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.