Our work began with the development of a viable route to an oxa-propellane precursor. After exploring a number of potential strategies (see the Supplementary Information for details), we identified a route to 3-oxa[3.1.1]propellane that began with a rhodium-catalysed cyclopropanation of 2,3-dibromopropene with dimethyl diazomalonate (6). This cyclopropanation benefited from use of the bulky triphenylacetate (TPA)-ligated rhodium catalyst, and could be performed on decagram scale at just 0.05 mol% catalyst loading (68% yield). Reduction of the resulting cyclopropane diester 7 proceeded optimally using DIBALH, and direct treatment of the product diol 8 with potassium hydroxide effected cyclisation of the alcohol syn to the bromomethyl group to form tetrahydrofuran With 3-oxa[3. 1.1]propellane in hand, we questioned whether we could leverage this synthetic route to access other heterocyclic [3.1.1]propellanes. We first addressed the synthesis of 3thia[3.1.1]propellane by intercepting diol 8 with potassium thioacetate, whereby substitution of the bromomethyl group afforded thioester 11 (54% over two steps). After some investigation, we found that bromination of this diol offered the optimal means to convert the two alcohols into suitable leaving groups for propellane synthesis, with NBS / PPh3 delivering dibromide 12 in 58% yield.