Methyl 2-methyl-4-oxo-4H-1-benzopyran-3-carboxylate → Methyl 2-(3,4-dichlorophenyl)-2-methyl-4-oxochroman-3-carboxylate

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Reaction Steps

A suspension of copper(I) chloride (454 mg, 4.58 mmol) in tetrahydrofuran (5.0 mL) was stirred in a dry flask under nitrogen on ice. A solution of (3,4-dichlorophenyl)magnesium bromide (0.5 M) in THF (9.17 mL, 4.58 mmol) was added over about a 2 min. period. The resulting mixture was stirred on ice for 5 min, and then treated with a solution of methyl 2-methyl-4-oxo-4H-chromene-3-carboxylate (500 mg, 2.29 mmol) in THF (6.0 mL) over about a 2 min. period. The mixture was stirred on ice for 10 min, and then allowed to warm to rt. After 4.5 h at rt, the reaction mixture was quenched by adding 9:1 saturated aqueous ammonium chloride/aqueous ammonia (20 mL). Upon completion of addition, the reaction mixture was stirred at rt for 10 min. and then ethyl acetate and additional ammonium chloride were added. The aqueous and organic layers were mixed well and then separated. The organic layer was washed twice with saturated ammonium chloride, dried over sodium sulfate and then concentrated under vacuum to yield a residue. The residue was purified by column chromatography (silica gel, 9:1 hexane-ethyl acetate) to provide methyl 2-(3,4-dichlorophenyl)-2-methyl-4-oxochroman-3-carboxylate as a colorless gum (518 mg, 62%). By NMR, this material was mixture of the enol form and 2 diastereomeric keto forms (ratio about 1:1:2). Mass spectrum m/z 387.01, 389.03 (M+Na)+.

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