Reaction of N-(1-(2-phenylethyl)-4-piperidinyl)propionanilide (I) with phosphorus pentasulfide gave the thioamide VI. Acylation of N-(1-(2-phenylethyl)-4-piperidinyl)aniline with 2-(methoxy)acetic and 2-(methylthio)acetic anhydrides afforded the amides II and III. Treatment of 4-anilino-1-benzylpiperidine-4-methanol with thionyl chloride gave the spirocyclic sulfurous acid ester amide XIV. Reduction of the hydrochloride of ethyl 3-(1-ethoxycarbonyl-4-phenylimino-3-piperidinyl)propionate (XXII) with sodium cyanoborohydride gave the perhydro-1,6-naphthyridine derivative XIX, a model compound in the synthesis of the cyclic analogue of fentanyl (I). Ethyl 4-anilino-1-(2-phenylethyl)-1,2,3,6-tetrahydropyridine-3-carboxylate (XXIX) hydrochloride, obtained by reaction of ethyl 4-oxo-1-(2-phenylethyl)piperidine-3-carboxylate hydrochloride with aniline, was reduced with lithium aluminium hydride to 4-anilino-1-(2-phenylethyl)piperidine-3-methanol (XXXI). 1-Methyl- and 1-benzyl-4-piperidone were reacted with 4-cyclopropylphenylmagnesium bromide and the tertiary alcohols XXXVII and XXXVIII obtained were acylated with propionyl chloride to give the esters XXXIX and XL. The piperidine derivatives XLI, XLVI and XLVIII were prepared as potential neurotropic agents. Alkylation of 8-hydroxy-6,11-dimethyl-1,2,3,4,5,6-hexahydro-2,6-methano-3-benzazocine (XLIX) with 2-(2-chloroethyl)-1,3-dioxane and -1,3-dioxolane resulted in the 6,7-benzomorphan derivatives L and LI. Out of the compounds prepared, only the closest fentanyl analogues II, III, and VI showed very strong analgetic activity.
