Efficient and reliable amplification of chirality has borne its greatest fruit with transition metal-catalyzed reactions since enantiocontrol may often be imposed by replacing an achiral or chiral racemic ligand with one that is chiral and scalemic While the most thoroughly developed enantioselective transition metal-catalyzed reactions are those involving transfer of oxygen (epoxidation and dihydroxylation)1,2 and molecular hydrogen,3 the focus of this review is on the area of enantioselective transition metal-catalyzed allylic alkylations which may involve C-C as well as C-X (X ) H or heteroatom) bond formation4-9 The synthetic utility of transitionmetal-catalyzed allylic alkylations has been soundly demonstrated since its introduction nearly three decades ago10-21 In contrast to processes where the allyl moiety acts as the nucleophilic partner, we will limit our discussion to processes which result in nucleophilic displacements on allylic substrates (eq 1) Such reactions have been recorded with a broad

http://web4.uwindsor.ca/users/j/jlichaa/reference.nsf/0/10ff8b04ff3a317885256d88005720f6/$FILE/cr-1996-96-395-allylpd-asym.pdf

Asymmetric Transition Metal-Catalyzed Allylic Alkylations.

Palladium catalysed allylic substitution has emerged as one of the more useful synthetic methods for the construction of C-C and C-X bonds. The reaction offers the advantages of mild reaction conditions, as well as the ability to accomodate a wide range of nucleophiles and their electrophilic partners. The issues of regiocontrol, diastereocontrol and enantiocontrol have been documented by a number of researchers over the last twenty years. The levels of selectivity in many cases are very high, and current research is driving these selectivities higher still. A greater understanding of the nature of the process is occurring as more detailed mechanistic and structural studies are being undertaken. Many uses have been found for palladium catalysed allylic substitution methodology, since the strong stereocontrol allows for the selective formation of numerous products. A few other metals are also able to catalyse allylic substitution, with modified stereochemical behaviour, although these are currently less well documented than for palladium catalysed process.

Selectivity in palladium catalysed allylic substitution

Palladium-assisted routes to nucleosides.

Allylic protecting groups and their use in a complex environment part II: Allylic protecting groups and their removal through catalytic palladium π-allyl methodology

Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio-, and enantioselective process for the synthesis of ketones bearing either a quaternary or a tertiary alpha-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic disubstituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium enolates, the DAAA reaction proceeds through an "outer sphere" S(N)2 type of attack on the pi-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the pi-allylpalladium cation must serve as the counterion for the enolate, the enolate probably exists as a tight-ion-pair. This largely prevents the common side reactions of enolates associated with the equilibrium between different enolates. The much milder reaction conditions as well as the much broader substrate scope also represent the advantages of the DAAA reaction over the direct allylation of preformed metal enolates.

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Palladium-catalyzed decarboxylative asymmetric allylic alkylation of enol carbonates.

Les reactions avec divers nucleophiles ont lieu avec les deux composes suivants: l'acetate du cyclopentene-2ol et l'acetate du methano-4,7 indenol-1 (hexahydro-«3a,4,5,6,7,7a»)

New method for the classification of nucleophiles in the palladium-catalyzed substitution of allylic acetates

The strong influence of the nature of the leaving group in allylic derivatives in their enantioselective Pd-catalyzed substitution by nucleophile is reported. Analysis of the stereochemical course of the Pd-catalyzed substitution of achiral trans-4-tert-butyl-1-vinylcyclohexyl derivatives with nucleophiles indicates the enantioselective step to be oxidative addition of the allylic substrate onto the chiral Pd complex. The asymmetric induction may be understood as the reuslt of the selection by the chiral Pd catalyst between two reactive enantiomeric conformations of the allylic substrate and, hence, was shown to be strongly dependent upon reaction conditions and especially upon the nature of the substrate leaving group

Substrate leaving group control of the enantioselectivity in the palladium-catalyzed asymmetric allylic substitution of 4-alkyl-1-vinylcyclohexyl derivatives

New Method for the Classification of Nucleophiles in the Palladium- Catalyzed Substitution of Allylic Acetates.

Substrate‐Leaving Group Control of the Enantioselectivity in the Palladium‐Catalyzed Asymmetric Allylic Substitution of 4‐Alkyl‐1‐ vinylcyclohexyl Derivatives.

Jean Yves Legros

Papers

New method for the classification of nucleophiles in the palladium-catalyzed substitution of allylic acetates

Substrate leaving group control of the enantioselectivity in the palladium-catalyzed asymmetric allylic substitution of 4-alkyl-1-vinylcyclohexyl derivatives

New Method for the Classification of Nucleophiles in the Palladium- Catalyzed Substitution of Allylic Acetates.

Substrate‐Leaving Group Control of the Enantioselectivity in the Palladium‐Catalyzed Asymmetric Allylic Substitution of 4‐Alkyl‐1‐ vinylcyclohexyl Derivatives.