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

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.