Asymmetric Construction of Chiral 2‐Azetines and Axially Chiral Tetrasubstituted Allenes via Phosphine Catalysis

Chiral 2-azetines and allenes are highly valuable structural units in natural products and useful chemicals. However, enantioselective synthesis of both 2-azetines and allenes has been extremely challenging. Herein, we present asymmetric construction of chiral 2-azetines (70-98 % yields and up to 96 % ee) through chiral phosphine-catalyzed [2+2] annulation of yne-enones with sulfamate-derived cyclic imines. These 2-azetines were easily transformed into chiral allenes upon treatment with Et