with electron-rich species was less facile (c.f. 18e vs. 18f), reflecting its greater stability (in some reactions, unreacted 5 could be observed in the crude reaction mixture). Reactions of 3thia[3.1.1]propellane were limited to those with very efficient propagation steps, as bridgehead thia-BCHep radicals were otherwise found to be prone to fragmentation of the ring before interception with a halogen or hydrogen atom source -a process not witnessed in radical-based propellane chemistry to date. In these cases, increasing the concentration of the thiol substrate was found to improve yields due to rapid capture of the bridehead radical (see the Supplementary Information for additional details of unsuccessful substrates, and thia-BCHep fragmentation). The preparation of bridge-substituted all-carbocyclic propellanes is very challenging, and typically requires low-yielding and lengthy multistep sequences . We were therefore pleased to find that variation of the exocyclic substituent on the nitrogen atom of 3-aza[3.1.1]propellanes is significantly easier, and can be achieved at a relatively late stage of the synthesis. Specifically, detosylation of the immediate aza-propellane precursor 17 using HBr and phenol, followed by reaction with a sulfonyl chloride, afforded quinoline, thiophene, and bis-sulfonamide propellane precursors 20a-c. We found that these compounds underwent smooth conversion to the corresponding propellanes 21a-c in excellent yields on treatment with methyllithium (70-99%). Particularly notable is the highly efficient synthesis of the 'double' propellane 21c in which two ring-closing events are required. Generally, we observed that propellane formation proceeds optimally with electron-withdrawing substituents on the nitrogen atom, especially sulfonamides (see the Supplementary Information for details), which opens up the possibility for further exploration of the scope of this substituent.