Dual Strain-Release Cascade for Accessing sp3-Rich Azetidine-Bicyclopentane Frameworks Bearing Multiple Quaternary Carbon Centers.

Azetidines and bicyclopentanes (BCPs) have emerged as valuable bioisosteres for pyridine and benzene rings, driving considerable interest in modern medicinal chemistry. Here, we report a photocatalytic strategy for the efficient and selective functionalization of azabicyclo[1.1.0]butanes (ABBs) and bicyclobutanes (BCBs), enabling direct access to saturated cyclic and bicyclic scaffolds under mild, environmentally benign conditions. The method demonstrates broad functional-group compatibility and accommodates extensive structural diversity. This strain-release approach significantly enhances synthetic flexibility, allowing a wide range of ABBs to undergo controlled ring-opening transformations to afford densely substituted azetidine-BCP architectures bearing three all-carbon quaternary centers, a structural motif that remains challenging to construct using conventional synthetic approaches.