Palladium-catalysed enantioselective bis-alkoxycarbonylation of 1-olefins. Synthesis of optically active 2-substituted-butanedioates

Cationic palladium(II) complexes of the type [Pd(L <^> L')(S-2)]X-2 (where L <^> L' is a chelate ligand with C-2 symmetry, S is a solvent molecule, and X is an anion with low coordination properties)are able to catalyse the enantioselective bis-alkoxycarbonylation of 1-olefins to substituted succinates. Using atropisomeric fully aromatic ligands high enantio- and chemoselectivity have been obtained when styrene is the substrate. I;or aliphatic olefins, such as propene and 4-methyl-1-pentene, the chemoselectivity is lower than for styrene owing to multiple olefin insertion. In these cases enantioselectivity is usually modest, probably due to two competing regiochemical pathways for the insertion of the olefin into the palladium carbomethoxy-intermediate. In the case of 3-phenyl-1-propene, dicarbonylation products after isomerization processes are also formed. (C) 1999 Elsevier Science B.V. All rights reserved.