Photoredox catalysis has transformed the landscape of radical-based synthetic chemistry. Additions of radicals generated through photo-redox catalysis to carbon–carbon pi bonds have become well-established; however, this approach has yet to be applied to the functionalization of carbon–carbon sigma bonds. Here we report the first such use of photoredox catalysis to promote the addition of organic hal-ides to the cage carbocycle [1.1.1]propellane; the product bicyclo[1.1.1]pentanes (BCPs) are motifs of high importance in the pharmaceutical industry, and in materials chemistry. Showing broad substrate scope and functional group tolerance, this methodology results in the first examples of bicyclopentylation of sp2 carbon–halogen bonds to access (hetero)arylated BCPs, as well as the functionalization of non-stabilized sp3 radicals. Substrates containing alkene acceptors allow the single-step construction of polycyclic bicyclopentane products through unprecedented atom transfer radical cyclization cascades, while the potential to accelerate drug discovery is demonstrated through late-stage bicyclopentylations of natural product- and drug-like molecules. Mechanistic investigations demonstrate the importance of the photocatalyst in this chemistry, and provide insight into the balance of radical stability and strain relief in the reaction cycle.

1,3‐Disubstituted bicyclo[1.1.1]pentanes (BCPs) are important motifs in drug design as surrogates for p‐substituted arenes and alkynes. Access to all‐carbon disubstituted BCPs via cross‐coupling has to date been limited to use of the BCP as the organometallic component, which restricts scope due to the harsh conditions typically required for the synthesis of metallated BCPs. Here we report a general method to access 1,3‐C‐disubstituted BCPs from 1‐iodo‐bicyclo[1.1.1]pentanes (iodo‐BCPs) by direct iron‐catalyzed cross‐coupling with aryl and heteroaryl Grignard reagents. This chemistry represents the first general use of iodo‐BCPs as electrophiles in cross‐coupling, and the first Kumada coupling of tertiary iodides. Benefiting from short reaction times, mild conditions, and broad scope of the coupling partners, it enables the synthesis of a wide range of 1,3‐C‐disubstituted BCPs including various drug analogues.