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

The 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.