Fig. 1: Multiple dynamic sp³-carbon centres.

a,b, Fluxional sp³-carbon stereochemistry arises in BBs when the structures interchanged by their Cope rearrangements (a) are desymmetrized with any of the three substitution patterns shown in b. Cahn–Ingold–Prelog priorities are chosen to be R¹ > C > R² for the assignment of absolute configuration. When assigning a descriptor to position 9 of 9-BB, the cyclopropyl bridgehead C1 has precedence over the divinyl bridgehead C5 (Supplementary Fig. 1). 3-BB and 2,4-BB each have four chirotopic (R/S) centres, whereas the 9-BB pattern gives rise to five stereogenic centres, of which three are chirotopic and two are achirotopic (r/s).