Tandem Michael–Aldol Assembly and Regioselective Aminohydroxylation of a Chlorinated Bicyclo[3.3.1]nonane Core Toward Gymnastatin G

An efficient and regioselective synthetic approach to the chlorinated bicyclo[3.3.1]nonane core of gymnastatin G is described. The densely functionalized bicyclic framework was assembled via a one‐pot Michael–Aldol cascade followed by silyl protection, enabling simultaneous construction of the bridged skeleton and installation of a bridgehead quaternary chloride with high diastereoselectivity (ca. 9:1 dr). Late‐stage functionalization of the sterically congested bicyclic alkene was achieved through regioselective aminohydroxylation, in which the electronic nature of the N ‐oxycarbamate reagent played a critical role in promoting nitrogen incorporation. Systematic variation of the arylsulfonyl group revealed that electron‐deficient substituents significantly enhance reactivity. Attempts to access the corresponding lactone via Baeyer–Villiger rearrangement toward gymnastatin G were unsuccessful, even after modification of the C9 carbonyl, highlighting pronounced steric and stereoelectronic constraints inherent to the rigid [3.3.1] framework. These findings provide insight into the reactivity and functionalization limits of highly substituted bicyclo[3.3.1] systems and offer guidance for future synthetic efforts toward gymnastatin‐type natural products.