Bicyclo1.1.0butyl Radical Cations: Synthesis and Application to 2π + 2σ Cycloaddition Reactions

As the chemistry that surrounds the field of strained hydrocarbons, such as bicyclo1.1.0butane, continues to expand, it becomes increasingly advantageous to develop alternative reactivity modes that harness their unique properties to access new regions of chemical space. Herein, we report the use of photoredox catalysis to promote the single-electron oxidation of bicyclo1.1.0butanes. The synthetic utility of the resulting radical cations is highlighted by their ability to undergo highly regio- and diastereoselective 2π + 2σ cycloaddition reactions. The most notable feature of this transformation is the breadth of alkene classes that can be employed, including nonactivated alkenes, which have so far been elusive for previous strategies. A rigorous mechanistic investigation, in conjunction with DFT computation, was undertaken in order to better understand the physical nature of bicyclo1.1.0butyl radical cations and thus provides a platform from which further studies into the synthetic applications of these intermediates can be built upon.