Chiral auxiliary

In stereochemistry, a chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions. The auxiliary can then be typically recovered for future use. Most biological molecules and pharmaceutical targets exist as one of two possible enantiomers; consequently, chemical syntheses of natural products and pharmaceutical agents are frequently designed to obtain the target in enantiomerically pure form. Chiral auxiliaries are one of many strategies available to synthetic chemists to selectively produce the desired stereoisomer of a given compound. Chiral auxiliaries were introduced by Elias James Corey in 1975 with chiral 8-phenylmenthol and by Barry Trost in 1980 with chiral mandelic acid. The menthol compound is difficult to prepare and as an alternat

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Palladium-Catalyzed Carbo-Oxygenation of Propargylic Amines using in Situ Tether Formation

Phillip Gulliver Dominic Greenwood, Erwann Stefan Grenet, Jérôme Waser

1,2-Amino alcohols and -aminocarbonyls are frequently found in natural products, drugs, chiral auxiliaries, and catalysts. This work reports a new method for the palladium-catalyzed oxyalkynylation and oxyarylation of propargylic amines. The reaction is perfectly regioselective based on the in situ introduction of a hemiacetal tether derived from trifluoroacetaldehyde. cis-Selective carbo-oxygenation was achieved for terminal alkynes, whereas internal alkynes gave trans-carbo-oxygenation products. The obtained enol ethers could be easily transformed into 1,2-amino alcohols or -amino ketones using hydrogenation or hydrolysis, respectively.

2019

Enantioselective Carboetherification/Hydrogenation for the Synthesis of Amino Alcohols via a Catalytically Formed Chiral Auxiliary

Luca Buzzetti, Phillip Gulliver Dominic Greenwood, Mikus Purins, Jérôme Waser

Chiral auxiliaries and asymmetric catalysis are the workhorses of enantioselective transformations, but they still remain limited in terms of either efficiency or generality. Herein, we present an alternative strategy for controlling the stereoselectivity of chemical reactions. Asymmetric catalysis is used to install a transient chiral auxiliary starting from achiral precursors, which then directs diastereoselective reactions. We apply this strategy to a palladium-catalyzed carboetherification/ hydrogenation sequence on propargylic amines, providing fast access to enantioenriched chiral amino alcohols, important building blocks for medicinal chemistry and drug discovery. All stereoisomers of the product could be accessed by the choice of ligand and substituent on the propargylic amine, leading to a stereodivergent process.

2020

Palladium-Catalyzed Functionalization of Olefins and Alkynes: From Oxyalkynylation to Tethered Dynamic Kinetic Asymmetric Transformations (DYKAT)

Luca Buzzetti, Phillip Gulliver Dominic Greenwood, Bastian Antoine Rodolphe Claude Muriel, Stefano Nicolai, Ugo Jonathan Orcel, Mikus Purins, Jérôme Waser

This review presents an account of the palladium-catalyzed functionalizations of alkenes and alkynes developed at the Laboratory of Catalysis and Organic Synthesis (LCSO). Starting from the intramolecular oxy- and aminoalkynylation of alkenes, tethered methods were then developed to functionalize allylic amines and alcohols, as well as propargylic amines. Finally, a new dynamic kinetic asymmetric transformation was developed based on the use of a 'one-arm' Trost-type ligand, giving access to enantiopure amino alcohols. Each section is a personal account by the researcher(s) who performed the work. 1 Introduction, 2 Oxy- and Aminoalkynylation of Olefins, 3 In Situ Tethering Strategies for the Synthesis of Vicinal Amino Alcohols and Diamines, 4 Carboamination of Allylic Alcohols, 5 Carbooxygenation of Propargylic Amines, 6 Enantioselective Carboetherification/Hydrogenation via a Catalytically Formed Chiral Auxiliary, 7 Conclusion

GEORG THIEME VERLAG KG2020

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