Oxygenated limonene analogs. Preparation of tetramethylated carvone and carveols via regiocontrolled opening of tetramethyllimonene oxide.

Regioselective opening of trans epoxide $\text{2}$ gave $\text{endo}$ and $\text{exo}$ tetramethylated $\text{trans}$ carveols $\text{3t}$ and $\text{4t}$ respectively, which were oxidized to tetramethylcarvone ($\text{5}$) and its unstable exocylic isomer $\text{6}$; reduction of $\text{5}$ with DIBAH gave tetramethylated $\text{cis}$ carveol $\text{3c}$ exclusively, whilst analogus reduction of $\text{6}$ produced an epimeric mixture of $\text{4c}$:$\text{4t}$=85:15.