Synthesis of Both Antipodal Forms of 7,7-Dimethylbicyclo[2.2.2]oct-2-en-5-one by Enantiomer Interconversion

An enantioselective synthesis of both enantiomers of the title ketone 5 from a common achiral β-diketone is reported. Bakers' yeast reduction of 6 cleanly differentiates between the two carbonyl groups to deliver (+)- 9 in >90% yield, and with an ee exceeding 98%. Direct xanthate elimination leads to (+)- 5 . To arrive at the levorotatory antipode, the OH group in the β-hydroxy ketone is transformed into the tetrahydropyranyl ether and the carbonyl group is subsequently reduced in advance of formal dehydration. Oxidation of the deprotected alcohol ultimately reestablishes the carbonyl functionality and delivers (−)- 5 of equally high optical purity.