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 t riflate gives rise to the formation of 2-substituted tetrahydropyran-4-ols and ethers in good overall yields and with 'all-cis' configurations and hig h diastereoselectivities. The stereochemistries of these products were assi gned with the assistance of coupling constants and NOE. Factors affecting t he reaction have been examined in detail. The reaction was found to be most effective in chloroform. Various aromatic and aliphatic aldehydes underwen t the cyclization smoothly. A catalytic cycle for this reaction has been pr oposed. (C) 2000 Elsevier Science Ltd. All rights reserved.