Iodine-Catalyzed Carbonyl-Alkyne Metathesis Reactions

The reaction between aldehydes or ketones and alkynes –the carbonyl-alkyne metathesis– constitutes a very useful strategy for the synthesis of ,-unsaturated carbonyls. We now demonstrate that iodine is a highly efficient catalyst for both the intra- and intermolecular metathesis reaction in very small concentrations (0.1–1 mol%). Our protocol outperforms other catalytic systems, is operationally very simple, cheap, metal-free, and tolerates a large variety of functional groups (e.g., –CN, –CO2Me, –Br, –OH) at very low catalyst loadings. We can furthermore show that iodine-catalyzed carbonyl-alkyne metatheses can be combined with other iodine-catalyzed reactions in one-pot procedures to afford larger and more complex molecular structures. Finally, our mechanistic studies indicate that the iodonium ion is the active catalyst under the reaction conditions.