rules (Figure , Panel A and Supporting Information). This analysis reveals significant diversity at the higher levels, despite the majority of the frameworks ultimately resolving to the same parent monocycle (pyrrolidine). The ability to cleave and expand rings within the complex intermediates 2, and to append additional rings, was critical to realising this scaffold diversity. We next sought to demonstrate the utility of these scaffolds in the synthesis of a small screening library. A library of 51 compounds was prepared; a selection of these compounds is shown in Figure , Panel B (see Supporting Information for the full library and synthetic details). The scaffolds 4a-c could be directly elaborated by reductive amination alone (e.g. to 19) or with an additional acylation; and the corresponding alcohols 6ac could also be converted to carbamates (e.g. to 20), alkylated or (hetero)arylated (e.g. to 21). Similar functionalisations, as well as addition of carbon nucleophiles (e.g. to give 22), could also be carried out on the ring-added, ring-expanded or ringcleaved products (giving e.g. 23-25). The library was further analysed for three-dimensionality (PMI plot) and the fraction of sp -hybridised carbons (Fsp 3 ) (Supporting Information), with >94% of compounds having Fsp 3 > 0.5.