The present invention relates to a process for preparing piperidine derivative compounds of the formulae: 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, The process comprises providing a regiosomer of the following formula: m is an integer from 1 to 6; Q and Y are the same or different and are selected from the group consisting of O, S, and NR5; G1, G2, and G3 are the same or different and are selected from the group consisting of OR8, SR8, and NR8R9; R6 and R7 are the same or different and are selected from the group consisting of hydrogen, an alkyl moiety, an aryl moiety, OR8, SR8, and NR8R9; and R5, R8, and R9 are the same or different and are selected from the group consisting of hydrogen, an alkyl moiety, and an aryl moiety and converting the regioisomer to the piperidine derivative compound with a piperidine compound.