A new class of chiral amidine-phosphine hybrid ligands 7a,b, which are readily accessible from the corresponding alpha-amino acids, were developed. A versatility for construction of new ligands is desirable, by which a variety of reactions and substrates become applicable. Indeed, a variety of modifications, such as exchange reactions to other amino groups in the amidine skeleton and the production of other types of ligands, are possible using the precursor compounds of 7a. Thus, novel chiral ligands 7c,d, 8, 11, and 13, which provide sterically and electronically different chiral circumstances, were prepared and used for the palladium-mediated asymmetric allylic substitutions of both acyclic and cyclic compounds. In these reactions, high levels of asymmetric induction were achieved for both substrates. A marked advancement of reactivity and enantioselectivity in palladium-catalyzed asymmetric allylations of 1,3-diphenylpropen-2-yl pivalate 14a was attained by examination of electronic substituent effects in a new series of chiral P-N and S-N hybrid ligands 8 and 11. Mechanistic views concerning the enantiodiscriminating step were demonstrated, in which a good correlation between a novel Pr/Mr concept and the absolute configuration of allylation products are discussed for the prediction of enantioselecting direction. The use of ketene silyl acetals as nucleophiles was investigated and compared with the corresponding harder anionic carbon nucleophiles. The former nucleophiles afforded higher enantioselectivity in asymmetric allylic transformations of 14a.

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A marked advancement of reactivity and enantioselectivity in palladium-catalyzed asymmetric allylations was achieved by variations of electronic substituent effects in a new series of chiral P-N hybrid ligands 1. The first evident observation demonstrates that the introduction of electron-donating groups is effective to improve the catalytic performance in the allylic transformation.Palladium-mediated allylic substitutions have been widely employed as efficient and convenient tools for carboncarbon and carbon-heteroatom bond formation in the field of organic synthesis. 1 High levels of enantiocontrol and reactivity toward various types of allylic transformation and substrates has been one of major goals for which chiral ligands have been developed extensively. 2 Substituents on the ligands often play key roles electronically in various types of transition metal-catalyzed asymmetric reactions, 3 however there are only a few attentions regarding electronic substituent effects of ligands in terms of both enantioselectivity and reactivity on palladium-catalyzed asymmetric allylations. 4 We envisaged that the ligand system having a variety of substituent effects could realize practical levels of catalytic performance regarding various types of reactions and substrates. Herein, we wish to report a drastic improvement of enantioselectivity and catalytic activity by electronic substituent effects on a new series of chiral P-N hybrid ligands 1 in palladium-catalyzed asymmetric allylations.Variations on mixed-donor bidentate ligands were planned under considerations based on Hammett's rule. As mentioned in our preceding paper, 2g the strategy for preparing VALAP 5,6 was applicable to produce a variety of chiral ligands (Scheme 1). Thus chiral P-N hybrid ligands 1 7 consisting of imino groups with various phenyl substituents and the diphenylphosphino group were easily accessible by simply mixing (2S)-2-amino-1-(diphenylphosphinyl)-3-methylbutane 3 2g and the corresponding aldehydes.The catalytic performance of palladium-1 complexes was examined in asymmetric allylic substitutions of 4 by a soft anionic nucleophile derived from dimethyl malonate (reaction type 1) and methyl trimethylsilyl dimethylketene acetal (type 2) 2e as depicted in Scheme 2. Scheme 2

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