B. Meynhardt et al., Concave Reagents, 30 - Diastereoselective generation of quaternary stereocenters by ligand-controlled palladium-catalyzed allylations, EUR J ORG C, (9), 1999, pp. 2327-2335
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.