Au -Catalyzed Haloalkynylation of Alkenes.

The formal insertion of alkenes into aromatic chloro- and bromoalkynes takes place under cationic gold catalysis. This haloalkynylation reaction can be performed with cyclic, gem-disubstituted and monosubstituted alkenes, using BINAP, triazolo[4,3-b]isoquinolin-3-ylidene ligands or SPhos, respectively. The products were isolated in moderate to excellent yields and with complete diastereo- and regioselectivity; the halogen atom bonding the more substituted carbon of the alkene. Preliminary experiments showed that the enantioselective haloalkynylation of cyclopentene can be performed with (S)-BINAP to afford the insertion products with moderate to good enantioselectivities.