Synthesis of Conjugated Ladder Systems by a Reductive Double Cyclization

Significance

The intramolecular cyclization of ortho-substituted benzene rings is a popular synthetic technique for the formation of benzene-fused five-membered rings. The authors have extended this technique to the synthesis of ladder-type polycyclic compounds by employing diaryl acetylene precursors. In previous reports, reduction of the acetylene moiety led to a double cyclization with heteroatoms. In the current paper, carbonyl substituents on the benzene ring act as the reducible moiety and are used to generate methylene-bridged stilbenes (2) and dibenzo[a,e]pentalenes (3).