Catalytic asymmetric photocycloaddition reactions mediated by enantioselective radical approaches

The use of olefins in the construction of cyclic compounds represents a powerful strategy for advancing the pharmaceutical industry. Photocycloaddition has attracted significant interest from chemists due to its ability to exploit simple and readily available olefins along with their reaction patterns under mild conditions. Moreover, the sustainable and versatile pathways for generating highly reactive intermediates can greatly enrich both substrate diversity and reaction patterns. As a result, numerous photocycloaddition reactions have been successfully developed, particularly asymmetric [2+2], [3+2], and [4+2] photocycloadditions mediated by enantioselective radical approaches, achieving remarkable enantioselectivities. This review offers a comprehensive overview of this rapidly evolving field, organizing the discussion into three distinct reaction types that facilitate the construction of enantioenriched derivatives of cyclobutanes, cyclopentanes, and cyclohexanes. Emphasis is placed on analyzing and summarizing established strategies aimed at circumventing the challenges posed by racemic background transformations. Additionally, the exploration of asymmetric [3+2] and [4+2] photocycloaddition reactions will be interwoven with a detailed discussion of the various substrate types involved. This systematic framework seeks to enhance understanding of the strategies employed to manage the high reactivity of radicals while achieving high enantioselectivity. Importantly, it aims to guide readers in identifying uncharted radical-based cycloaddition pathways, which possess significant potential to broaden the diversity of complex cyclic molecules.