Hydrolysis of the thioester (KOH) triggered cyclisation to the tetrahydrothiophene 13 (95%), treatment of which with methyllithium effected lithiation of the bridgehead bromide, followed by The synthesis of 3-aza[3.1.1]propellane brings opportunities to functionalise the propellane framework with an additional substituent on the heteroatom. To establish the synthesis, we first considered an N-tosyl group, which we anticipated would prove tolerant of the synthetic route. In the event, we were able to identify a suitable path to the 3-aza[3.1.1]propellane 5 from cyclopropanation product 7. Reaction of 7 with sodium azide (to give 14, 96%), followed by Staudinger reduction using tri-n-butylphosphine, afforded the lactam ester 15 (61%). A screening of various reducing agents revealed that Red-Al was uniquely effective for reduction of the lactam-ester to the corresponding pyrrolidine alcohol; direct N-tosylation gave the pyrrolidine sulfonamide 16 (40% over two steps).