CpRu/Brønsted Acid-Catalyzed Enantioselective Dehydrative Cyclization of Pyrroles N-Tethered with Allylic Alcohols.

A cationic CpRu/halogen/Brønsted acid hybrid catalyst (R cat) with the axially chiral Cl-Naph-PyCOOH ligand (naph = naphthyl, py = pyridine) is highly efficient for dehydrative cyclization of pyrroles to construct 1,2-fused-2-allylated pyrroles that, so far, have not been achieved. The mechanistic study has implied that hydrogen and halogen bonds play a key role for facilitating the R,SRu-catalyzed reaction pathway via a σ-allyl intermediate and that the diastereomeric R,RRu cat slowly gives the minor enantiomer via a π-allyl intermediate.