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A new synthesis of 1,2,3,4,5,6-hexahydro-l,5-methano-2-benzazocines (7,8-benzomorphans) based on the acid -catal ysed cyclizat ion of 2 -an/ I piperid i ne-4-carboxyl ic acids is reported. The required carboxylic acids were prepared from 2-aryl-4-piperidones, by reaction with tosylmethyl isocyanide followed by hydrolysis of the resulting 4-cyanopiperidines.

2‐Aryl‐4‐piperidones have been synthesized by condensation between an aromatic aldehyde and a β‐aminoketone ethylene ketal, and further cyclization of the resulting iminoketal with dry hydrogen chloride or anhydrous p‐toluensulfonic acid. Alternatively, reaction of the above iminoketals with methyl fluorosulfonate followed by dry hydrogen chloride treatment and acid hydrolysis gives directly N‐methyl‐4‐piperidones. The application of these reactions to the synthesis of some 2‐aryl‐3‐acetylpyrrolidine systems is also described.

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