Nucleophilic‐Addition‐Initiated Ring Expansion and Selectivity in Anionic Fragmentation
Résumé
The expansion of rings into larger ones by a mechanism of anionic fragmentation is a potent tool for exploring new structural space in a concise manner. As the concept has been known and applied for decades now, going a step further calls for selectivity in the production of new scaffolds. In this regard, recent results demonstrated promising levels of regio‐, dia‐ and enantioselectivity which give impulses to the concept of ring expansion involving the fragmentation of anionic species generated from unstrained cycles. Initiated by addition of a nucleophile, the energy received in the form of electrons triggered skeletal rearrangements of simple starting materials while revealing new stereocenters and/or regioisomers. Disrupting the symmetry of smaller rings in some cases, the strategy gives access to complex larger rings.