Concave Reagents, 30 - 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 contro lled 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 va rying substrates can be understood when modified Taft parameters, the homo- E-s values, are considered. The like/unlike isomers were assigned by using a combination of molecular modeling, NOE measurements and analyses of chemi cal shifts. An X-ray analysis of the acid 14 confirmed the structural assig nment.