Rhodium-Catalyzed Asymmetric Hydroboration/Cyclization of 1,6-Enynes Enabled by Spirosiladiphosphine Ligands: Constructing Chiral Five-Membered Rings with a Boron Handle

A rhodium-catalyzed enantioselective hydroboration/cyclization reaction of 1,6-enynes is achieved by employing a spirosiladiphosphine ligand. The process allows the synthesis of five-membered hetero- and carbocycles bearing a boron handle with high levels of activity and selectivity. Various enynes and organoboranes (HBdan, HBpin, HBmp, and HBamm) have been accommodated, and enynes containing terminal alkynes have been integrated into the process for the first time. The high yields and selectivities of the transformation highlight the synthetic utility of these novel spirosiladiphosphine ligands.