With a selection of hetero[3.1.1]propellanes in hand, their reactivity was explored under a range of radical ring-opening conditions (Fig. ). The atom transfer radical addition (ATRA) of carbonhalogen bonds across propellanes is one of the most versatile methods for ring-opening , and we were able to generate a range of oxa-and aza-BCHeps using either triethylborane as initiator , or iridium photocatalysis . This included the formation of iodo-hetero-BCHeps by addition of electrondeficient (18a-d) and electron-rich (18e, f) alkyl radicals; in the former case comparable yields were obtained for the addition of an acetate radical to both oxa-and aza for the latter, reaction with 3 proved superior. The addition of a benzyl radical (18g), and both unsaturated (pyridyl) and saturated (piperidine and azetidine) radicals on nitrogen heterocycles (18hj), as well as C-Br bonds also proved successful (18k-n). We further achieved the addition of heteroatom-centred radicals: an N-substituted oxa-BCHep (18o) was prepared by radical fragmentation of an iodomethyl aziridine 30 , while halosulfonylation of 3-oxa[3.1.1]propellane was also achieved in good yields (18p, q) . Treatment of 3-oxa-or 3-aza[3.1.1]propellane with iodine afforded a mixture of diiodo-BCHep (18r, s) and the corresponding [2]staffanes (18r', s') where, interestingly, the proportion of staffane was higher for the aza-BCHep; these adducts represent stable potential propellane precursors (see below). We also found that other radical addition methods could be applied, such as the addition of an α-amino radical via organophotoredox catalysis (18t) , while a range of chalcogen-substituted BCHeps (18u-z) were prepared by direct addition of the chalcogen or dichalcogen to the propellane . We were able to demonstrate the wider potential of these heteropropellanes by the synthesis of pharmaceutically-relevant compounds, including the cysteinesubstituted oxa-BCHep 18aa, galactopyranose derivative 18ab, and pretilachlor derivative 18ac.