Base‐Catalyzed Cyclization of 1,6‐Diynyl Carboxylates Involving Propargyl‐Allenyl Isomerization: Efficient Synthesis of Benzo[b]fluorene and Its Analogues

Abstract An efficient protocol for the synthesis of benzo[ b ]fluorenes via base‐catalyzed cyclization of 1,6‐diynyl carbonates, esters or ethers has been developed. The reaction likely proceeds via base‐induced propargyl‐allenyl isomerization followed by Schmittel‐type cyclization. Heterocycle‐fused fluorenes such as thiophene‐ or pyridine‐fused substrates could also be conveniently constructed by this method. The synthetic utility of this reaction was demonstrated by the preparation of up to seven‐ring fused polycyclic aromatic hydrocarbons. magnified image