COMPLEXES of manganese(II) with bipyridine (bpy) have the potential to act as catalysts for oxidation of alkanes and alkenes when the complex is oxidized in acidic conditions(1-6). But their catalytic activity in solution is limited by their catalase activity(7)-their tendency to decompose H2O2. Because of their polynuclear nature such complexes cannot induce epoxidation of alkenes, and other epoxidation catalysts suffer from self-oxidation and side reactions(8-11). Moreover, all of these homogeneous catalytic processes require phase-transfer conditions. Here we report that, when encapsulated in the supercages of zeolites X and Y, cis-[Mn(bpy)(2)](2+) complexes can catalyse selective epoxidation of alkenes without complications from competing processes such as self-oxidation or catalase activity. Epoxidation of cycloalkenes is followed by acid-catalysed ring-opening, carbon-carbon bond cleavage and formation of alkenedioic acids (Fig. 1). All of the various intermediates in the process can be obtained selectively by controlling the reaction conditions and zeolite acidity. Thus this supramolecular system provides a clean, one-step heterogeneous catalytic route to useful industrial products.