Asymmetric Photocycloadditions with Optically Pure, Spirocyclic Enones. Simple Synthesis of (+)‐ and (−)‐Grandisol

The directed synthesis of either one of two enantiomers by use of the same, readily available chiral auxilliary group, derived from (−)-menthone, is made possible by the a-selective addition of olefins to the spirocyclic enones (−)-1 and (−)-2. (+)-3 can be transformed into (+)-grandisol, (+)-4, and (+)-5 can be converted into (−)-grandisol.