Uncommon expansion of piperidine ring into hydroazocine ring in reactions of some piperidine β-acyl derivatives with acetylenecarboxylic acids esters

Cyclohexanone condensation with formaldehyde and methylamine led to the formation of 4ahydroxy-2-methyloctahydrospiro[isoquinoline-4,1′-cyclohexan]-2′-one whose structure was established by means of X-ray diffraction (XRD) analysis. This spiro compound reacted with acetylenecarboxylic acids esters with unexpected conversion of its piperidine ring into a hexahydroazocine cycle. The uncommon expansion reaction of the β-acyl-substituted piperidine ring into a hexahydroazocine cycle is confirmed by the analogous conversion of 4-hydroxy-1-methyl-4-phenylpiperidin-3-yl(phenyl)methanone into azocine derivative at treating with methyl propiolate. © 2016 Pleiades Publishing, Ltd.