Enantioselective photochemical [2+2] cycloaddition reactions

Enantioselective [2+2] photocycloadditions are a well-known method for accessing enantioenriched cyclobutanes. However, making this transformation catalytic has been a significant challenge. Several examples have appeared in the literature recently. They make use of a variety of techniques, including organocatalysis, transition-metal catalysis, and dual catalysis, among others. These examples have been collected and summarized in this chapter to give the reader a broad yet thorough overview of this developing field.