Lewis acid promoted cascades of a tris(disubstituted epoxide) triggered by silver-promoted abstraction of a bromide ion favors trans-dioxabicyclo[4.3.0]nonanes, rather than diads or triads of tetrahydropyrans (trans-dioxabicylco[4.4.0]decanes, for example). These results suggest that an epoxide-attacking-epoxonium mechanism is not operativein this system.