Regulation of cyclization for the stereoselective synthesis of substituted tetrahydrofurans and tetrahydrooxepines.

Dramatic solvent effect is observed during the cyclization of 1. Synthesis of 2 is achieved from the reaction of 1 with a hexamethylditin-catalyzed palladium complex followed by aldehydes in the presence of TMSOTf in THF, whereas 3 is formed in CH2Cl2. The method described herein is successful with various substrates 1 in good yields and high levels of diastereoselectivity.