The potent Diels-Alder diene, phencyclone,
1, reacts with
N-pentafluorophenylmaleimide,
2, to form an adduct,
3, characterized by
1H,
13C, and
19F NMR at 300, 75 and 282 MHz, respectively. The one-dimensional (1D) and two-dimensional (2D)
1H and
13C NMR spectra of
3 at ambient temperatures imply a slow exchange limit (SEL) regime with respect to rotation of the unsubstituted bridgehead phenyl groups about severely hindered C(sp
2)-C(sp
3) bonds. Major non-bonded interactions are expected between the
ortho protons of the C
6H
5 groups and H-1, 8 of the phenanthrenoid moiety of
3.
19F 1D and 2D (COSY) NMR spectra show that the SEL regime also obtains for rotation about the N-C
6F
5 bond of
3, with five separate fluorine signals seen, consistent with a preferred conformation in which the C
6F
5 may lie roughly perpendicular to the plane of the pyrrolidinedione moiety, and may be in the mirror symmetry plane of
3. The results are considered relevant to hindered aryl rotations in numerous Pharmaceuticals. Selected spectral data for
2 and precursors are also presented.
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