Gold-Catalyzed Domino Synthesis of Functionalized Benzofurans and Tetracyclic Isochromans via Formal Carboalkoxylation

A domino synthesis of benzofurans with the modification of side chains from α-alkoxyalkyl o-alkynylaryl ethers (n = 0) and electron-rich arenes has been developed. In the present domino reaction, which would proceed via the α-alkoxyalkylation of arenes with an intermediate in the migratory cycloisomerization of o-alkynylaryl ethers followed by the nucleophilic addition of benzofurans to benzyl ethers, a cationic Au­(III) catalyst activates the C–C π bond and the C–O σ bond. The present method could be extended to Au­(I)-catalyzed domino synthesis of tetracyclic isochromans from α-alkoxyalkyl (o-alkynylaryl)­methyl ethers (n = 1) and aryl methoxymethyl ethers.