Highly efficient, enantioselective synthesis of (+)-grandisol from a C<inf>2</inf>-symmetric bis(α,β-butenolide)

(equation presented) A new, very efficient, enantioselective synthesis of the sexual attracting insect pheromone (+)-grandisol has been developed, in which the key step is the double [2 + 2] photocycloaddition of ethylene to a bis(α,beta;-butenolide) readily available from D-mannitol. The C2symmetry of the substrate and the appropriate protection of the central diol unit are the crucial features for the high diastereofacial discrimination during the cycloaddition process.