1H, 13C and 19F NMR studies of the Diels-Alder adduct of p-fluoranil with phencyclone.: II.: Hindered phenyl rotations and anisotropic effects in a model compound for drugs.

The Diels-Alder adduct of phencyclone, compound (1) under bar, with (p) under bar-fluoranil, compound, (3) under bar has been prepared in refluxing toluene. The adduct, compound (2) under bar, has been examined by H-1, C-13 and F-19 NMR spectroscopy at 300, 75 and 282 MHz, respectively. At ambient temperature, the unsubstituted bridgehead phenyl groups in adduct (2) under bar are found to exhibit hindered rotation, resulting in slow exchange limit (SEL) H-1 NMR spectra. Full aryl proton assignments are made based on 1D and 2D (COSY45) NMR. The F-19 NMR (proton coupled) reveals one of the two F-19 signals to be a triplet. This resonance collapses to a singlet in the proton decoupled F-19 spectrum, implying an unexpected long range H-1-F-19 coupling. For the C-13 NMR spectrum, tentative assignments are presented. Data for compound (2) under bar as a model compound for drugs are discussed in terms of the hindered aryl rotation and evidence of magnetic anisotropic effects.