CYCLOADDITION REACTIONS OF 5H-BENZOCYCLOHEPTENE WITH SINGLET OXYGEN AND WITH 4-PHENYL-1,2,4-TRIAZOLINE-3,5-DIONE, AND THE CHEMISTRY OF THE 5H-BENZOCYCLOHEPTENE ENDOPEROXIDES

Article abstract of DOI:10.1016/S0040-4020(01)87365-8

The cycloaddition reactions of 5H-benzocycloheptene with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and singlet oxygen has been investigated. 1H-NMR spectra established structures formally derived from the cycloheptatriene valence isomer by (2+4)-Diels-Alder cycloaddition.The formation of these cycloheptatriene adducts is discussed in terms of cycloheptatriene-norcaradiene-equilibrium.The chemistry of the cycloheptatriene endoperoxide (6) was studied.Thermolysis of (6) gave a mixture of products; bis-epoxide, epoxy-ketone, and hydroxy-enone.However, base-catalyzed rearrangement of (6) gave diketone (14) instead of the expected hydroxy-enone.This observation is unprecedented.The formation-mechanism of (14) is also discussed.