Gold(I)-Catalyzed Chloroalkynylation of 1,1-Disubstituted Alkenes via 1,3-Chlorine Shift: A Combined Experimental and Theoretical Study.

The haloalkynylation reaction is of great interest for the synthesis of complex molecules as it represents a carbon-carbon bond-forming reaction where the reactive halide reappears in the product. The latter enables further chemical transformations. However, only a few examples of haloalkynylations have been described so far. By using alkenes as reactant, this reaction is strictly limited to norbornene systems proceeding via a nonclassical carbocation. Herein, we show by means of quantum chemical calculations and experiments that the chloroalkynylation of 1,1-disubstituted alkenes can be successfully achieved via gold(I) catalysis. The key step in the reaction mechanism is a 1,3-chlorine shift to a cationic center, leading selectively to the corresponding homopropargyl chlorides. As this gold(I)-catalyzed addition can be conducted on a preparative scale and tolerates a broad substrate scope of both alkyne and alkene reactants, the presented chloroalkynylation reaction is an attractive method en route to complex alkynes and their congeners.