Catalytic Cleavage of C(<i>sp</i>²)–C(<i>sp</i>²) Bonds with Rh-Carbynoids

We report a catalytic strategy that generates rhodium-carbynoids by selective diazo activation of designed carbyne sources. We found that rhodium-carbynoid species provoke C­(sp2)–C­(sp2) bond scission in alkenes by inserting a monovalent carbon unit between both sp2-hybridized carbons. This skeletal remodeling process accesses synthetically useful allyl cation intermediates that conduct to valuable allylic building blocks upon nucleophile attack. Our results rely on the formation of cyclopropyl-I(III) intermediates able to undergo electrocyclic ring-opening, following the Woodward–Hoffmann–DePuy rules.