Method for preparing 4-amino-4-phenylpiperidines

A process for preparing a 4-amino-4-phenylpiperidine of formula (I):

• 10
• in which R is hydrogen or a (C1-C3)alkyl group, characterized in that:
• (a) a 1-protected 4-piperidone of formula
• 11
• in which Pr′ represents a removable N-protecting group, is treated sequentially first with an alkali metal cyanide and then, in the reaction medium containing the cyanohydrin thus obtained, with an amine of formula:
• 12
• in which e represents a group R′=(C1-C3)alkyl, or an N-protecting group and Pr″ is an N-protecting group, the protecting group(s) being removable under the same conditions as Pr′;
• (b) the compound thus obtained of formula:
• 13
• in which Pr′, Pr″ and E are as defined above, is subjected to a Grignard reaction with a phenylmagnesium halide;
• and
• (c) the two or three protecting groups are removed from the compound thus obtained of formula:
• 14
• and compound (I) is isolated either in the form of one of its salts, which is converted into the free base, or in the form of the free base, which is converted into one of its salts.