Catalytic Nazarov Cyclization of Heteroaromatic Compounds

Significance

A general catalytic system was developed to achieve the Nazarov cyclization of typically unreactive aromatic heterocyclic substrates. The method allowed the selective preparation of disubstituted fused cyclopentenones 2 and 4 with only the trans stereochemistry observed. The mildness of the conditions obviates the need for protection of the pyrrole or indole and should also have a wide functional group tolerance. The cyclization precursors 1 and 2 were prepared by aldol/oxidation and TiCl₄-mediated Knoevenagel condensation.