Direct Access to Functional 2‐Azabicyclo[2.1.1]Hexanes via Hydrodearomative [2π + 2σ] Cycloaddition of Aza ‐Arenes

Abstract Converting planar six‐membered aza ‐arenes into C(sp 3 )‐rich three‐dimensional (3D) scaffolds is a promising way to obtain isosteric mimetics of numerous functional products, but it remains to date a formidable challenge due to the high thermodynamic stability and dynamic inertness as well as the selectivity control. Here, by applying a novel non‐noble bimetallic Mn/Fe catalyst system, we report, for the first time, an approach for direct construction of functional 3D 2‐azabicyclo[2.1.1]hexanes via a hydrodearomatization (HDA) of the aza ‐arenes and [2π + 2σ] cycloaddition cascade. Mechanistic investigations reveal that the triplet state of Fe(II) facilitates the activation of both aza ‐arenes and bicyclo[1.1.0]butanes (BCBs). The mild reduction nature of manganese catalysis and the steric effects of Fe(II) coordination result in an 1,4‐hydrodearomatization, and the imine species derived from the isomerization of 1,4‐hydrogenated aza ‐arenes are then effectively trapped by the polarized BCBs, thus suppressing the thermodynamically favorable over‐hydrogenation of aza ‐arenes into cyclic amine by‐products. Given the features of good substrate and functionality compatibility, high step and atom efficiency, and diversified product post‐transformations, the developed chemistry offers a practical platform to access various functional molecules.