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Relevant academic research and scientific papers

Mechanistic Studies on a Cu-Catalyzed Asymmetric Allylic Alkylation with Cyclic Racemic Starting Materials

Mechanistic studies on Cu-catalyzed asymmetric additions of alkylzirconocene nucleophiles to racemic allylic halide electrophiles were conducted using a combination of isotopic labeling, NMR spectroscopy, kinetic modeling, structure-activity relationships, and new reaction development. Kinetic and dynamic NMR spectroscopic studies provided insight into the oligomeric Cu-ligand complexes, which evolve during the course of the reaction to become faster and more highly enantioselective. The Cu-counterions play a role in both selecting different pathways and in racemizing the starting material via formation of an allyl iodide intermediate. We quantify the rate of Cu-catalyzed allyl iodide isomerization and identify a series of conditions under which the formation and racemization of the allyl iodide occurs. We developed reaction conditions where racemic allylic phosphates are suitable substrates using new phosphoramidite ligand D. D also allows highly enantioselective addition to racemic seven-membered-ring allyl chlorides for the first time.1H and2H NMR spectroscopy experiments on reactions using allylic phosphates showed the importance of allyl chloride intermediates, which form either by the action of TMSCl or from an adventitious chloride source. Overall these studies support a mechanism where complex oligomeric catalysts both racemize the starting material and select one enantiomer for a highly enantioselective reaction. It is anticipated that this work will enable extension of copper-catalyzed asymmetric reactions and provide understanding on how to develop dynamic kinetic asymmetric transformations more broadly.

Non-stabilized nucleophiles in Cu-catalysed dynamic kinetic asymmetric allylic alkylation

The development of new reactions forming asymmetric carbon-carbon bonds has enabled chemists to synthesize a broad range of important carbon-containing molecules, including pharmaceutical agents, fragrances and polymers1. Most strategies to obtain enantiomerically enriched molecules rely on either generating new stereogenic centres fromprochiral substratesor resolving racemicmixtures of enantiomers.Analternative strategy-dynamic kinetic asymmetric transformation-involves the transformation of a racemic starting material into a single enantiomer product, with greater than 50 per centmaximumyield2,3. The use of stabilized nucleophiles (pKaa is the acid dissociation constant) in palladium-catalysed asymmetric allylic alkylation reactions has proved to be extremely versatile in these processes4,5. Conversely, the use of non-stabilized nucleophiles insuch reactions is difficultand remains a key challenge6-9. Herewe report a copper-catalyseddynamic kinetic asymmetric transformation using racemic substrates and alkyl nucleophiles. These nucleophiles have a pKa of ≥ 50, more than 25 orders of magnitude more basic than the nucleophiles that are typically used in such transformations. Organometallic reagents are generatedin situ fromalkenes byhydrometallation and givehighly enantioenriched productsunder mild reaction conditions. The method is used to synthesize natural products that possess activity against tuberculosis and leprosy, and an inhibitor ofpara-aminobenzoate biosynthesis. Mechanistic studies indicate that the reaction proceeds through a rapidly isomerizing intermediate.We anticipate that this approach will be a valuable complement to existing asymmetric catalytic methods.

ASYMMETRIC SYNTHESIS OF CHIRAL COMPOUNDS

The present invention provides processes for the production of chiral compounds in a stereoisomeric excess, the processes comprising: (i) contacting a first compound comprising an alkene or alkyne bond with a hydrometallating agent, wherein the first compound and the hydrometallating agent are contacted under conditions such that the first compound is hydrometallated by said hydrometallating agent; and (ii) contacting the hydrometallated first compound with a second compound comprising an allylic group, wherein the hydrometallated first compound and the second compound are contacted under conditions such that they undergo an asymmetric allylic alkylation reaction in which a carbon atom of the hydrometallated first compound binds to a carbon atom of said allylic group, forming a stereoisomeric excess of a compound having a chiral centre in an allylic position, said chiral centre being located at the carbon atom bound by said first compound, wherein said asymmetric allylic alkylation reaction is performed in the presence of a metal catalyst comprising a chiral ligand. In particular, the present invention provides processes for the production of a stereoisomeric excess of a compound of the formula (IA), (IB), (IA') or (IB') as defined herein.

Copper-catalyzed asymmetric allylic alkylation of racemic cyclic substrates: Application of dynamic kinetic asymmetric transformation (DYKAT)

The copper-catalyzed asymmetric allylic alkylation (AAA) is of great interest in organic synthesis. This reaction was extensively studied using a broad range of substrates, ligands and organometallic reagents. However, the use of racemic substrates was still limited. Although some processes of kinetic resolution are reported in the literature, no examples of quantitative deracemization are described as is the case for the Pd-catalyzed allylic alkylation. We present here a full account of our investigations through the development of the first example of such a process in copper-catalyzed AAA. High enantioselectivities (up to 99% ee), scope of the reaction and mechanistic considerations are reported herein.