H-1, C-13 AND F-19 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 re fluxing 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, respec tively. At ambient temperature, the unsubstituted bridgehead phenyl gr oups in adduct (2) under bar are found to exhibit hindered rotation, r esulting in slow exchange limit (SEL) H-1 NMR spectra. Full aryl proto n 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. T his resonance collapses to a singlet in the proton decoupled F-19 spec trum, implying an unexpected long range H-1-F-19 coupling. For the C-1 3 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 effec ts.