Enantio selective synthesis of organic carbonates promoted by Nb(IV) and Nb(V) catalysts

In this paper, we describe the use of Nb(IV) and Nb(V) catalysts in the carboxylation of either pure enantiomers of chiral epoxides or racemic mixtures. The carboxylation of pure enantiomers with Nb(V)-oxide is very selective (100%), proceeds with a good TON and occurs with total retention of the configuration. Optically active Nb(IV) complexes have been synthesised and used in the conversion of a racemic mixture of epoxides. An enantiomeric excess (ee, up to 22%) has been observed, that varies with the catalyst and the reaction conditions. The enantiomeric excess depends on the liability of the chiral ligands on Nb(IV). (C) 2003 Elsevier B.V. All rights reserved.