Tackling reactivity and selectivity within a strained architecture: construction of the [6-6-5-7] tetracyclic core of Calyciphylline alkaloids.

A stereochemically controlled route to the enantiopure [6–6–5–7] tetracyclic core of Calyciphylline A class alkaloids was established, which involves Overman rearrangement, [2 + 2] photochemical cycloaddition, Grob fragmentation, C–N bond-forming nucleophilic displacement, and ring strain-directed hydrogenation as strategic steps.