Visible light-induced strain-release transformations of bicyclo[1.1.0]butanes

Bicyclo[1.1.0]butanes, as structurally unique compounds with high strain energy and diverse chemical properties, are becoming increasingly popular building blocks in organic and pharmaceutical chemistries. Strain-release transformation of bicyclo[1.1.0]butanes has received great attention from chemists as it is atom- and step-economical, and significant achievements have been made in this field. Visible-light photocatalysis, with its green and sustainable properties, enriches the strain-release strategy through an electron transfer or energy transfer pathway under mild conditions. In this review, we highlight the latest advancements in visible-light-induced strain-release reactions of bicyclobutanes, with a particular focus on the reaction mechanism. Organization of the content follows a subdivision based on reaction and product classes. Advances in obtaining unique chemical architectures continue to be breakthroughs in this fascinating field of research. This review aims to provide an overview on the recent visible light-mediated strain-release transformations of bicyclo[1.1.0]butanes. Prospects for future development of (aza)bicyclo[1.1.0]butanes in this fascinating field are outlined.