Synthesis of medium ring ethers. Part 4. Stereoselective Claisen-mediated ring expansion as a route to homochiral disubstituted medium ring lactones

Thermal elimination/Claisen rearrangement of selenoxides derived from the enantiomerically pure phenylselenomethyl-substituted cyclic acetals 4 and 8 proceeds stereospecifically to provide the homochiral 8- and 7-membered lactones 5 and 9 respectively.