Asymmetric Synthesis of Fluorinated Allenes by Rhodium‐Catalyzed Enantioselective Alkylation/Defluorination of Propargyl Difluorides with Alkylzincs

The reaction of propargyl difluorides R 1 CF 2 C≡CR 2 with alkylzincs R 3 ZnCl giving axially chiral fluorinated allenes R 1 FC=C=CR 2 R 3 with high enantioselectivity (up to 99 % ee ) was found to be catalyzed by a chiral diene/rhodium complex. A key step in the catalytic cycle is selective elimination of one of the enantiotopic fluorides at the β‐position of an alkenyl‐Rh intermediate, which is generated by regioselective addition of R 3 ‐Rh onto the triple bond of the starting difluorides.