New Convenient One-Pot Methods of Conversion of Alkynes to Cyclobutenediones or α,β-Unsaturated Carboxylic Acids Using Novel Reactive Iron Carbonyl Reagents

Reactions of NaHFe(CO) 4 /RX or [HFe 3 (CO) 11 ] - reagents with alkynes lead to the formation of the corresponding α,β-unsaturated carboxylic acids and/or the cyclobutenediones. The reagent generated in situ using the NaHFe(CO) 4 /CH 3 I combination in THF, on reaction with alkynes followed by CuCl 2 ·2H 2 O oxidation, gives the corresponding cyclobutenediones (27−42%) and α,β-unsaturated carboxylic acids (10−22%), whereas the reagent generated using CH 2 Cl 2 in place of CH 3 I leads to α,β-unsaturated carboxylic acids (37−60%) and their derivatives (35−55%) at 25 °C. The same reagent system in the presence of acetic acid (4 equiv) yields the corresponding cyclobutenedione (33%). The reaction using Me 3 SiCl gives the corresponding α,β-unsaturated carboxylic acids (45−54%) at 25 °C and the corresponding cyclobutenediones (51−63%) at 60 °C. Interestingly, the reaction of the [HFe 3 (CO) 11 ] - species generated using Fe(CO) 5 /NaBH 4 /CH 3 COOH, with alkynes at 25 °C, followed by CuCl 2 ·2H 2 O oxidation gives the corresponding cyclobutenediones (60−73%). The possible intermediates and pathways for the formation of α,β-unsaturated carboxylic acids and cyclobutenediones are discussed.