State-of-the-art strategies for Lewis acid-catalyzed strain-release cycloadditions of bicyclo[1.1.0]butanes (BCBs)

Due to their low activation energy barriers, small strained carbocyclic systems have always been fascinating building blocks in organic chemistry. Among them, BCBs, as the smallest bicyclic carbocycles, exhibit a molecular structure, bond angles, and orbital hybridization significantly different from those of strain-free hydrocarbons, resulting in unique reactivity. In recent years, Lewis acid-catalyzed strain-release cycloaddition reactions have made BCBs powerful synthetic tools, utilized in various laboratories to expand into other ring systems. This review primarily focuses on the latest developments in Lewis acid-catalyzed strain-release cycloaddition reactions of BCBs, highlighting the applications and limitations of this catalytic system in different types of cycloaddition reactions, providing professionals and non-professionals in the field with valuable insights and new inspiration.