The present invention discloses processes for preparing piperidine derivative compounds of the formulae: ##STR1##

wherein

• n is 0 or 1;
• R¹ is hydrogen or hydroxy;
• R² is hydrogen;
• or, when n is 0, R¹ and R² taken together form a second bond between the carbon atoms bearing R¹ and R², provided that when n is 1, R¹ and R² are each hydrogen;
• R³ is —COOH or —COOR⁴;
• R⁴ is an alkyl or aryl moiety;
• A, B, and D are the substituents of their rings, each of which may be different or the same, and are selected from the group consisting of hydrogen, halogens, alkyl, hydroxy, alkoxy, and other substituents.