Zn(OTf)2-Catalyzed Formal [3 + 3] Cascade Annulation of Propargylic Alcohols with 2-Aminochromones: Accessing the Chromeno[2,3-b]pyridines.

A Zn(OTf)2-catalyzed formal [3 + 3] cascade annulation strategy for the synthesis of functionalized chromeno[2,3-b]pyridines has been developed using propargylic alcohols and 2-aminochromones as the substrates. The protocol provides a convenient and atom-economical method of accessing a broad range of chromeno[2,3-b]pyridine derivatives in excellent yields with good functional-group tolerance. The method is also effective on the gram scale, which highlights the inherent practicality of this synthetic transformation.