Atroposelective [5+5] formation of Benzo[c]chromenone and Phenanthridinone by Carbene organocatalysis

The N-heterocyclic carbene organocatalyzed δ-LUMO activation strategy was used for the atroposelective [5+5] construction of benzo[c]chromenone and phenanthridinone. The cascades involved a regioselective and stereoselective 1,6-addition, an intramolecular aldol reaction, a chemoselective lactonization, dehydration, and the successive oxidative aromatization with the simultaneously point-to-axial chirality transfer process. Axially chiral biaryls with gradient rotation barriers were synthesized and investigated. The multicyclic aromatic products can be obtained on a gram scale and further transformed into several interesting molecules. This study further expands the organocatalyzed benzannulation methods to the construction of more sophisticated multicyclic aromatics.