Process for piperidine derivatives

A process for preparing a compound of the formula ##STR8## wherein R.sub.1 represents hydrogen or hydroxy;

• R.sub.2 represents hydrogen;
• or
• R.sub.1 and R.sub.2 taken together form a second bond between the carbon atoms bearing R.sub.1 and R.sub.2 ;
• n is an integer of from 1 to 5;
• R.sub.3 is --COOH or --COOalkyl wherein the alkyl moiety has from 1 to 6 carbon atoms and is straight or branched;
• A is hydrogen or hydroxy;
• and
• pharmaceutically acceptable salts, hydrates and individual optical isomers thereof comprising the steps of:
• (a) reacting a benzeneacetic acid compound of the formula ##STR9## wherein A is as defined above and R is hydrogen or C.sub.1 -C.sub.6 alkyl with a suitable reducing agent to give a phenethyl alcohol;
• (b) reacting the phenethyl alcohol with a .omega.-halo compound of the formula ##STR10## wherein wherein B is halo or hydroxy, Hal represents Cl, Br or I and n is as defined above, in the presence of a suitable Lewis acid to produce a .omega.-halo hydroxyethylphenylketone;
• and
• (c) reacting the .omega.-halo hydroxyethylphenylketone with a piperidine compound of the formula ##STR11## wherein R.sub.1 and R.sub.2 are as defined above in the presence of a suitable non-nucleophilic base to produce a piperidine hydroxyethylphenylketone;
• (d) reacting the piperidine hydroxyethylphenylketone with a suitable oxidizing agent to produce a piperidine formylphenyl ketone;
• (e) reacting the piperidine formylphenylketone with a suitable oxidizing agent to produce a piperidine carboxyphenylketone;
• (f) optionally reacting the piperidine carboxyphenylketone to form a piperidine carboxyphenylketone ester;
• and
• (g) optionally reacting the piperidine carboxyphenylketone or the piperidine carboxyphenylketone ester with an appropriate deprotecting reagent, with the proviso that each of the hydroxy groups present in the compounds described in steps a-f are optionally protected or unprotected.