Cross metathesis cleaves and restitches single bonds

Chemists have developed an array of chemical tools that rely on reactive carbon-carbon π bonds or on polar bonds in which charge is unevenly shared between the atoms to drive the formation of new carbon-carbon bonds. Yet methods that act on challenging, nonpolar carbon-carbon bonds are few. Researchers led by Masahiro Murakami of Kyoto University have expanded the synthetic options by demonstrating the efficient exchange of two low-polarity σ bonds in a cross-meta­thesis-type reaction catalyzed by a palladium isocyanide complex (J. Am. Chem. Soc. 2017 DOI: 10.1021/jacs.7b07667). The method regio­selectively opens the four-membered rings of benzocyclobutenone and silacyclobutane and exchanges C(aryl)–C(carbonyl) and C(sp³)–Si bonds to create C(aryl)–Si and C(carbonyl)–C(sp³) bonds and form an eight-membered-ring product. “The work provides a striking demonstration of how metallacycles derived from C–C bond activation can be used to access challenging medium-ring systems,” comments the University of Bristol’s John Bower. “These results suggest that a range of σ-bond-metathesis-based cycloadditions might be achievable by metal-catalyzed union of strained rings.”