2-Hydroxy-5-methyl-3-hexanone, which is a characteristic component of eucalyptus honeys, was synthesised by oxidation of the silyl enol ether of 5-methyl-3-hexanone. 5-Methyl-3-hexanone was prepared by Grignard reaction and oxidation starting from isovaleraldehyde and ethylmagnesium bromide. The desired silyl enol ether was produced with high selectivity by deprotonation of 5-methyl-3-hexanone with NaHMDS in n-hexane followed by reaction with chlorotrimethylsilane and then oxidised by MCPBA to give pure 2-hydroxy-5-methyl-3-hexanone in about 77% yield after purification by flash chromatography. 2-Hydroxy-5-methyl-3-hexanone has a cheese and sour milk odour.
