yl, affording stereospecifically the cis isomer of 2,2-dimethylbicyclo[4.4.0]dec-9-en-3-one. In contrast, the cis-disubstituted cyclohexene compound reacts only sluggishly to produce a mixture of the cis- and trans-fused octalones. Similar stereospecific effect of the allylic double bond configuration on the ease of cyclization has been observed in the synthesis of karahanaenone from 3,7-dimethyl-6-trimethylsiloxy-2