Microwave Induced Preparations of Incipient and Solvent Stabilized Cyclopentadiene for Diels-Alder Reactions with Kinetic Control

A microwave induced reaction of dicyclopentadiene (1) was used to rapidly and conveniently generate cyclopentadiene (2) which is stabilized in a polar solvent for subsequent use. In this case 2 was used for Diels-Alder reactions at ambient temperature. A 3 min microwave induced reaction of 1 in acetone gave a solution of 2, followed by a room temperature reaction with a limited amount of a highly active dienophile, maleic anhydride (3), which afforded pure cis-endo-5- norbornene-2,3-dicarboxilic anhydride (4). Simultaneous reactions were achieved in 0.5 min at 200°C but some of the exo-isomer 5 also resulted. Several maleimides also demonstrated the convenient utility of these microwave methods for reactions of 2 for valuable industrial compounds. This method now precludes the previous arduous thermal cracking of 1 along with the simultaneous fractional distillation of 2.