Ru(II)-Catalyzed Annulation of 2-Nitrostyrenes: Alcohols as Hydrogen Source and Alkoxylating Reagent

A new Ru(II)-catalyzed annulation pathway of 2-nitrostyrenes, distinct from the conventional 6π-electrocyclization, has been developed. This transformation employs alcohols as both the hydrogen source and alkoxylating reagent, enabling the efficient synthesis of 3-alkoxy-1 H -indoles. Mechanistic studies reveal that this domino transformation proceeds via four key steps: Michael addition of the enone moiety, nitro reduction, cyclization, and dehydration. Moreover, the vicinal alkoxy group acts as a critical determinant for preserving the carbonyl group under the reductive conditions.