Iodine-Substituted Phosphoric Acid Catalyst

Significance

A novel chiral phosphoric acid 1 (I₂-TRIP) substituted with iodine on the 6,6′-positions of the binaphthyl group is introduced. The Brønsted acid 1 catalyzes a vinylogous Mannich-type reaction of 2-trimethylsiloxyfuran (2) with aliphatic as well as aromatic and hetaromatic ald­imines 3 to give γ-butenolide derivatives 4. Interestingly, slightly higher enantioselectivity was achieved with the iodine-substituted phosphoric acid 1 (I₂-TRIP, er = 91:9) compared to the non-iodine-substituted phosphoric acid (TRIP, er = 87:13), retaining the same high yield (100% yield with both catalysts).