Synthesis of Fused and Linked Benzofurans from 2-Alkynylphenol Derivatives through Rhodium(I)-catalyzed Domino-type Addition Reactions

A rhodium(I)-catalyzed domino-type sequential 5-endo/5-exo cyclization reaction of [(2-acylphenyl) ethynyl]phenols produces indene/benzofuran-fused alcohols. A moderate asymmetric induction is observed when chiral diphosphine ligands are used for rhodium. Indene/indole-fused compounds are synthesized by a similar reaction of [(2-acetylphenyl)ethynyl]anilines. The domino-type 5-endo/5-exo cyclization reaction is extended to substrates having two phenolic hydroxy groups. A linearly-fused array of five- and six-membered rings is constructed. Fused and linked benzofurans possessing 2-cyanoethyl side chains are also synthesized through sequential formation of C-O and C-C bonds.