Highly Enantioselective [3 + 2] Annulation of 3-Butynoates with β-Trifluoromethyl Enones Promoted by an Amine-Phosphine Binary Catalytic System.

We report a highly enantioselective [3 + 2] annulation between 3-butynoates and β-trifluoromethyl enones, furnishing trifluoromethylated cyclopentenes with three contiguous stereogenic centers in good yields, high diastereoselectivities, and excellent enantioselectivities. A unique catalytic system consisting of a simple amine and a chiral phosphine was devised, and the synergistic play of Lewis basic amine and phosphine was crucial for alkyne isomerization and subsequent cyclization. The protocol disclosed herein allows facile activation of 3-butynoates in phosphine-mediated asymmetric transformations.