Iodine‐Catalyzed Carbonyl‐Alkyne Metathesis Reactions

Abstract The reaction between aldehydes or ketones and alkynes—the carbonyl‐alkyne metathesis—constitutes a very useful strategy for the synthesis of α,β‐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, −CO 2 Me, −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.