Recent Advances in the Cycloaddition Reactions of 2-Benzylidene-1-benzofuran-3-ones, and Their Sulfur, Nitrogen and Methylene Analogues.

Benzothiophene, benzofuran, indole, and indene derivatives are privileged heterocyclic motifs. These are present in a wide range of bioactive natural products and pharmaceutical drugs and are the subject of materials science research. However, the construction of benzothiophene, benzofuran, indole, and indene frameworks have been long-standing challenges to organic chemists. In this review, we classify the derivatives of four structures synthesized from 2-benzylidene-1-benzofuran-3-one and their analogues in terms of their ring size (from three- to ten-membered) and type (fused or spiro), as well as summarizing the developments of this field. Finally, we discuss the ring opening and 1,4-addition reactions.