Ring with oxygen-based nucleophiles

Ring-Opening meso-Oxabicyclic Alkenes with Oxygen-Based Nucleophiles... 

Oxygen nucleophiles usually attack a ring carbon atom rather than the sulfur atom of a thiirane, and those cases in which desulfurization is observed on treatment of a thiirane with oxygen bases probably involve the extrusion of sulfur by mechanisms other than a nucleophilic attack on sulfur, e.g. thermal. Desulfurization of thiirane intermediate (43)... 

Epoxy resins, which are used as adhesives, are also thermoset polymers that form by cross-linking when the two components of the resin are mixed. One component is a low-molecular-mass linear polymer formed by the reaction of the conjugate base of bisphenol A with epichlorohydrin. The nucleophilic oxygens of the phenolate dianion can either displace the chlorine or open the epoxide ring of epichlorohydrin. A slight excess of epichlorohydrin is used to keep these polymer chains short and to ensure that the linear molecules have epoxide groups at their ends. 

The propagation step is fast, aided by the coulombic interaction between the carbo-cation and the negatively polarized ether oxygen, and the strain in the three-membered ring. Termination may occur by the reaction of the carbocation with an adventitious nucleophile (a base, for example) or, very occasionally, with the anion of the initiator. ... 

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