2, 3, 4, 5-Tetrahydrodipicolinic acid (3) is a key intermediate in the diaminopimelate (DAP) pathway to l-lysine (7). It was synthesized as the stable racemic potassium salt (25) from dipicolinic acid (14) by esterification, hydrogenation to the cis-diester (17), followed by elimination of p-toluenesulfinic acid from the N-toluenesulfonyl derivative (24) of dimethyl cis- piperidine-2, 6-dicarboxylate with concomitant cleavage of the ester groups.(±)-2, 3, 4, 5- ...