A process for preparing certain 1,3,4,4-tetrasubstituted-1,2,3,4-tetrahydropyridines is provided as well as certain 4-carbonate-1,3,4-trisubstituted-piperidines.
3,4,4-trisubstitutedpiperidinyl-N-alkylcarboxylates and intermediates for their preparation are provided. These piperidine-N-alkylcarboxylates are useful as peripheral opioid antagonists.