Rh(III)‐Catalyzed Cascade C─H Activation/[4 + 1] Annulation: A Direct Route to Benzofuran‐Fused Succinimides From Aromatic Acids and 3‐Methylmaleimides
Hung‐Sheng Hsieh, Chen‐Ting Liao, Ting‐Yen Chu, Chien‐Chien Wu, Kuan‐Miao Liu, Chi‐Min Chao, Indrajeet J. Barve, Li Ching Shen, Sheng‐Cih Huang, Chung‐Ming SunA Rh(III)‐catalyzed [4 + 1] cyclization of aromatic carbocyclic/heterocyclic acids with 3‐methylmaleimides has been developed, providing an efficient route to benzofuran‐linked succinimides. In addition to various 3‐methylmaleimides, this strategy can be extended to sterically demanding 3,4‐dimethylmaleimides. Mechanistic studies revealed that the reaction proceeds via Rh(III)‐mediated in situ isomerization of 3‐methylmaleimide to form an exo methylidene succinimide intermediate. Subsequent C─H activation of the aromatic acid to generate a five‐membered rhodacycle, coordination and migratory insertion of the isomeric methylidene succinimide, accompanied by E2 elimination, yields an olefinic intermediate. This intermediate subsequently undergoes an intramolecular oxa‐Michael addition via a 5‐exo‐trig cyclization to furnish the benzofuran‐linked succinimide products.