Recent advances in the chemistry of bicyclo- and 1-azabicyclo1.1.0butanes

Abstract Bicyclo1.1.0- and 1-azabicyclo1.1.0butanes are structurally unique compounds that exhibit diverse chemistry. Bicyclo1.1.0butane is a four-membered carbocycle with a bridging C(1)-C(3) bond and 1-azabicyclo1.1.0butane is an analog of bicyclo1.1.0butane featuring a nitrogen atom at one bridgehead. These structures are highly strained, allowing them to participate in a range of strain-releasing reactions which typically cleave the central, strained bond to deliver cyclobutanes or azetidines. However, despite these molecules being discovered in the 1950s and 1960s, and possessing a myriad of alluring chemical features, the chemistry and applications of bicyclo1.1.0- and 1-azabicyclo1.1.0butanes remain underexplored. In the past 5 years, there has been a resurgent interest in their chemistry driven by the pharmaceutical industry’s increasing desire for new methods to access cyclobutanes and azetidines. This short review intends to provide a timely summary of the most recent developments in the chemistry of bicyclo1.1.0- and 1-azabicyclo1.1.0butane to highlight the diverse chemistry they can access, their value as synthetic precursors to cyclobutanes and azetidines, and to identify areas for future research.