added anhydrous toluene (55 ml), followed by 5-bromo-2-methylphenyllead triacetate (21.60 g, 38.99 mmol) in one portion and the reaction mixture is heated at 80° C. for 2 hours. The mixture is allowed to cool to room temperature, then diluted with dichloromethane (300 ml) and aqueous hydrochloric acid (300 ml), and the mixture is swirled for 5 minutes and filtered to remove inorganic residues. The filter cake is washed with dichloromethane, and all organic fractions are combined, dried over anhydrous magnesium sulfate, filtered and the filtrate is concentrated in vacuo to afford a crude solid which is recrystallised from dichloromethane/hexanes. This material is then further purified by flash column chromatography (hexane/ethyl acetate 5:1 ratio). The lead residues are removed by dissolving the resulting solid (approximately 6.50 g) in chloroform (100 ml) and stirring with 3-mercaptopropyl-functionalized silica gel (6.50 g, 1.20 mmol/g loading) overnight. The mixture is filtered and the filtrate concentrated in vacuo to afford 4-(5-bromo-2-methyl-phenyl)-2,2,6,6-tetramethylpyran-3,5-dione (6.50 g) as a cream powder.

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