Tetrahydropyran derivatives – and – are formed in good yields by cyclisation of methyl-6-hydroxy-2-hexenoate or 2-heptenoate mediated by various electrophilic reagents (mCPBA, benzeneselenyl chloride, N-bromosuccinimide, iodine). Cyclisations of Z and E isomers are stereospecific. The diastereoselectivity of cyclisation of the secondary alcohol varies with the nature of the electrophilic reagent.