Isomer chelate ring, dependence

Decarboxylation " of a-amino-a-isopropyl malonate, chelated to a cobalt(III) N4-chelate, where N4 is a chiral tetradentate amine ligand, in acidic media gives valine with considerable asymmetric induction. With N4 = l,7-bis(2(S)-pyrrolidyl)-2,6-diazaheptane, the ratio of S R isomers is 2 98 and it is thought that attack by is obstructed in this case by the in-plane pyrridoline ring and the bulky isopropyl substituent on the malonate. Other substituents show lesser asymmetric induction. The reaction kinetics are pH dependent with a pK 0. 

---