Acid-triggered cascade cyclization pathways of enynes: A rapid access to fused polycyclic products

Herein, we present a novel acid-triggered cyclization of enyne biaryl systems, producing discrete phenanthrene-fused polycyclic (tri-/tetra-/penta-cyclic) products, depending upon the stereoelectronic effects of substituents. Notably, the accomplished pentacyclic structures constitute the complete core structures of natural products, namely clostrubin and borolithochromes, offering a rapid synthetic route. In addition, the absorption and emission properties of the synthesized products have been studied.