[4+2] Cycloaddition of o-Xylylenes with Imines Using Palladium Catalyst

The cycloaddition of o-(silylmethyl)benzylic carbonates with imines proceeded in the presence of the Pd(eta(3)-C3H5)Cp-DPPPent catalyst, affording the tetrahydroisoquinolines in good to high yields. The reaction rate was remarkably increased by a fluoride additive. In the catalytic cycloaddition, the palladium(0) reacted with the benzylic substrate to form 2-palladaindane, which works as an o-xylylene equivalent. The catalytic reaction is equivalent to the hetero-Diets-Alder reaction of o-xylylene with imines.