Gold(I)-Catalyzed Haloalkynylation of Aryl Alkynes: Two Pathways, One Goal.

Haloalkynylation reactions provide an efficient method for the simultaneous introduction of a halogen atom and an acetylenic unit. For the first time, we report a gold(I)-catalyzed haloalkynylation of aryl alkynes that delivers exclusively the cis addition product. This method enables the simple synthesis of conjugated and halogenated enynes in yields of up to 90 %. Notably, quantum chemical calculations reveal an exceptional interplay between the place of the attack at the chloroacetylene: No matter which C-C bond is formed, the same enyne product is always formed. This is only possible through rearrangement of the corresponding skeleton. Hereby, one reaction pathway proceeds via a chloronium ion with a subsequent aryl shift; in the second case the corresponding vinyl cation is stabilized by a 1,3-chlorine shift. C-labeling experiments confirmed that the reaction proceeds through both reaction pathways.