The replacement of oxygen atoms in readily available oxetanes would offer a direct route to a variety of these cyclic pharmacophores, yet such atom swapping has been rarely reported for non-aromatic molecules. Here we report a general photocatalytic strategy that selectively substitutes the oxygen atom of an oxetane with a nitrogen-, sulfur- or carbon-based moiety, transforming it into a diverse range of saturated cyclic building blocks in a single operation.