Diastereoselective Synthesis of 2,4-Disubstituted Tetrahydropyranols and Ethers via a Prins-Type Cyclization Catalyzed by Scandium Triflate

The reaction of aldehydes with homoallylic alcohols catalyzed by scandium triflate gives rise to the formation of 2-substituted tetrahydropyran-4-ols and ethers in good overall yields and with ‘all-cis’ configurations and high diastereoselectivities. The stereochemistries of these products were assigned with the assistance of coupling constants and NOE. Factors affecting the reaction have been examined in detail. The reaction was found to be most effective in chloroform. Various aromatic and aliphatic aldehydes underwent the cyclization smoothly. A catalytic cycle for this reaction has been proposed.