Diels‐Alder Adducts From 4‐O‐Acetyl‐6‐Demethoxy‐N‐Formyl‐β‐Dihydro‐N‐Northebaine With Methyl Vinyl Ketone and Nitroethene (Chemistry of Opium Alkaloids, Part XXIX)

Abstract

AbstractReductive epoxy ring scission of 6‐demethoxy‐N‐northebaine (5) with zinc and potassium hydroxide gave a 85:15 mixture of 6a and its non‐conjugated isomer. Formylation with triethyl orthoformate, followed by acetylation with acetic anhydride in the presence of 4‐(dimethylamino)pyridine gave a 4:1 mixture of the title compound 6c and its non‐conjugated isomer in 80% overall yield.Diels‐Alder reaction of 6c with methyl vinyl ketone afforded a 2:1 mixture of 7β‐acetyl‐and 8β‐acetyl‐6β, 14β‐ethenomorphinan 7 and 8a. Cycloaddition of nitroethene yielded the 8β‐nitro‐6β, 14β‐ethenomorphinan 8b as major product.N‐Demethylation of 2b, the 4‐O‐phenyl ether of 6‐demethoxy‐β‐dihydrothebaine (2a), with diethyl azodicarboxylate failed to give the N‐norcompound.