Reaction of Alkynes with Cyclopropylcarbene-Chromium Complexes: A Versatile Cycloaddition Reaction for the Construction of Cyclopentenones

Article abstract of DOI:10.1021/ja00048a008

The scope and limitations of the reaction between cyclopropylcarbene-chromium complexes and alkynes have been examined.A variety of cyclopropylcarbene complexes and alkynes have been employed in these studies.The reaction appears to be general for most simple alkynes, producing cyclopentenones.A mechanism has been proposed involving metallacyclobutene formation, electrocyclic ring opening, electrocyclic ring closure, CO insertion, alkene insertion, metallacyclopentene fragmentation and cyclopentadienone reduction.The presence of these intermediates has been inferred from the structure of products obtained when the reaction was conducted in acetonitrile instead of dioxane.A trapping experiment employing 1,6-heptadiyne supports the intermediacy of vinylcarbene or vinylketene complexes.