Diastereoselective Generation of Quaternary Stereocenters by Ligand-Controlled Palladium-Catalyzed Allylations

The 1,2-asymmetric induction in the formation of new quaternary centers by palladium-catalyzed allylation of substituted cyanoacetates 1a–c was controlled by using 2,9-disubstituted 1,10-phenanthrolines as ligands, giving the allylated products 3a–c with like/unlike diastereoselectivities up to 94:6. The increased selectivities were caused by a tight wrapping of the allyl unit in the intermediate complexes. Differences in stereoselectivity for varying substrates can be understood when modified Taft parameters, the homo-Es values, are considered. The like/unlike isomers were assigned by using a combination of molecular modeling, NOE measurements and analyses of chemical shifts. An X-ray analysis of the acid 14 confirmed the structural assignment.