Ru(II)-Catalyzed Annulative Linear Dienylation with Allenyl Acetates and Applications in Photocatalytic Reductive Couplings

Allenes, especially those equipped with a leaving group, are privileged scaffolds for C–H activation, yet their exploration remains limited by the need for mechanistically distinct approaches. Herein, we report a Ru(II)-catalyzed annulative linear dienylation reaction of aromatic amides with allenyl acetates, which has been elusive so far. The protocol capitalizes on an oxidizing directing group and leverages regioselective 1,2-insertion of the allene motif to afford valuable 3-styrylisoquinolinones in high yields with exclusive trans-olefin geometry. This cascade protocol is operationally simple, scalable, features a wide substrate generality, and also remains effective in the presence of medicinally relevant scaffolds. Products are further transformed into π-extended tetracyclic pyrano[2,3,4-gh]phenanthridines with distinct photophysical and redox properties, enabling efficient photocatalysis in reductive couplings, exemplified by dehalogenative phenanthridinone synthesis and reductive pinacol coupling reaction.