Abstract
The spiroketal moiety is an important substructure within many biological natural products. One method to access them is via the oxidative cyclisation of a pendant hydroxyl group on to a pre-formed pyran. However access to such precursors has hitherto been challenging and requires multistep syntheses frequently with considerable protecting group manipulation. Herein we report a novel and high yielding method for the preparation of hydroxydi- and hydroxytetra-hydropyrans, as spiroketal precursors, utilizing a novel double-Prins cyclisation approach.