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Cross metathesis cleaves and restitches single bonds

Method merges two four-membered rings into an eight-membered macrocycle

by Tien Nguyen
September 11, 2017 | A version of this story appeared in Volume 95, Issue 36

Cross metathesis reaction between benzocyclobutenone and silacyclobutane to form eight-membered ring molecule.

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.”


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