ENANTIOSELECTIVE CONSTRUCTION OF CYCLIC ETHERS BY AN ALDOL-CYCLIZATION SEQUENCE

We have modified the substrate used in deconjugative aldol-cyclization s by incorporating the Evans chiral auxiliary. The deconjugative aldol step, using boron enolates, gave the expected products with complete syn-aldol stereochemistry. These compounds could then undergo an iodin e-mediated cyclization to form optically active products. Oxetanes and fused ring tetrahydrofurans were easily assembled with a variety of s ubstitution patterns and with excellent enantiocontrol. The deconjugat ion of acyclic chiral enimides resulted in the loss of control of olef in geometry. However, these compounds did appear to cyclize with excel lent enantiocontrol.