Reactive Iron Carbonyl Reagents via Reaction of Metal Alkoxides with Fe(CO)₅ or Fe₂(CO)₉: Synthesis of Cyclobutenediones via Double Carbonylation of Alkynes

Alkoxy bases such as t-BuOK react with Fe(CO)5 to give reactive iron carbonyl intermediates that in turn react with alkynes at 70 °C in THF to give 1,2-cyclobutenediones in 70−93% yields after CuCl2·2H2O oxidation. A novel 1,2-diacyloxyferrole derivative was isolated in the reaction of diphenylacetylene with Fe(CO)5/t-BuOK in the presence of acetyl chloride in contrast to the formation of a 1,4-diacyloxyferrole complex formed in the reaction using Fe(CO)5/Me3NO. The Fe2(CO)9/t-BuOK reagent system also converts the alkynes to corresponding cyclobutenediones in 63−90% yields under similar reaction conditions.