A simple synthetic method for the preparation of optically active ''di
cyclopentadienone'' is presented. The procedure involves the reaction
of the magnesium enolate of the racemic ketone (2) with S(S)-menthyl-p
-toluenesulfinate, giving a beta-ketosulfoxide as a single diastereois
omer. Conversions to enone (1) or saturated ketone (2) proceed with go
od optical and chemical yields.