Efficient and diastereoselective synthesis of (+)‐ and (−)‐grandisol and 2‐[(1R,2S)‐2‐isopropenylcyclobutyl]ethanol (demethylgrandisol) in high purity

Acetone‐sensitized [2 + 2] photocycloaddition of ethylene to chiral butenolides 3 and 15 yields diastereomeric cyclobutanes, which are transformed to (+)‐(1) and (−)‐grandisol (ent‐1) (overall yield 34–36%) and to 2‐[(1R,2S)‐2‐isopropenylcyclobutyl]ethanol (demethylgrandisol) (2) (overall yield 25%) in five steps.