Alkylation of mesityl oxide (7) with 1-chloro-3-methyl-2-butene (1) using potassium or sodium hydroxide in an aprotic solvent afforded a mixture of isopentenyl mesityl oxide, (4), (5) and (9) in 83% yield, which were hydrolytically decomposed to 6-methyl-5-hepten-2-one (3) in 95% yield in an autoclave.
