4-Bromophenol → (2S)-2-(4-Bromophenoxy)-3-methylbutanoic acid, methyl ester

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Reaction Steps

Diethylazodicarboxylate (17.5 ml) in dry toluene (60 ml) was added dropwise over 30 minutes to a cooled, stirred solution of triphenylphosphine (34 g), methyl (R)-2-hydroxy-3-methylbutanoate (17 g, J.Am. Chem. Soc., (1990), 112, 21, 7659) and 4-bromophenol (24 g) in dry toluene (180 ml). The resulting solution was stirred at room temperature for 30 minutes and was then concentrated under reduced pressure to approximately half the original volume. A mixture of isohexane (700 ml) was added and the mixture stirred at room temperature for 20 minutes. The solution was filtered to remove triphenylphosphine oxide and the filtrate concentrated under reduced pressure. The residue was purified by column chromatography over silica eluting with isohexane: dichloromethane (1:4) then (2:3) to give the sub-title compound as an oil (28 g).

Provenance & Evidence