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

摘要

O-Xylylenes, which are 1,3-cyclohexadienes bearing two exo-methylenes at the 5- and 6-positions, are often used as diene substrates for the Diels-Alder reaction. The [4+2] cycloaddition of o-xylylenes with alkenes or alkynes has been intensively studied. As with the carbon dienophiles, imines might be another attractive dienophile for the o-xylylene cycloaddition. The hetero-Diels-Alder reaction will afford tetrahydroisoquinoline frameworks, which are found in many useful biologically active compounds. Nevertheless, only a few reports have been made on the reaction with imines. In these works, the o-xylylenes were generated from the thermal ring-opening reaction of benzocyclobutenes. Herein, we describe a new approach to the [4+2] cycloaddition of o-xylylene with imines.