The stereochemical role of the phosphoramidite ligand in the asymmetric conjugate addition of alkylzirconium species to cyclic enones has been established through experimental and computational studies. Systematic, synthetic variation of the modular ligand established that the configuration of the binaphthol backbone is responsible for absolute stereocontrol, whereas modulation of the amido substituents leads to dramatic variations in the level of asymmetric induction. Chiral amido substituents are not required for enantioselectivity, leading to the discovery of a new family of easily synthesized phosphoramidites based on achiral amines that deliver equal levels of selectivity to Feringa's ligand. A linear correlation between the length of the aromatic amido groups and experimentally determined enantioselectivity was uncovered for this class of ligand, which, following an optimisation, leading to the highly selective ligands (up to 94% ee) with naphthyl rather than phenyl groups. An electronic effect of sterically similar aromatic substituents was investigated through NMR and DFT studies, showing that electron rich aryl groups allow better Cu-coordination. An interaction between the metal center and an aromatic group is responsible for this enhanced affinity and leads to a more tightly-coordinated transition structure leading to the major enantiomer. These studies illustrate the use of parametric quantitative structure-selectivity relationships to generate mechanistic models for asymmetric induction and catalyst structures that may be further probed by experiment and computation. This integrated approach leads to the rational modification of chiral ligands to achieve enhanced levels of selectivity.

Catalytic asymmetric conjugate addition reactions with organometallic reagents are powerful reactions in synthetic chemistry. Procedures that use non-stabilized carbanions have been developed extensively, but these suffer from a number of limitations that prevent their use in many situations. Here, we report that alkylmetal species generated in situ from alkenes can be used in highly enantioselective 1,4-addition initiated by a copper catalyst. Using alkenes as starting materials is desirable because they are readily available and have favourable properties when compared to pre-made organometallics. High levels of enantioselectivity are observed at room temperature in a range of solvents, and the reaction tolerates functional groups that are not compatible with comparable methods-a necessary prerequisite for efficient and protecting-group-free strategies for synthesis.

Alkenes are among the most readily available organic molecules, and are feedstocks for the preparation of many commodity chemicals. [1] Using alkenes as starting materials in synthesis is practical because they are inexpensive and easy to handle. We recently reported [2] that alkenes can be used as the equivalents to premade alkyl metal species in coppercatalyzed asymmetric conjugate additions (ACA). [3] In these reactions hydrometalation (HM) of terminal alkenes with the Schwartz reagent [4] generates alkylzirconocenes, [5] which undergo asymmetric 1,4-additions catalyzed by complex A (Scheme 1). These processes are currently limited to the formation of tertiary centers from ACA to unsubstituted cyclic enones. [2] Herein we report that this approach can be used to form quaternary centers. Scheme 1. Hydrometalation/asymmetric conjugate addition of alkenes. Cp = cyclopentadienyl, Tf = trifluoromethanesulfonyl, TMS = trimethylsilyl.

Copper catalysis allows alkyl zirconium species, generated in situ from alkenes, to undergo conjugate addition reactions. A hydrometallation-catalytic asymmetric 1,4-addition was used to synthesize either enantiomer of a natural product in one step from commercially available materials. Hydrometallation-addition sequences applied to steroids containing a cross-conjugated dienone or 1,6-acceptor give highly functionalized products.

This Minireview discusses catalytic asymmetric conjugate addition and allylic alkylation reactions where the nucleophiles were generated in situ by hydrometallation or carbometallation. This exciting recent trend in asymmetric catalysis promises to expand the range of transformations available for the rapid and selective assembly of complex, functional molecules for both academic and industrial research. This Minireview aims to serve as a reference for studies reported to date and discusses the current state-of-the-art, scope and limitations of these processes.