DescriptionDisclosed are studies on the mechanism and reactivity of spirodiepoxides (SDE) and their applications in synthesis. Experimental and computational data led to the establishment of three discernable mechanisms for nucleophilic opening of SDEs. New SDE-based methodologies have also been developed including the formation of functionalized azoles in a single flask from allenes and the addition of carbon nucleophiles to generate useful precursors to complex polyketides (i.e. erythromycin). Heteroatom additions to SDEs have been identified in the studies towards the potent proteasome inhibitor, epoxomicin. Syntheses of the AB spiroketal and C ring systems of the anticancer natural product, pectenotoxin 4, have also been achieved using SDE-based methods.