Benzomorphan related compounds. IV. The stevens rearrangement of a trimethoxybenzyl‐1,2,5,6‐tetrahydropyridinium salt

Abstract

AbstractThe potassium hydroxide‐induced (Stevens) rearrangement of 1,3,4‐trimethyl‐1‐(3,4,5‐trimethoxybenzyl)‐1,2,5,6‐tetrahydropyridinium chloride (I) gives the desired 1,3,4‐trimethyl‐2‐(3,4,5‐trimethoxybenzyl)‐1,2,5,6‐tetrahydropyridine (III) and the Hofmann elimination product, N‐methyl‐N‐(3,4,5‐trimethoxybenzyl)‐2,3‐dimethyl‐2,4‐pentadienamine (II). In the presence of ethereal phenyllithium, the salt I undergoes rearrangement giving the expected tetrahydropyridine III in about 17% yield and four other products, N‐(3,4,5‐trimethoxybenzyl)methylamine (VI), 1,3,4‐trimethyl‐2‐(6‐methyl‐2,3,4‐trimethoxyphenyl)‐1,2,5,6‐tetrahydropyridine (IV), 1,3,3‐trirnethyl‐2‐(3,4,5‐trimethoxyphenyl)‐4‐rnethylenepiperidine (V) and 1,3,4‐trimethyl‐4‐(3,4,5‐trimethoxybenzyl)‐1,4,5,6‐tetrahydropyridine (VII), the latter being the 1,4‐Stevens rearrangement product which cyclizes easily to β‐2′,3′,4′‐trimethoxy‐2,5,9‐trimethyl‐7,8‐benzomorphan (VIII). Their structures have been proved both by analytical and spectral data. A possible route for VIII and its stereochemical aspects are discussed.