Kinetic and thermodynamic control in the synthesis of tetrahydro-pyrans and -furans from 1,4-diols by stereospecific phenylsulfanyl (PhS) migration: Competition between exo and endo transition states and between [1,2] and [1,4] sulfanyl participation

The factors controlling the cyclisation of 1,4-diols with PhS migration to give THPs rather than THFs are reassessed. Furthermore we provide evidence for a competition between [1,2] and [1,4] sulfanyl participation and cyclis ation onto a five membered cyclic sulfonium salt.