Functionalized 1,2‐Dihydronaphthalenes from the Cu(OTf)2‐Catalyzed [4+2] Cycloaddition of o‐Alkynyl(oxo)benzenes with Alkenes

The [4+2] cycloaddition reaction between o-alkynyl(oxo)benzene 1 and olefins 2 in the presence of a catalytic amount of Cu(OTf)2 afforded 1,2-dihydronaphthalene derivatives 3 bearing an oxo function at the 1-position. The reaction proceeds most probably through the formation of benzo[c]pyrylium cupric ate complex.