The construction of the piperidine ring about an aromatic nitrogen atom, by a 5C + N reductiye condensation reaction, using glutaraldehyde (pentanedial) and sodium borohydride in acidic water/methanol medium is described. The reaction is fast, affords good to excellent yields and appears insensitive to electronic effects and severe steric hindrance; it is found to be compatible with a large variety of aryl substituents, including nitro and oxo groups.
