Cycloaddition of Substituted Bicycloocta-2,6-diene with 4-Phenyl-1,2,4-triazoline-3,5-dione

Article abstract of DOI:10.1021/jo00334a004

4,4-Dimethylbicyclo<3.2.1>octa-2,6-diene (1b) reacts with 4-phenyl-1,2,4-triazoline-3,5-dione to give the rearranged urazole 3b (via dipolar cycloaddition at the more strained C₆-C₇ double bond) as the only isolable (22percent yield) product, while 3-bromobicyclo<3.2.1>octa-2,6-diene (1c) affords the ene adduct 7 as the major product (60percent yield) together with a 10percent yield of the rearranged urazole 3c.Both dimethyl substitution at the C₄ position and bromo substitution at the C₃ position suppress effectively homocycloaddition and dipolar cycloaddition at the less strained C₂-C₃ double bond.The ene reactivity of the bromo diene 1c is surprising, since neither the parent diene 1a nor the dimethyl diene 1b exhibit this cycloaddition behavior.