Acetylation shift - aporphines

Acetylation of phenolic functions produces predictable effects on adjacent aromatic protons. For example, the assignment of the OH groups of thalictroga-mine (429) to C-l and C-7 was based on an upfield shift of H-ll and a downfield shift of H-8 in the diacetate (209). The NMR shifts of the C-8 hydrogen in several bisbenzylisoquinoline-aporphine dimers have been summarized (295). H-NMR spectra of some bisbenzylisoquinoline and related dimeric alkaloids have been tabulated (296,297). 

The most distinctive feature of the PMR spectrum of pennsylpavine (see Table 13.1) is the presence of a pair of low-field one-proton doublets for the C-6 and C-12 bridgehead protons of the pavine unit. As in the case of phenolic aporphine-benzylisoquinolines, comparison of the PMR spectrum of the natural product with that of the 0-acetate derivative yielded critical structural information. The magnitude of the downfield shift (0.2 ppm) of the C-9 aromatic proton resonance upon 0-acetylation is indicative of a meta relation with the acetate group. The accompanying upheld shift of only one of the bridgehead proton doublets (84.50 -> 4.35) denotes a close spatial relationship between the phenolic hydroxyl and the C-6 bridgehead proton in the natural product. This observation is also valid for phenolic monomeric pavines, where only the... 

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