Ene reaction of 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione with dicyclopentadiene

The kinetics of the ene reaction of endo -dicyclopentadiene with 4-phenyl-3 H -1,2,4-triazole-3,5(4 H )-dione in benzene, toluene, acetonitrile, 1,2-dichloroetane, and chloroform have been studied. The reaction volumes and enthalpies have been determined, and the activation volume in toluene has been calculated from the pressure kinetic data. The “anomalous” ratio Δ V corr ≠ /Δ V r = 1.34 corresponds to a concerted cyclic transition state, though the addition product has acyclic structure.