The 1,2-asymmetric induction in the formation of new Differences in stereoselectivity for varying substrates can be understood when modified Taft parameters, the homo-E s quaternary centers by palladium-catalyzed allylation of substituted cyanoacetates 1a-c was controlled by using 2,9-values, are considered. The like/unlike isomers were assigned by using a combination of molecular modeling, disubstituted 1,10-phenanthrolines as ligands, giving the allylated products 3a-c with like/unlike diastereoselectivities NOE measurements and analyses of chemical shifts. An Xray analysis of the acid 14 confirmed the structural up to 94:6. The increased selectivities were caused by a tight wrapping of the allyl unit in the intermediate complexes. assignment.
Palladium-catalyzed allylic substitutions are CϪC bond-other than acetate have also been used successfully; in addition, the nucleophile may be varied, too. formation reactions with wide synthetic applications. [2] In Scheme 1 the general reaction with allyl acetate as the allyl Depending on the substitution pattern of the allyl unit and the nucleophile, the formation of stereo-and regioiso-source and diethyl malonate as the nucleophile is shown. The allyl compound may be substituted, and leaving groups mers is possible. If substituted allyl units are employed, en-Scheme 1. Palladium catalyzed allylation of diethyl malonate with allyl acetate; L ϭ ligand Scheme 2. The palladium-catalyzed allylation of substituted cyanoacetates 1 gives diastereomeric allyl cyanoacetates 3 antiomers may be formed. [3] The enantioselectivity can be [ ] Part 29: Ref. [1] controlled by the ligand L. [4] If the allyl unit is part of a [a] Institut für Organische Chemie der cyclic molecule and the cycle carries at least one additional