The reaction of alkenes with conjugated ene-yne-ketones, such as 1-benzoyl-2-ethynylcycloalkenes, with a catalytic amount of Cr(CO)5(THF) gave 5-phenyl-2-furylcyclopropane derivatives in good yields. The key intermediate of this cyclopropanation is a (2-furyl)carbene complex generated by a nucleophilic attack of carbonyl oxygen to an internal alkyne carbon in π-alkyne complex or σ-vinyl cationic complex
Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation-cyclization, palladium carbene migratoryinsertion, β-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate