Electronic Substituent Effects on the Acid-Catalyzed (4+ + 2) Cycloaddition of Isopyrazoles with Cyclopentadiene and the Photochemical and Thermal Denitrogenation of the Resulting 1,4-Diaryl- 7,7-dimethyl-2,3-diazabicyclo(2.2.1)hept-2-ene Azoalkanes to Bicyclo(2. 1.0)pentanes.