A versatile and highly stereoselective synthesis of spiro ethers and spiro ketals is presented. The key step in the developed synthetic sequence is based on diastereoselective intramolecular photoaddition of dihydro-4-pyrones to chiral 1, 3-dioxin-4-ones. Subsequent fragmentation of the produced four-membered ring provides spiro ether structures. The spiro ethers can be transformed to their corresponding spiro ketals, with retention of ...