Cobalt(II)-Catalyzed Enantioselective Propargyl Claisen Rearrangement: Access to Allenyl-Substituted Quaternary ß-Ketoesters.

Highly enantioselective propargyl Claisen rearrangement of O-propargyl ß-ketoesters was achieved under 2.5 mol % of the chiral cobalt complex as the catalyst under mild reaction conditions. With Co(OTf)2 as the Lewis acid and C1-symmetric imidazoline-pyrroloimidazolone pyridine as the ligand, diverse chiral allenyl-substituted all-carbon quaternary ß-ketoesters were obtained in good yields (up to 97% yield) and high enantioselectivities (up to 98% ee).