~~ ~The 'H NMR and I3C NMR spectra of N-formylated morphinans were compared with those of the N-methyl and N-demethyl analogues. The magnitude of the changes in chemical shift of C-9, C-16 and C-10 depended crucially on the nature of the substituent at nitrogen. For the 6a,l4aethenoisomorphinans and 6~,14/?-ethenomorphinans, the proton chemical shifts of the 6,14-etheno bridge across ring C are differently affected by the nitrogen atom. In the 6a,14a-ethenoisomorphinans, the vinylic proton shifts are found between 65.3 and 5.9, whereas in the 68,148-ethenomorphinans these proton signals are found downfield from 66.0. A similar, but opposite, anisotropy effect of the nitrogen is observed for the 88-proton. These results are important for the elucidation of the structures of these types of compounds.

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Thebaine (1) was converted into N‐formylnorthebaine (4) via N‐demethylation using diethyl azodicarboxylate followed by treatment with ethyl formate. Diels‐Alder reaction of 4 with nitroethene yielded 5 exclusively with the 6α,14α‐etheno bridge and the nitro group in the 7α‐position. Hydrolysis of 5 and methylation then gave 7, the nitroethene addition product of thebaine. Reduction of 5 and 7 with aluminium amalgam gave the corresponding 7α‐amines 11 and 8, respectively. Reduction of 7 with formamidinesulfinic acid or with lithium aluminium hydride gave only the oxime 9.

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