Abstract:
Oxazaborolidines were employed as chiral Lewis acids in enantioselective variants of the intramolecular and intermolecular [2+2] photocycloaddition of simple cyclic enones. In both cases, photoadducts were obtained in high yields and enantiomeric excesses. A selection of photoadducts served as starting material for total syntheses of natural products. An extension of the method to the enantioselective cis-trans isomerization of simple cyclic enones was unsuccessful.