Metal-catalyzed ring-opening of alkylidenecyclopropanes: New access to building blocks with an acyclic quaternary stereogenic center

A study was conducted to investigate metal-catalyzed ring-opening of alkylidenecyclopropanes (ACP). The investigations focused on developing this concept and to delineate the reactivity of exo-alkylidene moiety towards the metal-catalyzed hydroboration reaction. Methylene- and ACPs were subjected to pinacol borane (HBPin) in the presence of the Wilkinson catalyst at room temperature. HBPin was selected to conduct the investigations, as the reductive elimination to form the carbon-boron bond was slower than other boronate esters. The formation of the single boronate ester was rationalized through the oxidative addition of the catalyst into the H-B bond of HBPin that gave the corresponding metal hydride species. The metal hydride species added to the double bond of methylenecyclopropane (MCP) through a hydrometalation reaction to form the alkyl metal.