Conversion of (−)-α-santonin into (+)-α-cyperone

An efficient, 8-step synthesis of (+)-α-cyperone (1) from (−)-α-santonin (5) is described. The key steps of the sequence involve the conversion of the keto ester 8 into the substituted octalone 9, by hydrogenation of the former in the presence of the homogeneous catalyst tris(triphenylphosphine)-chlororhodium, and the pyrolysis of the keto carbonate 16, which produces (+)-α-cyperone in good yield.