Stereocontrolled synthesis of 2,4,5-trisubstituted tetrahydropyrans

Cyclisation of homoallylic acetals under acidic conditions leads to the formation of 2,4,5-trisubstituted tetrahydropyrans with the creation of two new asymmetric centres with excellent stereocontrol. By varying the acid and the nucleophile, the reaction may be adapted for the preparation of 2,4,5-trisubstituted tetrahydropyrans with either a halide, alcohol, acetate or amide at C-4.