Visible‐Light‐Induced [2π+2σ] Cycloaddition Enabled by Cage‐Confined Photocatalysis for Precise Bicyclo[2.1.1]Hexane Construction

Abstract We disclose a visible‐light‐induced, diastereoselective [2π+2σ] photocycloaddition between readily available chalcones and 1,3‐disubstituted bicyclo[1.1.0]butanes (BCBs) promoted by photoactive metal–organic cage (PMOC). This confined supramolecular catalysis method enables efficient synthesis of pharmaceutically relevant bicyclo[2.1.1]hexane (BCH) bioisosteres with remarkable atom economy and excellent diastereoselectivities, necessitating only 0.1 mol% catalyst loading. The success of this organic transformation arises from the synergistic action of the PMOC as a nanoreactor to combine selective substrate preorganization through host–guest interactions, efficient Ru(II)‐mediated triplet energy transfer, and nano‐spatial confinement effect that precisely control [2π+2σ] cyclization geometry while preventing competitive homodimerization.