There have been recent reports on selective transformations of unprotected sugars and their derivatives using both biocatalytic and chemical approaches . De-oxygenation/dehydration of sugars is of particular interest and only a few approaches have been described. For example, Gagné has reported methods for the regioselective reductive cyclisation of protected sugar-derived polyols 1 using silane reagents in the presence of Lewis acids such as B(C6F5)3, leading to the formation of a range of chiral THFs and THPs 2 which can be accessed from sugars in a few steps (Scheme 1a). In previous work, we have developed methods for the regioselective dehydration of sugar hydrazones, e.g 3, (Scheme 1b) to give access to a range of chiral THFs (e.g. syn-4 and anti-4) under very mild conditions. These reactions are readily scalable and provided access to useful chiral building blocks in only a few steps. Importantly, it was also observed that cyclisation of the sugar hydrazones under acidic or basic conditions provided complementary stereoselectivities. The acid-catalysed cyclisation takes place under thermodynamic control, most likely proceeding via the stabilised diazenium cation, whereas the base-mediated cyclisation appears to involve a kinetically controlled SN2 ring-opening of a cyclic carbonate intermediate which can epimerise prior to cyclisation. In this latter reaction, it was rationalised that the main role of the hydrazone is to hold the sugar in the open-chain conformation which facilitates cyclisation to the THF. We therefore envisaged that this approach could be extended to other open chain sugars such as thioacetals. Given that the formation of dimethylhydrazones from hexoses is often slow and relatively low yielding, thioacetals might prove to be a more versatile alternative as they can readily be accessed from both pentoses and hexoses. In this paper, we describe methods for the regioselective dehydration of sugar thioacetals at C-2 and C-3 under mild and scalable conditions to provide access to novel chiral polyols and tetrahydrofurans (Scheme 1c).