NMR and Ultraviolet Spectral Characterization of Dihydrobenzene Intermediates in the Displacement of Hydrogen by Intramolecular Nucleophilic Aromatic Photosubstitution

Article abstract of DOI:10.1021/jo00289a043

Direct 1H NMR observation of reaction mixtures reveals that photolysis of 4-O2NC6H4OCH2CH2ND2 in NaOD/D2O generates a long-lived, oxygen-stable dihydrobenzene intermediate (11) resulting from formal intramolecular addition of an N-D bond across the C2-C1 double bond of the nitrophenyl ether.This species (UV λ_max at 321 and 260 nm) is proposed to rearrange thermally by a 1,5-sigmatropic hydrogen shift to a dihydrobenzene (9) that adds ^-OD (to give 16) and further rearranges to an open-chain structure (17).These intermediates exist in equilibrium in solution, are not oxidized by oxygen or 1,4-benzoquinone, but are oxidized thermally by 3,5-dinitrobenzoate ion.The aromatized photoproducts (2 and 3) reported earlier (ref 11) are generated from the array of intermediates by thermal reaction with 3,5-dinitrobenzoate ion or by prolonged photolysis.