Preparation of Several 1,5,5,11-Pentamethyltricyclo[6.2.1.02,6]undecane Derivatives

1,6-Diketone, available in eight steps from homocamphorquinone, was converted into 1,5,5,11,11-pentamethyltricyclo[6.2.1.02,6]undecan-7-one by treatment with potassium t-butoxide and then lithium dimethylcuprate, while α,α-dimethyl-γ-valerolactone, prepared in five steps from homocamphor, was converted into 1,5,5,11,11-pentamethyltricyclo[6.2.1.02,6]undec-2-en-4-one by treatment with diphosphorus pentoxide–methanesulfonic acid.