The first stereospecific synthesis of L-tetrahydrodipicolinic acid; a key intermediate of diaminopimelate metabolism

L-Tetrahydrodipicolinic acid 1, a key intermediate of diaminopimelate metab olism has been prepared in 6 steps and 23% overall yield from L-allylglycin e 4. The key step during this synthesis involves a base mediated cyclisatio n of dimethyl (2RS,6S)-2-[N-(benzyloxycarbonyl)-N-(p-tolylsulfonyl)amino]-6 -[N-(benzyloxycarbonyl)aminolheptane-1,7-dioate 8 to give (2S)-N-(benzyloxy carbonyl)-1,2,3,4-tetrahydropyridine-2,6-dicarboxylic acid 9. H-1 NMR studi es show this one pot transformation involves four steps; base elimination o f toluene-p-sulfinic acid, intramolecular nucleophilic attack of the 6-benz yloxycarbonylamino group on the resulting imine, followed by hydrolysis of the esters and elimination of benzyl carbamate under acidic work-up to give the cyclic enamine 9.