Method for the production of 4-formylaminopiperidine derivatives

A method for producing a 4-formylaminopiperidine compound of formula (I)

• in which
• n is 1 or 2,
• R1, R2, R3 and R4, independently of one another, are identical or different and are C1-C4-alkyl or R1 and R2 or R3 and R4 together are a tetramethylene or pentamethylene group,
• R5 is hydrogen or C1-C4-alkyl,
• R6 is hydrogen, oxygen, C1-C22-alkyl, C3-C22-alkenyl, C1-C22-alkoxy, unsubstituted or substituted C7-C12-phenylalkyl, C1-C22-alkanoyl, C2-C3-cyanoalkyl, C1-C22-hydroxyalkyl or C2-C22-aminoalkyl and
• —if n=1—
• Y is hydrogen, C1-C22-alkyl, C3-C22-alkenyl, C3-C12-cycloalkyl or bicycloalkyl, C2-C22-alkyl substituted by cyano, hydroxy or C1-C4-alkoxy, C4-C22-alkyl interrupted by ether oxygen, nitrogen or sulfur, unsubstituted or substituted C7-C22-phenyl or diphenylalkyl, unsubstituted or substituted phenyl, a radical of formula
• or C1-C22-alkyl comprising a heterocyclic radical, or
• —when n=2—
• Y is C2-C22-alkylene, C5-C22-cycloalkylene, C8-C14-phenylalkylene, phenylene or C4-C30-alkylene interrupted by ether oxygen, nitrogen, sulfur or 5- or 6-membered heterocycles, and also an acid addition salt thereof, comprising reacting a 4-aminopiperidine compound of formula (II) or an acid addition salt thereof,
• in the presence of a compound of formula (III)
• wherein
• R7, R8, independently of one another, are identical or different and are hydrogen, C1-C22-alkyl, C3-C22-alkenyl, unsubstituted or substituted C7-C12-phenylalkyl, or C1-C22-alkanoyl,
• and
• the reaction takes place in the presence of at least one protic acid and at least one Lewis acid.