Enantioselective Synthesis of Functionalised Decalones by Robinson Annulation of Substituted Cyclohexanones, Derived from R-(−)-Carvone

The copper catalysed conjugate addition of methyl magnesium iodide to cyclohexenones and trapping of the enolate as its trimethylsilyl enol ether, followed by a trityl hexachloroantimonate (TrSbCl6) catalysed Mukaiyama-reaction, was applied to R-(−)-carvone. This proved to be an efficient method for the preparation of C-2, C-3 functionalised chiral cyclohexanones. These compounds were converted into their α-cyano ketones, which were submitted to Robinson annulation reactions with methyl vinyl ketone. The scope and limitations of these annulations were investigated. A series of highly functionalised chiral decalones were obtained that can be used as starting compounds in the total syntheses of enantiomerically pure clerodanes.