[2 + 2] Photocycloadditions to Form Cyclobutanes and Bicyclo[2.1.1]hexanes Employing Copper-Based Photocatalysis
G. W. Roland, Kirsten N. Hurdal, Aness Bouchouicha, Nicolas Dowe, Rebecca L. Davis, Shawn K. Collins
Abstract
A first-row transition metal complex, Cu( dmp )( DPEPhos )BF 4, promotes the synthesis of boracyclobutanes (11 examples, 38 → 87%) and 2-oxa-BCHs (10 examples, 55 → 90%) via photocatalytic [2 + 2] cycloaddition. Computational analysis predicted the structures of the major and minor isomers of both processes. The catalyst structure was determined through screening of a variety of diimine and bisphosphine combinations that enabled optimization of a range of triplet energy levels, excited-state lifetimes, and photostabilities. The use of the Cu( dmp )( DPEPhos )BF 4 complex offers a mild alternative to reaction conditions employing UV light or iridium-based photocatalysts previously reported and validates the potential for copper-based photocatalysis for the preparation of skeletons for drug development.